Method for producing chalcopyrite-type quantum dot

Abstract

The present invention is a method for producing a chalcopyrite-type quantum dot including a core particle and a shell layer, the method comprising: a core forming step for forming a core particle having a chalcopyrite structure; a reducing agent treatment step for treating a surface forming a shell layer with a reducing agent; and a shell forming step for forming the shell layer on the surface treated with the reducing agent. Accordingly, the present invention provides a method for producing a chalcopyrite-type quantum dot having improved light emission characteristics and not containing harmful substances.

Description

Method for producing chalcopyrite quantum dots

[0001] The present invention relates to a method for producing chalcopyrite quantum dots.

[0002] Semiconductor crystal particles with nanometer-sized diameters are called quantum dots. The energy levels of the semiconductor crystal particles become discrete because excitons generated by light absorption are confined within nanometer-sized regions, and the band gap changes depending on the particle diameter. These effects make the fluorescent emission of quantum dots brighter, more efficient, and sharper than that of general phosphors.

[0003] Furthermore, because their band gap changes depending on their particle size, their emission wavelength can be controlled, and they are expected to be used as wavelength conversion materials in solid-state lighting and displays. For example, using quantum dots as wavelength conversion materials in displays can achieve a wider color gamut and lower power consumption than conventional phosphor materials.

[0004] As a mounting method for using quantum dots as a wavelength conversion material, a method has been proposed in which quantum dots are dispersed in a resin material, and the resin material containing the quantum dots is laminated with a transparent film, thereby incorporating the quantum dots into a backlight unit as a wavelength conversion film (Patent Document 1).

[0005] In addition, it has been proposed that quantum dots can be used as a color filter material to absorb blue monochromatic light from a backlight unit and emit red or green light, thereby functioning as a color filter and wavelength conversion material, thereby being applicable to image elements with high efficiency and excellent color reproducibility (Patent Document 2). For such applications, the light conversion efficiency of quantum dots, i.e., quantum yield, is an important characteristic.

[0006] Furthermore, quantum dots containing Cd are known to have excellent properties, but Cd is also known to be a harmful substance, and there is a need for quantum dots that do not contain harmful substances such as Cd and have excellent properties.

[0007] JP 2013-544018 A JP 2017-21322 A

[0008] Uematsu et al. , NPG Asia Materials Vol. 10, 2018, p713-726

[0009] Cd-free quantum dots are being developed, including InP-based, perovskite-based, carbon-based (e.g., graphene), and chalcopyrite-based quantum dots. Among these, chalcopyrite-based quantum dots have attracted attention because of their low toxicity, their ability to control the emission wavelength from the visible to near-infrared region depending on their composition, and their ability to exhibit large optical absorption.

[0010] However, it is known that chalcopyrite quantum dots are prone to defects and emit light due to defects. According to Non-Patent Document 1, it has been reported that using amorphous gallium sulfide as a shell suppresses defects and results in band-edge emission. Thus, it is known that suppressing surface defects on the core particles is important for chalcopyrite quantum dots. Furthermore, when comparing the luminescence properties with Cd-based quantum dots, further improvements are required in terms of quantum yield and other aspects.

[0011] The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for producing chalcopyrite quantum dots with improved luminescence properties.

[0012] The present invention has been made to achieve the above-mentioned object, and provides a method for producing chalcopyrite quantum dots comprising a core particle and a shell layer, the method comprising: a core formation step of forming a core particle having a chalcopyrite structure; a reducing agent treatment step of treating, with a reducing agent, a surface on which the shell layer is to be formed; and a shell formation step of forming a shell layer on the surface that has been treated with the reducing agent.

[0013] According to such a method for producing chalcopyrite quantum dots, it is possible to provide chalcopyrite quantum dots with improved luminescence properties, particularly improved quantum yield.

[0014] In this case, the method for producing chalcopyrite quantum dots can be one in which the reducing agent is any one of 2-mercaptoethanol, triphenylphosphine, tris(2-carboxyethyl)phosphine hydrochloride, dimethylaminophosphine, and diethylaminophosphine.

[0015] This allows the surface on which the shell layer is formed to be stably and effectively treated with a reducing agent, thereby providing chalcopyrite quantum dots with improved luminescence properties, particularly quantum yield.

[0016] In this case, the method for producing chalcopyrite quantum dots can include an intermediate layer forming step of forming an intermediate layer having a chalcopyrite structure on the core particle, and the surface on which the shell layer is formed in the shell forming step can be the surface of the intermediate layer.

[0017] As a result, even if the quantum dots have an intermediate layer having a chalcopyrite structure on the core particle, it is possible to provide chalcopyrite quantum dots with improved luminescence properties, particularly quantum yield.

[0018] As described above, the method for producing chalcopyrite quantum dots of the present invention makes it possible to provide chalcopyrite quantum dots with improved luminescence properties, particularly improved quantum yield.

[0019] 1 is a diagram illustrating a method for producing chalcopyrite quantum dots according to the present invention.

[0020] The present invention will be described in detail below, but the present invention is not limited thereto.

[0021] As described above, there is a need for a method for producing chalcopyrite quantum dots with improved luminescence properties that do not contain harmful substances.

[0022] As a result of extensive research into the above-mentioned problems, the present inventors have found that a method for producing chalcopyrite quantum dots comprising a core particle and a shell layer, the method comprising a core formation step of forming a core particle having a chalcopyrite structure, a reducing agent treatment step of treating the surface on which the shell layer is to be formed with a reducing agent, and a shell formation step of forming a shell layer on the surface that has been treated with the reducing agent, can provide chalcopyrite quantum dots with improved luminescence properties, in particular quantum yield, and have completed the present invention.

[0023] The following description will be made with reference to the drawings.

[0024] [Chalcopyrite Quantum Dots] First, the chalcopyrite quantum dots (hereinafter, sometimes simply referred to as "quantum dots") according to the present invention will be described. As shown in Fig. 2, the chalcopyrite quantum dots 10 according to the present invention comprise a core particle 1 having a chalcopyrite structure and a shell layer 2, and have a so-called core-shell structure. The chalcopyrite quantum dots 10 according to the present invention may also comprise an intermediate layer 3 between the core particle 1 and the shell layer 2.

[0025] The surface on which the shell layer 2 is formed is a reducing agent-treated surface that has been treated with a reducing agent, as described below. When the chalcopyrite quantum dots 10 according to the present invention include an intermediate layer 3, the interface between the intermediate layer 3 and the shell layer 2 is the reducing agent-treated surface. When the chalcopyrite quantum dots 10 according to the present invention do not include an intermediate layer 3, the interface between the core particle 1 and the shell layer 2 is the reducing agent-treated surface.

[0026] The shape of the chalcopyrite quantum dots according to the present invention may be spherical, cubic or rod-like, and the shape of the quantum dots is not limited and can be freely selected.

[0027] The average particle size of the chalcopyrite quantum dots according to the present invention is preferably 20 nm or less. When the average particle size is within this range, the quantum size effect is stably obtained, the luminous efficiency is stable, and band gap control by particle size becomes easy.

[0028] The average particle size of the chalcopyrite quantum dots according to the present invention can be calculated from the average value of the maximum diameter in a specific direction of 20 or more particles, i.e., the Feret diameter, measured by measuring particle images obtained by a transmission electron microscope (TEM). Of course, the method for measuring the average particle size is not limited to this, and other methods can also be used.

[0029] A ligand may be present on the surface of the chalcopyrite quantum dots according to the present invention, and examples thereof include oleic acid, stearic acid, palmitic acid, myristic acid, lauric acid, decanoic acid, octanoic acid, oleylamine, stearyl (octadecyl)amine, dodecyl (lauryl)amine, decylamine, octylamine, octadecanethiol, hexadecanethiol, tetradecanethiol, dodecanethiol, decanethiol, octanethiol, trioctylphosphine, trioctylphosphine oxide, triphenylphosphine, triphenylphosphine oxide, tributylphosphine, and tributylphosphine oxide.

[0030] (Core Particle) The core particle 1 is not particularly limited as long as it has a chalcopyrite structure. The shape, size, material, etc. of the core particle 1 are not particularly limited, and the shape, particle size, and material can be selected according to the purpose. Specifically, the material of the core particle 1 is CuInSe ２ , CuInS ２ , CuInTe ２ , CuGaSe ２ , CuGaS ２ , CuGaTe ２ , CuAlSe ２ , CuAlS ２ , CuAlTe ２ , AgInSe ２ , AgInS ２ , AgInTe ２ , AgGaSe ２ , AgGaS ２ , AgGaTe ２ , AgAlSe ２ , AgAlS ２, AgAlTe ２ , CuFeS ２ , AgFeS ２ Examples of the dopant include Zn, Ti, Mn, Sn, etc.

[0031] (Shell Layer) The composition and thickness of the shell layer 2 are not particularly limited and can be appropriately selected depending on the purpose. Examples of materials for the shell layer 2 include ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, and Al. ２ O ３ , AlSe, AlS, AlTe, AlN, AlP, AlAs, AlSb, Ga ２ O ３ , Ga ２ Se ３ , Ga ２ S ３ , GaN, GaP, GaAs, GaSb, InN, InP, InAs, AlSb, In ２ Se ３ , In ２ S ３ , BeS, BeSe, BeTe, MgO, MgS, MgSe, MgTe, PbS, PbSe, PbTe, SnS, SnSe, SnTe, CuF, CuCl, CuBr, CuI, and mixed crystals thereof.

[0032] (Intermediate Layer) When the chalcopyrite quantum dots according to the present invention have an intermediate layer 3, the thickness and material of the intermediate layer 3 are not particularly limited, and the layer thickness and material can be selected according to the purpose.

[0033] It is particularly preferable that the intermediate layer 3 is made of a material having a chalcopyrite structure. Specifically, the intermediate layer material is CuInSe ２ , CuInS ２ , CuInTe ２ , CuGaSe ２ , CuGaS ２ , CuGaTe ２ , CuAlSe ２ , CuAlS ２ , CuAlTe ２ , AgInSe ２ , AgInS ２ , AgInTe２ , AgGaSe ２ , AgGaS ２ , AgGaTe ２ , AgAlSe ２ , AgAlS ２ , AgAlTe ２ , CuFeS ２ , AgFeS ２ Further examples include mixed crystals of these and those to which a dopant is added. The intermediate layer 3 preferably has a composition different from that of the core particle and a band gap larger than that of the core particle.

[0034] [Method for producing chalcopyrite quantum dots] Next, a method for producing chalcopyrite quantum dots according to the present invention will be described. As shown in Fig. 1, the method for producing chalcopyrite quantum dots according to the present invention includes a core formation step of forming core particles having a chalcopyrite structure, a reducing agent treatment step of treating a surface on which a shell layer is to be formed with a reducing agent, and a shell formation step of forming a shell layer on the surface that has been treated with the reducing agent.

[0035] The materials, structures, etc. of the core particle, intermediate layer, and shell layer are as described above, and may be omitted in the following description.

[0036] (Core Formation Step) First, a core particle 1 having a chalcopyrite structure is formed. The reaction conditions for forming the core particle are not particularly limited and can be appropriately selected depending on the purpose and the material constituting the core particle.

[0037] (Intermediate Layer Forming Step) Following the core forming step, an intermediate layer forming step of forming an intermediate layer 3 may be performed. The thickness and material of the intermediate layer 3 are not particularly limited, and the layer thickness and material can be selected according to the purpose. Furthermore, it is preferable that the intermediate layer 3 has a composition different from that of the core particle and has a larger band gap than the core particle. Furthermore, it is preferable that the intermediate layer 3 is made of a material having a chalcopyrite structure.

[0038] (Reducing Agent Treatment Step) The reducing agent treatment step is a step of treating the surface on which the shell layer 2 is to be formed with a reducing agent. By treating the surface of the core particle 1 or the intermediate layer 3 with a reducing agent before the formation of the shell layer 2, it is possible to suppress defects on the surface of the core particle 1 or the intermediate layer 3 on which the shell layer 2 is to be formed. Then, by forming the shell layer 2 on the surface on which defects have been suppressed, chalcopyrite quantum dots with suppressed defects can be obtained.

[0039] The reducing agent can be appropriately selected depending on the composition and reaction conditions of the core particle 1. Furthermore, the treatment conditions for the reducing agent are not particularly limited and can be appropriately selected depending on the type of reducing agent and the conditions of the core particle 1. The reducing agent is preferably one that does not form hydride ions in order to maintain more appropriate reactivity.

[0040] As the reducing agent, it is particularly preferable to use any one of 2-mercaptoethanol, triphenylphosphine, tris(2-carboxyethyl)phosphine hydrochloride, dimethylaminophosphine, and diethylaminophosphine, which allows the reducing agent treatment of the shell layer formation surface to be carried out stably and more effectively, thereby obtaining chalcopyrite quantum dots with improved luminescence properties, particularly quantum yield.

[0041] Although the amount of the reducing agent added is not particularly limited, the amount of the reducing agent added to the core particles or core particles provided with an intermediate layer is preferably in the range of 0.1% to 30% by molar ratio, because within this range, defects can be stably suppressed and undesirable side reactions can also be stably suppressed.

[0042] The reaction temperature of the reducing agent treatment is preferably 20 to 200° C. Within this range, undesirable side reactions and particle growth of the core particles or intermediate layers can be stably suppressed, and shifts in emission wavelength and widening of the half-value width can be stably prevented.

[0043] The treatment time for the reducing agent treatment is preferably about 10 minutes to 2 hours, depending on the type of reducing agent. In addition, the reducing agent treatment is preferably carried out in an inert atmosphere to prevent oxidation of the core particles or the intermediate layer surface.

[0044] The reducing agent treatment may be carried out by adding the reducing agent directly to a reaction vessel after the formation of the core particles or intermediate layer, or may be carried out after the formation of the core particles or intermediate layer, by purifying the particles once and redispersing them in a solvent.

[0045] (Shell Formation Step) In the shell formation step, a shell layer is formed on the surface that has been treated with a reducing agent. The reaction conditions, shell thickness, material, etc. when forming the shell layer are not particularly limited and can be appropriately selected depending on the purpose and the material that constitutes the shell layer. Specific examples of the shell layer are as described above. Regarding the formation of the shell, the shell formation reaction may be carried out directly after the reduction treatment, or the shell may be formed by purifying the product after the reduction treatment and redispersing it in a solvent before the shell formation reaction.

[0046] The chalcopyrite quantum dots obtained by forming the shell layer 2 on the surface treated with the reducing agent have improved luminescence properties, particularly quantum yield, and have a high quantum yield.

[0047] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0048] [Example 1] (Quantum dot core formation process) 120 mg (0.41 mmol) of indium acetate, 60 mg (0.36 mmol) of silver (I) acetate, 10 mL of oleylamine, and 0.5 mL of 1-dodecanethiol were added to a flask. The mixture was heated and stirred at 50°C under reduced pressure, and degassed for 1 hour while dissolving the raw materials. Nitrogen was then purged into the flask, and the temperature was raised to 150°C. After reaching 150°C, a solution prepared by dissolving 25 mg (0.78 mmol) of sulfur in 1 mL of 1-dodecanethiol was quickly added dropwise. After the addition, the mixture was heated to 230°C and reacted at 230°C for 20 minutes to obtain AgInS ２ Core particles were obtained.

[0049] (Reducing Agent Treatment Step) Methanol was added to the obtained quantum dot solution to precipitate the core particles, and the precipitate was collected by centrifugation. 10 mL of oleylamine was added to the collected precipitate to re-disperse it.

[0050] This solution was placed in a flask, and 1.2 mg (0.004 mmol) of tris(2-carboxyethyl)phosphine hydrochloride was added, followed by degassing under reduced pressure for 1 hour. Nitrogen was purged into the flask, and the temperature was raised to 180° C., followed by reaction for 30 minutes.

[0051] (Quantum dot shell layer formation step) Methanol was added to the solution after the reaction to precipitate the core particles, and the precipitate was collected by centrifugation. 10 mL of oleylamine was added to the collected precipitate to re-disperse it.

[0052] This solution was placed in a flask, and 80 mg (0.22 mmol) of zinc diethyldithiocarbamate was added. The mixture was degassed under reduced pressure for 1 hour. The flask was purged with nitrogen, and the temperature was raised to 150°C and the mixture was allowed to react for 30 minutes. After the temperature reached 150°C, a solution of 6 mg (0.19 mmol) of sulfur dissolved in 1 mL of 1-dodecanethiol was quickly added dropwise. After the addition, the mixture was heated to 260°C and allowed to react at 260°C for 60 minutes, yielding AgInS ２ / ZnS core-shell quantum dots were obtained.

[0053] After the reaction was completed, the mixture was cooled to room temperature, ethanol was added to precipitate the quantum dots, the mixture was centrifuged, the supernatant was removed, and the mixture was purified in the same way again and dispersed in toluene.

[0054] The emission wavelength, fluorescence emission half-width, and fluorescence emission efficiency (internal quantum efficiency) of the quantum dots at an excitation wavelength of 450 nm were measured using a quantum efficiency measurement system (QE-2100) manufactured by Otsuka Electronics Co., Ltd., and the emission wavelength was 577 nm, the half-width was 44 nm, and the internal quantum efficiency was 68%.

[0055] [Example 2] (Quantum dot core formation process) 70 mg (0.27 mmol) of silver(I) diethyldithiocarbamate, 200 mg (0.55 mmol) of gallium acetylacetonate, 20 mL of oleylamine, and 2 mL of 1-dodecanethiol were added to a flask. The mixture was heated and stirred at 50°C under reduced pressure, and degassed for 1 hour while dissolving the raw materials. Thereafter, the flask was purged with nitrogen, and the temperature was raised to 150°C. After reaching 150°C, a solution prepared by dissolving 120 mg (1.5 mmol) of selenium in 1 mL of 1-dodecanethiol was quickly added dropwise. After the addition, the mixture was heated to 300°C and reacted at 300°C for 20 minutes, resulting in AgGaSe ２ Core particles were obtained.

[0056] (Quantum dot intermediate layer formation process) The solution after core synthesis was cooled to 150°C, and a solution of 60 mg (0.36 mmol) of silver acetate (I) dissolved in 1.5 mL of oleylamine, a solution of 60 mg (0.34 mmol) of gallium chloride dissolved in 0.5 mL of trioctylphosphine, and a solution of 26 mg of sulfur dissolved in 1 mL of 1-dodecanethiol were added, and the mixture was heated to 280°C and reacted at 280°C for 20 minutes to obtain AgGaSe. ２ / AgGaS ２ Quantum dots with the structure were obtained.

[0057] (Reducing Agent Treatment Step) The solution after the core synthesis was cooled to 120° C., and 0.03 mL (0.11 mmol) of diethylaminophosphine was added dropwise thereto, followed by reaction at 120° C. for 30 minutes.

[0058] (Quantum dot shell layer formation step) Methanol was added to the solution after the reaction to precipitate the core particles, and the precipitate was collected by centrifugation. 10 mL of oleylamine was added to the collected precipitate to re-disperse it.

[0059] This solution was placed in a flask, and 60 mg (0.11 mmol) of gallium acetylacetonate and 12 mg of 1,3-dimethylthiourea were added. The mixture was degassed under reduced pressure for 1 hour. Nitrogen was purged into the flask, and the temperature was raised to 150°C and the mixture was allowed to react for 30 minutes. After the temperature reached 150°C, a solution of 6 mg (0.19 mmol) of sulfur dissolved in 1 mL of 1-dodecanethiol was quickly added dropwise. After the addition, the mixture was heated to 280°C and allowed to react at 280°C for 10 minutes, yielding AgGaSe. ２ / AgGaS ２ / Ga ２ S ３ Core-shell quantum dots were obtained.

[0060] After the reaction was completed, the mixture was cooled to room temperature, and ethanol was added to precipitate the quantum dots. The mixture was then centrifuged to remove the supernatant. The same purification process was repeated once more, and the quantum dots were dispersed in toluene.

[0061] The emission wavelength, fluorescence emission half-width, and fluorescence emission efficiency (internal quantum efficiency) of the quantum dots were measured at an excitation wavelength of 450 nm, and the emission wavelength was found to be 621 nm, the half-width was 42 nm, and the internal quantum efficiency was 81%.

[0062] [Example 3] (Quantum dot core formation process) 40 mg (0.24 mmol) of silver acetate (I), 44 mg (0.2 mmol) of indium chloride, 154 mg (0.3 mmol) of gallium diethyldithiocarbamate, and 15 mL of oleylamine were added to a flask. The mixture was heated and stirred at 60°C under reduced pressure, and degassed for 1 hour while dissolving the raw materials. Thereafter, the flask was purged with nitrogen, and the temperature was raised to 200°C. The mixture was reacted at 200°C for 20 minutes to obtain AgInGaS. ２ Core particles were obtained.

[0063] (Quantum dot intermediate layer formation step) Methanol was added to the obtained quantum dot solution to precipitate core particles, and the precipitate was collected by centrifugation. 10 mL of oleylamine was added to the collected precipitate to re-disperse it.

[0064] A solution of 20 mg (0.12 mmol) of silver acetate (I) dissolved in 1.5 mL of oleylamine, a solution of 20 mg (0.11 mmol) of gallium chloride and 15 mg (0.11 mmol) of zinc chloride dissolved in 1.0 mL of trioctylphosphine, and a solution of 26 mg of sulfur dissolved in 1 mL of 1-dodecanethiol were added, heated to 280°C, and reacted at 280°C for 20 minutes to obtain AgInGaS. ２ / AgGaS ２ Quantum dots with the structure were obtained.

[0065] (Reducing Agent Treatment Step) Methanol was added to the solution after the reaction to precipitate the core particles, and the precipitate was collected by centrifugation. 10 mL of oleylamine was added to the collected precipitate to redisperse it.

[0066] This solution was placed in a flask, 10 mg (0.04 mmol) of triphenylphosphine was added, and the mixture was degassed under reduced pressure for 1 hour. The flask was purged with nitrogen, and 0.03 mL (0.11 mmol) of diethylaminophosphine was added dropwise. The mixture was heated to 180° C. and reacted for 30 minutes.

[0067] (Quantum dot shell layer formation process) The solution after the reducing agent treatment was heated to 230°C, and a solution of 150 mg (1.1 mmol) of zinc chloride dissolved in 2 mL of trioctylphosphine and a solution of 20 mg (0.63 mmol) of sulfur dissolved in 2 mL of trioctylphosphine were alternately added dropwise in four portions. After the dropwise addition, the mixture was allowed to react at 230°C for 120 minutes.

[0068] After the reaction was completed, the mixture was cooled to room temperature, and ethanol was added to precipitate the quantum dots. The mixture was then centrifuged to remove the supernatant. The same purification process was repeated once more, and the quantum dots were dispersed in toluene.

[0069] The emission wavelength, fluorescence emission half-width, and fluorescence emission efficiency (internal quantum efficiency) of the quantum dots were measured at an excitation wavelength of 450 nm, and the emission wavelength was found to be 535 nm, the half-width was 38 nm, and the internal quantum efficiency was 72%.

[0070] Comparative Example 1: Quantum dots were produced in Example 1 without the use of a reducing agent. After the quantum dot synthesis reaction was completed, the mixture was cooled to room temperature, ethanol was added to precipitate the quantum dots, and the mixture was centrifuged to remove the supernatant. The same purification process was repeated, and the resulting mixture was dispersed in toluene.

[0071] The emission wavelength, fluorescence emission half-width, and fluorescence emission efficiency (internal quantum efficiency) of the quantum dots were measured at an excitation wavelength of 450 nm, and the emission wavelength was found to be 570 nm, the half-width was 40 nm, and the internal quantum efficiency was 46%.

[0072] Comparative Example 2: Quantum dots were produced in Example 2 without the use of a reducing agent. After the quantum dot synthesis reaction was completed, the mixture was cooled to room temperature, ethanol was added to precipitate the quantum dots, and the mixture was centrifuged to remove the supernatant. The same purification process was repeated, and the resulting mixture was dispersed in toluene.

[0073] The emission wavelength, fluorescence emission half-width, and fluorescence emission efficiency (internal quantum efficiency) of the quantum dots were measured at an excitation wavelength of 450 nm, and the emission wavelength was found to be 610 nm, the half-width was 40 nm, and the internal quantum efficiency was 60%.

[0074] Comparative Example 3: Quantum dots were produced in Example 3 without the use of a reducing agent. After the quantum dot synthesis reaction was completed, the mixture was cooled to room temperature, ethanol was added to precipitate the quantum dots, and the mixture was centrifuged to remove the supernatant. The same purification process was repeated, and the resulting mixture was dispersed in toluene.

[0075] The emission wavelength, fluorescence emission half-width, and fluorescence emission efficiency (internal quantum efficiency) of the quantum dots were measured at an excitation wavelength of 450 nm, and the emission wavelength was found to be 568 nm, the half-width was 39 nm, and the internal quantum efficiency was 53%.

[0076] [Example 4] (Quantum dot core formation process) 40 mg (0.24 mmol) of silver acetate (I), 44 mg (0.2 mmol) of indium chloride, 154 mg (0.3 mmol) of gallium diethyldithiocarbamate, and 15 mL of oleylamine were added to a flask. The mixture was heated and stirred at 60°C under reduced pressure, and degassed for 1 hour while dissolving the raw materials. Thereafter, the flask was purged with nitrogen, and the temperature was raised to 200°C. The mixture was reacted at 200°C for 20 minutes to obtain AgInGaS. ２ Core particles were obtained.

[0077] (Reducing Agent Treatment Step) Methanol was added to the obtained quantum dot solution to precipitate the core particles, and the precipitate was collected by centrifugation. 10 mL of oleylamine was added to the collected precipitate to re-disperse it.

[0078] This solution was placed in a flask, and 0.02 mL (0.11 mmol) of dimethylaminophosphine was added dropwise thereto, followed by degassing under reduced pressure for 1 hour. Nitrogen was purged into the flask, and the temperature was raised to 100° C., followed by reaction for 30 minutes.

[0079] (Quantum dot intermediate layer formation step) Methanol was added to the solution after the core formation reaction to precipitate the core particles, and the precipitate was collected by centrifugation. 10 mL of oleylamine was added to the collected precipitate to re-disperse it.

[0080] This solution was placed in a flask, and 60 mg (0.11 mmol) of gallium acetylacetonate and 12 mg of 1,3-dimethylthiourea were added. The mixture was degassed under reduced pressure for 1 hour. The flask was purged with nitrogen, and the temperature was raised to 150°C and the mixture was allowed to react for 30 minutes. After the temperature reached 150°C, a solution of 6 mg (0.19 mmol) of sulfur dissolved in 1 mL of 1-dodecanethiol was quickly added dropwise. After the addition, the mixture was heated to 280°C and allowed to react at 280°C for 10 minutes, yielding AgGaSe. ２ / Ga ２ S ３ Quantum dots were obtained.

[0081] (Reducing Agent Treatment Step) The solution after the formation of the intermediate layer was cooled to 120° C., and 0.01 mL (0.14 mmol) of 2-mercaptoethanol was added dropwise, followed by reaction at 120° C. for 30 minutes.

[0082] (Quantum dot shell layer formation step) After the reaction, the mixture was cooled to room temperature, methanol was added to precipitate the core particles, and the precipitate was collected by centrifugation. 10 mL of oleylamine was added to the collected precipitate and it was re-dispersed.

[0083] The solution after the reducing agent treatment was heated to 230° C., and a solution of 150 mg (1.1 mmol) of zinc chloride dissolved in 2 mL of trioctylphosphine and a solution of 20 mg (0.63 mmol) of sulfur dissolved in 2 mL of trioctylphosphine were alternately added dropwise in four portions, respectively, and the mixture was allowed to react at 230° C. for 120 minutes.

[0084] After the reaction was completed, the mixture was cooled to room temperature, ethanol was added to precipitate the quantum dots, the mixture was centrifuged, the supernatant was removed, and the mixture was purified in the same way again and dispersed in toluene.

[0085] The emission wavelength, fluorescence emission half-width, and fluorescence emission efficiency (internal quantum efficiency) of the quantum dots were measured at an excitation wavelength of 450 nm, and the emission wavelength was found to be 533 nm, the half-width was 36 nm, and the internal quantum efficiency was 79%.

[0086] Comparative Example 4: Quantum dots were produced in Example 4 without the use of a reducing agent. After the quantum dot synthesis reaction was completed, the mixture was cooled to room temperature, ethanol was added to precipitate the quantum dots, and the mixture was centrifuged to remove the supernatant. The same purification process was repeated, and the resulting mixture was dispersed in toluene.

[0087] The emission wavelength, fluorescence emission half-width, and fluorescence emission efficiency (internal quantum efficiency) of the quantum dots were measured at an excitation wavelength of 450 nm, and the emission wavelength was found to be 546 nm, the half-width was 40 nm, and the internal quantum efficiency was 66%.

[0088] As described above, it was found that the quantum yield of the Examples was increased by the reducing agent treatment compared to the Comparative Examples. According to the Examples of the present invention, it was confirmed that the luminescence characteristics of the quantum dots, particularly the quantum yield, were improved by reducing the core or intermediate layer surface of the quantum dots.

[0089] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits similar effects is included within the technical scope of the present invention.

Claims

1. A method for producing chalcopyrite quantum dots comprising a core particle and a shell layer, the method comprising: a core formation step of forming a core particle having a chalcopyrite structure; a reducing agent treatment step of treating, with a reducing agent, a surface on which the shell layer is to be formed; and a shell formation step of forming a shell layer on the surface that has been treated with the reducing agent.

2. The method for producing chalcopyrite quantum dots according to claim 1, characterized in that the reducing agent is any one of 2-mercaptoethanol, triphenylphosphine, tris(2-carboxyethyl)phosphine hydrochloride, dimethylaminophosphine, and diethylaminophosphine.

3. A method for producing chalcopyrite quantum dots according to claim 1 or 2, characterized in that it includes an intermediate layer formation step of forming an intermediate layer having a chalcopyrite structure on the core particle, and the surface on which the shell layer is formed in the shell formation step is the surface of the intermediate layer.

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