A core-shell quantum dot for inhibiting Auger recombination and its preparation

Abstract

This invention proposes a simple and easy-to-operate method for preparing core-shell quantum dots that suppress Auger recombination, and develops Mn-doped CsPbCl3@Cs4PbCl6 core-shell nanocrystals. The Auger suppression performance was studied using wavefunction engineering. The method includes the following steps: ① Synthesizing CsPbCl3 nanocrystals via thermal injection. ② Forming a Cs4PbCl6 shell nanocrystal on the CsPbCl3 nanocrystals. An oleic acid solution containing Cs is added to the CsPbCl3 nanocrystals; Cs ions tend to react with free Pb ions, and the Cs4PbCl6 shell nanocrystals grow epitaxially on the surface of the CsPbCl3 core nanocrystals. ③ Injecting a MnCl2 precursor into the pre-synthesized core-shell nanostructure at room temperature yields highly efficient Mn-emitting nanocrystals with promising applications in optoelectronics, generating significant social and economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials, specifically relating to the preparation of core-shell quantum dots that inhibit Auger recombination. Background Technology

[0002] Manganese (Mn)-doped quantum dots (QDs) have attracted widespread attention due to their unique optoelectronic properties, particularly in fields such as light-emitting diodes (LEDs), solar cells, and bioimaging. By doping with specific elements, Mn-doped quantum dots can achieve tunable luminescence properties and enhanced light absorption characteristics. However, in these applications, Auger recombination severely affects the optoelectronic performance of Mn-doped quantum dots, leading to reduced light emission efficiency and increased energy loss. Auger recombination refers to the nonradiative recombination process of excited-state carriers (electrons and holes) within the quantum dot, a phenomenon particularly pronounced at high carrier concentrations or long periods of excited-state existence.

[0003] To address the Auger recombination problem, researchers have proposed various methods, including improving the quantum dot synthesis process, optimizing doping concentration, and adjusting the material morphology. However, most existing methods face challenges such as high cost, complex preparation, or strict limitations on manganese doping concentration. Therefore, developing a novel method for preparing Mn-doped core-shell quantum dots to effectively suppress Auger recombination has become an important research topic in materials science.

[0004] This invention proposes an innovative method for preparing Mn-doped core-shell quantum dots to suppress Auger recombination between excitons and Mn. By rationally designing the core-shell structure and altering the cesium carbonate injection amount to regulate the distribution of manganese doping, the occurrence rate of Auger recombination can be significantly reduced, thereby improving the light emission efficiency and overall performance of the quantum dots. This method not only possesses good scalability and economy but also provides new ideas and solutions for improving the performance of Mn-doped quantum dots in practical applications. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to propose a novel method for preparing tunable Mn and exciton Auger composite core-shell quantum dots, which addresses the problems of the prior art mentioned above.

[0006] Another technical problem to be solved by this invention is to adjust the Mn doping site so that it is doped only in the shell layer and not the core layer, so as to ensure that the core-shell structure is not destroyed during the synthesis process.

[0007] To solve the technical problem of this invention, the technical solution adopted is as follows: the core-shell structured quantum dot material comprises a core composed of cesium, lead, and chlorine, and a shell composed of cesium, lead, and chlorine in another ratio surrounding the core. The shell thickness is adjusted to 1–3 nm by utilizing the Cs source injection amount. The chemical formula of the core layer is CsPbCl3, and the chemical formula of the shell layer is Cs4PbCl6.

[0008] To solve another technical problem of the present invention, another technical solution is adopted: after the above-mentioned core-shell structure quantum dots are prepared, Mn is doped, and the main steps are as follows:

[0009] 1) CsPbCl3 quantum dots were synthesized using a hot-injection method reported in the literature. The specific steps were as follows: ① ODE, CsCO3, and OA were loaded into a reaction flask. Water and oxygen were removed by purging with nitrogen and evacuating the flask at 100°C. After complete dissolution at 130°C, the mixture was cooled to 80°C for later use. ② ODE, PbCl2, OA, and OLA were loaded into a reaction flask. Water and oxygen were removed by purging with nitrogen and evacuating the flask at 120°C. After complete dissolution at 160°C, 1 mL of the cesium oleate solution from step 1 was injected. The reaction mixture was then rapidly cooled using an ice-water bath to obtain CsPbCl3 nanocrystals.

[0010] 2) Add 0.013 g of ZnCl2 to the solution obtained in step 1) to adjust the nanocrystal size and make it uniform. After purging with nitrogen and evacuating to a vacuum, heat to 70°C and then inject the cesium oleate solution obtained in step 1). After reacting for a few minutes, cool in an ice-water bath. Cs + Ions are more likely to react with free Pb 2+ Due to the ionic reaction, the Cs4PbCl6 shell is epitaxially grown on the surface of the CsPbCl3 core nanocrystals. The prepared CsPbCl3@Cs4PbCl6 core-shell nanocrystals were centrifuged at 8000 rpm for 10 min, washed three times in hexane, and finally redispersed in 5 ml of hexane for later use.

[0011] 3) Next, prepare the MnCl2 precursor solution by dissolving 0.1 mmol of anhydrous MnCl2 and 15 μL of LOLA in 2 mL of toluene, stirring at 100 °C for 3 hours, and then stirring at 70 °C overnight.

[0012] 4) Take an appropriate amount of the MnCl2 solution from step 3) and inject it into an appropriate amount of the CsPbCl3@Cs4PbCl6 core-shell nanocrystal solution obtained in step 2) under high-speed stirring. The Mn doping reaction time is less than 1 minute. Wash the doped nanostructure in methyl acetate, and then precipitate and redisperse it in 5 ml of hexane to obtain core-shell quantum dots that inhibit Auger recombination.

[0013] Preferably, the solvent used to dissolve 1.2 mmol of cesium carbonate in step 1) is specifically 20 mL of octadecene and 1.5 mL of oleic acid.

[0014] Furthermore, in step 1), the experimental temperature is 80°C cesium oleate solution injected into 160°C lead chloride solution.

[0015] Preferably, the amounts of lead chloride, oleylamine, oleic acid and octadecene in step 1) are 0.2 mmol, 1.5 mL, 1.5 mL and 5 mL, respectively.

[0016] Preferably, steps 1) and 2) are required to be carried out in an anhydrous and oxygen-free environment, with repeated N2 purging and vacuuming, and cesium carbonate is injected rapidly.

[0017] Preferably, the reaction temperature in step 2) is 70°C.

[0018] Preferably, the amount of cesium carbonate solution injected in step 2) can be adjusted to control the shell thickness (1-2 nm).

[0019] Preferably, the amounts of manganese chloride, toluene, and oleylamine in step 3) are 0.1 mmol, 2 mL, and 15 μL, respectively.

[0020] Preferably, the reaction time in step 4) is less than 1 minute to protect the core-shell structure from damage.

[0021] Preferably, in step 4), the nanocrystals with uniform size are obtained by washing with methyl acetate, and the centrifugation speed is 8000 r / min and the time is 10 min.

[0022] This adjustment method not only has the advantages of being simple and easy to operate, with readily available raw materials and low equipment requirements, but also has the potential to produce highly efficient Mn luminescent nanocrystals with good application prospects in the optoelectronic field, generating positive social and economic benefits.

[0023] Beneficial effects:

[0024] This invention effectively suppresses the Auger recombination effect by doping manganese ions into the shell structure of core-shell quantum dots. Compared with traditional quantum dots, the quantum dots prepared by this invention have the following beneficial effects:

[0025] (1) Improved luminescence efficiency of quantum dots: Due to the significant suppression of Auger recombination effect, the recombination efficiency of electron-hole pairs is improved, and the fluorescence emission efficiency of quantum dots is greatly enhanced, enabling the acquisition of stronger optical signals.

[0026] (2) Enhanced stability of quantum dots: Through core-shell structure design and manganese ion doping, the quantum dots prepared by this invention exhibit better stability in high temperature and high humidity environments, reducing the light attenuation of quantum dots under harsh conditions, which is beneficial to practical applications.

[0027] (3) Adjustable optical performance has been achieved: By controlling the doping concentration of manganese ions and the size of the core-shell structure, the emission wavelength and fluorescence color of quantum dots can be precisely adjusted, expanding the application of quantum dots in LEDs, displays and optical sensors. For example, perovskite quantum dot LEDs (QLEDs) have achieved an external quantum efficiency of up to 20% or more and have been applied in display technology and lighting. Attached Figure Description

[0028] Figure 1 This is one of the results of characterizing the target product obtained by the preparation method using transmission electron microscopy (TEM). The TEM image shows that the target product has a core-shell structure.

[0029] Figure 2 This is one of the results of characterizing the core-shell structure during the preparation of the target product and the target product obtained after Mn doping using X-ray diffraction (XRD). The XRD pattern confirms the composition of the core-shell structure.

[0030] Figure 3 The UV-Vis absorption spectra are for pure CsPbCl3 doped with Mn and core-shell structures doped with Mn.

[0031] Figure 4 These are the fluorescence emission spectra of Mn-doped pure CsPbCl3 cores and Mn-doped core-shell structures. Detailed Implementation

[0032] This invention provides a method for preparing core-shell quantum dots that suppress Auger recombination. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0033] Example 1

[0034] The method for preparing the Mn-doped CsPbCl3@Cs4PbCl6 core-shell structure to suppress Auger recombination is as follows:

[0035] 1) Synthesis of CsPbCl3 quantum dots: ① 20 mL of octadecene (ODE), 0.407 g of cesium carbonate (CsCO3), and 1.5 mL of oleic acid (OA) were added to a reaction flask. After purging with nitrogen at 100°C and then evacuating under vacuum, the solution was heated to 130°C until completely dissolved, then cooled to 80°C for later use, yielding a cesium oleate solution. ② 5 mL of octadecene (ODE), 0.056 g of lead halide (PbCl2), 1.5 mL of oleic acid (OA), and 1.5 mL of oleylamine (OLA) were added to a reaction flask. After purging with nitrogen at 120°C and then evacuating under vacuum, the solution was heated to 160°C until completely dissolved. Then, 1 mL of the cesium oleate solution obtained in step ① was injected. After 5 seconds, the reaction mixture was rapidly cooled to room temperature using an ice-water bath, yielding a solution of CsPbCl3 nanocrystals.

[0036] 2) Add 0.013 g of ZnCl2 to the solution obtained in step 1) to adjust the nanocrystal size and make it uniform. After purging with nitrogen, evacuate the reaction flask to remove water and oxygen. Heat to 70°C, dissolve the ZnCl2, and then inject 1.5 mL of the cesium oleate solution obtained in step 1)①. React for 3 minutes, and then cool to room temperature in an ice-water bath. Cs + Ions are more likely to react with free Pb 2+ Due to ionic reactions, the Cs4PbCl6 shell is epitaxially grown on the surface of the CsPbCl3 core nanocrystals. The prepared CsPbCl3@Cs4PbCl6 core-shell nanocrystals with a shell thickness of 1-3 nm and a particle size of 12-15 nm were centrifuged at 8000 rpm for 10 min, washed three times in n-hexane, and finally redispersed in 5 ml of n-hexane for later use, yielding a CsPbCl3@Cs4PbCl6 core-shell nanocrystal solution.

[0037] 3) Next, prepare the MnCl2 precursor solution by dissolving 0.1 mmol of anhydrous MnCl2 and 15 μL of oleylamine in 2 mL of toluene, stirring at 100 °C for 3 hours, and stirring at 70 °C overnight to obtain the MnCl2 solution.

[0038] 4) Take 1 ml of the MnCl2 solution from step 3) and inject it into 1 ml of the CsPbCl3@Cs4PbCl6 core-shell nanocrystal solution obtained in step 2) under high-speed stirring at 6000 rpm. The Mn doping reaction time is 1 minute. Wash the doped nanostructure in 2 ml of methyl acetate, and then precipitate and redisperse it in 5 ml of n-hexane to obtain core-shell quantum dots that inhibit Auger recombination.

[0039] Figure 1The high-resolution transmission electron microscopy image of the core-shell CsPbCl3@Cs4PbCl6 nanocrystals shows that the core-shell structure is spherical, with a central lattice spacing of 0.41 nm (corresponding to the face (110) of the CsPbCl3 core) and an outer lattice spacing of 0.31 nm (corresponding to the face (214) of the Cs4PbCl6 core), directly confirming the core-shell structure of the nanocrystals.

[0040] Mn-doped CsPbCl3 quantum dots: The preparation process and conditions are the same as those for Mn-doped CsPbCl3@Cs4PbCl6 in Example 1, except that step 2) is omitted. The sample obtained in step 1 is directly washed, centrifuged at 8000 rpm for 10 min, washed three times in n-hexane, and finally redispersed in 5 ml of n-hexane for later use. Steps 3) and 4) are then performed. 1 ml of the MnCl2 solution from step 3) is injected into 1 ml of the CsPbCl3 nanocrystal solution obtained in step 1) which is stirred at 6000 rpm. Mn-doped CsPbCl3 (Mn-doped CsPbCl3 quantum dots) is obtained.

[0041] Example 2

[0042] To further verify the generation of the core-shell structure, X-ray diffraction (XRD) was performed on the core-shell quantum dots obtained in Example 1.

[0043] Figure 2 The XRD patterns of Mn-doped CsPbCl3 and Mn-doped core-shell carbide nanocrystals are similar to the standard pattern of CsPbCl3, indicating that these carbide nanocrystals have high crystallinity. In particular, compared with CsPbCl3 nanocrystals, the novel diffraction peaks of the core-shell nanocrystals agree well with the standard mode of Cs4PbCl6, strongly verifying the formation of the Cs4PbCl6 phase in these core-shell nanocrystals. This further corroborates the formation of the core-shell structure.

[0044] Example 3

[0045] Figure 3 The UV-Vis absorption spectra of Mn-doped CsPbCl3 and Mn-doped core-shell nanotubes are shown. The Mn-doped CsPbCl3 nanocrystals exhibit a characteristic band-edge exciton absorption peak at 390 nm. In addition to an absorption peak at 400 nm in the CsPbCl3 core, its absorption spectrum also includes another characteristic peak at 281 nm. Figure 3 The shaded area (in the image) is due to exciton absorption in the Cs4PbCl6 shell, further verifying the successful preparation of CsPbCl3@Cs4PbCl6 carbon nanotubes. It can be seen that during the preparation process, with the increase of cesium oleate implantation in step 2) of Example 1, the intensity of the Cs4PbCl6 absorption peak in the core-shell carbon nanotubes increases, indicating an increase in the Cs4PbCl6 shell thickness.

[0046] Example 4

[0047] The Mn-doped CsPbCl3@Cs4PbCl6 core-shell quantum dots prepared in Example 1 were dissolved in n-hexane solution, and their fluorescence emission intensity was measured using a fluorescence spectrometer. The experimental results were compared with the control group (Mn-doped CsPbCl3 quantum dots).

[0048] Figure 4 The results showed that under the same excitation conditions (375 nm excitation wavelength, 20 μW power), the fluorescence intensity of Mn-doped CsPbCl3@Cs4PbCl6 core-shell quantum dots was significantly enhanced, and the emission peak intensity was significantly higher than that of the Mn-doped non-core-shell control group (Mn-doped CsPbCl3 quantum dots).

[0049] Further analysis using time-resolved fluorescence spectroscopy revealed that the Auger recombination effect was effectively suppressed in the Mn-doped core-shell quantum dots, with the frequency of nonradiative recombination significantly reduced by half. The Mn-doped core-shell quantum dots effectively suppressed the Auger recombination effect and significantly enhanced the fluorescence emission intensity of the quantum dots. This verifies the feasibility and superiority of the present invention in suppressing Auger recombination through the Mn-doped core-shell structure. This embodiment fully demonstrates the significant effect of the core-shell structure design of the present invention in suppressing the Auger recombination effect and enhancing fluorescence performance, and has broad application prospects.

[0050] Mn-doped CsPbCl3@Cs4PbCl6 core-shell quantum dots are used in high dynamic range (HDR) displays for televisions and monitors. They achieve 100% NTSC color gamut coverage, with particularly excellent performance in the green and orange bands.

[0051] Mn-doped CsPbCl3@Cs4PbCl6 core-shell quantum dots are used as anti-counterfeiting markers on banknotes, certificates, and important documents. They exhibit special color fluorescence under ultraviolet light or specific excitation light, enhancing their anti-counterfeiting effect.

Claims

1. A method for preparing core-shell quantum dots that suppress Auger recombination, characterized in that... Includes the following steps: 1) Synthesis of CsPbCl3 quantum dots, the specific operation is as follows: ① Place 18-22 mL of octadecene (ODE), 0.39-0.42 g of cesium carbonate (CsCO3), and 1.2-1.8 mL of oleic acid (OA) into a container; purge the container with nitrogen at 90-110℃, then evacuate to remove water and oxygen. Heat to 120-140℃ until completely dissolved, then cool to 60-80℃ for later use, yielding a cesium oleate solution; ② Place 4-6 mL of octadecene (ODE) and 0.05-0.06 g of lead halide (CsCO3) into a container. PbCl2), 1.2-1.8 mL of oleic acid (OA) and 1.2-1.8 mL of oleylamine (OLA) were placed in another container; the water and oxygen in the reaction flask were removed by purging with nitrogen at 110-130℃ and then by vacuuming. After complete dissolution at 150-170℃, 0.8-1.2 mL of cesium oleate solution obtained in step ① was injected. After 3-8 seconds, the reaction mixture was rapidly cooled to room temperature by an ice-water bath to obtain a solution of CsPbCl3 nanocrystals. 2) Add 0.01-0.03g of ZnCl2 to the CsPbCl3 nanocrystal solution obtained in step 1)② to adjust the nanocrystal size to make it uniform. After purging with nitrogen, evacuate the reaction flask to remove water and oxygen. Heat to 60-80℃, dissolve ZnCl2, and then inject 1.2-1.8mL of the cesium oleate solution obtained in step 1)①. React for 2-5 minutes and then cool to room temperature in an ice-water bath. Centrifuge the prepared CsPbCl3@Cs4PbCl6 core-shell nanocrystals with a shell thickness of 1-3nm and a particle size of 12-15nm at 6000-10000rpm for 5-20min, wash in n-hexane, and finally redisperse in 4-6ml of n-hexane for later use to obtain the CsPbCl3@Cs4PbCl6 core-shell nanocrystal solution. 3) Next, prepare the MnCl2 precursor solution by dissolving 0.1-0.2 mmol of anhydrous MnCl2 and 12-18 μL of oleylamine in 1.8-2.2 mL of toluene, stirring at 95-110 °C for 2-6 hours, and then stirring at 60-80 °C for 8-24 hours to obtain the MnCl2 solution. 4) Take 0.8-1.2 ml of the MnCl2 solution from step 3) and inject it into 0.8-1.2 ml of the CsPbCl3@Cs4PbCl6 core-shell nanocrystal solution obtained in step 2) which is stirred at 5000-6000 rpm. The Mn doping reaction time is 0.5-1 minutes to obtain the doped nanostructure. Wash the doped nanostructure in methyl acetate to obtain core-shell quantum dots that inhibit Auger recombination.

2. The preparation of core-shell quantum dots for suppressing Auger recombination according to claim 1, characterized in that: Step 4) involves precipitating and redispersing the core-shell quantum dots that inhibit Auger recombination in 3-8 ml of n-hexane.

3. A core-shell quantum dot for suppressing Auger recombination obtained by the suppression preparation method according to any one of claims 1 to 2.

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