DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0021] Poly(alkylene glycol) Residue

[0022] The poly(alkylene glycol) residue in the present invention is a polymer represented by the following formula (3).

—(R ³ O)m—R ⁴ (3)

[0023] In the formula (3), R ³ is an alkylene group having 2-6 carbons; R ⁴ is a structure which is freely selected from a group consisting of hydrogen atom, an alkyl group having 1-10 carbon(s), an aryl group having 10 or less carbons and an acyl group having 2-5 carbons; and m is a natural number of 50 or less.

[0024] Specific examples of R ³ in the formula (3) are ethylene group, n-propylene group, isopropylene group, n-butylene group, isobutylene group, n-pentylene group, cyclopentylene group, n-hexylene group and cyclohexylene group. In view of solubility in aqueous solvents, preferably R ³ is an alkylene group having 2-4 carbons such as ethylene group, n-propylene group, isopropylene group and n-butylene group. More preferably R ³ is an alkylene group having 2 or 3 carbons such as ethylene group, n-propylene group and isopropylene group. Most preferably R ³ is an ethylene group. In the formula (3), plural types of R ³ may be present in a residue and, in that case, there is no limitation for the copolymerizing sequence thereof.

[0025] Specific examples of the alkyl group used for R ⁴ in the formula (3) are methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, n-pentyl group, cyclopentyl group, n-hexyl group, cyclohexyl group, vinyl group, benzyl group and vinylbenzyl group. In view of solubility in aqueous solvents, preferably R ⁴ is an alkyl group having 3 or less carbon(s) such as methyl group, ethyl group, n-propyl group and isopropyl group. More preferably R ⁴ is a methyl group or ethyl group. Most preferably R ⁴ is a methyl group. Specific examples of the aryl group used for the R ⁴ are phenyl group, toluyl group (monomethylphenyl group), dimethylphenyl group, ethylphenyl group, isopropylphenyl group, 4-tert-butylphenyl group, vinylphenyl group, pyridyl group, monomethylpyridyl group and dimethylpyridyl group and, in view of solubility in aqueous solvents, phenyl group or pyridyl group is preferably used. Specific examples of the acyl group used for the above R ⁴ are acetyl group, acryloyl group, methacryloyl group, crotonoyl group and maleoyl group and, in view of solubility in aqueous solvents, acetyl group is preferably used.

[0026] When a polymerizing group such as vinyl group, vinylbenzyl group, vinylphenyl group, acryloyl group, methacryloyl group, crotonoyl group and maleoyl group is used among the above-exemplified specific structures for the above R ⁴ , there are some cases where the semiconductor nanoparticles of the present invention acquire a copolymerizing property with, for example, radically polymerizing monomers or ionically polymerizing monomers.

[0027] The natural number (m) in the formula (3) is preferably 40 or less, more preferably 30 or less and, still more preferably, 20 or less and, in view of solubility, it is preferably 10 or less and, particularly preferably, 5 or less.

[0028] The particularly preferred structures of the formula (3) are a diethylene glycol residue (R ³ is ethylene group and m=2) and a triethylene glycol residue (R ³ is ethylene group and m=3), the more preferred ones are a diethylene glycol monoalkyl ether residue where R ⁴ is methyl group or ethyl group where R ⁴ is methyl group or ethyl group and a triethylene glycol monoalkyl ether residue and the most preferred ones are a diethylene glycol monomethyl ether residue and a triethylene glycol monomethyl ether residue (hereinafter, abbreviated as an MTEG residue) where R ⁴ is methyl group.

[0029] In the present invention, such a poly(alkylene glycol) residue is attached as a ligand onto the surface of the semiconductor crystals which will be mentioned later by any bonding manner to give the semiconductor nanoparticles of the present invention. With regard to such a bonding manner, any bonding manner which is possible for the elements contained in the semiconductor crystals such as coordinate bond, covalent bond and ionic bond will be exemplified and specific examples are bonding manners where there are utilized a sulfur-containing structure such as mercapto group (another name: thiol group which is SH), sulfide bond (another name: thioether bond), disulfide bond (—S—S—) and thiourea group (NHCSNH ₂ ), a group having a (P═O) structure such as phosphinic acid residue, phosphonic acid residue and phosphine oxide group, a nitrogen-containing structure such as nitrile group, amino group and pyridyl group, an acidic group such as carboxyl group and sulfonic acid group and a coordinating structure of amide group, etc. such as carboxylic acid amide group and sulfonic acid amide group. Preferred one among the above is a bond where any of a group having (P═O) structure, amino group and mercapto group is utilized.

[0030] The semiconductor nanoparticles of the present invention may contain a plurality of poly(alkylene glycol) residues.

[0031] Functional Group Having a (P═O) Structure

[0032] In the present invention, the above poly(alkylene glycol) residue is attached onto the surface of semiconductor crystals via an oxygen atom in a functional group having a (P═O) structure represented by the following formula (1) whereby, in addition to dispersity in solvents and resins, there is a significant improvement in absorption and luminescence efficiencies and, accordingly, that is particularly preferred. 1

[0033] In the formula (1), P is bonded to R ¹ , R ² , O and the poly(alkylene glycol) residue. R ¹ and R ² each is any member selected from hydrogen atom, hydroxyl group, optionally substituted alkyl group, aryl group, alkoxy group and trialkylsilyl group having 8 or less carbon(s) and halogen atom and R ¹ and R ² may be same or different. Examples of the substituent in that case are halogen atom, nitro group, hydroxyl group and carboxyl group.

[0034] As a result of utilization of a functional group represented by the formula (1), luminescence ability of the semiconductor nanoparticles after coordination is significantly improved. It is likely to be due to a strong coordinating power of oxygen atom in the functional group represented by the formula (1) to transition metal element existing on the surface of the semiconductor crystals. Although the actual bonding structure of the said strong coordination powder is ambiguous, there is presumed the presence of coordination bond, etc. of oxygen.

[0035] When R ¹ and R ² each in the functional group represented by the formula (1) contains carbon atom, it is more preferred that its carbon numbers are not more than 5 so that no steric hindrance is resulted upon coordination to the semiconductor nanoparticles. Specific examples of R ¹ and R ² in the preferred functional group are hydrogen atom, hydroxyl group, an alkyl group such as methyl group, ethyl group and butyl group, an alkoxyl group such as methoxyl group, ethoxyl group and butoxyl group, a trialkylsilyl group such as trimethylsilyl group and halogen atom such as fluorine atom, chlorine atom and bromine atom. Among them, it is more preferred that at least one of R ¹ and R ² is hydroxyl group and it is most preferred that both R ¹ and R ² are hydroxyl groups in view of coordination power to the semiconductor crystals.

[0036] Linking Group for a poly(alkylene glycol) Residue with the Functional Group Represented by the Formula (1)

[0037] In the present invention, a linking group for the poly(alkylene glycol) residue with the functional group represented by the formula (1) may be freely selected. Its specific examples are an alkylene group, an alkenylene group and an alkynylene group or a compound where its carbon chain contains ether bond, ester bond, amide bond, carbonyl bond, amino group, thiocarbonyl group, etc. and a compound where one or more of hydrogen atoms thereof is/are substituted with halogen atom, nitro group, hydroxyl group, carboxyl group, an alkyl group having 4 or less carbon(s), an alkoxyl group having 4 or less carbon(s), an aryl group having 8 or less carbons, etc. Among them, an alkylene group and an alkenylene group are preferably used. Particularly, an alkylene group where the carbon chain comprises 6 or more carbons or, preferably, an alkylene group where the carbon chain comprises 6-20 carbons is most preferred since there are some cases where the effects of protecting the semiconductor crystals from outside and of stabilizing the absorption and luminescence characteristics are noted.

[0038] It is also possible that the poly(alkylene glycol) residue is directly bonded to the functional group represented by the formula (1).

[0039] To be more specific, the semiconductor nanoparticles where a compound represented by the following formula (10) is attached onto the semiconductor crystal surface are preferred because of an excellent luminescence characteristic and an excellent miscibility with the resin. 2

[0040] In the formula (10), R is hydrogen atom or an alkyl group having 7 or less carbon(s); n is a natural number of 20 or less; and r is from 2 to 10 and, preferably, 5 or less.

[0041] Specific examples of the compound represented by the formula (10) are 3,6,9-trioxaalkylphosphonic acid (2-(2-(2-alkoxyethoxy)ethoxy)ethylphosphonic acid) (n=2, r=2) and n-phosphonoalkyl triethylene glycol monomethyl ether (r=3).

[0042] n-Phosphonoalkyl triethylene glycol ethers

[0043] With regard to the molecular structure where a poly(alkylene glycol) residue and a functional group represented by the formula (1) are bonded which is preferably used as a ligand to the semiconductor crystals in the present invention, there may be exemplified n-phosphonoalkyl triethylene glycol ethers represented by the following formula (2). 3

[0044] In the formula (2), R is hydrogen atom or an alkyl group having 7 or less carbon(s) and n is a natural number of 20 or less. Examples of the alkyl group used as R are as same as those in the case of R ⁴ in the already-mentioned formula (3). In the formula (2), the lower limit of the natural number (n) is preferably 1 or more, more preferably 3 or more and, most preferably, 6 or more while the upper limit thereof is preferably 17 or less, more preferably 14 or less and, most preferably, 12 or less and, when value of the natural number (n) is 6 or more, there are some cases where the effects of protecting the semiconductor crystals from outside and of stabilizing its absorption and luminescence characteristics are noted. With regard to a particularly preferred specific compound, 10-phosphonodecyl MTEG ether (10-(2-(2-methoxyethoxy)ethoxy)ethoxdecylphosphonic acid) represented by the following formula (4) is exemplified. 4

[0045] Functional Group Having an Amino Group

[0046] When such a poly(alkylene glycol) residue is attached onto the surface of the semiconductor crystals via an amino group or a functional group having an amino group in the present case, luminescence ability of the semiconductor nanoparticles after coordination is significantly improved. It is likely to be due to the fact that amino group has a strong coordinating power to transition metal element existing on the surface of the semiconductor crystals. Although the actual bonding structure of the amino group coordinating structure with the semiconductor crystal surface is ambiguous, the presence of coordination bond of nitrogen atom of the amino group or the like is presumed.

[0047] With regard to the functional group having an amino group, an ω-aminofatty acid residue is particularly preferred and that where a poly(alkylene glycol) residue is attached onto the semiconductor crystal surface via the said group is preferred in terms of luminescence characteristic and dispersity in solvents and resins. The ω-aminofatty acid residue used hereinabove is a structure represented by the following formula (5). 5

[0048] In the formula (5), p is a natural number of 20 or less and a circle with a broken line is a position to which the poly(alkylene glycol) residue is bonded.

[0049] Although there is no limitation for the bonding manner for the poly(alkylene glycol) residue with the ω-aminofatty acid residue, it is usually any of ester bond, amide bond and carbon-carbon single bond. Thus, in the case of an ester bond, it is a manner where a carbon atom in R ³ at the left end in the formula (3) is bonded to a carbon atom in the carbonyl group in the formula (5) via, for example, one oxygen atom while, in the case of an amide bond, it is a manner where they are similarly bonded via one nitrogen atom. In such an amide bond, both primary amide and secondary amide are possible.

[0050] With regard to a molecular structure where a poly(alkylene glycol) residue and an ω-aminofatty acid residue are bonded which is preferably used as a ligand, there may be exemplified triethylene glycol esters of ω-aminofatty acid represented by the following formula (6). 6

[0051] In the formula (6), R is hydrogen atom or an alkyl group having 7 or less carbon(s) and n is a natural number of 20 or less. Examples of the alkyl group used as R are the same as those in the case of R ⁴ in the already-mentioned formula (3). The lower limit of the natural number n in the formula (1) is preferably 1 or more, more preferably 3 or more and, most preferably, 6 or more while the upper limit thereof is preferably 17 or less, more preferably 14 or less and, most preferably, 10 or less. When the value of the natural number n is 6 or more, there are some cases where there is noted an effect in which the semiconductor crystals are protected from outside whereby its absorption and luminescence characteristics are stabilized. With regard to the particularly preferred specific compound, 11-aminoundecanoic acid MTEG ester (2-(2-(2-methoxyethoxy)ethoxy)ethyl 11-aminoundecanoate) having the following formula (7) may be exemplified.

NH ₂ (CH ₂ ) ₁₀ COO(CH ₂ CH ₂ O) ₃ CH ₃ (7)

[0052] The esters of the above formula (6) are synthesized, for example, by a method where a condensing agent such as carbodiimide is added to ω-aminofatty acid such as 3-aminopropanoic acid or 11-aminoundecanoic acid and poly(alkylene glycol) which is in nearly equivalent thereto to esterify; a method where the said ω-aminofatty acid and an excessive amount of poly(alkylene glycol) are subjected to dehydrating esterification in the presence of an acid catalyst such as sulfuric acid or p-toluenesulfonic acid (if necessary, heating or dehydration in vacuo is carried out to accelerate the equilibrium reaction); a method where a lower alkyl ester such as methyl ester or ethyl ester of the said ω-aminofatty acid and an excessive amount of poly(alkylene glycol) are subjected to a transesterification in the presence of a strong acid such as sulfuric acid or p-toluenesulfonic acid or in the presence of a catalyst such as Lewis acid (if necessary, heating or vacuation is carried out to accelerate the equilibrium reaction); and a method where the said aminofatty acid is converted to an active species such as the corresponding acid chloride or acid hydride and then subjected to condensation reaction with poly(alkylene glycol) in the presence of a base. In that case, a protective group may be introduced into the amino group for preventing the reaction between the amino group and the carboxyl group.

[0053] Functional Group Having a Mercapto Group

[0054] In the present invention, a poly(alkylene glycol) residue is preferably attached onto the semiconductor crystal surface via a mercapto group or a functional group having a mercapto group. Among the above, that which is attached via an ω-mercaptofatty acid residue is particularly preferred. The ω-mercaptofatty acid residue referred to hereinabove is a structure represented by the following structure (8). 7

[0055] In the formula (8), p is a natural number of 20 or less and a circle with a broken line shows a position to which the poly(alkylene glycol) is bonded.

[0056] The semiconductor nanoparticles as such can be utilized as a biological analytical reagent which has an excellent water solubility and has a significantly reduced non-specific adsorption worsening the analytical precision as compared with the conventional ones when a chemical structure (such as antibody, nucleic acid and protein) having a biological interaction with a specific structure is further introduced thereinto.

[0057] Although there is no limitation for the bonding manner of the poly(alkylene glycol) residue with the ω-mercaptofatty acid residue, it is usually made in any of ester bond, amide bond and carbon-carbon single bond. Thus, in the case of an ester bond, it is a manner where a carbon atom at the left terminal R ³ in the formula (3) and a carbon atom of carbonyl group in the formula (8) are bonded via, for example, one oxygen atom and, in the case of an amide bond, it is a manner where they are similarly bonded via one nitrogen atom. In such an amide bond, both primary amide and secondary amide are able to be used.

[0058] With regard to a molecular structure preferably used as a ligand where a poly(alkylene glycol) residue and an ω-mercaptofatty acid residue are bonded, there may be exemplified triethylene glycol esters of ω-mercaptofatty acid represented by the following formula (9). 8

[0059] In the formula (9), R is hydrogen or an alkyl group having 7 or less carbon(s) and n is a natural number of 20 or less. Examples of the alkyl group used as R are the same as those in the case of R ⁴ in the already-mentioned formula (3). The lower limit of the natural number n in the formula (9) is preferably 1 or more, more preferably 3 or more and, most preferably, 6 or more while the upper limit thereof is preferably 17 or less, more preferably 14 or less and, most preferably, 10 or less. When the value of the natural number n is 6 or more, there are some cases where an effect in which the semiconductor crystals are protected from outside whereby its absorption and luminescence characteristics are stabilized is noted. With regard to the particularly preferred specific compound, there are exemplified 11-mercaptoundecanoic acid MTEG esters (2-(2-(2-methoxyethoxy)ethoxy)ethyl 11-mercaptoundecanoate) having the following formula (10).

HS(CH ₂ ) ₁₀ COO(CH ₂ CH ₂ O) ₃ CH ₃ (10)

[0060] The esters of the above formula (10) are synthesized, for example, by a method where an ω-mercaptofatty acid such as 3-mercaptopropanoic acid or 11-mercaptoundecanoic acid and an excessive amount of poly(alkylene glycol) are subjected to a dehydrating esterification in the presence of an acid catalyst such as sulfuric acid or p-toluenesulfonic acid (if necessary, heating or dehydration in vacuo is carried out to accelerate the equilibrium reaction); a method where a lower alkyl ester such as methyl ester or ethyl ester of the said ω-mercaptofatty acid and an excessive amount of poly(alkylene glycol) are subjected to a transesterification in the presence of a strong acid such as sulfuric acid or p-toluenesulfonic acid or in the presence of a catalyst such as Lewis acid (if necessary, heating or vacuation is carried out to accelerate the equilibrium reaction); and a method where the said ω-mercaptofatty acid is converted to an active species such as the corresponding acid chloride or acid hydride and then subjected to a condensation reaction with poly(alkylene glycol) in the presence of a base.

[0061] Semiconductor Nanoparticles

[0062] In the semiconductor nanoparticles of the present invention, it mainly comprises the semiconductor crystals which will be mentioned later and the above-mentioned poly(alkylene glycol) residue is attached to the surface thereof. Accordingly, in the semiconductor nanoparticles of the present invention, the semiconductor crystals and the poly(alkylene glycol) residue attached to the surface thereof are essential constituent components.

[0063] It is preferred that the semiconductor crystals used in the present invention have exciton absorption and luminescence bands controlled by quantum effect in the absorption and luminescence spectra. The absorption and luminescence wavelengths which are particularly useful in practical use are light of from far-ultraviolet to infrared regions and its lower limit is within a region of usually 150 nm or more, preferably 180 nm or more, still more preferably 200 nm or more and, most preferably, 220 nm or more while the upper limit is within a region of usually 10,000 nm or less, preferably 8,000 nm or less, more preferably 6,000 nm or less and, most preferably, 4,000 nm or less. The above-mentioned exciton absorption and luminescence bands are phenomenalistically dependent upon the particle size of the said semiconductor crystals.

[0064] The semiconductor crystals may be any of semiconductor single crystal, mixed crystals where plural semiconductor crystal compositions are phase-separated and mixed semiconductor crystals where phase separation is not observed and also may be in a core-shell structure which will be mentioned later.

[0065] Particle size of such semiconductor crystals is usually from 0.5 nm or more to 20 nm or less in terms of a number-average particle size and, in view of controlling property of the absorption and luminescence wavelengths by quantum effect, the lower limit is preferably 1 nm or more, more preferably 2 nm or more and, most preferably, 3 nm or more while the upper limit is preferably 15 nm or less, more preferably 12 nm or less and, most preferably, 10 mn or less. For determining the said number-average particle size, the value measured from the image of the given semiconductor nanoparticles observed under a transmission electron microscope (TEM) is used. Thus, diameter of a circle having the same area with the particle image of the observed semiconductor crystals is defined as the particle size of the particle image. The particle size determined as such is used and the number-average particle size is calculated by, for example, means of a known statistically processing means for image data. It is of course preferred that the numbers of the particle images (numbers of the statistically processed data) of the semiconductor crystals used in such a statistical process are as many as possible and, in the present invention, the number of particle images randomly selected are at least 50 or more, preferably 80 or more and, more preferably, 100 or more in view of the reproducibility.

[0066] When the number-average particle size is too big, there are some cases where an aggregating property increases to a large extent or a controlling property of exciton absorption and luminescence by quantum effect decreases while, when it is too small, there some cases where a crystal function of the semiconductor crystal particle (such as formation of a band structure giving luminescence power) decreases or the isolation yield upon manufacture decreases to a large extent and none of these is preferred. Incidentally, when the atomic number of the element contained in the semiconductor crystals is too small whereby contrast by electron beam in an observation under a TEM is hardly available, it is possible to estimate the particle size by an observation under an atomic force microscope (AFM) or by a combination of a composition analysis result such as elementary analysis with measurement of neutron scattering or light scattering in a solution.

[0067] Although there is no limitation for the particle size distribution of the semiconductor crystals, it is possible to change the wavelength width of absorption and luminescence bands by changing such a distribution in case an exciton absorption and luminescence bands of the semiconductor crystals are utilized. When it is necessary to make the wavelength width narrow, the particle size distribution is made narrow and, usually, the standard deviation is made within ±40%, preferably within ±30%, more preferably within ±20% and, most preferably, within ±10%. In the case where the particle size distribution is more than the range of standard deviation, it is difficult to fully achieve an object of making the wavelength width of exciton absorption and luminescence bands narrow.

[0068] Composition of Semiconductor Crystals

[0069] When the composition example of the above-mentioned semiconductor crystals is expressed by a composition formula, the following may be exemplified: they are a single substance of element of group 14 of the periodic table such as C, Si, Ge and Sn; a single substance of element of group 15 of the periodic table such as P (black phosphorus); a single substance of element of group 16 of the periodic table such as Se and Te; a compound comprising plural elements of group 14 of the periodic table such as SiC; a compound of element of group 14 of the periodic table with element of group 16 of the periodic table such as SnO ₂ , Sn(II)Sn(IV)S ₃ , SnS ₂ , SnS, SnSe, SnTe, PbS, PbSe and PbTe; a compound of element of group 13 of the periodic table with element of group 15 of the periodic table (or semiconductor of a compound of group III-group V) such as BN, BP, BAs, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, Inp, InAs and InSb; a compound of element of group 13 of the periodic table with element of group 16 of the periodic table such as Al ₂ S ₃ , Al ₂ Se ₃ , Ga ₂ S ₃ , Ga ₂ Se ₃ , Ga ₂ Te ₃ , In ₂ O ₃ , In ₂ S ₃ , In ₂ Se ₃ and In ₂ Te ₃ ; a compound of element group 13 of the periodic table with element of group 17 of the periodic table such as TlCl, TlBr and TlI; a compound of element of group 12 of the periodic table with element of group 16 of the periodic table (or semiconductor of a compound of group II-group VI) such as ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, HgS, HgSe and HgTe; a compound of element of group 15 of the periodic table with element of group 16 of the periodic table such as As ₂ S ₃ , As ₂ Se ₃ , As ₂ Te ₃ , Sb ₂ S ₃ , Sb ₂ Se ₃ , Sb ₂ Te ₃ , Bi ₂ S ₃ , Bi ₂ Se ₃ and Bi ₂ Te ₃ ; a compound of element of group 11 of the periodic table with element of group 16 of the periodic table such as Cu ₂ O and Cu ₂ Se; a compound of element of group 11 of the periodic table with element of group 17 of the periodic table such as CuCl, CuBr, CuI, AgCl and AgBr; a compound of element of group 10 of the periodic table with element of group 16 of the periodic table such as NiO; a compound of element of group 9 of the periodic table with element of group 16 of the periodic table such as CoO and CoS; a compound of element of group 8 of the periodic table with element of group 16 of the periodic table such as iron oxide (e.g., Fe ₃ O ₄ ) and FeS; a compound of element of group 7 of the periodic table with element of group 16 of the periodic table such as MnO; a compound of element of group 6 of the periodic table with element of group 16 of the periodic table such as MoS ₂ and WO ₂ ; a compound of element of group 5 of the periodic table with element of group 16 of the periodic table such as VO, VO ₂ and Ta ₂ O ₅ ; a compound of element of group 4 of the periodic table with element of group 16 of the periodic table such as titanium oxide (e.g., TiO ₂ , Ti ₂ O ₅ , Ti ₂ O ₃ and Ti ₅ O ₉ ; where the crystal type may be any of a rutile type, a mixed type of rutile/anatase and an anatase type) and ZrO ₂ ; a compound of element of group 2 of the periodic table with element of group 16 of the periodic table such as MgS and MgSe; a chalcogen spinel such as CdCr ₂ O ₄ , CdCr ₂ Se ₄ , CuCr ₂ S ₄ and HgCr ₂ Se ₄ ; and BaTiO ₃ . Similarly are exemplified semiconductor clusters where their structures are established such as (BN) ₇₅ (BF ₂ ) ₁₅ F ₁₅ reported by G. Schmid, et al. in Adv. Mater., volume 4, page 494 (1991) and Cu ₁₄₆ Se ₇₃ (triethylphosphine) ₂₂ reported by D. Fenske, et al. in Angew. Chem. Int. Ed. Engl., volume 29, page 1452 (1990).

[0070] Among them, examples of the practically important ones are a single substance of group 14 such as Si and Ge; a compound of element of group 14 of the periodic table with element of group 16 of the periodic table such as SnO ₂ , SnS ₂ , SnS, SnSe, SnTe, Pbs, PbSe and PbTe; a group III-group V compound semiconductor such as GaN, GaP, GaAs, GaSb, InN, InP, InAs and InSb; a compound of element of group 13 of the periodic table with element of group 16 of the periodic table such as Ga ₂ O ₃ , Ga ₂ S ₃ , Ga ₂ Se ₃ , Ga ₂ Te ₃ , In ₂ O ₃ , In ₂ S ₃ , In ₂ Se ₃ and In ₂ Te ₃ ; a group II-group VI compound semiconductor such as ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, HgO, HgS, HgSe and HgTe; a compound of element of group 15 of the periodic table with element of group 16 of the periodic table such as As ₂ O ₃ , As ₂ S ₃ , As ₂ Se ₃ , As ₂ Te ₃ , Sb ₂ O ₃ , Sb ₂ S ₃ , Sb ₂ Se ₃ , Sb ₂ Te ₃ , Bi ₂ O ₃ , Bi ₂ S ₃ , Bi ₂ Se ₃ and Bi ₂ Te ₃ ; a compound of element of group 8 of the periodic table with element of group 16 of the periodic table such as iron oxide (e.g., Fe ₃ O ₄ ) and FeS; a compound of element of group 4 of the periodic table with element of group 16 of the periodic table such as the above-mentioned titanium oxide and ZrO ₂ ; and a compound of element of group 2 of the periodic table with element of group 16 of the periodic table such as MgS and MgSe.

[0071] Among the above, Si, Ge, SnO ₂ , GaN, GaP, In ₂ O ₃ , InN, InP, Ga ₂ O ₃ , Ga ₂ S ₃ , In ₂ O ₃ , In ₂ S ₃ , ZnO, ZnS, CdO, CdS, the above-mentioned titanium oxides, ZrO ₂ , MgS, etc. have a characteristic of having a high refractive index and, in addition, they do not contain a highly toxic negative element whereby they are preferred in view of prevention of environmental pollution and safety to living organisms. From such a viewpoint, the compositions containing no highly toxic positive elements such as SnO ₂ , In ₂ O ₃ , ZnO, ZnS, the above-mentioned titanium oxide and ZrO ₂ are more preferred and, among them, metal oxide semiconductor crystals such as ZnO or the above-mentioned titanium oxide (in view of an object of high refractive index, crystals of a rutile type is particularly preferred) and ZrO ₂ are most preferred. Incidentally, absorption edge at the long wavelength side of titanium oxide crystal particles of a rutile type is usually near 400 nm in its bulk state and, when number-average particle size of the crystal particles is made within the above-mentioned range, it is possible to shift the absorption edge wavelength at the long wavelength side to shorter wavelength and there are some cases where an advantage that colorless property in a visible region is improved can be resulted. Further, colored semiconductor crystals having absorption property in visible region such as iron oxides and cobalt blue (a compounded oxide of Co and Al) are important for the use as color materials such as pigments.

[0072] Important ones are those having luminescence bands at and near the practically important visible region are group III-group V compound semiconductors such as GaN, GaP, GaAs, InN and InP; group II-group VI compound semiconductors such as ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, HgO and HgS; Si; Ge; In ₂ O ₃ ; In ₂ S ₃ and the like. Among the above, preferred ones in view of a controlling property for crystal particle size and a luminescence property are group III-group V compound semiconductors such as GaN, GaP, GaAs, InN and InP and group II-group VI compound semiconductors such as ZnO, ZnS, ZnSe, ZnTe, CdO, CdS and CdSe. Particularly, ZnSe, CdS, CdSe, InP, etc. are more advantageously used for such an object.

[0073] If necessary, element such as Al, Mn, Cu, Zn, Ag, Cl, Ce, Eu, Tb or Er may be added to any of the above-exemplified semiconductor crystal compositions as a minor dopant substance (which means impurities are added intentionally).

[0074] Semiconductor Crystals of a Core-Shell Type

[0075] As reported by A. R. Kortan, et al.: J. Am. Chem. Soc., volume 112, page 1327 (1990) or in the specification of U.S. Pat. No. 5,985,173 (1999) for example, when the above-mentioned semiconductor crystals are made into the so-called core-shell structure comprising core and shell with an object of improving the electron excitation characteristic of the semiconductor crystals, there are some cases where the stability of quantum effect of the semiconductor crystals constituting the core is improved whereby there are some cases in which that is advantageous for a use where exciton absorption and luminescence bands are utilized. In that case, it is generally effective that, as a composition for the semiconductor crystals of the shell, the composition having more forbidden band gap than the core is used so as to form an energy barrier. This is presumed to be due to the construction which suppresses the influence from outside and also the influence such as that by undesired surface level caused by crystal lattice defect on the crystal surface.

[0076] With regard to the composition of the semiconductor crystals which is advantageously used for such a shell, although that is dependent upon the band gap of the core semiconductor crystals, that where the band gap in a bulk state is 2.0 electron volts or more at the temperature of 300° K is advantageous used and its examples are group III-group V compound semiconductors such as BN, BAs, GaN and GaP, group II-group VI compound semiconductors such as ZnO, ZnS, ZnSe, ZnTe, CdO and CdS and compounds of element of group 2 in the periodic table with element of group 16 of the periodic table such as MgS and MgSe. Among those, the semiconductor composition giving more preferred shell is that where the band gap in a bulk state is 2.3 electron volts (eV) or more at the temperature of 300° K and its examples are group III-group V compound semiconductors such as BN, BAS and GaN, group II-group VI compound semiconductors such as ZnO, ZnS, ZnSe and CdS and compounds of element of group 2 of the periodic table with element of group 16 of the periodic table such as MgS and MgSe. The most preferred one is that where the band gap in a bulk state is 2.5 electron volts (eV) or more at the temperature of 300° K and its examples are BN, BAS, GaN, ZnO, ZnS, ZnSe, MgS and MgSe. In view of chemical synthesis, ZnS is used most advantageously.

[0077] When examples of combination of the core-shell composition which is particularly advantageous upon use as the semiconductor crystals in the present invention are expressed by the composition formulae, they are CdSe—ZnS, CdSe—ZnO, CdSe—CdS, CdS—ZnS, CdS—ZnO, ZnSe—ZnS, InP—ZnS, etc.

[0078] Auxiliary Ligand

[0079] The semiconductor crystal nanoparticles of the present invention may have other auxiliary ligands than the above-mentioned poly(alkylene glycol) residue on their surface with an object of suppressing the undesired action such as aggregation resulting in stabilization. Such ligands will be exemplified hereunder.

[0080] (a) Sulfur-containing compounds: Mercaptoalkanes such as mercaptoethane, 1-mercapto-n-propane, 1-mercapto-n-butane, 1-mercapto-n-hexane, mercaptocyclohexane, 1-mercapto-n-octane and 1-mercapto-n-decane; thiophenol and thiophenol derivatives such as 4-methylthiophenol, 4-tert-butylthiophenol and 4-hydroxythiophenol; dialkyl sulfoxides such as dimethyl sulfoxide, diethyl sulfoxide, dibutyl sulfoxide, dihexyl sulfoxide, dioctyl sulfoxide and dodecyl sulfoxide; dialkyl disulfides such as dimethyl disulfide, diethyl disulfide, dibutyl disulfide, dihexyl disulfide, dioctyl disulfide and dodecyl disulfide; compounds having thiocarbonyl group such as thiourea and thioacetamide; sulfur-containing aromatic compounds such as thiophene; etc.

[0081] (b) Phosphorus-containing compounds: Trialkylphosphines such as triethylphosphine, tributylphosphine, trihexylphosphine, trioctylphosphine, tridecylphosphine and tris(3-hydroxypropyl)phosphine; trialkylphosphine oxides such as triethylphosphine oxide, tributylphosphine oxide, trihexylphosphine oxide, trioctylphosphine oxide (abbreviation: TOPO), tridecylphosphine oxide and tris(3-hydroxyprophyl)phosphine oxide; aromatic phosphines such as triphenylphosphine; aromatic phosphine oxides such as triphenylphosphine oxide; etc.

[0082] (c) Nitrogen-containing compounds: Nitrogen-containing aromatic compounds such as pyridine and quinoline; secondary amines such as diethylamine, dibutylamine, dihexylamine, dioctylamine, dodecylamine, diphenylamine, dibenzylamine and diethanolamine; primary amines such as hexylamine, octylamine, decylamine, dodecylamine, hexadecylamine, octadecylamine, phenylamine, benzylamine and 2-aminoethanol; carboxylates having amino group such as triethyl nitrilotriacetate; etc.

[0083] Among the auxiliary ligands exemplified hereinabove, preferred ones are the sulfur-containing compounds such as mercaptoalkanes having 6 or less carbons (e.g., mercaptoethane, 1-mercapto-n-propane, 1-mercapto-n-butane, 1-mercapto-n-hexane and mercaptocyclohexane), thiophenol and thiophenol derivatives (e.g., 4-methylthiophenol and 4-tert-butylthiophenol) and dialkyl sulfoxides having 8 or less total carbons (e.g., dimethyl sulfoxide, diethyl sulfoxide and dibutyl sulfoxide); the phosphorus-containing compounds such as trialkylphosphines (e.g., tributylphosphine, trihexylphosphine and trioctylphosphine) and trialkylphosphine oxides having 24 or less total carbons (e.g., triethylphosphine oxide, tributylphosphine oxide, trihexylphosphine oxide and trioctylphosphine oxide); and the primary amines (e.g., hexadecylamine). Among the above, the more preferred ones are the sulfur-containing compounds such as mercaptoalkanes having 4 or less carbons (e.g., mercaptoethane and 1-mercapto-n-butane) and thiophenol and its derivatives (e.g., 4-methylthiophenol and 4-tert-butylthiophenol); and the phosphorus-containing compounds such as trialkylphosphines having 18 or less total carbons (e.g., tributylphosphine and trihexylphosphine) and trialkylphosphine oxides having 18 or less total carbons (e.g., tributyl phosphine oxide and trihexylphosphine oxide).

[0084] Method for the Manufacture of the Semiconductor Crystals

[0085] Any method including the following conventionally conducted methods for the manufacture of semiconductor crystals may be used. Although the above-mentioned vacuum manufacturing process may be utilized, the following three liquid-phase methods may be exemplified as appropriate ones.

[0086] (a) A method where an aqueous solution of materials is made to exist as reversed micelle in a nonpolar organic solvent and crystal growth is carried out in the reversed micelle phase (hereinafter, referred to as “reversed micelle method”). This is a method reported, for example, in B. S. Zou, et al.: Int. J. Quant. Chem., volume 72, 439 (1999). This is a method suitable for an industrial production because of the reasons that the known reversed micelle stabilizing technique can be utilized in commonly-used reactors, that salts which are relatively less expensive and chemically stable can be used as the materials and further that the process is carried out at relatively low temperature which is not higher than the boiling point of water. However, as compared with the following hot soap method, there are some cases where luminescence characteristic is poor under the current state of technique.

[0087] (b) A method where thermodegradable materials are injected into a liquid-phase organic medium of high temperature whereby crystal growth is carried out (hereinafter, referred to as a hot soap method). This is a method reported, for example, in the already-mentioned literature by Katari, et al. As compared with the above reversed micelle method, it is now possible to give semiconductor crystal particles having excellent particle size distribution and purity and there is a characteristic that the product has an excellent luminescence characteristic and is usually soluble in organic solvents. With an object of desirable control of the reaction rate during the process of crystal growth in the liquid phase in the hot soap method, coordination organic compounds having an appropriate coordination power to the semiconductor-constituting elements are selected as liquid-phase components (acting as both solvent and ligand). Examples of such coordination organic compounds are the above-mentioned trialkylphosphines, the above-mentioned trialkylphosphine oxides, ω-aminoalkanes such as dodecylamine, tetradecylamine, hexadecylamine and octadecylamine and the above-mentioned dialkyl sulfoxides. Among those, preferred ones are the above-mentioned trialkylphosphine oxides such as TOPO, the ω-aminoalkanes such as hexadecylamine, etc.

[0088] (c) There has been already known a method which is a reaction solution where growth of semiconductor crystals similar to the above hot soap method takes place although an acid-base reaction is used as a driving force and the process is carried out at relatively low temperature (e.g., P. A. Jackson: J. Cryst. Growth, volumes 3-4, page 395 (1968)). Such a method may be sometimes classified under the name of a sol-gel method.

[0089] With regard to the semiconductor material substances which can be used for the above-mentioned three liquid-phase manufacturing methods, there are listed substances containing the positive elements selected from groups 2-15 of the periodic table and substances containing the negative elements selected from groups 15-17 of the periodic table. For example, in the above hot soap method, there is advantageously used a method where organic metal such as dimethyl cadmium or diethyl zinc is made to react in TOPO with a solution of a single substance of selenium in tertiary phosphine such as trioctylphosphine or tributylphosphine or with a chalcogenide element compound such as bis(trimethylsilyl) sulfide. When zinc oxide, for example, is manufactured in the above-mentioned solution reaction (c), there is advantageously used a method mentioned in L. Spanhel, et al.: J. Am. Chem. Soc., volume 113, page 2826 (1991) where zinc acetate is made to react with lithium hydroxide in ethanol. When there is a plurality of semiconductor material substances, they may be previously mixed or each of them may be injected into the reaction liquid phase. Those materials may be used as a solution using an appropriate diluting solvent.

[0090] Examples of the compound containing positive element used as the material compound for semiconductors are dialkylated compounds of element of group 2 of the periodic table such as diethyl magnesium and di-n-butyl magnesium; alkyl halides of element of group 2 of the periodic table such as methyl magnesium chloride, methyl magnesium bromide, methyl magnesium iodide and ethynyl magnesium chloride; dihalides of element of group 2 of the periodic table such as magnesium iodide; halides of element of group 4 of the periodic table such as titanium (IV) tetrachloride, titanium (IV) tetrabromide and titanium (IV) tetraiodide; halides of element of group 5 of the periodic table such as vanadium (II) dichloride, vanadium (IV) tetrachloride, vanadium (II) dibromide, vanadium (IV) tetrabromide, vanadium (II) diiodide, vanadium (IV) tetraiodide, tantalum (V) pentachloride, tantalum (V) pentabromide and tantalum (V) pentaiodide; halides of element of group 6 of the periodic table such as chromium (III) tribromide, chromium (III) triiodide, molybdenum (IV) tetrachloride, molybdenum (IV) tetrabromide, molybdenum (IV) tetraiodide, tungsten (IV) tetrachloride and tungsten (IV) tetrabromide; halides of element of group 7 of the periodic table such as manganese (II) dichloride, manganese (II) dibromide and manganese (II) diiodide; halides of element of group 8 of the periodic table such as iron (II) dichloride, iron (III) trichloride, iron (II) dibromide, iron (III) tribromide, iron (II) diiodide and iron (III) triiodide; halides of element of group 9 of the periodic table such as cobalt (II) dichloride, cobalt (II) dibromide and cobalt (II) diiodide; halides of element of group 10 of the periodic table such as nickel (II) dichloride, nickel (II) dibromide and nickel (II) diiodide; halides of element of group 11 of the periodic table such as copper (I) iodide; dialkylated compounds of element of group 12 of the periodic table such as dimethyl zinc, diethyl zinc, di-n-propyl zinc, diisopropyl zinc, di-n-butyl zinc, diisobutyl zinc, di-n-hexyl zinc, dicyclohexyl zinc, dimethyl cadmium, diethyl cadmium, dimethyl mercury (II), diethyl mercury (II) and dibenzyl mercury (II); alkyl halides of element of group 12 of the periodic table such as methyl zinc chloride, methyl zinc bromide, methyl zinc iodide, ethyl zinc iodide, methyl cadmium chloride and methyl mercury (II) chloride; dihalides of element of group 12 of the periodic table such as zinc dichloride, zinc dibromide, zinc diiodide, cadmium dichloride, cadmium dibromide, cadmium diiodide, mercury (II) dichloride, zinc chloride iodide, cadmium chloride iodide, mercury (II) chloride iodide, zinc bromide iodide, cadmium bromide iodide and mercury (II) bromide iodide; carboxylates of element of group 12 of the periodic table such as zinc acetate, cadmium acetate and cadmium 2-ethylhexanoate; oxides of element of group 12 of the periodic table such as cadmium oxide and zinc oxide; trialkylated compounds of element of group 13 of the periodic table such as trimethyl boron, tri-n-propyl boron, triisopropyl boron, trimethyl aluminum, triethyl aluminum, tri-n-butyl aluminum, tri-n-hexyl aluminum, trioctyl aluminum, tri-n-butyl gallium (III), trimethyl indium (III), triethyl indium (III) and tri-n-butyl indium (III); dialkyl monohalides of element of group 13 of the periodic table such as dimethyl aluminum chloride, diethyl aluminum chloride, di-n-butyl aluminum chloride, diethyl aluminum bromide, diethyl aluminum iodide, di-n-butyl gallium (III) chloride and di-n-butyl indium (III) chloride; monoalkyl dihalides of element of group 13 of the periodic table such as methyl aluminum dichloride, ethyl aluminum dichloride, ethyl aluminum dibromide, ethyl aluminum diiodide, n-butyl aluminum dichloride, n-butyl gallium (III) dichloride and n-butyl indium (III) dichloride; trihalides of element of group 13 of the periodic table such as boron trichloride, boron tribromide, boron triiodide, aluminum trichloride, aluminum tribromide, aluminum triiodide, gallium (III) trichloride, gallium (III) tribromide, gallium (III) triiodide, indium (III) trichloride, indium (III) tribromide, indium (III) triiodide, gallium (III) dichloride bromide, gallium (III) dichloride iodide, gallium (III) chloride diiodide and indium (III) dichloride iodide; carboxylates of element of group 13 of the periodic table such as indium (III) acetate and gallium (III) acetate; halides of element of group 14 of the periodic table such as germanium (IV) tetrachloride, germanium (IV) tetrabromide, germanium (IV) tetraiodide, tin (II) dichloride, tin (IV) tetrachloride, tin (II) dibromide, tin (IV) tetrabromide, tin (II) diiodide, tin (IV) tetrabromide, tin (IV) dichloride diiodide, tin (IV) tetraiodide, lead (II) dichloride, lead (II) dibromide and lead (II) diiodide; hydrides and alkylated products of element of group 14 of the periodic table such as such as diphenylsilane; trialkylated products of element of group 15 of the periodic table such as trimethyl antimony (III), triethyl antimony (III), tri-n-butyl antimony (III), trimethyl bismuth (III), triethyl bismuth (III) and tri-n-butyl bismuth (III); monoalkyl dihalides of element of group 15 of the periodic table such as such as methyl antimony (III) dichloride, methyl antimony (III) dibromide, methyl antimony (III) diiodide, ethyl antimony (III) diiodide, methyl bismuth (III) dichloride and ethyl bismuth (III) diiodide; trihalides of element of group 15 of the periodic table such as such as arsenic (III) trichloride, arsenic (III) tribromide, arsenic (III) triiodide, antimony (III) trichloride, antimony (III) tribromide, antimony (III) triiodide, bismuth (III) trichioride, bismuth (III) tribromide and bismuth (III) triiodide; etc.

[0091] Incidentally, halides of element of group 14 of the periodic table such as germanium (IV) tetrachloride, germanium (IV) tetrabromide, germanium (IV) tetraiodide, tin (II) dichloride, tin (IV) tetrachloride, tin (II) dibromide, tin (IV) tetrabromide, tin (II) diiodide, tin (IV) tetrabromide, tin (IV) dichloride diiodide, tin (IV) tetraiodide, lead (II) dichloride, lead (II) dibromide and lead (II) diiodide and hydrides and alkylated products of element of group 14 of the periodic table such as diphenylsilane may be solely used as a material for nanoparticles of single substance semiconductors of element of group 14 of the periodic table such as Si, Ge and Sn.

[0092] Examples of a compound containing the negative element to be used as a material compound for semiconductors are a single substance of element of groups 15-17 of the periodic table such as nitrogen, phosphorus, arsenic, antimony, bismuth, oxygen, sulfur, selenium, tellurium, fluorine, chlorine, bromine and iodine; hydrides of element of group 15 of the periodic table such as ammonia, phosphine (PH ₃ ), arsine (AsH ₃ ) and stibine (SbH ₃ ); silylated compounds of element of group 15 of the periodic table such as tris(trimethylsilyl)amine, tris(trimethylsilyl)phosphine and tris(trimehtylsilyl)arsine; silylated compounds of element of group 16 of the periodic table such as hydrogen arsenide, hydrogen selenide and hydrogen telluride; silylated compounds of element of group 16 of the periodic table such as bis(trimethylsilyl) sulfide and bis(trimethylsilyl) selenide; alkaline metal salts of element of group 16 of the periodic table such as sodium sulfide and sodium selenide; trialkylphosphine chalcogenides such as tributylphosphine sulfide, trihexylphosphine sulfide, trioctylphosphine sulfide, tributylphosphine selenide, trihexylphosphine selenide and trioctylphosphine selenide; hydrides of element of group 17 of the periodic table such as hydrogen fluoride, hydrogen chloride, hydrogen bromide and hydrogen iodide; and silylated products of element of group 17 of the periodic table such as trimethylsilyl chloride, trimethylsilyl bromide and trimethylsilyl iodide. Among them, in view of reactivity and stability as well as operability of the compound, preferably used ones are a single substance of element of groups 15-17 of the periodic table such as phosphorus, arsenic, antimony, bismuth, sulfur, selenium, tellurium and iodine; silylated products of element of group 15 of the periodic table such as tris(trimethylsilyl) phosphine and tris(trimethylsilyl) arsine; hydrides of element of group 16 of the periodic table such as hydrogen sulfide, hydrogen selenide and hydrogen telluride; silylated products of element of group 16 of the periodic table such as such as bis(trimethylsilyl) sulfide and bis(trimethylsilyl) selenide; alkaline metal salts of element of group 16 of the periodic table such as sodium sulfide and sodium selenide; trialkylphosphine chalcogenides such as tributylphosphine sulfide, trihexylphosphine sulfide, trioctylphosphine sulfide, tributylphosphine selenide, trihexylphosphine selenide and trioctylphosphine selenide; silylated products of element of group 17 of the periodic table such as trimethylsilyl chloride, trimethylsilyl bromide and trimethylsilyl iodide; etc. Among the above, the particularly preferably used ones are a single substance of element of groups 15 and 16 of the periodic table such as phosphorus, arsenic, antimony, sulfur and selenium; silylated products of element of group 15 of the periodic table such as tris(trimethylsilyl) phosphine and tris(trimethylsilyl) arsine; silylated products of element of group 16 of the periodic table such as bis(trimethylsilyl) sulfide and bis(trimethylsilyl) selenide; alkaline metal salts of element of group 16 of the periodic table such as such as sodium sulfide and sodium selenide; trialkylphosphine chalcogenides such as tributylphosphine sulfide, trioctylphosphine sulfide, tributylphosphine selenide and trioctylphosphine selenide; etc.

[0093] Although there is no limitation for the supplying rate of the above-mentioned material compound to the reaction liquid phase in a hot soap method which is a particularly preferred liquid-phase manufacturing method, it is sometimes advantageous to inject the predetermined amount within a period of as short as 0.1-60 second(s) when the particle size distribution of the resulting semiconductor crystal nanoparticles is made narrow. Further, although an appropriate crystal growth reaction time (retention time in the case of a flow method) after injection of the material solution varies depending upon the semiconductor species, desired particle size or reaction temperature, the representative condition is about from 1 minute to 10 hours at the reaction temperature of about 200-350° C.

[0094] In such a hot soap method, isolation and purification are usually carried out after completion of the growth reaction of the semiconductor crystals. With regard to a method therefor, concentration of the liquid phase components or a precipitation method is appropriate. Preferred and representative procedure for the precipitation method is as follows. Thus, after cooling to such an extent that solidifying temperature of the reaction solution is not achieved, toluene, hexane or the like is added thereto to suppress the solidifying property at room temperature and then the mixture is mixed with a poor solvent for the semiconductor nanoparticles such as lower alcohol (e.g., methanol, ethanol, n-propanol, isopropyl alcohol or n-butanol) or water followed by subjecting to a physical means such as centrifugal separation or decantation to separate. The separated product prepared as such is dissolved in toluene, hexane or the like again and the processes of isolation and separation are repeated whereby it is possible to further improve the purity. The solvent for the precipitation may be a mixed solvent.

[0095] Attachment of the poly(alkylene glycol) Residue to the Surface of Semiconductor Crystals

[0096] There is no limitation for a method for attaching poly(alkylene glycol) to the semiconductor crystals prepared by any of the above-exemplified manufacturing methods utilizing the above-mentioned coordination structure represented by mercapto group or phosphine oxide group. An example is a method where poly(alkylene glycol) having a mercapto group (hereinafter, abbreviated as PAG-SH) is coordinated on the surface of the semiconductor crystals and, to be more specific, a ligand exchange reaction where the semiconductor nanoparticles having coordination organic compound such as TOPO prepared in the above hot soap method on the surface are contacted to PAG-SH in a liquid phase is possible. In that case, a solution using the solvent which will be mentioned later may be used if necessary and, when the PAG-SH used therefor is liquid under the reaction condition, a reaction manner where PAG-SH per se is used as a solvent and no other solvent is added is possible as well.

[0097] With regard to the condition for such a ligand exchange reaction, there are exemplified a method where it is carried out in alcohol such as methanol according to a method mentioned in X. Peng, et al.: Angew. Chem. Int. Ed. Engl., volume 36, page 145 (1997); a method where it is carried out in a mixed solvent of dimethyl sulfoxide with alcohol such as methanol according to a method mentioned in M. Bruchez, Jr. et al.: Science, volume 281, page 2013 (1998); and a method where it is carried out in a halogenated solvent such as chloroform according to a method mentioned in C. W. Warren, et al.: Science, volume 281, page 2016 (1998). Moreover, as reported in the above-mentioned X. Peng, et al.: J. Am. Chem. Soc., volume 119, page 7019 (1997), it is also possible to apply a method where semiconductor nanoparticles having a coordination organic compound such as trioctylphosphine oxide obtained by the above hot soap method on the surface are dispersed in a liquid phase containing a weakly coordinating compound such as pyridine (usually, it is used in a large excess as a solvent) and the said coordination organic compound is removed. Thus, it is a two-step reaction comprising the first step where a coordination organic compound is removed in a weakly coordination compound such as pyridine and the second step where PAG-SH is added thereto. In any of the methods, the reaction solution may be heated or vacuated if necessary.

[0098] With regard to the solvent used for such a ligand exchange reaction, there may be exemplified nitrogen-containing aromatic compounds such as pyridine, lutidine, collidine and quinoline; alkyl halides such as methylene chloride, chloroform, carbon tetrachloride and 1,2-dichloroethane; aromatic hydrocarbons such as benzene, toluene, xylene, naphthalene, chlorobenzene and dichlorobenzene; alkanes such as n-pentane, n-hexane, cyclohexane, n-octane and isooctane; aliphatic ethers such as diethyl ether and tetrahydrofuran; aliphatic ketones such as acetone and methyl ethyl ketone; solvents of an ester type such as methyl acetate and ethyl acetate; alcohols such as methanol, ethanol, n-propanol, isopropyl alcohol, n-butanol and ethylene glycol; phenols such as phenol and cresol; compounds having hydroxyl group such as water; primary amines having about 20 or less carbons such as butylamine, hexylamine, cyclohexylamine, octylamine, decylamine, dodecylamine, hexadecylamine, octadecylamine, phenylamine and aniline; secondary amines having about 20 or less carbons such as diethylamine, dibutylamino, dihexylamino, dioctylamine, dodecylamine, diphenylamine, methylphenylalanine, pyrrolidone, piperidine, morpholine and methylaniline; tertiary amines having about 20 or less carbons such as triethylamine, tributylamine, ethyl diisopropylamino, trihexylamine, phenyl dimethylamine, methyl diphenylamine, N-methylpyrrolidine, N-methylpiperidine, N-methylmorpholine and dimethylaniline; aprotic solvents of an amide type such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc) and N-methylpyrrolidone (NMP); sulfoxides such as dimethyl sulfoxide; and water. Solvents as such may be used in any type, combination and ratio depending upon the necessity of adjustment of solubility, etc. of the semiconductor nanoparticles and products thereof. It is also possible to use the above solvent to which acid or base is added.

[0099] When the amount of PAG-SH used is controlled in the above ligand exchange reaction, it is possible to attach a desired amount of PAG-SH to the surface of semiconductor crystals. As a result of control of attached amount of PAG-SH as such, it is possible to control hydrophilicity and water solubility of the semiconductor nanoparticles of the present invention. The attached amount of PAG-SH in the semiconductor nanoparticles of the present invention in terms of weight percentage (wt %) of the said nanoparticles in the organic components is usually from 0.1 wt % to 100 wt % and, in view of hydrophilicity, its lower limit is 1 wt % or more, more preferably 10 wt % or more and, most preferably, 20 wt % or more. The weight percentage can be estimated by a combination of various analytical means such as nucleomagnetic resonance spectrum (NMR), infrared absorption spectrum (IR), elementary analysis and thermogravimetric analysis (TG).

[0100] The above ligand exchange reaction is usually carried out within a temperature range of −10-250° C. and, for preventing the thermal deterioration of the organic compound and the unfinished exchange reaction, the temperature range is made preferably about 0-200° C., more preferably about 10-150° C. and, most preferably, about 20-120° C. With regard to the reaction time, that depends upon the material and temperature but, usually, it is from 1 minute to 100 hours, preferably from 5 minutes to 70 hours, more preferably from 10 minutes to 50 hours and, most preferably, from 10 minutes to 30 hours. Further, in the ligand exchange reaction as such, there is no limitation for the order of addition of the semiconductor nanoparticles and PAG-SH to the reaction solution.

[0101] In order to avoid the side reaction such as oxidation, it is preferred to carry out the ligand exchange reaction in an atmosphere of inert gas such as nitrogen and argon. Not only for such a ligand exchange reaction, there are also some cases where the after-treatment steps for the manufacture of the nanoparticles are carried out under shielding from the light.

[0102] In isolating the product after such a ligand exchange reaction, any purifying methods such as filtration, combination of precipitation and centrifugal separation, distillation and sublimation may be used and the particularly effective one is a combination of precipitation with centrifugal separation where the fact that specific gravity of semiconductor crystals is bigger than those of usual organic compounds. The centrifugal separation is carried out in such a manner that liquid containing a product of the ligand exchange reaction is poured over a poor solvent (an organic solvent containing hydrocarbon such as n-hexane, cyclohexane, heptane, octane or isooctane) for the semiconductor nanoparticles of the present invention to which PAG-SH is bonded and the suspension containing the resulting precipitate is subjected to centrifugal separation. The resulting precipitate is separated from the supernatant liquid by, for example, decantation and, if necessary, subjected to repeated washings with a solvent and re-dissolving as well as re-precipitation/centrifugal separation to improve the degree of purification. In the re-dissolving, there may be used a solvent such as aromatic hydrocarbons (e.g., toluene), lower alcohols having about 4 or more carbons (e.g., ethanol, isopropyl alcohol, n-butanol and tert-butyl alcohol), ketones (e.g., acetone), cyclic ethers (e.g., tetrahydrofuran), esters (e.g., ethyl acetate), water, etc. and any kinds thereof may be mixed and used. Revolution at the centrifugal separation is usually about 100-8,000 rpm, preferably about 300-6,000 rpm and, more preferably, about 500-4,000 rpm while the temperature is within a range of usually about −10-100° C., preferably about 0-80° C., more preferably about 10-70° C. and, most preferably, about 20-60° C. There are some cases that such a purifying step may be also carried out in the atmosphere of inert gas such as nitrogen or argon so as to avoid the side reaction such as oxidation.

[0103] Resin Composition

[0104] The semiconductor nanoparticles of the present invention may be used as a resin composition by dispersing into any resin matrix. Even in that case, any of the above-mentioned additives or the like may be added thereto. Although there is no particular limitation for the method of manufacturing the resin composition, a method where the semiconductor nanoparticles of the present invention are mixed with any resin by any of known methods and a method where the semiconductor nanoparticles are mixed with a monomer giving the desired resin matrix followed by conducting the polymerization reaction of the monomer may be usually and advantageously used.

[0105] With regard to a method where the semiconductor nanoparticles are mixed with a desired resin, there may be exemplified a fusion kneading and a solution blending.

[0106] With regard to a method for the fusion kneading, there may be exemplified a method where the above-exemplified thermoplastic resin pellets, powder, flakes, etc. are mixed with the semiconductor nanoparticle powder (dry blending), then poured into any fusion kneading machine such as uniaxial kneader, biaxial kneader, brabender, roll, labo plastomill, etc. and mixed with a thermoplastic resin which is fused by application of shearing at the temperature of the softening point of the said thermoplastic resin or higher. There is no particular limitation for the shape of the stirring mechanism such a screw used therefor and, for example, a screw block such as reversely rotating disk and kneading disk may be inserted for enhancing the shearing of the biaxial kneader for example. The resulting resin composition may be taken out in any shape such as strand, resin block, plate and pellet. During such a fusion kneading, there may be added water and/or an alcoholic solvent represented by methanol and, with an object of removal of volatile components, vacuation of the fusion kneading system (the so-called evacuation from a vent) may be carried out.

[0107] With regard to a method for the solution blending, there may be exemplified a method where the thermoplastic resin pellets, powder, flakes, etc. and the semiconductor nanoparticle powder or flakes are dissolved in an appropriate common solvent (representative ones are a solvent having hydroxyl group such as water and alcohol; nitrogen-containing aromatic compound such as pyridine; cyclic ether such as THF and 1,4-dioxane; alkyl halide such as methylene chloride and chloroform; aprotic polar solvent of an amide type such as DMF and NMP; etc.) and well mixed in the solvent and the solvent is removed by means of distillation or drying and a method where the solution is poured over a poor solvent such as cyclohexane to precipitate the resin composition. In dissolving as such, heating may be carried out if necessary. Distillation of the solvent may be carried out in vacuo. With regard to the solvent used for preparing the solution and the poor solvent used for the precipitation, plural types of solvents may be used.

[0108] On the other hand, with regard to a method where the semiconductor nanoparticles are mixed with a monomer giving any desired resin matrix and then the polymerization reaction of the monomer is carried out, it is common that, at first, the semiconductor nanoparticles are dissolved in an aromatic vinyl compound such as styrene, α-methylstyrene, p-chlorostyrene, p-methylstyrene, p-chloromethylstyrene, p-hydroxystyrene, p-acetoxystyrene, vinylnaphthalene, 2-vinylpyridine and 4-vinylpyridine; an acrylic acid or methacrylic acid derivative such as methyl acrylate, ethyl acrylate, butyl acrylate, benzyl acrylate, phenyl acrylate, isobomyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, hydroxyethyl methacrylate, benzyl methacrylate, phenyl methacrylate, norbornane methyl methacrylate, isobornyl methacrylate, adamantyl methacrylate, acrylamide, methacrylamide, acrylonitrile and methacrylonitrile; a vinyl ester such as vinyl acetate; a radical polymerizing monomer such as N-vinylpyrrolidone and N-vinyloxazoline; a cyclic ether such as THF, propylene oxide and epichlorohydrin; a cyclic amide such as ε-caprolactam; a cyclic ester such as ε-caprolactone and γ-butyrolactone; and other ring-opening polymerizing monomer; or a polymerizing monomer such as metal alkoxide (e.g., tetraethoxysilane) used for a hydrolyzing condensation (the so-called sol-gel method) and then a predetermined monomer polymerization reaction is carried out. At that time, an appropriate solvent may be used together.

[0109] If necessary, a cross-linking polyvalent monomer may be added to the above-mentioned monomer and its examples as a radically polymerizing cross-linking agent are an aromatic vinyl compound such as divinylbenzene, trivinylbenzene and divinylpyridine; bisacryloyloxyethane; pentaerythritol tetrakis(meth)acrylate; and pentaerythritol tris(meth)acrylate. In that case, there may be some cases where the resin composition loses its thermoplastic property.

[0110] In conducting a radical polymerization of such a radically polymerizing monomer in the presence of the semiconductor nanoparticles, a radical initiator is usually added. There is no limitation for the radical initiator which is able to be used here and, as a thermodegradable radical initiator, representative one is that which is soluble in the above radically polymerizing monomer such as an azo compound (e.g., azobisisobutyronitrile (AIBN)) and a peroxide (e.g., benzoyl peroxide and tert-butyl peroxide) although it is also possible to use a water-soluble radical generator such as a persulfate (e.g., sodium persulfate, potassium persulfate, lithium persulfate and ammonium persulfate). It is further possible to use a photodegradable radical initiator such as an aminoacetophenone (e.g., α-aminoacetophenone and 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butane-1) as well as a benzyldimethylketal, a glyoxy ester, an acylphosphineoxy, etc.

[0111] In the above-mentioned method for the manufacture of any desired resin composition, the semiconductor nanoparticles may be used in a form of the so-called master batch where they are previously contained in a high concentration in an appropriate organic substance. With regard to the matrix organic substance in the master batch as such, there may be used any thermoplastic resin, wax, solvent, any of the above-mentioned polymerizing monomer (including a cross-linking multivalent monomer), etc. Method for preparing such a master batch may be conducted by means of any of known methods such as the above-mentioned fusion kneading and solution blending.

[0112] In the manufacturing steps for the above-mentioned any desired resin composition, there are some cases where atmosphere of inert gas (such as dry nitrogen or argon) and shielding from light are preferred for suppressing the oxidation reaction by heat and light upon mixing the materials.

[0113] Thin Film

[0114] The semiconductor nanoparticles of the present invention are applicable to various uses after shaping by common methods and an example thereof is thin film.

[0115] Such a thin film can be prepared in such a manner that the semiconductor nanoparticles of the present invention prepared by the above-mentioned manufacturing method are dissolved or dispersed in an appropriate solvent (for example, an aromatic solvent such as toluene; a ketone solvent such as acetone; an ether solvent such as tetrahydrofuran; or a halogenated solvent such as chloroform, methylene chloride and chlorobenzene) and the solution or dispersion is applied by flowing on a desired substrate such as a glass substrate, an electroconductive substrate (e.g., indium dope tin oxide (usually called ITO), metal or graphite), a semiconductor substrate (e.g., silicone) and a resin substrate of an amorphous polyolefin (e.g., polymethyl methacrylate (PMMA), polystyrene and polycycloolefin) or an aromatic polycarbonate. With regard to the term “applied by flowing” used here, there may be exemplified a flowing method where spreading on a substrate is conducted using a bar coater, an applicator, a doctor blade, etc.; a dip method where a substrate is dipped in a material liquid followed by pulling out therefrom; a spin coat method where the material liquid is applied; and other known methods. Viscosity of the material liquid is usually 0.1-1,000 centipoise(s), preferably 0.5-500 centipoise(s) and, more preferably, 1-100 centipoise(s). Temperature for the formation of film is usually −10-150° C., preferably 0-120° C. and, more preferably, 10-100° C. Flowing rate in the flowing method is usually 0.1-1000 m/minute, preferably 0.5-700 m/minute and, more preferably, 1-500 m/minute. Revolutions in the spin coat method is usually 10-100,000 rpm, preferably 50-50,000 rpm and, more preferably, 100-10,000 rpm.

[0116] At that time, the poly(alkylene glycol) residue which is a ligand functions as a continuous matrix whereby the semiconductor crystals are made into such a state that they are hardly aggregated each other and there is prepared a stable coated film achieving the absorption and luminescence characteristics of the said semiconductor crystals. Thus, one of the characteristics of the semiconductor nanoparticles of the present invention is that, since a poly(alkylene glycol) residue is available on the surface thereof, a coated film having excellent transparency and mechanical strength is resulted by itself even when an organic binder component such as resin is not jointly used.

[0117] During the shaping by such an application by way of flowing, it is also possible that an appropriate organic binder component such as resin (e.g. polymethyl methacrylate (PMMA), polystyrene or aromatic polycarbonate), wax, silicone fat/oil or the like is previously dissolved into a solvent. Amount of the organic binder in that case to the sum thereof with the nanoparticles is usually from 0% by weight to 90% by weight and, in view of mechanical strength and optical characteristics such as luminance, absorbance and light transmittance of the film, the lower limit is preferably 5% by weight or more, more preferably 10% by weight or more and, most preferably, 15% by weight or more while the upper limit is preferably 80% by weight or less, more preferably 70% by weight or less and, most preferably, 60% by weight or less.

[0118] It is further possible to add any of additives such as thermostabilizers, absorbers of light such as ultraviolet rays, antioxidants, oxygen scavengers and moisture absorbers to the thin film of the present invention so far as the advantage thereof is not significantly deteriorated.

[0119] The thin film may be shaped in a plane surface or in a curved surface having any curvature. Although there is no particular limitation for thickness, it is for example from 0.003 μm to 5,000 μm and, in view of luminance, absorbance or light transmittance, its lower limit is preferably 0.004 μm or more and, more preferably, 0.005 μm or more while its upper limit is preferably 1,000 μm or less, more preferably 500 μm or less and, still more preferably, 100 μm or less.

[0120] It is also possible that one or both side(s) of the thin film is/are installed, if necessary, with a layer having additional functions (such as protective layer against mechanical damage, gas barrier layer, light shielding layer, heat insulating layer and electrode layer).

[0121] The above-mentioned thin film of the present invention is useful in industry as an optical material such as a planar luminescent substance used for display, illumination instrument, etc. where luminescent characteristic of the nanoparticles is utilized, a super resolution layer or an ultraviolet absorbing film where absorption characteristic thereof is utilized or a high-density recording layer where absorption and luminescence characteristics thereof are utilized.

[0122] Optical Materials

[0123] The semiconductor nanoparticles of the present invention are able to be utilized as various optical materials by, for example, making into thin film or bulk-shaped substance. Uses as particularly important optical materials will be illustrated as follows.

[0124] 1) Super Resolution Film

[0125] As a result of making the nanoparticles of the present invention into a form of thin film, they are used as a super resolution film which is installed in optical recording media such as an optical disk by utilization of saturated absorption characteristic of semiconductor crystal particles contained therein. The term “super resolution” used in the present invention means a technical concept that, in reading-out and writing-in of data (hereinafter, abbreviated as “reading and writing of data”) in an optical disk for example, its degree of resolution or, in other words, area of the unit recording region is made smaller than the original diameter of incident beam used for reading and writing of data so that improvement in the recording density is achieved.

[0126] The above-mentioned saturated absorption characteristic means a characteristic that, when light of a specific wavelength (hereinafter, referred to as “light of incidence”) which is absorbed by the above semiconductor crystal particles is applied, absorbance of the semiconductor crystals at the specific wavelength decreases as a result of an increase in intensity of the incident light. Quantitatively, such a saturated absorption characteristic is understood as a phenomenon that, as a result of an increase in intensity of the incident light (in other words, an increase in photon numbers in the incident light), excitation frequency of electron to excitation level participating in absorption of light increases whereby possibility of existence of electrons of the excitation level increases as well and, as a result, possibility of transfer of electrons to the excitation level decreases. When intensity of the incident light is sufficiently high, there is supposed a state where light absorption does not substantially take place any more and, therefore, such a phenomenon is called “saturated absorption”.

[0127] When the semiconductor nanoparticles of the present invention are applied to thin film, absorbance of the thin film at the desired incident light wavelength is made usually 0.1 or more, preferably 0.3 or more and, more preferably, 0.5 or more. The absorbance value is measured in such a manner that, in a thin film of 23° C., incident light of intensity of usually about 0.3 mW or less or, preferably, 0.1 mW or less is applied from the direction of normal line of the surface of the film.

[0128] Although there is no limitation for the thickness of the thin film so far as an effective saturated absorption can be detected, its lower limit is usually 50 nm or more, preferably 100 nm or more and, more preferably, 150 nm or more while its upper limit is usually 10,000 nm or less, preferably 5,000 nm or less and, more preferably, 3,000 nm or less where distribution of the thickness is preferably to be as little as possible. It is preferred that the surface of the film is as smooth as possible for suppressing the light scattering.

[0129] The semiconductor crystal particles which are advantageously used for application of the thin film of the present invention to the super solution film are CdS and ZnSe as mentioned already. When they are made in particles of a core-shell type where shell of semiconductor crystals having a big band gap such as in the case of ZnS, there are some cases where behavior of exciton absorption on the basis of quantum effect is stabilized and that is preferred. Content of the semiconductor crystal particles in the super resolution film is usually from 10% by volume to 60% by volume and, in view of the detective property of the saturated absorption and mechanical property of the film, the lower limit is made preferably 20% by volume or more and, more preferably, 25% by volume or more while the upper limit is made preferably 55% by volume or less or, more preferably, 50% by volume or less.

[0130] (2) Filter

[0131] By making into thin film, the nanoparticles of the present invention are able to be utilized as a filter by utilization of transparency and light absorption characteristic of the semiconductor crystal particles contained therein. In the semiconductor nanoparticles, light absorption wavelength can be changed depending upon their particle size and, therefore, it is possible to prepare a filter where the light absorption wavelength is precisely controlled. Since such a filter is able to take out the light of a specific wavelength region only, it is used as a color filter for display. With regard to semiconductor crystal particles suitable for such an object, there are exemplified cadmium selenide (CdSe) and cadmium sulfide (CdS). When ultraviolet ray is to be absorbed, it is used, for example, by closely adhering and shaping on the surface of transparent material where ultraviolet ray such as sunlight is absorbed to suppress or shield the transmittance such as window glass of automobiles, airplanes and buildings or lens of sunglasses, etc. With regard to the semiconductor crystal particles suitable for such an object, there are exemplified the above-mentioned titanium oxide, zirconium oxide (ZrO ₂ ), zinc oxide (ZnO) and zinc sulfide (ZnS) where the wavelength at the absorption edge on the long-wavelength side of its absorption spectrum is 400 nm or less.

[0132] In view of a light absorbing ability, although it is preferred that the content of the semiconductor crystal particles in the thin film is as much as possible, it is usually from 10% by volume to 60% by volume and, in view of ultraviolet absorbing ability and mechanical strength of the film, the lower limit is made preferably 20% by volume or more or, more preferably, 30% by volume or more while the upper limit is made preferably 55% by volume or less or, more preferably, 50% by volume or less. When the content of the semiconductor particles in the thin film becomes big, there is noted another characteristic that hardness as the filter becomes high and, therefore, it is suitable when surface hardness is needed for window glass or lenses.

[0133] Although there is no limitation for the thickness of such a filter so far as an effective ultraviolet absorbing ability is achieved, the lower limit is made usually 0.05 μm or more, preferably 0.1 μm or more and, more preferably, 0.5 μm or more while the upper limit is made usually 2,000 μm or less, preferably 1,000 μm or less and, more preferably, 500 μm or less. Distribution of the thickness may be freely designed depending upon the function of the aimed transparent material. It is preferred that surface of the film is as smooth as possible for suppressing the reduction in light transmittance by light scattering but, depending upon the object, an appropriate unevenness may be applied thereto.

[0134] (3) Anti-Reflection Film

[0135] When the semiconductor nanoparticles of the present invention are made into thin film, they are utilized as an anti-reflection film utilizing the transparency and the high refractive index of the semiconductor crystal particles contained therein. Such an anti-reflection film is installed on the surface of the transparent material such as display panel, lens, prism or window glass whereupon there is achieved an effect of suppression, etc. of the light reflection at the surface of the said transparent material. With regard to the semiconductor crystal particles suitable for such an object, there are exemplified the above-mentioned titanium oxide, zirconium oxide (ZrO ₂ ), zinc oxide (ZnO) and zinc sulfide (ZnS).

[0136] In view of making the refractive index of the thin film high, although it is preferred that the content of the semiconductor crystal particles in the thin film is as high as possible, it is usually from 10% by volume to 60% by volume and, in view of making refractive index high and also of mechanical strength of the film, the lower limit is made preferably 15% by volume or more and, more preferably, 20% by volume or more while the upper limit is made usually 50% by volume or less or, preferably, 45% by volume or less. Practically, refractive index of the thin film at 23° C. at the wavelength of D line of sodium is made usually 1.6 or more, preferably 1.7 or more, more preferably 1.8 or more and, most preferably 1.9 or more. Incidentally, when the content of the semiconductor particles in the above thin film becomes high, there is achieved another characteristic that hardness as the anti-reflection film becomes high and, therefore, it is suitable when the surface hardness of the above-mentioned transparent material is necessary.

[0137] On the surface of the anti-reflection film of the present invention, there may be installed a film comprising a material having a relatively low refractive index such as PMMA or silica. When such a film of low refractive index is installed, there are some cases where an excellent reflection-preventing function is achieved and that is suitable. Especially when it is formed on the surface of silica film, the resulting function as a layer having a protective function due to the excellent surface hardness against mechanical force from outside (such as abrasion and scratch) is useful.

[0138] Although there is no limitation for the thickness of the anti-reflection film so far as an effective anti-reflection ability is achieved, the upper limit is made usually 0.05 μm or more, preferably 0.1 μm or more and, more preferably, 0.2 μm or more while the upper limit is made usually 500 μm or less, preferably 100 μm or less and, more preferably, 10 μm or less. Distribution of the said film thickness may be freely designed depending upon the function of the aimed transparent material. Although it is preferred that the surface of the film is usually as smooth as possible for suppressing the reduction in light transmittance by light scattering, it is also possible to form an appropriate unevenness depending upon an object.

[0139] (4) Optical Waveguide

[0140] The nanoparticles of the present invention are used as an optical waveguide utilizing their transparency and high refractive index, etc. of the semiconductor crystal particles contained therein. The optical waveguide as such is used as an optical connector and an optical amplifier in optical telecommunication. Refractive index of the optical waveguide according to the present invention at the wavelength of D line of sodium at 23° C. is usually made 1.6 or more and, therefore, it is now possible that a commonly used resin material such as PMMA (refractive index: 1.49) is easily applied by making into rods or thin film by, for example, a solution application method without the use of expensive resin containing fluorine atoms or the like as a clad material. Refractive index of the optical waveguide is made preferably 1.7 or more and, more preferably, 1.75 or more.

[0141] With regard to the semiconductor crystal particles which are advantageous for such an object, there are exemplified the above-mentioned titanium oxides, zi