Preparation method of CdZnS / ZnSe / ZnS parabolic energy band structure quantum dots

Abstract

The invention relates to a preparation method of CdZnS / ZnSe / ZnS parabolic energy band structure quantum dots. The preparation method comprises the following steps: preparing an S-ODE precursor solution, an S-TOP precursor solution and a Se-TBP precursor solution; preparing a CdZnS core solution from cadmium oxide, zinc acetate, oleic acid, 1-octadecene and the S-ODE precursor solution; preparing a CdZnS / ZnSe solution from zinc acetate, oleic acid, 1-octadecene, the CdZnS core solution and the Se-TBP precursor solution; the preparation method comprises the following steps: preparing a CdZnS / ZnSe / ZnS parabolic band structure quantum dot solution from zinc acetate, oleic acid, a 1-octadecene CdZnS / ZnSe solution and an S-TOP precursor solution; according to the invention, efficient and stable pure blue light emission is realized through a preparation method of three-shell collaborative design of a CdZnS core, a ZnSe intermediate layer and a ZnS shell.

Description

Technical Field

[0001] This invention relates to the fields of quantum dot synthesis technology and optoelectronic materials applications, and particularly to a method for preparing CdZnS / ZnSe / ZnS parabolic band structure quantum dots. Background Technology

[0002] Quantum dots, as semiconductor nanocrystals with unique size-dependent optical properties, have shown broad application prospects in fields such as displays, lighting, and photoelectric detection. Among them, blue quantum dots are one of the core materials for realizing full-color gamut high-definition displays, and their performance directly determines the color gamut width and color purity of display devices. Among many material systems, CdZnS-based quantum dots are considered highly promising candidate materials because they can achieve efficient emission in the blue light band by precisely adjusting the composition and have a narrow half-width at half-maximum (HWHM). To improve the fluorescence quantum yield and stability of quantum dots, the mainstream technical route usually adopts a core-shell structure, with wide-bandgap semiconductor materials (such as ZnS) encapsulating the luminescent CdZnS core being the most common. However, this structure still faces significant bottlenecks in the actual preparation of high-performance blue quantum dots. Due to the large lattice mismatch between the CdZnS core and the ZnS shell, direct epitaxial growth leads to high-density defects at the interface, which become non-radiative recombination centers. This not only limits the further improvement of fluorescence quantum yield but also causes spectral broadening and redshift of the emission wavelength, making it difficult to obtain pure and stable blue light. Meanwhile, traditional single-shell structures often lack stability in terms of light, heat, and environment. The shell is prone to degradation under harsh conditions, leading to exposure of the core material and fluorescence quenching. Although introducing intermediate layers (such as ZnSe) to form gradient shells is an effective approach to alleviate mismatch and improve stability, existing fabrication methods still face challenges in the precise and controllable growth of multilayer structures. The complexity of the process results in poor controllability of shell thickness, interface composition, and structure, making it difficult to achieve reproducible and scalable fabrication with excellent stability while ensuring high quantum yield. Therefore, developing a precise, efficient, and reproducible fabrication method that can precisely control the core-shell structure to obtain CdZnS-based blue quantum dots with both high fluorescence efficiency and excellent stability is crucial for their commercial application. Summary of the Invention

[0003] Technical problem solved: To address the shortcomings of existing blue quantum dots, such as weak exciton confinement, severe nonradiative recombination, and poor stability, this invention provides a method for preparing CdZnS / ZnSe / ZnS parabolic band structure quantum dots. Through a three-shell synergistic design of "CdZnS core - ZnSe intermediate layer - ZnS shell", efficient and stable pure blue light emission is achieved.

[0004] Technical solution: A method for preparing CdZnS / ZnSe / ZnS parabolic band structure quantum dots, the steps of which are as follows:

[0005] (1) Preparation of S-ODE precursor solution, S-TOP precursor solution and Se-TBP precursor solution: S powder was dissolved in 1-octadecene in an inert gas environment and at a temperature of 150-180℃ to obtain an S-ODE precursor solution with a concentration of 0.5 mmol / mL; S powder was dissolved in tri-n-octylphosphine in an inert gas environment and at a temperature of 130-150℃ to obtain an S-TOP precursor solution with a concentration of 0.2 mmol / mL; Se powder was dissolved in tributyl phosphate in an inert gas environment and at a temperature of 130-150℃ to obtain a Se-TBP precursor solution with a concentration of 0.2 mmol / mL.

[0006] (2) Preparation of CdZnS core solution: Under argon protection, cadmium oxide, zinc acetate, oleic acid and 1-octadecene were added to a three-necked flask. The mixture was vented and dehydrated at 130℃ for 30 min. Then the temperature was raised to 300℃ and stabilized before injecting the S-ODE precursor solution prepared in step (1). After reacting for 30 min, the mixture was cooled to room temperature to obtain crude CdZnS core product. After purification, it was dispersed in 1-octadecene to obtain CdZnS core solution. The molar ratio of cadmium oxide and zinc acetate added to the three-necked flask was 1:5 and each mmol of cadmium oxide corresponded to 10 mL of oleic acid and 40 mL of 1-octadecene. The ratio of the number of moles of S in the S-ODE precursor solution to the total number of moles of cadmium oxide and zinc acetate was 1:2. Each mL of crude CdZnS core product was dispersed in 0.4 mL of 1-octadecene after purification.

[0007] (3) Preparation of CdZnS / ZnSe solution: Under argon protection, zinc acetate, oleic acid and 1-octadecene were added to another three-necked flask. The mixture was vented and dehydrated at 130°C for 30 min. Then the temperature was raised to 280°C and stabilized before the CdZnS core solution prepared in step (2) was injected. Then the Se-TBP precursor solution prepared in step (1) was injected in portions using a peristaltic pump. After all the solution was injected, the reaction continued for 30 min. After cooling, the crude CdZnS / ZnSe core-shell intermediate product was obtained. After purification, it was dispersed in 1-octadecene to obtain the CdZnS / ZnSe solution. Each mmol of zinc acetate added to the other three-necked flask corresponded to 2.5 mL of oleic acid, 10 mL of 1-octadecene, 5 mL of CdZnS core solution and 5 mL of Se-TBP precursor solution. Each 3 mL of CdZnS / ZnSe core-shell intermediate crude product was purified and dispersed in 2 mL of 1-octadecene.

[0008] (4) Preparation of CdZnS / ZnSe / ZnS parabolic band structure quantum dot solution: Under argon protection, zinc acetate, oleic acid and 1-octadecene were added to the reaction flask. The mixture was vented and dehydrated at 130°C for 30 min. Then the temperature was raised to 280°C and stabilized before injecting the CdZnS / ZnSe solution prepared in step (3). Then the S-TOP precursor solution prepared in step (1) was injected using a peristaltic pump. After reacting for 30 min, the mixture was cooled to room temperature. The resulting product was purified to obtain the CdZnS / ZnSe / ZnS parabolic band structure quantum dot solution with n-hexane as solvent. Each mmol of zinc acetate added to the reaction flask corresponds to 2.5 mL of oleic acid, 10 mL of 1-octadecene, 5 mL of CdZnS / ZnSe solution and 5 mL of S-TOP precursor solution.

[0009] The purification steps in step (2) described above are as follows: Add the same volume of n-hexane and 6 times the volume of ethanol to the crude CdZnS core product, mix well, centrifuge, discard the supernatant, and obtain the precipitate; disperse the precipitate in the same volume of n-hexane as the crude CdZnS core product, centrifuge, repeat 2-3 times, discard the precipitate, and obtain the supernatant; add 4 times the volume of ethanol to the supernatant, continue centrifugation, discard the supernatant, and obtain the precipitate, thus completing the purification.

[0010] The purification steps in step (3) described above are as follows: Add the same volume of n-hexane and 6 times the volume of ethanol to the crude CdZnS / ZnSe core-shell intermediate, mix well, and centrifuge to separate the precipitate by discarding the supernatant; disperse the precipitate in the same volume of n-hexane as the crude CdZnS / ZnSe core-shell intermediate, centrifuge to separate the precipitate, repeat 2-3 times, discard the precipitate, and obtain the supernatant; add 4 times the volume of ethanol to the supernatant, centrifuge again, discard the supernatant, and obtain the precipitate, thus completing the purification.

[0011] The purification step (4) described above is as follows: add the same volume of n-hexane and 6 times the volume of ethanol to the product, mix well, separate by centrifugation, and discard the supernatant; disperse the precipitate in n-hexane of the same volume as the product, separate by centrifugation, repeat 2-3 times, discard the precipitate, and the obtained supernatant is the CdZnS / ZnSe / ZnS parabolic band structure quantum dot solution with n-hexane as solvent.

[0012] Beneficial Effects: The method for preparing CdZnS / ZnSe / ZnS parabolic band structure quantum dots provided by this invention has the following beneficial effects: The preparation method of this invention is simple and efficient, and successfully prepares efficient and stable blue quantum dots. Its unique parabolic band structure design and three-shell passivation strategy provide a new path to solve the performance bottleneck of blue quantum dots. The obtained quantum dots meet the application requirements of the display industry in terms of luminous efficiency, color purity and thermal stability, laying a solid foundation for the subsequent construction and performance optimization of QLED devices. Attached Figure Description

[0013] Figure 1 The flowchart shows the preparation process of the CdZnS / ZnSe / ZnS parabolic band structure quantum dots in Example 1.

[0014] Figure 2 The image shows the TEM morphology of the CdZnS / ZnSe / ZnS parabolic band structure quantum dot from Example 1.

[0015] Figure 3 EDS diagram of the CdZnS / ZnSe / ZnS parabolic band structure quantum dot of Example 1.

[0016] Figure 4 This is a schematic diagram showing the electron-hole wave function distribution of the CdZnS / ZnSe / ZnS parabolic band structure quantum dots in Example 1 as a function of the shell.

[0017] Figure 5 The fluorescence decay kinetics of CdZnS, CdZnS / ZnSe, and the CdZnS / ZnSe / ZnS parabolic band structure quantum dots of Example 1 are shown.

[0018] Figure 6 This study investigates the stability of the CdZnS / ZnSe / ZnS parabolic band structure quantum dots in Example 1. Figure (a) shows the change in PL intensity (PL) of the CdZnS / ZnSe / ZnS parabolic band structure quantum dots over time (under natural conditions). Figure (b) shows the change in PL intensity of the CdZnS / ZnSe / ZnS parabolic band structure quantum dots over time (at 60°C). Figure (c) shows the change in PL intensity of the CdZnS / ZnSe / ZnS parabolic band structure quantum dots over time (under UV irradiation). Figure (d) shows the change in PL intensity of the CdZnS / ZnSe / ZnS parabolic band structure quantum dots with laser intensity. Detailed Implementation

[0019] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. After reading this invention, any modifications of the invention in various equivalent forms by those skilled in the art will fall within the scope defined by the appended claims.

[0020] The reagents used in the following examples are from the following sources:

[0021] S powder: Sulfur powder (S, 99.999%), purchased from Ron Company, without further purification before use;

[0022] Se powder: Se powder (Se, 99.999%), purchased from Aladdin, was not further purified before use;

[0023] 1-Octadecene (ODE): 1-Octadecene (ODE, 90%), purchased from Aladdin.

[0024] Tributyl phosphate (TBP): Tributyl phosphate (C 12 H 27 P, 90%, purchased from Aladdin;

[0025] Tri-n-octylphosphine (TOP): Tri-n-octylphosphine (C 24 H 51 P, 90%, purchased from Aladdin;

[0026] Cadmium oxide (CdO): Cadmium oxide (CdO, 99.9%), purchased from Aladdin.

[0027] Zinc acetate (Zn(Ac)2): Zinc acetate (Zn(Ac)2, 99%), purchased from Aladdin;

[0028] Oleic acid (OA): Oleic acid (C) 18 H 34 O2 (85%), purchased from Aladdin;

[0029] n-Hexane (C6H) 14 ): n-Hexane (C6H) 14 (97%), purchased from Macklin;

[0030] Ethanol (C2H5OH): Ethanol (C2H5OH, 99%) was purchased from Aladdin.

[0031] Example 1

[0032] This embodiment provides a method for preparing CdZnS / ZnSe / ZnS parabolic band structure quantum dots (specific steps are as follows) Figure 1 (As shown), the steps are as follows:

[0033] (1) In an inert gas environment and at a temperature of 180℃, 1 mmol of S powder was dissolved in 2 mL of 1-octadecene to obtain an S-ODE precursor solution; in an inert gas environment and at a temperature of 150℃, 0.4 mmol of S powder was dissolved in 2 mL of tri-n-octylphosphine to obtain an S-TOP precursor solution; in an inert gas environment and at a temperature of 150℃, 0.4 mmol of Se powder was dissolved in 2 mL of tributyl phosphate to obtain a Se-TBP precursor solution.

[0034] (2) Under argon protection, 0.2 mmol of cadmium oxide, 1 mmol of zinc acetate, 2 mL of oleic acid, and 8 mL of 1-octadecene were added to a 100 mL three-necked flask. The mixture was degassed and dehydrated at 130 °C for 30 min. The temperature was then raised to 300 °C and stabilized. 1.2 mL of the S-ODE precursor solution prepared in step (1) was quickly injected. After reacting for 30 min, the mixture was cooled to room temperature to obtain crude CdZnS core products. Purification was then performed. 1 mL of the crude CdZnS core products was transferred to a centrifuge tube each time, and 1 mL of n-hexane and 6 mL of ethanol were slowly added. The mixture was gently inverted and mixed until the solution became turbid. The centrifuge tube was then placed in a centrifuge and centrifuged at 6000 rpm for 3 min. The supernatant was discarded after centrifugation to obtain a precipitate containing CdZnS core quantum dots. Dissolve the precipitate in 1 mL of n-hexane, centrifuge again, discard the precipitate, and obtain a supernatant containing CdZnS quantum dots (if the supernatant is turbid, repeat the above operation). Add 4 mL of ethanol to the supernatant containing CdZnS quantum dots, centrifuge again, and obtain a precipitate containing CdZnS quantum dots, completing the purification. A total of 10 mL of crude CdZnS quantum dots product was purified. After purification, the precipitate was dispersed in 4 mL of 1-octadecene to obtain a CdZnS quantum dot solution.

[0035] (3) Under argon protection, add 0.4 mmol of zinc acetate, 1 mL of oleic acid and 4 mL of 1-octadecene to another three-necked flask. Remove water by venting at 130°C for 30 min. Then raise the temperature to 280°C and, after stabilization, inject 2 mL of the CdZnS core solution prepared in step (2). Then, use a peristaltic pump to slowly inject 2 mL of the Se-TBP precursor solution prepared in step (1) in 5 portions, with a 3 min interval between each injection. After all the injections are completed, continue the reaction for 30 min. After cooling, the crude CdZnS / ZnSe core-shell intermediate product is obtained. Then, purification is performed. Each time, take 1 mL of the synthesized crude CdZnS / ZnSe core-shell intermediate product and transfer it to a centrifuge tube. Slowly add 1 mL of n-hexane and 6 mL of ethanol, gently invert and mix. Observe that the solution becomes turbid. The centrifuge tubes were then placed in a centrifuge and centrifuged at 6000 rpm for 3 min. After centrifugation, the supernatant was discarded, yielding a precipitate containing CdZnS / ZnSe core-shell intermediate quantum dots. The precipitate was dissolved in 1 mL of n-hexane, and centrifugation was continued. The precipitate was discarded after centrifugation, yielding a supernatant containing CdZnS / ZnSe core-shell intermediate quantum dots (if the supernatant is turbid, the above operation can be repeated). 4 mL of ethanol was added to the supernatant containing CdZnS / ZnSe core-shell intermediate quantum dots, and centrifugation was continued to obtain a precipitate containing CdZnS / ZnSe core-shell intermediate quantum dots, completing the purification. A total of 6 mL of CdZnS / ZnSe core-shell intermediate crude product was purified. After purification, the precipitate was dispersed in 4 mL of 1-octadecene to obtain a CdZnS / ZnSe solution.

[0036] (4) Under argon protection, add 0.4 mmol of zinc acetate, 1 mL of oleic acid and 4 mL of 1-octadecene to the reaction flask. Remove water by venting at 130℃ for 30 min, then raise the temperature to 280℃. After stabilization, inject 2 mL of the CdZnS / ZnSe solution prepared in step (3). Then, slowly inject 2 mL of the S-TOP precursor solution prepared in step (1) using a peristaltic pump. After reacting for 30 min, cool to room temperature. Add 1 mL of n-hexane and 6 mL of ethanol to the resulting product, gently invert and mix to precipitate the quantum dots. Separate by centrifugation and discard the supernatant. The precipitate can be redispersed in 1 mL of n-hexane. Separate by centrifugation and discard the precipitate. Repeat this purification process twice to remove excess reaction precursors, byproducts and free ligands. Finally, a well-dispersed, high-purity CdZnS / ZnSe / ZnS parabolic band structure quantum dot colloidal solution with n-hexane as solvent is obtained.

[0037] The TEM morphology of the CdZnS / ZnSe / ZnS parabolic band structure quantum dots prepared in this embodiment is as follows: Figure 2 As shown, by Figure 2It can be seen that the prepared quantum dot particles have uniform morphology and good dispersion, and no obvious agglomeration phenomenon was observed.

[0038] EDS diagram of CdZnS / ZnSe / ZnS parabolic band structure quantum dots is shown below. Figure 3 As shown, by Figure 3 It is evident that Zn is distributed throughout the entire particle, but its signal intensity decreases significantly in the central region, while Cd intensity reaches its maximum in this region. This indicates that the CdZnS core is not a homogeneous alloy structure but rather exhibits a compositional gradient. Se signals mainly appear in the central region of the particle and highly overlap with the Zn signals in this region, confirming the successful coating of the ZnSe inner shell. Combined with the significant distribution of S at the particle edges, the formation of the ZnS outer shell can be further confirmed. The regional and gradient characteristics of the EDS element distribution directly validate the successfully constructed gradient CdZnS alloy-ZnSe inner shell-ZnS outer shell core-shell structure in this study.

[0039] A schematic diagram illustrating the electron-hole wavefunction distribution of CdZnS / ZnSe / ZnS parabolic band structure quantum dots as a function of shell layers is shown below. Figure 4 As shown, by Figure 4 It is evident that the band structure becomes quite unique after coating with a ZnSe shell. On one hand, the valence band peak of ZnSe is significantly higher than that of CdZnS, forming a steep valence band step that forces holes to completely delocalize to the shell. On the other hand, the gradient distribution of the parabolic potential well within the core drives a small number of electrons to migrate from the core center to the core-shell interface, while the gentle barrier between the conduction bands allows high-energy electrons at the interface to penetrate into the shell in a limited manner through tunneling or thermal excitation. This precise spatial distribution control maintains the necessary radiative recombination probability to avoid the inefficient luminescence defects of pure type II structures, and significantly suppresses Auger recombination and nonradiative relaxation caused by strong electron-hole coupling, thus overcoming the bottleneck of excessively fast recombination rates in traditional type I structures.

[0040] Fluorescence lifetime tests were performed on CdZnS, CdZnS / ZnSe, and CdZnS / ZnSe / ZnS quantum dots (CdZnS / ZnSe / ZnS parabolic band structure quantum dots), and the results are as follows: Figure 5 As shown. By Figure 5 It can be seen that although the fluorescence lifetime of CdZnS / ZnSe quantum dots is improved compared with that of CdZnS cores, it is still significantly lower than that of CdZnS / ZnSe and CdZnS / ZnSe / ZnS samples. This result indicates that the CdZnS / ZnSe system with its parabolic band structure can significantly suppress strong electron-hole coupling, thereby reducing Auger recombination and nonradiative relaxation probabilities and achieving superior optical performance.

[0041] Finally, the optical stability of CdZnS / ZnSe / ZnS parabolic band structure quantum dots under long-term storage, thermal, optical, and high excitation power conditions was studied, and the results are as follows: Figure 6 As shown. By Figure 6 It can be seen that the normalized photoluminescence intensity (PL) change of quantum dots stored at room temperature for 30 days has a decay slope of only about 0.002, indicating that the material has excellent long-term storage stability. Under heating at 60℃, although the PL intensity decays somewhat within 1 hour, this decay is still within an acceptable range considering the typical operating temperature rise range of devices, demonstrating good thermal stability. Under continuous ultraviolet irradiation, although the PL intensity of the quantum dots gradually decreases, its emission peak position and full width at half maximum (FWHM) do not show significant shifts, indicating that the material has good resistance to photobleaching. When the pump laser power increases from 100 μW to 9000 μW, the PL intensity of the quantum dots increases linearly, and the emission spectrum morphology remains consistent, without concentration quenching or spectral broadening, proving that it can meet the needs of high-power excitation applications such as high-brightness LEDs and laser displays.

[0042] The embodiments of the present invention have been described in detail above. For those skilled in the art, there may be changes in the specific implementation methods and application scope based on the ideas of the embodiments of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for preparing CdZnS / ZnSe / ZnS parabolic band structure quantum dots, characterized in that... The steps are as follows: (1) Preparation of S-ODE precursor solution, S-TOP precursor solution and Se-TBP precursor solution: S powder was dissolved in 1-octadecene in an inert gas environment and at a temperature of 150-180℃ to obtain an S-ODE precursor solution with a concentration of 0.5 mmol / mL; S powder was dissolved in tri-n-octylphosphine in an inert gas environment and at a temperature of 130-150℃ to obtain an S-TOP precursor solution with a concentration of 0.2 mmol / mL; Se powder was dissolved in tributyl phosphate in an inert gas environment and at a temperature of 130-150℃ to obtain a Se-TBP precursor solution with a concentration of 0.2 mmol / mL. (2) Preparation of CdZnS core solution: Under argon protection, cadmium oxide, zinc acetate, oleic acid and 1-octadecene were added to a three-necked flask. The mixture was vented and dehydrated at 130℃ for 30 min. Then the temperature was raised to 300℃ and stabilized before injecting the S-ODE precursor solution prepared in step (1). After reacting for 30 min, the mixture was cooled to room temperature to obtain crude CdZnS core product. After purification, it was dispersed in 1-octadecene to obtain CdZnS core solution. The molar ratio of cadmium oxide and zinc acetate added to the three-necked flask was 1:5 and each mmol of cadmium oxide corresponded to 10 mL of oleic acid and 40 mL of 1-octadecene. The ratio of the number of moles of S in the S-ODE precursor solution to the total number of moles of cadmium oxide and zinc acetate was 1:

2. Each mL of crude CdZnS core product was dispersed in 0.4 mL of 1-octadecene after purification. (3) Preparation of CdZnS / ZnSe solution: Under argon protection, zinc acetate, oleic acid and 1-octadecene were added to another three-necked flask. The mixture was vented and dehydrated at 130°C for 30 min. Then the temperature was raised to 280°C and stabilized before the CdZnS core solution prepared in step (2) was injected. Then the Se-TBP precursor solution prepared in step (1) was injected in portions using a peristaltic pump. After all the solution was injected, the reaction continued for 30 min. After cooling, the crude CdZnS / ZnSe core-shell intermediate product was obtained. After purification, it was dispersed in 1-octadecene to obtain the CdZnS / ZnSe solution. Each mmol of zinc acetate added to the other three-necked flask corresponded to 2.5 mL of oleic acid, 10 mL of 1-octadecene, 5 mL of CdZnS core solution and 5 mL of Se-TBP precursor solution. Each 3 mL of CdZnS / ZnSe core-shell intermediate crude product was purified and dispersed in 2 mL of 1-octadecene. (4) Preparation of CdZnS / ZnSe / ZnS parabolic band structure quantum dot solution: Under argon protection, zinc acetate, oleic acid and 1-octadecene were added to the reaction flask. The mixture was vented and dehydrated at 130°C for 30 min. Then the temperature was raised to 280°C and stabilized before injecting the CdZnS / ZnSe solution prepared in step (3). Then the S-TOP precursor solution prepared in step (1) was injected using a peristaltic pump. After reacting for 30 min, the mixture was cooled to room temperature. The resulting product was purified to obtain the CdZnS / ZnSe / ZnS parabolic band structure quantum dot solution with n-hexane as solvent. Each mmol of zinc acetate added to the reaction flask corresponds to 2.5 mL of oleic acid, 10 mL of 1-octadecene, 5 mL of CdZnS / ZnSe solution and 5 mL of S-TOP precursor solution.

2. The method for preparing CdZnS / ZnSe / ZnS parabolic band structure quantum dots according to claim 1, characterized in that... The purification steps in step (2) are as follows: Add the same volume of n-hexane and 6 times the volume of ethanol to the crude CdZnS core product, mix well, and centrifuge to separate the product. Discard the supernatant to obtain a precipitate. Disperse the precipitate in the same volume of n-hexane as the crude CdZnS core product, and centrifuge to separate the product. Repeat this process 2-3 times, discard the precipitate, and obtain a supernatant. Add 4 times the volume of ethanol to the supernatant, centrifuge again, discard the supernatant, and obtain a precipitate. The purification is then complete.

3. The method for preparing CdZnS / ZnSe / ZnS parabolic band structure quantum dots according to claim 1, characterized in that... The purification step (3) is as follows: add the same volume of n-hexane and 6 times the volume of ethanol as the crude CdZnS / ZnSe core-shell intermediate to the crude CdZnS / ZnSe core-shell intermediate, mix well, and separate by centrifugation. Discard the supernatant to obtain the precipitate. The precipitate was dispersed in n-hexane of the same volume as the crude CdZnS / ZnSe core-shell intermediate. The mixture was centrifuged and repeated 2-3 times. The precipitate was discarded, and the supernatant was obtained. Four times the volume of ethanol was added to the supernatant, and the mixture was centrifuged again. The supernatant was discarded, and the precipitate was obtained, thus completing the purification.

4. The method for preparing CdZnS / ZnSe / ZnS parabolic band structure quantum dots according to claim 1, characterized in that... The purification step (4) is as follows: add the same volume of n-hexane and 6 times the volume of ethanol to the product, mix well, separate by centrifugation, and discard the supernatant; disperse the precipitate in n-hexane of the same volume as the product, separate by centrifugation, repeat 2-3 times, discard the precipitate, and the obtained supernatant is the CdZnS / ZnSe / ZnS parabolic band structure quantum dot solution with n-hexane as solvent.

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