JP7098555B2 - Manufacturing method of core-shell type quantum dot dispersion liquid and manufacturing method of quantum dot dispersion liquid - Google Patents

Description

The present invention relates to a method for producing a core-shell type quantum dot dispersion liquid and a method for producing a quantum dot dispersion liquid, which have both stability (robustness) and fluorescence characteristics (luminescence).

Quantum dots are examples of next-generation semiconductor nanoparticles used in fluorescence-conversion LEDs, radiation EL displays, fluorescence imaging, and the like.
Among the metal nitride nanoparticles, a core-shell type quantum having a core composed of semiconductor fine particles having a predetermined bandgap and a shell composed of a semiconductor having a bandgap larger than the core covering the surface of the core. Dots are attracting attention.

This type of quantum dot is known, for example, in Non-Patent Document 1. In such a quantum dot, the core is composed of InP and the shell is composed of ZnS having a band gap larger than that of InP, so that the quantum dot has excellent emission characteristics as compared with the case where the quantum dot is composed of only InP. (Non-Patent Document 1).

However, since it is necessary to use a relatively expensive phosphorus-containing substance as a raw material for InP, the cost of the core-shell type quantum dots is high. As a solution to this problem, the present inventors can produce it without using a relatively expensive phosphorus-containing compound, and can emit light at an emission wavelength equivalent to that of a core-shell quantum dot composed of InP / ZnS. A core-shell type quantum dot has been developed and proposed earlier (Patent Documents 1 and 2).

In recent years, a direct current light emitting device (QLED) using such a quantum dot as an active layer has been studied. It has been reported that these quantum dots have poor withstand voltage resistance and are deteriorated by the application of direct current (Non-Patent Document 2). In addition, an example of synthesizing nitride nanocrystals has been reported in order to realize more robust quantum dots, but there is a problem that the particle size cannot be controlled and metal is mixed due to decomposition of the nitride, so that it exhibits luminescence. Quantum dots having the same crystalline property as above have not been obtained (Non-Patent Document 3). Therefore, the development of quantum dots made of nitrides that are robust and emit light has been awaited.

Japanese Unexamined Patent Publication No. 2018-140931 Japanese Unexamined Patent Publication No. 2018-154666

American Chemical Society, Vol.8, No.1, p977-985, 2014. ACS Appl. Mater. Interface 2014, 6, 495-499 J.Mater.Chem., 2010, 20, 1435-1437 Phys. Chem. Chem. Phys. 13, 10635, 2011. J. Phys. Chem. C 116, 18655, 2012. Small 5 (2), 154-168, 2009. J. Mater. Chem. C 2, 4379-4382, 2014.

The present invention has been made in view of the above circumstances, and is a method for producing a core-shell type quantum dot dispersion liquid and a method for producing a quantum dot dispersion liquid, which have both stability (robustness) and fluorescence characteristics (emission property). The purpose is to provide.

In order to solve the above problems, the method for producing a core-shell type quantum dot dispersion liquid of the present invention has a core composed of semiconductor fine particles having a predetermined bandgap and a bandgap larger than the core that covers the surface of the core. It is a method of manufacturing a core-shell type quantum dot dispersion liquid including a shell made of a semiconductor. The core-shell type quantum dot obtained by this manufacturing method is characterized in that the core is made of metal nitride and the shell is made of ZnS, and the shell emits fluorescence by continuous irradiation of excitation light.

According to the present invention, the core is composed of metal nitride and the shell is composed of ZnS, and the core contains a crystal growth inhibitor composed of HMDS (1,1,1,3,3,3-hexamethyldisilazane). Through the synthesis process, core-shell quantum dots that emit fluorescence by continuous irradiation of excitation light can be obtained. Therefore, the present invention contributes to the provision of a method for producing a core-shell type quantum dot dispersion liquid having both stability (robustness) and fluorescence characteristics (emission).
In the core-shell type quantum dots obtained by this manufacturing method, the emission intensity of the fluorescence is increased by continuous irradiation of the excitation light. As a result, the core-shell type quantum dots obtained by the manufacturing method of the present invention have excellent long-term stability and light emission characteristics.

In the present invention, the metal nitride is preferably at least one selected from InN, GaInN, AlN, ZnInN, ZnPbN ₂ , ZnSnN ₂ , ZnGeN ₂ , ZnSiN ₂ , and Zn ₃ N ₂ . As the quantum dots made of these metal nitrides, core-shell type quantum dots that exhibit fluorescence equivalent to that of the conventional core-shell type quantum dots composed of InP / ZnS can be obtained. Moreover, the core-shell quantum dots obtained by the production method of the present invention do not need to use a relatively expensive phosphorus-containing compound as a raw material.

In the present invention, the core is ZnO, ZnS, ZnSe, InN, GaInN, GaN, AlN, AlInN, ZnMgO, InP, GaP, AlP, Zn ₃ P ₂ , Cd ₃ P ₂ , ZnPbN ₂ , ZnSnN ₂ , ZnGeN ₂ . , ZnSiN ₂ , LiGaO ₂ , LiAlO ₂ , NaGaO ₂ , NaAlO ₂ , CuGaO ₂ , and AgAlO ₂ preferably composed of at least one crystal nucleus. By growing the core from the crystal nucleus, the crystallinity of the core can be enhanced.

In the present invention, the surface of the shell is covered with a passivation layer, and the passivation layer is ZnS, ZnSe, ZnO, ZnSO, ZnSSe, ZnSeO, MgO, InN _x O _x , GaN _x O _x , AlN _x O _x , In. ₂ O ₃ , Ga ₂ O ₃ , Al ₂ O ₃ , SiO ₂ , SiNO _x , LiInO ₂ , LiGaO ₂ , LiAlO ₂ , NaGaO ₂ , NaAlO ₂ , CuGaO ₂ , AgAlO ₂ , AgGaO ₂ , and AgInO ₂ . It is preferable that it is composed of at least one type. According to this, the stability of the core-shell type quantum dot can be improved.

A method for producing a core-shell type quantum dot dispersion liquid (hereinafter referred to as the first invention), which comprises dispersing the above-mentioned core-shell type quantum dots in a dispersion medium, that is,
A core made of semiconductor fine particles having a predetermined bandgap and a shell made of a semiconductor having a bandgap larger than the core covering the surface of the core are provided, and the core is made of metal nitride. The method for producing a core-shell type quantum dot dispersion liquid, wherein the shell is composed of ZnS and the core-shell type quantum dots that emit fluorescence by continuous irradiation of excitation light are dispersed in a dispersion medium.
Each of the following steps (α1) to (α4) is provided.

(Α1) A first compound containing a metal that is a raw material for a core, a metal amide that functions as a nitrogen supply source for nitriding the metal contained in the first compound, and a by-product can be dispersed in a solvent. A step of mixing a solubilizer and a solvent to prepare a reaction solution, and
(Α2) The reaction solution is heated to a predetermined first temperature, a core is synthesized by a heating reaction between the first compound and the metal amide, and a by-product produced by the heating reaction is produced by the solubilizer. The process of dispersing in a solvent and
(Α3) The reaction solution after core synthesis contains a second compound containing zinc, which is a raw material for the shell, and a sulfur source for sulfurizing zinc contained in the second compound, and these second compounds and The reaction solution containing the sulfur source is heated to a predetermined second temperature, and the core is covered with a shell made of a ZnS film produced by the heating reaction between the second compound and the sulfur source. And the process of forming
(Α4) A step of extracting core-shell type quantum dots from the reaction solution after the heating reaction between the second compound and the sulfur supply source and dispersing them in the dispersion medium.
Including
In the step of preparing the reaction solution, a crystal growth inhibitor composed of HMDS (1,1,1,3,3,3-hexamethyldisilazane) is further mixed.
In particular, in the step of preparing the reaction solution, by further mixing the crystal growth inhibitor made of HMDS, according to the above-mentioned invention (first invention), the core-shell type quantum dots are dispersed in the dispersion medium. A core-shell type quantum dot dispersion liquid can be stably obtained.

In the present invention (first invention), prior to the step of preparing the reaction solution, a step of mixing the raw materials of the crystal nuclei and heating the mixed raw materials to a predetermined third temperature to synthesize the crystal nuclei is further performed. It is preferable to further mix the crystal nuclei in the step of preparing the reaction solution.

In the present invention (first invention), the raw material of the passivation layer is added to the reaction solution after the heating reaction between the second compound and the sulfur supply source, and the reaction solution to which the raw material of the passivation layer is added is predetermined. It is preferable to further include a step of heating to the fourth temperature of the above and covering the surface of the shell with the passivation layer.

In the present invention (first invention), as raw materials for crystal nuclei, ZnO, ZnS, ZnSe, InN, GaInN, GaN, AlN, AlInN, ZnMgO, InP, GaP, AlP, Zn ₃ P ₂ , Cd ₃ P ₂ , ZnPbN _{2. It is preferable to use at least one selected from 2} , ZnSnN ₂ , ZnGeN ₂ , ZnSiN ₂ , LiGaO ₂ , LiAlO ₂ , NaGaO ₂ , NaAlO ₂ , CuGaO ₂ , and AgAlO ₂ .

In the present invention (first invention), ZnS, ZnSe, ZnO, ZnSO, ZnSSe, ZnSeO, MgO, InN _x O _x , GaN _x O _x , AlN _x O _x , In ₂ O are used as raw materials for the passion layer. ₃ , Ga ₂ O ₃ , Al ₂ O ₃ , SiO ₂ , SiNO _x , LiInO ₂ , LiGaO ₂ , LiAlO ₂ , NaGaO ₂ , NaAlO ₂ , CuGaO ₂ , AgAlO ₂ , AgGaO ₂ , and AgInO ₂ at least. It is preferable to use one type.

In the present invention (first invention), as the solubilizer, trialkylphosphine oxides, trialkylphosphine sulfides, trialkylphosphine serenides, trialkyliminophosphorans, monophosphate esters, diphosphate esters, etc. , Triphosphate esters, dimethyl sulfoxide, hexamethylphosphate triamide and at least one selected from N, N'-dimethylpropylene urea is preferably used.

In the present invention (first invention), it is preferable to further mix the electron acceptor in the step of preparing the reaction solution.
In the present invention (first invention), as the electron acceptor, iodophosphine, halogen, superatomic iodine reagents, and iodination having a redox potential at a position noble than the redox potential of the metal to be nitrided. Agent, N, N'-dicyclohexylcarbodiimide, N-chlorosuccinimide, N-promoscusinimide, N-iodosuccinimide, 2,3-dichloro-5,6-dicyano-p-benzoquinone, nitroxyl radical, sulfur, alkyl At least one selected from thiol, alkyl disulfide, alkyl trisulfide, tetracyanoquinodimethane, 2,3-dichloro-5,6-dicyano-p-benzoquinone and crown ether may be used.

In the present invention (first invention), it is preferable to further mix the dispersant covering the core-shell type quantum dots in the step of preparing the reaction solution.

In the present invention (first invention), as the dispersant, alkylcarboxylic acids, monoalkylamines, dialkylamines, trialkylamines, trialkylphosphins, alkyl esters, alkylthiols, sulfides, tricaprylic acids It is preferable to use at least one selected from glycerin, alkylnitriles and steaic acid anhydrides.

In the present invention (first invention), after synthesizing the core-shell type quantum dots, a substance having an acid dissociation constant larger than 4.5 and having hydrogen at the terminal of a functional group is added to the reaction solution and remains in the reaction solution. It is preferable to further include a step of removing the metal. In this case, oleic acid or dodecanethiol can be used as the substance.

The method for producing the quantum dot dispersion liquid of the present invention (hereinafter referred to as the second invention), that is,
A method for producing a quantum dot dispersion liquid, wherein a core composed of semiconductor fine particles having a predetermined band gap is composed of metal nitride, and quantum dots that emit fluorescence by continuous irradiation of excitation light are dispersed in a dispersion medium. teeth,
Each of the following steps (β1) to (β3) is provided.

(Β1) A first compound containing a metal that is a raw material of the core, a metal amide that functions as a nitrogen supply source for nitriding the metal contained in the first compound, and a by-product can be dispersed in a solvent. The step of mixing the solubilizer and the solvent to prepare the reaction solution, and
(Β2) The reaction solution is heated to a predetermined first temperature, a core is synthesized by a heating reaction between the first compound and the metal amide, and a by-product produced by the heating reaction is produced by the solubilizer. The process of dispersing in a solvent and
(Β3) A step of extracting quantum dots from the reaction solution after the heating reaction and dispersing them in the dispersion medium.
Including
In the step of preparing the reaction solution, a crystal growth inhibitor composed of HMDS (1,1,1,3,3,3-hexamethyldisilazane) is further mixed.
In particular, in the step of preparing the reaction solution, by further mixing a crystal growth inhibitor made of HMDS, according to the above-mentioned invention (second invention), quantum dots are dispersed in a dispersion medium. A dot dispersion can be stably obtained.

In the present invention (second invention), prior to the step of preparing the reaction solution, a step of mixing the raw materials of the crystal nuclei and heating the mixed raw materials to a predetermined third temperature to synthesize the crystal nuclei is further performed. It is preferable to further mix the crystal nuclei in the step of preparing the reaction solution.

In the present invention (second invention), it is preferable to use at least one selected from InN and GaInN as the raw material for the crystal nucleus.

In the present invention (second invention), as the solubilizer, trialkylphosphine oxides, trialkylphosphine sulfides, trialkylphosphine serenides, trialkyliminophosphorans, monophosphate esters, diphosphate esters, etc. , Triphosphate esters, dimethyl sulfoxide, hexamethylphosphate triamide and at least one selected from N, N'-dimethylpropylene urea is preferably used.

In the present invention (second invention), it is preferable to further mix the dispersant covering the quantum dots in the step of preparing the reaction solution.

In the present invention (second invention), as the dispersant, alkylcarboxylic acids, monoalkylamines, dialkylamines, trialkylamines, trialkylphosphins, alkyl esters, alkylthiols, sulfides, tricaprylic acids It is preferable to use at least one selected from glycerin, alkylnitriles and steaic acid anhydrides.

In the present invention (second invention), it is preferable to use octadecanethiol as the dispersant. By using octadecanethiol, it is possible to prevent the binding of quantum dots and narrow the distribution range of the particle size.

In the present invention (second invention), after synthesizing the quantum dots, a substance having an acid dissociation constant larger than 4.5 and having hydrogen at the end of the functional group is added to the reaction solution to remove the metal remaining in the reaction solution. It is preferable to further include a step of removing. In this case, oleic acid or dodecanethiol can be used as the substance.

The schematic diagram which shows one structure example of the core-shell type dot of this invention. The schematic diagram which shows the other structural example of the core-shell type dot of this invention. The schematic diagram which shows the other structural example of the core-shell type dot of this invention. The graph which shows the irradiation time dependence of the peak intensity. The graph which shows the irradiation time dependence of an emission spectrum. List of Experimental Examples 6-10. The graph which shows the emission spectrum of Experimental Example 6. The graph which shows the emission spectrum of Experimental Example 7. The graph which shows the emission spectrum of Experimental Example 8. The graph which shows the emission spectrum of Experimental Example 9. The graph which shows the emission spectrum of Experimental Example 10. The graph which shows the emission spectrum of Experimental Examples 6 to 10 collectively. XYZ color system chromaticity diagram with CIE of Experimental Examples 9 and 10 added. A photograph that evaluates changes over time according to appearance. A graph that evaluates changes over time using an optical energy gap. Pictures of XRD patterns and suspensions of various quantum dots. Photographs such as TEM images of various quantum dots. Graph fitted with N1s spectrum and In3d _5/2 spectrum using Voigt function. A list showing Peak and FWHM for the N1s spectrum and the In3d _5/2 spectrum. The graph which shows the UV-vis spectrum and the light absorption spectrum of various quantum dots. A list showing the optical bandgap Eg of various quantum dots. The graph which shows PL and absorption spectrum of various quantum dots. A list showing PL peaks and FWHM of various quantum dots.

Hereinafter, the core-shell type quantum dots and the quantum dots of the embodiment of the present invention will be described with reference to the drawings by taking a dispersion liquid dispersed in the dispersion medium Ld as an example.

With reference to FIG. 1, the QD is a core-shell type quantum dot (hereinafter referred to as “quantum dot”) of the present embodiment. The quantum dot QD includes a core 1 made of semiconductor nanoparticles having a predetermined bandgap, and a shell 2 made of a semiconductor having a bandgap larger than that of the core 1 and covering the surface of the core 1. In the case of a quantum dot composed of the core 1, the portion of the shell 2 indicates the interface surface layer portion of the core 1.

The core 1 is a nanoparticle composed of a metal nitride. As the metal nitride, at least one selected from InN, GaInN, AlN, ZnInN, ZnPbN ₂ , ZnSnN ₂ , ZnGeN ₂ , _{ZnSiN 2} , and Zn 3N ₂ can be used, and InN or GaInN is preferably used. be able to.

Core 1 is produced by a synthetic process containing a crystal growth inhibitor consisting of HMDS (1,1,1,3,3,3-hexamethyldisilazane). As will be described later, the quantum dots having this configuration and the core-shell type quantum dots emit fluorescence by continuous irradiation of excitation light [FIGS. 6, FIG. 9 (Experimental Example 3), FIG. 10 (Experimental Example 4). ]. Therefore, the present invention contributes to the provision of quantum dots and core-shell type quantum dots having both stability (robustness) and fluorescence characteristics (emission).

Further, as will be described later, the quantum dots have increased emission intensity of the fluorescence due to continuous irradiation of the excitation light [FIGS. 4 and 5]. As a result, the quantum dots of the present invention have excellent emission characteristics for long-term stability.

In the present invention, the typical nanoparticles used for the purpose of light emission mean those having an average particle size (in the present invention, indicating the interface between the core 1 and the shell 2) in the range of 0.1 nm to 20 nm. By controlling the average particle size in such a range. The quantum size effect widens the semiconductor bandgap and can increase the emission energy when electrons recombine with holes.

The shell 2 can be made of ZnS. The thickness of the shell 2 is preferably in the range of, for example, 0.1 to 50 nm.

The surface of the shell 2 is covered with the dispersant 3, whereby the quantum dot QD can be dispersed in the dispersion medium L with good dispersibility. The dispersant 3 includes alkyl carboxylic acids having an alkyl chain having 6 or more carbon atoms, trialkyl amines, trialkyl phosphins, trialkyl phosphin sulfides, trialkyl phosphine serenides, trialkyl phosphin oxides, and trialkyl. At least one selected from anionic surfactants such as iminophosphorans, alkyl esters, alkylthiols, sulfides, glycerin tricaprylate, sodium alkylate, sodium alkylsulfate, sodium alkylthiolate and sodium alkylsulfonate. Can be used, and alkyl carboxylic acids can be preferably used.

As the dispersion medium Ld, it is preferable to use an organic solvent having 6 to 18 carbon atoms, and for example, the organic solvents listed below are suitable. The dispersion medium Ld can be used alone or in combination with these organic solvents.
Suitable organic solvents for the dispersion medium Ld include, for example, hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, and octadecane, which have 6 to 18 carbon atoms in the main chain. Long-chain alkanes; cyclic alkanes such as cyclohexane, cycloheptane, cyclooctane, cyclodecene; aromatic hydrocarbons such as benzene, toluene, xylene, trimethylbenzene, dodecylbenzene; hexanol, heptanol, octanol, decanol, cyclohexanol. , Alcohols such as terpineol; ethers such as diethyl ether, dibutyl ether, dihexyl ether, tetrahydrofuran, cyclopentylmethyl ether, phenyl ether; dimethylformamide, N-N'-dimethylpropylene urea, tris (N, N-dimethylamino) Hofffin oxide, diazabicycloundecene, and the like.

Hereinafter, the method for producing a quantum dot QD of the present invention will be described by taking as an example a case where a quantum dot dispersion liquid in which quantum dots are dispersed in a dispersion medium is produced.

First, a first compound containing a metal that is a raw material for a core, a metal amide that functions as a nitrogen supply source for nitriding the metal contained in the first compound, and a solubilizer that disperses a by-product in a solvent. And the solvent are mixed to prepare a reaction solution.

Here, the first compound is not particularly limited as long as it can supply a metal necessary for synthesis described later, and for example, a halide of the metal or a metal complex containing the metal and the dispersant may be used. Can be done. As the metal, one or more metals selected from Al, Ga, In, Fe, Cu, Mn, W, Ta and Zr or alloys of these metals can be used. Further, the metal shall contain B and Si. The molar ratio of the first compound to the metal amide can be set in the range of 1: 1 to 1: 1000.

Metal amides include metal amides including metals selected from lithium, sodium, potassium, boron, aluminum, gallium, indium, zinc, tin, germanium, lead, cadmium, iron, copper, manganese, tungsten, tantalum and zirconium. It is preferable to use at least one selected from the metal alkylsilylamide containing the metal, the metal alkylamide containing the metal, and the metal disinaamide containing the metal.

As the metal alkylsilylamide, a metal trialkylsilylamide can be used. In this case, the above metal can be used as the metal contained in the metal trialkylsilylamide, and the number of carbon atoms of the alkyl group is preferably 18 or less. Further, the metal trialkylsilylamide may be produced by mixing a strong base such as butyllithium with bis (trimethylsilyl) amine. Further, as the nitrogen supply source, in addition to the metal amide, a metal nitride such as lithium nitride or magnesium nitride may be further mixed.

Examples of the solubilizer include trialkylphosphine oxides, trialkylphosphine sulfides, trialkylphosphine serenides, trialkyliminophosphorans, monophosphate esters, diphosphate esters, triphosphate esters, dimethyl sulfoxide, and the like. It is preferable to use at least one selected from hexamethylphosphate triamide and N, N'-dimethylpropylene urea, and most preferably trialkylphosphine oxides. The molar ratio of the solubilizer to the metal amide can be set in the range of 1: 1 to 1: 100.

As the solvent, it is preferable to use an organic solvent having 8 to 35 carbon atoms, and for example, the organic solvents listed below are suitable. As the solvent, these organic solvents can be used alone or in combination as a solvent having a melting point of 24 ° C. or lower and a boiling point of 100 ° C. or higher.

Suitable organic solvents such as octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane, and liquid paraffin have a length of 8 to 35 carbon atoms in the main chain. Chain saturated alkanes and mixtures thereof; alkenes with unsaturated bonds such as octene, nonene, decene, undecene, dodecene, tridecene, tetradecene, pentadecene, hexadecene, heptadecene, octadecene; cyclohexane, cycloheptane, cyclooctane, cyclodecene, etc. Cyclic alkanes; aromatic hydrocarbons such as benzene, toluene, xylene, trimethylbenzene, dodecylbenzene, biphenyl; ethers such as diethyl ether, dibutyl ether, dihexyl ether, tetrahydrofuran, cyclopentylmethyl ether, phenyl ether; DOWNHERM (registered). Examples include mixed solvents such as A; phenyl sulfides, sulfides such as didodecyl sulfides;

Further, as the solvent, it is preferable to add the aromatic hydrocarbons by mixing different aromatic hydrocarbons with each other or dissolving the aromatic hydrocarbons in the long-chain saturated alkane. This makes it possible to enhance the effect of suppressing impurities from being mixed into the quantum dots.

In the step of preparing the above reaction solution, the dispersant may be further mixed. Dispersants include alkylcarboxylic acids, monoalkylamines, dialkylamines, trialkylamines, trialkylphosphins, alkyl esters, alkylthiols, sulfides, glycerin tricaprylate, alkylnitriles and anhydrous stearate. It is preferable to use at least one selected from the substances, and it is more preferable to use one having a functional group at the end which does not contain a hydrogen atom. Since the hydrogen atom reacts with sodium amide and causes a decrease in the nitrogen raw material, it is most preferable to react with sodium amide using an alkylthiol (metal complex) represented by the following formula (1) as a raw material.

According to this, the decomposition of sodium amide can be suppressed, and the effect of reducing the amount of sodium impurities in the system can be obtained. Therefore, it is advantageous because the amount of the electron acceptor added and the amount of the solubilizer added can be reduced. The molar ratio of the metal-containing compound to the dispersant can be set in the range of 1: 1 to 1: 100. According to this, the average particle size can be changed without changing the particle size distribution of the metal nitride nanoparticles. When octadecanethiol is used as the sulfur supply source, it can also be used as a dispersant, but other dispersants may be further mixed.

In the step of preparing the above reaction solution, the electron acceptor may be further mixed. As the electron acceptor, one having an oxidation-reduction potential at a position in a noble direction than the oxidation-reduction potential of the metal to be nitrided can be used.

For example, when the metal to be nitrided is indium, iodophosphine, halogens, superatomic iodine reagents, iodine agents, as electron acceptors whose redox potential is located in a noble direction than -0.34 V vs SHE, N, N'-dicyclohexylcarbodiimide, N-chlorosuccinimide, N-promoscusinimide, N-iodosuccinimide, 2,3-dichloro-5,6-dicyano-p-benzoquinone, nitroxyl radical, sulfur, alkylthiol, At least one selected from alkyl disulfide, alkyl trisulfide, tetracyanoquinodimethane, 2,3-dichloro-5,6-dicyano-p-benzoquinone and crown ethers, manganese and chromiums can be used. Among them, disulfide iodide and crown ether can be more preferably used.

As the iodination agent, for example, 1,3-jode-5,5-dimethylhydantoin can be used. The molar ratio of electron acceptor to metal amide can be set in the range of 1: 1 to 1: 5. According to this, since the electrons generated by the decomposition of sodium amide are used for the reduction reaction of the electron acceptor contained in the reaction solution, the reduction reaction of the first compound is suppressed, and the quantum dot or core-shell type quantum dot dispersion is suppressed. It is possible to prevent metal from remaining or being mixed in the liquid as much as possible. Moreover, it is possible to prevent an increase in the manufacturing process and obtain quantum dots or core-shell type quantum dots having long-term stable dispersibility.

The electron acceptor does not function below the decomposition temperature of the metal amide, and is effective when the reaction of the above-mentioned formula (1) proceeds at a temperature of 280 ° C. or higher, for example, when the reaction temperature is 280 ° C. or higher. be. This means that the synthesis rate of the core can be improved by raising the reaction temperature, so that the effect of increasing the average particle size of the core immediately after synthesis is utilized. That is, the electron acceptor can be used for the purpose of controlling the average particle size of the quantum dot dispersion liquid to be produced. As a matter of course, the lower limit temperature at which the effect of the electron acceptor is exhibited changes depending on the difference in the decomposition temperature of the metal amide and the difference in the reaction behavior due to the thermal history of the reaction solution.

Next, the reaction solution is housed in a reaction vessel (not shown), and the reaction solution is heated to a predetermined first temperature using a heating means (not shown) such as a heater attached to the reaction vessel. The first temperature can be set, for example, in the range of 100 ° C to 600 ° C. By this heating, the first compound and the metal amide are heated and reacted, so that the metal nitride nanoparticles to be the core 1 are synthesized.

As the reaction vessel and the heating means, those having a known structure can be used, and therefore detailed description thereof will be omitted here. Further, by conducting a heating reaction while introducing a nitrogen-containing gas such as ammonia gas or nitrogen gas into the reaction vessel, the supply amount of nitrogen can be increased and the decomposition reaction of the metal amide can be suppressed. As a result, the core can be efficiently synthesized.

Further, the reaction solution may be prepared by mixing the first compound, the metal amide, the dispersant, the solubilizer, the electron acceptor, and the solvent in the reaction vessel. However, it is more preferable to mix the first compound, the dispersant, the solubilizer and the electron acceptor before contacting with the metal amide because the reaction between the proton and the metal amide can be suppressed and the loss can be suppressed.

After holding the reaction solution at the first temperature for a predetermined time, the reaction solution is cooled to room temperature. The holding time can be set, for example, in the range of 1 minute to 240 minutes. The cooling method may be natural cooling or forced cooling in which a refrigerant (for example, cooling water) is circulated in the reaction vessel. The cooled reaction solution contains a second compound containing zinc, which is a raw material of the shell 2, and a sulfur source for sulfurizing the zinc contained in the second compound. Then, the reaction solution to which these second compounds and the sulfur supply source are added is heated to a predetermined second temperature. The second temperature can be set, for example, in the range of 100 ° C to 600 ° C. By this heating, the surface of the core 1 is covered with the shell 2 made of the ZnS film synthesized by the heating reaction between the second compound and the sulfur source, and the core-shell type quantum dots are formed.

As the second compound, for example, a halide of zinc or a metal complex containing zinc and the dispersant can be used. For example, zinc iodide can be preferably used. As the sulfur source, at least one selected from thiols such as butanethiol, dodecanethiol, hexadecanethiol and octadecanethiol, and sulfides such as phenylsulfide and didodecylsulfide can be used. Since octadecanethiol can also be used as a dispersant, it is preferable to use octadecanethiol. The molar ratio of sulfur source to metal amide can be set in the range of 1: 1 to 1: 100.

When a sulfur supply source having a decomposition temperature higher than the first temperature is used, for example, when the first temperature is set to 230 ° C., the decomposition temperature (240 ° C.) higher than this first temperature is used. In the case of using dodecanethiol having such a sulfur source, in order to include such a sulfur source in the reaction solution after core 1 synthesis, the sulfur source is prepared in the step of preparing the reaction solution before heating to the first temperature. It shall include mixing in advance.

After holding the reaction solution at the second temperature for a predetermined time, the reaction solution is cooled to room temperature. The holding time can be set, for example, in the range of 1 minute to 240 minutes. The cooling method may be natural cooling or forced cooling in which a refrigerant (for example, cooling water) is circulated in the reaction vessel. Quantum dots covered with a dispersant are extracted by adding a substance having an acid dissociation constant pKa of more than 4.5 and hydrogen at the terminal of a functional group together with ethanol to the reaction solution after cooling. As the substance, oleic acid or dodecanethiol can be used. In this way, a weak acid is used rather than acetic acid, and the reaction is made to react with the metal existing in the reaction solution after cooling to form an ionized metal salt solution, and at the same time, it is weakly bonded to the quantum dot surface to cause mutual aggregation of the quantum dots. It becomes a capping agent that interferes. That is, when the sediment, which is the target intermediate product, is separated by centrifugation and decantation, it has the effect of preventing XPS / EDX from detecting metals other than quantum dots in the sediment, and at the same time, the next final When a quantum dot dispersion liquid is used in the process, it has the effect of suppressing aggregation and can suppress deterioration of the measured value of the average particle size in the liquid. In this way, the step of removing the metal other than the quantum dots can be repeated as needed.

Finally, the extracted quantum dots covered with the dispersant are dispersed in the dispersion medium. As a result, a quantum dot dispersion liquid that can be stably dispersed for one week or longer can be obtained. As the dispersion medium, it is preferable to use an organic solvent having 6 to 18 carbon atoms, for example, hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane and the like. Long-chain alkanes with 6-18 carbon atoms in the main chain; cyclic alkanes such as cyclohexane, cycloheptane, cyclooctane, cyclodecene; aromatic hydrocarbons such as benzene, toluene, xylene, trimethylbenzene, dodecylbenzene; Alcohols such as hexanol, heptanol, octanol, decanol, cyclohexanol, terpineol; ethers such as diethyl ether, dibutyl ether, dihexyl ether, tetrahydrofuran, cyclopentylmethyl ether, phenyl ether; dimethylformamide, N-N'-dimethylpropylene urea , Tris (N, N-dimethylamino) hoffin oxide, diazabicycloundecene, can be used alone or in admixture.

By the way, to explain the case where sodium amide is used as the metal amide as an example, when the first compound and the sodium amide are heated and reacted to synthesize the core 1 composed of the metal nitride, the sodium amide has the following formula (2). ) Decomposes to generate electrons.

Since these electrons are used in the reduction reaction of the electron acceptor contained in the reaction solution, the reduction reaction of the first compound is suppressed. Therefore, it is possible to prevent the metal from remaining and being mixed in the quantum dot or the core-shell type quantum dot dispersion liquid as much as possible.

According to the above-described embodiment, by configuring the core 1 with quantum dots made of metal nitride and the shell 2 with ZnS, the emission wavelength is equivalent to that of the core-shell type quantum dots made of InP / ZnS. A core-shell type quantum dot QD capable of emitting light can be obtained. Moreover, the quantum dot or core-shell quantum dot QD can be produced without using a relatively expensive phosphorus-containing compound.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above. For example, as shown in FIG. 2, by forming the core 1 around the crystal nucleus 10, it is possible to obtain the core 1 having high crystallinity. In this case, a semiconductor having a bandgap larger than that of the core 1 can be used as the crystal nucleus 10, and for example, ZnO, ZnS, ZnSe, InN, GaInN, GaN, AlN, AlInN, ZnMgO, Zn 3N ₂ , and _ZnPbN can be used. _2. At least one selected from ZnSnN _{2, ZnGeN 2, ZnSiN 2 , LiGaO 2} , LiAlO ₂ , NaGaO ₂ , NaAlo ₂ , CuGaO ₂ , and AgAlO ₂ can be used. The crystal nuclei 10 can be synthesized by mixing the raw materials of the crystal nuclei and heating the mixed raw materials to a predetermined third temperature. The third temperature can be set, for example, in the range of 100 ° C to 600 ° C. By mixing the crystal nuclei 10 thus synthesized with the reaction solution before heating to the first temperature, the core 1 can be formed around the crystal nuclei 10. For example, when synthesizing a crystal nucleus 10 made of ZnS, zinc oleate and dodecanethiol can be used as raw materials for the crystal nucleus 10.

Further, as shown in FIG. 3, a passivation layer 4 that covers the surface of the shell 2 may be further provided, and the surface of the passivation layer 4 may be covered with the dispersant 3. According to this, the dangling bond (unbonded hand) existing on the surface of the shell 2 is terminated, so that the quantum dot can be kept stable for a long period of time.

The passivation layer 4 includes ZnS, ZnSe, ZnO, ZnSO, ZnSSe, ZnSeO, ZnMgO, Zn ₂ LiGaO ₄ , NaGaO ₂ , MgO, InN _x O _x , GaN _x O _x , AlN _x O _x , In ₂ O ₃ , At least one selected from Ga ₂ O ₃ , Al ₂ O ₃ , SiO ₂ , SiNO _x , LiOnO ₂ , LiGaO ₂ , LiAlO ₂ , NaGaO ₂ , NaAlO ₂ , CuGaO ₂ , AgAlO ₂ , AgGaO ₂ , and AgInO ₂ . Can be used.

The band gap of the passivation layer 4 is not particularly limited, but ZnO, ZnMgO, Zn ₂ LiGaO ₄ , and NaGaO ₂ having a structure in which the crystal lattice parameters a ₀ of the metal nitride constituting the core 1 and ZnS constituting the shell 2 are close to each other are used. It can be used more preferably. This is advantageous because it is difficult for oxygen and water vapor to permeate.

The thickness of the passivation layer 4 is preferably in the range of, for example, 0.1 to 10 nm. Such a passivation layer 4 can be formed by adding the raw material of the passivation layer 4 to the reaction solution after forming the shell 2 and heating it to a predetermined fourth temperature. The fourth temperature can be set, for example, in the range of 100 ° C to 600 ° C. For example, when the passivation layer 4 made of ZnMgO is synthesized, zinc acetate, magnesium acetate, dodecanol, and oleic acid can be used as the raw materials for the passivation layer 4. Further, the passivation layer 4 may be a natural oxide film formed by exposing the surface of the shell 2 to the atmosphere.

As the shell 2, for example, ZnS, ZnO, and ZnSe can be used. Above all, ZnS can be preferably used.

Hereinafter, an example of an experiment conducted to specifically confirm the embodiment of the present invention will be described.
Experimental Examples 1 to 5 are "synthesis examples of a nitride core", Experimental Examples 6 to 10 are "constituent examples of a nitride core / ZnS shell", and Experimental Examples 11 to 15 are "other structural examples".

<Nitride core synthesis example>
(Experimental Example 1): InN
In Experimental Example 1, a method for producing a quantum dot dispersion liquid using core 1 as InN without using a crystal growth inhibitor (HMDS) will be described.
0.050 g (0.1 mmol) of indium iodide as the first compound, 0.04 g (1 mmol) of sodium amide as the metal amide, and 0.44 g (1.14 mmol) of trioctylphosphine oxide as the solubilizer. ), 0.02 g (0.3 mmol) of dodecanethiol as a sulfur supply source, and 2 ml of DOWNHERM A as a solvent were mixed in a reaction vessel to prepare a reaction solution. The reaction solution was rapidly heated to 220 ° C. (first temperature) (150 ° C./min) and held for 10 minutes, after which the reaction solution was cooled to room temperature.
0.5 ml of oleic acid and 20 ml of ethanol are added to the cooled reaction solution, and sodium iodide, sodium thiolate and sodium oleate, which are by-products remaining in the reaction solution, are dispersed in ethanol to form a core composed of InN. Quantum dots consisting of only sodium were settled by centrifugation, and this process was repeated 3 times. This precipitate was redistributed in cyclohexane as a dispersion medium to obtain a quantum dot dispersion.

(Experimental Example 2): InGaN
In Experimental Example 2, a method for producing a quantum dot dispersion liquid in which the core 1 is composed of InGaN without using a crystal growth inhibitor (HMDS) will be described.
0.015 g (0.3 mmol) of indium iodide and 0.032 g (0.7 mmol) of gallium iodide as the first compound, 0.04 g (1 mmol) of sodium amide as the metal amide, and as a solubilizer. A reaction solution is prepared by mixing 0.44 g (1.14 mmol) of trioctylphosphine oxide, 0.02 g (0.3 mmol) of dodecanethiol as a sulfur source, and 2 ml of DOWNHERM A as a solvent. did. The reaction solution was rapidly heated to 220 ° C. (first temperature) (150 ° C./min) and held for 10 minutes, after which the reaction solution was cooled to room temperature. The reaction solution was cooled to room temperature.
0.5 ml of oleic acid and 20 ml of ethanol are added to the cooled reaction solution, and sodium iodide, sodium thiolate and sodium oleate, which are by-products remaining in the reaction solution, are dispersed, and the core is composed of InGaN only. The quantum dots were settled by centrifugation and this process was repeated 3 times. This precipitate was redistributed in cyclohexane as a dispersion medium to obtain a quantum dot dispersion.

(Experimental Example 3): InN (HMDS)
In Experimental Example 3, a method for producing a quantum dot dispersion liquid in which the core 1 is composed of InN will be described using a crystal growth inhibitor (HMDS).
0.05 g (0.1 mmol) of indium iodide as the first compound, 0.04 g (1 mmol) of sodium amide as the metal amide, and 0.44 g (1.14 mmol) of trioctylphosphine oxide as the solubilizer. ), 0.02 g (0.3 mmol) of dodecanethiol as a sulfur supply source, HMDS (0.3 mmol) as a crystal growth inhibitor, and 2 ml of DOWNHERM A as a solvent to prepare a reaction solution. did. The reaction solution was rapidly heated to 220 ° C. (first temperature) (150 ° C./min) and held for 10 minutes, after which the reaction solution was cooled to room temperature.
0.5 ml of oleic acid and 20 ml of ethanol are added to the cooled reaction solution, and sodium iodide, sodium thiolate and sodium oleate, which are by-products remaining in the reaction solution, are dispersed, and the core is composed only of InN. The quantum dots were settled by centrifugation and this process was repeated 3 times. This precipitate was redistributed in cyclohexane as a dispersion medium to obtain a quantum dot dispersion.

(Experimental Example 4): GaInN (HMDS)
In Experimental Example 4, a method for producing a quantum dot dispersion liquid in which the core 1 is composed of GaInN will be described using a crystal growth inhibitor (HMDS).
0.015 g (0.03 mmol) of indium iodide and 0.032 g (0.07 mmol) of gallium iodide as the first compound, 0.04 g (1 mmol) of sodium amide as the metal amide, and as a solubilizer. 0.44 g (1.14 mmol) of trioctylphosphine oxide, 0.02 g (0.3 mmol) of dodecanethiol as a sulfur source, HMDS (0.3 mmol) as a crystal growth inhibitor, and DOWNHERM A 2 ml as a solvent. Was mixed in a reaction vessel to prepare a reaction solution. The reaction solution was rapidly heated to 220 ° C. (first temperature) (150 ° C./min) and held for 10 minutes, after which the reaction solution was cooled to room temperature.
0.5 ml of oleic acid and 20 ml of ethanol are added to the cooled reaction solution, and sodium iodide, sodium thiolate and sodium oleate, which are by-products remaining in the reaction solution, are dispersed, and the core is composed only of GaInN. The quantum dots were settled by centrifugation and this process was repeated 3 times. This precipitate was redistributed in cyclohexane as a dispersion medium to obtain a quantum dot dispersion.

(Experimental Example 5): ZnInN
In Experimental Example 5, a method for producing a quantum dot dispersion liquid in which the core 1 is composed of ZnInN without using a crystal growth inhibitor (HMDS) will be described.
0.025 g (0.5 mmol) of indium iodide and 0.16 g (0.5 mmol) of zinc iodide as the first compound, 0.04 g (5 mmol) of sodium amide as the metal amide, and as a solubilizer. A reaction solution is prepared by mixing 0.44 g (1.14 mmol) of trioctylphosphine oxide, 0.02 g (0.3 mmol) of dodecanethiol as a sulfur source, and 2 ml of DOWNHERM A as a solvent in a reaction vessel. did. The reaction solution was rapidly heated to 220 ° C. (first temperature) (150 ° C./min) and held for 10 minutes, after which the reaction solution was cooled to room temperature.
0.5 ml of oleic acid and 20 ml of ethanol are added to the cooled reaction solution, and sodium iodide, sodium thiolate and sodium oleate, which are by-products remaining in the reaction solution, are dispersed, and the core is composed only of ZnInN. The quantum dots were settled by centrifugation and this process was repeated 3 times. This precipitate was redistributed in cyclohexane as a dispersion medium to obtain a quantum dot dispersion.

<Structure example of nitride core / ZnS shell>
(Experimental Example 6): InN / ZnS
In Experimental Example 6, a method for producing a quantum dot dispersion liquid in which the core 1 is InN and the shell 2 is ZnS without using a crystal growth inhibitor (HMDS) will be described.
0.050 g (0.1 mmol) of indium iodide as the first compound, 0.04 g (1 mmol) of sodium amide as the metal amide, and 0.44 g (1.14 mmol) of trioctylphosphine oxide as the solubilizer. ), 0.02 g (0.3 mmol) of dodecanethiol as a sulfur supply source, and 2 ml of DOWNHERM A as a solvent were mixed in a reaction vessel to prepare a reaction solution. This reaction solution is rapidly heated to 220 ° C. (first temperature) (150 ° C./min) and held for 10 minutes, and then 0.1 M zinc stearate octadecene solution (corresponding to the second compound) 1 ml (0) as a zinc source. .1 mmol) was added, the mixture was heated at 260 ° C. (second temperature), held for 20 minutes, and then the reaction solution was cooled to room temperature. The reaction solution was cooled to room temperature.
A core-shell type composed of InN / ZnS by adding 0.5 ml of oleic acid and 20 ml of ethanol to the cooled reaction solution and dispersing sodium iodide, sodium thiolate and sodium oleate, which are by-products remaining in the reaction solution. The quantum dots were settled by centrifugation and this process was repeated 3 times. This precipitate was redistributed in cyclohexane as a dispersion medium to obtain a core-shell type quantum dot dispersion.

(Experimental Example 7): InGaN / ZnS
In Experimental Example 7, a method for producing a core-shell type quantum dot dispersion liquid in which the core 1 is made of InGaN and the shell 2 is made of ZnS without using a crystal growth inhibitor (HMDS) will be described.
0.015 g (0.3 mmol) of indium iodide and 0.032 g (0.7 mmol) of gallium iodide as the first compound, 0.04 g (1 mmol) of sodium amide as the metal amide, and as a solubilizer. A reaction solution is prepared by mixing 0.44 g (1.14 mmol) of trioctylphosphine oxide, 0.02 g (0.3 mmol) of dodecanethiol as a sulfur source, and 2 ml of DOWNHERM A as a solvent. did. This reaction solution is rapidly heated to 220 ° C. (first temperature) (150 ° C./min) and held for 10 minutes, and then 0.1 M zinc stearate octadecene solution (corresponding to the second compound) 1 ml (0) as a zinc source. .1 mmol) was added, the mixture was heated at 260 ° C. (second temperature), held for 20 minutes, and then the reaction solution was cooled to room temperature. The reaction solution was cooled to room temperature.
A core-shell type composed of InGaN / ZnS by adding 0.5 ml of oleic acid and 20 ml of ethanol to the cooled reaction solution and dispersing sodium iodide, sodium thiolate and sodium oleate, which are by-products remaining in the reaction solution. The quantum dots were settled by centrifugation and this process was repeated 3 times. This precipitate was redistributed in cyclohexane as a dispersion medium to obtain a core-shell type quantum dot dispersion.

(Experimental Example 8): InN / ZnS (HMDS)
In Experimental Example 8, a method for producing a dispersion liquid of core-shell type quantum dots in which the core 1 is composed of InN and the shell 2 is composed of ZnS will be described using a crystal growth inhibitor (HMDS).
0.05 g (1 mmol) of indium iodide as the first compound, 0.04 g (1 mmol) of sodium amide as the metal amide, and 0.44 g (1.14 mmol) of trioctylphosphine oxide as the solubilizer. , 0.02 g (0.3 mmol) of dodecanethiol as a sulfur source, HMDS (0.3 mmol) as a crystal growth inhibitor, and 2 ml of DOWNHERM A as a solvent were mixed in a reaction vessel to prepare a reaction solution. This reaction solution is rapidly heated to 220 ° C. (first temperature) (150 ° C./min) and held for 10 minutes, and then 0.1 M zinc stearate octadecene solution (corresponding to the second compound) 1 ml (0) as a zinc source. .1 mmol) was added, the mixture was heated at 260 ° C. (second temperature), held for 20 minutes, and then the reaction solution was cooled to room temperature. The reaction solution was cooled to room temperature.
A core-shell type composed of InN / ZnS by adding 0.5 ml of oleic acid and 20 ml of ethanol to the cooled reaction solution and dispersing sodium iodide, sodium thiolate and sodium oleate, which are by-products remaining in the reaction solution. The quantum dots were settled by centrifugation and this process was repeated 3 times. This precipitate was redistributed in cyclohexane as a dispersion medium to obtain a core-shell type quantum dot dispersion.

(Experimental Example 9): GaInN / ZnS (HMDS)
In Experimental Example 9, a method for producing a core-shell type quantum dot dispersion liquid in which the core 1 is composed of GaInN and the shell 2 is composed of ZnS using a crystal growth inhibitor (HMDS) will be described.
As the first compound, 0.015 g (0.03 mmol) of indium iodide and 0.032 g (0.07 mmol) of gallium iodide, 0.04 g (1 mmol) of sodium amide as a metal amide, and as a solubilizer. 0.44 g (1.14 mmol) of trioctylphosphine oxide, 0.02 g (0.3 mmol) of dodecanethiol as a sulfur source, HMDS (0.3 mmol) as a crystal growth inhibitor, and DOWNHERM A 2 ml as a solvent. Was mixed in a reaction vessel to prepare a reaction solution. This reaction solution is rapidly heated to 220 ° C. (first temperature) (150 ° C./min) and held for 10 minutes, and then 0.1 M zinc stearate octadecene solution (corresponding to the second compound) 1 ml (0) as a zinc source. .1 mmol) was added, the mixture was heated at 260 ° C. (second temperature), held for 20 minutes, and then the reaction solution was cooled to room temperature.
A core-shell type composed of GaInN / ZnS by adding 0.5 ml of oleic acid and 20 ml of ethanol to the cooled reaction solution and dispersing sodium iodide, sodium thiolate and sodium oleate, which are by-products remaining in the reaction solution. The quantum dots were settled by centrifugation and this process was repeated 3 times. This precipitate was redistributed in cyclohexane as a dispersion medium to obtain a core-shell type quantum dot dispersion.

(Experimental Example 10): ZnInN / ZnS
In Experimental Example 10, a method for producing a core-shell type quantum dot dispersion liquid in which the core 1 is made of ZnInN and the shell 2 is made of ZnS without using a crystal growth inhibitor (HMDS) will be described.
0.025 g (0.5 mmol) of indium iodide and 0.16 g (0.5 mmol) of zinc iodide as the first compound, 0.04 g (5 mmol) of sodium amide as the metal amide, and as a solubilizer. A reaction solution is prepared by mixing 0.44 g (1.14 mmol) of trioctylphosphine oxide, 0.02 g (0.3 mmol) of dodecanethiol as a sulfur source, and 2 ml of DOWNHERM A as a solvent in a reaction vessel. did. This reaction solution was rapidly heated to 220 ° C. (first temperature) (150 ° C./min) and held for 10 minutes, then heated at 260 ° C. (second temperature), held for 20 minutes, and then the reaction solution was kept at room temperature. Cooled down to. The second compound is a residual sulfur supply source.
A core-shell type composed of ZnInN / ZnS by adding 0.5 ml of oleic acid and 20 ml of ethanol to the cooled reaction solution and dispersing sodium iodide, sodium thiolate and sodium oleate, which are by-products remaining in the reaction solution. The quantum dots were settled by centrifugation and this process was repeated 3 times. This precipitate was redistributed in cyclohexane as a dispersion medium to obtain a core-shell type quantum dot dispersion.

FIG. 4 is a graph showing the irradiation time dependence of the peak intensity. In FIG. 4, the horizontal axis is the time during which the quantum dots are continuously irradiated with the excitation light having a wavelength of 365 nm, and the vertical axis is the peak intensity of the fluorescence emitted by the quantum dots. In FIG. 4, the □ mark is Experimental Example 3, the ◇ mark is Experimental Example 4, the Δ mark is Experimental Example 5, and the × mark is a conventional example (when the core is InP and the shell is ZnS).
FIG. 5 is a graph showing the irradiation time dependence of the emission spectrum, and is the result of evaluating the quantum dots of Experimental Example 4 (GaInN using HMDS).

From FIGS. 4 and 5, the following points became clear.
(A1) The quantum dot of the present invention emits fluorescence by continuous irradiation of excitation light.
(A2) In the quantum dots of the present invention, the emission intensity (peak intensity) of the fluorescence increases due to the continuous irradiation of the excitation light, that is, as the irradiation time becomes longer.
(A3) The quantum dots of the conventional example emit fluorescence by continuous irradiation of excitation light, but the emission intensity (peak intensity) of the fluorescence decreases as the irradiation time becomes longer.
From the above results, it was found that according to the present invention, core-shell quantum dots having both stability (robustness) and fluorescence characteristics (emission) can be obtained. Further, since the emission intensity of the fluorescence is increased by the continuous irradiation of the excitation light, it was confirmed that the core-shell type quantum dot of the present invention has excellent emission characteristics for long-term stability.

FIG. 6 is a list of Experimental Examples 1 to 5 described above. FIG. 6 shows the materials constituting the core (Compounds), the presence or absence of HDMS, the evaluation of the fluorescence characteristics (emission spectrum) described later, and the evaluation of the fluorescence lifetime.
In the evaluation of the fluorescence characteristics, the x mark indicates that no light is emitted, and the ○ mark indicates that fluorescence emission is confirmed.
In the evaluation of the lifetime, the-mark indicates that no fluorescence is observed, and the ○ mark indicates that the initial fluorescence intensity is maintained by continuous irradiation with excitation light for 3 hours (Intensity standard value is 1.0 or more). , X indicates that the attenuation of the fluorescence intensity can be confirmed when the excitation light is continuously irradiated for 3 hours (Intensity standard value is less than 1.0).

7 to 11 are graphs showing the emission spectra of the quantum dots of Experimental Examples 1 to 5 in order. FIG. 12 is a graph showing the emission spectra of Experimental Examples 1 to 5 (FIGS. 7 to 11) collectively.

From FIGS. 7 to 11 and FIGS. 12, the following points became clear.
(B1) In the quantum dots containing HDMS (Experimental Examples 3 and 4), the emission spectrum (fluorescence) was confirmed in the vicinity of the wavelength of 550 to 600 nm, and the fluorescence peak wavelength was 576 nm (half width FWHM: 195 nm).
(B2) Quantum dots containing no HDMS (Experimental Examples 1 and 2) had no emission spectrum confirmed at a wavelength of around 550 to 600 nm. (Only excitation light is observed)
(B3) The results of (B1) and (B2) above do not depend on the materials (InN, GaInN) constituting the core.
(B4) When the material constituting the core contains Zn instead of Ga (Experimental Example 5: ZnInN), an emission spectrum (fluorescence) is confirmed in the vicinity of a wavelength of 550 to 600 nm, and the fluorescence peak wavelength is 579 nm (half width at half maximum). FWHM: 134 nm). In this case (Experimental Example 5), it was found that the lifetime was short while having excellent fluorescence characteristics.
From the above results, the stability (robustness) and fluorescence characteristics (emission) of the core-shell quantum dots of the present invention are as follows: Core 1 is HMDS (1,1,1,3,3,3-hexamethyldisilazane). It was confirmed that this was achieved by being produced by a synthetic process containing a crystal growth inhibitor.

FIG. 13 is an XYZ color system chromaticity diagram in which the CIEs of the quantum dots of Experimental Example 4 and Experimental Example 5 are added. In FIG. 13, the circle on the left side indicates Experimental Example 4 (GaInN), and the ● mark on the right side indicates Experimental Example 5 (ZnInN).
In the case of Experimental Example 4 (GaInN), the fluorescence peak wavelength was 576 nm (half width FWHM: 195 nm), and the CIE (x, y) was (0.440, 0.460).
In the case of Experimental Example 5 (ZnInN), the fluorescence peak wavelength was 579 nm (half width FWHM: 134 nm), and the CIE (x, y) was (0.478, 0.474).
From the above results, it was confirmed that the core-shell quantum dots of Experimental Example 4 (GaInN) can emit light at the same emission wavelength as the core-shell quantum dots of Experimental Example 5 (ZnInN).
In addition, the obtained InN quantum dots were subjected to narrow scan analysis of the 3d5 / 2 orbit of In using X-ray photoelectron spectroscopy (XPS). When the binding energy of the orbit was measured by XPS, it was confirmed that the peak corresponding to 443.5 eV derived from the In—In bond was not observed. As a matter of course, the In-N peak of 444.0 eV was observed as the main, and it was confirmed that InN nanoparticles with high purity were obtained.

FIG. 14 is a photograph in which the change with time is evaluated by the appearance, and the photograph on the left side shows the state immediately after synthesis, and the photograph on the right side shows the state one month after the atmosphere. Further, in each photograph, the sample in the bottle on the left side is InN, and the sample in the bottle on the right side is InP.
From FIG. 14, the following points became clear.
(C1) In the sample (InN) in the bottle on the left side, no change was observed in the color tone of the sample as compared with the photograph immediately after synthesis and the photograph one month after the atmosphere.
(C2) The sample (InP) in the bottle on the right side has a change in the color tone of the sample and a change in the light absorption characteristics, and the deterioration of the material is observed by comparing the photograph immediately after synthesis with the photograph one month after the atmosphere. Was confirmed.
From the above results, it was inferred that InN may be qualitatively more stable than InP.

FIG. 15 is a graph in which the time course of the two samples shown in FIG. 14 was evaluated by an optical energy gap. In FIG. 15, the horizontal axis is Photon Energy and the vertical axis is (αhν) ² . The solid line represents immediately after synthesis, and the dotted line represents one month after the atmosphere.
From FIG. 15, the following points became clear.
(D1) When the sample was InN, the amount of change in the optical energy gap after 1 month in the atmosphere was +0.05 eV.
(D2) When the sample was InP, the amount of change in the optical energy gap after 1 month in the atmosphere was +0.17 eV.
From the above results, it was confirmed that InN can obtain a core with higher optical stability than InP.

(Experimental Example 11): InN / In ₂ O ₃
In Experimental Example 11, a method for producing a core-shell type quantum dot dispersion liquid in which the core ₁ is composed of InN and the shell ₂ is composed of In2O3 will be described using a crystal growth inhibitor (HMDS).
0.05 g (1 mmol) of indium iodide as the first compound, 0.04 g (5 mmol) of sodium amide as the metal amide, and 0.44 g (1.14 mmol) of trioctylphosphine oxide as the solubilizer. , 0.02 g (0.3 mmol) of dodecanethiol as a sulfur source, HMDS (0.3 mmol) as a crystal growth inhibitor, and 2 ml of DOWNHERM A as a solvent were mixed in a reaction vessel to prepare a reaction solution. The reaction solution was rapidly heated to 220 ° C. (first temperature) (150 ° C./min) and held for 10 minutes, after which the reaction solution was cooled to room temperature.
To the cooled reaction solution, 0.5 ml of oleic acid and 20 ml of ethanol are added, and sodium iodide, sodium thiolate and sodium oleate, which are by-products remaining in the reaction solution, are dispersed, and a core-shell type quantum dot composed of InN. Was settled by centrifugation, and this step was repeated 3 times. This precipitate was redistributed in cyclohexane as a dispersion medium to obtain a core-shell type quantum dot dispersion. When the surface was oxidized by irradiating with excitation light in the atmosphere, an increase in fluorescence intensity was observed as compared with the quantum dots having only the InN core. It can be said that the second compound is oxygen in the atmosphere and the second temperature is normal temperature.

(Experimental Example 12): InN / In ₂ S ₃
In Experimental Example 12, a method for producing a core-shell type quantum dot dispersion liquid in which the core 1 is composed of InN and the shell ₂ is composed of _In2S3 will be described using a crystal growth inhibitor (HMDS).
0.05 g (1 mmol) of indium iodide as the first compound, 0.04 g (5 mmol) of sodium amide as the metal amide, and 0.44 g (1.14 mmol) of trioctylphosphine oxide as the solubilizer. , 0.02 g (0.3 mmol) of dodecanethiol as a sulfur source, HMDS (0.3 mmol) as a crystal growth inhibitor, and 2 ml of DOWNHERM A as a solvent were mixed in a reaction vessel to prepare a reaction solution. This reaction solution was rapidly heated to 220 ° C. (first temperature) (150 ° C./min) and held for 10 minutes, then heated at the second temperature of 260 ° C. and held for 20 minutes, and then the reaction solution was kept at room temperature. Cooled down to. The second compound is a residual sulfur supply source.
To the cooled reaction solution, 0.5 ml of oleic acid and 20 ml of ethanol are added, and sodium iodide, sodium thiolate and sodium oleate, which are by-products remaining in the reaction solution, are dispersed, and a core-shell type quantum dot composed of InN. Was settled by centrifugation, and this step was repeated 3 times. This precipitate was redistributed in cyclohexane as a dispersion medium to obtain a core-shell type quantum dot dispersion.

(Experimental Example 13): GaInN / GaInO _x
In Experimental Example 13, a method for producing a dispersion liquid of core-shell type quantum dots in which the core 1 is composed of GaInN and the shell 2 is composed of _GaInOx using a crystal growth inhibitor (HMDS) will be described.
0.015 g (0.3 mmol) of indium iodide and 0.032 g (0.7 mmol) of gallium iodide as the first compound, 0.04 g (5 mmol) of sodium amide as the metal amide, and as a solubilizer. 0.44 g (1.14 mmol) of trioctylphosphine oxide, 0.02 g (0.3 mmol) of dodecanethiol as a sulfur source, HMDS (0.3 mmol) as a crystal growth inhibitor, and DOWNHERM A 2 ml as a solvent. Was mixed in a reaction vessel to prepare a reaction solution. The reaction solution was rapidly heated to 220 ° C. (first temperature) (150 ° C./min) and held for 10 minutes, after which the reaction solution was cooled to room temperature.
A core-shell type quantum dot composed of GaInN by adding 0.5 ml of oleic acid and 20 ml of ethanol to the cooled reaction solution and dispersing sodium iodide, sodium thiolate and sodium oleate, which are by-products remaining in the reaction solution. Was settled by centrifugation, and this step was repeated 3 times. This precipitate was redistributed in cyclohexane as a dispersion medium to obtain a core-shell type quantum dot dispersion. When the surface was oxidized by irradiating with excitation light in the atmosphere, an increase in fluorescence intensity was observed as compared with the quantum dots of only the GaInN core. It can be said that the second compound is oxygen in the atmosphere and the second temperature is normal temperature.

(Experimental Example 14): GaInN / GaInS _x
In Experimental Example 14, a method for producing a core-shell type quantum dot dispersion liquid in which the core 1 is composed of GaInN and the shell 2 is composed of GaInS _x using a crystal growth inhibitor (HMDS) will be described.
As the first compound, 0.015 g (0.3 mmol) of indium iodide and 0.032 g (0.7 mmol) of gallium iodide, 0.04 g (5 mmol) of sodium amide as a metal amide, and as a solubilizer. 0.44 g (1.14 mmol) of trioctylphosphine oxide, 0.02 g (0.3 mmol) of dodecanethiol as a sulfur source, HMDS (0.3 mmol) as a crystal growth inhibitor, and DOWNHERM A 2 ml as a solvent. Was mixed in a reaction vessel to prepare a reaction solution. This reaction solution was rapidly heated to 220 ° C. (first temperature) (150 ° C./min) and held for 10 minutes, then heated at the second temperature of 260 ° C. and held for 20 minutes, and then the reaction solution was kept at room temperature. Cooled down to. The second compound is a residual sulfur supply source.
To the cooled reaction solution, 0.5 ml of oleic acid and 20 ml of ethanol are added, and sodium iodide, sodium thiolate and sodium oleate, which are by-products remaining in the reaction solution, are dispersed, and a core-shell type quantum dot composed of GaInN. Was settled by centrifugation, and this step was repeated 3 times. This precipitate was redistributed in cyclohexane as a dispersion medium to obtain a core-shell type quantum dot dispersion.

Hereinafter, Experimental Examples 21 to 25 further examined for the present invention will be described.
Traditionally, there have been some serious problems that have hindered the study of metal nitride QDs, such as long reaction times, metal indium contamination, and uncontrollable single nanoparticle size. In order to solve these problems, the present inventors have developed a method for efficiently synthesizing InN quantum dots under mild conditions (220 ° C., 10 minutes, 0.15 MPa). The methods developed by the present inventors will be described in detail in Experimental Examples 21 to 25 described later. According to this method, the synthesized InN nanocrystals were not contaminated with metallic indium, and their average diameter was about 2 to 6 nm as shown in FIG. 17 (c), and they were stable for a long period of time in an organic solvent. Shows dispersion. Furthermore, GaInN and ZnInN nanoparticles synthesized using this method exhibited photoluminescence (PL).

<Preparation of the solution used in Experimental Examples 21 to 25>
Chemicals: Indium iodide (99.99%), gallium iodide (99.99%) and zinc iodide (99.99%) were purchased from Kojundo Chemical in Japan.
Sodium amide (98%) and octadecanethiol (98%, ODT) were purchased from Sigma-Aldrich.
Oleylamine (> 50.0%, OLA), trioctylphosphine oxide (> 95.0%, TOPO), and phenyl ether (> 99%) were purchased from TCI, Japan.
Hexamethyldisilazane (> 98%, HMDS), oleic acid (> 85%, OA), and cyclohexane (99.5%) were purchased from Kanto Chemical Co., Japan.
OLA was used after distillation. Other chemicals were used without further purification.

(Experimental Example 21) Synthesis of OLA-InN Quantum Dots The following describes a method for producing OLA-InN quantum dots (also referred to as OLA-InN QD). This production method was synthesized with some modifications according to the previously reported production method.
Indium iodide (0.05 g, 0.1 mmol), sodium amide (0.04 g, 1 mmol), and OLA (0.1 mL, 0.03 mmol) in a 10 mL vial in a glove box with 1.5 mL of phenyl ether ( 1.5 mL) and mixed.
Then, the vial was heated to 220 ° C. (150 ° C./min), kept at that temperature for 10 minutes, and then cooled to room temperature (RT).
Then, as a washing step, 0.5 mL of OA is added, and the mixture is stirred at room temperature to replace the ligands and remove excess sodium amide, the QD is precipitated with 20 mL of ethanol and at 6000 rpm for 3 minutes. QDs were collected by performing the process up to centrifugation three times. This precipitate was redistributed in cyclohexane as a dispersion medium to obtain a quantum dot dispersion.

(Experimental Example 22) Synthesis of TOPO-InN Quantum Dots The following describes a method for producing TOPO-InN quantum dots (also referred to as TOPO-InN QD).
It differs from the synthesis method described in Experimental Example 21 only in that 0.5 mL (0.11 mmol) of TOPO was used instead of 0.03 mmol of OLA. Other points were the same as the synthesis method described in Experimental Example 21.

(Experimental Example 23) Synthesis of TOPO / ODT-InN Quantum Dots The following describes a method for producing TOPO / ODT-InN quantum dots (also referred to as TOPO / ODT-InN QD).
It differs from the synthesis method described in Experimental Example 21 only in that 0.5 mL (0.11 mmol) of TOPO and 0.1 mL (0.03 mmol) of ODT were used instead of 0.03 mmol of OLA. Other points were the same as the synthesis method described in Experimental Example 21.

(Experimental Example 24) Synthesis of TOPO / ODT-GaInN Quantum Dots The following describes a method for producing TOPO / ODT-GaInN quantum dots (also referred to as TOPO / ODT-GaInN QD).
Indium iodide (0.025 g, 0.05 mmol), gallium iodide (0.023 g, 0.05 mmol), sodium amide (0.04 g, 1 mmol), TOPO (0.5 mL, 0.11 mmol), ODT (0) .1 mL, 0.03 mmol) and HMDS (0.062 mL, 0.03 mmol in a 10 mL vial in a glove box) were mixed with 1.5 mL of phenyl ether (1.5 mL).
The vial was then heated to 220 ° C. (150 ° C./min), kept at that temperature for 10 minutes and then cooled to room temperature.
The purification step was the same as the synthesis method described in Experimental Example 21 (OLA-InN QD).

(Experimental Example 25) Synthesis of TOPO / ODT-ZnInN Quantum Dots The following describes a method for producing TOPO / ODT-ZnInN quantum dots (also referred to as TOPO / ODT-ZnInN QD).
Indium iodide (0.025 g, 0.05 mmol), zinc iodide (0.016 g, 0.05 mmol), sodium amide (0.04 g, 1 mmol), TOPO (0.5 mL, 0.11 mmol), and ODT ( 0.1 mL, 0.03 mmol) was mixed.
1.5 mL of phenyl ether (1.5 mL) was added to a 10 mL vial in the glove box.
The vial was then heated to 220 ° C. (150 ° C./min), kept at that temperature for 10 minutes and then cooled to room temperature.
The purification step was the same as the synthesis method described in Experimental Example 21 (OLA-InN QD).

<Characteristic evaluation [analysis / measurement]>
X-ray diffraction (XRD) patterns were obtained by using a Bruker D8 DISCOVER equipped with a Cu KαX source (λ = 1.5418 Å).
Samples for XRD analysis were prepared by drop casting the purified QD dispersed in cyclohexane onto a glass substrate.
A transmission electron microscope (TEM) and a high angle annular dark field scanning TEM (STEM-HAADF) image were obtained using a JEOL JEM-ARM200F microscope operating at 200 kV.
TEM samples were prepared by dropping diluted QD onto a carbon coated 200 mesh copper grid.
X-ray photoelectron spectroscopy (XPS) spectra were obtained by using ULVAC-PHI Quantera SXM with a pass energy of 224.0 eV and a step size of 0.1 eV.
All binding energies were calibrated using C 1 (284.6 eV).
UV-vis spectra of quantum dots (QDs) dispersed in cyclohexane were recorded on a quartz cuvette with an optical path length of 1 cm using a JASCO V-770 UV-vis-NIR spectrophotometer.
The PL spectrum of the QD dispersed in cyclohexane was recorded using Otsuka Electronics' MCPD-7000 array spectrometer (λexc = 365 nm).

<Results and discussion>
FIG. 16 (a) is a graph showing the out-of-plane XRD pattern of InN nanoparticles prepared on a microscope slide. The XRD patterns of three types of quantum dots (OLA-InN QD, TOPO-InN QD, and TOPO / ODT-InN QD) are listed side by side.
According to a previous report, a peak corresponding to an indium metal was observed in the XRD pattern of OLA-InN quantum dots [Non-Patent Document 4]. This observation is probably due to the reduction of InN due to the electrons generated during the decomposition of sodium amide.
However, when TOPO was used as the ligand instead of OLA, the XRD peak of the indium metal disappeared. The addition of TOPO improved the ability to disperse sodium amide in organic solvents and tended to accelerate InN particle growth.
It was clarified that the diffraction peak of InN (002) became sharp when TOPO and ODT were co-added. It is considered that this is because the highly polar TOPO molecule surrounding sodium amide prevents the decomposition and generation of electrons.

FIG. 16 (b) is a photograph of a suspension of InN quantum dots (QD). FIG. 16 (b) shows the variances of OLA-InN QD (left), TOPO-InN QD (middle), and TOPO / ODT-InN QD (right) in cyclohexane.
The suspension of TOPO-InN QD did not form aggregates in contrast to OLA-InN QD and showed stable dispersion in organic solvents for over a month.
The suspension of TOPO / ODT-InN QD also showed similar uniform dispersion.
From the above results, it was found that the formation of indium metal was suppressed during the synthesis, and stable dispersion in cyclohexane was achieved by adding TOPO.

FIG. 17A is a TEM image of the OLA-InN QD.
FIG. 17B is a STEM-HAADF image of TOPO-InN QD.
FIG. 17 (c) is a STEM-HAADF image of the TOPO / ODT-InN QD.
The insets of FIGS. 17 (b) and 17 (c) are the size distribution histogram of the QD and the corresponding standard deviations.
FIG. 17D is an enlarged TEM image of quantum dots.
FIG. 17 (e) is an enlarged TEM image of TOPO / ODT-InN QD.

FIG. 17 (a) shows that the indium metal was formed as spherical particles having a size of 20 to 40 nm. This was presumed to be the origin of the XRD peak of the indium metal.
In FIG. 17 (b), TOPO-InN QD is in the form of aggregates containing 2-3 particles, the average diameter of which is 4.3 nm and the standard deviation is about 38%.
The indium metal particles observed in FIG. 17 (a) were not identified in FIG. 17 (b). From this, it was found that the indium metal did not contaminate the quantum dots (QD) by the addition of TOPO.
FIG. 17 (c) shows that the average diameter of the TOPO / ODT-InN QD is 2.9 nm and the standard deviation is about 45%.

In general, thiol-based ligands bind very strongly to metals.
Therefore, the particle size was controlled to be smaller by adding ODT, including dispersion.
The particles appear to be agglomerated, but it is not clear whether they were agglomerated during or during sample preparation for TEM.
This is the first report to simultaneously achieve suppression of decomposition of InN quantum dots into indium metal and control of particle size below the exciton Bohr radius.
Further, FIGS. 17 (d) and 17 (e) show the crystallinity of TOPO-InN and TOPO / ODT-InN QD having a lattice constant of 0.31 nm corresponding to the (100) lattice fringes of InN.

FIG. 18A is a graph in which the N1s spectrum is fitted using the Voigt function after the background is removed.
FIG. 18 (b) is a graph in which the In3d _5/2 spectrum is fitted using a function after removing the background.
In the N 1s photoelectron energy region diagram shown in FIG. 18 (a), the peak was divided into two components.
FIG. 19 is a list showing Peak and FWHM for the N1s spectrum and the In3d _5/2 spectrum.

Based on a previous study (FIG. 19), the peak of 395.9 eV was assigned to the N of the N—In bond and the peak of 397.3 eV was assigned to the N associated with the defect.
The origin of these peaks was identified as defects on the surface of InN nanocrystals and nanoparticles.
On the other hand, in the case of In3d _5/2 shown in FIG. 18B, the peak near 444.0 eV belongs to the In of the In—N bond, and the peak of 445.0 eV belongs to the In of the In—O bond. Attributed to.
It is considered that the In—N bond is derived from the InN crystal and the In—O bond is derived from the OA coordination on the surface.
On the other hand, no peak at 443.5 eV that can be attributed to the In-In bond was observed, suggesting that the indium metal was not formed as a by-product of the quantum dots (QD).
Furthermore, based on the results of XPS wide scan measurements, it was found that the amount of sodium contamination was surprisingly below the detection limit (<0.1%).

FIG. 20 (a) is a graph showing UV-vis spectra of OLA-InN quantum dots, TOPO-InN quantum dots, and TOPO / ODT-InN quantum dots.
FIG. 20B is a graph showing the light absorption spectrum of the quantum dots.
FIG. 20 (a) is the result of ultraviolet-visible spectroscopic measurement.

The OLA-InN QD showed metal absorption over the entire wavelength range. In contrast, TOPO-InN QD and TOPO / ODT-InN QD showed selective absorption below 800 nm.
In particular, it was observed that the absorption start wavelength was blueshifted at about 50 nm by adding ODT.
Peaks near 1200 nm are experimental artifacts caused by strong absorption of cyclohexane.
FIG. 20B shows a light absorption spectrum.
The optical energy gap ( _Eg ) of the direct band-to-band transition and the absorption coefficient (α) are related by the following equation (1) [Non-Patent Documents 4 and 5].

Here, the optical bandgap Eg with respect to the absorption edge is the linear portion in the plot of the vertical axis [(αhν) ² ] with respect to the horizontal axis [Photon Energy (hν)] in the graph of FIG. 20 (b), α = 0. It can be obtained by extrapolating to.
The Eg values of the TOPO-InN QD (referred to as Sample b in FIG. 21) and the TOPO / ODT-InN QD (referred to as Sample c in FIG. 21) were estimated to be approximately 1.66 eV and approximately 1.77 eV, respectively. (Fig. 21). In FIG. 21, the case of metal is referred to as Sample a.
This is because the addition of ODT changes the average diameter of the QD from 4.3 nm to 2.9 nm, resulting in a larger energy gap due to the quantum size effect.
Therefore, quantum dots may be suitable for use as photoelectric conversion materials in red phosphors and solar cells.

FIG. 22A is the PL and absorption spectra of TOPO-InN QD and TOPO / ODT-InN QD.
FIG. 22B is the PL and absorption spectra of TOPO / ODT-GaInN QD and TOPO / ODT-ZnInN QD.
FIG. 23 is a list showing PL peaks and FWHM in GaInN quantum dots (QD) and ZnInN quantum dots.

The TOPO-InN QD and TOPO / ODT-InN QD synthesized without HMDS did not show fluorescence [FIG. 22 (a)].
The reason is that the defects present on the surface of the nanoparticles caused non-radiative recombination of excitons.
It has been reported that by forming a core / shell structure, surface defects can be covered and the possibility of exciton recombination in the core is increased [Non-Patent Document 6].

The newly developed method for synthesizing InN quantum dots is also applied to a mixed crystal of GaInN quantum dots and ZnInN quantum dots, and their PL spectra are shown in FIG. 22 (b).

The PL peak of the GaInN quantum dots (QD) was 576 nm, and the full width at half maximum (FWHM) was 195 nm [FIG. 22 (a), FIG. 23]. Since there is no example of the PL spectrum of GaInN quantum dots (QD), it is difficult to clarify the mechanism of emission, but it was found that the addition of HMDS increases the emission intensity.
In the case of ZnInN quantum dots, the Pl peak was 579 nm and the FWHM was 134 nm [FIG. 22 (b), FIG. 23].

The synthesis and optical properties of Zn ₃ N ₂ quantum dots (QDs) have been previously reported [Non-Patent Document 7].
Although the synthesis method of the present invention is different, the zinc nitride-containing InN as a mixed crystal is considered to be the same as that reported in the previous study.
As described above, it was confirmed that the luminescent nitride quantum dots can be stably produced by using the synthesis method (first invention, second invention) of the present invention.

<Conclusion>
The present inventors have developed a synthetic method capable of preventing decomposition of InN and achieving a short reaction time by co-adding TOPO and ODT ligand to the raw material.
The resulting nanocrystals were identified as InN from the XRD peak and showed stable dispersion in cyclohexane.
Moreover, in contrast to those obtained using previously reported methods, the crystal size was controlled to 2-6 nm with no large impurities.
XPS measurements mainly showed the presence of In-N bonds, no In-In bonds were observed.
In addition, the InN quantum dots absorb a specific wavelength, and the band gap is estimated to be 1.66 eV to 1.77 eV from the light absorption spectrum.
Further, the GaInN quantum dots and ZnInN quantum dots synthesized by the method of the present invention showed PL.
The methods of the present invention (first and second inventions) contribute to the production of new types of quantum dots (QDs) that are more robust and exhibit high performance in a variety of optoelectronic applications.

The present invention contributes to the provision of a method for producing a core-shell type quantum dot dispersion liquid and a method for producing a quantum dot dispersion liquid, which have both stability (robustness) and fluorescence characteristics (luminescence). Therefore, the present invention can be widely applied when mass-producing quantum dots.

QD quantum dots, 1 core, 10 crystal nuclei, 2 shells, 3 dispersants, 4 passivation layers, Ld dispersion medium (solvent).

Claims (21)

A core made of semiconductor fine particles having a predetermined bandgap and a shell made of a semiconductor having a bandgap larger than the core covering the surface of the core are provided.
A core-shell type quantum dot dispersion liquid in which the core is made of metal nitride and the shell is made of ZnS, and core-shell type quantum dots that emit fluorescence by continuous irradiation of excitation light are dispersed in a dispersion medium. It is a manufacturing method of
A first compound containing a metal that is a raw material for a core, a metal amide that functions as a nitrogen source for nitriding the metal contained in the first compound, and a solubilizer that disperses a by-product in a solvent. , The step of mixing with a solvent to prepare a reaction solution, and
The reaction solution is heated to a predetermined first temperature, a core is synthesized by a heating reaction between the first compound and the metal amide, and a by-product produced by the heating reaction is dispersed in the solvent by the solubilizer. And the process of making
The reaction solution after core synthesis contains a second compound containing zinc, which is a raw material for the shell, and a sulfur source for sulfurizing zinc contained in the second compound, and these second compound and a sulfur source. The reaction solution containing the above is heated to a predetermined second temperature, and the core is covered with a shell made of a ZnS film produced by a heating reaction between the second compound and the sulfur supply source to form a core-shell type quantum dot. Process and
A step of extracting core-shell quantum dots from the reaction solution after the heating reaction between the second compound and the sulfur supply source and dispersing them in the dispersion medium.
Including
A core-shell type quantum dodd dispersion liquid characterized by further mixing a crystal growth inhibitor composed of HMDS (1,1,1,3,3,3-hexamethyldisilazane) in the step of preparing the reaction solution. Production method. Prior to the step of preparing the reaction solution, a step of mixing the raw materials of the crystal nuclei and heating the mixed raw materials to a predetermined third temperature to synthesize the crystal nuclei is further included.
The method for producing a core-shell type quantum dot dispersion liquid according to claim 1, wherein the crystal nuclei are further mixed in the step of preparing the reaction solution. The raw material of the passivation layer is added to the reaction solution after the heating reaction between the second compound and the sulfur supply source, and the reaction solution to which the raw material of the passivation layer is added is heated to a predetermined fourth temperature. The method for producing a core-shell type quantum dot dispersion liquid according to claim 1 or 2, further comprising a step of covering the surface of the shell with the passivation layer. As raw materials for the crystal nuclei, ZnO, ZnS, ZnSe, InN, GaInN, GaN, AlN, AlInN, ZnMgO, InP, GaP, AlP, Zn ₃ P ₂ , Cd ₃ P ₂ , ZnPbN ₂ , ZnSnN ₂ , ZnGeN ₂ , The method for producing a core-shell type quantum dot dispersion according to claim 2, wherein at least one selected from ZnSiN ₂ , LiGaO ₂ , LiAlO ₂ , NaGaO ₂ , NaAlO ₂ , CuGaO ₂ , and AgAlO ₂ is used. .. As raw materials for the passion layer, ZnS, ZnSe, ZnO, ZnSO, ZnSSe, ZnSeO, MgO, InN _x O _x , GaN _x O _x , AlN _x O _x , In ₂ O ₃ , Ga ₂ O ₃ , Al ₂ It is characterized by using at least one selected from O ₃ , SiO ₂ , SiNO _x , LiInO ₂ , LiGaO ₂ , LiAlO ₂ , NaGaO ₂ , NaAlO ₂ , CuGaO ₂ , AgAlO ₂ , AgGaO ₂ , and AgInO ₂ . The method for producing a core-shell type quantum dot dispersion liquid according to claim 3. As the solubilizer, trioctylphosphine, trialkylphosphine oxides, trialkylphosphine sulfides, trialkylphosphine serenides, trialkyliminophosphorans, monophosphate esters, diphosphate esters, triphosphate esters, etc. , The method for producing a core-shell type quantum dot dispersion according to claim 1, wherein at least one selected from dimethyl sulfoxide, hexamethylphosphate triamide and N, N'-dimethylpropylene urea is used. The method for producing a core-shell type quantum dot dispersion liquid according to claim 1, wherein an electron acceptor is further mixed in the step of preparing the reaction solution. As the electron acceptor, iodophosphine, halogen, superatomic iodine reagents, iodination agent, N, N'-dicyclohexylcarbodiimide having a redox potential at a position noble than the redox potential of the metal to be nitrided. , N-chlorosuccinimide, N-promosquinimide, N-iodosuccinimide, 2,3-dichloro-5,6-dicyano-p-benzoquinone, nitroxyl radical, sulfur, alkylthiol, alkyl disulfide, alkyl trisulfide, The core-shell type quantum dot dispersion according to claim 7, wherein at least one selected from tetracyanoquinodimethane, 2,3-dichloro-5,6-dicyano-p-benzoquinone and crown ether is used. Manufacturing method. The method for producing a core-shell type quantum dot dispersion liquid according to claim 1, wherein in the step of preparing the reaction solution, a dispersant covering the core-shell type quantum dots is further mixed. As the dispersant, alkylcarboxylic acids, monoalkylamines, dialkylamines, trialkylamines, trialkylphosphins, alkyl esters, alkylthiols, sulfides, glycerin tricaprylate, alkylnitriles and stearate anhydride are used. The method for producing a core-shell type quantum dot dispersion liquid according to claim 9, wherein at least one selected from the substances is used. After synthesizing the core-shell type quantum dots, a step of adding a substance having an acid dissociation constant of more than 4.5 and having hydrogen at the end of the functional group to the reaction solution and removing the metal remaining in the reaction solution is further included. The method for producing a core-shell type quantum dot dispersion liquid according to any one of claims 1 to 10. The method for producing a core-shell type quantum dot dispersion liquid according to claim 11, wherein oleic acid or dodecanethiol is used as the substance. A method for producing a quantum dot dispersion liquid, wherein a core composed of semiconductor fine particles having a predetermined band gap is composed of metal nitride, and quantum dots that emit fluorescence by continuous irradiation of excitation light are dispersed in a dispersion medium. And,
A first compound containing a metal that is a raw material for a core, a metal amide that functions as a nitrogen source for nitriding the metal contained in the first compound, and a solubilizer that disperses a by-product in a solvent. , The step of mixing the solvent to prepare the reaction solution, and
The reaction solution is heated to a predetermined first temperature, a core is synthesized by a heating reaction between the first compound and the metal amide, and a by-product produced by the heating reaction is dispersed in the solvent by the solubilizer. And the process of making
A step of extracting quantum dots from the reaction solution after the heating reaction and dispersing them in the dispersion medium.
Including
A method for producing a quantum dodd dispersion liquid, which comprises further mixing a crystal growth inhibitor composed of HMDS (1,1,1,3,3,3-hexamethyldisilazane) in the step of preparing the reaction solution. .. Prior to the step of preparing the reaction solution, a step of mixing the raw materials of the crystal nuclei and heating the mixed raw materials to a predetermined third temperature to synthesize the crystal nuclei is further included.
The method for producing a quantum dot dispersion liquid according to claim 13, wherein the crystal nuclei are further mixed in the step of preparing the reaction solution. The method for producing a quantum dot dispersion liquid according to claim 14, wherein at least one selected from InN and GaInN is used as the raw material for the crystal nucleus. As the solubilizer, trioctylphosphine, trialkylphosphine oxides, trialkylphosphine sulfides, trialkylphosphine serenides, trialkyliminophosphorans, monophosphate esters, diphosphate esters, triphosphate esters, etc. The method for producing a quantum dot dispersion according to claim 13, wherein at least one selected from dimethyl sulfoxide, hexamethylphosphate triamide and N, N'-dimethylpropylene urea is used. The method for producing a quantum dot dispersion liquid according to claim 13, wherein in the step of preparing the reaction solution, a dispersant covering the core-shell type quantum dots is further mixed. As the dispersant, alkylcarboxylic acids, monoalkylamines, dialkylamines, trialkylamines, trialkylphosphins, alkyl esters, alkylthiols, sulfides, glycerin tricaprylate, alkylnitriles and anhydrous stearate are used. The method for producing a quantum dot dispersion liquid according to claim 17, wherein at least one selected from the substances is used. The method for producing a quantum dot dispersion liquid according to claim 17, wherein octadecanethiol is used as the dispersant. After synthesizing the core-shell type quantum dots, a step of adding a substance having an acid dissociation constant of more than 4.5 and having hydrogen at the end of the functional group to the reaction solution and removing the metal remaining in the reaction solution is further included. The method for producing a quantum dot dispersion liquid according to any one of claims 13 to 19. The method for producing a quantum dot dispersion liquid according to claim 20, wherein oleic acid or dodecanethiol is used as the substance.

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