Buretea, Mihai (San Francisco, CA, US)
Empedocles, Stephen (Mountain View, CA, US)
Niu, Chunming (Lexington, MA, US)
Scher, Erik C. (San Francisco, CA, US)

10/656916

05/20/2004

09/04/2003

Images are available in PDF form when logged in. To view PDFs, Login  or  Create Account (Free!)

View patents that cite this patent

Click for automatic bibliography generation

NANOSYS, Inc. (Palo Alto, CA)

359/853

(IPC1-7): G02B005/10

Quine Intellectual, Property Law Group P. C. (P O BOX 458, ALAMEDA, CA, 94501, US)

What is claimed is:

1. A light concentrator, comprising: at least one core; at least one adjacent material that has a lower index of refraction than the core and that is in contact with at least a portion of a surface of the core; a plurality of nanostructures, wherein the nanostructures absorb light impinging on a surface of the concentrator and emit light, and wherein the nanostructures are located or orientated within the concentrator such that the fraction of the light emitted by the nanostructures that is waveguided by the at least one core is greater than ½*(cos(asin(n₁/n₂))−cos(pi−asin(n₁/n₂))), where n₁ is the refractive index of the adjacent material and n₂ is the refractive index of the core; and, at least one collector which collects the waveguided light, the collector being operably connected to the core.

2. A light concentrator as in claim 1, wherein at least 1%, at least 10%, or at least 50% of the total nanostructures are located or orientated within the concentrator such that greater than ½*(cos(asin(n₁/n₂))−cos(pi−asin(n₁/n₂))), where n₁ is the refractive index of the adjacent material and n₂ is the refractive index of the core, of the light emitted by the nanostructures is waveguided by the at least one core.

3. A light concentrator, comprising: at least one core; a cladding having a lower index of refraction than the core; and a plurality of nanowires, which nanowires absorb light impinging on a surface of the concentrator and emit light, and which nanowires are oriented substantially nonrandomly within the core, with a vector average of the nanowires' orientations having a nonzero component perpendicular to a surface of the core, whereby the fraction of the light emitted by the nanowires that is waveguided by the at least one core is greater than ½*(cos(asin(n₁/n₂))−cos(pi−asin(n₁/n₂))), where n₁ is the refractive index of the cladding and n₂ is the refractive index of the core.

4. A light concentrator as in claim 3, wherein at least 1%, at least 10%, or at least 50% of the total nanowires within the core are substantially nonrandomly oriented.

5. A light concentrator as in claim 3, wherein at least one collector which collects the waveguided light is operably connected to the core.

6. A light concentrator, comprising: at least one core; and a first layer comprising one or more nanostructures, which one or more nanostructures absorb light impinging on a surface of the concentrator and emit light, and which first layer is disposed on a surface of the core, such that the fraction of the light emitted by the nanostructures that is waveguided by the at least one core is greater than ½*(cos(asin(n₁/n₂))−cos(pi−asin(n₁/n₂))), where n₁ is the refractive index of the first layer and n₂ is the refractive index of the core.

7. A light concentrator as in claim 6, wherein the one or more nanostructures comprise a plurality of nanowires, which nanowires are substantially nonrandomly oriented, with a vector average of the nanowires' orientations having a nonzero component perpendicular to the surface of the core.

8. A light concentrator as in claim 7, wherein at least 1%, at least 10%, or at least 50% of the total nanowires disposed on the core are substantially nonrandomly oriented.

9. A light concentrator as in claim 6, wherein the orientation of the one or more nanostructures is random.

10. A light concentrator as in claim 6, wherein at least one collector which collects the waveguided light is operably connected to the core.

11. A waveguide, comprising: a cladding; and a core, the core having a first surface and a second surface that are substantially parallel to each other, the core having a higher index of refraction than the cladding, the core comprising one or more nanowires or one or more branched nanowires and a matrix, and the core being in contact with the cladding over at least a majority of the first and second surfaces of the core.

12. A waveguide as in claim 11, wherein the one or more branched nanowires comprise one or more nanotetrapods.

13. A waveguide as in claim 11, wherein the cladding is air.

14. A waveguide as in claim 11, wherein the waveguide is a flat sheet.

15. A waveguide as in claim 11, wherein the core has an index of refraction between about 1.35 and about 4.

16. A waveguide as in claim 11, wherein the matrix is substantially nonabsorbing and nonscattering with respect to light at wavelengths greater than about 300 nm.

17. A waveguide as in claim 11, wherein the matrix comprises a glass, a polymer, a small molecule or molecular matrix, a liquid, a crystal, or a polycrystal.

18. A waveguide as in claim 11, wherein the one or more nanowires have an average diameter between about 2 nm and about 100 nm or between about 2 nm and about 20 nm.

19. A waveguide as in claim 11, wherein the one or more nanowires have an aspect ratio between about 1.5 and about 100, or between about 5 and about 30.

20. A waveguide as in claim 11, wherein the waveguide comprises a plurality of nanowires.

21. A waveguide as in claim 20, wherein the orientation of the nanowires is substantially nonrandom, with a vector average of the nanowires' orientations having a nonzero component perpendicular to the first surface of the core.

22. A waveguide as in claim 21, wherein at least 1%, at least 10%, or at least 50% of the total nanowires within the core are substantially nonrandomly oriented.

23. A waveguide as in claim 21, wherein a majority of the nanowires each has a long axis oriented more nearly perpendicular than parallel to the first surface of the core.

24. A waveguide as in claim 21, wherein the plurality of nanowires form a liquid crystal phase in which each nanowire has a long axis oriented substantially normal to the first surface of the core.

25. A waveguide as in claim 20, wherein the nanowires absorb light impinging on the first or second surface of the core and emit light, and wherein the nanowires are oriented within the core such that a majority of the light emitted from the nanowires is emitted at an angle greater than the critical angle Θ_crit, where Θ_crit=sin⁻¹(n_r/n_i), n_r is the index of refraction of the cladding, and n_i is the index of refraction of the core, thereby directing a majority of the emitted light toward at least one edge of the core, providing a light concentrator.

26. A waveguide as in claim 11, wherein the one or more nanowires or one or more branched nanowires comprise one or more of: a fluorescent material, a semiconducting material, a material comprising a first element selected from group 2 of the periodic table and a second element selected from group 16, a material comprising a first element selected from group 12 and a second element selected from group 16, a material comprising a first element selected from group 13 and a second element selected from group 15, a material comprising a group 14 element, or an alloy or a mixture thereof.

27. A waveguide as in claim 26, wherein the one or more nanowires or one or more branched nanowires comprise one or more of: ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe, MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, Ge, Si, PbS, PbSe, PbTe, AlS, AlP, AlSb, or an alloy or a mixture thereof.

28. A waveguide as in claim 11, wherein the one or more nanowires or one or more branched nanowires comprise one or more materials, each material having a band-gap energy between about 0.4 eV and about 4.1 eV.

29. A waveguide as in claim 11, wherein the one or more nanowires or one or more branched nanowires are heterostructures comprising at least two different materials.

30. A waveguide as in claim 29, wherein the at least two materials are distributed radially about a long axis of the one or more nanowires or about a long axis of an arm of the one or more branched nanowires.

31. A waveguide as in claim 11, wherein at least one collector which collects waveguided light is operably connected to at least one edge of the core.

32. A multilayer light concentrator comprising: a stack comprising two or more waveguides as described in claim 11.

33. A multilayer light concentrator as described in claim 32, wherein the two or more waveguides comprise one or more nanowires or one or more branched nanowires that absorb light of different wavelengths, and wherein the waveguide comprising the one or more nanowires or one or more branched nanowires that absorb the shortest wavelength light is located closest to a light source and the waveguide comprising the one or more nanowires or one or more branched nanowires that absorb the longest wavelength light is located farthest from the light source.

34. A waveguide, comprising: a first core having a first surface and a second surface, the first and second surfaces being substantially parallel to each other; a first layer comprising one or more nanostructures, wherein the one or more nanostructures are selected from the group consisting of nanowires, nanocrystals, branched nanowires, or nanotetrapods, the first layer being distributed on the first surface of the first core, the first layer having a first surface and a second surface; and a cladding, the cladding having a first portion that is distributed on the second surface of the first core and having a second portion that is distributed on the first surface of the first layer.

35. A waveguide as in claim 34, wherein the second surface of the first layer is in contact with at least a majority of the first surface of the first core, the first portion of the cladding is in contact with at least a majority of the second surface of the first core, and the second portion of the cladding is in contact with at least a majority of the first surface of the first layer.

36. A waveguide as in claim 35, wherein the one or more nanostructures absorb light impinging on a surface of the waveguide and emit light, wherein a majority of the light is emitted into the first core at an angle greater than the critical angle Θ_crit, wherein Θ_crit=sin⁻¹(n_r/n_i), and wherein n_r is the index of refraction of the first layer, and n_i is the index of refraction of the first core, thereby directing a majority of the emitted light toward at least one edge of the substrate, providing a light concentrator.

37. A waveguide as in claim 34, further comprising a second core, the second core having two substantially parallel surfaces, and the second core located between the first layer and the second portion of the cladding.

38. A waveguide as in claim 37, wherein the first core and second core comprise the same material.

39. A waveguide as in claim 37, further comprising: a second layer located between the second core and the first layer; and a third layer located between the first layer and the first core, wherein the second layer and the third layer have an index of refraction greater than the index of refraction of the first layer and less than the index of refraction of the first and second cores.

40. A waveguide as in claim 34, wherein the one or more nanostructures are in a small molecule or molecular matrix or a matrix comprising at least one polymer or glass.

41. A waveguide as in claim 40, wherein the matrix comprising at least one polymer comprises polydimethylsiloxane.

42. A waveguide as in claim 40, wherein the first layer has an index of refraction that is less than the index of refraction of the first core.

43. A waveguide as in claim 34, wherein the first layer consists of a plurality of substantially pure nanostructures.

44. A waveguide as in claim 34, wherein the cladding is air.

45. A waveguide as in claim 34, wherein the waveguide is a flat sheet.

46. A waveguide as in claim 34, wherein the first core has an index of refraction between about 1.35 and about 4.

47. A waveguide as in claim 34, wherein the first core is substantially nonabsorbing and nonscattering with respect to light at wavelengths greater than about 300 nm.

48. A waveguide as in claim 34, wherein the first layer is substantially nonscattering with respect to light at wavelengths greater than about 300 nm, the nanostructures absorb light impinging on the first or second surface of the first core and emit light, and the first layer is substantially nonabsorbing with respect to the wavelength or wavelengths of light emitted by the nanostructures.

49. A waveguide as in claim 34, wherein the first core comprises a glass, a polymer, a small molecule or molecular matrix, a liquid, a crystal, or a polycrystal.

50. A waveguide as in claim 34, wherein the nanowires have an average diameter between about 2 nm and about 100 nm or between about 2 nm and about 20 nm.

51. A waveguide as in claim 34, wherein the nanocrystals have an average diameter between about 1.5 nm and about 15 nm.

52. A waveguide as in claim 34, wherein the nanowires have an aspect ratio between about 1.5 and about 100, or between about 5 and about 30.

53. A waveguide as in claim 34, wherein the nanocrystals have an aspect ratio between about 1 and about 1.5.

54. A waveguide as in claim 34, wherein the one or more nanostructures comprise one or more of: a fluorescent material, a semiconducting material, a material comprising a first element selected from group 2 of the periodic table and a second element selected from group 16, a material comprising a first element selected from group 12 and a second element selected from group 16, a material comprising a first element selected from group 13 and a second element selected from group 15, a material comprising a group 14 element, or an alloy or a mixture thereof.

55. A waveguide as in claim 54, wherein the one or more nanostructures comprise one or more of: ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe, MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, Ge, Si, PbS, PbSe, PbTe, AlS, AlP, AlSb, or an alloy or a mixture thereof.

56. A waveguide as in claim 34, wherein the one or more nanostructures comprise one or more materials, each material having a band-gap energy between about 0.4 eV and about 4.1 eV.

57. A waveguide as in claim 34, wherein the one or more nanostructures are heterostructures comprising at least two different materials.

58. A waveguide as in claim 34, wherein the at least two materials are distributed radially about a long axis of the one or more nanowires, a long axis of an arm of the one or more branched nanowires, a long axis of an arm of the one or more nanotetrapods, or a center of the one or more nanocrystals.

59. A waveguide as in claim 34, wherein the one or more nanostructures comprise a plurality of nanostructures.

60. A waveguide as in claim 34, wherein the waveguide comprises a plurality of nanowires, and wherein the orientation of the nanowires is substantially nonrandom, with a vector average of the nanowires' orientations having a nonzero component perpendicular to the first surface of the first core.

61. A waveguide as in claim 60, wherein at least 1%, at least 10%, or at least 50% of the total nanowires within the first layer are substantially nonrandomly oriented.

62. A waveguide as in claim 60, wherein the majority of the nanowires each has a long axis oriented more nearly perpendicular than parallel to the first surface of the first core.

63. A waveguide as in claim 62, wherein the nanowires form a liquid crystal phase in which each nanowire has a long axis oriented substantially normal to the first surface of the first core.

64. A waveguide as in claim 36, wherein the first layer has a thickness less than about one wavelength of the light emitted by the one or more nanostructures.

65. A waveguide as in claim 34, wherein the first layer has a thickness less than about 1000 nm, less than about 900 nm, less than about 800 nm, less than about 700 nm, less than about 600 nm, less than about 500 nm, or less than about 400 nm.

66. A waveguide as in claim 34, wherein at least one collector which collects waveguided light is operably connected to at least one edge of the first core.

67. A multilayer light concentrator comprising: a stack comprising two or more waveguides as described in claim 34.

68. A multilayer light concentrator as described in claim 67, wherein the two or more waveguides comprise one or more nanostructures that absorb light of different wavelengths, and wherein the waveguide comprising the one or more nanostructures that absorb the shortest wavelength light is located closest to a light source and the waveguide comprising the one or more nanostructures that absorb the longest wavelength light is located farthest from the light source.

69. A composite material, comprising: a plurality of nanowires; and a small molecule or molecular matrix or a matrix comprising at least one polymer, which small molecule or molecular matrix or components thereof or which matrix comprising at least one polymer or components thereof are used to orient the nanowires.

70. A composite material, comprising one or more nanostructures and a polymeric matrix comprising a polysiloxane.

71. A composite material as in claim 70, wherein the matrix comprises polydimethylsiloxane.

72. A composite material as in claim 70, wherein the matrix comprises a copolymer between dimethylsiloxane and another siloxane.

73. A composite material as in claim 70, wherein the one or more nanostructures comprise one or more of: nanowires, nanocrystals, branched nanowires, or nanotetrapods.

74. A composite material as in claim 70, wherein the one or more nanostructures comprise one or more of: a metal, a ferroelectric material, a ferroelectric ceramic material, a perovskite-type material, a KDP-type material, a TGS-type material, a fluorescent material, a semiconducting material, a material comprising a first element selected from group 2 of the periodic table and a second element selected from group 16, a material comprising a first element selected from group 12 and a second element selected from group 16, a material comprising a first element selected from group 13 and a second element selected from group 15, a material comprising a group 14 element, or an alloy or a mixture thereof.

75. A composite material as in claim 74, wherein the one or more nanostructures comprise one or more of: BaTiO₃, SrTiO₃, CaTiO₃, KNbO₃, PbTiO₃, LiTiO₃, LiTaO₃, LiNbO₃, Ba_(1−x)Ca_xTiO₃ where x is between 0 and 1, PbTi_(1−x)Zr_xO₃ where x is between 0 and 1, KH₂PO₄, KD₂PO₄, RbH₂PO₄, RbH₂AsO₄, KH₂AsO₄, GeTe, tri-glycine sulfate, tri-glycine selenate, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe, MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, Ge, Si, PbS, PbSe, PbTe, AlS, AlP, AlSb, or an alloy or a mixture thereof.

76. A composite material as in claim 70, further comprising at least one surfactant or at least one solvent.

77. A shaped article of a composite material according to claim 70.

78. An LED, laser, waveguide, or amplifier comprising a composite as in claim 70.

79. A composite material, comprising: a small molecule or molecular matrix or a matrix comprising at least one organic polymer or inorganic glass; and one or more branched nanowires, one or more inorganic nanowires, or a combination thereof, wherein the one or more inorganic nanowires are selected from the group consisting of semiconducting inorganic nanowires and ferroelectric inorganic nanowires, and wherein the one or more inorganic nanowires have an aspect ratio greater than about 10.

80. A composite material as in claim 79, wherein the one or more branched nanowires comprise one or more nanotetrapods.

81. A composite material as in claim 79, wherein the composite material comprises one or more inorganic nanowires and the one or more inorganic nanowires comprise a plurality of inorganic nanowires.

82. A composite material as in claim 81, wherein the orientation of the nanowires is substantially nonrandom.

83. A composite material as in claim 82, wherein the composite material is formed into a thin film, the thin film being substantially free of strain.

84. A composite material as in claim 82, wherein the composite material is formed into a highly-strained stretched film.

85. A composite material as in claim 82, wherein the composite material is formed into a thin film within which a majority of the nanowires have their long axes oriented substantially parallel to a surface of the film.

86. A composite material as in claim 82, wherein the composite material is formed into a thin film within which a majority of the nanowires are oriented such that each has its long axis more nearly perpendicular than parallel to a surface of the film.

87. A composite material as in claim 82, wherein the composite material is formed into a thin film within which a majority of the nanowires are oriented such that each has its long axis substantially perpendicular to a surface of the film.

88. A composite material as in claim 79, wherein the ferroelectric inorganic nanowires comprise one or more of: ferroelectric ceramic, perovskite-type, KDP-type, or TGS-type nanowires.

89. A composite material as in claim 88, wherein the ferroelectric inorganic nanowires comprise one or more of: BaTiO₃, SrTiO₃, CaTiO₃, KNbO₃, PbTiO₃, LiTiO₃, LiTaO₃, LiNbO₃, Ba_(1−x)Ca_xTiO₃ where x is between 0 and 1, PbTi_(1−x)Zr_xO₃ where x is between 0 and 1, KH₂PO₄, KD₂PO₄, RbH₂PO₄, RbH₂AsO₄, KH₂AsO₄, GeTe, tri-glycine sulfate, or tri-glycine selenate nanowires.

90. A composite material as in claim 79, wherein the semiconducting inorganic nanowires comprise one or more of: a material comprising a first element selected from group 2 of the periodic table and a second element selected from group 16, a material comprising a first element selected from group 12 and a second element selected from group 16, a material comprising a first element selected from group 13 and a second element selected from group 15, a material comprising a group 14 element, or an alloy or a mixture thereof.

91. A composite material as in claim 90, wherein the semiconducting inorganic nanowires comprise one or more of: ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe, MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, Ge, Si, PbS, PbSe, PbTe, AlS, AlP, AlSb, or an alloy or a mixture thereof.

92. A composite material as in claim 79, wherein the small molecule or molecular matrix comprises one or more of: N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′biphenyl)-4,4′-diamine); (3-(4-biphenyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazole); tris-(8-hydroxyquinoline)aluminum; benzoic acid; phthalic acid; benzoin; hydroxyphenol; nitrophenol; chlorophenol; chloroaniline; or chlorobenzoamide.

93. A composite material as in claim 79, wherein the at least one organic polymer comprises one or more of: a thermoplastic polymer, a polyolefin, a polyester, a polysilicone, a polyacrylonitrile resin, a polystyrene resin, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, a fluoroplastic, a thermosetting polymer, a phenolic resin, a urea resin, a melamine resin, an epoxy resin, a polyurethane resin, an engineering plastic, a polyamide, a polyacrylate resin, a polyketone, a polyimide, a polysulfone, a polycarbonate, a polyacetal, a liquid crystal polymer, a main chain liquid crystal polymer, poly(hydroxynapthoic acid), a side chain liquid crystal polymer, poly <n-((4′(4″-cyanphenyl)phenoxy)alkyl)vinyl ether>, a conductive polymer, poly(3-hexylthiophene), poly[2-methoxy, 5-(2′-ethyl-hexyloxy)-p-phenylene-vinylene], poly(phenylene vinylene), or polyaniline.

94. A composite material as in claim 79, wherein the one or more inorganic nanowires have an average diameter between about 2 nm and about 100 nm, between about 2 nm and about 5 nm, or between about 10 nm and about 50 nm.

95. A composite material as in claim 79, wherein the one or more inorganic nanowires have an aspect ratio between about 10 and about 10,000, between about 20 and about 10,000, between about 50 and about 10,000, or between about 100 and about 10,000.

96. A composite material, comprising: a plurality of nanostructures; and a small molecule or molecular matrix, a glassy or crystalline inorganic matrix, or a matrix comprising at least one polymer, wherein the composite material is distributed on a first layer of a material that conducts substantially only electrons or substantially only holes.

97. A composite material as in claim 96, wherein the composite and the first layer are in contact.

98. A composite material as in claim 96, wherein the composite and the first layer are separated by a second layer, the second layer comprising a material that conducts electrons or holes or both electrons and holes.

99. A composite material as in claim 96, wherein the first layer is distributed on an electrode.

100. A composite material as in claim 99, wherein the first layer and the electrode are in contact.

101. A composite material as in claim 99, wherein the first layer and the electrode are separated by a third layer, the third layer comprising a material that conducts electrons or holes or both electrons and holes.

102. A composite material, comprising: a matrix; and one or more nanostructures, the one or more nanostructures each comprising a core and at least one shell, the core comprising a first semiconducting material having a conduction band and a valence band, the shell comprising a second semiconducting material having a conduction band and a valence band, and the first and second materials having a type I band offset.

103. A composite material as in claim 102, wherein the conduction band of the first material is lower than the conduction band of the second material, and the valence band of the first material is higher than the valence band of the second material.

104. A composite material as in claim 102, wherein the conduction band of the first material is higher than the conduction band of the second material, and the valence band of the first material is lower than the valence band of the second material.

105. A composite material as in claim 102, wherein the matrix comprises at least one polymer, comprises at least one glass, or is a small molecule or molecular matrix.

106. A composite material as in claim 102, wherein the matrix conducts both electrons and holes, conducts substantially only holes, conducts substantially only electrons, is semiconducting, or is substantially nonconductive.

107. A composite material as in claim 102, wherein the one or more nanostructures comprise one or more of: nanocrystals, nanowires, branched nanowires, or nanotetrapods.

108. A composite material, comprising: one or more nanostructures comprising a first semiconducting material having a conduction band and a valence band; and a matrix comprising a second semiconducting material having a conduction band and a valence band, wherein the first and second materials have a type I band offset.

109. A composite material as in claim 108, wherein the conduction band of the first material is lower than the conduction band of the second material, and the valence band of the first material is higher than the valence band of the second material.

110. A composite material as in claim 108, wherein the conduction band of the first material is higher than the conduction band of the second material, and the valence band of the first material is lower than the valence band of the second material.

111. A composite material as in claim 108, wherein each nanostructure comprises substantially a single material, the single material being the first material.

112. A composite material as in claim 108, wherein each nanostructure comprises a core and at least one shell, the core comprising the first material.

113. A composite material as in claim 108, wherein each nanostructure comprises a core and at least one shell, the shell comprising the first material.

114. A composite material as in claim 108, wherein the matrix comprises at least one polymer, comprises at least one glass, or is a small molecule or molecular matrix.

115. A composite material as in claim 108, wherein the one or more nanostructures comprise one or more of: nanocrystals, nanowires, branched nanowires, or nanotetrapods.

116. A composite material, comprising: a matrix; and one or more nanostructures, the one or more nanostructures each comprising a core and at least one shell, the core comprising a first semiconducting material having a conduction band and a valence band, the shell comprising a second semiconducting material having a conduction band and a valence band, and the first and second materials having a type II band offset.

117. A composite material as in claim 116, wherein the conduction band of the first material is lower than the conduction band of the second material, and the valence band of the first material is lower than the valence band of the second material.

118. A composite material as in claim 116, wherein the conduction band of the first material is higher than the conduction band of the second material, and the valence band of the first material is higher than the valence band of the second material.

119. A composite material as in claim 116, wherein the matrix comprises at least one polymer, comprises at least one glass, or is a small molecule or molecular matrix.

120. A composite material as in claim 116, wherein the matrix conducts both electrons and holes, conducts substantially only holes, conducts substantially only electrons, is semiconducting, or is substantially nonconductive.

121. A composite material as in claim 116, wherein the one or more nanostructures comprise one or more of: nanocrystals, nanowires, branched nanowires, or nanotetrapods.

122. A composite material, comprising: one or more nanostructures comprising a first semiconducting material having a conduction band and a valence band; and a matrix comprising a second semiconducting material having a conduction band and a valence band, wherein the first and second materials have a type II band offset.

123. A composite material as in claim 122, wherein the conduction band of the first material is lower than the conduction band of the second material, and the valence band of the first material is lower than the valence band of the second material.

124. A composite material as in claim 122, wherein the conduction band of the first material is higher than the conduction band of the second material, and the valence band of the first material is higher than the valence band of the second material.

125. A composite material as in claim 122, wherein each nanostructure comprises substantially a single material, the single material being the first material.

126. A composite material as in claim 122, wherein each nanostructure comprises a core and at least one shell, the core comprising the first material.

127. A composite material as in claim 122, wherein each nanostructure comprises a core and at least one shell, the shell comprising the first material.

128. A composite material as in claim 127, wherein the core comprises a third semiconducting material having a conduction band and a valence band, the third and first materials having a type II band offset.

129. A composite material as in claim 122, wherein the matrix comprises at least one polymer, comprises at least one glass, or is a small molecule or molecular matrix.

130. A composite material as in claim 122, wherein the one or more nanostructures comprise one or more of: nanocrystals, nanowires, branched nanowires, or nanotetrapods.

131. A composite material, comprising: a plurality of nanostructures; and a small molecule or molecular matrix or a matrix comprising at least one polymer, the at least one polymer or constituents of the small molecule or molecular matrix having an affinity for at least a portion of a surface of the nanostructures.

132. A composite material, comprising: a plurality of nanostructures, wherein the nanostructures each comprise one or more surface ligands; and a small molecule or molecular matrix or a matrix comprising at least one polymer, the at least one polymer or constituents of the small molecule or molecular matrix having an affinity for the one or more surface ligands.

133. A composite material as in claim 132, wherein the one or more surface ligands each comprise at least one small molecule found in the small molecule or molecular matrix or a derivative thereof or at least one monomer found in the at least one polymer or a derivative thereof.

134. A composite material as in claim 132, wherein the one or more surface ligands each comprise at least one functional group selected from the group consisting of: an amine, a phosphine, a phosphine oxide, a phosphonate, a phosphonite, a phosphinic acid, a phosphonic acid, a thiol, an alcohol, and an amine oxide.

135. A composite material, comprising: one or more ferroelectric nanowires or one or more ferroelectric nanoparticles and a small molecule or molecular matrix or a matrix comprising one or more polymers.

136. A composite material as in claim 135, wherein the one or more ferroelectric nanowires or nanoparticles comprise one or more of: ferroelectric ceramic, perovskite-type, KDP-type, or TGS-type nanowires or nanoparticles.

137. A composite material as in claim 136, wherein the one or more ferroelectric nanowires or nanoparticles comprise one or more of: BaTiO₃, SrTiO₃, CaTiO₃, KNbO₃, PbTiO₃, LiTiO₃, LiTaO₃, LiNbO₃, Ba_(1−x)Ca_xTiO₃ where x is between 0 and 1, PbTi_(1−x)Zr_xO₃ where x is between 0 and 1, KH₂PO₄, KD₂PO₄, RbH₂PO₄, RbH₂AsO₄, KH₂AsO₄, GeTe, tri-glycine sulfate, or tri-glycine selenate nanowires or nanoparticles.

138. A composite material as in claim 135, wherein the one or more polymers comprise one or more of: an inorganic polymer, a polysiloxane, a polycarbonessiloxane, a polyphosphazene, an organic polymer, a thermoplastic polymer, a polyolefin, a polyester, a polysilicone, a polyacrylonitrile resin, a polystyrene resin, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, a fluoroplastic, a thermosetting polymer, a phenolic resin, a urea resin, a melamine resin, an epoxy resin, a polyurethane resin, an engineering plastic, a polyamide, a polyacrylate resin, a polyketone, a polyimide, a polysulfone, a polycarbonate, a polyacetal, a liquid crystal polymer, a main chain liquid crystal polymer, poly(hydroxynapthoic acid), a side chain liquid crystal polymer, or poly <n-((4′(4″-cyanphenyl)phenoxy)alkyl)vinyl ether>.

139. A composite material as in claim 135, wherein the small molecule or molecular matrix comprises one or more of: N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′biphenyl)-4,4′-diamine); (3-(4-biphenyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazole); tris-(8-hydroxyquinoline)aluminum; benzoic acid; phthalic acid; benzoin; hydroxyphenol; nitrophenol; chlorophenol; chloroaniline; or chlorobenzoamide.

140. A composite material as in claim 135, wherein the matrix comprises one or more additives.

141. A composite material as in claim 140, wherein the one or more additives comprise one or more of: a surfactant, a plasticizer, a catalyst, an antioxidant, or a strengthening fiber.

142. A composite material as in claim 135, wherein the one or more ferroelectric nanowires or nanoparticles are included in sufficient quantity that the composite material has a dielectric constant of at least about 2, at least about 5, or at least about 10.

143. A composite material as in claim 135, wherein the one or more ferroelectric nanowires or nanoparticles are included in the composite in an amount greater than 0% and less than about 90% by volume.

144. A composite material as in claim 135, wherein the one or more ferroelectric nanowires have an average diameter between about 2 nm and about 100 nm, between about 2 nm and about 5 nm, or between about 10 nm and about 50 nm.

145. A composite material as in claim 135, wherein the one or more ferroelectric nanowires have an aspect ratio between about 1.5 and about 10000, between about 1.5 and about 10, between about 10 and about 20, between about 20 and about 50, between about 50 and about 10,000, or between about 100 and about 10,000.

146. A composite material as in claim 135, wherein the one or more ferroelectric nanoparticles have an average diameter less than about 200 nm.

147. A composite material as in claim 135, wherein the one or more ferroelectric nanoparticles have an aspect ratio between about 0.9 and about 1.2.

148. A film formed from a composite material as described in claim 135.

149. A substrate to which a composite material as in claim 135 has been applied.

150. A substrate as in claim 149, wherein the substrate comprises silicon, glass, an oxide, a metal, or a plastic.

151. A composition comprising particles of the composite material as in claim 135, at least one solvent, and at least one glue agent.

152. A composition as in claim 151, wherein the particles of the composite material have an average diameter between about 20 nm and about 20 micrometers.

153. A composition as in claim 151, wherein the glue agent is a polymer.

154. A film formed from a composition as described in claim 151.

155. A composition comprising one or more ferroelectric nanowires or nanoparticles, at least one solvent, and one or more polymers.

156. A composition as in claim 155, wherein the one or more ferroelectric nanowires or nanoparticles comprise one or more of: ferroelectric ceramic, perovskite-type, KDP-type, or TGS-type nanowires or nanoparticles.

157. A composition as in claim 156, wherein the one or more ferroelectric nanowires or nanoparticles comprise one or more of: BaTiO₃, SrTiO₃, CaTiO₃, KNbO₃, PbTiO₃, LiTiO₃, LiTaO₃, LiNbO₃, Ba_(1−x)Ca_xTiO₃ where x is between 0 and 1, PbTi_(1−x)Zr_xO₃ where x is between 0 and 1, KH₂PO₄, KD₂PO₄, RbH₂PO₄, RbH₂AsO₄, KH₂AsO₄, GeTe, tri-glycine sulfate, or tri-glycine selenate nanowires or nanoparticles.

158. A composition as in claim 155, wherein the one or more polymers comprise one or more of: an inorganic polymer, a polysiloxane, a polycarbonessiloxane, a polyphosphazene, an organic polymer, a thermoplastic polymer, a polyolefin, a polyester, a polysilicone, a polyacrylonitrile resin, a polystyrene resin, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, a fluoroplastic, a thermosetting polymer, a phenolic resin, a urea resin, a melamine resin, an epoxy resin, a polyurethane resin, an engineering plastic, a polyamide, a polyacrylate resin, a polyketone, a polyimide, a polysulfone, a polycarbonate, a polyacetal, a liquid crystal polymer, a main chain liquid crystal polymer, poly(hydroxynapthoic acid), a side chain liquid crystal polymer, or poly <n-((4′(4″-cyanphenyl)phenoxy)alkyl)vinyl ether>.

159. A composition as in claim 155, wherein the one or more ferroelectric nanowires have an average diameter between about 2 nm and about 100 nm, between about 2 nm and about 5 nm, or between about 10 nm and about 50 nm.

160. A composition as in claim 155, wherein the one or more ferroelectric nanowires have an aspect ratio between about 1.5 and about 10000, between about 1.5 and about 10, between about 10 and about 20, between about 20 and about 50, between about 50 and about 10,000, or between about 100 and about 10,000.

161. A composition as in claim 155, wherein the one or more polymers are soluble in the at least one solvent.

162. A composition as in claim 155, wherein the one or more polymers comprise emulsion polymerized polymer particles suspended in the at least one solvent.

163. A composition as in claim 162, further comprising at least one glue agent.

164. A composition as in claim 155, wherein the one or more polymers comprise oligomers soluble in the at least one solvent.

165. A composition as in claim 164, further comprising at least one cross-linking agent.

166. A composition as in claim 155, wherein the at least one solvent is water or an organic solvent.

167. A composition as in claim 155, further comprising at least one surfactant.

168. A composition as in claim 167, wherein the at least one surfactant is selected from the group consisting of a cationic surfactant, an anionic surfactant, and a nonionic surfactant.

169. A composition as in claim 155, further comprising at least one humectant.

170. A composition as in claim 169, wherein the at least one humectant is selected from the group consisting of a glycol, a diol, a sulfoxide, a sulfone, an amide, and an alcohol.

171. A composition as in claim 155, wherein the composition is a liquid suitable for use as an inkjet printing ink or a paste suitable for use as a screen printing ink.

172. A composition as in claim 155, wherein the composition has a consistency that makes the composition suitable for applying to a surface by brushing or by spraying.

173. A substrate to which a composition as in claim 155 has been applied.

174. A substrate as in claim 173, wherein the substrate comprises silicon, glass, an oxide, a metal, or a plastic.

175. A film formed from a composition as described in claim 155.

176. A composition, comprising one or more ferroelectric nanowires or nanoparticles and at least one monomeric precursor of at least one polymer.

177. A composition as in claim 176, wherein the ferroelectric nanowires or nanoparticles comprise one or more of: ferroelectric ceramic, perovskite-type, KDP-type, or TGS-type nanowires or nanoparticles.

178. A composition as in claim 177, wherein the ferroelectric nanowires or nanoparticles comprise one or more of: BaTiO₃, SrTiO₃, CaTiO₃, KNbO₃, PbTiO₃, LiTiO₃, LiTaO₃, LiNbO₃, Ba_(1−x)Ca_xTiO₃ where x is between 0 and 1, PbTi_(1−x)Zr_xO₃ where x is between 0 and 1, KH₂PO₄, KD₂PO₄, RbH₂PO₄, RbH₂AsO₄, KH₂AsO₄, GeTe, tri-glycine sulfate, or tri-glycine selenate nanowires or nanoparticles.

179. A composition as in claim 176, further comprising at least one solvent.

180. A composition as in claim 176, further comprising at least one catalyst.

181. A substrate to which a composition as in claim 176 has been applied.

182. A substrate as in claim 181, wherein the substrate comprises silicon, glass, an oxide, a metal, or a plastic.

183. A film formed from a composition as described in claim 176.

184. A method of making a composite material, the method comprising: preparing one or more branched nanowires or one or more inorganic nanowires, wherein the one or more inorganic nanowires are selected from the group consisting of semiconducting inorganic nanowires and ferroelectric inorganic nanowires, and wherein the one or more inorganic nanowires have an aspect ratio greater than about 10; and combining the one or more branched nanowires, one or more inorganic nanowires, or a combination thereof and at least one organic polymer or inorganic glass or precursors of a small molecule or molecular matrix.

185. A method of making a composite material, the method comprising: preparing one or more ferroelectric nanowires or nanoparticles; and combining the one or more ferroelectric nanowires or nanoparticles and at least one polymer or precursors of a small molecule or molecular matrix.

186. The method of claim 185, wherein the one or more ferroelectric nanowires or nanoparticles comprise one or more of: ferroelectric ceramic, perovskite-type, BaTiO₃, SrTiO₃, CaTiO₃, KNbO₃, PbTiO₃, LiTiO₃, LiTaO₃, LiNbO₃, Ba_(1−x)Ca_xTiO₃ where x is between 0 and 1, PbTi_(1−x)Zr_xO₃ where x is between 0 and 1, KDP-type, KH₂PO₄, KD₂PO₄, RbH₂PO₄, RbH₂AsO₄, KH₂AsO₄, GeTe, TGS-type, tri-glycine sulfate, or tri-glycine selenate nanowires or nanoparticles.

187. The method of claim 185, wherein the at least one polymer comprises one or more of: an inorganic polymer, a polysiloxane, a polycarbonessiloxane, a polyphosphazene, an organic polymer, a thermoplastic polymer, a polyolefin, a polyester, a polysilicone, a polyacrylonitrile resin, a polystyrene resin, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, a fluoroplastic, a thermosetting polymer, a phenolic resin, a urea resin, a melamine resin, an epoxy resin, a polyurethane resin, an engineering plastic, a polyamide, a polyacrylate resin, a polyketone, a polyimide, a polysulfone, a polycarbonate, a polyacetal, a liquid crystal polymer, a main chain liquid crystal polymer, poly(hydroxynapthoic acid), a side chain liquid crystal polymer, or poly <n-((4′(4″-cyanphenyl)phenoxy)alkyl)vinyl ether>.

188. The method of claim 185, wherein the one or more ferroelectric nanowires or nanoparticles and the at least one polymer are combined with one or more additives.

189. The method of claim 188, wherein the one or more additives comprise one or more of: a surfactant, a plasticizer, a catalyst, an antioxidant, or a strengthening fiber.

190. The method of claim 185, wherein the one or more ferroelectric nanowires or nanoparticles are included in sufficient quantity that the composite material has a dielectric constant of at least about 2, at least about 5, or at least about 10.

191. The method of claim 185, wherein the one or more ferroelectric nanowires or nanoparticles are included in the composite in an amount greater than 0% and less than about 90% by volume.

192. A method of making a composition, the method comprising: preparing particles of a composite material as in claim 135; and combining the particles with at least one solvent and at least one glue agent.

193. A method of making a composition, the method comprising: preparing one or more ferroelectric nanowires or nanoparticles; and combining the one or more nanowires or nanoparticles with at least one solvent and one or more polymers.

194. The method of claim 193, wherein the one or more polymers are soluble in the at least one solvent.

195. The method of claim 193, wherein the one or more polymers comprise emulsion polymerized particles capable of being suspended in the at least one solvent.

196. The method of claim 193, wherein the one or more polymers comprise oligomers soluble in the at least one solvent.

197. A method of making a composition, the method comprising: preparing one or more ferroelectric nanowires or nanoparticles; and combining the one or more nanowires or nanoparticles with at least one monomeric precursor of at least one polymer.

198. A method of making a composite material, the method comprising: preparing one or more nanostructures; and incorporating the preformed nanostructures into a polymeric matrix comprising a polysiloxane.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and benefit of U.S. Provisional Patent Application No. 60/408,722, filed Sep. 5, 2002, “Nanocomposites” Mihai Buretea et al., which is incorporated herein by reference in its entirety for all purposes.

FIELD OF THE INVENTION

[0002] The present invention is in the field of nanocomposites. More particularly, the invention includes composite materials comprising nanostructures (e.g., nanowires, nanorods, branched nanowires, nanotetrapods, nanocrystals, quantum dots, and nanoparticles), methods and compositions for making such composites, and articles comprising such composites. Waveguides and light concentrators comprising nanostructures that are not necessarily part of a nanocomposite are also features of the invention.

BACKGROUND OF THE INVENTION

[0003] A composite material (a composite) is formed by combining two or more materials that have different properties. The composite typically has properties different from those of its constituent materials, but within the composite the original materials can still be identified (they do not dissolve; an interface is maintained between them). Typically, one material, called the matrix, surrounds and binds together discrete units (e.g., particles, fibers, or fragments) of a second material, called the filler.

[0004] Many composite materials are currently known and widely used, for example, concrete (a composite in which the matrix is cement and the filler is aggregate), fiberglass (glass fibers in a plastic matrix), and many other types of reinforced plastics. However, there is continued demand for novel composites with desirable properties for many applications.

[0005] For example, the electronics industry utilizes materials that have high dielectric constants and that are also flexible, easy to process, and strong. Finding single component materials possessing these properties is difficult. For example, high dielectric constant ceramic materials such as ferroelectric SrTiO ₃ , BaTiO ₃ , or CaTiO ₃ are brittle and are processed at high temperatures that are incompatible with current microcircuit manufacturing processes, while polymer materials are very easy to process but have low dielectric constants. Composite materials with micron-scale ferroelectric ceramic particles as the filler in liquid crystal polymer, fluoropolymer, or thermoplastic polymer matrices are taught in U.S. Pat. No. 5,962,122 to Walpita et al (Oct. 5, 1999) entitled “Liquid crystalline polymer composites having high dielectric constant,” U.S. Pat. No. 5,358,775 to Horn et al (Oct. 25, 1994) entitled “Fluoropolymeric electrical substrate material exhibiting low thermal coefficient of dielectric constant,” U.S. Pat. No. 5,154,973 to Imagawa et al (Oct. 13, 1992) entitled “Composite material for dielectric lens antennas,” and U.S. Pat. No. 4,335,180 to Traut (Jun. 15, 1982) entitled “Microwave circuit boards.” However, these materials do not possess ideal processing characteristics. For example, they are difficult to form into the thin uniform films used for many microelectronics applications.

[0006] Novel materials would also be useful in other industries, for example, in solar energy technology. The development of solar energy technology is primarily concerned with reducing the cost of energy conversion. This is typically achieved in one of two ways: 1) increasing the conversion efficiency of light in a solar cell without proportionately increasing its cost, or 2) increasing the size of the cell without proportionately increasing its cost. In the first case, the same number of photons hit the solar cell, but a larger number of them are converted into electricity (or the ones that are converted are converted at a higher total power). In the second, the conversion efficiency is the same, but the larger surface area means that more photons are collected per unit time. Since the sun is free, this results in improved cost efficiency. Unfortunately, at the moment neither of these strategies is effective. The complexity of increased-efficiency solar cells causes their cost to be substantially greater than the increase in performance. Similarly, larger solar panels are proportionately more expensive due to difficulties in fabricating uniform devices over large areas.

[0007] Among other aspects, the present invention provides high dielectric constant nanocomposites that overcome the processing issues noted above and solar concentrators comprising nanostructures. A complete understanding of the invention will be obtained upon review of the following.

SUMMARY OF THE INVENTION

[0008] The present invention provides nanocomposites (composite materials comprising nanostructures such as nanowires, branched nanowires, nanotetrapods, nanocrystals, and nanoparticles, for example), compositions and methods for making such nanocomposites, and articles comprising such composites.

[0009] One aspect of the invention provides waveguides and light concentrators comprising nanostructures, which in some but not all embodiments are provided as part of a nanocomposite. The nanostructures absorb light impinging on the waveguide or light concentrator and re-emit light. The nanostructures can be located and/or oriented within the waveguide or light concentrator in a manner that increases the percentage of re-emitted light that can be waveguided. For example, the nanostructures can be located and/or oriented within a light concentrator in such a manner that a greater percentage of the reemitted light is waveguided (and can thus be collected at the edge of the concentrator) than would be waveguided if emission by the collection of nanostructures were isotropic (equal in every direction).

[0010] One class of embodiments provides a waveguide comprising a cladding (e.g., a material that has a lower refractive index than the core, e.g., a lower refractive index solid, liquid, or gas, e.g., air) and a core, where the core comprises one or more nanowires or branched nanowires (e.g., nanotetrapods) and a matrix. The first and second surfaces of the core are substantially parallel so light emitted by the nanowires or branched nanowires can be efficiently waveguided by total internal reflection, and the core has a higher index of refraction than the cladding, for a similar reason. The nanowires or branched nanowires can comprise essentially any convenient material (e.g., a fluorescent material, a semiconducting material) and can comprise essentially a single material or can be heterostructures. The size of the nanostructures (e.g., the diameter and/or aspect ratio of nanowires) can be varied. In embodiments in which the core comprises a plurality of nanowires, the nanowires can be either randomly or substantially nonrandomly oriented (e.g., with a majority of the nanowires being more nearly perpendicular than parallel to a surface of the core, or with the nanowires forming a liquid crystal phase). Nonrandom orientation of the nanowires can increase the efficiency of the waveguide by increasing the percentage of light that is reemitted at angles greater than the critical angle for the particular core-cladding combination. The waveguides can be connected to a collector for collecting waveguided light, and can be used in stacks to form a multilayer light concentrator, in which the different layers comprise waveguides that can be optimized to collect light of different wavelengths.

[0011] Another class of embodiments provides a waveguide comprising a cladding (e.g., a material that has a lower refractive index than the core, e.g., a lower refractive index solid, liquid, or gas, e.g., air), a first core, and a first layer that comprises one or more nanostructures. The first layer is distributed on but is not necessarily in contact with the first core, whose first and second surfaces are substantially parallel. Some embodiments further comprise a second core. The first layer can be in direct contact with the first and/or second core(s), or can be separated from either or both, e.g., by a layer of a material whose refractive index is between that of the first layer and the core. The first layer preferably has a thickness less than about one wavelength of the light emitted by the nanostructures. The nanostructures can be nanowires, nanocrystals, or branched nanowires (e.g., nanotetrapods). The nanostructures can comprise essentially any convenient material (e.g., a fluorescent material, a semiconducting material) and can comprise essentially a single material or can be heterostructures. The size of the nanostructures (e.g., the diameter and/or aspect ratio of nanowires) can be varied. The nanostructures can be provided in various manners, e.g., as substantially pure nanostructures or as part of a nanocomposite. In embodiments in which the waveguide comprises a plurality of nanowires, the nanowires can be either randomly or substantially nonrandomly oriented (e.g., with a majority of the nanowires being more nearly perpendicular than parallel to a surface of the first core, or with the nanowires forming a liquid crystal phase). Nonrandom orientation of the nanowires can increase the efficiency of the waveguide by increasing the percentage of light that is reemitted at angles greater than the critical angle. The waveguides can be connected to a collector for collecting waveguided light, and can be used in stacks to form a multilayer light concentrator, in which the different layers comprise waveguides that can be optimized to collect light of different wavelengths.

[0012] Another aspect of the invention provides various nanocomposites. One composite material comprises a plurality of nanowires and a polymeric or small molecule or molecular matrix that is used to orient the nanowires. Another class of embodiments provides composites comprising one or more nanostructures (for example, nanowires, nanocrystals, or branched nanowires, e.g. nanotetrapods) and a polymeric matrix comprising polysiloxane (e.g., polydimethylsiloxane). The nanostructures can comprise essentially any material (e.g., a ferroelectric, fluorescent, or semiconducting material). The composite can further comprise an additive such as e.g. a surfactant or solvent. Articles comprising such composites (e.g., an LED, laser, waveguide, or amplifier) are also features of the invention.

[0013] Yet another class of embodiments provides nanocomposites comprising a small molecule or molecular matrix or a matrix comprising an organic polymer or an inorganic glass and one or more branched nanowires (e.g., nanotetrapods) or ferroelectric or semiconducting nanowires having an aspect ratio greater than about 10. The size of the nanostructures (e.g., the diameter and/or aspect ratio of nanowires) can be varied. In embodiments in which the composite comprises a plurality of nanowires, the nanowires can be either randomly or substantially nonrandomly oriented. For example, the composite can be formed into a thin film (strained or unstrained) within which a majority of the nanowires can be substantially parallel to or more nearly perpendicular than parallel to a surface of the film.

[0014] An additional class of embodiments provides composite materials comprising nanostructures and a polymeric matrix, a small molecule or molecular matrix, or a glassy or crystalline inorganic matrix where the composite is distributed on a first layer of a material that conducts substantially only electrons or substantially only holes. The composite and the first layer can be in contact or can be separated, for example, by a second layer comprising a conductive material. The first layer can be distributed on an electrode, and can be in contact with the electrode or separated from it, for example, by a third layer comprising a conductive material. The conductive material may conduct electrons or holes or both.

[0015] In another class of embodiments, the invention provides nanocomposites that support charge recombination or charge separation. These composites comprise a matrix and one or more nanostructures (e.g., nanocrystals, nanowires, branched nanowires, or nanotetrapods), where semiconducting materials comprising the matrix and/or the nanostructures have a type I or type II band offset with respect to each other.

[0016] An additional class of embodiments provides composites comprising nanostructures and a polymeric or small molecule or molecular matrix, in which the components of the matrix have an affinity for the surface of the nanostructure or for surface ligands on the nanostructures. For example, the surface ligands can each comprise a molecule found in the small molecule or molecular matrix or a derivative thereof or a monomer found in the polymeric matrix or a derivative thereof.

[0017] Another class of embodiments provides composite materials comprising one or more ferroelectric nanowires or nanoparticles and a small molecule or molecular matrix or a matrix comprising one or more polymers (e.g., an organic, inorganic, or organometallic polymer). The nanowires or nanoparticles can comprise essentially any convenient ferroelectric material, and their size (e.g., their diameter and/or aspect ratio) can be varied. The dielectric constant of the composite can be adjusted by adjusting the amount of ferroelectric nanowires or nanoparticles included in the composite. The composite (or its matrix) can further comprise an additive, for example, a surfactant, solvent, catalyst, plasticizer, antioxidant, or strengthening fiber. The composite material can be formed into a film or applied to a substrate. An additional embodiment provides a composition comprising such a composite; the composition comprises particles of the composite material, at least one solvent whose concentration can be varied, and at least one glue agent (e.g., a polymer or cross-linker). The composition can form a film, e.g., after application to a substrate.

[0018] Compositions that can be used to form a nanocomposite comprising ferroelectric nanowires or nanoparticles are another feature of the invention. In one embodiment, the composition comprises one or more ferroelectric nanowires or nanoparticles, at least one solvent, and one or more polymers. The polymers can be provided in any of a number of forms. For example, the polymer can be soluble in the solvent or can comprise oligomers soluble in the solvent, or the polymer can comprise emulsion polymerized particles. The materials and size of the nanowires and nanoparticles can be varied essentially as described above. The composition can further comprise a glue agent, cross-linking agent, surfactant, or humectant. The consistency of the composition can be controlled (e.g., by varying the solvent concentration) to make the composition suitable for use as an inkjet printing ink or screenprinting ink, or for brushing or spraying onto a surface or substrate. The composition can be used to form a film (e.g., a high dielectric nanocomposite film).

[0019] In a similar embodiment, the composition comprises one or more ferroelectric nanowires or nanoparticles, at least one solvent, and at least one monomeric precursor of at least one polymer. The materials and size of the nanowires and nanoparticles can be varied essentially as described above. The composition can further comprise a catalyst, cross-linking agent, surfactant, or humectant. The consistency of the composition can be controlled (e.g., by varying the solvent concentration) to make the composition suitable for use as an inkjet printing ink or screenprinting ink, or for brushing or spraying onto a surface or substrate. The composition can be used to form a film (e.g., a high dielectric nanocomposite film).

[0020] Methods for making the composite materials and compositions described above provide an additional feature of the invention.

DEFINITIONS

[0021] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. The following definitions supplement those in the art and are directed to the current application and are not to be imputed to any related or unrelated case, e.g., to any commonly owned patent or application. Although any methods and materials similar or equivalent to those described herein can be used in the practice for testing of the present invention, the preferred materials and methods are described herein. Accordingly, the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

[0022] As used in this specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a nanostructure” includes a plurality of such nanostructures, and the like.

[0023] An “aspect ratio” is the length of a first axis of a nanostructure divided by the average of the lengths of the second and third axes of the nanostructure, where the second and third axes are the two axes whose lengths are most nearly equal each other. For example, the aspect ratio for a perfect rod would be the length of its long axis divided by the diameter of a cross-section perpendicular to (normal to) the long axis.

[0024] A “branched nanowire” is a nanostructure having three or more arms, where each arm has the characteristics of a nanowire, or a nanostructure having two or more arms, each arm having the characteristics of a nanowire and emanating from a central region that has a distinct crystal structure, e.g., having cubic symmetry, e.g., where the angle between any two arms is approximately 109.5 degrees. Examples include, but are not limited to, bipods, tripods, and nanotetrapods (tetrapods). A branched nanowire can be substantially homogenous in material properties or can be heterogeneous (a heterostructure). For example, a branched nanowire can comprise one material at the center of the branch which is a single crystal structure and a second material along the arms of the structure that is a second crystal structure, or the materials along each of the arms can differ, or the material along any single arm can change as a function of length or radius of the arm. Branched nanowires can be fabricated from essentially any convenient material or materials. Branched nanowires can comprise “pure” materials, substantially pure materials, doped materials and the like, and can include insulators, conductors, and semiconductors.

[0025] The terms “crystalline” or “substantially crystalline,” when used with respect to nanostructures, refer to the fact that the nanostructures typically exhibit long-range ordering across one or more dimensions of the structure. It will be understood by one of skill in the art that the term “long range ordering” will depend on the absolute size of the specific nanostructures, as ordering for a single crystal cannot extend beyond the boundaries of the crystal. In this case, “long-range ordering” will mean substantial order across at least the majority of the dimension of the nanostructure. In some instances, a nanostructure can bear an oxide or other coating, or can be comprised of a core and at least one shell. In such instances it will be appreciated that the oxide, shell(s), or other coating need not exhibit such ordering (e.g. it can be amorphous, polycrystalline, or otherwise). In such instances, the phrase “crystalline,” “substantially crystalline,” “substantially monocrystalline,” or “monocrystalline” refers to the central core of the nanostructure (excluding the coating layers or shells). The terms “crystalline” or “substantially crystalline” as used herein are intended to also encompass structures comprising various defects, stacking faults, atomic substitutions, and the like, as long as the structure exhibits substantial long range ordering (e.g., order over at least about 80% of the length of at least one axis of the nanostructure or its core). In addition, it will be appreciated that the interface between a core and the outside of a nanostructure or between a core and an adjacent shell or between a shell and a second adjacent shell may contain non-crystalline regions and may even be amorphous. This does not prevent the nanostructure from being crystalline or substantially crystalline as defined herein.

[0026] The “diameter of a nanocrystal” refers to the diameter of a cross-section normal to a first axis of the nanocrystal, where the first axis has the greatest difference in length with respect to the second and third axes (the second and third axes are the two axes whose lengths most nearly equal each other). The first axis is not necessarily the longest axis of the nanocrystal; e.g., for a disk-shaped nanocrystal, the cross-section would be a substantially circular cross-section normal to the short longitudinal axis of the disk. Where the cross-section is not circular, the diameter is the average of the major and minor axes of that cross-section.

[0027] The “diameter of a nanowire” refers to the diameter of a cross-section normal to the major principle axis (the long axis) of the nanowire. Where the cross-section is not circular, the diameter is the average of the major and minor axes of that cross-section.

[0028] The term “heterostructure” when used with reference to nanostructures refers to nanostructures characterized by at least two different and/or distinguishable material types. Typically, one region of the nanostructure comprises a first material type, while a second region of the nanostructure comprises a second material type. In certain embodiments, the nanostructure comprises a core of a first material and at least one shell of a second (or third etc.) material, where the different material types are distributed radially about the long axis of a nanowire, a long axis of an arm of a branched nanowire, or the center of a nanocrystal, for example. (A shell need not completely cover the adjacent materials to be considered a shell or for the nanostructure to be considered a heterostructure; for example, a nanocrystal characterized by a core of one material covered with small islands of a second material is a heterostructure.) In other embodiments, the different material types are distributed at different locations within the nanostructure; e.g., along the major (long) axis of a nanowire or along a long axis of arm of a branched nanowire. Different regions within a heterostructure can comprise entirely different materials, or the different regions can comprise a base material (e.g., silicon) having different dopants or different concentrations of the same dopant.

[0029] The term “monocrystalline” when used with respect to a nanostructure indicates that the nanostructure is substantially crystalline and comprises substantially a single crystal. When used with respect to a nanostructure heterostructure comprising a core and one or more shells, “monocrystalline” indicates that the core is substantially crystalline and comprises substantially a single crystal.

[0030] A “nanocrystal” is a nanostructure that is substantially monocrystalline. Nanocrystals typically have an aspect ratio between about 0.1 and about 1.5 (e.g., between about 0.1 and about 0.5, between about 0.5 and about 1, or between about 1 and about 1.5). Thus, nanocrystals include, for example, substantially spherical nanocrystals with aspect ratios between about 0.8 and about 1.2 and disk-shaped nanocrystals. Nanocrystals typically have a diameter between about 1.5 nm and about 15 nm (e.g., between about 2 nm and about 5 nm, between about 5 nm and about 10 nm, or between about 10 nm and about 15 nm). Nanocrystals can be substantially homogeneous in material properties, or in certain embodiments can be heterogeneous (e.g. heterostructures). In the case of nanocrystal heterostructures comprising a core and one or more shells, the core of the nanocrystal is substantially monocrystalline, but the shell(s) need not be. The nanocrystals can be fabricated from essentially any convenient material or materials. The nanocrystals can comprise “pure” materials, substantially pure materials, doped materials and the like, and can include insulators, conductors, and semiconductors.

[0031] A “nanoparticle” is any nanostructure having an aspect ratio less than about 1.5. Nanoparticles can be of any shape, and include, for example, nanocrystals, substantially spherical particles (having an aspect ratio of about 0.9 to about 1.2), and irregularly shaped particles. Nanoparticles can be amorphous, crystalline, partially crystalline, polycrystalline, or otherwise. Nanoparticles can be substantially homogeneous in material properties, or in certain embodiments can be heterogeneous (e.g. heterostructures). The nanoparticles can be fabricated from essentially any convenient material or materials. The nanoparticles can comprise “pure” materials, substantially pure materials, doped materials and the like, and can include insulators, conductors, and semiconductors.

[0032] A “nanostructure” is a structure having at least one region or characteristic dimension with a dimension of less than about 500 nm, e.g., less than about 200 nm, less than about 100 nm, less than about 50 nm, or even less than about 20 nm. Typically, the region or characteristic dimension will be along the smallest axis of the structure. Examples of such structures include nanowires, nanorods, nanotubes, branched nanowires, nanotetrapods, tripods, bipods, nanocrystals, nanodots, quantum dots, nanoparticles, and the like. Nanostructures can be substantially homogeneous in material properties, or in certain embodiments can be heterogeneous (e.g. heterostructures). The nanostructures can be fabricated from essentially any convenient material or materials. The nanostructures can comprise “pure” materials, substantially pure materials, doped materials and the like, and can include insulators, conductors, and semiconductors. A nanostructure can optionally comprise one or more surface ligands (e.g., surfactants).

[0033] A “nanotetrapod” is a generally tetrahedral branched nanowire having four arms emanating from a central region, where the angle between any two arms is approximately 109.5 degrees.

[0034] A “nanowire” is a nanostructure that has one principle axis that is longer than the other two principle axes. Consequently, the nanowire has an aspect ratio greater than one; nanowires of this invention have an aspect ratio greater than about 1.5 or greater than about 2. Short nanowires, sometimes referred to as nanorods, typically have an aspect ratio between about 1.5 and about 10. Longer nanowires have an aspect ratio greater than about 10, greater than about 20, greater than about 50, or greater than about 100, or even greater than about 10,000. The diameter of a nanowire is typically less than about 500 nm, preferably less than about 200 nm, more preferably less than about 150 nm, and most preferably less than about 100 nm, about 50 nm, or about 25 nm, or even less than about 10 nm or about 5 nm. The nanowires of this invention can be substantially homogeneous in material properties, or in certain embodiments can be heterogeneous (e.g. nanowire heterostructures). The nanowires can be fabricated from essentially any convenient material or materials. The nanowires can comprise “pure” materials, substantially pure materials, doped materials and the like, and can include insulators, conductors, and semiconductors. Nanowires are typically substantially crystalline and/or substantially monocrystalline, but can be, e.g., polycrystalline or amorphous. Nanowires can have a variable diameter or can have a substantially uniform diameter, that is, a diameter that shows a variance less than about 20% (e.g., less than about 10%, less than about 5%, or less than about 1%) over the region of greatest variability and over a linear dimension of at least 5 nm (e.g., at least 10 nm, at least 20 nm, or at least 50 nm). Typically the diameter is evaluated away from the ends of the nanowire (e.g. over the central 20%, 40%, 50%, or 80% of the nanowire). A nanowire can be straight or can be e.g. curved or bent, over the entire length of its long axis or a portion thereof. In certain embodiments, a nanowire or a portion thereof can exhibit two- or three-dimensional quantum confinement. Nanowires according to this invention can expressly exclude carbon nanotubes, and, in certain embodiments, exclude “whiskers” or “nanowhiskers”, particularly whiskers having a diameter greater than 100 nm, or greater than about 200 nm.

[0035] The phrase “substantially nonrandom” used to describe the orientation of nanowires means that the nanowires do not occupy a purely random distribution of orientations with respect to each other. A collection of nanowires is substantially nonrandomly oriented if, when the position of each nanowire is represented as a vector of unit length in a three-dimensional rectangular coordinate system, at least one component of the vector average of the nanowires' orientations is non-zero (when representing a nanowire by a vector, any intrinsic difference between the two ends of the nanowire can typically be ignored). For example, the nanowires in a collection of nanowires (e.g., the nanowires in a composite material comprising nanowires) would have substantially nonrandom orientations if a higher percentage of the nanowires pointed in one direction (or in one of at least two specific directions) than in any other direction (e.g., if at least 10%, at least 50%, at least 75%, or at least 90% of the nanowires pointed in a particular direction). As another example, nanowires in a thin film of a composite comprising nanowires would be substantially nonrandomly oriented if a majority of the nanowires had their long axes more nearly perpendicular than parallel to a surface of the film (or vice versa) (the nanowires can be substantially nonrandomly oriented yet not point in at least one specific direction). The preceding examples are for illustration only; a collection of nanowires could possess less order than these examples yet still be substantially nonrandomly oriented.

[0036] A “surface ligand” of a nanostructure is a molecule that has an affinity for and is capable of binding to at least a portion of the nanostructure's surface. Examples include various surfactants. Surface ligands or surfactants can comprise e.g. an amine, a phosphine, a phosphine oxide, a phosphonate, a phosphonite, a phosphinic acid, a phosphonic acid, a thiol, an alcohol, an amine oxide, a polymer, a monomer, an oligomer, or a siloxane.

[0037] A “type I band offset” between two semiconducting materials means that both the conduction band and the valence band of the semiconductor with the smaller bandgap are within the bandgap of the other semiconductor.

[0038] A “type II band offset” between two semiconducting materials means that either the conduction band or the valence band, but not both, of one semiconductor is within the bandgap of the other semiconductor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] FIG. 1 schematically depicts a quantum dot solar concentrator.

[0040] FIG. 2 schematically illustrates a waveguide in which the core comprises substantially nonrandomly oriented nanowires.

[0041] FIG. 3 schematically depicts a waveguide comprising a first core and a first layer in contact with each other.

[0042] FIG. 4 schematically depicts a waveguide comprising a first layer in contact with two cores.

[0043] FIG. 5 schematically depicts a waveguide comprising a first, a second, and a third layer and two cores.

[0044] FIG. 6 illustrates absorption and emission by the organic dye fluorescein (Panel A) and by spherical CdSe nanocrystals with an aspect ratio of about 1.1 and an average diameter of about 2.3 nm (Panel B).

[0045] FIG. 7 depicts examples of vinyl-terminated polydimethylsiloxane oligomers (Panel A) and siloxane cross-linkers (Panel B) and illustrates the formation of cross-links between them (Panel C).

[0046] FIG. 8 schematically depicts examples of type II (Panels A and C) and type I (Panels B and D) band offsets.

DETAILED DESCRIPTION

[0047] Composite materials comprising nanostructures (nanocomposites) are provided, along with articles comprising nanocomposites and methods and compositions for making such composites.

[0048] One class of embodiments provides waveguides and light concentrators comprising nanostructures. This class of embodiments is based on the ability of certain nanostructures (e.g., nanostructures comprising a fluorescent material) to absorb and re-emit light that can then be waveguided by total internal reflection within at least one core. In many but not all embodiments, the nanostructures are provided in the form of a nanocomposite. In some embodiments, the nanostructures are substantially nonrandomly oriented to increase the efficiency of the waveguide or light concentrator.

[0049] Methods for orienting nanostructures within a composite material are discussed, including using the matrix or components thereof to orient the nanostructures. Accordingly, one aspect of the invention provides nanocomposites in which the matrix is used to orient nanowires.

[0050] The invention also provides nanocomposites comprising nanostructures and a polysiloxane matrix, as well as articles comprising such composites. Another class of embodiments provides nanocomposites comprising branched nanowires or ferroelectric or semiconducting nanowires. Yet another class of embodiments includes the use of nanocomposites with blocking layers that conduct substantially only electrons or substantially only holes. Other nanocomposites are provided that support charge recombination or charge separation (e.g., for use in luminescent or photovoltaic devices). An additional class of embodiments provides composites in which interaction between the nanostructures and the matrix is enhanced, for example, by surface ligands on the nanostructures.

[0051] One general class of embodiments provides nanocomposites that comprise ferroelectric nanowires or ferroelectric nanoparticles and that can thus possess high dielectric constants. Compositions for making such nanocomposites (e.g., compositions suitable for use as inkjet or screen printing inks) are also provided, as are methods for making all the above composites and compositions. The following sections describe the invention in more detail.

[0052] Waveguides and Light Concentrators

[0053] One aspect of the present invention provides waveguides and light concentrators (e.g., solar concentrators) comprising nanostructures. Energy (e.g., light) is absorbed and re-emitted by the nanostructures and is waveguided by total internal reflection within a core. In many embodiments, the nanostructures are provided in the form of a nanocomposite.

[0054] Dye and Quantum Dot Solar Concentrators

[0055] As mentioned previously, typical approaches to reducing the cost of solar energy conversion are to increase the efficiency and/or size of a solar cell without proportionately increasing its cost. A different method of improving cost performance is to increase the intensity of light on a single cell. Assuming that the cell does not burn or saturate under the increased illumination, and assuming that the apparatus used to concentrate the light does not cost proportionately more than the increase in intensity, this can also produce an improvement in cost efficiency. One idea for this type of device is to take a large plastic or glass sheet and dope it with organic dye molecules that absorb and reemit light with high efficiency. Solar concentrators of this type are described in e.g., Weber et al. (1976) Appl. Opt . 15, 2299 and Goetzberger et al. (1977) Appl. Phys . 14, 123. As illustrated in FIG. 1 , light ( 4 , squiggly arrows) impinging on the sheet 1 from a light source 3 located above the sheet is absorbed by the dye molecules ( 5 , circles) and then re-emitted in all directions equally (isotropic emission). (Strictly speaking, most dye molecules emit light that is polarized along a single axis. In this type of solar concentrator, the individual dye molecules are isotropically oriented relative to each other within the sheet. As a result, the average emission profile of all of the dye molecules looks isotropic.) A few emitted light rays are indicated by solid arrows; continuing paths for some of these emitted rays are indicated by dashed arrows. Light that is re-emitted at angles that are greater than the critical angle for the interface between the sheet and the surrounding air is waveguided by total internal reflection and travels to the edge of the sheet before it escapes. Thus, light emitted at angles greater than the critical angle can be collected at the edge by a solar cell 2 . The critical angle (Θ _crit ) for a given sheet-air interface depends on the indices of refraction of the sheet and air: Θ _crit =sin ⁻¹ (n _r /n _i ), where n _r is the refractive index of air and n _i is the refractive index of the sheet. As illustrated for the critical angle 6 , an angle of incidence is measured between the incident ray 7 and a line 8 normal to the surface of the sheet.

[0056] By using a very large area concentrator, the intensity of the impinging light can be greatly concentrated, as represented by the equation C=S*G, where C is the ratio of light concentration collected, S is the ratio of the surface area of the sheet being illuminated by impinging light to the area of the collector at the edge of the sheet, and G represents losses in the concentrator that affect the ratio of the photons striking the surface of the concentrator to the number of photons that get guided to the edge of the sheet. In a standard concentrator, there are a number of inefficiencies that influence G. First, dye molecules only absorb a narrow band of wavelengths, and so most of the light that hits the concentrator is not absorbed, but simply passes through and is lost. This can be a substantial loss in overall efficiency. Second, dye molecules emit with finite quantum efficiency. As a result, even the photons that are absorbed do not all get re-emitted. Third, dye molecules are photo-unstable and eventually the concentrator stops working as the dye photobleaches. Finally, of the photons that are re-emitted, only those that emit at angles greater than the critical angle actually get wave guided and eventually collected. All other photons are lost. Other factors such as losses due to reabsorption or scatter within the concentrator also affect G, however, the factors above represent the major contributors to loss in this type of concentrator. As a result of these issues, solar concentrators of this type have not been implemented in a commercial product to date.

[0057] In order to improve the overall efficiency of a concentrator of the type described above, improvements in the following five characteristics are possible: 1) absorption efficiency; 2) absorption bandwidth (the breadth of the absorption spectrum); 3) quantum yield of the fluorophores in the concentrator; 4) photostability of the fluorophores in the concentrator; and 5) the angular distribution of intensities emitted from the fluorophores in the concentrator after illumination from above (the percentage of the reemitted photons have an angle greater than the critical angle and therefore get waveguided).

[0058] An improvement upon the dye molecule concentrator was made by replacing the dye molecules with quantum dots. See, e.g., Barnham et al. (2000) “Quantum-dot concentrator and thermodynamic model for the global red-shift” Applied Physics Letters 76, 1197-1199. Quantum dots have a number of substantial advantages over dye molecules: 1) they are extremely photostable and do not bleach, even under solar radiation; 2) they have an extremely broad absorption spectrum with extinction coefficients as much as 10 times greater than typical organic dye molecules and therefore absorb solar radiation much more efficiently than dye molecules; and 3) they can be fabricated with quantum efficiencies as high as 80%. Use of quantum dots in a solar concentrator therefore improves performance of the concentrator by improving the first four contributions to G described above (absorption efficiency, absorption bandwidth, quantum yield, and photostability). Like a collection of dye molecules, however, the collection of quantum dots emits isotropically and thus their use does not increase the percentage of emitted photons that are waveguided (the fifth contribution to G). In the case of solar concentrators comprising quantum dots, there are two effects that produce an isotropic emission profile from the collection of dots. First, for some quantum dots with a wurtzite crystal structure, the light emitted is not strictly polarized in the traditional sense, but along a 2-dimensional dipole moment oriented in the x-y plane of the nanocrystal. In other nanocrystals with a more symmetric crystal structure such as zincblend, light is emitted isotropically from the crystal in all three dimensions. Second, the quantum dots are not oriented within the sheet and therefore, even if they were polarized, they would still have an ensemble average emission profile that is isotropic. In both existing dye and quantum dot solar concentrators, it is significant that there is no consistent average orientation of the emission transition dipole to enhance collection efficiency as is described in the present invention.

[0059] In a quantum dot concentrator having quantum dots embedded in a transparent sheet surrounded by air, where the collection of dots emits light isotropically, at most ½*(cos(asin(n ₁ /n ₂ ))−cos(pi−asin(n ₁ /n ₂ ))) of the light emitted by the quantum dots can be waveguided and thus collected, where n ₁ is the refractive index of air and n ₂ is the refractive index of the sheet, cos is cosine, asin is arcsine, and pi is the Greek letter approximately equal to 3.14159265.

[0060] Ideas for improving the performance of a quantum dot concentrator include incorporating quantum dots with higher fluorescence quantum efficiency (e.g., greater than 30% or greater than 50%) or quantum dots with a substantially monodisperse size and/or shape distribution (see e.g., U.S. patent application Ser. No. 20020,071,952 by Bawendi et al entitled “Preparation of nanocrystallites”).

[0061] Light Concentrators

[0062] In a first general class of embodiments, the light concentrators of this invention comprise at least one core, at least one adjacent material that has a lower index of refraction than the core and that is in contact with at least a portion of a surface of the core, and a plurality of nanostructures. The nanostructures absorb light that impinges on a surface of the concentrator and re-emit light. The location of the nanostructures within the concentrator and/or the orientation of the nanostructures is controlled such that the fraction of the light emitted by the nanostructures that is waveguided by the core or cores is greater than ½*(cos(asin(n ₁ /n ₂ ))−cos(pi−asin(n ₁ /n ₂ ))), where n ₁ is the refractive index of the adjacent material and n ₂ is the refractive index of the core. (This fraction represents the amount of light that would be emitted at angles greater than the critical angle for a particular dielectric interface if the population of emitters were located within the core and were collectively emitting isotropically.) Preferably at least 1%, more preferably at least 10%, or most preferably at least 50% of the total nanostructures in the concentrator are located or oriented such that greater than ½*(cos(asin(n ₁ /n ₂ ))−cos(pi−asin(n ₁ /n ₂ ))), where n ₁ is the refractive index of the adjacent material and n ₂ is the refractive index of the core, of the light emitted by the nanostructures is waveguided by the core(s). At least one collector for collecting the waveguided light is operably connected to the core, e.g., to an edge of the core. Any type of collector can be used for collecting the light and/or measuring its intensity, for example, a detector, fiber optic cable, photocell, or solar cell. Optionally, any edges or portions of an edge of the core not occupied by the collector can be mirrored or silvered, so the waveguided light does not escape through these regions and decrease the efficiency of the concentrator. The adjacent material can be e.g., a cladding, a first layer comprising the nanostructures, or a layer of any low refractive index material.

[0063] The location of the nanostructures within the concentrator can be controlled. For example, the nanostructures can be located within the core or can be outside the core, e.g., in the material adjacent to the core. Alternatively or in addition, the orientation of the nanostructures can be controlled. For example, the light concentrator can comprise any nanostructures that have a definable unique axis of symmetry (e.g. a unique crystal axis such as the c-axis of a wurtzite na