Gradient gradient core-shell type quantum dot and preparation method thereof

Abstract

The invention discloses a preparation method of gradient core-shell quantum dots, and belongs to the technical field of functional materials, and the preparation method specifically comprises the following steps: S1, respectively preparing a core-layer precursor solution and a shell-layer precursor solution; s2, in an N2 atmosphere, preparing a ZnSeTe quantum dot core by using the core layer precursor solution; s3, keeping the prepared ZnSeTe quantum dot core solution in an N2 atmosphere, and carrying out gradient gradual change shell layer growth by adopting the shell layer precursor solution at 310 DEG C; and S4, cooling the obtained quantum dots to room temperature, adding absolute ethyl alcohol, performing centrifugal precipitation, and washing the precipitate to obtain a final product. The components of the prepared quantum dot shell layer change slowly, and interlayer growth defects do not exist; the shell layer grows uniformly, and the quantum dots are regular in shape; the outermost layer is completely coated with ZnS, the quantum dots are good in stability, the shell layer is high in adjustability, and various requirements can be conveniently met; in addition, through detection, the fluorescent quantum yield is high, and the half-peak width is narrow.

Description

Technical Field

[0001] The invention relates to the technical field of functional materials, and in particular to a gradient core-shell quantum dot and a preparation method thereof. Background Art

[0002] Quantum dots are semiconductor nanostructures that bind excitons in three spatial directions. Their unique quantum confinement effect makes the luminescent color and size of quantum dots closely related, so they have broad application prospects in the fields of lighting and display. At present, quantum dots have huge market potential. At the same time, because they are electroluminescent, they do not require a backlight module, so they are lighter and more energy-efficient. And they have excellent performance. Therefore, quantum dots are the mainstream material for the next generation of lighting and display.

[0003] However, due to the small size and large specific surface area of ​​quantum dots, surface defects have a greater impact on them. At present, the mainstream methods to reduce the impact of defects are long-chain organic ligand passivation and inorganic shell coating. Compared with some disadvantages of organic ligand passivation, inorganic shell coating has obvious advantages.

[0004] Due to the band gap width and injection barrier, the efficiency of blue light QLED lags behind red and green light. Among the current deep blue light quantum dots, Cd-based quantum dots have high performance, but there is heavy metal pollution; and the current environmentally friendly blue light materials are InP and ZnSe. The InP bulk band gap is narrow (1.35eV), making it difficult to achieve efficient blue light emission, while pure ZnSe quantum dots emit in the blue-violet range (<440nm). Therefore, doping Te in ZnSe quantum dots to adjust the spectrum to deep blue light is a better choice.

[0005] Considering the energy level factor, the optimal shell material is ZnS. However, due to the large lattice constant difference between ZnS and the core material ZnSeTe, the current mainstream method is to first coat the ZnSeTe quantum dot core with ZnSe, and then coat it with ZnS to alleviate the lattice mismatch problem. However, this method still cannot avoid the interlayer growth defect problem caused by the lattice constant difference between ZnSe and ZnS.

[0006] Based on the above problems, a gradient core-shell quantum dot and a preparation method thereof are proposed. Summary of the invention

[0007] The purpose of the present invention is to provide a gradient core-shell quantum dot and a preparation method thereof to solve the problems in the background technology.

[0008] To achieve the above object, the present invention provides a method for preparing gradient core-shell quantum dots, comprising the following steps:

[0009] S1, preparing a core layer precursor solution and a shell layer precursor solution respectively;

[0010] S2, in a N2 atmosphere, using a core layer precursor solution to prepare a ZnSeTe quantum dot core;

[0011] S3, keeping the prepared ZnSeTe quantum dot core solution in a N2 atmosphere at 310°C, and using a shell precursor solution to perform gradient shell growth;

[0012] S4. Cool the obtained quantum dots to room temperature, add anhydrous ethanol and centrifuge to precipitate, wash the precipitate, and obtain the final product.

[0013] Preferably, in S1, the core layer precursor solution includes a core Te precursor solution, a core Zn precursor solution and a core Se precursor solution; the shell layer precursor solution includes a shell Zn precursor solution, a shell S precursor solution and a shell Se precursor solution.

[0014] Preferably, the core Te precursor is prepared from tellurium powder and trioctyl phosphine; the core Zn precursor is prepared from zinc acetate, oleic acid and oleylamine; the shell Zn precursor is prepared from zinc acetate, oleic acid, oleylamine, trioctylamine and trioctyl phosphine; the core Se precursor and the shell Se precursor are both prepared from selenium powder and one of trioctyl phosphine, octadecene or diphenylphosphine; the shell S precursor is prepared from one of octanethiol, dodecyl mercaptan, sulfur powder and trioctyl phosphine or octadecene.

[0015] Preferably, the specific step of S2 is to heat the core Zn precursor solution to 310° C., rapidly inject 0.3-0.7 mL of core Se precursor solution and 0.4-0.8 mL of core Te precursor solution, and react for 40-80 min to obtain a ZnSeTe quantum dot core solution.

[0016] Preferably, the S3 specifically includes the following steps:

[0017] (1) injecting a certain amount of shell Zn precursor solution, and then injecting shell Se precursor solution at a certain speed;

[0018] (2) Subsequently, different ratios of shell layer Se precursor solution and shell layer S precursor solution are injected multiple times;

[0019] (3) A certain amount of shell Zn precursor solution is injected, and then a shell S precursor solution is injected at a certain speed to obtain quantum dots.

[0020] Preferably, in S3, the addition amount of the shell Zn precursor solution is 2-5 mL, and the addition rate is 20-45 mL / h; the addition rates of the shell Se precursor solution and the shell S precursor solution are 0.8-1.2 mL / h.

[0021] Preferably, the amount of the shell layer Se precursor added in step (1) of S3, the amount of the shell layer S precursor solution added in step (3) is the same as the sum of the amounts of the shell layer Se precursor solution and the shell layer S precursor solution added in step (2).

[0022] Preferably, in S4, the rotation speed during the centrifugation process is 6000-8500 rpm, and the time is 3-6 min; the washing process is to use n-hexane and ethanol for washing 2-3 times.

[0023] The present invention also provides a gradient core-shell quantum dot, which is prepared by the above preparation method.

[0024] Preferably, the core-shell quantum dot is composed of a ZnSeTe quantum dot core and a gradient shell, the innermost layer of the shell is made of ZnSe, the outermost layer of the shell is made of ZnS, and the gradient shell region is between the innermost and outermost layers. x S 1-x , x∈0,1).

[0025] Therefore, the present invention provides a gradient core-shell quantum dot and a preparation method thereof. By using a gradient core-shell structure instead of a traditional direct-change core-shell structure, the growth defects at the interface between two different shells of ZnSe and ZnS are reduced, thereby improving the fluorescence quantum yield of the core-shell quantum dots. Secondly, during the growth of the shell, the type and injection rate of the Se precursor and the S precursor are adjusted to regulate the anion concentration and the overall reaction activity in the system, thereby achieving slow and uniform growth of the shell. At the same time, the Zn precursor solution is supplemented in stages, so that the cations in the system are always maintained at a high level, thereby avoiding the ripening of the quantum dots due to too low a monomer concentration.

[0026] The deep blue light colloidal quantum dots with a gradient core-shell structure prepared by the present invention have a shell component that changes slowly and has no interlayer growth defects; the outer shell grows evenly and the quantum dots have a regular shape; in addition, the outermost layer is completely coated with ZnS, the quantum dots are stable, and the shell has a strong adjustable ability, which is convenient for adapting to various needs; in addition, after testing, the quantum dots prepared by the present invention have a high fluorescence quantum yield (PLQY) and a narrow half-maximum width (FWHM).

[0027] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A comparison diagram of quantum dots prepared by an embodiment of the present invention and quantum dots prepared by a traditional method, wherein (a) is the method of this embodiment, and (b) is the traditional method;

[0029] Figure 2The size distribution of the gradient shell quantum dots prepared in the embodiment of the present invention Figure 1 ;

[0030] Figure 3 The size distribution of the gradient shell quantum dots prepared in the embodiment of the present invention Figure 2 ;

[0031] Figure 4 The light-induced performance change of the gradient-graded shell quantum dot shell growth of the embodiment of the present invention Figure 1 ;

[0032] Figure 5 The light-induced performance change of the gradient-graded shell quantum dot shell growth of the embodiment of the present invention Figure 2 . DETAILED DESCRIPTION

[0033] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0034] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0035] Example

[0036] The product obtained in this embodiment is ZnSeTe / ZnSe / ZnSexS1-x / ZnS, and the specific preparation steps are as follows:

[0037] S1. Prepare the core layer precursor solution and the shell layer precursor solution respectively:

[0038] 1) Preparation of core Se precursor solution: Take 2 mmol of selenium powder, add 1 mL of diphenylphosphine, and heat at 80 °C for 20 min under N2 atmosphere to obtain 2M Se-DPP solution;

[0039] 2) Preparation of core Te precursor solution: 1 mmol tellurium powder was added with 20 mL trioctylphosphine, and heated at 120 °C for 30 min under N2 atmosphere to obtain 0.05 M Te-TOP solution;

[0040] 3) Preparation of core Zn precursor solution: Take 2 mmol zinc acetate, add 2 mL oleic acid and oleylamine, heat to 120 °C, and evacuate for 30 min to obtain a light yellow solution;

[0041] 4) Preparation of shell Zn precursor solution: Take 15 mmol zinc acetate, add 10 mL oleic acid, 5 mL trioctylamine, and 5 mL trioctylphosphine, and evacuate at 140 °C for 30 min under N2 atmosphere to obtain a light yellow solution;

[0042] 5) Preparation of shell Se precursor solution 1: Take 4 mmol of selenium powder, add 4 mL of trioctylphosphine, and heat at 100 °C for 20 min under N2 atmosphere to obtain 1 M Se-TOP solution;

[0043] 6) Preparation of shell Se precursor solution 2: Take 4 mmol of selenium powder, add 4 mL of octadecene, and heat at 100 °C for 20 min under N2 atmosphere to obtain 1 M Se-ODE solution;

[0044] 7) Preparation of shell S precursor solution 1: Take 4 mmol sulfur powder, add 4 mL trioctylphosphine, heat at 100 ° C for 20 min under N2 atmosphere to obtain 1M S-TOP solution;

[0045] 8) Preparation of shell S precursor solution 2: Take 4 mmol sulfur powder, add 4 mL octadecene, and heat at 100° C. for 20 min under N 2 atmosphere to obtain 1 M S-ODE solution.

[0046] S2. Preparation of ZnSeTe quantum dot cores: The Zn precursor solution was heated to 310°C under a N2 atmosphere, and then 0.5 mL of core Se precursor solution and 0.6 mL of core Te precursor solution were rapidly injected and reacted for 60 min to obtain a quantum dot core solution.

[0047] S3, maintaining the quantum dot core solution prepared above in a N2 atmosphere at 310°C for gradient shell growth:

[0048] (1) 3 mL of shell Zn precursor solution was injected at a rate of 30 mL / h, and 1 mL of shell Se precursor solution 1 was injected at a rate of 1 mL / h;

[0049] (2) Then, 3 mL of shell Zn precursor solution was injected at a rate of 30 mL / h, and 0.7 mL of shell Se precursor solution 1 and 0.3 mL of shell S precursor solution 1 were injected at a rate of 1 mL / h; then, 3 mL of shell Zn precursor solution was injected at a rate of 30 mL / h, and 0.5 mL of shell Se precursor solution 1 and 0.5 mL of shell S precursor solution 1 were injected at a rate of 1 mL / h; then, 3 mL of shell Zn precursor solution was injected at a rate of 30 mL / h, and 0.3 mL of shell Se precursor solution 2 and 0.7 mL of shell S precursor solution 2 were injected at a rate of 1 mL / h;

[0050] (3) Then, 3 mL of the shell Zn precursor solution was injected at a rate of 30 mL / h, and 1 mL of the shell S precursor solution 2 was injected at a rate of 1 mL / h; finally, 3 mL of the shell Zn precursor solution was injected at a rate of 30 mL / h, and 0.5 mL of octanethiol was injected at a rate of 0.5 mL / h.

[0051] S4. Cool the quantum dots obtained in S3 to room temperature, add anhydrous ethanol, centrifuge at 8000 rpm for 5 minutes, and take the precipitate; wash with n-hexane and ethanol 2-3 times, and place the washed quantum dots in n-octane solution.

[0052] The quantum dots were tested and compared with those grown by conventional methods, such as Figure 1-Figure 5 As shown, its photoemission peak (PL) is near 450nm, the fluorescence quantum yield (PLQY) is greater than 90%, and the half maximum width (FWHM) is less than 22nm.

[0053] Therefore, the present invention provides a gradient core-shell quantum dot and a preparation method thereof, wherein the shell components of the prepared quantum dots change slowly and there are no interlayer growth defects; the outer shell grows evenly and the quantum dots have a regular shape; the outermost layer is completely coated with ZnS, the quantum dots are stable, the shell has a strong adjustable ability, and it is convenient to adapt to various needs; in addition, after testing, the fluorescence quantum yield is high and the half-peak width is narrow.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing gradient core-shell quantum dots, characterized in that: The following steps are involved: S1, preparing a core layer precursor solution and a shell layer precursor solution respectively; S2, in a N2 atmosphere, using a core layer precursor solution to prepare a ZnSeTe quantum dot core; S3, keeping the prepared ZnSeTe quantum dot core solution in N2 atmosphere at 310°C, and using the shell precursor solution to perform gradient shell growth; S4. Cool the obtained quantum dots to room temperature, add anhydrous ethanol and centrifuge to precipitate, wash the precipitate, and obtain the final product.

2. The method for preparing gradient core-shell quantum dots according to claim 1, characterized in that: In said S1, the core layer precursor solution includes a core Te precursor solution, a core Zn precursor solution and a core Se precursor solution; The shell layer precursor solution includes a shell layer Zn precursor solution, a shell layer S precursor solution and a shell layer Se precursor solution.

3. The method for preparing gradient core-shell quantum dots according to claim 2, characterized in that: The core Te precursor is prepared from tellurium powder and trioctyl phosphine; the core Zn precursor is prepared from zinc acetate, oleic acid and oleylamine; the shell Zn precursor is prepared from zinc acetate, oleic acid, oleylamine, trioctylamine and trioctyl phosphine; the core Se precursor and the shell Se precursor are both prepared from selenium powder and one of trioctyl phosphine, octadecene or diphenylphosphine; the shell S precursor is prepared from one of octanethiol, dodecyl mercaptan, sulfur powder and trioctyl phosphine or octadecene.

4. The method for preparing gradient core-shell quantum dots according to claim 1, characterized in that: The specific steps of S2 are to heat the core Zn precursor solution to 310° C., rapidly inject 0.3-0.7 mL of core Se precursor solution and 0.4-0.8 mL of core Te precursor solution, and react for 40-80 minutes to obtain a ZnSeTe quantum dot core solution.

5. The method for preparing gradient core-shell quantum dots according to claim 1, characterized in that: The S3 specifically includes the following steps: (1) injecting a certain amount of shell Zn precursor solution, and then injecting shell Se precursor solution at a certain speed; (2) Subsequently, different ratios of shell layer Se precursor solution and shell layer S precursor solution are injected multiple times; (3) Inject a certain amount of shell Zn precursor solution, and then inject the shell S precursor solution at a certain speed to obtain quantum dots.

6. The method for preparing gradient core-shell quantum dots according to claim 5, characterized in that: In the S3, the addition amount of the shell Zn precursor solution is 2-5 mL, and the addition speed is 20-45 mL / h; the addition speeds of the shell Se precursor solution and the shell S precursor solution are 0.8-1.2 mL / h.

7. The method for preparing gradient core-shell quantum dots according to claim 1, characterized in that: The amount of the shell layer Se precursor added in step (1) of S3 and the amount of the shell layer S precursor solution added in step (3) are the same as the sum of the amounts of the shell layer Se precursor solution and the shell layer S precursor solution added in step (2).

8. The method for preparing gradient core-shell quantum dots according to claim 1, characterized in that: In S4, the rotation speed during the centrifugation process is 6000-8500 rpm, and the time is 3-6 minutes; the washing process is to use n-hexane and ethanol for washing 2-3 times.

9. A gradient core-shell quantum dot, characterized in that: The compound is prepared by the preparation method described in any one of claims 1 to 8.

10. The gradient core-shell quantum dot according to claim 9, characterized in that: The core-shell quantum dots are composed of a ZnSeTe quantum dot core and a gradient shell. The innermost layer of the shell is made of ZnSe, the outermost layer of the shell is made of ZnS, and the gradient shell region is between the innermost and outermost layers. x S 1-x , x∈(0,1).

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