Method for improving stability of quantum dots

Abstract

The invention discloses a method for improving the stability of quantum dots, which comprises the following operation steps: preparing nuclear quantum dots; processing the double-shell structure quantum dots; processing a passivation layer on the double-shell basis; and testing the processed double-shell core-shell quantum dot. The passivation layer is processed on the surface of the CdSe / CdZnS quantum dot, so that the function degradation and oxidation probability of the CdSe / CdZnS quantum dot is effectively reduced; the CdSe / CdZnS quantum dot has good light-emitting monochromaticity and quantum yield, so that the stability of the CdSe / CdZnS quantum dot is improved; the stability and the service life when the quantum dot is applied to a liquid phase chip platform are improved, a layer of SiO2 film is deposited on the quantum dot through a magnetron sputtering method, water vapor and oxygen molecules in air can be effectively blocked, oxidation of the surface of the quantum dot is slowed down, and therefore the light emitting stability of the quantum dot is improved.

Description

Technical Field

[0001] The present invention relates to the field of quantum dots, and particularly to a method for improving the stability of quantum dots. Background Art

[0002] A quantum dot is a semiconductor nanostructure that confines excitons in three spatial dimensions. Sometimes it is called an "artificial atom" or "quantum dot atom". This confinement can be attributed to an electrostatic potential, the interface between two different semiconductor materials, such as in self-assembled quantum dots, the surface of a semiconductor, such as a semiconductor nanocrystal, or a combination of the above three. Quantum dots have discrete quantized energy spectra. The corresponding wave functions are located in the quantum dot in space but extend over several lattice periods. A quantum dot has a small number (1 - 100) of integer numbers of electrons, holes, or hole-electron pairs, that is, the electric charge it carries is an integer multiple of the elementary charge.

[0003] In the prior art, in order to improve the luminescence efficiency and stability of quantum dots, a shell layer of another semiconductor material with a wider bandgap is usually used to protect the quantum dots. The quantum dots produced in this way are called core / shell quantum dots. However, even for core / shell structured quantum dots, especially green quantum dots, there will be a significant attenuation of the photoluminescence intensity under strong light irradiation, resulting in a decrease in the stability and luminescence efficiency of the quantum dots. Therefore, a single shell coating is not an ideal barrier layer, and oxygen can diffuse through the zinc sulfide shell and oxidize the quantum dot core, resulting in the inability to guarantee the stability of the quantum dots.

[0004] Based on the above situation, the present invention proposes a method for improving the stability of quantum dots to effectively solve the above problems. Summary of the Invention

[0005] In order to solve the problems in the background art, the present invention provides a method for improving the stability of quantum dots.

[0006] The present invention adopts the following technical solutions: A method for improving the stability of quantum dots, comprising the following operating steps: S1. Preparation of core quantum dots; S2. Processing of double-shell structure quantum dots; S3. Processing a passivation layer on the basis of the double shell; S4. Testing the core-shell quantum dots of the double shell processed in S3.

[0007] Further, in step S1, the core quantum dots are prepared by a one-step method, which specifically includes the following steps: S11. Providing a solution for preparing CdSe quantum dots; Further, in step S2, it specifically includes the following steps: S21. Mix a Cd source, a Zn source with a first ligand and a first solvent to obtain a mixed solvent A; the first solvent is a carboxylic acid with 14 to 18 carbon atoms, and the first solvent is 1-octadecene or liquid paraffin; S22. Mix an S source with a second solvent to obtain a mixed solvent B. The second solvent can be one or more of tri-n-butylphosphine, tri-n-octylphosphine, triphenylphosphine, octadecene, and liquid paraffin; S23. Heat the solution A to 298 - 302 °C, inject the CdSe quantum dot solution of S1, then inject the mixed solution B at 305 - 310 °C, and then react at 298 - 302 °C to obtain monolayer CdSe / CdZnS quantum dots. Then, operate in the same way to obtain double-shell CdSe / CdZnS quantum dots.

[0008] Furthermore, in step S3, the passivation layer is processed by radio frequency magnetron sputtering method. Specifically: S31. Grow a 40 - 50 nm thick silicon dioxide layer on a silicon substrate by PECVD method; S32. Spin-coat the quantum dot solution on the silicon dioxide; S33. Finally, cover a 10 - 18 nm SiO2 thin film by radio frequency magnetron sputtering method.

[0009] Furthermore, in step S3, Ar gas is used as the sputtering gas in the experiment, the working pressure is 0.5 - 0.7 Pa, the self-bias voltage is 500 - 600 V, the sputtering power is 60 - 100 W, and the deposition time is 6 - 10 min.

[0010] Furthermore, in step S4, the tests include the absorption spectrum of the quantum dots, the PL spectrum, the luminescence performance tests of passivated and non-passivated quantum dots, and the accelerated stability test.

[0011] A method for improving the stability of quantum dots provided by the present invention: By processing a passivation layer on the surface of CdSe / CdZnS quantum dots, the functional degradation and oxidation probability of CdSe / CdZnS quantum dots are effectively reduced; it has good luminescence monochromaticity and quantum yield, thereby increasing the stability of CdSe / CdZnS quantum dots; increasing the stability and service life when applied in a liquid-phase chip platform. By depositing a layer of SiO2 thin film on the quantum dots by magnetron sputtering method, water vapor and oxygen molecules in the air can be effectively blocked, and the oxidation on the surface of the quantum dots can be slowed down, thereby improving its luminescence stability. Description of the Drawings

[0012] Figure 1 For monitoring the change of the integrated area of the PL fluorescence peak of the 525 nm quantum dots for stability; Figure 2For monitoring the change in the integrated area of the PL fluorescence peak of 605 nm quantum dots; Figure 3 For monitoring the change in the integrated area of the PL fluorescence peak of 630 nm quantum dots. Detailed implementation mode

[0013] The present invention will be further described in detail below with reference to the accompanying drawings and specific implementation modes.

[0014] Refer to the attached Figures 1-3 A method for improving the stability of quantum dots includes the following steps: Step 1: Add 0.533 g of cadmium acetate dihydrate, 1.6 g of oleic acid, and 20 g of octadecene into a 100 ml flask. Under the protection of nitrogen or argon, raise the temperature to around 170 °C and exhaust for about 30 min to remove water, oxygen, and impurities. Weigh 0.158 g of selenium powder, add it to 3 g of ODE, and ultrasonicate for about 10 min until completely dispersed. Additionally, prepare 0.1 mmol / ml selenium powder-octadecene solution and 0.1 mmol / ml cadmium oleate solution as supplementary solutions. Under the protection of inert gas, heat the water- and oxygen-free system to 250 °C, quickly inject the mixed solution of Se-ODE, then set the temperature to 240 °C. After reacting for 10 min, add 1 ml of 0.1 mmol / ml selenium powder-octadecene solution and 0.1 mmol / ml cadmium oleate solution respectively, and continuously add the OD value to 490 nm at intervals of 3 min. Add the synthesized CdSe quantum dots to acetone for purification and then dissolve them in 5 ml of octadecene.

[0015] In addition, by increasing the supplementary amount and the number of supplementary times (Se-ODE and cadmium oleate), a CdSe core that absorbs 490 nm to 560 nm can be obtained. Add the synthesized CdSe quantum dots to acetone for purification and then dissolve them in 5 ml of octadecene.

[0016] Step 2: Preparation of double-shell structure quantum dots: Specific implementation case 1: Preparation of the first layer: (1) Dissolve 0.3 g of sulfur in 10 mL of tributylphosphine under anaerobic conditions; (2) Take 0.133 g of cadmium acetate dihydrate, 1.2 g of oleic acid, and 16 g of octadecene and add them into a 100 ml flask. Under the protection of nitrogen or argon, raise the temperature to around 170 °C and exhaust for about 30 min to remove water and oxygen; (3) After raising the temperature to 305 °C, inject 100 OD of the prepared CdSe core (absorbing 490 nm), and then inject the S-TBP mixed solution at 305 °C. The system reacts at 300 °C for 2 - 3 min; (4) Add the prepared first-layer CdSe / CdZnS quantum dots to acetone for purification and then dissolve them in 5 ml of octadecene.

[0017] Preparation of the second layer: (1) Dissolve 0.25 g of sulfur in 10 mL of tributylphosphine under anaerobic conditions; (2) Take 0.133 g of cadmium acetate dihydrate, 1.2 g of oleic acid, and 12 g of octadecene and add them to a 100 ml flask. Under the protection of nitrogen or argon, raise the temperature to around 170 °C and exhaust for about 30 min to remove water and oxygen; (3) After raising the temperature to 310 °C, inject the CdSe / CdZnS quantum dots coated in one layer, and then inject the sulfur-tributylphosphine mixed solution at 305 °C. The system reacts at 300 °C for 2 - 3 min; (4) Add the prepared CdSe / CdZnS quantum dots to acetone for purification and then dissolve them in an appropriate amount of toluene for storage, and 525 nm green quantum dots can be obtained.

[0018] Specific implementation case two: Preparation of the first layer: (1) Dissolve 0.5 g of sulfur in 10 mL of tributylphosphine under anaerobic conditions; (2) Take 0.266 g of cadmium acetate dihydrate, 1.468 g of oleic acid, and 24 g of octadecene and add them to a 100 ml flask. Under the protection of nitrogen or argon, raise the temperature to around 170 °C and exhaust for about 30 min to remove water and oxygen; (3) After raising the temperature to 305 °C, inject the prepared CdSe core with 100 OD (absorbing 525 nm), and then inject the S-TBP mixed solution at 305 °C. The system reacts at 300 °C for 2 - 3 min; (4) Add the prepared one-layer CdSe / CdZnS quantum dots to acetone for purification and then dissolve them in 5 ml of octadecene.

[0019] Preparation of the first layer: Dissolve 0.3 g of sulfur in 10 mL of tributylphosphine under anaerobic conditions; Take 0.266 g of cadmium acetate dihydrate, 8.8 g of oleic acid, and 20 g of octadecene and add them to a 100 ml flask. Under the protection of nitrogen or argon, raise the temperature to around 170 °C and exhaust for about 30 min to remove water and oxygen; After raising the temperature to 310 °C, inject the CdSe / CdZnS quantum dots coated in one layer, and then inject the S-TBP mixed solution at 305 °C; (4) Add the prepared CdSe / CdZnS quantum dots to acetone for purification and then dissolve them in an appropriate amount of toluene for storage, and 605 nm orange-red quantum dots can be obtained.

[0020] Specific implementation case three: First layer preparation: (1) Dissolve 1.0 g of sulfur in 10 mL of tributylphosphine under anaerobic conditions; (2) Take 0.4256 g of cadmium acetate dihydrate, 2.3488 g of zinc acetate, 14 g of oleic acid, and 30 g of octadecene and add them to a 100 ml flask. Under the protection of nitrogen or argon, raise the temperature to around 170 °C and exhaust for about 30 min to remove water and oxygen; (3) After raising the temperature to 305 °C, inject 100 OD of the prepared CdSe core (absorbing at 560 nm), and then inject the S-TBP mixed solution at 305 °C. The system reacts at 300 °C for 2 - 3 min; (4) Add the prepared first layer of CdSe / CdZnS quantum dots to acetone for purification and then dissolve them in 5 ml of octadecene.

[0021] First layer preparation: Dissolve 0.6 g of sulfur in 10 mL of tributylphosphine under anaerobic conditions; Take 0.4256 g of cadmium acetate dihydrate, 2.3488 g of zinc acetate, 14 g of oleic acid, and 24 g of octadecene and add them to a 100 ml flask. Under the protection of nitrogen or argon, raise the temperature to around 170 °C and exhaust for about 30 min to remove water and oxygen; After raising the temperature to 310 °C, inject the coated first layer of CdSe / CdZnS quantum dots, and then inject the S-TBP mixed solution at 305 °C. (4) Add the prepared CdSe / CdZnS quantum dots to acetone for purification and then dissolve them in appropriate toluene for storage, and red quantum dots with a wavelength of 630 nm and a full width at half maximum of around 28 nm can be obtained.

[0022] Specific implementation case four: Processing the passivation layer: Use PECVD method to grow a 40 nm thick silicon dioxide layer on a silicon substrate, spin-coat the quantum dot solution on the silicon dioxide, and finally cover a 16 nm SiO2 thin film by radio frequency magnetron sputtering; In the experiment, Ar gas is used as the sputtering gas, the working pressure is 0.6 Pa, the self-bias voltage is 600 V, the sputtering power is 75 W, and the deposition time is 8 min. Depositing a layer of SiO2 thin film on the quantum dots by magnetron sputtering can effectively block water vapor and oxygen molecules in the air and slow down the oxidation on the surface of the quantum dots, thereby improving their luminescence stability; Testing: The following table shows the relative quantum yields of quantum dots with different wavelengths coated with a single shell, a double shell, and passivated. From the table, it can be seen that regardless of the quantum yield rate, it reaches more than 75%, and its optical performance is excellent.

[0023] Table 1 Table 1 shows the relative quantum yields of quantum dots with different wavelengths after coating the shell layer and magnetron sputtering passivation. Subsequently, monitoring was carried out at a temperature of 37 °C and a humidity of 60%. The concentration of the prepared solution was 10 mg / mL. After testing with a fluorescence spectrophotometer, the integrated area of its fluorescence peak was obtained. A total of 3000 h was monitored. The results are shown in the following figure (with the single-shell layer at 0 h as the control). It can be seen that the 525-nm green quantum dots are slightly less stable than the 605-nm and 630-nm ones. However, due to the presence of the passivation layer, the relative ratio of the fluorescence peak area is about 1.2. For the quantum dots with only a single-shell layer coated, the relative value is only 0.4 compared to the initial value. This shows the importance of the stability of the double-shell-coated quantum dots and the passivation layer. In addition, the changes in the 605-nm and 630-nm quantum dots are basically the same. The passivated quantum dots can maintain relatively good stability. The stability of the double-shell-coated ones is slightly worse, and the stability of the single-shell-coated quantum dots is only about 60% of the initial value.

[0024] There are numerous hole and electron defect states on the surface of pure CdSe core quantum dots, which affect the luminescence properties of the quantum dots. There are mainly two ways to passivate the surface states of quantum dots and increase the luminescence efficiency and photochemical stability of quantum dots: First, modify the surface of the quantum dots with organic ligands; Second, coat an inorganic shell layer on the surface of the quantum dots. Usually, the shell material can passivate its surface layer to reduce the surface dangling bonds. At the same time, a thick inorganic shell layer can increase the photochemical stability of the quantum dots. In this process, the CdZnS alloy layer is selected compared with other traditional CdS / ZnS layers or other alloy layers, which can better improve its luminescence performance and stability.

[0025] This method performs alloying coating in two steps, with a higher degree of alloying, which better solves the problem of lattice mismatch, and its stability can be significantly improved.

[0026] This method has differences in the alloy layer structure and coats a more stable double-layer structure; on the basis of the double-layer structure, a silica coating layer is added through magnetron sputtering.

[0027] A single quantum dot cannot be directly exposed to harsh conditions such as water vapor and oxygen. In this method, on the premise that the quantum dot itself has excellent luminescence and stability, a silica layer is coated through magnetron sputtering technology, so that the fluorescent material can be directly exposed to conditions such as water and oxygen.

[0028] By processing a passivation layer on the surface of CdSe / CdZnS quantum dots, this method effectively reduces the functional degradation and oxidation probability of CdSe / CdZnS quantum dots; has good luminescence monochromaticity and quantum yield, thereby increasing the stability of CdSe / CdZnS quantum dots; increases the stability and service life when applied in a liquid-phase chip platform. By depositing a SiO2 thin film on the quantum dots by magnetron sputtering, water vapor and oxygen molecules in the air can be effectively blocked, and the oxidation on the surface of the quantum dots can be slowed down, thereby improving its luminescence stability.

[0029] Note that the above is only the preferred embodiment of the present invention and the technical principles applied. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described here. Various obvious changes, re-adjustments and substitutions can be made by those skilled in the art without departing from the protection scope of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments. Without departing from the concept of the present invention, more other equivalent embodiments can be included, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A method for improving the stability of quantum dots, characterized in that: The steps include: S1, preparation of core quantum dots; S2, double shell structure quantum dot processing; S3, processing the passivation layer on the double shell basis; S4. Testing the double-shell core-shell quantum dots processed in S3.

2. A method for improving the stability of quantum dots according to claim 1, characterized in that: In step S1, the core quantum dots are prepared by a one-step method, which specifically includes the following steps: S11, providing a solution for preparing CdSe quantum dots.

3. The method for improving the stability of quantum dots according to claim 1, characterized in that: In step S2, the following steps are specifically included: S21, mixing a Cd source, a Zn source, a first ligand and a first solvent to obtain a mixed solvent A; the first solvent is a C14-C18 carboxylic acid, and the first solvent is 1-octadecene or liquid paraffin; S22, mixing the S source with a second solvent to obtain a mixed solvent B, wherein the second solvent may be one or more of tri-n-butylphosphine, tri-n-octylphosphine, triphenylphosphine, octadecene, and liquid paraffin; S23, heat solution A to 298-302°C, inject the CdSe quantum dot solution of S1, then inject the mixed solution B at 305-310°C, and then react at 298-302°C to obtain a single-layer CdSe / CdZnS quantum dots, and then operate in the same manner to obtain a double-shell CdSe / CdZnS quantum dots.

4. The method for improving the stability of quantum dots according to claim 1, characterized in that: In step S3, the passivation layer is processed by radio frequency magnetron sputtering, specifically: S31, growing a 40-50 nm thick silicon dioxide layer on a silicon substrate using the PECVD method; S32, spin coating the quantum dot solution on silicon dioxide; S33. Finally, a 10~18 nm SiO2 film is covered by RF magnetron sputtering method.

5. The method for improving the stability of quantum dots according to claim 1 or 4, characterized in that: In step S3, the experiment uses Ar gas as the sputtering gas, the working gas pressure is 0.5~0.7 Pa, the self-bias voltage is 500~600V, the sputtering power is 60~100W, and the deposition time is 6~10 min.

6. The method for improving the stability of quantum dots according to claim 1, characterized in that: In step S4, the tests include absorption spectrum of quantum dots, PL spectrum, luminescence performance test of passivated and non-passivated quantum dots, and accelerated stability test.

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