Zn-doped AlSe-ZnS core-shell structure quantum dot material and preparation method thereof

Abstract

The invention discloses a Zn-doped AlSe-ZnS core-shell structure quantum dot material and a preparation method thereof. The preparation method comprises the following steps: step 1, synthesizing ZAISe quantum dots; step 2, synthesis of the ZAISe / ZnS quantum dots; and step 3, purification of the ZAISe / ZnS quantum dots. According to the prepared Zn-doped AlSe-ZnS core-shell structure quantum dot material, the surfaces of the ZAISe quantum dots are rich in Zn ions, a first layer of ZnS can be formed after an S-TOP solution is injected, the first layer of ZnS serves as a buffer layer, formation of an island-shaped shell layer is inhibited to a certain degree, and the thickness of a critical shell layer is increased. The buffer layer slowly releases lattice mismatch strain to a certain extent. Then, a Zn-S precursor is injected to form a second layer of Zn-S. After the second layer of ZnS is coated, the total thickness of the shell layer is higher, and even the uniform spherical morphology can be kept. The ZnS shell layer has good crystallinity on the surface of the ZAISe quantum dot core, so that the ZnS shell layer has a good surface passivation effect, and the luminous efficiency of the ZAISe quantum dot is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of materials, and particularly relates to a Zn-doped AlSe@ZnS core-shell structure quantum dot material and a preparation method thereof. Background Art

[0002] Quantum dots with a pure core structure have a large specific surface area, and most of the surface atoms are connected to organic ligands. Although these ligands can play a role in purifying surface defects of quantum dots to a certain extent, due to the existence of many non-ideal ratio atoms and unsaturated dangling bonds on the surface, many surface defect states will be formed. These surface defects will act as fast non-radiative recombination channels for photo-generated carriers, thereby reducing the fluorescence quantum efficiency. Therefore, controlling surface defects is particularly crucial for obtaining quantum dots with high luminescence performance. A very important strategy for passivating surface defects is to epitaxially grow a semiconductor material with a wider bandgap on the surface of the quantum dot to form a core-shell structure, thereby significantly improving its luminescence efficiency and anti-photobleaching properties. At the same time, by reasonably selecting the core-layer quantum dots and the shell-layer material, it is even possible to tune the original emission wavelength to a spectral range that neither the core nor the shell material can reach alone.

[0003] AgInSe (AISe) quantum dots exhibit a narrow bandgap (the semiconductor bandgap is about 1.9 eV), so they have a wide absorption rate from the UV to the near-infrared (NIR) region. However, bare AISe core quantum dots usually have problems such as abundant surface defects and high sensitivity to the environment (such as being sensitive to humidity and light), which may hinder their optical properties and chemical stability. Summary of the Invention

[0004] To solve the above technical problems, the technical solution adopted by the present invention is: a preparation method of a Zn-doped AlSe@ZnS core-shell structure quantum dot material, including the following steps:

[0005] Step 1: Synthesis of ZAISe quantum dots: Take a certain amount of selenium powder, 1-dodecanethiol, and oleylamine and mix them to obtain a selenium precursor solution; take a certain amount of zinc acetate, silver nitrate, and indium acetate and place them in a three-necked flask containing a mixed solution of 1-octadecene, 1-dodecanethiol, and oleic acid. Magnetically stir and degas in a protective gas environment, and then raise the temperature to dehydrate; quickly inject the selenium precursor solution to obtain a quantum dot solution; take a certain amount of the quantum dot solution and mix it evenly with a certain amount of toluene by shaking, and then purify by centrifugal separation; take the liquid part after separation, add ethanol, and then centrifuge to obtain a precipitate, which is the purified ZAISe quantum dot; wait for the ZAISe quantum dot to dry naturally and then disperse it in toluene for standby;

[0006] Step 2: Synthesis of ZAISe / ZnS quantum dots: Take a certain amount of Zn(OAc) 2The powder, oleylamine and 1-octadecene were mixed, and a certain amount of 1-octanethiol was injected to obtain a Zn-S precursor solution; at a certain temperature, a certain amount of S-TOP solution was added dropwise to the toluene solution of the above-mentioned ZAISe quantum dots. After reacting for a period of time, the above-mentioned Zn-S precursor solution was injected to obtain a ZAISe / ZnS quantum dot stock solution;

[0007] Step 3: Purification of ZAISe / ZnS quantum dots: The above-mentioned ZAISe / ZnS quantum dot stock solution was purified, and the purified ZAISe / ZnS quantum dot sample was stored in n-hexane to obtain a Zn-doped AlSe@ZnS core-shell structured quantum dot material.

[0008] As an optimization of the above technical solution, the synthesis process of the ZAISe quantum dots in Step 1 includes: dissolving 0.54 mmol of selenium powder in a mixed solvent of 0.4 mL of 1-dodecanethiol and 1 mL of oleylamine, and ultrasonically dispersing to obtain a selenium precursor solution; placing 0.04 mmol of zinc acetate, 0.08 mmol of silver nitrate and 0.2 mmol of indium acetate in a 50 mL three-necked flask containing an 8 mL mixed solution of 1-octadecene, 1 mL of 1-dodecanethiol and 100 μL of OA. At room temperature, the three-necked flask was placed in a nitrogen stream and magnetically stirred for degassing for 10 minutes; then the mixed solution was heated to 120 °C and maintained for 20 minutes to remove the water in the solution until the mixed solution became clear and transparent; next, the reactants were heated to 175 °C at a heating rate of 2 °C per minute and maintained for 10 minutes; then the selenium precursor solution was immediately and rapidly injected into the reaction solution, and the solution immediately turned dark brown; finally, the reaction system was kept at 175 °C for 40 minutes to obtain a quantum dot solution; taking 2 mL of the synthesized quantum dot solution in a 15 mL centrifuge tube, mixing it thoroughly with 2 mL of toluene by shaking, and separating and purifying it in a centrifuge at a speed of 4000 revolutions per minute; adding ethanol to the separated liquid part until the total volume reached 12 mL, and then separating at a speed of 12000 revolutions per minute to obtain a precipitate, which was the purified ZAISe quantum dot; after the ZAISe quantum dot was naturally dried, it was redispersed in toluene for standby.

[0009] As an optimization of the above technical solution, the synthesis process of the ZAISe / ZnS quantum dots in Step 2 includes: 8 mmol of Zn(OAc) 2Powder, 3 mL of oleylamine, and 16 mL of 1-octadecene were added to a 50 mL three-necked flask. The stirring rate was 900 revolutions per minute, and the mixture was evacuated at 120 °C for 1 hour. Then, nitrogen was introduced, and 1.6 mL of octanethiol was injected. The solution immediately changed from a suspension to a colorless clear solution, obtaining a Zn-S precursor solution. At 280 °C, 2 mL of a 0.4 M S-TOP solution was added dropwise to the toluene solution of the above ZAISe quantum dots. The 0.4 M S-TOP solution was prepared by dissolving 0.4 mmol of S powder in 1 mL of trioctylphosphine. After reacting for 30 minutes, the temperature was lowered to 260 °C, and the above Zn-S precursor solution was injected into the reaction solution at a rate of 3.6 mL / hour, with a total injection of 1 - 8 mL. After continuing to react for 10 minutes, the reaction was stopped and cooled to room temperature to obtain the ZAISe / ZnS quantum dot stock solution.

[0010] As a preference of the above technical solution, the injection volume of the Zn-S precursor solution is 5 mL.

[0011] As a preference of the above technical solution, the purification process of the ZAISe / ZnS quantum dots in step three includes: adding the ZAISe / ZnS quantum dot stock solution to an equal volume of n-hexane solution for dilution, then adding 2 times the amount of absolute ethanol as an antisolvent. After adding absolute ethanol, a turbid solution was obtained. Centrifugation was carried out at a rotation speed of 8000 revolutions per minute, and the precipitate was retained. Then, the precipitate was redissolved and dispersed in the n-hexane solution, and an appropriate amount of oleylamine was added to make it completely dissolve to obtain a transparent bright yellow solution. The above operation was repeated 2 - 3 times. Finally, the purified ZAISe / ZnS quantum dot sample was stored in n-hexane.

[0012] The Zn-doped AlSe@ZnS core-shell structure quantum dot material was prepared by the above preparation method.

[0013] The beneficial effects of the present invention are as follows: For the Zn-doped AlSe@ZnS core-shell structure quantum dot material prepared by the present invention, the surface of the ZAISe quantum dots is rich in Zn ions. After injecting the S-TOP solution, the first layer of ZnS can be formed. The first layer of ZnS serves as a buffer layer, which can inhibit the formation of island-like shell layers to a certain extent, increasing the critical shell thickness. The buffer layer releases the lattice mismatch strain to a certain extent. Subsequently, the Zn-S precursor is injected to form the second layer of Zn-S. After the second layer of ZnS is coated, the total shell thickness can reach a higher value while maintaining a uniform spherical morphology. The ZnS shell has good crystallinity on the surface of the ZAISe quantum dot core, so it has a good surface passivation effect, greatly improving the luminescence efficiency of the ZAISe quantum dots. Description of the Drawings

[0014] Figure 1 It is a graph showing the change trend of PLQY with the injection volume of the Zn-S precursor.

[0015] Figure 2 It is a graph showing the change of the relative PLQY of ZAISe and ZAISe / ZnS quantum dot solutions with the storage time in air;

[0016] Figure 3 It is the XRD pattern of the ZAISe / ZnS quantum dots prepared in Example 1;

[0017] Figure 4 It is the SEM image of the ZAISe / ZnS quantum dots prepared in Example 1. Detailed implementation manners

[0018] The technical solutions of the present invention will be described clearly and completely below. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0019] Example 1

[0020] Synthesize ZAISe quantum dots: Dissolve 0.54 mmol of selenium powder in a mixed solvent of 0.4 mL of 1-dodecanethiol and 1 mL of oleylamine, and ultrasonically disperse to obtain a selenium precursor solution; Place 0.04 mmol of zinc acetate, 0.08 mmol of silver nitrate, and 0.2 mmol of indium acetate in a 50 mL three-necked flask containing an 8 mL mixed solution of 1-octadecene, 1 mL of 1-dodecanethiol, and 100 μL of OA (oleic acid). At room temperature, place the three-necked flask in a nitrogen stream and under magnetic stirring for degassing for 10 minutes; Subsequently, heat the mixed solution to 120 °C and hold for 20 minutes to remove the water in the solution until the mixed solution becomes clear and transparent; Next, heat the reactants to 175 °C at a heating rate of 2 °C per minute and hold for 10 minutes; Then immediately inject the selenium precursor solution rapidly into the reaction solution, and the solution immediately turns dark brown; Finally, keep the reaction system at 175 °C for 40 minutes to obtain a quantum dot solution; Take 2 mL of the synthesized quantum dot solution in a 15 mL centrifuge tube, mix it thoroughly with 2 mL of toluene by shaking, and separate and purify it in a centrifuge at a speed of 4000 revolutions per minute; Take the liquid part after separation and add ethanol until the total volume reaches 12 mL, and then separate at a speed of 12000 revolutions per minute to obtain a precipitate, which is the purified ZAISe quantum dot; After the ZAISe quantum dots are naturally dried, disperse them in toluene for standby.

[0021] Synthesize ZAISe / ZnS quantum dots: Dissolve 8 mmol of Zn(OAc) 2Powder, 3 mL of oleylamine, and 16 mL of 1-octadecene were added to a 50 mL three-necked flask. The stirring rate was 900 revolutions per minute, and the mixture was evacuated at 120 °C for 1 hour. Then, nitrogen was introduced, and 1.6 mL of octanethiol was injected. The solution immediately changed from a suspension to a colorless clear solution, obtaining a Zn-S precursor solution. At 280 °C, 2 mL of a 0.4 M S-TOP solution was added dropwise to the toluene solution of the above ZAISe quantum dots. The 0.4 M S-TOP solution was prepared by dissolving 0.4 mmol of S powder in 1 mL of trioctylphosphine. After reacting for 30 minutes, the temperature was lowered to 260 °C, and the above Zn-S precursor solution was injected into the reaction solution at a rate of 3.6 mL / hour, with a total injection of 1 mL. The reaction continued for 10 minutes and then stopped, and the temperature was lowered to room temperature to obtain the ZAISe / ZnS quantum dot stock solution.

[0022] Purification of ZAISe / ZnS quantum dots: The ZAISe / ZnS quantum dot stock solution was added to an equal volume of n-hexane solution for dilution, and then 2 times the amount of absolute ethanol was added as an antisolvent. A turbid solution was obtained after adding absolute ethanol. Centrifugation was carried out at a speed of 8000 revolutions per minute, and the precipitate was retained. Then, the precipitate was redissolved and dispersed in the n-hexane solution, and an appropriate amount of oleylamine was added to make it completely dissolve to obtain a transparent bright yellow solution. The above operation was repeated 2 - 3 times, and finally, the purified ZAISe / ZnS quantum dot sample was stored in n-hexane.

[0023] Examples 2 - 6

[0024] During the synthesis of ZAISe / ZnS quantum dots, the volumes of the injected Zn-S precursor solution were 2 mL, 4 mL, 5 mL, 6 mL, and 8 mL respectively, and the other steps were the same as in Example 1.

[0025] Comparative Example 1

[0026] During the synthesis of ZAISe / ZnS quantum dots, no Zn-S precursor solution was injected, and ZAISe quantum dots without a coated shell were obtained.

[0027] The photoluminescence quantum yield PLQY of the samples prepared in the above Examples 1 - 6 and the comparative example was measured. The sample to be tested was dried and ground to avoid caking, and then it was placed in an integrating sphere. An absolute fluorescence quantum efficiency measuring instrument (using the Hamamatsu Photonics / C9920-02 absolute PL quantum efficiency measuring instrument from Japan) was used to calibrate the photoluminescence quantum efficiency of the sample, and the light source was a 365 nm LED. The test results are shown in the following table and Figure 1 as follows:

[0028]

[0029] First, inject 2 mL of [0.2 M] S-TOP solution into the ZAISe quantum dot solution with a Zn-rich surface, which reacts with the excess Zn ions in the solution to form the first layer of ZnS. This can serve as a buffer layer, which can, to a certain extent, inhibit the formation of an island-like shell layer and increase the critical shell thickness. Subsequently, inject the pre-prepared Zn-S precursor to form the second layer of Zn-S. During the coating process of the second layer of ZnS shell, as the Zn-S precursor is continuously injected, the change trend of the photoluminescence quantum yield (PLQY) of the Zn-doped AlSe@ZnS core-shell structured quantum dots is as Figure 1 shown, presenting a trend of first increasing and then decreasing. When 5 mL is injected, the PLQY reaches a maximum value of approximately 61%. The thickness of the first layer of ZnS can serve as a buffer layer, which can, to a certain extent, release the lattice mismatch strain. After the second layer of ZnS is coated, the total shell thickness reaches a higher value and can still maintain a uniform spherical morphology. The ZnS shell has good crystallinity on the surface of the ZAISe quantum dot core, so it has a good surface passivation effect, which greatly improves the luminescence efficiency of the ZAISe quantum dots.

[0030] After washing the above-prepared ZAISe quantum dots without a coated shell (Comparative Example 1) and ZAISe / ZnS quantum dots with a coated Zn-S passivation shell (Example 4) twice, they are respectively dispersed in n-octane solution to obtain quantum dot colloidal solutions. After being placed in the air for a period of time, samples are taken to measure their relative PLQY values to test the stability of the synthesized samples. The change trend of the relative PLQY of the obtained ZAISe and ZAISe / ZnS quantum dot solutions with the placement time is as Figure 2 shown. It can be seen from this that after the ZAISe quantum dot solution without surface passivation treatment is placed for 30 days, its relative PLQY drops to about 30%. After the ZAISe / ZnS quantum dot solution with a coated Zn-S passivation shell is placed in the air for 30 days, its relative PLQY can still remain at about 90%, indicating that it has good stability.

[0031] It is worth mentioning that technical features such as centrifuges involved in this invention patent application should be regarded as prior art. The specific structures, working principles, and possible control methods and spatial arrangement methods involved in these technical features can be selected conventionally in this field and should not be regarded as the invention points of this invention patent. This invention patent will not be further specifically elaborated.

[0032] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations based on the concept of the present invention without creative labor. Therefore, all technical solutions that can be obtained by those skilled in the art in this technical field based on the concept of the present invention through logical analysis, reasoning, or limited experiments on the basis of the prior art should fall within the protection scope determined by the claims.

Claims

1. A method for preparing Zn-doped AlSe@ZnS core-shell structure quantum dot material, characterized in that: The following steps are included: Step 1, synthesis of ZAISe quantum dots: take a certain amount of selenium powder, 1-dodecanethiol and oleylamine and mix them to obtain a selenium precursor solution; take a certain amount of zinc acetate, silver nitrate and indium acetate and place them in a three-necked flask containing a mixed solution of 1-octadecene, 1-dodecanethiol and oleic acid, degas by magnetic stirring in a protective gas environment, and then heat up for dehydration; quickly inject the selenium precursor solution to obtain a quantum dot solution; take a certain amount of the quantum dot solution and a certain amount of toluene, shake and mix them evenly, and centrifuge to purify; take the separated liquid part and add ethanol, and then centrifuge to obtain a precipitate, which is the purified ZAISe quantum dots; after the ZAISe quantum dots are naturally dried, they are dispersed in toluene for use; Step 2, synthesis of ZAISe / ZnS quantum dots: a certain amount of Zn(OAc)2 powder, oleylamine and 1-octadecene are mixed, and a certain amount of octanethiol is injected to obtain a Zn-S precursor solution; a certain amount of S-TOP solution is added dropwise to the toluene solution of the above ZAISe quantum dots at a certain temperature, and after a period of reaction, the above Zn-S precursor solution is injected to obtain a ZAISe / ZnS quantum dot stock solution; Step 3, purification of ZAISe / ZnS quantum dots: purify the above ZAISe / ZnS quantum dot stock solution, store the purified ZAISe / ZnS quantum dot sample in n-hexane, and obtain Zn-doped AlSe@ZnS core-shell structure quantum dot material.

2. The method for preparing the Zn-doped AlSe@ZnS core-shell structure quantum dot material according to claim 1, characterized in that: The synthesis process of ZAISe quantum dots in step 1 includes: taking 0.54mmol selenium powder and dissolving it in a mixed solvent of 0.4mL 1-dodecanethiol and 1mL oleylamine, and ultrasonically dispersing it to obtain a selenium precursor solution; taking 0.04mmol zinc acetate, 0.08mmol silver nitrate and 0.2mmol indium acetate and placing them in a 50mL three-necked flask containing 8mL 1-octadecene, 1mL 1-dodecanethiol and 100μL OA mixed solution, and placing the three-necked flask in a nitrogen flow and magnetic stirring for degassing for 10 minutes at room temperature; then heating the mixed solution to 120°C and keeping it for 20 minutes to remove the water in the solution, and until the mixed solution becomes clear and transparent; then heating at 2°C / min heating rate to heat the reactants to 175 ° C and maintain for 10 minutes; then immediately inject the selenium precursor solution into the reaction solution, and the solution immediately turns dark brown; finally, the reaction system is kept at 175 ° C for 40 minutes to obtain a quantum dot solution; 2mL of the synthesized quantum dot solution is taken in a 15mL centrifuge tube, and it is thoroughly shaken and mixed with 2mL of toluene, and separated and purified in a centrifuge at a speed of 4000 rpm; ethanol is added to the separated liquid part until the total volume reaches 12mL, and then separated at a speed of 12000 rpm to obtain a precipitate, which is the purified ZAISe quantum dots; after the ZAISe quantum dots are naturally dried, they are dispersed in toluene for later use.

3. The method for preparing the Zn-doped AlSe@ZnS core-shell structure quantum dot material according to claim 1, characterized in that: The synthesis process of ZAISe / ZnS quantum dots in step 2 includes: adding 8 mmol of Zn(OAc)2 powder, 3 mL of oleylamine and 16 mL of 1-octadecene to a 50 mL three-necked flask, stirring at a rate of 900 rpm, and evacuating at 120°C for 1 hour, then filling with nitrogen, injecting 1.6 mL of octanethiol, and the solution immediately changes from a suspension to a colorless clear solution to obtain a Zn-S precursor solution; at 280°C, dropwise adding 2 mL of a 0.4 M S-TOP solution to the above ZAISe quantum dot toluene solution, the 0.4 M S-TOP solution being prepared by dissolving 0.4 mmol of S powder in 1 mL of trioctylphosphine, reacting for 30 minutes, cooling to 260°C, injecting the above Zn-S precursor solution into the reaction solution at a rate of 3.6 mL / hour, injecting a total of 1-8 mL, continuing the reaction for 10 minutes, stopping the reaction, and cooling to room temperature to obtain a ZAISe / ZnS quantum dot stock solution.

4. The method for preparing the Zn-doped AlSe@ZnS core-shell structure quantum dot material according to claim 3, characterized in that: The injection volume of the Zn-S precursor solution is 5 mL.

5. The method for preparing the Zn-doped AlSe@ZnS core-shell structure quantum dot material according to claim 1, characterized in that: The purification process of ZAISe / ZnS quantum dots in step 3 includes: adding the ZAISe / ZnS quantum dot stock solution to an equal volume of n-hexane solution for dilution, then adding 2 times the amount of anhydrous ethanol as an anti-solvent, obtaining a turbid solution after adding anhydrous ethanol, centrifuging at a speed of 8000 rpm, retaining the precipitate, and then redissolving the precipitate and dispersing it in n-hexane solution, adding an appropriate amount of oleylamine to completely dissolve it to obtain a transparent bright yellow solution, repeating the above operation 2-3 times, and finally storing the purified ZAISe / ZnS quantum dot sample in n-hexane.

6. Zn-doped AlSe@ZnS core-shell structure quantum dot material, characterized in that: Prepared by the preparation method described in any one of claims 1 to 5.

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