Quantum dot and preparation method thereof

Abstract

The invention discloses a quantum dot preparation method which comprises the following steps: S100, mixing a first indium source, a first gallium source, a first sulfur source and a first solvent to obtain a first mixed solution, mixing a first silver source and a second solvent to obtain a second mixed solution, and respectively preheating the first mixed solution and the second mixed solution; s200, in an inert atmosphere, mixing the first mixed solution and the second mixed solution, heating for reaction, purifying a nuclear product from the reacted mixed solution, and dissolving the nuclear product in a third solvent to prepare a third mixed solution; s300, mixing a second gallium source, a second sulfur source and a fourth solvent, heating and stirring to obtain a fourth mixed solution, mixing the fourth mixed solution with the third mixed solution, and heating for reaction; s400, adding a third gallium source and a third sulfur source into the mixed solution to react so as to coat the shell layer; and S500, the step S400 is repeated for multiple times, the gallium source used for coating the shell layer each time and the gallium source used for coating the shell layer last time are different types of gallium sources, and the quantum dots are prepared.

Description

Technical Field

[0001] The present application relates to the field of quantum dot light conversion technology, and in particular to a quantum dot and a preparation method thereof. Background Art

[0002] Traditional lead- and cadmium-based quantum dots contain heavy metals such as lead and cadmium, which are highly biotoxic and environmentally polluting, severely hindering their practical application and development. Group I-III-VI quantum dots, however, are environmentally friendly due to their lack of lead and cadmium. Furthermore, due to their tunable band gap, large absorption coefficient, high light radiation stability, and large Stokes shift, Group I-III-VI quantum dots have become a research hotspot in fields such as displays, photovoltaic devices, and bioimaging.

[0003] I-III-VI group quantum dots primarily include ternary quantum dots such as silver indium sulfide (AgInS2), copper indium sulfide (CuInS2), and silver gallium sulfide (AgGaS2). However, these quantum dots primarily emit light through electron transitions generated by defect energy levels, and exhibit a broad spectral characteristic of defect-state emission, with a spectral width greater than 80nm. In contrast, quaternary quantum dots can be adapted to a variety of applications by adjusting their composition. Therefore, non-stoichiometric Ag-In-Ga-S quaternary quantum dots have been prepared by alloying AgInS2 and AgGaS2. However, their half-width (FWHM) is still wider than that of cadmium-based quantum dots. Therefore, there is an urgent need to develop I-III-VI group quantum dots with a simpler production process, higher stability, and a narrower FWHM. Summary of the Invention

[0004] One object of the present application is to provide a quantum dot and a preparation method thereof, which is conducive to reducing the full width at half maximum of the quantum dot and preparing quantum dots with a narrow spectral band.

[0005] Another object of the present application is to provide a quantum dot and a preparation method thereof, which is conducive to reducing the risk of defective state luminescence and improving the quantum fluorescence yield, performance and stability of the quantum dots.

[0006] Another object of the present application is to provide a quantum dot and a preparation method thereof, which is conducive to simplifying the production process and further reducing the production cost consumed during preparation.

[0007] To achieve the above objectives, the technical solution adopted in this application is: a method for preparing quantum dots, characterized in that it includes the steps of: S100, mixing a first indium source, a first gallium source, a first sulfur source, and a first solvent to obtain a first mixed liquid, mixing a first silver source and a second solvent to obtain a second mixed liquid, and preheating the first mixed liquid and the second mixed liquid respectively; S200, under an inert atmosphere, mixing the first mixed solution and the second mixed solution, heating the mixture to react, purifying a nuclear product from the reaction mixture, and dissolving the nuclear product in a third solvent to prepare a third mixed solution; S300, mixing a second gallium source, a second sulfur source, and a fourth solvent, heating and stirring, to obtain a fourth mixed liquid, mixing the fourth mixed liquid with the third mixed liquid, and heating to react; S400: After a period of reaction in step S300, a third gallium source and a third sulfur source are added to the mixed solution to react to form a shell layer; S500, repeating step S400 multiple times, wherein the gallium source used in each coating shell layer is a different type of gallium source from the gallium source used in the previous coating shell layer, and purifying the product from the reaction mixture to obtain the quantum dots.

[0008] In some embodiments, the first gallium source is the same as the second gallium source, the third gallium source is different from the second gallium source, and the first gallium source, the second gallium source, the third gallium source, and the gallium source used in step S500 are each independently selected from a mixture of one or more of the following: gallium acetylacetonate, gallium chloride, gallium iodide, gallium bromide, and gallium diethyldithiocarbamate.

[0009] In some embodiments, the first indium source is one or more of indium acetylacetonate, indium chloride, indium iodide, indium diethyldithiocarbamate, indium nitrate, indium bromide, and indium acetate; the first sulfur source and the second sulfur source are each independently selected from a mixture of one or more of the following: sulfur powder, N,N-diphenylthiourea, thiourea, 1,3-dimethylthiourea, and gallium diethyldithiocarbamate; and the first silver source is one or more of silver acetate, silver fluoride, silver chloride, silver bromide, silver iodide, and silver trifluoroacetate.

[0010] In some embodiments, the first solvent, the second solvent, and the fourth solvent are each independently selected from a mixture of one or more of the following: 1-octadecene, oleic acid, oleylamine, octadecylamine, n-dodecyl mercaptan, and octanol; the third solvent is one or more of 1-octadecene, toluene, chloroform, dichloromethane, n-octane, n-hexane, cyclohexane, xylene, and isobornyl acrylate.

[0011] In some embodiments, the particle size of the core product is 2 nm to 5 nm, and the thickness of the shell layer of a single coating is 0.2 nm to 0.4 nm; in the step S500, the number of the coating shell layers is not greater than 5.

[0012] In some embodiments, in step S100, the temperature for mixing the first indium source, the first gallium source, the first sulfur source and the first solvent is 60°C~120°C; in step S300, the temperature for heating and stirring the second gallium source, the second sulfur source and the fourth solvent is 60°C~120°C; in step S200, the reaction temperature for heating the first mixed liquid and the second mixed liquid is 130°C~280°C, the reaction time is 1min~120min, and the heating rate is 2°C / min~20°C / min.

[0013] In some embodiments, in step S300, the third mixed liquid and the fourth mixed liquid are heated to react at a reaction temperature of 240°C to 310°C, a reaction time of 1 min to 120 min, and a heating rate of 2°C / min to 20°C / min.

[0014] In some embodiments, step S200 specifically includes the steps of: mixing the first mixed liquid and the second mixed liquid under an inert atmosphere, heating the mixture for reaction, lowering the temperature of the mixture and adding an antisolvent, and placing the product obtained by centrifugal separation into a third solvent to obtain a core product; and step S500 specifically includes the steps of: repeating step S400 multiple times, and the gallium source used for each coating shell layer is a different type of gallium source from the gallium source used for the previous coating shell layer. After the coating is completed, the temperature of the mixture is lowered and an antisolvent is added, and the product obtained by centrifugal separation is placed in a fifth solvent to obtain quantum dots.

[0015] In some embodiments, the anti-solvent is one or more of ethyl acetate, methanol, ethanol, isopropanol and acetone tert-butanol, and the fifth solvent is one or more of 1-octadecene, toluene, chloroform, dichloromethane, n-octane, n-hexane, cyclohexane, xylene, and isobornyl acrylate.

[0016] To achieve the above objectives, the present application also provides quantum dots prepared by the aforementioned preparation method.

[0017] Compared with the prior art, the present invention has the following advantages: (1) This application is to coat the core of Ag-In-Ga-S quantum dots (AIGS quantum dots) with multilayer gallium sulfide (GaS y ) shell, passivating the defect states in the internal structure, which is beneficial to reducing the half-peak width of the quantum dots and preparing quantum dots with narrow spectral bands, further optimizing the luminescence performance of the quantum dots, and improving the high monochromaticity of the quantum dots, which is beneficial to reducing the risk of defect state luminescence and improving the performance and stability of the quantum dots.

[0018] (2) This application uses the same gallium source when coating the core layer for the first time, thereby enhancing the initial adhesion between the core and the shell layer, increasing the stability of the quantum dots in use, and reducing the risk of removal. Furthermore, when coating the shell layer, different gallium sources are used to coat adjacent shell layers, which is beneficial to further improve the defect state luminescence phenomenon, reduce the full width at half maximum of the quantum dots, and improve the uniformity of the size distribution of the quantum dots. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the photoluminescence spectrum of the quantum dots in Example 1 of this application.

[0020] Figure 2 This is the absorption spectrum of the quantum dots in Example 1 of this application.

[0021] Figure 3 1 to 3 and comparative examples 1 to 3 of the present application. DETAILED DESCRIPTION

[0022] Below, the present application is further described in conjunction with specific implementation methods. It should be noted that, under the premise of no conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0023] In the description of this application, it should be noted that for directional words, such as the terms "center", "horizontal", "longitudinal", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and so on, indicating the direction and position relationship are based on the direction or position relationship shown in the accompanying drawings, which is only for the convenience of describing this application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and cannot be understood as limiting the specific scope of protection of this application.

[0024] It should be noted that the terms "first", "second", etc. in the description and claims of this application are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence.

[0025] The terms "comprises" and "having" and any variations thereof in the specification and claims of this application are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus that includes a series of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, product or apparatus.

[0026] To achieve the above objectives, the technical solution adopted in this application is: a method for preparing quantum dots, comprising the steps of: S100, mixing a first indium source, a first gallium source, a first sulfur source, and a first solvent to obtain a first mixed liquid, mixing a first silver source and a second solvent to obtain a second mixed liquid, and preheating the first mixed liquid and the second mixed liquid respectively; S200, mixing the first mixed solution and the second mixed solution under an inert atmosphere, heating the mixture to react, purifying a nuclear product from the reaction mixture, and dissolving the nuclear product in a third solvent to prepare a third mixed solution; S300, mixing the second gallium source, the second sulfur source and the fourth solvent, heating and stirring to obtain a fourth mixed liquid, mixing the fourth mixed liquid with the third mixed liquid, and heating to react; S400: After a period of reaction in step S300, a third gallium source and a third sulfur source are added to the mixed solution to react to form a shell layer; S500, repeating step S400 multiple times, wherein the gallium source used in each coating shell layer is a different type of gallium source from the gallium source used in the previous coating shell layer, and purifying the product from the reaction mixture to obtain quantum dots.

[0027] The present invention is to coat the core of Ag-In-Ga-S quantum dots (AIGS quantum dots) with multilayer gallium sulfide (GaS y ) shell, passivating defect states within the internal structure, helps reduce the full width at half maximum (FWHM) of the quantum dots and produce quantum dots with narrow spectral bands. This further optimizes the luminescence performance and quantum fluorescence yield of the quantum dots, enhances their high monochromaticity, reduces the risk of defect-state luminescence, and improves the performance and stability of the quantum dots. Furthermore, by using different gallium sources for coating adjacent shells during shell coating, defect-state luminescence can be further improved, reducing the full width at half maximum (FWHM) of the quantum dots and improving the uniformity of their size distribution.

[0028] In some embodiments, the first gallium source is the same as the second gallium source, the third gallium source is different from the second gallium source, and the first gallium source, the second gallium source, the third gallium source, and the gallium source used in step S500 are each independently selected from a mixture of one or more of the following: gallium acetylacetonate, gallium chloride, gallium iodide, gallium bromide, and gallium diethyldithiocarbamate. Specifically, by selecting the same gallium source when the core layer is first coated with the shell layer, the initial adhesion between the core part and the shell layer is enhanced, the stability of the quantum dots is increased, and the risk of removal is reduced. Moreover, the use of different gallium sources for coating the outer layer is conducive to passivating the internal defects of the quantum dots. Compared with the use of a single gallium source for the preparation of core products and multi-layer coated shells, a single gallium source is more difficult to coat multiple shells. Therefore, the quantum dots prepared in this application have good stability in use and processing performance. It is worth mentioning that the rational selection of the gallium source is conducive to precise control of reaction kinetics, optimization of crystal structure, and thus improvement of defect passivation efficiency. Among them, gallium acetylacetonate (Ga(acac)3) can slow down the release rate of gallium ions, reduce the phenomenon of explosive nucleation, and improve the size uniformity of quantum dots; gallium chloride (GaCl3), gallium iodide (GaI3), gallium bromide (GaBr3) and gallium diethyldithiocarbamate (Ga(DDTC)3) can stably provide gallium ions, which is beneficial to enhance the stability and uniformity of quantum dots and further reduce the risk of defect state luminescence.

[0029] In some embodiments, the multiple coated shells can be named from the inside to the outside as the first shell, the second shell, the third shell, the fourth shell, and the fifth shell, etc., wherein the gallium source used in each coating shell is a different type of gallium source from the gallium source used in the previous coating shell. That is, an unused gallium source is used for coating between the first shell and the second shell, an unused gallium source is used for coating between the second shell and the third shell, an unused gallium source is used for coating between the third shell and the fourth shell, and an unused gallium source is used for coating between the fourth shell and the fifth shell.

[0030] In some embodiments, when the outer layer of the quantum dot has been coated with a certain amount of GaS y After the shell layer, the outer layer can also be coated with other materials of the same or different types, and this application is not limited to this. For example, the outer surface of the quantum dots obtained in step S500 can be coated with a zinc sulfide shell layer, which is beneficial to eliminate GaS y The surface scattering of the shell and the luminescence phenomenon of interface defects further reduce the full width at half maximum, thereby enhancing the performance of quantum dots.

[0031] In some embodiments, the first indium source is one or more of indium acetylacetonate, indium chloride, indium iodide, indium diethyldithiocarbamate, indium nitrate, indium bromide, and indium acetate. It is understood that the appropriate selection of the indium source facilitates precise control of reaction kinetics and improves element incorporation efficiency. The acetylacetonate group in indium acetylacetonate (In(acac)3) can slow the release rate of the indium element, enabling controlled nucleation and improving size uniformity. Indium chloride (InCl3), indium iodide (InI3), and indium bromide (InBr3) exhibit excellent reactivity and can rapidly release indium ions at low temperatures, thereby shortening synthesis time. Indium diethyldithiocarbamate (In(DDTC)3) can simultaneously provide indium and sulfur ions, further reducing sulfur usage and thus production costs. The high solubility of indium nitrate (In(NO3)3) and the environmentally friendly nature of indium acetate (In(OOCCH3)3) facilitate the preparation of quantum dots.

[0032] In some embodiments, the first sulfur source and the second sulfur source are each independently selected from a mixture of one or more of the following: sulfur powder, N,N-diphenylthiourea, thiourea, 1,3-dimethylthiourea, and gallium diethyldithiocarbamate. Specifically, by properly selecting the sulfur source, such as thiourea and 1,3-dimethylthiourea, which have good solubility, they are more evenly dispersed in the reaction system, thereby improving reaction efficiency and quantum dot uniformity. Furthermore, although sulfur powder has relatively low reactivity, it facilitates uniform synthesis, further reducing the problem of uneven quantum dot size caused by excessively fast reaction rates and facilitating the control of quantum dot preparation size and morphology.

[0033] In some embodiments, the first silver source is one or more of silver acetate, silver fluoride, silver chloride, silver bromide, silver iodide, and silver trifluoroacetate. It is worth noting that selecting an appropriate silver source facilitates controlling the reaction rate and, further, the size and morphology of the quantum dots. Among them, silver acetate, silver chloride, silver bromide, and silver iodide have good solubility properties and can release silver ions at a moderate reaction rate during the reaction, thereby enhancing the uniformity of quantum dot preparation and performance.

[0034] In some embodiments, the first solvent, the second solvent, and the fourth solvent are each independently selected from a mixture of one or more of the following: 1-octadecene, oleic acid, oleylamine, octadecylamine, n-dodecyl mercaptan, and octanethiol; and the third solvent is one or more of 1-octadecene, toluene, chloroform, dichloromethane, n-octane, n-hexane, cyclohexane, xylene, and isobornyl acrylate. The selection of a chemically stable storage solvent provides a stable chemical environment for the preparation of quantum dots, thereby improving the uniformity of the quantum dots.

[0035] In some embodiments, the particle size of the core product is 2nm~5nm, specifically, the particle size of the core product is 2nm, 2.5nm, 3nm, 3.5nm, 4nm, 4.5nm, and 5nm. Further preferably, the particle size of the core product is 3nm~4nm, and the thickness of the shell layer of a single coating is 0.2nm~0.4nm, specifically, the thickness of the shell layer of a single coating is 0.2nm, 0.25nm, 0.3nm, 0.35nm, and 0.4nm; in step S800, the number of coating shell layers is not more than 5, specifically, the number of coating shell layers is 1, 2, 3, 4, and 5, and the steps can be repeated multiple times to coat different gallium sources until the target number of layers is reached. It is understandable that although the shell coating on the surface of Ag-In-Ga-S quaternary quantum dots can achieve spectral narrowband edge emission, when the coating shell is thick, the luminescence efficiency of the quantum dots will be reduced, and when the coating shell is thin, the defect state luminescence phenomenon is still more obvious. At this time, the internal defect state is not fully passivated, so that the quantum dots after the shell coating have a smaller half-peak width (<40nm) than the quantum dots without the shell coating, but still wider than the half-peak full width of the cadmium-based quantum dots. However, the present application not only achieves the same effect when coating GaS with different thicknesses, but also achieves the same effect when coating GaS with different thicknesses. y After the shell, the full width at half maximum of the quantum dot does not change, while suppressing the defect state emission phenomenon of GaS y The shell thickness is increased, further reducing the full width at half maximum of the quantum dots and increasing the quantum fluorescence yield.

[0036] Among them, when coated with GaS y When the shell thickness is thin, the defect state luminescence phenomenon of quantum dots is more obvious, and the full width at half maximum is still maintained above 30nm. At this time, the luminescence performance and performance of quantum dots are poor. When the GaS y When the shell thickness is too large, the lattice mismatch between the core product and the shell leads to stress accumulation, which further causes non-radiative recombination of the quantum dots, resulting in energy dissipation and reducing the luminescence efficiency of the quantum dots.

[0037] On the other hand, the GaS coating y The particle size range of the quantum dots after the shell layer is 4.5nm~5.5nm. Specifically, the particle size range is 4.5nm, 4.6nm, 4.7nm, 4.8nm, 4.9nm, 5.0nm, 5.1nm, 5.2nm, 5.3nm, 5.4nm, 5.5nm. When coated with GaS y As the shell thickness gradually increases within an appropriate range, the full width at half maximum of the quantum dots gradually decreases, reaching a minimum of 26 nm. This indicates that the prepared AIGS quantum dots have good size distribution uniformity, and the luminescence phenomenon of the quantum dots is mainly concentrated in a very narrow wavelength range, with good monochromaticity.

[0038] In some embodiments, in step S100, the temperature for the mixed treatment of the first indium source, the first gallium source, the first sulfur source and the first solvent is 60°C~120°C, specifically, the treatment temperature is 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C; in step S300, the temperature for the heated and stirred treatment of the second gallium source, the second sulfur source and the fourth solvent is 60°C~120°C, specifically, the treatment temperature is 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C; in step S200, the reaction temperature of the first mixed solution and the second mixed solution during the heated reaction is 130°C~280°C, specifically, the reaction temperature is 130°C~280°C. 0℃, 150℃, 170℃, 190℃, 210℃, 230℃, 250℃, 270℃, 280℃, the reaction time is 1min~120min, specifically, the reaction time is 1min, 10min, 30min, 40min, 50min, 60min, 70min, 80min, 90min, 100min, 120min, the heating rate is 2℃ / min~20℃ / min, specifically, the heating rate is 2℃ / min, 5℃ / min, 8℃ / min, 10℃ / min, 12℃ / min, 15℃ / min, 18℃ / min, 20℃ / min. Through appropriate reaction conditions, the performance and distribution uniformity of quantum dots can be improved, the half-peak width of quantum dots can be further reduced, and the luminescence performance can be enhanced.

[0039] In some embodiments, in step S300, the third mixed solution and the fourth mixed solution are heated at a reaction temperature of 240°C to 310°C, specifically 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, and 310°C; the reaction time is 1 min to 120 min, specifically 1 min, 10 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, and 120 min; and the heating rate is 2°C / min to 20°C / min, specifically 2°C / min, 5°C / min, 8°C / min, 10°C / min, 12°C / min, 15°C / min, 18°C / min, and 20°C / min. Appropriate reaction conditions can improve the performance and distribution uniformity of quantum dots, further reduce the half-value width of quantum dots, and enhance luminescence performance.

[0040] In some embodiments, step S200 specifically includes the steps of: mixing the first mixed liquid and the second mixed liquid under an inert atmosphere, heating the mixture for reaction, lowering the temperature of the mixture and adding an antisolvent, and placing the product obtained by centrifugal separation into a third solvent to obtain a core product; and step S500 specifically includes the steps of: repeating step S400 multiple times, and the gallium source used for each coating shell layer is a different type of gallium source from the gallium source used for the previous coating shell layer. After the coating is completed, lowering the temperature of the mixture and adding an antisolvent, and placing the product obtained by centrifugal separation into a fifth solvent to obtain quantum dots.

[0041] In some embodiments, the antisolvent is one or more of ethyl acetate, methanol, ethanol, isopropanol, and acetone-t-butyl alcohol. It is understood that the use of an antisolvent can rapidly reduce the solubility of the solution, allowing the quantum dots to precipitate rapidly from the solution and removing impurities such as unreacted indium source, gallium source, sulfur source, and solvent from the product. Furthermore, the quantum dots can be further purified by centrifugation to improve the purity of the quantum dot product.

[0042] In some embodiments, the fifth solvent is one or more of 1-octadecene, toluene, chloroform, dichloromethane, n-octane, n-hexane, cyclohexane, xylene, and isobornyl acrylate. Selecting a chemically stable storage solvent provides a stable chemical environment for the preparation of quantum dots, which helps improve the uniformity of the quantum dots.

[0043] To achieve the above objectives, the present application also provides quantum dots prepared by the above preparation method. The present application is to coat the core of Ag-In-Ga-S quantum dots (AIGS quantum dots) with multiple layers of gallium sulfide (GaS y ) shell, passivating the defect states in the internal structure, which is beneficial to reducing the half-peak width of the quantum dots and preparing quantum dots with narrow spectral bands, further optimizing the luminescence performance of the quantum dots, and improving the high monochromaticity of the quantum dots, which is beneficial to reducing the risk of defect state luminescence and improving the performance and stability of the quantum dots.

[0044] In some embodiments, the photoluminescence peak of the quantum dots prepared in the present application is located at 490nm~550nm, and the luminescence peak position can be regulated by regulating the ratio between silver ions, indium ions and gallium ions. For example, appropriately increasing the ratio of silver ions to indium ions and gallium ions helps to reduce the half-peak width of the quantum dots. The increase of indium ions can change the lattice parameters and band structure of the quantum dots, causing the emission wavelength to blue-shift, while improving the luminescence efficiency of the quantum dots. When the gallium ions are increased in an appropriate amount, the luminescence performance of the quantum dots can be optimized by adjusting the ratio of gallium ions to indium ions. However, an excessive increase in gallium ions may introduce more defect state structures into the quantum dots, resulting in an increase in the half-peak width of the quantum dots.

[0045] Example 1 A method for preparing quantum dots, characterized by comprising the steps of: (1) 0.4 mmol of InCl3, 0.7 mmol of Ga(DDTC)3 (the first gallium source), and 20 mL of oleylamine were mixed in a 100 mL three-necked flask and heated at 90 °C for 15 min until the raw materials were completely dissolved. The mixture was then heated to 150 °C at a heating rate of 5 °C / min under a nitrogen atmosphere. (2) Prepare a mixed solution of 0.5 mmol silver trifluoroacetate and 3 mL oleylamine; (3) Inject the mixture prepared in step S200 into the reaction system in step S100, heat them together to 200°C and react for 15 minutes, then cool them to room temperature to obtain a reaction stock solution; (4) The reaction stock solution: acetone: methanol in a ratio of 1:2:1 was centrifuged at 10,000 r / min for 5 min, and the precipitate was dissolved in 1 mL of 1-octadecene for later use to obtain the AIGS core product; (5) Dissolve 0.2 mmol of Ga(DDTC)3 and 0.2 mmol of gallium chloride (the second gallium source) in 20 mL of oleylamine and exhaust the mixture under nitrogen atmosphere at 90°C for 15 min to obtain a fourth liquid; (6) The fourth liquid was heated to 160°C at a rate of 5°C / min, 0.5 ml of AIGS nuclear product was injected to react and the temperature was continued to be raised to 300°C; (7) Inject 1 mL of 0.2 mmol / ml GaCl3 / oleylamine (third gallium source) solution and react for 15 minutes, then inject 1 mL of 0.2 mmol / ml Ga(DDTC)3 / oleylamine (fourth gallium source) solution and react for 15 minutes; (8) Inject 1 mL of a 0.2 mmol / ml Ga(acac)3 / oleylamine (fifth gallium source) solution and react for 15 minutes, then inject 1 mL of a 0.2 mmol / ml GaCl3 / oleylamine (sixth gallium source) solution and react for 15 minutes, and cool to room temperature to obtain a fifth liquid; (9) The fifth liquid: acetone: methanol was centrifuged at a mass ratio of 1:2:1 at a speed of 10000 r / min for 5 min, and the obtained precipitate was dissolved in 1 mL of toluene to prepare quantum dots.

[0046] Example 2 The difference between Example 2 and Example 1 is that step (7) is: injecting 1 mL of a 0.2 mmol / ml GaCl3 / oleylamine solution and reacting for 15 minutes (without the fourth gallium source).

[0047] Example 3 The difference between Example 3 and Example 1 is that step (8) is: inject 1 mL of Ga(acac)3 / oleylamine solution (fifth gallium source) with a concentration of 0.2 mmol / ml and react for 1 min, then inject 1 mL of S-OLA with a concentration of 0.3 mmol / mL and react for 15 min, inject 1 mL of GaCl3 / oleylamine solution (sixth gallium source) with a concentration of 0.2 mmol / ml and react for 1 min, inject 1 mL of S-OLA with a concentration of 0.3 mmol / mL and react for 15 min, inject 1 mL of GaI3 / OLA solution (seventh gallium source) with a concentration of 0.2 mmol / ml and react for 1 min, inject 1 mL of sulfur-oleylamine solution (S-OLA) with a concentration of 0.3 mmol / mL and react for 15 min, inject 1 mL of GaCl3 / OLA solution (eighth gallium source) with a concentration of 0.2 mmol / mL and react for 1 min, inject 1 mL of S-OLA with a concentration of 0.3 mmol / mL and react for 15 min, and cool to room temperature to obtain a fifth liquid.

[0048] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the steps are: 0.1 mmol of InCl₃, 0.15 mmol of Ga(DDTC)₃ (the first gallium source), 0.05 mmol of In(DDTC)₃, and 5 mL of oleylamine were mixed in a 50 mL three-necked flask. Stirring and evacuating the mixture at room temperature for 30 minutes until the raw materials were completely dissolved was complete. The mixture was then heated to 80°C and degassed for 5 minutes, followed by three nitrogen replacements. Under a nitrogen atmosphere, the temperature was maintained at 80°C until the powder in the flask was completely dissolved and the solution became clear. The target temperature was then set at 200°C. When the temperature reached 130°C, 0.5 mL of a 0.25 mol / L Ag(OAc)-OLA solution was rapidly injected. The temperature was then raised to 200°C and maintained for 20 minutes. After cooling to room temperature, the temperature was raised to 110°C and 50 μL of a 3 wt.% HF solution diluted with acetone was injected. The reaction mixture was held at 110°C for 30 minutes to etch the adsorption layer on the core product surface. The core product solution was then heated to 240°C for AGS shell coating. A certain amount of Ag2S NPs, Ga(OA)3-OLA (a second gallium source), and S-OLA shell precursors were sequentially injected to coat the AGS shell layer. Starting from the third AGS shell layer, an additional 10 mol / L GaCl3 solution (a third gallium source) dissolved in ethanol at the same molar amount as Ga(OA)3 was injected to promote effective shell coating. After coating five shell layers, the reaction mixture was cooled to room temperature and centrifuged at 10,000 rpm for 5 minutes using a 1:2:1 ratio of the reaction solution to acetone to methanol. The resulting precipitate was dissolved in 1 mL of toluene to produce quantum dots.

[0049] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that step (7) and step (8) are: (7) Inject 1 mL of 0.2 mmol / ml Ga(DDTC)3 / oleylamine (the first gallium source used for the core product) solution and react for 15 minutes; (8) Inject 1 mL of 0.2 mmol / ml Ga(DDTC)3 / oleylamine solution (first gallium source) and react for 15 minutes, then inject 1 mL of 0.2 mmol / ml Ga(DDTC)3 / oleylamine solution (first gallium source) and react for 15 minutes, then inject 1 mL of 0.2 mmol / ml Ga(DDTC)3 / oleylamine solution (first gallium source) and react for 15 minutes, and then cool to room temperature to obtain the fifth liquid.

[0050] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that step (5) is: (5) 0.4 mmol of Ga(acac)3 and 0.3 mmol of N,N'-dimethylthiourea (DMTU) were dissolved in 20 mL of oleylamine and evacuated under nitrogen atmosphere at 90°C for 15 min to prepare a fourth liquid.

[0051] Performance Testing The quantum dots prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were tested for wavelength, half-peak width, and quantum fluorescence yield using a fluorescence spectrometer. The test results are shown in Table 1.

[0052] Table 1: Performance test of quantum dots

[0053] like Figure 1 and Figure 2 As shown, the quantum dots prepared in Example 1 have narrow spectrum characteristics, with a half-peak width as low as 25.5 nm, and a photoluminescence peak located at 490 nm ~ 550 nm, indicating that the quantum dots have good luminescence performance and high monochromaticity, further improving the performance and stability of use.

[0054] Furthermore, it can be seen from Examples 1 to 3 that when the shell thickness is low, the quantum fluorescence yield is further reduced because the defect states inside the quantum dots are not passivated; when the shell thickness is high, stress accumulation occurs between the shells due to the lattice mismatch phenomenon, thereby increasing the half-width of the quantum dots and reducing the monochromaticity.

[0055] By comparing Example 1 with Comparative Examples 1 to Comparative Examples 3, when silver is doped in the shell, the quantum fluorescence yield of the quantum dots decreases significantly; when the same gallium source is used in adjacent shells, or when the core product and the adjacent shell use the same gallium source, the half-width of the quantum dots is wider and the luminescence performance of the quantum dots is poor.

[0056] The above describes the basic principles, main features, and advantages of the present application. Those skilled in the art should understand that the present application is not limited to the above-described embodiments. The above-described embodiments and the specification merely illustrate the principles of the present application. Various changes and improvements may be made to the present application without departing from the spirit and scope of the present application. These changes and improvements fall within the scope of the present application for which protection is sought. The scope of protection claimed by the present application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing quantum dots, characterized in that: Including steps: S100, mixing a first indium source, a first gallium source, a first sulfur source, and a first solvent to obtain a first mixed liquid, mixing a first silver source and a second solvent to obtain a second mixed liquid, and preheating the first mixed liquid and the second mixed liquid respectively; S200, under an inert atmosphere, mixing the first mixed solution and the second mixed solution, heating the mixture to react, purifying a nuclear product from the reaction mixture, and dissolving the nuclear product in a third solvent to prepare a third mixed solution; S300, mixing a second gallium source, a second sulfur source, and a fourth solvent, heating and stirring, to obtain a fourth mixed liquid, mixing the fourth mixed liquid with the third mixed liquid, and heating to react; S400: After a period of reaction in step S300, a third gallium source and a third sulfur source are added to the mixed solution to react to form a shell layer; S500, repeating step S400 multiple times, wherein the gallium source used in each coating shell layer is a different type of gallium source from the gallium source used in the previous coating shell layer, and purifying the product from the reaction mixture to obtain the quantum dots.

2. The preparation method according to claim 1, characterized in that The first gallium source is the same as the second gallium source, the third gallium source is different from the second gallium source, and the first gallium source, the second gallium source, the third gallium source and the gallium source used in step S500 are each independently selected from a mixture of one or more of the following: gallium acetylacetonate, gallium chloride, gallium iodide, gallium bromide, and gallium diethyldithiocarbamate.

3. The preparation method according to claim 1, characterized in that The first indium source is one or more of indium acetylacetonate, indium chloride, indium iodide, indium diethyldithiocarbamate, indium nitrate, indium bromide, and indium acetate; the first sulfur source and the second sulfur source are each independently selected from a mixture of one or more of the following: sulfur powder, N,N-diphenylthiourea, thiourea, 1,3-dimethylthiourea, and gallium diethyldithiocarbamate; the first silver source is one or more of silver acetate, silver fluoride, silver chloride, silver bromide, silver iodide, and silver trifluoroacetate.

4. The preparation method according to claim 1, characterized in that The first solvent, the second solvent and the fourth solvent are each independently selected from a mixture of one or more of the following: 1-octadecene, oleic acid, oleylamine, octadecylamine, n-dodecyl mercaptan, and octanol; the third solvent is one or more of 1-octadecene, toluene, chloroform, dichloromethane, n-octane, n-hexane, cyclohexane, xylene, and isobornyl acrylate.

5. The preparation method according to claim 1, characterized in that The particle size of the core product is 2 nm to 5 nm, and the thickness of the shell layer of a single coating is 0.2 nm to 0.4 nm; in the step S500, the number of the coating shell layers is not greater than 5.

6. The preparation method according to claim 1, characterized in that In the step S100, the temperature for mixing the first indium source, the first gallium source, the first sulfur source and the first solvent is 60°C to 120°C; in the step S300, the temperature for heating and stirring the second gallium source, the second sulfur source and the fourth solvent is 60°C to 120°C; in the step S200, the reaction temperature for heating the first mixed liquid and the second mixed liquid is 130°C to 280°C, the reaction time is 1 min to 120 min, and the heating rate is 2°C / min to 20°C / min.

7. The preparation method according to claim 1, characterized in that In step S300, the third mixed solution and the fourth mixed solution are heated to react at a temperature of 240°C to 310°C, a reaction time of 1 min to 120 min, and a heating rate of 2°C / min to 20°C / min.

8. The preparation method according to claim 1, characterized in that The step S200 specifically includes the steps of: mixing the first mixed solution and the second mixed solution under an inert atmosphere, heating the mixed solution to react, lowering the temperature of the mixed solution and adding an anti-solvent, and placing the product obtained by centrifugation into a third solvent to obtain a core product; as well as The step S500 specifically includes the steps of: repeating step S400 multiple times, and the gallium source used in each coating shell layer is a different type of gallium source from the gallium source used in the previous coating shell layer; after the coating is completed, lowering the temperature of the mixed solution and adding an anti-solvent; and placing the product obtained by centrifugal separation into a fifth solvent to obtain quantum dots.

9. The preparation method according to claim 8, characterized in that The anti-solvent is one or more of ethyl acetate, methanol, ethanol, isopropanol and acetone tert-butanol, and the fifth solvent is one or more of 1-octadecene, toluene, chloroform, dichloromethane, n-octane, n-hexane, cyclohexane, xylene and isobornyl acrylate.

10. A quantum dot, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 9.

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