JP2018154666A - Core-shell quantum dot and method for producing core-shell quantum dot dispersion liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a core-shell quantum dot which can be produced without using a relatively expensive phosphorus-containing compound and is capable of emitting light at an emission wavelength equivalent to that of a core-shell quantum dot composed of InP/ZnS, and to provide a method for producing a core-shell quantum dot dispersion liquid.SOLUTION: A core-shell quantum dot QD of the present invention includes: a core 1 which is composed of semiconductor fine particles having a predetermined band gap; and a shell 2 which is composed of a semiconductor having a larger band gap than the core and covers the surface of the core. The core is composed of at least one metal nitride selected from InN, GaN, AlN, ZnInN, ZnPbN, ZnSnN, ZnGeN, ZnSiNand ZnN, and the shell is composed of ZnS.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a core-shell type quantum dot comprising a core composed of semiconductor fine particles having a predetermined band gap, and a shell composed of a semiconductor having a larger band gap than the core and covering the surface of the core. The present invention relates to a method for producing a core-shell type quantum dot dispersion in which type quantum dots are dispersed in a dispersion medium.

  This type of quantum dot is known from Non-Patent Document 1, for example. In this structure, the core is made of InP, and the shell is made of ZnS having a larger band gap than InP, so that the quantum dots have excellent emission characteristics compared to the case where the quantum dots are made only of InP. Yes.

  However, since it is necessary to use a relatively expensive phosphorus-containing compound as a raw material for InP, the cost of the core-shell type quantum dot is increased. Therefore, development of a core-shell type quantum dot that can be produced without using a relatively expensive phosphorus-containing compound and can emit light at an emission wavelength equivalent to that of a core-shell type quantum dot composed of InP / ZnS is desired. It was.

Clare E. Rowland, 5 others, “Thermal Stability of Colloidal InP Nanocrystals: Small Inorganic Ligands Boost High-Temperature Photoluminescence”, American Chemical Society, Vol. 8, No. 1, pp. 977-985, 2014

  In view of the above, the present invention can be manufactured 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. It is an object of the present invention to provide a method for producing dots and core-shell type quantum dot dispersions.

In order to solve the above problems, the core-shell quantum dot of the present invention is composed of a core composed of semiconductor fine particles having a predetermined band gap and a semiconductor having a larger band gap than the core covering the surface of the core. The core is made of at least one metal nitride selected from InN, GaN, AlN, ZnInN, ZnPbN ₂ , ZnSnN ₂ , ZnGeN ₂ , ZnSiN ₂ and Zn ₃ N ₂ , The shell is composed of at least one selected from ZnO, ZnS, and ZnSe.

  According to the present invention, it is possible to obtain a core-shell type quantum dot that can emit light at an emission wavelength equivalent to that of a core-shell type quantum dot composed of InP / ZnS by configuring the core with metal nitride and the shell with ZnS. it can. Moreover, the core-shell type quantum dot of the present invention does not need to use a relatively expensive phosphorus-containing compound as a raw material.

In the present invention, the core is composed of ZnO, ZnS, ZnSe, InN, InGaN, GaN, AlN, AlInN, ZnMgO, InP, GaP, AlP, Zn ₃ N ₂ , Zn ₃ P ₂ , Cd ₃ P ₂ , ZnPbN ₂ , _{ZnSnN 2, ZnGeN 2, ZnSiN 2} , LiGaO 2, LiAlO 2, NaGaO 2, NaAlO 2, it is preferable to have about a constituted crystal nuclei at least one selected from CuGaO ₂ and AgAlO _2. The crystallinity of the core can be increased by growing the core from the crystal nucleus.

In the present invention, the surface of the shell is covered with a passivation layer, and the passivation layer includes ZnS, ZnSe, ZnO, ZnSO, ZnSSe, ZnSeO, MgO, InNxOx, GaNxOx, AlNxOx, In ₂ O ₃ , Ga ₂ O ₃ , _{al 2 O 3, SiO 2,} SiNOx, LiInO 2, LiGaO 2, LiAlO 2, NaGaO 2, NaAlO 2, is preferably constituted by CuGaO _2, AgAlO _2, AgGaO ₂ and at least one selected from AgInO ₂ . According to this, the stability of the core-shell type quantum dot can be improved.

  The method for producing a core-shell type quantum dot dispersion liquid of the present invention for producing a core-shell type quantum dot dispersion liquid in which the core-shell type quantum dots are dispersed in a dispersion medium includes: a first compound containing a metal that is a raw material of the core; A step of preparing a reaction solution by mixing a metal amide that functions as a nitrogen supply source for nitriding the metal contained in the first compound, a solubilizing agent that disperses the by-product in the solvent, and the solvent; The reaction solution is heated to a predetermined first temperature, a core is synthesized by a heating reaction of the first compound and the metal amide, and a by-product generated by the heating reaction is converted into the solvent by the solubilizer. A step of dispersing, a second compound containing zinc as a raw material of the shell, and a sulfur source for sulfiding zinc contained in the second compound in the reaction solution after the core synthesis. A reaction solution containing a compound and a sulfur supply source is heated to a predetermined second temperature, and the core is covered with a shell made of ZnS generated by a heating reaction between the second compound and the sulfur supply source. A step of forming dots, and a step of extracting the core-shell quantum dots from the reaction solution after the heating reaction between the second compound and the sulfur supply source and dispersing the core-shell quantum dots in the dispersion medium. In the present invention, when a sulfur source having a decomposition temperature higher than the first temperature is used, the step of adjusting the reaction solution is to include this sulfur source in the reaction solution after the core synthesis. And pre-mixing the sulfur source.

  In the present invention, prior to the step of preparing the reaction solution, the method further includes the step of mixing the raw material of the crystal nucleus and synthesizing the crystal nucleus by heating the mixed raw material to a predetermined third temperature. It is preferable to further mix the crystal nuclei in the step of preparing the solution.

  In the present invention, the material for 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 material for the passivation layer is added is heated to a predetermined fourth temperature. Preferably, the method further includes a step of covering the surface of the shell with the passivation layer.

  In the present invention, as the solubilizer, trialkylphosphine oxides, trialkylphosphine sulfides, trialkylphosphine selenides, trialkyliminophosphoranic acid, monophosphate esters, diphosphate esters, triphosphate esters It is preferable to use at least one selected from dimethyl sulfoxide, hexamethylphosphoric triamide, and N, N′-dimethylpropyleneurea.

  In the present invention, it is preferable to further mix an electron acceptor in the step of preparing the reaction solution. In this case, as an electron acceptor, iodophosphine, halogen, hypervalent iodine reagent, iodinating agent, N, N′dicyclohexyl having a redox potential at a position in a noble direction relative to the redox potential of the metal to be nitrided Carbodiimide, N-chlorosuccinimide, N-promosuccinimide, N-iodosuccinimide, 2,3-dichloro-5,6-dicyano-p-benzoquinone, nitroxyl radical, sulfur, alkylthiol, alkyl disulfide, alkyl trisulfide , Tetracyanoquinodimethane, 2,3-dichloro-5,6-dicyano-p-benzoquinone and crown ether can be preferably used.

  In this invention, it is preferable to further mix the dispersing agent which covers the said core-shell type quantum dot in the process of adjusting the said reaction solution. In this case, as the dispersant, alkyl carboxylic acids, monoalkyl amines, dialkyl amines, trialkyl amines, trialkyl phosphines, alkyl esters, alkyl thiols, sulfides, glycerin tricaprylate, alkyl nitriles and At least one selected from stearic anhydride can be suitably used.

  In the present invention, after synthesizing the core-shell type quantum dots, a step of adding a substance having an acid dissociation constant larger than 4.5 and having hydrogen at the terminal of the functional group to the reaction solution to remove the metal remaining in the reaction solution It is preferable that it is further included. In this case, oleic acid or dodecanethiol can be suitably used as the substance.

The schematic diagram which shows the structure of the core-shell type quantum dot of embodiment of this invention. The schematic diagram which shows the structure of the core-shell type quantum dot which concerns on the modification of this invention. The schematic diagram which shows the structure of the core-shell type quantum dot which concerns on the modification of this invention. 6 is a graph showing XRD measurement results of core-shell quantum dots according to Example 1. The graph which shows the emission spectrum of each core-shell type quantum dot which concerns on Example 1, 3, and 4. FIG.

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

  Referring to FIG. 1, 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 band gap, and a shell 2 made of a semiconductor having a band gap larger than the core 1 and covering the surface of the core 1.

Core _{1, InN, GaN, AlN, ZnInN} , composed of nanoparticles of _{ZnPbN 2, ZnSnN 2, ZnGeN 2} , at least one metal nitride selected from ZnSiN ₂ and _Zn 3 _{N 2.} Note that typical nanoparticles used for the purpose of light emission are those having an average particle diameter (in this application, indicating an interface between the core 1 and the shell 2) in the range of 0.1 nm to 20 nm. By controlling to such an average particle size, the semiconductor band gap is increased by the quantum size effect, and the emission energy when electrons recombine with holes can be increased.

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

  The surface of the shell 2 is covered with the dispersant 3, whereby the quantum dots QD can be dispersed in the dispersion medium L with good dispersibility. The dispersant 3 includes alkyl carboxylic acids having an alkyl chain of 6 or more carbon atoms, trialkylamines, trialkylphosphines, trialkylphosphine sulfides, trialkylphosphine selenides, trialkylphosphine oxides, trialkyl. At least one selected from anionic surfactants such as iminophosphoranic acid, alkyl esters, alkylthiols, sulfides, glyceryl tricaprylate, sodium alkylate, sodium alkylsulfate, sodium alkylthiolate and sodium alkylsulfonate And trialkylphosphine oxides can be preferably used.

  As the dispersion medium Ld, an organic solvent having 6 to 18 carbon atoms is preferably used. For example, hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, Long-chain alkanes having 6 to 18 carbon atoms in the main chain such as octadecane; cyclic alkanes such as cyclohexane, cycloheptane, cyclooctane, and cyclododecene; aromatics such as benzene, toluene, xylene, trimethylbenzene, and dodecylbenzene Hydrocarbons; alcohols such as hexanol, heptanol, octanol, decanol, cyclohexanol, terpineol; diethyl ether, dibutyl ether, dihexyl ether, tetrahydrofuran, cyclopentyl methyl ether , Ethers such as phenyl ether; dimethylformamide, N-N'-dimethyl propylene urea, tris (N, N- dimethylamino) phosphine oxide, diazabicycloundecene can be used singly or as a mixture.

  Next, the manufacturing method of the quantum dots QD will be described by taking as an example the case of manufacturing a quantum dot dispersion liquid in which the quantum dots QD are dispersed in a dispersion medium.

  First, 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 solubilizer that disperses the by-product in a solvent And a 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 the synthesis described later. For example, a metal complex containing the metal halide or the metal and the dispersant is used. Can do. As the metal, for example, one metal selected from Al, Ga, In, Fe, Cu, Mn, W, Ta, and Zr or an alloy of these metals can be used. In addition, the metal includes B and Si. The molar ratio between the first compound and the metal amide can be set within a range of 1: 1 to 1: 1000. Metal amides include metal amides containing 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 metal alkylsilylamides containing the metal, metal alkylamides containing the metal, and metal dicinaamides containing the metal. A metal trialkylsilylamide can be used as the metal alkylsilylamide. In this case, the above metal can be used as the metal contained in the metal trialkylsilylamide, and the alkyl group preferably has 18 or less carbon atoms. Further, the metal trialkylsilylamide may be produced by mixing a strong base such as butyl lithium and bis (trimethylsilyl) amine. In addition to the metal amide, a metal nitride such as lithium nitride or magnesium nitride may be further mixed as a nitrogen supply source.

  Examples of solubilizers include trialkylphosphine oxides, trialkylphosphine sulfides, trialkylphosphine selenides, trialkyliminophosphoranic acid, monophosphate esters, diphosphate esters, triphosphate esters, dimethyl sulfoxide, It is preferable to use at least one selected from hexamethylphosphoric triamide and N, N′-dimethylpropyleneurea, and it is most preferable to use trialkylphosphine oxides. The molar ratio of solubilizer and metal amide can be set within the range of 1: 1 to 1: 100.

  As the solvent, an organic solvent having 8 to 35 carbon atoms is preferably used. For example, main solvents such as octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane, and liquid paraffin are used. Long-chain saturated alkanes having a chain carbon number of 8 to 35 and mixtures thereof; alkenes having an unsaturated bond such as octene, nonene, decene, undecene, dodecene, tridecene, tetradecene, pentadecene, hexadecene, heptadecene, octadecene; Cyclic alkanes such as cyclohexane, cycloheptane, cyclooctane, cyclododecene; aromatic hydrocarbons such as benzene, toluene, xylene, trimethylbenzene, dodecylbenzene, biphenyl; diethyl ether, dibutyl ether Melting point of ether, dihexyl ether, tetrahydrofuran, cyclopentyl methyl ether, phenyl ether; mixed solvent such as DOWTHERM® A; sulfides such as phenyl sulfide and didodecyl sulfide; It can be used as a solvent having a boiling point of 24 ° C. or lower and a boiling point of 100 ° C. or higher. Furthermore, it is preferable to add aromatic hydrocarbons by mixing different aromatic hydrocarbons or by dissolving aromatic hydrocarbons in a long-chain saturated alkane. According to this, the suppression effect of the impurity mixing into the quantum dot can be enhanced.

In the step of preparing the reaction solution, a dispersant may be further mixed. As the dispersant, at least one selected from alkyl carboxylic acids, monoalkyl amines, dialkyl amines, trialkyl amines, alkyl esters, alkyl thiols, sulfides, glycerin tricaprylate and alkyl nitriles is used. Among these, it is more preferable to use one having a functional group containing no hydrogen atom at the terminal. Since a hydrogen atom reacts with sodium amide to cause a decrease in nitrogen raw material, it is most preferable to react with sodium amide using an alkylthiol (metal complex) represented by the following formula (2) 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, the addition amount of the electron acceptor and the addition amount of the solubilizer can be reduced, which is advantageous. The molar ratio between the metal-containing compound and the dispersant can be set within a 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. In addition, when octadecanethiol is used as a sulfur supply source, it can be used as a dispersant, but other dispersants may be further mixed.
R-SH + NaNH ₂ → R-SNa + NH ₃ (2)

  In the step of preparing the reaction solution, an electron acceptor may be further mixed. As the electron acceptor, one having a redox potential located in a noble direction relative to the redox potential of the metal to be nitrided can be used. For example, when the metal to be nitrided is indium, iodophosphine, halogen, hypervalent iodine reagents, iodinating agent, as an electron acceptor whose oxidation-reduction potential is located in a more noble direction than −0.34 V vs SHE, Oxidizing agents such as N, N′dicyclohexylcarbodiimide, N-chlorosuccinimide, N-promosuccinimide, N-iodosuccinimide, 2,3-dichloro-5,6-dicyano-p-benzoquinone, nitroxyl radical, sulfur, At least one selected from alkyl thiol, alkyl disulfide, alkyl trisulfide, tetracyanoquinodimethane, crown ether, manganese and chromium can be used, and iodinated disulfide and crown ether can be more preferably used. . As the iodinating agent, for example, 1,3-diiodo-5,5-dimethylhydantoin can be used. The molar ratio between the electron acceptor and the metal amide can be set within a 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 core-shell type quantum dot dispersion liquid contains metal. Can be suppressed as much as possible. Moreover, an increase in the number of manufacturing steps can be prevented, and a core-shell type quantum dot having long-term stable dispersibility can be obtained, which is advantageous.

  The electron acceptor does not function below the decomposition temperature of the metal amide, and is effective when the reaction temperature is 280 ° C. or higher when the reaction of the above formula (2) proceeds at a temperature of 280 ° C., for example. This means that by increasing the reaction temperature, the core synthesis rate can be improved, and the effect that the average particle size of the core immediately after synthesis increases can be utilized. That is, an electron acceptor can be used for the purpose of controlling the average particle size of the manufactured quantum dot dispersion. Naturally, the lower limit temperature at which the effect of the electron acceptor is exhibited varies 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 accommodated 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, within a range of 100 ° C to 600 ° C. By this heating, the first compound and the metal amide are reacted by heating to synthesize the metal nitride nanoparticles serving as the core 1.

  As the reaction vessel and the heating means, those having a known structure can be used, and detailed description thereof is omitted here. In addition, by introducing ammonia gas or nitrogen gas, which is a nitrogen-containing gas, into the reaction vessel, a heating reaction can be performed, so that the supply amount of nitrogen can be increased and the decomposition reaction of the metal amide can be suppressed. It can be synthesized and is advantageous.

  Alternatively, 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. Before the first compound, the dispersant, the solubilizer, and the electron acceptor are mixed, the reaction between the proton and the metal amide is suppressed, and 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 within a range of 1 minute to 240 minutes, for example. 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 as a raw material for the shell 2 and a sulfur supply source for sulfiding zinc contained in the second compound. Then, the reaction solution to which the second compound and the sulfur supply source are added is heated to a predetermined second temperature. The second temperature can be set, for example, within a range of 100 ° C to 600 ° C. By this heating, the surface of the core 1 is covered with the shell 2 made of a ZnS film synthesized by a heating reaction between the second compound and the sulfur supply source, thereby forming a core-shell type quantum dot.

  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 suitably used. As the sulfur source, at least one selected from thiols such as butanethiol, dodecanethiol, hexadecanethiol and octadecanethiol, and sulfides such as phenyl sulfide and didodecyl sulfide can be used. Since octadecanethiol can be used also as a dispersant, it is preferable to use octadecanethiol. The molar ratio of the sulfur source to the metal amide can be set within the range of 1: 1 to 1: 100.

  In addition, when using what has a decomposition temperature higher than 1st temperature as a sulfur supply source, for example, when 1st temperature is set to 230 degreeC, decomposition temperature higher than this 1st temperature (240 degreeC) In the case of using dodecanethiol having the above, in order to include such a sulfur source in the reaction solution after the synthesis of the core 1, sulfur is supplied in the step of adjusting the reaction solution before heating to the first temperature. This includes pre-mixing the sources.

  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 within a range of 1 minute to 240 minutes, for example. The cooling method may be natural cooling or forced cooling in which a refrigerant (for example, cooling water) is circulated in the reaction vessel. A quantum dot covered with a dispersing agent is extracted by adding a substance having an acid dissociation constant pKa larger than 4.5 to the reaction solution after cooling and having hydrogen at the terminal of the functional group together with ethanol. As the substance, oleic acid or dodecanethiol can be used. In this way, a weak acid is used rather than acetic acid, and it reacts with the metal present in the reaction solution after cooling to form an ionized metal salt solution. It becomes a capping agent that prevents it. In other words, when centrifugal separation and decantation are performed to separate the sediment that is the target intermediate product, XPS / EDX does not detect metals other than quantum dots in the sediment, and the following final When a quantum dot dispersion liquid is used in the process, it has an effect of suppressing aggregation and can suppress deterioration of the measured average particle diameter in the liquid. Thus, the process of removing metals other than quantum dots can be repeated as necessary.

  Finally, the quantum dots covered with the extracted dispersant are dispersed in a dispersion medium. Thereby, the quantum dot dispersion liquid which can be stably dispersed for one week or more is obtained. As the dispersion medium, an organic solvent having 6 to 18 carbon atoms is preferably used. For example, hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane, and octadecane are used. Long-chain alkanes having 6 to 18 carbon atoms in the main chain; cyclic alkanes such as cyclohexane, cycloheptane, cyclooctane, and cyclododecene; aromatic hydrocarbons such as benzene, toluene, xylene, trimethylbenzene, and dodecylbenzene Alcohols such as hexanol, heptanol, octanol, decanol, cyclohexanol, terpineol; diethyl ether, dibutyl ether, dihexyl ether, tetrahydrofuran, cyclopentyl methyl ether Such ether; dimethylformamide, N-N'-dimethyl propylene urea, tris (N, N- dimethylamino) phosphine oxide, diazabicycloundecene can be used singly or as a mixture.

By the way, the case where sodium amide is used as the metal amide will be described as an example. When the core 1 composed of metal nitride is synthesized by heating reaction of the first compound and sodium amide, the sodium amide is represented by the following formula (1). Electrons are generated by decomposition.
2NaNH ₂ → 2Na ⁺ + N ₂ + 2H ₂ + 2e ⁻ (1)

  Since these electrons are used for 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 suppress as much as possible that metal remains in the core-shell type quantum dot dispersion liquid and is mixed therein.

  According to the embodiment described above, the core-shell type that can emit light at the same emission wavelength as the core-shell type quantum dot composed of InP / ZnS by configuring the core 1 with metal nitride and the shell 2 with ZnS. A quantum dot QD is obtained. Moreover, the core-shell type quantum dots QD can be manufactured without using a relatively expensive phosphorus-containing compound.

As mentioned above, although embodiment of this invention was described, this invention is not limited above. For example, as shown in FIG. 2, the core 1 having high crystallinity can be obtained by forming the core 1 around the crystal nucleus 10. In this case, a semiconductor having a band gap larger than that of the core 1 can be used as the crystal nucleus 10, for example, ZnO, ZnS, ZnSe, InN, InGaN, GaN, AlN, AlInN, ZnMgO, Zn ₃ N ₂ , ZnPbN. _{2, ZnSnN 2, ZnGeN 2,} ZnSiN 2, LiGaO 2, LiAlO 2, NaGaO 2, NaAlO 2, it is possible to use at least one selected from CuGaO ₂ and AgAlO _2. The crystal nucleus 10 can be synthesized by mixing crystal nucleus raw materials and heating the mixed raw materials to a predetermined third temperature. The third temperature can be set within a range of 100 ° C. to 600 ° C., for example. The core 1 can be formed around the crystal nucleus 10 by mixing the synthesized crystal nucleus 10 in the reaction solution before heating to the first temperature. For example, when synthesizing the crystal nucleus 10 made of ZnS, zinc oleate and dodecanethiol can be used as raw materials for the crystal nucleus 10.

Moreover, 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, since the dangling bonds (unbonded hands) existing on the surface of the shell 2 are terminated, the quantum dots can be kept stable for a long period of time. As the passivation layer 4, ZnS, ZnSe, ZnO, ZnSO, ZnSSe, ZnSeO, ZnMgO, Zn ₂ LiGaO ₄ , NaGaO ₂ , MgO, InNxOx, GaNxOx, AlNxOx, In ₂ O ₃ , Ga ₂ O ₃ , Al ₂ O ₃ it can be used _{SiO 2, SiNOx, LiInO 2,} LiGaO 2, LiAlO 2, NaGaO 2, NaAlO 2, CuGaO 2, AgAlO 2, at least one selected from AgGaO ₂ and AgInO _2. 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 parameter a _{0 of} the metal nitride constituting the core 1 and the shell 2 constituting the core 2 are close to each other. It can be used more preferably, and this is advantageous because it is difficult for oxygen and water vapor to pass therethrough. The thickness of the passivation layer 4 is preferably in the range of 0.1 to 10 nm, for example. Such a passivation layer 4 can be formed by adding the raw material of the passivation layer 4 to the reaction solution after the shell 2 is formed and heating it to a predetermined fourth temperature. The fourth temperature can be set, for example, within a range of 100 ° C to 600 ° C. For example, when synthesizing the passivation layer 4 made of ZnMgO, zinc acetate, magnesium acetate, dodecanol, and oleic acid can be used as 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.

  In addition to ZnS, ZnO or ZnSe can be used as the shell 2.

  Next, examples that further embody the embodiment of the present invention will be described.

Example 1
The present Example 1 demonstrates the manufacturing method of the dispersion liquid of the core-shell type quantum dot which comprised the core 1 with ZnInN and the shell 2 with ZnS, respectively. 0.046 g (1 mmol) of indium iodide and 0.032 g (0.1 mmol) of zinc iodide as a first compound, 0.04 g (5 mmol) of sodium amide as a metal amide, and trioctyl as a solubilizer A reaction solution was prepared by mixing 0.44 g (1.14 mmol) of phosphine oxide, 0.02 g (0.3 mmol) of dodecanethiol as a sulfur source, and 2 ml of DOWTHERM A as a solvent in a reaction vessel. This reaction solution was rapidly heated to 230 ° C. (first temperature) (150 ° C./min) and held for 20 minutes, and then cooled to room temperature. After adding 0.063 g (0.1 mmol) of zinc stearate as the second compound to the cooled reaction solution, it was heated to 250 ° C. (second temperature) and held for 10 minutes. Thereafter, the reaction solution was cooled to room temperature. Add 0.5 ml of oleic acid and 20 ml of ethanol to the cooled reaction solution, and disperse sodium iodide, sodium thiolate and sodium oleate, which are by-products remaining in the reaction solution, in ethanol, and consist of ZnInN / ZnS. The core-shell quantum dots were sedimented by centrifugation, and this process was repeated three times. This sediment was redispersed in cyclohexane as a dispersion medium to obtain a core-shell type quantum dot dispersion. The XRD measurement result of the core-shell type quantum dot dispersion liquid thus obtained is shown in FIG. In FIG. 4, the XRD measurement result of only the core comprised of ZnInN is also shown as Comparative Example 1. According to this, diffraction peaks of ZnInN and ZnS were confirmed. Further, since the X-ray reflection intensity corresponding to ZnS is small, it is assumed that the shell 2 is formed relatively thin. As a result of measuring the emission spectrum of the core-shell type quantum dot dispersion obtained in Example 1, the peak wavelength of the fluorescence spectrum shown in FIG. 5 is 558.1 nm, the half-value width is 156.1 nm, and InP / ZnS It was confirmed that light can be emitted at the same emission wavelength as that of the core-shell type quantum dots.

(Example 2)
In Example 2, 0.063 g (0.1 mmol) of zinc oleate which is a raw material of the crystal nucleus 10 and 0.02 g (0.1 mmol) of dodecanethiol are mixed and heated to 280 ° C. (third temperature). Then, the crystal nucleus 10 composed of ZnS is synthesized by holding for 30 minutes, and the synthesized crystal nucleus 10 is mixed with the reaction solution to form the core 1 around the crystal nucleus 10. A core-shell quantum dot dispersion was obtained in the same manner as in Example 1. Although the illustration of the emission spectrum of the core-shell type quantum dot dispersion thus obtained is omitted, the core-shell type quantum dot having a peak wavelength of 634.33 nm and a half-value width of 138.15 nm and composed of InP / ZnS It was confirmed that light can be emitted at an equivalent emission wavelength. And it turned out that it can be used as a yellow fluorescent substance or a photoelectric conversion material. In addition, it was suggested that the half width was narrower than that in Example 1 and the crystallinity of the core was improved.

(Example 3)
In Example 3, a core-shell type quantum dot dispersion was obtained in the same manner as in Example 2 except that the surface of the shell 2 was covered with a ZnMgO film as the passivation layer 4. This passivation layer 4 has 0.018 g (0.1 mmol) of zinc acetate, 0.021 g (0.1 mmol) of magnesium acetate, and 0.019 g (0.1 mmol) of dodecanol, which are the raw materials of the passivation layer 4 after shell formation. And 0.14 g (0.4 mmol) of oleic acid were mixed, heated to 250 ° C. (fourth temperature) and held for 30 minutes. The emission spectrum of the core-shell type quantum dot dispersion liquid thus obtained is also shown in FIG. According to this, it was confirmed that the peak wavelength was 650.5 nm, the half-value width was 137.9 nm, and it was possible to emit light at the same emission wavelength as the core-shell type quantum dot composed of InP / ZnS. And it turned out that it can be used as a red fluorescent substance or a photoelectric conversion material. In addition, it was confirmed that the decay rate of light emission was slow compared to Example 2.

Example 4
In Example 4, a core-shell type quantum dot dispersion was obtained in the same manner as in Example 3 except that the formation temperature (second temperature) of the shell 2 was changed to 260 ° C. The emission spectrum of the core-shell type quantum dot dispersion liquid thus obtained is also shown in FIG. According to this, it was confirmed that the peak wavelength was 670.8 nm, the half-value width was 138.7 nm, and it was possible to emit light at the same emission wavelength as that of the core-shell type quantum dot composed of InP / ZnS. It was also confirmed that by controlling the shell formation temperature, the particle size was changed, and as a result, the emission wavelength could be changed.

  QD: Core-shell type quantum dot, 1 ... Core, 10 ... Crystal nucleus, 2 ... Shell, 3 ... Dispersant, 4 ... Passivation layer, Ld ... Dispersion medium (solvent).

Claims (13)

In a core-shell type quantum dot comprising a core composed of semiconductor fine particles having a predetermined band gap, and a shell composed of a semiconductor having a larger band gap than the core, covering the surface of the core.
The core is composed of at least one metal nitride selected from InN, GaN, AlN, ZnInN, ZnPbN ₂ , ZnSnN ₂ , ZnGeN ₂ , ZnSiN ₂ and Zn ₃ N ₂ ;
The core-shell type quantum dot, wherein the shell is made of ZnS. A crystal nucleus is further provided at the center of the core, and the crystal nucleus is ZnO, ZnS, ZnSe, InN, InGaN, GaN, AlN, AlInN, ZnMgO, Zn ₃ N ₂ , ZnPbN ₂ , ZnSnN ₂ , ZnGeN ₂ , ZnSiN _{2 , LiGaO 2, LiAlO 2, NaGaO} 2, NaAlO 2, CuGaO 2 and core-shell quantum dot according to claim 1, characterized in that it is composed of at least one selected from the AgAlO _2. A passivation layer covering the surface of the shell is further provided, and the passivation layer is ZnS, ZnSe, ZnO, ZnSO, ZnSSe, ZnSeO, ZnMgO, Zn ₂ LiGaO ₄ , NaGaO ₂ , MgO, InNxOx, GaNxOx, AlNxOx, In _{2. O 3, Ga 2 O 3,} Al 2 O 3, SiO 2, SiNOx, LiInO 2, LiGaO 2, LiAlO 2, NaGaO 2, NaAlO 2, CuGaO 2, AgAlO 2, at least one selected from AgGaO ₂ and AgInO ₂ The core-shell type quantum dot according to claim 1 or 2, comprising a seed. A core-shell type quantum dot dispersion manufacturing method for manufacturing a core-shell type quantum dot dispersion in which the core-shell type quantum dots according to claim 1 are dispersed in a dispersion medium,
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 solubilizer that disperses the by-product in a solvent; A step of mixing a solvent to prepare a reaction solution;
The reaction solution is heated to a predetermined first temperature, a core is synthesized by a heating reaction of the first compound and the metal amide, and a by-product generated by the heating reaction is dispersed in the solvent by the solubilizer. A process of
The reaction solution after the core synthesis includes a second compound containing zinc as a raw material of the shell and a sulfur source for sulfiding zinc contained in the second compound, and these second compound and sulfur source And heating the reaction solution including the core to a predetermined second temperature, and covering the core with a shell made of a ZnS film formed by a heating reaction between the second compound and the sulfur supply source to form a core-shell type quantum dot. Process,
A step of extracting a core-shell type quantum dot from a reaction solution after the heating reaction between the second compound and the sulfur supply source and dispersing the same in the dispersion medium. Method. Prior to the step of preparing the reaction solution, the method further comprises the step of mixing the crystal nucleus raw material according to claim 2 and synthesizing the crystal nucleus by heating the mixed raw material to a predetermined third temperature,
The method for producing a core-shell type quantum dot dispersion according to claim 4, wherein the crystal nuclei are further mixed in the step of preparing the reaction solution.   4. The raw material for the passivation layer according to claim 3 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 for the passivation layer is added is heated to a predetermined fourth temperature. The method for producing a core-shell type quantum dot dispersion according to claim 4, further comprising a step of covering the surface of the shell with the passivation layer.   The solubilizer includes trialkylphosphine oxides, trialkylphosphine sulfides, trialkylphosphine selenides, trialkyliminophosphoranic acid, monophosphate esters, diphosphate esters, triphosphate esters, dimethyl sulfoxide, The method for producing a core-shell type quantum dot dispersion according to any one of claims 4 to 6, wherein the method is at least one selected from hexamethylphosphoric triamide and N, N'-dimethylpropyleneurea.   The method for producing a core-shell type quantum dot dispersion according to any one of claims 4 to 7, wherein an electron acceptor is further mixed in the step of adjusting the reaction solution.   The electron acceptor is an iodophosphine, a halogen, a hypervalent iodine reagent, an iodinating agent, N, N′dicyclohexylcarbodiimide having a redox potential at a position that is noble than the redox potential of the metal to be nitrided, N-chlorosuccinimide, N-promosuccinimide, N-iodosuccinimide, 2,3-dichloro-5,6-dicyano-p-benzoquinone, nitroxyl radical, sulfur, alkylthiol, alkyldisulfide, alkyltrisulfide, tetra The core-shell type quantum dot dispersion liquid according to claim 8, wherein the dispersion liquid is at least one selected from cyanoquinodimethane, 2,3-dichloro-5,6-dicyano-p-benzoquinone and crown ether. Method.   The method for producing a core-shell type quantum dot dispersion liquid according to any one of claims 4 to 9, wherein a dispersing agent that covers the core-shell type quantum dots is further mixed in the step of adjusting the reaction solution.   The dispersants include alkyl carboxylic acids, monoalkyl amines, dialkyl amines, trialkyl amines, trialkyl phosphines, alkyl esters, alkyl thiols, sulfides, glycerin tricaprylate, alkyl nitriles and stearic anhydride. The method for producing a core-shell type quantum dot dispersion liquid according to claim 10, wherein the method is at least one selected from a product.   After synthesizing the core-shell type quantum dots, the method further includes a step of adding a substance having an acid dissociation constant greater than 4.5 and having hydrogen at the end of the functional group to the reaction solution to remove the metal remaining in the reaction solution. The manufacturing method of the core-shell type quantum dot dispersion liquid according to any one of claims 4 to 11. The method for producing a core-shell type quantum dot dispersion according to claim 12, wherein the substance is oleic acid or dodecanethiol.

Images