A copper-based core / multilayer shell structure quantum dot based on a gradient active zinc source and a preparation method thereof

Abstract

The application discloses a copper-based core / multilayer shell structure quantum dot based on gradient active zinc source and a preparation method thereof, and relates to the technical field of quantum dot materials. The application adopts a CuInZnS quaternary alloy core-three-layer ZnS shell structure design, cooperates with zinc source types and solvent coordination system to synergistically control a gradient active zinc source, performs quantum dot step-by-step growth through gradually reducing the activity of the zinc source from inside to outside, realizes fast and uniform nucleation, releases interface stress from inside to outside of the ZnS shell layer in stages, passivates defects and avoids stress concentration to introduce new defects. The prepared copper-based core / multilayer shell structure quantum dot has a significantly improved fluorescence quantum yield; the stability of the quantum dot film in luminescence properties is obviously increased under the condition of a general indoor environment below 200 DEG C high temperature. Compared with a regulation mode of changing the zinc source type alone, the regulation precision is higher, the step-by-step growth requirement of the multilayer shell can be accurately matched, the preparation process is an oil phase conventional process, the operation is simple, the repeatability is good, and the application is suitable for industrialized scale production.

Description

Technical Field

[0001] This invention relates to the field of quantum dot materials technology, specifically to a copper-based core / multilayer shell quantum dot based on a gradient active zinc source and its preparation method. Background Technology

[0002] Quantum dots, with their unique optical and electrical properties, have broad application prospects in lighting, displays, solar cells, and bioimaging. Group I-III-VI quantum dots, being free of heavy metals harmful to human health and the environment, are considered green and environmentally friendly materials, and their flexible tunable band gap has attracted widespread attention. However, due to their small bulk surface area and high tolerance for defects, group I-III-VI quantum dots exhibit various defects such as substitution defects, vacancy defects, and surface defects. These defects lead to multiple relaxation pathways for charge carriers after excitation, increasing the probability of nonradiative recombination of excitons and reducing their fluorescence quantum yield. This limits their application in lighting, displays, and other fields requiring high luminous efficiency.

[0003] Copper is an abundant natural resource. With the increasing global awareness of environmental protection and the ever-increasing demands of various industries for material performance, the development of non-toxic, high-fluorescence quantum yield Cu-based I-III-VI group and derived quantum dots is imperative. Among existing technologies, patent CN115651643A discloses a near-infrared quantum dot material of zinc sulfide-encapsulated copper indium sulfide, its preparation method, and its applications. A two-step method was used to synthesize CuInS2@ZnS near-infrared quantum dot material, achieving precise detection of adenosine triphosphate bodies in plant cells. This provides technical support for monitoring plant growth and development and predicting the impact of external environmental factors, and has significant practical value. Research in the literature (Chemical Materials, 2018, 30: 2400-2413) indicates that the process of ZnS coating CuInS2 involves multiple competing reactions, including heteroepitaxial shell growth, alloying, etching, and cation exchange, which are closely related to the reactivity of the precursor, surface ligand residues, temperature, and other experimental conditions. The literature (Advanced Functional Materials, 2017, 27: 1602638) investigated the synthesis and luminescence properties of Zn-Ag-In-S / Zn-In-S / ZnS quantum dots. Their results showed that the concentration of precursors with the same reactivity has a regulatory effect on alloying or shell growth. Description

[0004] One objective of this invention is to provide a copper-based core / multilayer shell quantum dot material based on a gradient active zinc source. The prepared quantum dots exhibit fluorescence emission in the 450–700 nm wavelength range, with a fluorescence emission half-width ≤95 nm, a fluorescence quantum yield ≥70%, and good stability of luminescence properties at high temperatures.

[0005] The second objective of this invention is to provide a method for preparing copper-based core / multilayer shell quantum dot materials based on a gradient active zinc source, which has a simple preparation process and low energy consumption.

[0006] The present invention adopts the following technical solution.

[0007] A copper-based core / multilayer shell quantum dot based on a gradient active zinc source, characterized in that:

[0008] (1) The quantum dot is a core-three-shell structure. The core is a CuInZnS quaternary alloy quantum dot, and the shell is three ZnS layers that are tightly wrapped around the core surface. The three shells are defined as the first shell, the second shell, and the third shell from the inside to the outside.

[0009] (2) The CuInZnS quaternary alloy quantum dot core is derived from a highly active zinc source; the first shell is ZnS, derived from a medium-high active zinc source; the second shell is ZnS, derived from a medium active zinc source; and the third shell is ZnS, derived from a low active zinc source.

[0010] (3) The copper-based core / multilayer shell structure quantum dot CuInZnS / ZnS / ZnS / ZnS is characterized in that: as the number of shells increases, the average particle size of the quantum dots gradually increases;

[0011] The copper-based core / multilayer shell quantum dot CulnZnS / ZnS / ZnS / ZnS is characterized by: fluorescence emission in the 450-700nm wavelength range, fluorescence emission half-width ≤95nm, fluorescence quantum yield ≥70%, fluorescence quantum yield retention ≥72% after heating at 160℃ for 5min relative to the initial fluorescence quantum yield of the film, emission peak redshift ≤8am, and fluorescence emission half-width change ≤5nm.

[0012] A method for preparing copper-based core / multilayer shell quantum dots based on a gradient active zinc source, characterized by comprising the following steps:

[0013] (1) Preparation of CuInZnS quaternary alloy quantum dots: Cuprous iodide (CuI), indium acetate (In(Ac)3), highly active zinc source zinc iodide (ZnI2), elemental sulfur (S), oleylamine (OLA), n-dodecyl mercaptan (DDT) and octadecene (ODE) were placed in a three-necked flask, the mixture was purged with nitrogen and heated to 80°C, vacuumed for 30 min, and then heated to 210°C under nitrogen purging for 5 min to obtain CuInZnS quaternary alloy quantum dot stock solution;

[0014] (2) Preparation of CuInZnS / ZnS quantum dots: Maintain the reaction temperature of step (1), inject a medium-high activity zinc source, and react for 75 min under nitrogen atmosphere protection to obtain CuInZnS / ZnS quantum dot stock solution;

[0015] (3) Preparation of CuInZnS / ZnS / ZnS quantum dots: Maintain the reaction temperature of step (2), inject a medium active zinc source, and react for 30 min under nitrogen atmosphere protection to obtain CuInZnS / ZnS / ZnS quantum dot stock solution;

[0016] (4) Preparation of CuInZnS / ZnS / ZnS / ZnS quantum dots: The stock solution from step (3) was heated to 250°C, a low-activity zinc source was injected, and the reaction was carried out for 60 min under nitrogen atmosphere protection to obtain CuInZnS / ZnS / ZnS / ZnS quantum dot stock solution.

[0017] (5) Purification: Cool the stock solution from step (4) to room temperature, mix x mL of CuInZnS / ZnS / ZnS / ZnS quantum dot stock solution with 3 x mL of ethanol, centrifuge at 9000 rpm for 5 min, and collect the precipitate; mix the precipitate with x mL of n-hexane, centrifuge at 9000 rpm for 3 min, collect the precipitate again, and vacuum dry to obtain CuInZnS / ZnS / ZnS quantum dots.

[0018] Specifically, the preparation of CuInZnS quantum dots in step (1) above is characterized by the following: the molar ratio of ZnI2 to In(Ac)3 is (3-4):1, the molar ratio of CuI to In(Ac)3 is (0.1-0.25):1, and the amounts of S, OLA, DDT and ODE added per 0.5 mmol In(Ac)3 are 1 mmol, 3 mL, 0.5 mL and 1.5 mL, respectively.

[0019] Specifically, the medium-high activity zinc source described in step (2) above is characterized as a mixture of zinc acetate (Zn(Ac)2) dissolved in oleic acid (OA) and ODE. The preparation method of each part of the medium-high activity zinc source is as follows: 4 mmol of zinc acetate (Zn(Ac)2) is dissolved in 4 mL of OA and 4 mL of ODE, heated to 200°C and held for 30 min.

[0020] Specifically, the preparation of CuInZnS / ZnS quantum dots in step (2) above is characterized by injecting one part of a medium-high activity zinc source based on each 0.5 mmol In(Ac)3 of CuInZnS quantum dot stock solution prepared according to step (2).

[0021] Specifically, the active zinc source described in step (3) above is characterized as a mixed system of Zn(Ac)2 dissolved in OA, ODE and DDT. The preparation method of each part of the active zinc source is as follows: 2 mmol Zn(Ac)2 is dissolved in 2 mL OA, 3 mL ODE and 1 mL DDT, and heated to 200°C and held for 30 min.

[0022] Specifically, the preparation of CuInZnS / ZnS / ZnS quantum dots in step (3) above is characterized by injecting one part of a medium-active zinc source based on each 0.5 mmol In(Ac)3 prepared in accordance with steps (1) and (2) of CuInZnS / ZnS quantum dot stock solution.

[0023] Specifically, the low-activity zinc source described in step (4) above is characterized as a zinc stearate (Zn(St)2) dissolved in a mixture of ODE and DDT. The preparation method of each part of the low-activity zinc source is as follows: 2 mmol of zinc stearate (Zn(St)2) is dissolved in 3.5 mL of ODE and 1 mL of DDT, and the temperature is raised to 200°C and held for 30 min.

[0024] Specifically, the preparation of CuInZnS / ZnS / ZnS / ZnS quantum dots in step (4) above is characterized by injecting one part of low-activity zinc source based on each 0.5 mmol In(Ac)3 prepared according to steps (1), (2) and (3) of claim 2.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] This invention employs a CuInZnS quaternary alloy core-three-layer ZnS shell structure, combined with a stepwise growth design using a four-level active zinc source. By progressively decreasing the Zn source activity from the inside out, rapid and uniform nucleation is achieved, and the shell growth rate is gradient-controlled. This allows the ZnS shell to grow slowly and uniformly from the inside out, gradually releasing interfacial stress, passivating defects, and preventing stress concentration that could introduce new defects. The prepared copper-based core / multi-layer shell quantum dots exhibit significantly improved fluorescence quantum yield compared to nuclear quantum dots, and the stability of the quantum dot film's luminescence properties is also significantly enhanced at indoor temperatures below 200℃.

[0027] The highly active zinc source ZnI2 rapidly dissociates and releases Zn 2+ , with Cu + In 3+ and S 2- The combination forms uniformly sized CuInZnS quaternary alloy quantum dots; the medium-to-high activity zinc source coordinates with the carboxyl groups in OA, enabling rapid dissociation and release of Zn. 2+ , with S 2-By combining the first-shell ZnS, highly reactive dangling bond defects on the surface of CuInZnS quaternary alloy quantum dots are passivated: the thiol groups of DDT in the intermediate-active zinc source react with Zn... 2+ The resulting complex is more stable and releases Zn more slowly. 2+ This allows for the gentle growth of the second-shell ZnS, avoiding lattice distortion caused by rapid growth, and releasing stress at the core-shell interface. It further eliminates non-radiative recombination centers of excitons, significantly improving the fluorescence quantum yield of quantum dots; Zn from a low-activity zinc source... 2+ Due to the strong binding of stearate and thiol groups, the third shell of ZnS slowly and densely coats the quantum dots, preventing the intrusion of oxygen and water and effectively improving the thermal and air stability of the quantum dots.

[0028] This invention achieves zinc source activity gradient design through synergistic regulation of zinc source type and solvent coordination system. Compared with the regulation method of simply changing the zinc source type, the regulation accuracy is higher, which can accurately match the stepwise growth requirements of multi-layer shells. Moreover, the preparation process is a conventional oil phase process, which is simple to operate, has good repeatability, and is suitable for industrial scale-up production. Attached Figure Description

[0029] Figure 1 (a)-(d) respectively show the TEM images of the microstructures and corresponding particle size distributions of CuInZnS, CuInZnS / ZnS, CuInZnS / ZnS / ZnS and CuInZnS / ZnS / ZnS quantum dots prepared with Cu:In:Zn ratio of 1:8:12.

[0030] Figure 2 (a)-(d) respectively show the PL spectra and absorption spectra of CuInZnS, CuInZnS / ZnS, CuInZnS / ZnS / ZnS and CuInZnS / ZnS / ZnS quantum dots prepared with Cu:In:Zn ratio of 1:8:12, and their corresponding second-order differential curves.

[0031] Figure 3 (a)-(d) respectively show the PL spectra of thin films made from CuInZnS, CuInZnS / ZnS, CuInZnS / ZnS / ZnS and CuInZnS / ZnS / ZnS / ZnS quantum dots prepared with Cu:In:Zn ratio of 1:8:12 after heating at different temperatures for 5 min.

[0032] Figure 4(a)-(d) respectively show the changes in PL intensity and fluorescence quantum yield (PLQY) of thin films prepared using CuInZnS, CuInZnS / ZnS, CuInZnS / ZnS / ZnS and CuInZnS / ZnS / ZnS / ZnS quantum dots with a Cu:In:Zn ratio of 1:8:12 as a function of heating temperature.

[0033] Figure 5 (a)-(d) respectively show the changes in the full width at half maximum (FWHM) and emission peak position of the thin films prepared using Cu:In:Zn quantum dots of CulnZnS, CulnZnS / ZnS, CuInZnS / ZnS / ZnS and CuInZnS / ZnS / ZnS / ZnS as a function of heating temperature.

[0034] Figure 6 (a)-(d) respectively show the PL and absorption spectra of CunZnS / ZnS / ZnS / ZnS quantum dots prepared with Cu:In:Zn ratios of 1:4:12, 1:10:30 and 1:10:40. Detailed Implementation

[0035] To better understand the present invention, the technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0036] Example 1

[0037] Preparation of CuInZnS quantum dots: 0.0625 mmol CuI, 0.5 mmol In(Ac)3, 1.5 mmol ZnI2 and 1 mmol S powder, 3 mL LOAm, 0.5 mL DDT and 1.5 mL ODE were placed in a three-necked flask. The solution was heated to 80 °C under nitrogen purging at room temperature and evacuated for 30 min. Then, under nitrogen purging, the solution was heated to 210 °C and reacted for 5 min to obtain CuInZnS quantum dots.

[0038] Preparation of a highly active zinc source: Dissolve 4 mmol Zn(Ac)2 in 4 mL OA and 4 mL ODE, heat to 200 °C and maintain for 30 min.

[0039] The active zinc source for preparation was 2 mmol Zn(Ac)2 dissolved in 2 mL OA, 3 mL ODE and 1 mL DDT, and heated to 200 °C and held for 30 min.

[0040] Preparation of low-activity zinc source: 2 mmol Zn(St)2 was dissolved in 3.5 mL ODE and 1 mL DDT, and the temperature was raised to 200 °C and held for 30 min.

[0041] Preparation of CulnZnS / ZnS quantum dots: After the synthesis of CulnZnS quantum dots, a medium-to-high activity zinc source was injected into the CulnZnS core solution at 210℃ and kept at this temperature for 75 min under nitrogen atmosphere protection to grow CulnZnS / ZnS quantum dots.

[0042] Preparation of CulnZnS / ZnS / ZnS quantum dots: After the synthesis of CulnZnS / ZnS quantum dots, a moderately active zinc source was injected into the CulnZnS / ZnS solution at 210℃ and kept at this temperature for 30 min under nitrogen atmosphere protection to grow CulnZnS / ZnS / ZnS quantum dots.

[0043] Preparation of CuInZnS / ZnS / ZnS / ZnS quantum dots: After the synthesis of CuInZnS / ZnS / ZnS quantum dots, a low-activity zinc source was injected into the CuInZnS / ZnS / ZnS solution at 250℃ and kept at this temperature for 30 min under nitrogen atmosphere protection to grow CuInZnS / ZnS / ZnS quantum dots.

[0044] Purification: Cool the stock solution from step (4) to room temperature, mix x mL of CuInZnS / ZnS / ZnS / ZnS quantum dot stock solution with 3 x mL of ethanol, centrifuge at 9000 rpm for 5 min, and collect the precipitate; mix the precipitate with x mL of n-hexane, centrifuge at 9000 rpm for 3 min, collect the precipitate again, and vacuum dry to obtain CuInZnS / ZnS / ZnS quantum dots.

[0045] Example 2

[0046] Preparation of CuInZnS quantum dots: 0.125 mmol CuI, 0.5 mmol In(Ac)3, 1.5 mmol ZnI2 and 1 mmol S powder, 3 mL LOAm, 0.5 mL DDT and 1.5 mL ODE were placed in a three-necked flask. The solution was heated to 80 °C under nitrogen purging at room temperature and evacuated for 30 min. Then, under nitrogen purging, the solution was heated to 210 °C and reacted for 5 min to obtain CuInZnS quantum dots.

[0047] Preparation of a highly active zinc source: Dissolve 4 mmol Zn(Ac)2 in 4 mL OA and 4 mL ODE, heat to 200 °C and maintain for 30 min.

[0048] The active zinc source for preparation was 2 mmol Zn(Ac)2 dissolved in 2 mL OA, 3 mL LODE and 1 mL LDDT, and heated to 200 °C and held for 30 min.

[0049] Preparation of low-activity zinc source: 2 mmol Zn(St)2 was dissolved in 3.5 mL ODE and 1 mL DDT, and the temperature was raised to 200 °C and held for 30 min.

[0050] Preparation of CuInZnS / ZnS quantum dots: After the synthesis of CuInZnS quantum dots, a medium-high activity zinc source was injected into the CuInZnS core solution at 210℃ and kept at this temperature for 75 min under nitrogen atmosphere protection to grow CuInZnS / ZnS quantum dots.

[0051] Preparation of CuInZnS / ZnS / ZnS quantum dots: After the synthesis of CuInZnS / ZnS quantum dots, a medium-active zinc source was injected into the CuInZnS / ZnS solution at 210℃ and kept at this temperature for 30 min under nitrogen atmosphere protection to grow CuInZnS / ZnS / ZnS quantum dots.

[0052] Preparation of CuInZnS / ZnS / ZnS / ZnS quantum dots: After the synthesis of CuInZnS / ZnS / ZnS quantum dots, a low-activity zinc source was injected into the CuInZnS / ZnS / ZnS solution at 250℃ and kept at this temperature for 30 min under nitrogen atmosphere protection to grow CuInZnS / ZnS / ZnS / ZnS quantum dots.

[0053] Purification: Cool the stock solution from step (4) to room temperature, mix x mL of CuInZnS / ZnS / ZnS / ZnS quantum dot stock solution with 3x mL of ethanol, centrifuge at 9000 rpm for 5 min, and collect the precipitate; mix the precipitate with x mL of n-hexane, centrifuge at 9000 rpm for 3 min, collect the precipitate again, and vacuum dry to obtain CuInZnS / ZnS / ZnS quantum dots.

[0054] Example 3

[0055] Preparation of CuInZnS quantum dots: 0.05 mmol CuI, 0.5 mmol In(Ac)3, 1.5 mmol ZnI2 and 1 mmol S powder, 3 mL OAm, 0.5 mL DDT and 1.5 mL ODE were placed in a three-necked flask. The solution was heated to 80 °C under nitrogen purging at room temperature, and after vacuuming for 30 min, the solution was heated to 210 °C under nitrogen purging and the reaction was continued for 5 min to obtain CuInZnS quantum dots.

[0056] Preparation of a highly active zinc source: Dissolve 4 mmol Zn(Ac)2 in 4 mL OA and 4 mL ODE, heat to 200 °C and maintain for 30 min.

[0057] The active zinc source for preparation was 2 mmol Zn(Ac)2 dissolved in 2 mL OA, 3 mL ODE and 1 mL DDT, and heated to 200 °C and held for 30 min.

[0058] Preparation of low-activity zinc source: 2 mmol Zn(St)2 was dissolved in 3.5 mL ODE and 1 mL DDT, and the temperature was raised to 200 °C and held for 30 min.

[0059] Preparation of CuInZnS / ZnS quantum dots: After the synthesis of CuInZnS quantum dots, a medium-high activity zinc source was injected into the CuInZnS core solution at 210℃ and kept at this temperature for 75 min under nitrogen atmosphere protection to grow CuInZnS / ZnS quantum dots.

[0060] Preparation of CuInZnS / ZnS / ZnS quantum dots: After the synthesis of CuInZnS / ZnS quantum dots, a medium-active zinc source was injected into the CuInZnS / ZnS solution at 210℃ and kept at this temperature for 30 min under nitrogen atmosphere protection to grow CuInZnS / ZnS / ZnS quantum dots.

[0061] Preparation of CuInZnS / ZnS / ZnS / ZnS quantum dots: After the synthesis of CuInZnS / ZnS / ZnS quantum dots, a low-activity zinc source was injected into the CuInZnS / ZnS / ZnS solution at 250℃ and kept at this temperature for 30 min under nitrogen atmosphere protection to grow CuInZnS / ZnS / ZnS quantum dots.

[0062] Purification: Cool the stock solution from step (4) to room temperature, mix x mL of CuInZnS / ZnS / ZnS / ZnS quantum dot stock solution with 3 x mL of ethanol, centrifuge at 9000 rpm for 5 min, and collect the precipitate; mix the precipitate with x mL of n-hexane, centrifuge at 9000 rpm for 3 min, collect the precipitate again, and vacuum dry to obtain CuInZnS / ZnS / ZnS quantum dots.

[0063] Example 4

[0064] Preparation of CuInZnS quantum dots: 0.05 mmol CuI, 0.5 mmol In(Ac)3, 2 mmol ZnI2 and 1 mmol S powder, 3 mL LOAm, 0.5 mL DDT and 1.5 mL ODE were placed in a three-necked flask. The solution was heated to 80 °C under nitrogen purging at room temperature, and after vacuuming for 30 min, the solution was heated to 210 °C under nitrogen purging and the reaction was continued for 5 min to obtain CuInZnS quantum dots.

[0065] Preparation of a highly active zinc source: Dissolve 4 mmol Zn(Ac)2 in 4 mL OA and 4 mL ODE, heat to 200 °C and maintain for 30 min.

[0066] The active zinc source for preparation was 2 mmol Zn(Ac)2 dissolved in 2 mL OA, 3 mL ODE and 1 mL DDT, and heated to 200 °C and held for 30 min.

[0067] Preparation of low-activity zinc source: 2 mmol Zn(St)2 was dissolved in 3.5 mL ODE and 1 mL DDT, and the temperature was raised to 200 °C and held for 30 min.

[0068] Preparation of CulnZnS / ZnS quantum dots: After the synthesis of CulnZnS quantum dots, a medium-to-high activity zinc source was injected into the CulnZnS core solution at 210℃ and kept at this temperature for 75 min under nitrogen atmosphere protection to grow CulnZnS / ZnS quantum dots.

[0069] Preparation of CuInZnS / ZnS / ZnS quantum dots: After the synthesis of CuInZnS / ZnS quantum dots was completed, a medium-active zinc source was injected into the CuInZnS / ZnS solution at 210℃ and kept at this temperature for 30 min under nitrogen atmosphere protection to grow CuInZnS / ZnS / ZnS quantum dots.

[0070] Preparation of CuInZnS / ZnS / ZnS / ZnS quantum dots: After the synthesis of CuInZnS / ZnS / ZnS quantum dots, a low-activity zinc source was injected into the CuInZnS / ZnS / ZnS solution at 250℃ and kept at this temperature for 30 min under nitrogen atmosphere protection to grow CuInZnS / ZnS / ZnS quantum dots.

[0071] Purification: Cool the stock solution from step (4) to room temperature, mix x mL of CulnZnS / ZnS / ZnS / ZnS quantum dot stock solution with 3x mL of ethanol, centrifuge at 9000 rpm for 5 min, and collect the precipitate; mix the precipitate with x mL of n-hexane, centrifuge at 9000 rpm for 3 min, collect the precipitate again, and vacuum dry to obtain CulnZnS / ZnS / ZnS quantum dots.

[0072] The test results are as follows:

[0073] Figure 1 (a)-(d) sequentially present TEM images and corresponding particle size distribution diagrams of the microstructures of CuInZnS, CuInZnS / ZnS, CuInZnS / ZnS / ZnS, and CuInZnS / ZnS / ZnS / ZnS quantum dots prepared according to Example 1. The average particle size of the CuInZnS core is 1.98 nm, the average particle size of CuInZnS / ZnS is 2.3 nm, the average particle size of CuInZnS / ZnS / ZnS is 2.37 nm, and the average particle size of CuInZnS / ZnS / ZnS / ZnS quantum dots is 3.75 nm. The average particle size increases with the number of shell layers, proving that the shell layers have been successfully epitaxially grown. The third shell layer is significantly thicker than the first two shell layers. This is due to the difference in the reactivity of the shell precursors. The slower reaction rate of zinc stearate is conducive to the formation of a denser and more uniform final outer shell layer.

[0074] Figure 2 (a)-(d) sequentially present the PL and absorption spectra and their corresponding second-order differential curves of CuInZnS, CuInZnS / ZnS, CuInZnS / ZnS / ZnS, and CuInZnS / ZnS / ZnS / ZnS quantum dots prepared according to Example 1. With the increase of the number of shells, the emission peak of the emission spectrum exhibits a blue shift, and the Stokes shift decreases. The fluorescence quantum yields of CuInZnS / ZnS, CuInZnS / ZnS / ZnS, and CuInZnS / ZnS / ZnS quantum dots are significantly improved compared to CuInZnS quantum dots. Specifically, the fluorescence quantum yields of CuInZnS / ZnS / ZnS and CuInZnS / ZnS / ZnS / ZnS quantum dots are 82.1% and 74.6%, respectively; the full width at half maximum (FWHM) of the fluorescence emission of all quantum dots is <100 nm.

[0075] Figure 3 (a)-(d) sequentially show the PL spectra of thin films made from CuInZnS, CuInZnS / ZnS, CuInZnS / ZnS / ZnS, and CuInZnS / ZnS / ZnS / ZnS quantum dots prepared according to Example 1 after heating at different temperatures for 5 min. The PL spectral intensity decreased with increasing annealing temperature.

[0076] Figure 4(a)-(d) sequentially show the changes in photoluminescence intensity (PL) and fluorescence quantum yield (PL QY) of the CuInZnS, CuInZnS / ZnS, CuInZnS / ZnS / ZnS, and CuInZnS / ZnS / ZnS / ZnS quantum dots prepared according to Example 1 as a function of heating temperature (room temperature to 200°C). With increasing heating temperature, the integrated PL intensity, peak PL intensity, and fluorescence quantum yield decrease accordingly. Compared to the decrease in PL integrated intensity, PL peak intensity, and fluorescence quantum yield of quantum dot films at room temperature, after heating at 160℃ for 5 min, the retention rates of PL integrated intensity, PL peak intensity, and fluorescence quantum yield for CuInZnS quantum dot films are as follows: ≥85%, ≥77%, and ≥60%; ≥52%, ≥49%, and ≥27% for CuInZnS / ZnS / ZnS quantum dot films; ≥75%, ≥73%, and ≥70% for CuInZnS / ZnS / ZnS quantum dot films; and ≥79%, ≥76%, and ≥72% for CuInZnS / ZnS / ZnS / ZnS quantum dot films. It can be seen that as the number of shells increases, the retention rate of fluorescence quantum yield of quantum dot films at high temperatures is higher.

[0077] Figure 5 (a)-(d) respectively show the changes in the full width at half maximum (FWHM) and emission peak position of the PL spectra of the CuInZnS, CuInZnS / ZnS, CuInZnS / ZnS / ZnS, and CuInZnS / ZnS / ZnS / ZnS quantum dot films prepared according to Example 1 as a function of heating temperature (room temperature to 200°C). Relative to the FWHM and emission peak positions of the quantum dot films at room temperature, the FWHM of the CuInZnS quantum dot film changes by ≤10 nm and the emission peak redshift is ≤18 nm; the FWHM of the CuInZnS / ZnS quantum dot film changes by ≤4 nm and the emission peak redshift is ≤2 nm; the FWHM of the CuInZnS / ZnS / ZnS quantum dot film changes by ≤2 nm and the emission peak blueshift is ≤2 nm; and the FWHM of the CuInZnS / ZnS / ZnS / ZnS quantum dot film changes by ≤5 nm and the emission peak redshift is ≤8 nm. It can be seen that, compared to CuInZnS quantum dots, the shell helps to increase the stability of the luminescence properties of quantum dot films at high temperatures.

[0078] Therefore, the prepared copper-based core / multilayer shell quantum dots have a significantly higher fluorescence quantum yield than nuclear quantum dots, and the stability of the quantum dot film's luminescence properties is also significantly increased under typical indoor high-temperature conditions.

[0079] Figure 6 (a)-(d) respectively show the photoluminescence (PL) and absorption spectra of CuInZnS / ZnS / ZnS / ZnS quantum dots prepared according to Examples 2, 3, and 4, i.e., Cu:In:Zn ratios of 1:4:12, 1:10:30, and 1:10:40. Combined with the PL and absorption spectra of CuInZnS / ZnS / ZnS / ZnS quantum dots prepared according to Example 1, i.e., Cu:In:Zn ratio of 1:8:24, it can be seen that the emission wavelength of the quantum dots can be adjusted by regulating the cation ratio.

[0080] It should be noted that those skilled in the art can make various improvements and modifications without departing from the concept of this invention, and these improvements and modifications are also considered to be within the scope of protection of this invention.

Claims

1. A copper-based core / multilayer shell quantum dot based on a gradient-active zinc source, characterized in that: (1) The quantum dot is a core-three-shell structure. The core is a CuInZnS quaternary alloy quantum dot, and the shell is three ZnS layers that are tightly wrapped around the core surface. The three shells are defined as the first shell, the second shell, and the third shell from the inside to the outside. (2) The CuInZnS quaternary alloy quantum dot core is derived from a highly active zinc source; the first shell is ZnS, derived from a medium-high active zinc source; the second shell is ZnS, derived from a medium-active zinc source. The third shell layer is ZnS, and the Zn is derived from a low-activity zinc source. (3) The copper-based core / multi-shell structured quantum dot CulnZnS / ZnS / ZnS / ZnS is characterized in that: as the number of shells increases, the average particle size of the quantum dots gradually increases; (4) The copper-based core / multilayer shell structure quantum dot CulnZnS / ZnS / ZnS / ZnS is characterized by: fluorescence emission in the 450-700nm band, fluorescence emission half-width ≤95nm, fluorescence quantum yield ≥70%; fluorescence quantum yield decreases after film formation; relative to the initial fluorescence quantum yield of the film, fluorescence quantum yield retention rate is ≥72% after heating at 160℃ for 5min, emission peak redshift ≤8nm, fluorescence emission half-width change ≤5nm.

2. A method for preparing CullZnS / ZnS / ZnS / ZnS copper-based core / multilayer shell structured quantum dots as described in claim 1, characterized in that, Includes the following steps: (1) Preparation of CuInZnS quaternary alloy quantum dots: Cuprous iodide (CuI), indium acetate (In(Ac)3), highly active zinc source zinc iodide (ZnI2), elemental sulfur (S), oleylamine (OLA), n-dodecyl mercaptan (DDT) and octadecene (oDE) were placed in a three-necked flask, the mixture was purged with nitrogen and heated to 80°C, vacuumed for 30 min, and then heated to 210°C under nitrogen purging for 5 min to obtain CuInZnS quaternary alloy quantum dot stock solution; (2) Preparation of CuInZnS / ZnS quantum dots: Maintain the reaction temperature of step (1), inject a medium-high activity zinc source, and react for 75 min under nitrogen atmosphere protection to obtain CuInZnS / ZnS quantum dot stock solution; (3) Preparation of CuInZnS / ZnS / ZnS quantum dots: Maintain the reaction temperature of step (2), inject a medium active zinc source, and react for 30 min under nitrogen atmosphere protection to obtain CuInZnS / ZnS / ZnS quantum dot stock solution; (4) Preparation of CuInZnS / ZnS / ZnS / ZnS quantum dots: The stock solution from step (3) was heated to 250°C, a low-activity zinc source was injected, and the reaction was carried out under a nitrogen atmosphere for 60 min to obtain CuInZnS / ZnS / ZnS / ZnS quantum dot stock solution. (5) Purification: Cool the stock solution from step (4) to room temperature, mix x mL of CuInZnS / ZnS / ZnS / ZnS quantum dot stock solution with 3 x mL of ethanol, centrifuge at 9000 rpm for 5 min, and collect the precipitate; mix the precipitate with x mL of n-hexane, centrifuge at 9000 rpm for 3 min, collect the precipitate again, and vacuum dry to obtain CuInZnS / ZnS / ZnS quantum dots.

3. The preparation of CuInZnS quantum dots according to step (1) of claim 2, characterized in that, The molar ratio of ZnI2 to In(Ac)3 is (3-4):1, and the molar ratio of CuI to In(Ac)3 is (0.25-0.1):

1. For every 0.5 mmol of In(Ac)3, the amounts of S, OLA, DDT, and ODE added are 1 mmol, 3 mL, 0.5 mL, and 1.5 mL, respectively.

4. The medium-to-high activity zinc source according to step (2) of claim 2, characterized in that, The method for preparing one part of the high-activity zinc source is as follows: 4 mmol Zn(Ac)2 is dissolved in 4 mL OA and 4 mL ODE, heated to 200℃ and held for 30 min.

5. The preparation of CuInZnS / ZnS quantum dots according to step (2) of claim 2, characterized in that, Based on the CuInZnS quantum dot stock solution prepared in step (2) with each 0.5 mmol In(Ac)3, one part of medium-high activity zinc source is injected.

6. The active zinc source according to step (3) of claim 2, characterized in that, The active zinc source in each part of the Zn(Ac)2 mixture dissolved in OA, ODE and DDT is prepared as follows: 2 mmol Zn(Ac)2 is dissolved in 2 mL OA, 3 mL ODE and 1 mL DDT, and heated to 200℃ and held for 30 min.

7. The preparation of CuInZnS / ZnS / ZnS quantum dots according to step (3) of claim 2, characterized in that, Based on the CuInZnS / ZnS quantum dot stock solution prepared according to steps (1) and (2) with each 0.5 mmol In(Ac)3, one part of medium-active zinc source is injected.

8. The low-activity zinc source according to step (4) of claim 2, characterized in that, The method for preparing one part of low-activity zinc source is as follows: 2 mmol of zinc stearate (Zn(St)2) is dissolved in 3.5 mL of ODE and 1 mL of DDT, and the temperature is raised to 200℃ and held for 30 min.

9. The preparation of CullZnS / ZnS / ZnS / ZnS quantum dots according to step (4) of claim 2, characterized in that, Based on the CuInZnS / ZnS / ZnS quantum dot stock solution prepared according to steps (1), (2) and (3) of claim 2, 1 part of low-activity zinc source is injected.

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