A core-shell quantum dot, its preparation method and application

Abstract

This invention relates to a core-shell quantum dot, its preparation method, and its applications. The preparation method includes the following steps: (1) mixing an indium halogen source, a zinc halogen source, and oleylamine, and reacting at a temperature at least twice; mixing a phosphorus source and reacting at a temperature at least once to obtain a core; (2) sequentially coating the surface of the core with an inner shell layer, a transition layer, and an outer shell layer to form a shell layer, thereby obtaining a core-shell quantum dot. The core-shell quantum dots obtained by the preparation method of this invention have high fluorescence efficiency, narrow light emission half-width, high structural stability, and good photoelectro-induced compatibility. They can be prepared in a cadmium-free and low-biotoxic environment, making them environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of quantum dot technology, and in particular to a core-shell quantum dot, its preparation method, and its applications. Background Technology

[0002] Colloidal quantum dots are a type of semiconductor nanocrystal. They possess excellent optoelectronic properties, including tunable emission wavelength, a wide emission wavelength coverage, high fluorescence quantum yield, high brightness, broad color gamut, and high color purity. Based on these properties, colloidal quantum dots are widely used in solar lighting, novel displays, and medical labeling. Currently, cadmium-based quantum dots are commercially available, but their high biotoxicity due to the presence of heavy metals like cadmium limits their development. Therefore, cadmium-free and low-biotoxic quantum dot materials have emerged as a solution.

[0003] The most representative example is indium phosphide (InP) quantum dots, which possess the excellent photoelectric properties of cadmium-based quantum dots while ensuring that the material is cadmium-free and has low biotoxicity. However, compared with conventional cadmium-based quantum dots, current indium phosphide quantum dots still have many disadvantages: lower quantum yield, severe peak broadening, and poor stability.

[0004] CN112608752A discloses a core-shell InP / ZnSe / ZnS quantum dot and its preparation method and application. The preparation method includes the following steps: (1) mixing selenium powder with a first solvent until the selenium powder is completely dissolved or uniformly dispersed to obtain a selenium precursor; (2) mixing an indium source, a first zinc source, a phosphorus source, and a second solvent to prepare a first system; (3) mixing a second zinc source, a third solvent, and the first system obtained in step (2) to obtain a second system; (4) mixing a sulfur source, the selenium precursor obtained in step (1), and the second system obtained in step (3) to react and obtain core-shell InP / ZnSe / ZnS quantum dots; wherein the first solvent, the second solvent, and the third solvent are independently octadecene and / or oleylamine, respectively. The disclosed method produces a selenium precursor with higher activity, a simpler operating environment, and uses more environmentally friendly solvents, which helps the ZnSe transition layer to successfully coat the InP core surface.

[0005] CN112824477A discloses a method for preparing core-shell quantum dots and its application, comprising: (1) providing a solution containing quantum dots, wherein the solution containing quantum dots is a raw material for preparing core-shell quantum dots; (2) mixing the raw material for preparing core-shell quantum dots with short-chain fatty acid zinc with a carbon chain length of less than or equal to 8 and long-chain fatty acid with a carbon chain length of greater than or equal to 12, and reacting at a first temperature to obtain an intermediate solution; (3) mixing the intermediate solution with a precursor containing Se, and reacting at a second temperature to coat the surface of the quantum dots with a ZnSe shell layer to obtain a solution containing a core-shell quantum dot intermediate; (4) using the solution containing the core-shell quantum dot intermediate as the raw material for preparing core-shell quantum dots in step (1), and repeating steps (2) and (3) at least once for coating to obtain core-shell quantum dots. The quantum yield of the disclosed core-shell quantum dots remains above 95% with the increase of ZnSe shell layer thickness, thereby improving the external quantum efficiency and lifespan of optoelectronic devices using the core-shell quantum dots.

[0006] In the existing technology, the preparation methods of core-shell quantum dots have the following problems: (1) Conventional nucleation methods do not pay attention to the control of the environment system and reaction rate, resulting in uneven particle size of the generated indium phosphide cores, which directly affects the subsequent reaction; (2) Due to the large difference between the nucleation reaction system and the shelling reaction system, some materials of nucleation seriously affect the efficiency of shelling, and at the same time, the oxide complex impurities on the core surface inhibit the shell coating during the nucleation process; (3) There is a serious difference in lattice mismatch between the core and the adjacent shell, which leads to a decrease in the structural stability of the final quantum dot material; 4. Aliphatic acid ligands can easily fall off from the surface of quantum dots, which may lead to dangling bonds and surface defect states, and even quantum dot aggregation, which ultimately reduces the overall performance of quantum dot materials.

[0007] In conclusion, it is crucial to develop a core-shell quantum dot material that can solve the aforementioned technical problems. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a core-shell quantum dot, its preparation method, and its applications. The core-shell quantum dots prepared by the method exhibit high fluorescence efficiency, narrow emission half-width, high structural stability, and good photoelectro-induced compatibility. They can be prepared in an environment free of cadmium and with low biotoxicity, making them environmentally friendly.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a method for preparing core-shell quantum dots, the method comprising the following steps:

[0011] (1) Mix indium halogen source, zinc halogen source and oleylamine, and heat and react at least twice (e.g., 3 times, 4 times, 5 times, etc.). Mix phosphorus source and heat and react at least once (e.g., 2 times, 3 times, 4 times, 5 times, etc.) to obtain core;

[0012] (2) The inner shell, transition layer and outer shell are sequentially coated on the core surface to form a shell layer, thus obtaining a core-shell quantum dot.

[0013] In this invention, the nucleation stage in step (1) involves low-temperature nucleation and high-temperature growth to ensure the uniformity of the core. The introduction of the transition layer compensates for the lattice fit difference between the inner and outer shell layers, resulting in better structural stability of the quantum dot material. The core-shell quantum dots prepared by the method described in this invention have high fluorescence efficiency, narrow emission half-width, high structural stability, and good photoelectro-induced compatibility. They can be prepared in a cadmium-free and low-biotoxic environment, making them environmentally friendly.

[0014] Preferably, in step (1), the indium halogen source includes any one or a combination of at least two of indium fluoride, indium chloride, indium bromide or indium iodide, wherein typical but non-limiting combinations include: a combination of indium fluoride and indium chloride, a combination of indium chloride, indium bromide and indium iodide, a combination of indium fluoride, indium chloride, indium bromide and indium iodide, etc.

[0015] Preferably, the halogen zinc source includes any one or a combination of at least two of zinc fluoride, zinc chloride, zinc bromide, or zinc iodide, wherein typical but non-limiting combinations include: a combination of zinc fluoride and zinc chloride, a combination of zinc chloride, zinc bromide, and zinc iodide, a combination of zinc fluoride, zinc chloride, zinc bromide, and zinc iodide, etc.

[0016] Preferably, the phosphorus source comprises any one or a combination of at least two of tris(dimethylamino)phosphine, tris(diethylamino)phosphine, tri-n-octylphosphine, or tris(trimethylsilyl)phosphine, wherein typical but non-limiting combinations include: a combination of tris(dimethylamino)phosphine and tris(diethylamino)phosphine, a combination of tris(diethylamino)phosphine and tri-n-octylphosphine, a combination of tris(diethylamino)phosphine, tri-n-octylphosphine, and tris(trimethylsilyl)phosphine, etc.

[0017] Preferably, based on a total volume of 10 mL of oleylamine, the amount of indium halogen source added is 0.1-2.4 g, for example, 0.4 g, 0.6 g, 0.7 g, 0.8 g, 0.9 g, 1.0 g, 1.2 g, 1.4 g, 1.6 g, 1.8 g, 2 g, 2.2 g, etc.

[0018] Preferably, based on a total volume of 10 mL of oleylamine, the amount of halogen zinc source added is 0.2-2.0 g, for example, 0.3 g, 0.4 g, 0.6 g, 0.8 g, 1 g, 1.2 g, 1.4 g, 1.6 g, 1.8 g, etc.

[0019] Preferably, based on a total volume of 10 mL of oleylamine, the amount of phosphorus source added is 0.05-1 mL, such as 0.06 mL, 0.07 mL, 0.08 mL, 0.09 mL, 0.1 mL, 0.2 mL, 0.4 mL, 0.6 mL, 0.8 mL, etc.

[0020] Preferably, the molar amount of the phosphorus source is greater than the molar amount of the indium halogen source.

[0021] Preferably, the indium halogen source, the zinc halogen source, and the oleylamine are mixed, and the heating reaction includes a first heating, a second heating, and a third heating.

[0022] Preferably, the first temperature rise is to 80-100℃, such as 82℃, 84℃, 86℃, 88℃, 90℃, 92℃, 94℃, 96℃, 98℃, etc.

[0023] Preferably, after the first heating, the temperature is maintained for 10-50 minutes, such as 20 minutes, 30 minutes, 40 minutes, etc.

[0024] Preferably, the second temperature increase is to 120-150℃, such as 125℃, 130℃, 135℃, 140℃, 145℃, etc.

[0025] Preferably, after the second heating, the temperature is maintained for 1-3 hours, such as 1.5 hours, 2 hours, 2.5 hours, etc.

[0026] Preferably, the first heating and the second heating are performed under vacuum.

[0027] Preferably, the vacuum degree of the first heating and the second heating is independently -0.08 to -0.1 MPa, for example -0.085 MPa, -0.09 MPa, -0.095 MPa, etc.

[0028] Preferably, the third temperature increase is to 180-200℃, such as 185℃, 190℃, 195℃, etc.

[0029] Preferably, after the third heating, it is mixed with a phosphorus source and kept for 1-10 minutes, such as 2 minutes, 3 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, etc.

[0030] Preferably, after mixing with the phosphorus source, the heating reaction includes a fourth heating.

[0031] Preferably, the fourth heating is to 220-250℃, for example, 210℃, 220℃, 230℃, 240℃, etc.

[0032] Preferably, after the fourth heating, the temperature is maintained for 0.5-2 hours, such as 0.6 hours, 0.8 hours, 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, etc.

[0033] Preferably, the heating reaction is carried out under a protective atmosphere.

[0034] Preferably, the process of mixing with a phosphorus source and reacting at a higher temperature further includes a purification step.

[0035] Preferably, in step (2), before coating the inner shell, the core material is mixed with a solvent, kept warm, and then the inner shell is coated.

[0036] Preferably, the solvent comprises any one or a combination of at least two of octadecene, methyl tetradecanoate, or liquid paraffin, wherein typical but non-limiting combinations include: a combination of octadecene and methyl tetradecanoate, a combination of methyl tetradecanoate and liquid paraffin, a combination of octadecene, methyl tetradecanoate, and liquid paraffin, etc.

[0037] In this invention, the solvent, as a non-coordinating solvent for the reaction, can act as a stabilizer and a surfactant.

[0038] Preferably, the insulation temperature is 120-150℃, such as 125℃, 130℃, 135℃, 140℃, 145℃, etc.

[0039] Preferably, the heat preservation is carried out under vacuum conditions.

[0040] Preferably, the vacuum degree of the insulation is -0.08 to -0.1 MPa, such as -0.085 MPa, -0.09 MPa, -0.095 MPa, etc.

[0041] Preferably, the heat preservation time is 1-3 hours, such as 1.5 hours, 2 hours, 2.5 hours, etc.

[0042] Preferably, during the preparation of the shell, the preparation temperatures of the inner shell, the transition layer, and the outer shell are increased sequentially.

[0043] Preferably, the preparation of each shell layer independently includes surface etching and coating.

[0044] Preferably, the material for surface etching includes any one or a combination of at least two of hydrofluoric acid, hydrochloric acid, phosphoric acid, or perchloric acid, wherein typical but non-limiting combinations include: a combination of hydrofluoric acid and hydrochloric acid, a combination of hydrochloric acid, phosphoric acid, and perchloric acid, a combination of hydrofluoric acid, hydrochloric acid, phosphoric acid, and perchloric acid, etc.

[0045] Preferably, the coating shell material includes any one or a combination of at least two of zinc source precursors, selenium source precursors, sulfur source precursors, or mixed selenium-sulfur source precursors. Typical but non-limiting combinations include: combinations of zinc source precursors and selenium source precursors, combinations of selenium source precursors, sulfur source precursors, and mixed selenium-sulfur source precursors, and combinations of zinc source precursors, selenium source precursors, sulfur source precursors, and mixed selenium-sulfur source precursors, etc.

[0046] In this invention, the zinc source precursor refers to a mixture of a zinc source and a solvent, with the zinc source uniformly dispersed in the solvent; the same applies to the other precursors.

[0047] In this invention, the zinc source precursor comprises a combination of a zinc source, a fatty acid solvent, and a non-coordinating solvent.

[0048] Preferably, the zinc source includes any one or a combination of at least two of zinc acetate, zinc oxide, or zinc chloride, wherein typical but non-limiting combinations include: a combination of zinc acetate and zinc oxide, a combination of zinc oxide and zinc chloride, a combination of zinc acetate, zinc oxide, and zinc chloride, etc.

[0049] Preferably, the fatty acid solvent includes any one or a combination of at least two of oleic acid, palmitic acid, or stearic acid, wherein typical but non-limiting combinations include: a combination of oleic acid and palmitic acid, a combination of palmitic acid and stearic acid, a combination of oleic acid, palmitic acid, and stearic acid, etc.

[0050] Preferably, the noncoordinating solvent comprises any one or a combination of at least two of octadecene, methyl tetradecanoate, or liquid paraffin, wherein typical but non-limiting combinations include: a combination of octadecene and methyl tetradecanoate, a combination of methyl tetradecanoate and liquid paraffin, a combination of octadecene, methyl tetradecanoate, and liquid paraffin, etc.

[0051] Preferably, the mass ratio of the zinc source, fatty acid solvent, and non-coordinating solvent is 1:(2-5):(4-10), wherein 2-5 can be 2.5, 3, 3.5, 4, 4.5, etc., and 4-10 can be 5, 6, 7, 8, 9, etc.

[0052] For example, the zinc source precursor preparation method includes the following steps:

[0053] The zinc source, fatty acid solvent, and non-coordinated solvent are dispersed by heating under a protective atmosphere to obtain the zinc source precursor.

[0054] Preferably, the heating and dispersion temperature is 150-250℃, such as 160℃, 180℃, 200℃, 220℃, 240℃, etc.

[0055] In this invention, the selenium source precursor comprises a combination of selenium powder and trioctylphosphine.

[0056] Preferably, the mass ratio of selenium powder to trioctylphosphine is 1:(3-10), where 3-10 can be 4, 5, 6, 7, 8, 9, etc.

[0057] For example, the method for preparing the selenium source precursor includes the following steps:

[0058] Selenium powder and trioctylphosphine were heated and dispersed under a protective atmosphere to obtain the selenium source precursor.

[0059] Preferably, the heating and dispersion temperature is 50-150℃, such as 60℃, 80℃, 100℃, 120℃, 140℃, etc.

[0060] In this invention, the sulfur source precursor comprises a combination of sulfur powder and trioctylphosphine.

[0061] Preferably, the mass ratio of sulfur powder to trioctylphosphine is 1:(10-100), wherein 10-100 can be 20, 30, 40, 50, 60, 70, 80, 90, etc.

[0062] For example, the method for preparing the sulfur source precursor includes the following steps:

[0063] The sulfur source and trioctylphosphine were dispersed by heating under a protective atmosphere to obtain the sulfur source precursor.

[0064] Preferably, the heating and dispersion temperature is 50-150℃, such as 60℃, 80℃, 100℃, 120℃, 140℃, etc.

[0065] In this invention, the selenium-sulfur source mixed precursor comprises a combination of selenium powder, sulfur powder, and trioctylphosphine.

[0066] Preferably, the mass ratio of selenium powder, sulfur powder and trioctylphosphine is (1-3):1:(10-100), wherein 1-3 can be 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, etc.; and 10-100 can be 20, 30, 40, 50, 60, 70, 80, 90, etc.

[0067] For example, the method for preparing the selenium-sulfur source mixed precursor includes the following steps:

[0068] Selenium powder, sulfur source, and trioctylphosphine were heated and dispersed under a protective atmosphere to obtain the selenium-sulfur source mixed precursor.

[0069] Preferably, the heating and dispersion temperature is 50-150℃, such as 60℃, 80℃, 100℃, 120℃, 140℃, etc.

[0070] Preferably, the inner shell layer comprises at least three layers (e.g., 4, 5, 6, 7, etc.) structure.

[0071] Preferably, during the preparation of the inner shell layer, the amount of shell material added, the reaction temperature, and the reaction time are increased sequentially from the inside out.

[0072] In this invention, the encapsulation of the multi-layer inner shell adopts a segmented, material-incremental, and reaction-temperature-incremental method to ensure that the particle size, wavelength, half-width at half-maximum, and quantum efficiency are reduced and improved after encapsulation.

[0073] Preferably, the inner shell layer comprises, from the inside out, a first inner shell layer, a second inner shell layer, and a third inner shell layer.

[0074] Preferably, the method for preparing the first inner shell layer includes the following steps: mixing the core with the surface-etched material and the shell material in sequence, reacting them to obtain the first inner shell layer.

[0075] Preferably, the temperature at which the core and the surface-etched material are mixed is 180-200℃, such as 185℃, 190℃, 195℃, etc.

[0076] Preferably, the mixing time between the core and the surface etched material is 10-50 minutes, such as 20 minutes, 30 minutes, 40 minutes, etc.

[0077] Preferably, the mixing time between the core and shell materials is 30-60 minutes, such as 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, etc.

[0078] Preferably, the method for preparing the second inner shell layer includes the following steps: mixing the core containing the first inner shell layer with the surface-etched material and the shell material in sequence, reacting them to obtain the second inner shell layer.

[0079] Preferably, the mixing temperature of the core and the surface etching material is 200-250℃, such as 210℃, 220℃, 230℃, 240℃, etc.

[0080] Preferably, the mixing time between the core and the surface etched material is 10-50 minutes, such as 20 minutes, 30 minutes, 40 minutes, etc.

[0081] Preferably, the mixing time between the core and shell materials is 45-75 minutes, such as 50 minutes, 55 minutes, 60 minutes, 65 minutes, 70 minutes, etc.

[0082] Preferably, the preparation method of the third inner shell layer includes the following steps: mixing the core containing the first inner shell layer and the second inner shell layer sequentially with the surface-etched material and the shell material, reacting to obtain the third inner shell layer.

[0083] Preferably, the temperature at which the core and the surface etched material are mixed is 250-300℃, such as 260℃, 270℃, 280℃, 290℃, 300℃, etc.

[0084] Preferably, the mixing time between the core and the surface etched material is 10-50 minutes, such as 20 minutes, 30 minutes, 40 minutes, etc.

[0085] Preferably, the mixing time between the core and shell materials is 60-90 minutes, such as 65 minutes, 70 minutes, 75 minutes, 80 minutes, 85 minutes, etc.

[0086] Preferably, the method for preparing the transition layer includes the following steps:

[0087] The core with the inner shell layer is etched and coated to obtain the transition layer.

[0088] Preferably, the temperature at which the core and the surface etched material are mixed is 250-300℃, such as 260℃, 270℃, 280℃, 290℃, etc.

[0089] Preferably, the mixing time between the core and the surface etched material is 10-50 minutes, such as 20 minutes, 30 minutes, 40 minutes, etc.

[0090] Preferably, the mixing time between the core and shell materials is 30-60 minutes, such as 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, etc.

[0091] Preferably, the method for preparing the outer shell layer includes the following steps:

[0092] The core, which has an inner shell layer and a transition layer, is etched and coated to obtain the outer shell layer.

[0093] Preferably, the mixing temperature of the core and the surface etching material is 300-330℃, such as 310℃, 315℃, 320℃, 325℃, etc.

[0094] Preferably, the mixing time between the core and the surface etched material is 10-50 minutes, such as 20 minutes, 30 minutes, 40 minutes, etc.

[0095] Preferably, the mixing time between the core and shell materials is 30-60 minutes, such as 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, etc.

[0096] Preferably, the inner shell, transition layer and outer shell are each purified independently after preparation.

[0097] In this invention, quantum dot surface etching is performed in advance using a surface etching material such as hydrofluoric acid during the encapsulation of each shell layer to ensure the encapsulation capability of the shell layer.

[0098] Preferably, after the coating layer is applied, a ligand replacement operation is also included.

[0099] Preferably, the process before ligand replacement includes mixing the core of the coating layer with a solvent and keeping it at a constant temperature.

[0100] Preferably, the solvent comprises any one or a combination of at least two of octadecene, methyl tetradecanoate, or liquid paraffin, wherein typical but non-limiting combinations include: a combination of octadecene and methyl tetradecanoate, a combination of methyl tetradecanoate and liquid paraffin, a combination of octadecene, methyl tetradecanoate, and liquid paraffin, etc.

[0101] In this invention, the solvent, as a non-coordinating solvent for the reaction, can act as a stabilizer and a surfactant.

[0102] Preferably, the insulation temperature is 120-150℃, such as 125℃, 130℃, 135℃, 140℃, 145℃, etc.

[0103] Preferably, the heat preservation is carried out under vacuum conditions and a protective atmosphere.

[0104] Preferably, the vacuum degree of the insulation is -0.08 to -0.1 MPa, such as -0.085 MPa, -0.09 MPa, -0.095 MPa, etc.

[0105] Preferably, the heat preservation time is 1-3 hours, such as 1.5 hours, 2 hours, 2.5 hours, etc.

[0106] Preferably, the ligand replaced by the ligand includes a thiol ligand.

[0107] In this invention, by replacing fatty acid ligands with thiol ligands, thiol groups have a strong binding force on the surface cations of quantum dots and are not easily separated, thus solving the problem of agglomeration and sedimentation of core solutions such as indium phosphide solutions and improving the stability of core-shell quantum dots.

[0108] Preferably, the thiol ligand comprises any one or a combination of at least two of 2-ethylhexane-1-thiol, octylthiol, dodecylthiol, or 2-ethylhexyl mercaptoacetate, wherein typical but non-limiting combinations include: a combination of 2-ethylhexane-1-thiol and octylthiol, a combination of octylthiol, dodecylthiol, and 2-ethylhexyl mercaptoacetate, a combination of 2-ethylhexane-1-thiol, octylthiol, dodecylthiol, and 2-ethylhexyl mercaptoacetate, etc.

[0109] Preferably, the number of ligand replacements is at least 1, such as 2, 3, 4, 5, 6, etc.

[0110] Preferably, the ligand substitution includes repeating the ligand addition and insulated reaction at least once (e.g., 2, 3, 4, etc.) in a system containing a core with a coated shell.

[0111] Preferably, the ligand replacement includes: in a system containing a core with a coated shell, adding a ligand for the first time and performing a first heat preservation reaction, then adding a ligand for the second time and performing a second heat preservation reaction, and then adding a ligand for the third time and performing a third heat preservation reaction.

[0112] Preferably, the temperature of the first heat preservation reaction is 80-150℃, such as 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, etc.

[0113] Preferably, the duration of the first heat preservation reaction is 10-50 minutes, such as 20 minutes, 30 minutes, 40 minutes, etc.

[0114] Preferably, the temperature of the second heat preservation reaction is 150-200℃, such as 160℃, 170℃, 180℃, 190℃, etc.

[0115] Preferably, the second heat preservation reaction time is 15-60 min, such as 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, etc.

[0116] Preferably, the temperature of the third heat preservation reaction is 200-250℃, such as 210℃, 220℃, 230℃, 240℃, etc.

[0117] Preferably, the time for the third heat preservation reaction is 0.5-2 hours, such as 0.6 hours, 0.8 hours, 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, etc.

[0118] Preferably, the ligand replacement is followed by purification.

[0119] In this invention, both the coating and ligand replacement are purified beforehand to remove impurities that could affect the subsequent coating and ligand replacement reactions, thereby promoting the coating and ligand replacement reactions.

[0120] As a preferred technical solution, the preparation method includes the following steps:

[0121] (1) Mix the indium halogen source, the zinc halogen source and oleylamine, and keep them at 80-100℃ for 10-50 min under a protective atmosphere;

[0122] Under vacuum conditions and a protective atmosphere, control the vacuum level to -0.08 to -0.1 MPa, raise the temperature to 120-150℃, and hold for 1-3 hours to ensure that the system is free of water and oxygen.

[0123] Under a protective atmosphere, heat to 180-200℃, add a phosphorus source to the system, and maintain for 1-10 minutes;

[0124] Under a protective atmosphere, the temperature is raised to 220-250℃ and held for 0.5-2 hours to purify and obtain the core.

[0125] (2) Disperse the core in a solvent, and under vacuum conditions, adjust the temperature to 120℃-150℃ and maintain it for 1-3 hours, controlling the vacuum degree to -0.08~-0.1MPa to ensure that the system is free of water and oxygen;

[0126] Under a protective atmosphere, the temperature is raised to 180-200℃, the surface-etched material is added to the system and kept for 10-50 minutes, then the shell material is added to the system and kept for 30-60 minutes to obtain the first inner shell layer;

[0127] Under a protective atmosphere, the temperature is raised to 200-250℃, which is higher than the preparation temperature of the first inner shell layer. The surface etching material is added to the system and kept for 10-50 minutes. Then the shell material is added to the system and kept for 45-75 minutes, which is higher than the holding time of the first inner shell layer, to obtain the second inner shell layer.

[0128] Under a protective atmosphere, the temperature is raised to 250-300℃, which is higher than the preparation temperature of the second inner shell layer. The surface etching material is added to the system and kept for 10-50 minutes. Then the shell material is added to the system and kept for 60-90 minutes, which is higher than the holding time of the second inner shell layer, to obtain the third inner shell layer. After purification, the inner shell layer is obtained.

[0129] Adjust the system temperature to 250-300℃, higher than the preparation temperature of the third inner shell layer, then add the surface-etched material to the system and maintain for 10-50 minutes. Then add the shell material to the system and maintain for 30-60 minutes. Purify to obtain the transition layer. Adjust the system temperature to 300-330℃, higher than the preparation temperature of the transition layer, then add the surface-etched material to the system and maintain for 10-50 minutes. Then add the shell material to the system and maintain for 30-60 minutes. Purify to obtain the outer shell layer.

[0130] (3) Disperse the core containing the inner shell, transition layer and transition layer (the core containing the inner shell, transition layer and transition layer is already a quantum dot with a preliminary core-shell structure) in a solvent, and under vacuum conditions and a protective atmosphere, adjust the system temperature to 120-150℃ and maintain it for 1-3h, control the vacuum degree to -0.08~-0.1MPa, and ensure that the system is free of water and oxygen;

[0131] In a protective atmosphere, adjust the temperature to 80-150℃, add the thiol ligand to the system, and keep it at that temperature for 10-50 minutes.

[0132] In a protective atmosphere, adjust the temperature to 150-200℃, add the thiol ligand to the system, and keep it at that temperature for 15-60 minutes.

[0133] In a protective atmosphere, the temperature is adjusted to 200-250℃, the thiol ligand is added to the system, and the temperature is maintained for 0.5-2h to complete the ligand replacement. After purification and drying, the core-shell quantum dots are obtained.

[0134] The preferred technical solution of the present invention has the following characteristics:

[0135] (1) The nucleation stage ensures a reaction environment free of water, oxygen, halogens, and amines, while low-temperature nucleation and high-temperature growth ensure the uniformity of the core.

[0136] (2) When each shell is coated, the quantum dot surface is etched with a surface etching material in advance to ensure the coating of the shell. The coating of the multi-layer inner shell adopts a segmented, material incremental, and reaction temperature incremental method to ensure that the particle size, wavelength, half peak width are reduced and the quantum efficiency is improved after coating. The introduction of the transition layer makes up for the difference in lattice fit between the inner shell and the outer shell, so that the quantum dot material structure is more stable.

[0137] (3) Purification is performed before coating and ligand replacement to remove impurities that may affect subsequent coating and ligand replacement and to promote the coating and ligand replacement reaction.

[0138] (4) By replacing the fatty acid ligand with a thiol ligand, the thiol has a strong binding force on the surface cations of the quantum dots and is not easy to separate, thus solving the problem of aggregation and sedimentation of the core solution and improving the stability of the core-shell quantum dots.

[0139] In a second aspect, the present invention provides a core-shell quantum dot, wherein the core-shell quantum dot is obtained by the preparation method described in the first aspect.

[0140] Preferably, the core-shell quantum dot comprises, in sequence, a core, an inner shell, a transition layer, an outer shell, and a ligand layer;

[0141] The core includes indium phosphide;

[0142] The inner shell layer includes zinc selenide;

[0143] The transition layer comprises zinc sulfide selenide;

[0144] The outer shell layer comprises zinc sulfide;

[0145] The ligand layer includes thiol ligands.

[0146] Thirdly, the present invention provides a display device comprising the core-shell quantum dot described in the second aspect.

[0147] Compared with the prior art, the present invention has the following beneficial effects:

[0148] (1) The core-shell quantum dots prepared by the method described in this invention have high fluorescence efficiency, narrow light emission half-width, high structural stability, and good photoelectric compatibility. They can be prepared in an environment free of cadmium and with low biotoxicity, making them environmentally friendly.

[0149] (2) The fluorescence emission peak of the core-shell quantum dots obtained by the preparation method of the present invention is between 520-532nm, the fluorescence efficiency is above 63%, and the emission half width is within 40nm. Detailed Implementation

[0150] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0151] Example 1

[0152] This embodiment provides a core-shell quantum dot, which is obtained by the following preparation method, which includes the following steps:

[0153] (1) 1.5 g of indium iodide, 2 g of zinc chloride, and 20 mL of oleylamine were mixed in a three-necked flask and dissolved completely at the first temperature (90 °C) for 30 min under a nitrogen atmosphere. Then, the mixture was transferred to a vacuum atmosphere and the temperature was adjusted to the second temperature (130 °C) and held for 2 h, with the vacuum degree controlled at -0.09 MPa. The mixture was then transferred to a nitrogen atmosphere and the temperature was adjusted to the third temperature (190 °C). 1.5 mL of tris(dimethylamino)phosphine was rapidly injected into the flask reaction system and held for 5 min. Then, the temperature was adjusted to the fourth temperature (240 °C) and held for 1 h to obtain the InP core. After purification, the core was dispersed in 20 mL of octadecene.

[0154] (2) Place the InP core dispersed in 20 mL of octadecene in a three-necked flask, and maintain the temperature at 130 °C for 2 h under a vacuum atmosphere, controlling the vacuum degree to -0.09 MPa. Then, switch to a nitrogen atmosphere and adjust the temperature to 190 °C. Inject 2 mL of hydrofluoric acid into the reaction system and maintain for 30 min. Then, inject 8 mL of zinc source precursor and 3 mL of selenium source precursor into the reaction system sequentially and maintain for 45 min, thereby coating the first layer of ZnSe.

[0155] The temperature was raised to 230℃ and 3 mL of hydrofluoric acid was injected into the reaction system and kept for 30 min. Then, 12 mL of zinc source precursor and 4 mL of selenium source precursor were injected into the reaction system and kept for 60 min, thereby coating the second layer of ZnSe.

[0156] The temperature was raised to 280℃ and 4 mL of hydrofluoric acid was injected into the reaction system and kept for 30 min. Then, 18 mL of zinc source precursor and 5 mL of selenium source precursor were injected into the reaction system and kept for 75 min, thereby coating the third ZnSe layer and obtaining the core layer.

[0157] The system temperature was adjusted to 290℃, 3 mL of hydrofluoric acid was injected into the reaction system and kept for 30 min, and then 12 mL of zinc source precursor and 10 mL of selenium-sulfur source mixed precursor were injected into the reaction system and kept for 70 min, thereby coating the transition layer ZnSeS.

[0158] The temperature was raised to 310℃ and 3 mL of hydrofluoric acid was injected into the reaction system and kept for 30 min. Then, 12 mL of zinc source precursor and 3 mL of sulfur source precursor were injected into the reaction system and kept for 45 min, thereby coating the outer shell layer of ZnS; InP / ZnSe / ZnSeS / ZnS core-shell structured quantum dots were obtained, which were then purified and dispersed in 20 mL of octadecene.

[0159] (3) InP core-shell quantum dots dispersed in 20 mL of octadecene were placed in a three-necked flask. The temperature was adjusted to 130 °C and maintained for 2 h under a vacuum atmosphere, with the vacuum degree controlled at -0.09 MPa to ensure an anhydrous and oxygen-free reaction environment. Then, the atmosphere was switched to nitrogen and the temperature was lowered to 120 °C. 2-Ethylhexane-1-thiol (2 mL) was injected into the reaction system and maintained for 30 min. The temperature was then raised to 180 °C and 2-ethylhexane-1-thiol (3 mL) was injected into the reaction system and maintained for 45 min. The temperature was then raised to 230 °C and 2-ethylhexane-1-thiol (4 mL) was injected into the reaction system and maintained for 1 h. InP / ZnSe / ZnSeS / ZnS core-shell thiol ligand quantum dots were obtained. After purification and vacuum drying, the core-shell quantum dots were obtained.

[0160] In this embodiment (and similarly in other embodiments and comparative examples), the preparation of the zinc source precursor, selenium source precursor, sulfur source precursor, and mixed selenium-sulfur source precursor are as follows:

[0161] The specific preparation process of the zinc source precursor is as follows: 11g of zinc acetate, 34g of oleic acid and 64g of octadecene are added to a 250mL three-necked flask, nitrogen gas is introduced and the mixture is heated to 200℃ to completely disperse the zinc acetate.

[0162] The specific preparation process of the selenium source precursor is as follows: 10g of selenium powder and 50g of trioctylphosphine are added to a 250mL three-necked flask, nitrogen gas is introduced and heated to 100℃ to completely disperse the selenium powder.

[0163] The specific preparation process of the sulfur source precursor is as follows: 0.2g of sulfur powder and 10g of trioctylphosphine are added to a 50mL three-necked flask, nitrogen gas is introduced and heated to 100℃ to completely disperse the sulfur powder.

[0164] The preparation process of the selenium-sulfur source mixed precursor is as follows: 0.4g of selenium powder, 0.2g of sulfur powder, and 20g of trioctylphosphine are added to a 50mL three-necked flask, nitrogen gas is introduced, and the mixture is heated to 100℃ to completely disperse the selenium powder and sulfur powder.

[0165] Example 2

[0166] This embodiment provides a core-shell quantum dot, which is obtained by the following preparation method, which includes the following steps:

[0167] (1) 1.0 g of indium iodide, 3.0 g of zinc chloride, and 20 mL of oleylamine were mixed in a three-necked flask and dissolved completely at the first temperature (80 °C) for 30 min under a nitrogen atmosphere. Then, the mixture was transferred to a vacuum atmosphere and the temperature was adjusted to the second temperature (120 °C) and held for 2 h, with the vacuum degree controlled at -0.08 MPa. The mixture was then transferred to a nitrogen atmosphere and the temperature was adjusted to the third temperature (180 °C). 0.1 mL of tris(dimethylamino)phosphine was rapidly injected into the flask reaction system and held for 5 min. Then, the temperature was adjusted to the fourth temperature (220 °C) and held for 1 h to obtain the InP core. After purification, the core was dispersed in 20 mL of octadecene.

[0168] (2) Place the indium phosphide core dispersed in 20 mL of octadecene in a three-necked flask, and maintain the temperature at 150 °C for 2 h under a vacuum atmosphere, controlling the vacuum degree to -0.1 MPa. Then switch to a nitrogen atmosphere and adjust the temperature to 200 °C. Inject 2 mL of hydrofluoric acid into the reaction system and maintain for 30 min. Then inject 5 mL of zinc source precursor and 4 mL of selenium source precursor into the reaction system in sequence and maintain for 60 min, thereby coating the first layer of ZnSe.

[0169] The temperature was raised to 250℃ and 3 mL of hydrofluoric acid was injected into the reaction system and kept for 30 min. Then, 10 mL of zinc source precursor and 6 mL of selenium source precursor were injected into the reaction system and kept for 75 min, thereby coating the second layer of ZnSe.

[0170] The temperature was raised to 290℃ and 4 mL of hydrofluoric acid was injected into the reaction system and kept for 30 min. Then, 20 mL of zinc source precursor and 8 mL of selenium source precursor were injected into the reaction system and kept for 90 min, thereby coating the third ZnSe layer and obtaining the core layer.

[0171] The system temperature was adjusted to 300℃, 3 mL of hydrofluoric acid was injected into the reaction system and kept for 30 min, and then 15 mL of zinc source precursor and 5 mL of selenium-sulfur source mixed precursor were injected into the reaction system and kept for 60 min, thereby coating the transition layer ZnSeS.

[0172] The temperature was raised to 330℃ and 3 mL of hydrofluoric acid was injected into the reaction system and kept for 30 min. Then, 10 mL of zinc source precursor and 5 mL of sulfur source precursor were injected into the reaction system and kept for 30 min, thereby coating the outer shell layer of ZnS; InP / ZnSe / ZnSeS / ZnS core-shell structured quantum dots were obtained, which were then purified and dispersed in 20 mL of octadecene.

[0173] (3) Indium phosphide core-shell quantum dots dispersed in 20 mL of octadecene were placed in a three-necked flask. The temperature was adjusted to 120 °C and maintained for 2 h under a vacuum atmosphere, with the vacuum degree controlled at -0.08 MPa to ensure an anhydrous and oxygen-free reaction environment. Then, the atmosphere was switched to nitrogen and the temperature was lowered to 80 °C. 2-Ethylhexane-1-thiol (2 mL) was injected into the reaction system and maintained for 30 min. The temperature was then raised to 150 °C and 2-ethylhexane-1-thiol (3 mL) was injected into the reaction system and maintained for 45 min. The temperature was then raised to 200 °C and 2-ethylhexane-1-thiol (4 mL) was injected into the reaction system and maintained for 1 h. InP / ZnSe / ZnSeS / ZnS core-shell thiol ligand quantum dots were obtained. After purification and vacuum drying, the core-shell quantum dots were obtained.

[0174] Example 3

[0175] This embodiment provides a core-shell quantum dot, which is obtained by the following preparation method, which includes the following steps:

[0176] (1) 2.0 g of indium iodide, 0.5 g of zinc chloride, and 20 mL of oleylamine were mixed in a three-necked flask and dissolved completely at the first temperature (100 °C) for 30 min under a nitrogen atmosphere. Then, the mixture was transferred to a vacuum atmosphere and the temperature was adjusted to the second temperature (150 °C) and held for 2 h, with the vacuum degree controlled at -0.1 MPa. The mixture was then transferred to a nitrogen atmosphere and the temperature was adjusted to the third temperature (200 °C). 2 mL of tris(dimethylamino)phosphine was rapidly injected into the flask reaction system and held for 5 min. Then, the temperature was adjusted to the fourth temperature (250 °C) and held for 1 h to obtain the InP core. After purification, the core was dispersed in 20 mL of octadecene.

[0177] (2) Place the indium phosphide core dispersed in 20 mL of octadecene in a three-necked flask, and maintain the temperature at 120 °C for 2 h under a vacuum atmosphere, controlling the vacuum degree to -0.08 MPa. Then, switch to a nitrogen atmosphere and adjust the temperature to 180 °C. Inject 2 mL of hydrofluoric acid into the reaction system and maintain for 30 min. Then, inject 10 mL of zinc source precursor and 1 mL of selenium source precursor into the reaction system sequentially and maintain for 30 min, thereby coating the first layer of ZnSe.

[0178] The temperature was raised to 200℃ and 3 mL of hydrofluoric acid was injected into the reaction system and kept for 30 min. Then, 12 mL of zinc source precursor and 2 mL of selenium source precursor were injected into the reaction system and kept for 45 min, thereby coating the second layer of ZnSe.

[0179] The temperature was raised to 250℃ and 4 mL of hydrofluoric acid was injected into the reaction system and kept for 30 min. Then, 15 mL of zinc source precursor and 3 mL of selenium source precursor were injected into the reaction system and kept for 60 min, thereby coating the third ZnSe layer and obtaining the core layer.

[0180] The system temperature was adjusted to 260℃, 3 mL of hydrofluoric acid was injected into the reaction system and kept for 30 min, then 10 mL of zinc source precursor and 4 mL of selenium-sulfur source mixed precursor were injected into the reaction system and kept for 90 min, thereby coating the transition layer ZnSeS.

[0181] The temperature was raised to 300℃ and 3 mL of hydrofluoric acid was injected into the reaction system and kept for 30 min. Then, 15 mL of zinc source precursor and 1 mL of sulfur source precursor were injected into the reaction system and kept for 60 min, thereby coating the outer shell layer of ZnS; InP / ZnSe / ZnSeS / ZnS core-shell structured quantum dots were obtained, which were then purified and dispersed in 20 mL of octadecene.

[0182] (3) Indium phosphide core-shell quantum dots dispersed in 20 mL of octadecene were placed in a three-necked flask. The temperature was adjusted to 150 °C and maintained for 2 h under a vacuum atmosphere, with the vacuum degree controlled at -0.1 MPa to ensure an anhydrous and oxygen-free reaction environment. Then, the atmosphere was switched to nitrogen and the temperature was lowered to 120 °C. 2-Ethylhexane-1-thiol (2 mL) was injected into the reaction system and maintained for 30 min. The temperature was then raised to 200 °C and 2-ethylhexane-1-thiol (3 mL) was injected into the reaction system and maintained for 45 min. The temperature was then raised to 2250 °C and 2-ethylhexane-1-thiol (4 mL) was injected into the reaction system and maintained for 1 h. InP / ZnSe / ZnSeS / ZnS core-shell thiol ligand quantum dots were obtained. After purification and vacuum drying, the core-shell quantum dots were obtained.

[0183] Example 4

[0184] The difference between this embodiment and embodiment 1 is that the preparation method of the inner shell in step (2) is different, while the rest is the same as that in embodiment 1;

[0185] Step (2) of this embodiment is as follows:

[0186] (2) Place the InP core dispersed in 20 mL of octadecene in a three-necked flask, and maintain the temperature at 130 °C for 2 h under a vacuum atmosphere, controlling the vacuum degree to -0.09 MPa. Then, switch to a nitrogen atmosphere and adjust the temperature to 190 °C. Inject 9 mL of hydrofluoric acid into the reaction system and maintain for 30 min. Then, inject 38 mL of zinc source precursor and 12 mL of selenium source precursor into the reaction system sequentially and maintain for 180 min, thereby coating ZnSe and obtaining the core layer.

[0187] The system temperature was adjusted to 290℃, and then 3 mL of hydrofluoric acid was injected into the reaction system and kept for 30 min. Then, 12 mL of zinc source precursor and 10 mL of selenium-sulfur source mixed precursor were injected into the reaction system and kept for 70 min, thereby coating the transition layer ZnSeS.

[0188] The temperature was raised to 310℃ and 3 mL of hydrofluoric acid was injected into the reaction system and kept for 30 min. Then, 12 mL of zinc source precursor and 3 mL of sulfur source precursor were injected into the reaction system and kept for 45 min, thereby coating the outer shell layer of ZnS. After purification and vacuum drying, InP / ZnSe / ZnSeS / ZnS core-shell structured quantum dots were obtained.

[0189] Example 5

[0190] The difference between this embodiment and embodiment 1 is that the preparation method of the inner shell in step (2) is different, while the rest is the same as that in embodiment 1;

[0191] Step (2) of this embodiment is as follows:

[0192] InP cores dispersed in 20 mL of octadecene were placed in a three-necked flask. The temperature was adjusted to 130 °C and maintained for 2 h under a vacuum atmosphere, with the vacuum level controlled at -0.09 MPa. Then, the mixture was switched to a nitrogen atmosphere and the temperature was adjusted to 280 °C. 2 mL of hydrofluoric acid was injected into the reaction system and maintained for 30 min. Then, 8 mL of zinc source precursor and 3 mL of selenium source precursor were injected into the reaction system sequentially and maintained for 45 min, thereby coating the first layer of ZnSe.

[0193] Adjust the temperature to 230℃, inject 3 mL of hydrofluoric acid into the reaction system and keep it for 30 min, then inject 12 mL of zinc source precursor and 4 mL of selenium source precursor into the reaction system in sequence and keep it for 60 min, thereby coating the second layer of ZnSe.

[0194] Adjust the temperature to 190℃ and inject 4 mL of hydrofluoric acid into the reaction system and maintain for 30 min. Then, inject 18 mL of zinc source precursor and 5 mL of selenium source precursor into the reaction system and maintain for 75 min, thereby coating the third ZnSe layer and obtaining the core layer.

[0195] 3 mL of hydrofluoric acid was injected into the reaction system and kept for 30 min. Then, 12 mL of zinc source precursor and 10 mL of selenium-sulfur source mixed precursor were injected into the reaction system and kept for 70 min to coat the transition layer ZnSeS.

[0196] The temperature was raised to 310℃ and 3 mL of hydrofluoric acid was injected into the reaction system and kept for 30 min. Then, 12 mL of zinc source precursor and 3 mL of sulfur source precursor were injected into the reaction system and kept for 45 min, thereby coating the outer shell layer of ZnS. After purification and vacuum drying, InP / ZnSe / ZnSeS / ZnS core-shell structured quantum dots were obtained.

[0197] Example 6

[0198] The difference between this embodiment and embodiment 1 is that step (3) is different, while the rest is the same as in embodiment 1;

[0199] Step (3) in this embodiment is as follows:

[0200] InP core-shell quantum dots dispersed in 20 mL of octadecene were placed in a three-necked flask. The temperature was adjusted to 130 °C and maintained for 2 h under a vacuum atmosphere, with the vacuum level controlled at -0.09 MPa to ensure an anhydrous and oxygen-free reaction environment. Then, the atmosphere was switched to nitrogen and the temperature was lowered to 120 °C. 9 mL of 2-ethylhexane-1-thiol was injected into the reaction system and maintained for 135 min. InP / ZnSe / ZnSeS / ZnS core-shell quantum dots with thiol ligands were obtained. After purification and vacuum drying, the core-shell quantum dots were obtained.

[0201] Example 7

[0202] The difference between this embodiment and Example 1 is that 2-ethylhexane-1-thiol in step (3) is replaced with an equal volume of octylthiol, while the rest is the same as in Example 1.

[0203] Comparative Example 1

[0204] The difference between this comparative example and Example 1 is that step (1) is different, while the rest is the same as Example 1;

[0205] The specific steps (1) of this comparative example are as follows:

[0206] 1.5 g of indium iodide, 2 g of zinc chloride, and 20 mL of oleylamine were mixed in a three-necked flask and dissolved completely at a first temperature (90 °C) for 30 min under a nitrogen atmosphere. Then, the mixture was transferred to a vacuum atmosphere and the temperature was adjusted to a second temperature (130 °C) and maintained for 2 h, with the vacuum level controlled at -0.09 MPa. The mixture was then transferred to a nitrogen atmosphere and the temperature was adjusted to a third temperature (190 °C). 1.5 mL of tris(dimethylamino)phosphine was rapidly injected into the flask reaction system and maintained for 5 min. The mixture was then maintained at the third temperature (190 °C) for 1 h to obtain the InP core, which was then purified and dispersed in 20 mL of octadecene.

[0207] Performance testing

[0208] The core-shell quantum dots described in Examples 1-6 and Comparative Example 1 were tested as follows:

[0209] (1) Fluorescence efficiency: tested with a C11347 photoluminescence quantum yield spectrometer in n-octane solution;

[0210] (2) Light emission half-width: Absolute photoluminescence quantum yield spectrometer C11347, n-octane solution test;

[0211] (3) Structural stability: Dispersed in n-octane solution, stored in the dark for 1 month, the precipitation was observed and the quantum efficiency was tested: The more precipitation, the worse the stability, and the more the quantum efficiency decreased, the worse the stability.

[0212] (4) Photoelectric compatibility: the degree of compatibility between quantum dots and glue and ink.

[0213] The test results are summarized in Table 1.

[0214] Table 1

[0215]

[0216]

[0217] Analysis of the data in Table 1 shows that the fluorescence emission peak of the core-shell quantum dots obtained by the preparation method of the present invention is between 520-532 nm, the fluorescence efficiency is above 63%, and the emission half-width is within 40 nm. The core-shell quantum dots obtained by the preparation method of the present invention have high fluorescence efficiency, narrow emission half-width, high structural stability, good photoelectric compatibility, and can be prepared in a cadmium-free and low-biotoxic environment, making them environmentally friendly.

[0218] Analysis of Comparative Example 1 and Example 1 shows that the performance of Comparative Example 1 is not as good as that of Example 1, which proves that when preparing the core, low-temperature nucleation and high-temperature growth at the same time ensure the uniformity of the core, and the resulting core-shell quantum dot material has better performance.

[0219] Analysis of Examples 4-5 and Example 1 shows that the performance of Examples 4-5 is not as good as that of Example 1. This proves that when preparing the inner shell, multiple coatings are applied and the zinc source precursor, selenium source precursor, reaction temperature, and reaction time are increased sequentially, resulting in a core-shell quantum dot material with better performance.

[0220] Analysis of Examples 6 and 1 shows that the performance of Example 6 is inferior to that of Example 1, proving that core-shell quantum dots formed by multiple ligand replacement processes have better performance. Analysis of Examples 7 and 1 shows that the performance of Example 7 is inferior to that of Example 1, proving that core-shell quantum dots formed by thiol ligands have better performance during ligand replacement.

[0221] The present invention has been illustrated with the above embodiments to explain the detailed method of the present invention. However, the present invention is not limited to the detailed method described above, that is, it does not mean that the present invention must rely on the detailed method described above to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing core-shell quantum dots, characterized in that, The preparation method comprises the following steps: (1) mixing halogen indium source, halogen zinc source and oleylamine, keeping at 80-100℃ for 10-50 min under protective atmosphere; controlling the vacuum degree to be -0.08~-0.1 MPa, and heating to 120-150℃ under vacuum condition and protective atmosphere, and keeping for 1-3 h to ensure that the system is free of water and oxygen; heating to 180-200℃ under protective atmosphere, and adding phosphorus source into the system, and keeping for 1-10 min; heating to 220-250℃ under protective atmosphere, and keeping for 0.5-2 h to purify and obtain the core; (2) dispersing the core in a solvent, and adjusting the temperature to 120-150℃ under vacuum condition, and keeping for 1-3 h to control the vacuum degree to be -0.08~-0.1 MPa to ensure that the system is free of water and oxygen; heating to 180-200℃ under protective atmosphere, and adding surface etching material into the system, and keeping for 10-50 min, and then adding shell material into the system, and keeping for 30-60 min to obtain a first inner shell layer; heating to 200-250℃ under protective atmosphere, which is higher than the preparation temperature of the first inner shell layer, and adding surface etching material into the system, and keeping for 10-50 min, and then adding shell material into the system, and keeping for 45-75 min, which is higher than the keeping time of the first inner shell layer, to obtain a second inner shell layer; heating to 250-300℃ under protective atmosphere, which is higher than the preparation temperature of the second inner shell layer, and adding surface etching material into the system, and keeping for 10-50 min, and then adding shell material into the system, and keeping for 60-90 min, which is higher than the keeping time of the second inner shell layer, to obtain a third inner shell layer, and purifying to obtain the inner shell layer; adjusting the temperature of the system to 250-300℃, which is higher than the preparation temperature of the third inner shell layer, and then adding surface etching material into the system, and keeping for 10-50 min, and then adding shell material into the system, and keeping for 30-60 min, and purifying to obtain a transition layer; adjusting the temperature of the system to 300-330℃, which is higher than the preparation temperature of the transition layer, and then adding surface etching material into the system, and keeping for 10-50 min, and then adding shell material into the system, and keeping for 30-60 min, and purifying to obtain an outer shell layer; (3) dispersing the core containing the inner shell layer, the transition layer and the transition layer in a solvent, and adjusting the temperature of the system to 120-150℃ under vacuum condition and protective atmosphere, and keeping for 1-3 h to control the vacuum degree to be -0.08~-0.1 MPa to ensure that the system is free of water and oxygen; adjusting the temperature to 80-150℃ under protective atmosphere, and adding mercapto ligand into the system, and keeping for 10-50 min; adjusting the temperature to 150-200℃ under protective atmosphere, and adding mercapto ligand into the system, and keeping for 15-60 min; adjusting the temperature to 200-250℃ under protective atmosphere, and adding mercapto ligand into the system, and keeping for 0.5-2 h to complete ligand replacement, and purifying and drying to obtain the core-shell quantum dot.

2. The production method according to claim 1, characterized by, In step (1), the halogen-indium source includes any one or a combination of at least two of indium fluoride, indium chloride, indium bromide or indium iodide.

3. The preparation method according to claim 1, characterized in that, The halogen-zinc source includes any one or a combination of at least two of zinc fluoride, zinc chloride, zinc bromide or zinc iodide.

4. The preparation method according to claim 1, characterized in that, The phosphorus source includes any one or a combination of at least two of tris(dimethylamino)phosphine, tris(diethylamino)phosphine, tri-n-octylphosphine or tris(trimethylsilyl)phosphine.

5. The preparation method according to claim 1, characterized in that, The halogen-indium source is added in an amount of 0.1-2.4 g, based on the total volume of the oleylamine of 10 mL.

6. The method of claim 1, wherein, The halogen-zinc source is added in an amount of 0.2-2.0 g, based on the total volume of the oleylamine of 10 mL.

7. The preparation method according to claim 1, characterized in that, The phosphorus source is added in an amount of 0.05-1 mL, based on the total volume of the oleylamine of 10 mL.

8. The method of claim 1, wherein, The molar amount of the phosphorus source > the molar amount of the halogen-indium source.

9. The method of claim 1, wherein, In step (2), the solvent includes any one or a combination of at least two of octadecene, methyl tetradecanoate or liquid paraffin.

10. The method of claim 1, wherein, The surface-etching material includes any one or a combination of at least two of hydrofluoric acid, hydrochloric acid, phosphoric acid or perchloric acid.

11. The method of claim 1, wherein, The shell material includes any one or a combination of at least two of a zinc source precursor, a selenium source precursor, a sulfur source precursor or a selenium-sulfur source mixed precursor.

12. The method of claim 1, wherein, In step (3), the solvent includes any one or a combination of at least two of octadecene, methyl tetradecanoate or liquid paraffin.

13. The method of claim 1, wherein, The mercapto ligand includes any one or a combination of at least two of 2-ethylhexane-1-thiol, octanethiol, dodecanethiol or 2-ethylhexyl mercaptoacetate.

14. A core-shell quantum dot, characterized in that, The core-shell quantum dot is obtained by the preparation method of any one of claims 1-13.

15. The core-shell quantum dot according to claim 14, characterized in that, The core-shell quantum dot sequentially includes a core, an inner shell layer, a transition layer, an outer shell layer and a ligand layer. The core includes indium phosphide. The inner shell layer includes zinc selenide. The transition layer includes zinc sulfoselenide. The outer shell layer includes zinc sulfide. The ligand layer includes a mercapto ligand.

16. A display device comprising: The display device includes the core-shell quantum dot of claim 14 or 15.

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