Method for synthesizing quantum dots

Abstract

The objective is to provide a method for synthesizing quantum dots that have uniform composition, consistent particle size, and excellent luminescence properties. [Solution] A method for synthesizing chalcopyrite-based quantum dots, comprising a nanoparticle generation step of reacting a group I element with a group VI element to produce nanoparticles, and a cation diffusion step of cationically diffusing a group III element into the nanoparticles by heat treatment.

Description

Technical Field

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

Background Art

[0002] Semiconductor crystal particles with a nanosize particle diameter are called quantum dots. When excitons generated by light absorption are confined in a nanosize region, the energy levels of the semiconductor crystal particles become discrete, and their band gaps change depending on the particle diameter. Due to these effects, the fluorescence emission of quantum dots is high-brightness, high-efficiency, and sharp compared to general phosphors.

[0003] Also, it has the characteristic that the emission wavelength can be controlled due to the change in the band gap depending on the particle diameter, and it is expected to be applied as a wavelength conversion material for solid lighting and displays. For example, by using quantum dots as a wavelength conversion material in a display, a wider color gamut and lower power consumption can be achieved compared to conventional phosphor materials.

[0004] As a mounting method for using quantum dots as a wavelength conversion material, Patent Document 1 discloses a method of dispersing quantum dots in a resin material and laminating a resin material containing quantum dots with a transparent film to incorporate it into a backlight unit as a wavelength conversion film.

[0005] Also, in Patent Document 2, by using quantum dots as a color filter material, the quantum dots absorb blue monochromatic light from a backlight unit and emit red or green light, thereby functioning as a color filter and a wavelength conversion material, and an application to a pixel device with high efficiency and excellent color reproducibility is proposed.

[0006] Micro-LED displays, in which the backlight unit is replaced with a micro-sized LED array, are attracting attention. In micro-LED displays, it is necessary to form color filters on micro-sized LEDs. In recent years, the size of these LED arrays has been miniaturized, requiring even finer patterning of quantum dots than before.

[0007] Furthermore, for color filter applications, it is necessary to increase the light absorption capacity of the color filter in order to suppress leakage of blue monochromatic light, which is the excitation light, from the color filter. Increasing the light absorption capacity of the color filter requires increasing the quantum dot density.

[0008] Furthermore, while quantum dots containing cadmium (Cd) are known to possess excellent properties, Cd is also known to be a harmful substance. Therefore, there is a need for quantum dots that do not contain Cd or other harmful substances, yet possess excellent properties. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Special Publication No. 2013-544018 [Patent Document 2] Japanese Patent Publication No. 2017-021322 [Patent Document 3] Patent No. 7319402 [Non-patent literature]

[0010] [Non-Patent Document 1] Nanomaterials 2019,vol.9,Issue 12,page 1763 [Overview of the project] [Problems that the invention aims to solve]

[0011] Development is underway on quantum dots that do not contain cadmium, including InP-based, perovskite-based, carbon-based (such as graphene), and chalcopyrite-based quantum dots. Among these, chalcopyrite-based quantum dots are attracting attention because they are low in toxicity, their emission wavelength can be controlled from the visible to near-infrared region depending on their composition, and they can exhibit large light absorption.

[0012] In this context, the visible region refers to light that can be perceived by the naked eye, generally encompassing light with wavelengths between 380 and 780 nm, while the near-infrared region generally refers to light with wavelengths between 780 and 2500 nm.

[0013] However, chalcopyrite quantum dots are known to be prone to defects, which can lead to defect-induced luminescence. According to Non-Patent Literature 1, it has been reported that using amorphous gallium sulfide as a shell can suppress defects and enable band-edge luminescence. Thus, it is known that suppressing surface defects in the core particles is important in chalcopyrite quantum dots. In addition, chalcopyrite quantum dots are composed of many elements, and problems such as uneven composition distribution during reactions and non-uniform growth exist.

[0014] Therefore, when comparing its luminescence properties with those of Cd-based quantum dots, further improvements are needed in terms of quantum yield and other aspects.

[0015] Patent Document 3 discloses a method for improving the properties of chalcopyrite-based quantum dots by adjusting the composition ratio of chalcopyrite. However, there are limitations on the elemental composition ratio, which restricts the control of the emission wavelength by composition. Furthermore, as the number of elements constituting the quantum dot increases, differences in the reactivity of the precursors of each element occur, leading to uneven composition of the quantum dot during the reaction, expansion of particle size distribution, and generation of defects, resulting in a decrease in emission properties. Moreover, changing the composition ratio to control the emission wavelength alters the reaction process, changing not only the composition ratio but also the particle size simultaneously, making it difficult to control the emission wavelength and affecting properties such as the full width at half maximum of emission.

[0016] The present invention has been made to solve the above problems, and an object thereof is to provide a method for synthesizing quantum dots having good luminescence characteristics with uniform composition and uniform particle size.

Means for Solving the Problems

[0017] The present invention has been made to achieve the above object, and is a method for synthesizing quantum dots for synthesizing chalcopyrite-based quantum dots, the method including a nanoparticle generation step of reacting a Group I element and a Group VI element to generate nanoparticles, and a cation diffusion step of cation-diffusing a Group III element into the nanoparticles by heat treatment.

[0018] According to such a method for synthesizing quantum dots, quantum dots having good luminescence characteristics with uniform composition and uniform particle size can be synthesized.

[0019] At this time, the Group I element may include one or more elements selected from Ag, Cu, Au, Na, K, and Cs, the Group III element may include one or more elements selected from Ga, In, Al, and Tl, and the Group VI element may include one or more elements selected from S, Se, and Te.

[0020] Thereby, the above-described chalcopyrite-based quantum dots can be synthesized more stably.

[0021] At this time, the chalcopyrite-based quantum dots may include four or more constituent elements.

[0022] Thereby, chalcopyrite-based quantum dots according to desired characteristics can be synthesized.

[0023] At this time, the chalcopyrite-based quantum dots may have a full width at half maximum of luminescence of 60 nm or less and a luminescence quantum yield of 50% or more.

[0024] This makes it possible to synthesize quantum dots with less compositional uniformity, more uniform particle size, and even better luminescence properties.

[0025] In this case, the chalcopyrite-based quantum dot can have a core-shell structure.

[0026] This makes it possible to further improve the fluorescence emission efficiency and stability of quantum dots. [Effects of the Invention]

[0027] As described above, the quantum dot synthesis method of the present invention makes it possible to synthesize quantum dots with uniform composition and consistent particle size, and that have good luminescence properties. [Modes for carrying out the invention]

[0028] The present invention will be described in detail below, but the present invention is not limited to these descriptions.

[0029] As mentioned above, there was a need for a method to synthesize quantum dots with uniform composition, consistent particle size, and good luminescence properties.

[0030] As a result of diligent research into the above-mentioned problems, the present inventors have discovered that a quantum dot synthesis method for chalcopyrite-based quantum dots, comprising a nanoparticle generation step of reacting a group I element with a group VI element to produce nanoparticles, and a cation diffusion step of cationically diffusing a group III element into the nanoparticles by heat treatment, can synthesize quantum dots with uniform composition, uniform particle size, and excellent luminescence properties, thereby completing the present invention.

[0031] The present invention will be described in detail below.

[0032] The quantum dot synthesis method according to the present invention is a quantum dot synthesis method for synthesizing chalcopyrite-based quantum dots, and includes a nanoparticle generation step of reacting a group I element with a group VI element to produce nanoparticles, and a cation diffusion step of cationically diffusing a group III element into the nanoparticles by heat treatment. The group VI element may also be referred to as a "chalcogen element".

[0033] In the present invention, the composition ratio of the constituent elements in the chalcopyrite-based quantum dot is not particularly limited, and quantum dots with composition ratios suitable for the purpose can be synthesized.

[0034] In the quantum dot according to the present invention, the Group I element may include one or more elements selected from Ag, Cu, Au, Na, K, and Cs, the Group III element may include one or more elements selected from Ga, In, Al, and Tl, and the Group VI element may include one or more elements selected from S, Se, and Te. This allows for the more stable synthesis of chalcopyrite-based quantum dots. Furthermore, the composition of the quantum dot may be, for example, M α M β X2(M α :I group element, M β: It can be a group III element (X: chalcogen element).

[0035] Quantum dots can be spherical, cubic, or rod-shaped. The shape of the quantum dots is not restricted and can be freely chosen.

[0036] The average particle diameter of quantum dots should preferably be 20 nm or less. If the average particle diameter is 20 nm or less, the quantum size effect allows for stable maintenance of luminescence efficiency and control of the band gap based on particle size.

[0037] The particle size of quantum dots can be calculated by measuring particle images obtained using a transmission electron microscope (TEM) and averaging the maximum diameter in a specific direction for 20 or more particles, i.e., the Ferret diameter. However, the method for measuring the average particle size is not limited to this, and other methods are possible.

[0038] (Nanoparticle production process) The method for producing nanoparticles is not limited to methods involving the reaction of a group I element with a group VI element. For example, a method can be used in which a group I element precursor is mixed in a coordinating organic solvent to produce a mixture, and a solution in which a chalcogen element precursor is dissolved is added dropwise to the heated mixture to produce nanoparticles.

[0039] The coordinating organic solvent is not particularly limited, but examples include oleylamine, hexadecylamine, octylamine, oleic acid, tri-n-octylphosphine, and dodecanethiol. Multiple coordinating organic solvents may also be mixed.

[0040] While there are no particular limitations on the precursors of Group I elements, examples include metal salts and acetylacetone complexes of each element, such as acetates, nitrates, carboxylates, thiocarbamites, and halides.

[0041] The chalcogen element precursor is not particularly limited, and sulfur, selenium, tellurium, thiourea, 1,3-dibutylthiourea, 1,3-dimethylthiourea, N,N'-diethylthiourea, bis(trimethylsilyl) sulfide, trioctylphosphine sulfide, trioctylphosphine selenide, trioctylphosphine telllide, tributylphosphine sulfide, tributylphosphine selenide, tributylphosphine telllide, tetramethylthiuram disulfide, dimethyl diselenide, diphenyl diselenide, dimethyl diterlide, and diphenyl diterlide can be used.

[0042] In the nanoparticle production process, there may be one or more Group I element precursors, and they can be appropriately selected according to the desired composition. Similarly, there may be one or more Chalcogen element precursors, and they can be appropriately selected according to the desired composition.

[0043] The nanoparticle generation process is preferably carried out under an inert atmosphere. The reaction temperature can be appropriately selected depending on the properties of the target quantum dots and the type of precursor, but is preferably between 100°C and 250°C, and particularly preferably between 120°C and 200°C. Similarly, the reaction time can be appropriately selected according to the purpose, but is preferably between 5 minutes and 60 minutes.

[0044] Ligands may be added during the nanoparticle production process, and the type of ligand to be added is not limited and can be appropriately selected depending on the desired properties and the type of precursor. Examples of ligands include phosphorus compounds such as trioctylphosphine oxide and triphenylphosphine, fatty acids such as palmitic acid, and alkylamines such as hexadequilamine.

[0045] Purification may be performed between the nanoparticle generation step and the cation diffusion step. As a purification method, a solution prepared by adjusting the mixing ratio of a nonpolar solvent such as toluene or ethanol with a polar solvent is added as a poor solvent to the solution containing the reaction nanoparticles, causing the nanoparticles to aggregate and be recovered by centrifugation. The nanoparticles recovered by centrifugation are redispersed in an organic solvent and then processed in the next step.

[0046] (Cation diffusion process) By dispersing the nanoparticles obtained in the nanoparticle generation process in, for example, an organic solvent, and then adding a precursor of a group III element and heating the mixture, the group III element can be diffused into the nanoparticles by cation exchange, thereby obtaining chalcopyrite-based quantum dots.

[0047] In the cation diffusion process, the organic solvent is not particularly limited and can be appropriately selected according to the desired properties. Examples of organic solvents include 1-octadecene, oleylamine, hexadecylamine, octylamine, oleic acid, tri-n-octylphosphine, and dodecanethiol, and multiple types of these organic solvents may be mixed.

[0048] Ligands may also be added to these organic solvents. The ligand species is not particularly limited and can be appropriately selected depending on the desired properties and reaction conditions. Examples of ligands include phosphorus compounds such as trioctylphosphine oxide and triphenylphosphine, fatty acids such as palmitic acid, and alkylamines such as hexadequilamine.

[0049] While there are no particular limitations on the precursors of Group III elements, examples include metal salts and acetylacetone complexes of each element, such as acetates, nitrates, carboxylates, thiocarbamites, and halides.

[0050] In the cation diffusion step, the reaction temperature and reaction time can be appropriately selected depending on the desired properties and type of precursor. A reaction temperature of 200°C to 300°C is preferred, and a reaction time of 20 minutes to 120 minutes is preferred. Within this range of reaction temperature and time, cation exchange can be performed more uniformly and effectively. Furthermore, the cation diffusion step is preferably carried out under an inert atmosphere.

[0051] As one embodiment of the quantum dot synthesis method of the present invention, the chalcopyrite-based quantum dots can contain four or more constituent elements. This makes it possible to synthesize chalcopyrite-based quantum dots that have the desired properties.

[0052] When the composition of chalcopyrite quantum dots is greater than that of a quaternary system and contains two or more Group III elements, in addition to the method of simultaneously adding precursors of two or more Group III elements and performing cation exchange in the cation diffusion process, it is also possible to gradually increase the composition of chalcopyrite by adding one Group III element precursor, performing cation exchange by heat treatment, and then adding another Group III element precursor and performing cation exchange by heat treatment.

[0053] In the stepwise cation exchange process described above, purification may be performed between each step, and this can be appropriately selected depending on the reaction conditions.

[0054] Furthermore, quantum dots may consist only of a core or have a core-shell structure, and the shell structure and shell composition are not particularly limited and can be selected as appropriate. By giving quantum dots a core-shell structure, the fluorescence emission efficiency and stability of the quantum dots can be further improved.

[0055] As for the shell composition, M α M β It can be a chalcopyrite type having a composition consisting of X2. As for the shell material, M α It is a group I element and includes one or more elements selected from Ag, Cu, Au, Na, K, and Cs, M β X is a group III element and includes one or more elements selected from Ga, In, Al, and Tl, and X is a chalcogen element and may include one or more elements selected from S, Se, and Te. However, the band gap of the shell is larger than the band gap of the core. Other examples include ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, AlN, AlP, AlAs, Ga2S3, GaN, GaP, InN, InP, MgS, MgSe, MgTe, ZnO, Al2O3, Ga2O3, MgO, ZrO2, TiO2, and mixed crystals of these.

[0056] The shell layer may be a single layer or multiple layers, and can be selected as appropriate to suit the desired properties. Similarly, the thickness of the shell layer can be selected as appropriate to suit the desired properties.

[0057] The method for forming the shell is not particularly limited and can be selected as appropriate. An example of a shell formation method is to redisperse quantum dots in an organic solvent, and then add a cation precursor and an anion precursor while heating to allow them to react.

[0058] Examples of organic solvents include 1-octadecene, oleylamine, hexadecylamine, octylamine, oleic acid, tri-n-octylphosphine, and dodecanethiol, and a mixture of several of these organic solvents may also be used.

[0059] Examples of cation precursors include metal salts and acetylacetone complexes, such as acetates, carboxylates, thiocarbamites, and halides. Examples of anion precursors include sulfur, selenium, tellurium, thiourea, 1,3-dibutylthiourea, 1,3-dimethylthiourea, N,N'-diethylthiourea, bis(trimethylsilyl) sulfide, trioctylphosphine sulfide, trioctylphosphine selenide, trioctylphosphine telllide, tributylphosphine sulfide, tributylphosphine selenide, tributylphosphine telllide, tetramethylthiuram disulfide, dimethyl diselenide, diphenyl diselenide, dimethyl diterlide, diphenyl diterlide, dimethylaminophosphine, diethylaminophosphine, tris(trimethylsilyl)phosphine, and sodium amide. These precursors may be used individually or in combination.

[0060] The synthesized chalcopyrite-based quantum dots can have an emission half-width of 60 nm or less and an emission quantum yield of 50% or more. This makes it possible to synthesize quantum dots with less compositional uniformity, uniform particle size, and excellent luminescence properties. [Examples]

[0061] The present invention will be described more specifically below with reference to examples and comparative examples, but the present invention is not limited thereto.

[0062] (Example 1) (Nanoparticle production process) 0.3 mmol of silver acetate and 20 mL of oleylamine were added to a flask, and the mixture was heated and stirred under reduced pressure at 100°C for 1 hour while dissolving the raw materials. After that, nitrogen was purged into the flask to create an inert atmosphere.

[0063] 1.5 mL of a solution prepared by adding sulfur to 1-dodecanethiol and heating it to adjust the concentration to 0.2 mol / L was added dropwise to a solution in a flask heated to 140°C and allowed to react for 20 minutes. The solution changed from colorless to brown, confirming the formation of nanoparticles.

[0064] (Cation diffusion process) Next, a solution was prepared by dispersing 0.12 mmol of indium acetylacetonate and 0.24 mmol of gallium acetylacetonate in 1 mL of 1-dodecanethiol and 2 mL of oleylamine. This solution was added to the heated reaction solution after nanoparticle synthesis and held at 300°C for 60 minutes. The resulting solution was cooled to room temperature, and chalcopyrite-based quantum dots (cores) made of AgInGaS2 were synthesized.

[0065] (Shell formation process) Ethanol was added to the solution cooled to room temperature to precipitate the reaction solution, and the supernatant was removed by centrifugation. The same purification was performed again, and the solution was dispersed in 10 mL of oleylamine and 4 mL of 1-dodecanethiol in a flask. The flask was then purged with nitrogen gas to create an inert atmosphere.

[0066] A solution of 0.9 mmol of gallium bromide mixed with 2 mL of trioctylphosphine, and a solution of 1-dodecanethiol heated with sulfur to a concentration of 0.2 mol / L, were each added dropwise to a solution containing dispersed nanoparticles in a flask heated to 240°C, and the mixture was allowed to react for 30 minutes to create chalcopyrite-based quantum dots with a core-shell structure composed of AgInGaS2 / Ga2S3.

[0067] After the reaction was complete, the mixture was cooled to room temperature, ethanol was added to precipitate the quantum dots, and the supernatant was removed by centrifugation. The same purification process was repeated, and the mixture was dispersed in toluene.

[0068] Using a quantum efficiency measurement system (QE-2100) manufactured by Otsuka Electronics Co., Ltd., the emission wavelength, fluorescence full width at half maximum (FWHM), and fluorescence emission efficiency (internal quantum efficiency) of quantum dots at an excitation wavelength of 450 nm were measured. The emission wavelength was 521 nm, the FWHM was 34 nm, and the internal quantum efficiency was 66%.

[0069] (Example 2) (Nanoparticle production process) 0.3 mmol of silver acetate, 0.03 mmol of copper(I) acetate, and 10 mL of oleylamine were added to a flask. The mixture was heated and stirred under reduced pressure at 100°C for 1 hour while dissolving the starting materials. After that, nitrogen was purged into the flask to create an inert atmosphere.

[0070] When 1 mL of a solution prepared by adding sulfur to 1-dodecanethiol and heating it to adjust the concentration to 0.2 mol / L, and 1 mL of a solution prepared by adding selenium to 1-dodecanethiol and heating it to adjust the concentration to 0.2 mol / L, were added dropwise to a solution in a flask heated to 150°C and held for 20 minutes, the solution changed from colorless to brown, confirming the formation of nanoparticles.

[0071] (Cation diffusion process) After the reaction was complete, the mixture was cooled to room temperature, ethanol was added to precipitate the reaction solution, and the supernatant was removed by centrifugation. The same purification was repeated, and then the solution was dispersed in 10 mL of oleylamine and 4 mL of 1-dodecanethiol. This solution was transferred to another flask, and the flask was purged with nitrogen gas to create an inert atmosphere.

[0072] Next, a solution was prepared by dispersing 0.12 mmol of indium acetylacetonate in 2 mL of oleylamine. This solution was added to a solution containing nanoparticles heated to 290°C and held for 40 minutes. Subsequently, a solution of 0.25 mmol of gallium acetylacetonate dispersed in 2 mL of oleylamine was added and held at 290°C for another 40 minutes to synthesize chalcopyrite-based quantum dots (cores) composed of AgCuInGaSSe.

[0073] (Shell formation process) After the reaction was complete, the mixture was cooled to room temperature, ethanol was added to precipitate the reaction solution, and the supernatant was removed by centrifugation. The same purification was repeated, and the solution was dispersed in 10 mL of oleylamine and 4 mL of 1-dodecanethiol in a flask. The flask was then purged with nitrogen gas to create an inert atmosphere.

[0074] A solution of 0.4 mmol of zinc bromide mixed with 2 mL of trioctylphosphine, and a solution of 1-dodecanethiol heated with sulfur to a concentration of 0.2 mol / L, were each added dropwise to a solution containing dispersed nanoparticles in a flask heated to 200°C, and the mixture was allowed to react for 60 minutes to produce chalcopyrite-based quantum dots with a core-shell structure composed of AgCuInGaSSe / ZnS.

[0075] The emission wavelength, fluorescence full width at half maximum (FWHM), and fluorescence emission efficiency (internal quantum efficiency) of quantum dots at an excitation wavelength of 450 nm were measured. The emission wavelength was 630 nm, the FWHM was 36 nm, and the internal quantum efficiency was 73%.

[0076] (Example 3) (Nanoparticle production process) 0.3 mmol of silver diethyldithiocarbamate and 10 mL of oleylamine were added to the flask, and the flask was purged with nitrogen to create an inert atmosphere.

[0077] 1.5 mL of a solution prepared by adding selenium to 1-dodecanethiol and heating it to adjust the concentration to 0.2 mol / L was added dropwise to a solution in a flask heated to 150°C and held for 20 minutes. The solution changed from colorless to brown, confirming the formation of nanoparticles.

[0078] (Cation diffusion process) Next, a solution was prepared by dispersing 0.5 mmol of gallium acetylacetonate and 0.05 mmol of aluminum acetylacetonate in 2 mL of oleylamine. This solution was added to the reaction solution after nanoparticle synthesis, which had been heated to 300°C, and held for 20 minutes. The resulting solution was cooled to room temperature, and chalcopyrite-based quantum dots (cores) made of AgAlGaSe were synthesized.

[0079] (Shell formation process) Next, a solution of 0.2 mmol silver bromide mixed with 2 mL oleylamine, a solution of 0.2 mmol gallium chloride mixed with 2 mL trioctylphosphine, and a solution of 1-dodecanethiol heated with sulfur to a concentration of 0.2 mol / L were each added dropwise to a solution containing dispersed nanoparticles in a flask heated to 280°C, and held for 20 minutes.

[0080] After the reaction was complete, the mixture was cooled to room temperature, ethanol was added to precipitate the reaction solution, and the supernatant was removed by centrifugation. The same purification was repeated, and the solution was dispersed in 10 mL of oleylamine and 4 mL of 1-dodecanethiol in a flask. The flask was then purged with nitrogen gas to create an inert atmosphere.

[0081] A solution of 0.1 mmol of gallium diethyldithiocarbamate mixed with 2 mL of oleylamine, and a solution of 1-dodecanethiol heated with sulfur to a concentration of 0.2 mol / L, were each added dropwise to a solution containing dispersed nanoparticles in a flask heated to 230°C, and held for 5 minutes.

[0082] After the reaction was complete, the mixture was cooled to room temperature, ethanol was added to precipitate the reaction solution, and the supernatant was removed by centrifugation. The same purification was performed again, and the resulting mixture was dispersed in 10 mL of octadecene and 4 mL of 1-dodecanethiol in a flask. The flask was then purged with nitrogen gas to create an inert atmosphere.

[0083] 0.2 mmol of zinc acetate, 2 mL of oleic acid, and 2 mL of octadecene were mixed and heated under reduced pressure at 120°C with stirring, and degassed for 1 hour while dissolving the raw materials. 1 mL of a solution prepared by adding sulfur to 1-dodecanethiol and heating to adjust it to 0.2 mol / L was added dropwise to a solution containing dispersed nanoparticles in a flask heated to 230°C, and the zinc solution was added dropwise for 60 minutes to produce chalcopyrite-based quantum dots having a core-shell structure composed of AgAlGaSe / AgGaS / Ga2S3 / ZnS.

[0084] The emission wavelength, fluorescence full width at half maximum (FWHM), and fluorescence emission efficiency (internal quantum efficiency) of quantum dots at an excitation wavelength of 450 nm were measured. The emission wavelength was 618 nm, the FWHM was 29 nm, and the internal quantum efficiency was 80%.

[0085] (Example 4) (Nanoparticle production process) 0.3 mmol of silver nitrate, 0.1 mmol of copper(I) iodide, and 10 mL of oleylamine were added to a flask. The mixture was heated and stirred under reduced pressure at 100°C for 1 hour while dissolving the starting materials. After that, nitrogen was purged into the flask to create an inert atmosphere.

[0086] A 1.5 mL solution of oleylamine mixed with diphenyl diterlide and adjusted to a concentration of 0.2 mol / L was added dropwise to a solution in a flask heated to 150°C and held for 30 minutes. The solution changed from colorless to brown, confirming the formation of nanoparticles.

[0087] (Cation diffusion process) Next, a solution was prepared by dispersing 0.5 mmol of indium nitrate in 2 mL of oleylamine. This solution was added to the reaction solution after nanoparticle synthesis, which had been heated to 260°C, and held for 40 minutes. The resulting solution was cooled to room temperature, and chalcopyrite-based quantum dots (cores) made of AgCuInTe were synthesized.

[0088] (Shell formation process) After the reaction was complete, the mixture was cooled to room temperature, ethanol was added to precipitate the reaction solution, and the supernatant was removed by centrifugation. The same purification was repeated, and the solution was dispersed in 10 mL of oleylamine and 4 mL of 1-dodecanethiol in a flask. The flask was then purged with nitrogen gas to create an inert atmosphere.

[0089] A solution of 0.4 mmol of zinc bromide mixed with 2 mL of trioctylphosphine, and a solution of 1-dodecanethiol heated with sulfur to a concentration of 0.2 mol / L, were each added dropwise to a solution containing dispersed nanoparticles in a flask heated to 200°C, and the mixture was allowed to react for 60 minutes to produce chalcopyrite-based quantum dots with a core-shell structure composed of AgCuInTe / ZnS.

[0090] The emission wavelength, fluorescence full width at half maximum (FWHM), and fluorescence emission efficiency (internal quantum efficiency) of quantum dots at an excitation wavelength of 450 nm were measured. The emission wavelength was 1018 nm, the FWHM was 60 nm, and the internal quantum efficiency was 50%.

[0091] (Comparative Example 1) 0.3 mmol of silver acetate, 0.12 mmol of indium acetylacetonate, and 0.24 mmol of gallium acetylacetonate were dispersed in a flask, and nitrogen was purged into the flask to create an inert atmosphere.

[0092] A chalcopyrite-based quantum dot made of AgInGaS2 was synthesized by adding sulfur to 1-dodecanethiol, heating it to adjust the solution to 0.2 mol / L, and then adding 1.5 mL of the aforementioned silver solution dropwise to a solution in a flask heated to 280°C and allowing it to react for 20 minutes.

[0093] After the reaction was complete, the mixture was cooled to room temperature, ethanol was added to precipitate the reaction solution, and the supernatant was removed by centrifugation. The same purification was repeated, and the solution was dispersed in 10 mL of oleylamine and 4 mL of 1-dodecanethiol in a flask. The flask was then purged with nitrogen gas to create an inert atmosphere.

[0094] A solution of 0.9 mmol of gallium bromide mixed with 2 mL of trioctylphosphine, and a solution of 1-dodecanethiol heated with sulfur to a concentration of 0.2 mol / L, were each added dropwise to a solution containing dispersed nanoparticles in a flask heated to 240°C, and the mixture was allowed to react for 30 minutes to create chalcopyrite-based quantum dots with a core-shell structure composed of AgInGaS2 / Ga2S3.

[0095] After the reaction was complete, the mixture was cooled to room temperature, ethanol was added to precipitate the quantum dots, and the supernatant was removed by centrifugation. The same purification process was repeated, and the mixture was dispersed in toluene.

[0096] The emission wavelength, fluorescence full width at half maximum (FWHM), and fluorescence emission efficiency (internal quantum efficiency) of quantum dots at an excitation wavelength of 450 nm were measured. The emission wavelength was 541 nm, the FWHM was 67 nm, and the internal quantum efficiency was 53%.

[0097] (Comparative Example 2) 0.36 mmol of indium acetylacetonate, 0.25 mmol of gallium acetylacetonate, and 10 mL of oleylamine were dispersed in a flask, and nitrogen was purged into the flask to create an inert atmosphere.

[0098] A solution of 0.3 mmol of silver acetate and 1 mL of oleylamine, and a solution of 0.03 mmol of copper(I) acetate and 1 mL of oleylamine were both heated and stirred under reduced pressure at 100°C for 1 hour while dissolving the raw materials. Then, the solutions in the flasks were heated to 290°C, and the silver and copper solutions were added dropwise, respectively, and held for 60 minutes.

[0099] One mL of a solution prepared by adding sulfur to 1-dodecanethiol and heating it to adjust the concentration to 0.2 mol / L, and one mL of a solution prepared by adding selenium to 1-dodecanethiol and heating it to adjust the concentration to 0.2 mol / L, were each added dropwise to a solution in a flask heated to 150°C and held for 20 minutes.

[0100] After the reaction was complete, the mixture was cooled to room temperature, ethanol was added to precipitate the reaction solution, and the supernatant was removed by centrifugation. The same purification was repeated, and the solution was dispersed in 10 mL of oleylamine and 4 mL of 1-dodecanethiol in a flask. The flask was then purged with nitrogen gas to create an inert atmosphere.

[0101] A solution of 0.4 mmol of zinc bromide mixed with 2 mL of trioctylphosphine, and a solution of 1-dodecanethiol heated with sulfur to a concentration of 0.2 mol / L, were each added dropwise to a solution containing dispersed nanoparticles in a flask heated to 200°C, and the mixture was allowed to react for 60 minutes to synthesize chalcopyrite-based quantum dots having a core-shell structure composed of AgCuInGaSSe / ZnS.

[0102] After the reaction was complete, the mixture was cooled to room temperature, ethanol was added to precipitate the quantum dots, and the supernatant was removed by centrifugation. The same purification process was repeated, and the mixture was dispersed in toluene.

[0103] The emission wavelength, fluorescence full width at half maximum (FWHM), and fluorescence emission efficiency (internal quantum efficiency) of quantum dots at an excitation wavelength of 450 nm were measured. The emission wavelength was 680 nm, the FWHM was 84 nm, and the internal quantum efficiency was 55%.

[0104] (Comparative Example 3) 0.5 mmol of gallium acetylacetonate, 0.05 mmol of aluminum acetylacetonate, and 10 mL of oleylamine were dispersed in a flask, and the flask was purged with nitrogen to create an inert atmosphere.

[0105] A solution of 0.3 mmol of silver diethyldithiocarbamate mixed with 1 mL of oleylamine, and 1.5 mL of a solution of 1-dodecanethiol heated with selenium to a concentration of 0.2 mol / L, were each added dropwise to a solution in a flask heated to 280°C and held for 20 minutes.

[0106] Next, a solution of 0.2 mmol silver bromide mixed with 2 mL oleylamine, a solution of 0.2 mmol gallium chloride mixed with 2 mL trioctylphosphine, and a solution of 1-dodecanethiol heated with sulfur to a concentration of 0.2 mol / L were each added dropwise to a solution containing dispersed nanoparticles in a flask heated to 280°C, and held for 20 minutes.

[0107] After the reaction was complete, the mixture was cooled to room temperature, ethanol was added to precipitate the reaction solution, and the supernatant was removed by centrifugation. The same purification was repeated, and the solution was dispersed in 10 mL of oleylamine and 4 mL of 1-dodecanethiol in a flask. The flask was then purged with nitrogen gas to create an inert atmosphere.

[0108] A solution prepared by mixing 0.1 mmol of gallium diethyldithiocarbamate and 10 mL of oleylamine, and a solution prepared by adding sulfur to 1-dodecanethiol and heating it to adjust the concentration to 0.2 mol / L, were each added dropwise to a solution containing dispersed nanoparticles in a flask heated to 230°C, and held for 5 minutes.

[0109] After the reaction was complete, the mixture was cooled to room temperature, ethanol was added to precipitate the reaction solution, and the supernatant was removed by centrifugation. The same purification was performed again, and the resulting mixture was dispersed in 10 mL of octadecene and 4 mL of 1-dodecanethiol in a flask. The flask was then purged with nitrogen gas to create an inert atmosphere.

[0110] 0.2 mmol of zinc acetate, 2 mL of oleic acid, and 2 mL of octadecene were mixed and heated under reduced pressure at 120°C with stirring, degassing for 1 hour while dissolving the raw materials. 1 mL of a solution prepared by adding sulfur to 1-dodecanethiol and heating to adjust it to 0.2 mol / L was added dropwise to a solution containing dispersed nanoparticles in a flask heated to 230°C, and the zinc solution was added dropwise for 60 minutes to synthesize chalcopyrite-based quantum dots having a core-shell structure composed of AgAlGaSe / AgGaS / Ga2S3 / ZnS.

[0111] The emission wavelength, fluorescence full width at half maximum (FWHM), and fluorescence emission efficiency (internal quantum efficiency) of quantum dots at an excitation wavelength of 450 nm were measured. The emission wavelength was 642 nm, the FWHM was 78 nm, and the internal quantum efficiency was 61%.

[0112] (Comparative Example 4) 0.3 mmol of silver nitrate, 0.1 mmol of copper(I) iodide, 0.5 mmol of indium nitrate, and 10 mL of oleylamine were added to a flask. The mixture was heated and stirred under reduced pressure at 100°C for 1 hour while dissolving the starting materials. After that, nitrogen was purged into the flask to create an inert atmosphere.

[0113] 1.5 mL of a solution prepared by mixing oleylamine with diphenyl diterlide to a concentration of 0.2 mol / L was added dropwise to a solution in a flask heated to 150°C, and the flask was further heated to 260°C and held for 30 minutes.

[0114] After the reaction was complete, the mixture was cooled to room temperature, ethanol was added to precipitate the reaction solution, and the supernatant was removed by centrifugation. The same purification was repeated, and the solution was dispersed in 10 mL of oleylamine and 4 mL of 1-dodecanethiol in a flask. The flask was then purged with nitrogen gas to create an inert atmosphere.

[0115] A solution of 0.4 mmol of zinc bromide mixed with 2 mL of trioctylphosphine, and a solution of 1-dodecanethiol heated with sulfur to a concentration of 0.2 mol / L, were each added dropwise to a solution containing dispersed nanoparticles in a flask heated to 200°C, and the mixture was allowed to react for 60 minutes to produce chalcopyrite-based quantum dots with a core-shell structure composed of AgCuInTe / ZnS.

[0116] The emission wavelength, fluorescence full width at half maximum (FWHM), and fluorescence emission efficiency (internal quantum efficiency) of quantum dots at an excitation wavelength of 450 nm were measured. The emission wavelength was 1082 nm, the FWHM was 114 nm, and the internal quantum efficiency was 19%.

[0117] As described above, according to the embodiments of the present invention, it was possible to synthesize chalcopyrite-based quantum dots in which the emission wavelength was controlled from the visible region to the near-infrared region and which had a good full width at half maximum. This demonstrates that quantum dots with uniform composition and consistent particle size, possessing excellent emission characteristics, could be synthesized.

[0118] This specification includes the following embodiments: [1]: A method for synthesizing chalcopyrite-based quantum dots, comprising a nanoparticle generation step of reacting a group I element with a group VI element to produce nanoparticles, and a cation diffusion step of cationally diffusing a group III element into the nanoparticles by heat treatment. [2] A method for synthesizing the quantum dots described in [1], wherein the Group I element comprises one or more elements selected from Ag, Cu, Au, Na, K, and Cs, the Group III element comprises one or more elements selected from Ga, In, Al, and Tl, and the Group VI element comprises one or more elements selected from S, Se, and Te. [3]: A method for synthesizing the quantum dots according to [1] or [2] above, comprising the chalcopyrite-based quantum dots containing four or more constituent elements. [4]: A method for synthesizing the quantum dots according to [1], [2], or [3], wherein the chalcopyrite-based quantum dot has a emission full width at half maximum of 60 nm or less and an emission quantum yield of 50% or more. [5]: A method for synthesizing the quantum dots according to [1], [2], [3], or [4], comprising the chalcopyrite-based quantum dot having a core-shell structure.

[0119] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and achieves similar effects is included within the technical scope of the present invention.

Claims

1. A method for synthesizing chalcopyrite-based quantum dots, A nanoparticle production process involves reacting a group I element with a group VI element to produce nanoparticles, A method for synthesizing quantum dots, characterized by including a cation diffusion step in which a group III element is cationically diffused into the nanoparticles by heat treatment.

2. The aforementioned Group I element includes one or more elements selected from Ag, Cu, Au, Na, K, and Cs. The aforementioned Group III element includes one or more elements selected from Ga, In, Al, and Tl. The method for synthesizing quantum dots according to claim 1, characterized in that the group VI element includes one or more elements selected from S, Se, and Te.

3. The method for synthesizing quantum dots according to claim 1 or 2, characterized in that the chalcopyrite-based quantum dot contains four or more constituent elements.

4. The method for synthesizing quantum dots according to claim 1 or 2, characterized in that the chalcopyrite-based quantum dot has a emission half-width of 60 nm or less and an emission quantum yield of 50% or more.

5. The method for synthesizing quantum dots according to claim 1 or 2, characterized in that the chalcopyrite-based quantum dot has a core-shell structure.