Quantum dot producing additive, shell formation mixed solution, core-shell type quantum dot production method and dialkyl amine-halogen halide

Abstract

To provide an additive for the production of quantum dots that can repair defects on a surface of quantum dots without volatilizing in a flow method, has excellent reactivity allowing for reduced reaction time, and can obtain a reaction liquid that can be pumped without containing solids near room temperature, as well as a mixing solution for shells formation containing the additive and a method for producing core-shell type quantum dots by the flow method.SOLUTION: A method for producing an additive for quantum dots composed of dialkylamine-halogenated acid salts, and a mixed solution for shell formation containing the additive, as well as a production method for core-shell type quantum dots using a flow method.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an additive for producing quantum dots, which contains a dialkylamine hydrohalide salt as an active ingredient, a mixed solution for forming a shell containing the additive, and a method for producing core-shell quantum dots by a flow method using the same. [Background technology]

[0002] In recent years, the development of quantum dots as luminescent materials has progressed. Cadmium-based quantum dots such as CdSe, CdTe, and CdS are being developed as representative quantum dots due to their excellent luminescence properties. In addition, due to the toxicity and high environmental impact of cadmium, cadmium-free quantum dots such as InP, CuInS2, AgInS2, PbS, and InAs are also being actively developed.

[0003] In order to improve the performance of quantum dots, it is necessary to control the individual variations in particle size and surface state of the reaction product and to impart more uniform quality. From this perspective, the synthesis of quantum dots by a flow method using devices such as a microreactor and a tube reactor has been considered. For example, Patent Document 1 describes that two or more raw material solutions are joined in a flow path with an inner diameter of 1 μm to 1 mm, and a first heating reaction is performed to form semiconductor fine particle precursors, and then a second heating reaction is performed at a higher temperature than the first heating reaction to obtain semiconductor fine particles with a uniform particle size. In addition, Patent Document 2 describes that a joining section where a solution of a compound containing a group III element and a solution of a compound containing a group V element are joined is configured with a multilayer cylindrical mixer, and thereby III-V group semiconductor quantum dots exhibiting sharper luminescence characteristics are obtained compared to uniform mixing using a T-shaped mixer.

[0004] By using the flow method for synthesis in this way, it becomes easier to control the reaction temperature and reaction time, which results in quantum dots with a uniform particle size, and is expected to improve the full width at half maximum (FWHM) of the emission peak.

[0005] However, if oxides or defects occur on the quantum dot surface during quantum dot synthesis, excitons are trapped in the impurity levels they form, causing thermal energy deactivation, making it difficult to obtain efficient light emission and raising concerns about a decrease in quantum yield (Photoluminescence Quantum Yield, hereafter also referred to as PLQY). For this reason, removing oxides and defects on the quantum dot surface and forming a shell layer to protect the easily oxidized surface are important for the synthesis of highly efficient and stable quantum dots.

[0006] To repair defects on the quantum dot surface, a method is adopted in which oxides on the quantum dot surface are removed by etching with hydrofluoric acid or the like to create a clean surface. In addition, it has been reported that extremely efficient and stable quantum dots can be synthesized by forming a shell after obtaining a clean surface with hydrofluoric acid (see, for example, Non-Patent Document 1).

[0007] However, it is considered difficult to perform surface treatment and shell formation to obtain a clean quantum dot surface by the flow method. For this reason, for example, in Non-Patent Document 2, the core is manufactured by the flow method, but the surface treatment process and shell formation process are performed by the batch method using a batch reaction vessel. In addition, Non-Patent Document 3 reports continuous synthesis from core synthesis to shell formation, but the light emission performance is significantly inferior to that of the batch method. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2008-37716 A [Patent Document 2] International Publication WO2018 / 180456 Brochure [Non-patent literature]

[0009] [Non-Patent Document 1] Reinout F. Ubbink, et al., “A Water-Free In Situ HF Treatment for Ultrabright InP Quantum Dots” Chemistry of Materials 2022, 34, 22, 10093-10103 [Non-Patent Document 2] Takafumi Moriyama, et al., “Highly luminescent and narrow-band-emitting InP / ZnSe / ZnS quantum dot synthesis by halide modified shell reaction” Appl. Phys. Express 2023, 16, 015504 [Non-Patent Document 3] Ajit Vikram, et al., “A Millifluidic Reactor System for Multistep Continuous Synthesis of InP / ZnSeS Nanoparticles” ChemNanoMat 2018, 4, 943-953 Summary of the Invention [Problem to be solved by the invention]

[0010] As mentioned above, the improvement of the performance of quantum dots by the flow method is limited to core synthesis, and there are no examples of surface treatment and shell formation being performed by the flow method to obtain the same quality as the batch method. Therefore, the advantages of synthesizing quantum dots by the flow method are extremely limited. The reason for this is that the precursor solution is not optimized when the surface treatment and shell formation processes after the quantum dot core synthesis are performed by the flow method. In other words, depending on the quantum dot synthesis conditions, it is necessary to flow the reaction solution at a high temperature through a fine flow path, but at this time, the components in the reaction solution volatilize and become gas and remain in the flow path, causing the subsequent reaction to stop or the residence time to become uncontrollable, resulting in problems such as only quantum dots with poor PLQY being obtained.

[0011] In addition, the long time required for surface treatment and shell formation also made it difficult to apply the flow method. Generally, the reaction time for core synthesis is several minutes, whereas the surface treatment and shell formation are very long, taking from several tens of minutes to several hours. For this reason, if we try to achieve a similar residence time using the flow method, an extremely long flow path would be required, which is not realistic. Furthermore, in the case of the flow method, the precursor solution must be pumpable at around room temperature. In some synthesis methods, the precursor solution is heated from a state containing solids such as powder or slurry, dissolved at high temperature, and reacted using a batch method, but in such a state containing solids, good pumping is not possible, making it impossible to apply the flow method.

[0012] Therefore, an object of the present invention is to provide an additive for quantum dot production that can repair defects on the surface of quantum dots in a flow method without volatilization, has excellent reactivity so that the reaction time can be shortened, and can give a reaction liquid that does not contain solids and can be pumped at around room temperature, a mixed solution for shell formation containing the additive, and a method for producing core-shell quantum dots by a flow method. [Means for solving the problem]

[0013] Hydrofluoric acid, which is added as a surface treatment agent to improve the luminescence characteristics of quantum dots, is highly volatile and cannot be used in the flow method. The inventors therefore investigated whether it might be possible to use a salt of hydrogen fluoride as a surface treatment agent by reducing its volatility, and discovered that a salt of hydrogen fluoride and an amine having a specific structure does not volatilize in a flow method and can also repair defects on the quantum dot surface, thereby completing the present invention.

[0014] That is, the present invention provides an additive for producing quantum dots, which comprises a dialkylamine hydrohalide salt represented by the following general formula (1).

[0015] [ka] (In the formula, R each independently represents an optionally substituted branched alkyl group having 4 to 20 carbon atoms, and X represents a halogen atom.)

[0016] The present invention also provides a mixed solution for forming a shell, which contains at least the additive for producing quantum dots and a shell precursor.

[0017] The present invention also provides a method for producing core-shell quantum dots by a flow method, which includes a step of obtaining a mixed solution by merging a flow path through which a solution containing a core flows, a flow path through which a solution containing the additive flows, and a flow path through which a shell precursor solution flows, and a step of supplying the obtained mixed solution to a tubular reactor and causing a reaction while passing the mixed solution through the tubular reactor, and which continuously performs these steps.

[0018] The present invention also provides a method for producing core-shell quantum dots by a flow method, which includes a step of obtaining a mixed solution by merging a flow path through which a core-containing solution flows and a flow path through which the shell-forming mixed solution flows, and a step of supplying the obtained mixed solution to a tubular reactor and carrying out a reaction while passing the mixed solution through the tubular reactor, and which continuously performs these steps.

[0019] The present invention also provides a dialkylamine hydrofluoride salt represented by the following general formula (2):

[0020] [ka] (In the formula, each R' independently represents an optionally substituted branched alkyl group having 4 to 20 carbon atoms.) Effect of the Invention

[0021] According to the present invention, it is possible to provide an additive for quantum dot production that can repair defects on the quantum dot surface without volatilizing in a flow method, a mixed solution for shell formation that contains the additive, and a method for producing core-shell quantum dots by a flow method using the same. [Brief description of the drawings]

[0022] [Figure 1] 1 is a diagram showing a preferred embodiment of the method for producing core-shell quantum dots of the present invention. [Diagram 2] 1 is a diagram showing a preferred embodiment of the method for producing core-shell quantum dots of the present invention. [Diagram 3] 1 is a diagram showing a preferred embodiment of the method for producing core-shell quantum dots of the present invention. [Figure 4] FIG. 2 is a diagram showing emission spectra of octane dispersions of InP / ZnSe / ZnS quantum dots obtained in Example 1 and Comparative Example 1. [Diagram 5] 1 is a 1H-NMR spectrum of di(2-ethylhexyl)amine hydrofluoride used in Example 1. [Figure 6] 1 is a 19F-NMR spectrum of di(2-ethylhexyl)amine hydrofluoride used in Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The additive for producing quantum dots of the present invention (hereinafter referred to as "the additive of the present invention") comprises a dialkylamine hydrohalide salt represented by the following general formula (1).

[0024] [ka] (In the formula, R each independently represents an optionally substituted branched alkyl group having 4 to 20 carbon atoms, and X represents a halogen atom.)

[0025] The dialkylamine hydrohalide salt is difficult to volatilize due to its high boiling point, and is liquid at room temperature. Therefore, when treating the surface of quantum dots by the flow method, gas does not remain in the flow channel of the reactor, and the liquid can be easily pumped by a pump. Therefore, the dialkylamine hydrohalide salt can be used as an additive in the synthesis of quantum dots by the flow method.

[0026] In the general formula (1), R is a branched alkyl group having 4 to 20 carbon atoms, preferably 6 to 18 carbon atoms, which may be substituted independently. Examples of such branched alkyl groups include sec-butyl, isobutyl, tert-butyl, isopentyl, neopentyl, tert-pentyl, isohexyl, isoheptyl, isooctyl, 2-ethylbutyl, 2-ethyl-1-pentyl, 2-ethylhexyl, 3-methylhexyl, 2,4-dimethyl-3-hexyl, and isodecyl. These branched alkyl groups may have a substituent, and examples of the substituent include a hydroxyl group, a halogen atom, a cyano group, and an amino group. Among these, R is preferably an unsubstituted branched alkyl group, and particularly preferably a 2-ethylhexyl group, from the viewpoint of imparting a high boiling point without losing the function of the hydrogen halide as a surface treatment agent when forming a salt with the hydrogen halide. That is, the dialkylamine of the dialkylamine hydrohalide salt represented by the general formula (1) is preferably di(2-ethylhexyl)amine.

[0027] In the general formula (1), X is a halogen element. Examples of the halogen element include fluorine, chlorine, bromine, and iodine. Among these, fluorine is preferable from the viewpoint of effectively repairing defects on the quantum dot surface. That is, the dialkylamine hydrohalide salt represented by the general formula (1) is preferably a dialkylamine hydrofluoride salt represented by the following general formula (2).

[0028] [ka] (In the formula, each R' independently represents an optionally substituted branched alkyl group having 4 to 20 carbon atoms.)

[0029] Examples of R' in the general formula (2) include the same groups as R in the general formula (1), and preferred groups are also the same.

[0030] The synthesis method of the dialkylamine-hydrohalide salt represented by the general formula (1) is not particularly limited, but may be, for example, a method of mixing hydrohalic acid, dialkylamine and a reaction solvent, and then degassing water. When the dialkylamine is liquid, the hydrohalic acid and the dialkylamine may be mixed without using a solvent, and the water may be degassed. As the reaction solvent, water, acetonitrile, propionitrile, isovaleronitrile, benzonitrile, acetone, methyl ethyl ketone, methyl isobutyl ketone, acetylacetone, acetophenone, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, methanol, ethanol, isopropanol, cyclohexanol, phenol, methyl acetate, ethyl acetate, isopropyl acetate, phenyl acetate, tetrahydrofuran, tetrahydropyran, diethyl ether, t-butyl methyl ether, cyclohexyl methyl ether, anisole, diphenyl ether, hexane, cyclohexane, benzene, toluene, 1-decene, 1-octadecene, squalane, etc. may be used.

[0031] The synthesis reaction of the hydrohalic acid and the dialkylamine may be carried out in the above-mentioned solvent, or if the dialkylamine is liquid at room temperature, a solvent may not be used. If the synthesis is carried out without a solvent, the process of removing the solvent is not required, and the reaction can be directly used in the flow-type manufacturing method of core-shell type quantum dots described later. When a solvent is used, for example, the hydrohalic acid and the solvent may be mixed to obtain a solution, and then the dialkylamine may be added, or the dialkylamine and the solvent may be mixed to obtain a solution, or the hydrohalic acid and the dialkylamine may be added to the solvent. Among these, from the viewpoint of easy handling of the hydrohalic acid, it is preferable to mix the hydrohalic acid and the solvent to obtain a solution, and then add the dialkylamine. The content of hydrogen halide in the solution using the solvent-free liquid dialkylamine-hydrohalide salt and the solvent is preferably 0.1% by mass or more and 50% by mass or less, particularly 1% by mass or more and 20% by mass or less. When 1-octadecene or squalane, which have high boiling points, are used as the solvent, the obtained dialkylamine hydrohalide solution can be used as it is in the flow-type manufacturing method for core-shell quantum dots described later without removing the solvent.

[0032] In the case of salts of hydrogen fluoride and amines, it is known that hydrogen fluoride is extremely stable up to about 10 equivalents relative to the amines, and hardly releases hydrogen fluoride even at 60°C. Therefore, the amount of dialkylamine used is preferably 0.1 mol to 5 mol, particularly 0.2 mol to 2 mol, relative to 1 mol of hydrogen halide. Although the reaction at this time ends instantly, it is preferable to control the temperature to 0°C to 100°C, particularly 0°C to 80°C, since reaction heat is generated.

[0033] The dialkylamine hydrohalide salt has a boiling point of 300°C or higher and is therefore unlikely to volatilize even at high temperatures. In addition, since it is a liquid even at room temperature, it is possible to carry out a surface treatment to repair defects on the quantum dot surface. In addition, since gas does not remain in the flow path such as a tube in the flow method and liquid can be easily pumped using a pump, it can be used as an additive in the synthesis of quantum dots by the flow method.

[0034] The method for producing core-shell quantum dots of the present invention is a method for producing core-shell quantum dots by a flow method using the additive of the present invention. More specifically, a solution containing a core, a shell precursor solution, and a solution of the additive of the present invention are supplied to a tubular reactor, and reacted while passing through the reactor to continuously obtain core-shell quantum dots. Examples of the reactor include those shown in Figures 1, 2, and 3.

[0035] By using the additive of the present invention, it is possible to send the liquid by a liquid sending means such as a pump without volatilization or solid precipitation in the flow path, so that defects on the quantum dot surface can be repaired by the flow method, and quantum dots with excellent luminescence properties can be efficiently obtained. Note that the flow method is a synthesis method in which a reaction is continuously performed, in which raw materials are continuously poured into a tubular reactor to perform the reaction and the product is continuously obtained. In particular, in the present invention, it refers to a synthesis method in which a reaction liquid is continuously passed through a minute flow path such as a microreactor and a tube reactor to perform the reaction. Hereinafter, a preferred embodiment of the method for producing quantum dots of the present invention will be described.

[0036] (core) In the method for producing core-shell quantum dots of the present invention, a solution in which cores are dispersed is used. Examples of the cores include cadmium-based quantum dots such as CdSe, CdTe, and CdS, and cadmium-free quantum dots such as InP, CuInS, and ZnTeSe. The following describes in detail an embodiment in which the core is an InP-based quantum dot.

[0037] As the phosphorus source used in the core InP-based quantum dots, various substances can be used according to the chemical synthesis method adopted, and examples thereof include phosphine derivatives such as silylphosphine compounds and aminophosphine compounds, phosphine gas, etc. From the viewpoint of easy production of quantum dots, ease of availability, and control of the particle size distribution of the obtained quantum dots, a silylphosphine compound represented by the following general formula (a) is preferable. The silylphosphine compound used as the phosphorus source is a tertiary compound, that is, a compound in which three silyl groups are bonded to a phosphorus atom.

[0038] [ka] (In the formula, each R independently represents an alkyl group having 1 to 5 carbon atoms or an aryl group having 6 to 10 carbon atoms.)

[0039] The alkyl group having 1 to 5 carbon atoms, represented by R in the general formula (a), is preferably a linear or branched alkyl group, and specific examples thereof include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, an isobutyl group, an n-amyl group, an isoamyl group, and a tert-amyl group.

[0040] Examples of the aryl group having 6 to 10 carbon atoms represented by R in the general formula (a) include a phenyl group, a tolyl group, an ethylphenyl group, a propylphenyl group, an iso-propylphenyl group, a butylphenyl group, a sec-butylphenyl group, a tert-butylphenyl group, an iso-butylphenyl group, a methylethylphenyl group, and a trimethylphenyl group.

[0041] These alkyl and aryl groups may have one or more substituents, and examples of the substituents for the alkyl group include a hydroxy group, a halogen atom, a cyano group, an amino group, etc., and examples of the substituents for the aryl group include an alkyl group having from 1 to 5 carbon atoms, an alkoxy group having from 1 to 5 carbon atoms, a hydroxy group, a halogen atom, a cyano group, an amino group, etc. When the aryl group is substituted with an alkyl group or an alkoxy group, the number of carbon atoms of the aryl group includes the number of carbon atoms of the alkyl group or alkoxy group.

[0042] The multiple R in the general formula (a) may be the same or different. The three silyl groups (-SiR3) present in the general formula (a) may be the same or different. As the silylphosphine compound represented by the general formula (a), those in which R is an alkyl group having 1 to 4 carbon atoms or a phenyl group unsubstituted or substituted with an alkyl group having 1 to 4 carbon atoms are preferred from the viewpoint of excellent reactivity with other molecules such as an indium source as a phosphorus source during the synthesis reaction, and a trimethylsilyl group is particularly preferred.

[0043] As the indium source used in the core InP-based quantum dots, various sources can be used according to the chemical synthesis method adopted. From the viewpoint of easy obtaining quantum dots, easy availability, and control of the particle size distribution of the obtained quantum dots, organic indium carboxylates are suitable, such as saturated aliphatic indium carboxylates such as indium acetate, indium formate, indium propionate, indium butyrate, indium valerate, indium caproate, indium enanthate, indium caprylate, indium pelargonate, indium caprate, indium laurate, indium myristate, indium palmitate, indium margarate, indium stearate, indium oleate, and indium 2-ethylhexanoate; and unsaturated indium carboxylates such as indium oleate and indium linoleate. In particular, from the viewpoints of availability and control of particle size distribution, it is preferable to use at least one selected from the group consisting of indium acetate, indium laurate, indium myristate, indium palmitate, indium stearate, and indium oleate, and it is most preferable to use an indium salt of a higher carboxylic acid having from 12 to 18 carbon atoms.

[0044] Examples of the chemical synthesis method of the InP-based quantum dots include known methods such as the sol-gel method (colloid method), hot soap method, reverse micelle method, solvothermal method, molecular precursor method, hydrothermal synthesis method, and flux method. In addition, it may be a batch reaction or a flow reaction. The method for producing InP-based quantum dots in the present invention is preferably a method for producing InP-based quantum dots by mixing a phosphorus source and an indium source, reacting them at a temperature of 20°C to 150°C to obtain an InP quantum dot precursor, and then reacting them at a temperature of 200°C to 350°C to obtain an InP-based quantum dot.

[0045] The reaction between the phosphorus source and the indium source is preferably carried out in an organic solvent from the viewpoint of reactivity and stability. As the organic solvent, a non-polar solvent is used from the viewpoint of the stability of the phosphorus source, the indium source, etc., and aliphatic hydrocarbons, unsaturated aliphatic hydrocarbons, aromatic hydrocarbons, trialkylphosphines, trialkylphosphine oxides, etc. are preferred from the viewpoint of reactivity and stability. As the aliphatic hydrocarbons, n-hexane, n-heptane, n-octane, n-nonane, n-decane, n-dodecane, n-hexadecane, n-octadecane, etc. are included. As the unsaturated aliphatic hydrocarbons, 1-undecene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, etc. are included. As the aromatic hydrocarbons, benzene, toluene, xylene, styrene, etc. are included. As the trialkylphosphine, triethylphosphine, tributylphosphine, tridecylphosphine, trihexylphosphine, trioctylphosphine, tridodecylphosphine, etc. are included. Examples of the trialkylphosphine oxide include triethylphosphine oxide, tributylphosphine oxide, tridecylphosphine oxide, trihexylphosphine oxide, trioctylphosphine oxide, and tridodecylphosphine oxide.

[0046] The core InP-based quantum dot may be a quantum dot made of a composite compound having an element M other than phosphorus and indium in addition to In and P (also called a composite quantum dot of In, P, and M). The element M is preferably at least one selected from the group consisting of Be, Mg, Ca, Mn, Cu, Zn, Cd, B, Al, Ga, N, As, Sb, and Bi from the viewpoint of improving the quantum yield. Representative examples of InP-based quantum dots containing element M include, for example, InGaP, InZnP, InAlP, InGaAlP, InNP, InAsP, InPSb, and InPBi. In order to obtain InP-based quantum dots containing element M, a liquid containing a compound containing element M may be added to the reaction liquid when heating a liquid containing an InP quantum dot precursor, or a liquid containing an InP quantum dot precursor may be added to the reaction liquid when heating a liquid containing a compound containing element M. The compound containing the element M means, when the element M is Be, Mg, Ca, Mn, Cu, Zn, Cd, B, Al, or Ga, a chloride, bromide, or iodide of the element M, or a higher carboxylate having 12 to 18 carbon atoms. When the higher carboxylate is used, the higher carboxylate may be the same as or different from the carboxylic acid of the indium carboxylate used in the reaction. When the element M is N, As, Sb, or Bi, a compound having three silyl groups or amino groups bonded to the element M can be preferably used.

[0047] (Shell precursor) The shell precursor used in the method for producing core-shell quantum dots of the present invention is a raw material solution made of a compound containing a shell-forming element. The shell precursor solution preferably contains an element selected from Zn, S, Se, Te, Ga, P, N, Cd, Mg, and Al as a shell-forming element, and preferably contains at least Zn. Suitable examples of the coating compound constituting the shell to be formed include ZnS, ZnSe, ZnSeS, ZnTe, ZnSeTe, ZnTeS, ZnO, ZnOS, ZnSeO, and ZnTeO.

[0048] As the metal source such as Zn in the shell precursor solution, it is preferable to use a halide or an organic carboxylate of the metal. As the metal halide, for example, as the zinc source, zinc fluoride, zinc chloride, zinc bromide, zinc iodide, etc. are listed. As the organic carboxylate of the metal, it is particularly preferable to use a long-chain fatty acid salt having 12 to 18 carbon atoms in terms of particle size control, particle size distribution control, and improvement of quantum yield.

[0049] In addition, preferred examples of the sulfur source include linear or branched long-chain alkanethiols having 8 to 18 carbon atoms, such as dodecanethiol, and trialkylphosphine sulfide compounds having 4 to 12 carbon atoms, such as trioctylphosphine sulfide. In addition, preferred examples of the sulfur itself include sulfur solutions in which powdered sulfur is dissolved in a high-boiling solvent having a diene structure, such as octadecene or oleylamine. Preferred examples of the selenium source include trialkylphosphine selenide compounds having 4 to 12 carbon atoms, such as trioctylphosphine selenide. Preferred examples of the tellurium source include trialkylphosphine telluride compounds having 4 to 12 carbon atoms, such as trioctylphosphine telluride.

[0050] (Method of manufacturing core-shell quantum dots) The quantum dots obtained by the method for producing core-shell quantum dots of the present invention have a core-shell structure in which the InP-based quantum dots are used as a core and the core is covered with a shell (a coating compound). When covering the core with a shell, defects on the core surface can be repaired by treating the core surface with the additive of the present invention, so that quantum dots with excellent light-emitting properties can be efficiently obtained.

[0051] In the method for producing core-shell quantum dots of the present invention, first, a mixed solution is obtained by mixing a solution containing the core as raw materials, a shell precursor solution, and a solution containing the additive of the present invention. For example, a mixed solution can be obtained by merging a flow path through which a solution containing the core flows, a flow path through which a solution containing the additive of the present invention flows, and a flow path through which a shell precursor solution flows.

[0052] The order in which the raw material solutions are mixed is not particularly limited as long as a mixed solution is obtained before supplying it to the reactor. A mixed solution for forming the shell containing the additive of the present invention and a shell precursor can be prepared in advance, and the mixed solution can be obtained by merging a flow path through which the mixed solution for forming the shell flows into a flow path through which a solution containing the core flows.

[0053] The respective solutions can be delivered using general-purpose delivery pumps such as a syringe pump, a plunger pump, a diaphragm pump, etc. Furthermore, it is preferable to provide a static mixer in the flow path after the merging, since this makes it possible to obtain a more uniform mixed solution.

[0054] The material constituting the flow path is not particularly limited, and examples thereof include stainless steel, Hastelloy, fluororesin, glass, etc., and may be selected from the viewpoints of heat resistance, flexibility, chemical resistance, etc. Tubes made of these materials may be connected or combined for use. The inner diameter of the flow path is preferably 0.1 to 50 mm, particularly preferably 1 to 10 mm.

[0055] The resulting mixed solution is then supplied to a tubular reactor, and the reaction is carried out while the mixed solution is passing through the reactor. As the tubular reactor, for example, a microreactor in which a reaction is carried out in a microchannel having a diameter of several tens to several hundreds of micrometers engraved on a glass substrate or the like, and a tube reactor in which a reaction is carried out in a tube having a diameter of several millimeters to several tens of millimeters can be used. The material of the reactor can be the same as that of the above-mentioned channel, and a material that allows the reaction to proceed appropriately can be selected from the viewpoints of heat resistance, chemical resistance, and the like. The material used for the channel up to obtaining the mixed solution may be the same as or different from the material of the reactor.

[0056] The flow rate of the mixed solution differs depending on the capacity of the reactor used, but is preferably, for example, 0.005 to 5000 mL / min, and particularly preferably 0.05 to 200 mL / min.

[0057] The reactor is heated for surface treatment of the core and formation of the shell. The heating temperature for the reaction varies depending on the material for forming the desired shell, but is preferably, for example, 80 to 360°C, particularly 100 to 340°C. In addition, from the viewpoint of generating quantum dots free of oxides and defects, this heating may be performed in multiple stages by directly connecting multiple reactors. For example, it is preferable to heat in the first reactor at 50 to 250°C, particularly 120 to 230°C, and then continuously heat in the second reactor at 230 to 350°C, particularly 240 to 320°C. This allows efficient generation of core-shell type quantum dots having a shell free of oxides and defects.

[0058] The pressure in the reactor can be adjusted by disposing a back pressure control device on the outlet side of the reactor, and is preferably set to, for example, 0.1 to 15 MPa, and more preferably 0.2 to 5 MPa.

[0059] In the method for producing core-shell quantum dots of the present invention, the amount of shell precursor used is preferably 0.5 mol to 100 mol, more preferably 4 mol to 50 mol, per mol of indium in the solution containing InP-based quantum dots, when a metal such as zinc is used. It is also preferable to use the sulfur source and selenium source in amounts corresponding to the above metal amounts.

[0060] The amount of the additive of the present invention used is preferably, for example, 0.1 mol to 100 mol, more preferably 0.5 mol to 50 mol, per mol of indium in the solution containing InP-based quantum dots.

[0061] In the method for producing core-shell quantum dots of the present invention, in order to improve the stability of the obtained quantum dots, a shell can be further formed on the surface of the core-shell quantum dots obtained as described above to produce multi-shell quantum dots. In this case, a flow path through which a solution containing the additive of the present invention flows and a flow path through which a shell precursor solution flows can be merged into a flow path through which a solution containing the core-shell quantum dots flows, or a flow path through which a mixed solution for forming a shell flows can be merged to mix the respective solutions, and the surface treatment and shell formation reaction can be performed under the same conditions as those described above. In order to further provide stability and form a thick shell, the shell raw material can be injected in multiple stages in one reactor as shown in FIG. 3. This makes it possible to efficiently produce quantum dots having a multi-shell that does not contain oxides or defects.

[0062] The solution containing the core-shell quantum dots after the reaction is collected in a collection vessel. From the viewpoints of workability and safety, the content of the core-shell quantum dots in this case is preferably 0.1 to 50% by mass, particularly preferably 1 to 30% by mass.

[0063] The obtained solution containing the core-shell quantum dots may be used as it is depending on the purpose of use, or may be subjected to a purification process for the purpose of purifying by-products and unreacted impurities in the solution. This purification process can be performed by adding an organic solvent such as ethanol, methanol, 2-propanol, acetone, or acetonitrile to the solution containing the core-shell quantum dots to precipitate the core-shell quantum dots, separating the solution containing the impurities from the core-shell quantum dots, and dispersing the separated core-shell quantum dots in an organic solvent such as toluene or hexane. The solution containing the impurities and the core-shell quantum dots can be separated by operations such as centrifugation, decantation, and suction filtration.

[0064] The core-shell quantum dots obtained by the above method can be suitably used in single-electron transistors, security inks, quantum teleportation, lasers, solar cells, quantum computers, biomarkers, light-emitting diodes, display backlights, color filters, etc. EXAMPLES

[0065] The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto. The properties in the examples were measured by the following methods. (1) Emission spectrum, maximum fluorescence wavelength, FWHM and PLQY The hexane dispersion of the obtained quantum dots was measured using an absolute fluorescence quantum yield measurement device (Quantaurus-QY, manufactured by Hamamatsu Photonics KK) under measurement conditions of an excitation wavelength of 400 nm and a measurement wavelength of 200 to 1100 nm. (2) NMR spectrum measurement The di(2-ethylhexyl)amine hydrofluoride salt synthesized as the additive was identified by dissolving the sample in CDCl3 and then measuring in CDCl3 with an NMR measuring device (manufactured by JEOL) under the following conditions. 1 H-NMR measurement conditions Observation frequency: 500MHz, number of integrations: 16, standard substance: tetramethylsilane (internal standard) 19 F-NMR measurement conditions Observation frequency: 470MHz, Number of integrations: 16, Standard substance: trifluoromethylbenzene (external standard)

[0066] [Synthesis Example 1] <Synthesis of InP core for yellow light emission> 12.0 g of indium myristate was added to 35.6 g of 1-octadecene, and the mixture was heated to 120° C. under reduced pressure with stirring and degassed for 1.5 hours. After degassing, the mixture was returned to atmospheric pressure with nitrogen gas and cooled to 40° C. to obtain a 1-octadecene solution of indium myristate. The obtained 1-octadecene solution of indium myristate was kept at 40° C. under a nitrogen atmosphere, and 25.1 g of a trioctylphosphine solution containing 10% by mass of tris(trimethylsilyl)phosphine was added thereto, and the mixture was held for 10 minutes and then naturally cooled to 20° C. As a result, a yellow liquid containing an InP quantum dot precursor was obtained. Next, the InP quantum dot precursor solution was heated to 250° C. to obtain a solution containing cores for producing core-shell quantum dots with a yellow emission color. This solution was used in the examples and comparative examples by adding 108.3 g of trioctylphosphine and 106.9 g of 1-octadecene to the solution so that the concentration was suitable for the flow method.

[0067] [Synthesis Example 2] <Synthesis of InP core for orange light emission> 14.3 g of indium myristate was added to 35.6 g of 1-octadecene, and the mixture was heated to 120° C. under reduced pressure with stirring and degassed for 1.5 hours. After degassing, the mixture was returned to atmospheric pressure with nitrogen gas and cooled to 40° C. to obtain a 1-octadecene solution of indium myristate. The obtained 1-octadecene solution of indium myristate was kept at 40° C. under a nitrogen atmosphere, and 25.1 g of a trioctylphosphine solution containing 10% by mass of tris(trimethylsilyl)phosphine was added thereto, and the mixture was held for 10 minutes and then naturally cooled to 20° C. As a result, a yellow liquid containing an InP quantum dot precursor was obtained. Next, the InP quantum dot precursor solution was heated to 280° C. to obtain a solution containing cores for producing core-shell quantum dots with an orange luminescent color. This solution was used in the examples by adding 108.3 g of trioctylphosphine and 106.9 g of 1-octadecene to the solution to obtain a concentration suitable for the flow method.

[0068] [Synthesis Example 3] <Synthesis of InP core for green light emission> 12.0 g of indium myristate, 1.6 g of zinc myristate, and 0.6 g of zinc acetate were added to 142.5 g of 1-octadecene, and the mixture was heated to 120°C under reduced pressure with stirring and degassed for 1.5 hours. After degassing, the mixture was returned to atmospheric pressure with nitrogen gas and cooled to 40°C to obtain a 1-octadecene solution of indium zinc myristate. The obtained 1-octadecene solution of indium zinc myristate was kept at 40° C. under a nitrogen atmosphere, and 25.1 g of a trioctylphosphine solution containing 10% by mass of tris(trimethylsilyl)phosphine was added thereto, and the mixture was held for 10 minutes and then naturally cooled to 20° C. As a result, a yellow liquid containing an InP quantum dot precursor was obtained. Next, the InP quantum dot precursor solution was heated to 250° C. to obtain a solution containing cores for producing core-shell quantum dots with a green emission color. This solution was used in the examples after adding 108.3 g of trioctylphosphine to the solution to obtain a concentration suitable for the flow method.

[0069] [Synthesis Example 4] <Synthesis of InP core for red light emission> 6.4 g of indium myristate was added to 14.3 g of 1-octadecene, and the mixture was heated to 120° C. under reduced pressure with stirring and degassed for 1.5 hours. After degassing, the mixture was returned to atmospheric pressure with nitrogen gas and cooled to 40° C. to obtain a 1-octadecene solution of indium myristate. The obtained 1-octadecene solution of indium myristate was kept at 40° C. under a nitrogen atmosphere, and 10.0 g of a trioctylphosphine solution containing 10% by mass of tris(trimethylsilyl)phosphine was added thereto, and the mixture was held for 10 minutes and then naturally cooled to 20° C. As a result, a yellow liquid containing an InP quantum dot precursor was obtained. Next, the InP quantum dot precursor solution was heated to 280° C. to obtain a reaction solution of the base InP quantum dots. 9.5 g of indium myristate was added to 21.4 g of 1-octadecene in another reaction vessel, and the mixture was heated to 120 °C with stirring under reduced pressure and degassed for 1.5 hours. After degassing, the pressure was returned to atmospheric pressure with nitrogen gas and cooled to 40 °C to obtain a 1-octadecene solution of indium myristate. While maintaining the obtained 1-octadecene solution of indium myristate at 40 °C under a nitrogen atmosphere, 15.0 g of a trioctylphosphine solution containing 10 mass% of tris(trimethylsilyl)phosphine was added, and after holding for 10 minutes, it was naturally cooled to 20 °C. As a result, a yellow liquid containing an InP quantum dot precursor was obtained. The reaction solution of InP quantum dots as the previously prepared base was reheated to 260 °C, and a newly prepared InP quantum dot precursor solution was added over 60 minutes to obtain a solution containing a core for producing core-shell type quantum dots with a red emission color. This solution was used in the examples by adding 108.3 g of trioctylphosphine and 106.9 g of 1-octadecene so as to have a concentration preferable for the flow method.

[0070] [Example 1] [Additive for Quantum Dot Production] 20.84 g of an aqueous solution containing 48 mass% of hydrogen fluoride was added to 40.0 g of di(2-ethylhexyl)amine, and the mixture was heated to 100 °C with stirring under reduced pressure and degassed for 3 hours. After degassing, the pressure was returned to atmospheric pressure with nitrogen gas and cooled to room temperature to obtain a liquid di(2-ethylhexyl)amine-hydrogen fluoride acid salt (hereinafter also referred to as HF additive). The obtained liquid contained 10 mass% of hydrogen fluoride and had a colorless and clear property at room temperature. Also, 1 The results of measuring the 1H-NMR spectrum are shown in Fig. 5, 19 The results of measuring the 19F-NMR spectrum are shown in Fig. 6.

[0071] [ZnSe Shell Precursor] 33.03 g of zinc acetate and 101.69 g of oleic acid were added to 439.02 g of oleylamine, and the mixture was heated to 120 °C with stirring under reduced pressure for 3 hours for degassing. After degassing, the pressure was returned to atmospheric pressure with nitrogen gas and cooled to 60 °C. Then, 98.1 g of an ethanol solution in which 50 mass% of zinc chloride was dissolved, which was prepared separately, was added. The mixture was heated to 80 °C with stirring under reduced pressure for 1 hour for degassing to distill off ethanol. After degassing, the pressure was returned to atmospheric pressure with nitrogen gas and cooled to 60 °C. 78.56 g of trioctylphosphine selenide was added, and the mixture was heated to 80 °C with stirring under reduced pressure for 1 hour for degassing, and then allowed to cool naturally to prepare a ZnSe shell precursor solution with a yellowish color. Since the obtained solution solidified and lost fluidity at around 20 °C, it was used after heating to 40 °C when used in the subsequent flow reaction.

[0072] <ZnS shell precursor> 33.03 g of zinc acetate and 101.69 g of oleic acid were added to 80.51 g of trioctylphosphine, and the mixture was heated to 120 °C with stirring under reduced pressure for 3 hours for degassing. After degassing, the pressure was returned to atmospheric pressure with nitrogen gas and cooled to 60 °C. 75.12 g of trioctylphosphine sulfide was added, and the mixture was heated to 80 °C with stirring under reduced pressure for 1 hour for degassing, and then allowed to cool naturally to prepare a ZnS shell precursor solution. The obtained solution had a colorless and clear property at room temperature.

[0073] <Shell formation by flow method> The solution containing the core for manufacturing a core-shell type quantum dot for yellow light emission obtained in Synthesis Example 1, the HF additive, the ZnSe shell precursor solution, and the ZnS shell precursor solution were each held in a screw-cap bottle and connected to a liquid feed pump through a PTFE tube. An outer diameter 3.2 mm stainless steel tube was connected to the outlet side of the pump, and quantum dot surface treatment and shell formation were carried out using a coiled tube reactor in which the part where the tubes were bundled in a coil shape as shown in Fig. 1 was heated by a heater. The three reactors 1, 2, and 3 were each adjusted in length to have a capacity of 10 ml and connected in series. The InP core quantum dot solution and the ZnSe shell precursor solution were delivered at 0.7 ml / min and 0.7 ml / min, respectively, by the respective pumps, and mixed before the reactor 1, the HF additive delivered at 0.1 ml / min was mixed, and the mixture was sent to the reactor 1 and heated to 200°C, whereby the surface oxide of the InP quantum dots was removed and the dangling bonds on the surface were capped with zinc chloride. The reaction solution was sent directly to the reactor 2, which was set at 280°C, where quantum dots with a core-shell structure of InP / ZnSe were synthesized. Next, the reaction solution was mixed with an HF additive and a ZnS shell precursor solution, and sent to reactor 3 set at 280°C, where quantum dots with a multi-shell structure of InP / ZnSe / ZnS were synthesized. The reaction solution was cooled by flowing through a tube that was connected to a water tank, and then passed through a back pressure control device set at 0.3 MPa and collected in a screw-cap bottle installed at the outlet of the tube.

[0074] <Cleaning process> 10g of hexane was added to 10g of the obtained dispersion, and then 20g of ethanol was added and stirred, and the InP / ZnSe / ZnS quantum dots were collected as a precipitate by centrifugation. The collected InP / ZnSe / ZnS quantum dots were suspended in 10g of hexane to obtain a hexane dispersion of InP / ZnSe / ZnS quantum dots. 10g of ethanol was further added to this dispersion, and the mixture was stirred, and the InP / ZnSe / ZnS quantum dots were collected as a precipitate by centrifugation. The collected InP / ZnSe / ZnS quantum dots were suspended in 2g of octane to obtain an octane dispersion of purified InP / ZnSe / ZnS quantum dots.

[0075] [Examples 2 to 13] In Example 1, the liquid flow rates of the solution containing the core for producing core-shell quantum dots corresponding to the desired emission color (core solution), the ZnSe shell precursor solution (ZnSe precursor), the ZnS shell precursor solution (ZnS precursor), and the HF additive (additive) were set to the conditions in Table 1, and the set temperatures of reactors 1, 2, and 3 were changed as shown in Table 1. InP / ZnSe / ZnS quantum dots were synthesized by a flow method under the same conditions as in Example 1, and were evaluated after a cleaning process.

[0076] [Examples 14 to 15] An octane dispersion of InP / ZnSe / ZnS quantum dots was obtained by carrying out the same operations as in Example 1, except that when preparing the ZnS precursor solution in Example 1, oleylamine was used instead of trioctylphosphine and the liquid delivery conditions were set as shown in Table 1.

[0077] [Examples 16 to 17] An octane dispersion of InP / ZnSe / ZnS quantum dots was obtained by carrying out the same operations as in Example 1, except that dodecanethiol was used as the sulfur source instead of the ZnS precursor solution in Example 1 and the liquid delivery conditions were set as shown in Table 1.

[0078] [Comparative Example 1] InP / ZnSe / ZnS quantum dots were continuously synthesized by carrying out the reaction under the same conditions as in Example 1, except that no HF additive was fed, and the quantum dots were evaluated after a cleaning process.

[0079] [Comparative Examples 2 to 8] The additives for quantum dot production in Example 1 were synthesized using oleylamine, 3-(undecyloxy)propylamine, dioctylamine, dibenzylamine, dicyclohexylamine, trioctylamine, and tri(2-ethylhexyl)amine instead of di(2-ethylhexyl)amine. However, the obtained amine hydrofluorides were all solids and could not be pumped, and therefore could not be used for shell formation by the flow method.

[0080] [Comparative Example 9] When a commercially available reagent triethylamine hydrofluoride salt was diluted with triethylamine to a hydrogen fluoride content of 10% by weight and used in place of the HF additive in Example 1, the gasification of triethylamine in the reactor 1 caused a rapid expansion of the volume, making it impossible to control the residence time in the reactor, and therefore it was not possible to form a shell thereafter.

[0081] [Comparative Example 10] When a commercially available reagent pyridine hydrofluoride salt was diluted with pyridine to a hydrogen fluoride content of 10% by weight and used in place of the HF additive in Example 1, gasification occurred in reactor 1, and the residence time in the reactor could not be controlled due to a significant increase in volume, and a shell could not be formed thereafter.

[0082] [Comparative Example 11] When hydrofluoric acid was diluted with acetone to a hydrogen fluoride content of 10% by weight and used instead of the HF additive in Example 1, gasification occurred in reactor 1, and the residence time in the reactor could not be controlled due to a significant increase in volume, and a shell could not be formed thereafter.

[0083] [Table 1]

[0084] The results in Table 1 show that by using the additive of the present invention, core-shell quantum dots with high quantum yield can be produced by the flow method. 4, comparing Example 1 using the additive of the present invention with Comparative Example 1 not using the additive of the present invention, a shoulder-shaped emission spectrum is observed at around 480 to 530 nm on the short wavelength side in the emission spectrum of Comparative Example 1 not using the additive of the present invention. This indicates that some quantum dots cannot form a shell properly because the surface of some InP cores is not clean.

Claims

1. An additive for quantum dot production comprising a dialkylamine hydrohalide salt represented by the following general formula (1): 【Chemistry 1】 (In the formula, each R independently represents an optionally substituted branched alkyl group having 4 to 20 carbon atoms, and X represents a halogen atom.)

2. 2. The additive for producing quantum dots according to claim 1, wherein X is fluorine, chlorine or bromine.

3. The additive for producing quantum dots according to claim 1, which is used for surface treatment of quantum dots.

4. A mixed solution for forming a shell, comprising at least the additive for producing quantum dots according to any one of claims 1 to 3 and a shell precursor.

5. 5. The shell-forming mixed solution according to claim 4, wherein the shell precursor contains at least one element selected from the group consisting of Zn, S, Se, Te, Ga, P, N, Cd, Mg and Al as a shell-forming element.

6. A method for producing core-shell quantum dots by a flow method, comprising the steps of: A method for producing core-shell quantum dots, comprising the steps of: obtaining a mixed solution by merging a flow path through which a solution containing a core flows, a flow path through which a solution containing the additive according to any one of claims 1 to 3 flows, and a flow path through which a shell precursor solution flows; and supplying the obtained mixed solution to a tubular reactor and carrying out a reaction while passing the mixed solution through the reactor, the method comprising the steps of: continuously carrying out these steps.

7. A method for producing core-shell quantum dots by a flow method, comprising the steps of: A method for producing core-shell quantum dots, comprising the steps of: obtaining a mixed solution by merging a flow path through which a core-containing solution flows and a flow path through which the shell-forming mixed solution described in claim 4 flows; and supplying the obtained mixed solution to a tubular reactor and carrying out a reaction while passing the mixed solution through the tubular reactor, the method comprising the steps of:

8. A dialkylamine hydrofluoride salt represented by the following general formula (2): 【Chemistry 2】 (In the formula, each R' independently represents an optionally substituted branched alkyl group having 4 to 20 carbon atoms.)

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