A two-step method for synthesizing aluminum-doped indium phosphide quantum dots and products thereof

Abstract

The application discloses a two-step method for synthesizing aluminum-doped indium phosphide quantum dots and a product thereof, and belongs to the technical field of luminescent materials. The method comprises the following steps: (1) reacting an indium source and a phosphorus source in a solution environment in the presence of zinc halide to form an indium phosphide core; (2) reacting the indium phosphide core with zinc halide in a solution environment to form a passivated indium phosphide core; (3) taking aluminum isopropoxide, a zinc source, a selenium source and a sulfur source as shell layer raw materials, and reacting the shell layer raw materials in batches in a solution environment to layer by layer coat the passivated indium phosphide core to form a gradient aluminum-doped zinc sulfoselenide shell layer; and (4) reacting sulfur on a surface layer of the gradient aluminum-doped zinc sulfoselenide shell layer to form an aluminum-doped zinc sulfide shell layer; and performing surface treatment on the aluminum-doped zinc sulfide shell layer by reacting zinc acetate in a solution environment to obtain a core-shell quantum dot. The application has the advantages of simple process, convenient synthesis, easy scale production, excellent luminous performance and stability of the product, environmental friendliness and suitability for popularization and application.

Description

Technical Field

[0001] This invention relates to the field of luminescent materials technology, and in particular to a two-step method for synthesizing aluminum-doped indium phosphide quantum dots and the product thereof. Background Technology

[0002] Colloidal nanocrystals have been extensively studied over the past three decades due to their unique size-dependent optical, photocatalytic, and electronic properties. These unique size-dependent absorption and emission properties span the entire visible spectrum, and their high stability makes them attractive for applications such as lasers, bioimaging, and solid-state lighting. Cadmium (Cd)-based quantum dots (QDs) and metal halide perovskites (CsPbX3, where X represents a halogen Cl, Br, or I) have been well-developed to produce excellent physical properties that meet the optical specifications for commercial display technologies. However, based on the European RoHS (Royal Harmful Substances Restriction) regulations, these cadmium and lead materials are restricted from use in electrical and electronic commercial products due to their toxicity and environmental concerns associated with large-scale production. Indium phosphide quantum dots are considered the best environmentally friendly alternative to these toxic materials in commercial display applications. Indium phosphide has a Bohr exciton radius of 9.6 nm and a band gap of 1.34 V. These InP QDs exhibit good stability and high luminous efficiency for type I core-shell structures, making them promising emitters and novel materials for wide color gamut display applications.

[0003] However, for the practical commercialization of indium phosphide quantum dot displays, their optical properties still lag behind cadmium-based quantum dots, mainly due to their broader fluorescence half-width (FWHM) and lower photoluminescence quantum yield (PLQY). This is attributed to a lack of comprehensive understanding and control over their reaction kinetics and mechanisms, resulting in smaller size uniformity and unit quantum yields. For a long time, the further development of indium phosphide quantum dots has been mainly hindered by the following aspects: (I) The high covalent nature of indium phosphide means that more energy is needed to form indium-phosphine bonds during the synthesis process; (II) The high oxyphilicity of indium and phosphorus means that water and oxygen in the system need to be more strictly controlled during the reaction process; (III) The choice of phosphorus source is limited. The most widely used phosphorus precursor, tris(trimethylsilyl)phosphine ((TMS)3P), is an expensive, reactive, and highly toxic organic compound. During the synthesis process, its high reactivity causes the phosphorus precursor to be consumed instantly during nucleation, leaving insufficient monomer supply for subsequent synthesis. This easily leads to Ostwald ripening, which is one of the main reasons for the broadening of the free-weighted mean square distance (FWHM) of InP quantum dots. Due to the oxyphilicity of indium and phosphorus, indium phosphide is easily oxidized to form a series of complex oxides, such as P2O3 and In2O3. These oxides have an adverse effect on the optical properties of quantum dots, causing the optical properties of indium phosphide quantum dots to lag far behind other types of quantum dots. Meanwhile, the large specific surface area of ​​defects formed on the quantum dot surface becomes another factor limiting its high-quality luminescence. To address issues such as oxidation and defects, improve the optical performance of indium phosphide quantum dots, and obtain high-quality fluorescent materials, scientists have conducted tireless exploration and research. Common strategies for improving the optical performance of indium phosphide quantum dots include etching and surface shell passivation. Doping the shell material with group IIIA elements such as gallium and aluminum helps to regulate the electronic structure and charge distribution between the shell and the core, and passivates surface defects in quantum dots, which is an effective way to improve quantum dot luminescence.

[0004] For example, our research group disclosed an aluminum-doped indium phosphide core-shell quantum dot with tunable emission spectrum and its preparation method in Chinese invention patent publication number CN117487538A. This aluminum-doped indium phosphide core-shell quantum dot is synthesized using a simple one-pot method. In the same reaction vessel, an indium phosphide core is first prepared, and then coated with a zinc sulfide shell. During the coating process, a certain proportion of aluminum isopropoxide is added, allowing aluminum to be doped into the zinc sulfide shell in the form of aluminum phosphate. This significantly suppresses the formation of oxidation defects on the indium phosphide surface, alleviates the charge mismatch at the core-shell interface, and yields quantum dots with improved luminescence efficiency and narrowed emission peak width at half maximum (FWHM). Further research in this invention revealed that there is still considerable room for improvement based on this quantum dot. Introducing selenium helps to further alleviate the lattice mismatch between indium phosphide and zinc sulfide, improving the overall performance of the quantum dots. However, under the original preparation conditions, how to introduce and coordinate the structure to fully utilize the function of selenium remains a technical problem to be solved. In addition, the generation of defect states and the decrease in quantum yield caused by Ostwald ripening during the synthesis of indium phosphide are also obstacles to improving the performance of quantum dots. The original process can no longer meet the requirements for the preparation of quantum dots with new compositions and structures.

[0005] Therefore, developing a novel method for improving the luminescence performance of indium phosphide core-shell quantum dots by aluminum doping, in order to enhance the luminescence performance and stability of quantum dots, is of great significance for promoting the large-scale production and commercialization of indium phosphide quantum dots. Summary of the Invention

[0006] In view of the above-mentioned deficiencies of the prior art, in a first aspect of the present invention, a two-step method for synthesizing aluminum-doped indium phosphide quantum dots is provided, which is simple in process, convenient in synthesis, and easy to scale up, comprising the following steps:

[0007] (1) The indium source and the phosphorus source react in a solution environment in which zinc halide is present to form an indium phosphide core;

[0008] (2) The indium phosphide core reacts with zinc halide in a solution environment to form a passivated indium phosphide core;

[0009] (3) Using aluminum isopropoxide, zinc source, selenium source and sulfur source as shell material, the shell material is reacted in batches in solution environment to coat the passivated indium phosphide core layer by layer to form a gradient aluminum doped zinc sulfide selenide shell.

[0010] (4) Sulfur originates from the surface reaction of the gradient aluminum-doped zinc sulfide shell to form an aluminum-doped zinc sulfide shell; in a solution environment, zinc acetate is reacted to treat the surface and obtain core-shell quantum dots.

[0011] Preferably, in step (1), the indium source includes at least one of indium chloride, indium bromide, indium iodide, and indium acetate; the phosphorus source includes at least one of tris(trimethylsilyl)phosphine, tris(dimethylamino)phosphine, and tris(diethylamino)phosphine; and the zinc halide includes at least one of zinc chloride, zinc bromide, and zinc iodide.

[0012] Preferably, in step (1), the molar ratio of the indium source to the phosphorus source is 1:2 to 4; and the molar ratio of the indium source to the zinc halide is 1:2 to 5.

[0013] Preferably, in step (1), the reaction temperature is 120-220°C and the reaction time is 1-60 min.

[0014] The recovery and purification of indium phosphide cores can be carried out using general methods. For example, a desolventizing agent can be added to the reaction solution to precipitate the product, followed by centrifugation to collect the lower precipitate. Ethanol, acetone, methanol, etc., can all be used as suitable desolventizing agents.

[0015] Preferably, in step (2), the zinc halide includes at least one of zinc chloride, zinc bromide, and zinc iodide.

[0016] Preferably, in step (2), the molar ratio of zinc halide to indium source in step (1) is 2 to 5:1.

[0017] Preferably, in step (2), the reaction temperature is 240-300℃, the reaction time is 1-3h, and the heating rate is 20-50℃ / min.

[0018] Preferably, in step (3), the zinc source includes at least one of zinc stearate and zinc(II) acetate; the selenium source includes at least one of selenium and selenium oxide; and the sulfur source includes at least one of sulfur, 1-dodecyl mercaptan, and octyl mercaptan.

[0019] Preferably, in step (3), based on the molar ratio of the raw material to the indium source in step (1), the molar ratio of the zinc source to the indium source is 1 to 5:1; the molar ratio of the sulfur source to the indium source is 0.5 to 10:1; the molar ratio of the selenium source to the indium source is 0.5 to 5:1; and the molar ratio of the aluminum isopropoxide to the sulfur source in step (3) is 0.2 to 3:1.

[0020] Preferably, in step (3), the reaction temperature is 240-320°C and the reaction time is 0.5-2h.

[0021] In a further preferred embodiment, the shell material is reacted in solution in four batches to coat the passivated indium phosphide core layer by layer; the first batch is reacted at 250°C for 2 hours; the second batch is reacted at 260°C for 2 hours; the third batch is reacted at 270°C for 2 hours; and the fourth batch is reacted at 280°C for 3 hours.

[0022] Preferably, in step (4), the sulfur source includes at least one of sulfur, 1-dodecyl mercaptan, and octyl mercaptan.

[0023] Preferably, in step (4), the molar ratio of the sulfur source to the indium source in step (1) is 0.5 to 10:1; and the molar ratio of the zinc acetate to the sulfur source in step (4) is 1:2 to 5.

[0024] Preferably, in step (4), aluminum isopropoxide is also added. The sulfur source and aluminum isopropoxide react with the surface of the gradient-type aluminum-doped zinc sulfide shell to form an aluminum-doped zinc sulfide shell.

[0025] More preferably, the molar ratio of aluminum isopropoxide to the sulfur source in step (4) is 1:2 to 15.

[0026] The solution environment involved in the process of this invention is created by a suitable type of solvent. In this art, the function of a solvent is to promote substrate dispersion and normal reaction; it is chemically inert relative to the substrate and does not participate in the reaction. Therefore, those skilled in the art can select the appropriate type and amount of solvent based on the types of raw materials mentioned above. For example, as presented in one or more embodiments of this invention, in step (1), the indium source and zinc halide are soluble in oleylamine, and the phosphorus source is soluble in tri-n-octylphosphine; in step (2), zinc halide is soluble in oleylamine and octadecene; in step (3), aluminum isopropoxide is soluble in oleylamine, the zinc source is soluble in octadecene, and the selenium and sulfur sources are soluble in tri-n-octylphosphine; in step (4), zinc acetate is soluble in oleylamine and octadecene. Other suitable solvent types can also achieve the purpose of this invention.

[0027] In a second aspect of the invention, a core-shell quantum dot with excellent luminescence properties and stability is provided, which is manufactured using the method of the first aspect of the invention.

[0028] Based on the above technical solution, unlike the existing technology that uses a "one-pot" process, the design concept of this invention is to use a "two-step method" to introduce a certain amount of aluminum isopropoxide in the intermediate step of the reaction to prepare core-shell indium phosphide, namely, the heating step after the indium phosphide core is purified and before the shell (ZnSeS / ZnS) coating. The addition of aluminum isopropoxide has two main benefits. First, it passivates surface defects in indium phosphide quantum dots, resulting in a more uniform particle size distribution, a smaller full width at half maximum (FWHM) in the fluorescence spectrum, and improved quantum yield. Second, aluminum isopropoxide may form an oxide film on the outer layer of the quantum dots, further inhibiting oxidation at the core-shell interface, improving the photothermal stability of the quantum dots, and alleviating Ostwald ripening. Adding a certain amount of zinc halide before the second reaction after nucleation can act as ion passivation. Third, introducing the shell material in batches during the formation of the ZnSeS shell to prepare a gradient shell can greatly alleviate the problem of lattice mismatch at the core-shell interface. Coating with an aluminum-doped ZnS shell results in a significantly reduced FWHM and a significantly improved quantum yield, with more uniform quantum dot size and better dispersion. Furthermore, the indium phosphide quantum dots prepared by this invention are free of heavy metals and environmentally friendly, making them suitable for widespread application.

[0029] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0030] This invention provides a two-step method for synthesizing aluminum-doped indium phosphide quantum dots, which has the advantages of simple process, convenient synthesis and easy large-scale production.

[0031] This invention provides a core-shell quantum dot with excellent luminescence performance and stability. Its components do not contain heavy metal elements, making it environmentally friendly and suitable for promotion and application. Attached Figure Description

[0032] Figure 1 The image shows the ultraviolet absorption spectrum (UV-vis) and fluorescence spectrum (PL) of the core-shell quantum dots in Example 1.

[0033] Figure 2 The image shows a transmission electron microscope (TEM) image of the core-shell quantum dots in Example 1.

[0034] Figure 3 The ultraviolet absorption and fluorescence spectra of the core-shell quantum dots in Example 2 are shown.

[0035] Figure 4 This is a transmission electron microscope image of the core-shell quantum dots from Example 2;

[0036] Figure 5 The UV absorption and fluorescence spectra of the core-shell quantum dots in Example 3 are shown below.

[0037] Figure 6 This is a transmission electron microscope image of the core-shell quantum dots in Example 3;

[0038] Figure 7 The UV absorption and fluorescence spectra of undoped core-shell quantum dots are shown in Comparative Example 1.

[0039] Figure 8 This is a transmission electron microscope (TEM) image of the undoped core-shell quantum dot in Comparative Example 1. Detailed Implementation

[0040] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0041] Example 1

[0042] The two-step method for synthesizing aluminum-doped indium phosphide quantum dots comprises the following steps:

[0043] (1) Take 0.8920 g of indium triiodide and 0.5998 g of zinc chloride, dissolve them in a 50 mL three-necked flask containing 12 mL of oleylamine, first evacuate for 1 h, add 2 mL of tri-n-octylphosphine (TOP) solution containing 0.7 mL of tri(dimethylamino)phosphine under argon conditions, heat to 180 °C and react for 5 min; during this period, the solution color changes from colorless to orange and then to brown; after 5 min, immediately cool the solution to room temperature, then mix the obtained indium phosphide core with excess anhydrous ethanol, centrifuge at high speed (10000 rpm, 5 min) to collect the precipitate, and then completely dissolve the indium phosphide core with n-hexane;

[0044] (2) Mix 6 mL of oleylamine, 6 mL of octadecene and 0.5998 g of zinc chloride in a 100 mL four-necked flask. First, evacuate the flask at room temperature, and then heat it to 130 °C for 1 h in an argon atmosphere (to keep the whole apparatus in an anhydrous and oxygen-free environment) to completely dissolve the zinc chloride. At this time, add the indium phosphide core solution dissolved in n-hexane into the reaction system and collect the n-hexane vapor through a reflux condenser to passivate the indium phosphide core with ions.

[0045] (3) For the further shell-forming process, aluminum isopropoxide solution (0.5 mmol aluminum isopropoxide dissolved in 0.5 mL oleylamine), zinc source (1.0 g zinc stearate dissolved in 4 mL octadecene), selenium source, and sulfur source (0.8 mmol selenium powder and 0.9 mmol sulfur powder dissolved in 1.25 mL tri-n-octylphosphine) were rapidly injected into the reaction flask and heated to 200 °C and mixed continuously for 30 min; next, the mixture was heated to 250 °C and reacted for 2 h; a second injection of aluminum isopropoxide solution (0.5 mmol aluminum isopropoxide dissolved in 0.5 mL oleylamine), zinc source (1.0 g zinc stearate dissolved in 4 mL octadecene), selenium source, and sulfur source (0.6 mmol selenium powder and 1.8 mmol sulfur powder dissolved in 1.5 mL oleylamine) was injected. The mixture was reacted at 260°C for 2 hours. A third reaction was performed with aluminum isopropoxide solution (0.5 mmol aluminum isopropoxide dissolved in 0.5 mL oleylamine), zinc source (1.0 g zinc stearate dissolved in 4 mL octadecene), selenium source, and sulfur source (0.4 mmol selenium powder and 2.7 mmol sulfur powder dissolved in 1.75 mL tri-n-octylphosphine), and the mixture was reacted at 270°C for 2 hours. A fourth reaction was performed with aluminum isopropoxide solution (0.5 mmol aluminum isopropoxide dissolved in 0.5 mL oleylamine), zinc source (1.0 g zinc stearate dissolved in 4 mL octadecene), selenium source, and sulfur source (0.2 mmol selenium powder and 3.6 mmol sulfur powder dissolved in 2 mL tri-n-octylphosphine), and the mixture was reacted at 280°C for 3 hours, forming a gradient aluminum-doped zinc sulfoselenide shell.

[0046] (4) The temperature was rapidly cooled to 210℃, 1.5 mL of octyl mercaptan was added, and the reaction was carried out at 210℃ for 30 min. The temperature was then lowered to 190℃, and zinc acetate solution (2 mmol of zinc acetate dihydrate dissolved in 2 mL of oleylamine and 10 mL of octadecene) was added. The reaction was carried out at 190℃ for 1 h and then cooled to room temperature to obtain core-shell quantum dots. The obtained quantum dots were mixed with anhydrous ethanol at a volume ratio of 1:7, centrifuged to precipitate and purified, and then redispersed in n-hexane.

[0047] Example 2

[0048] The method for synthesizing aluminum-doped indium phosphide quantum dots in this embodiment is the same as that in Example 1, and steps (1) and (2) are the same. The operations of steps (3) and (4) in this embodiment are as follows:

[0049] (3) For the further shell-forming process, the zinc source (1.0 g of zinc stearate dissolved in 4 mL of octadecene), selenium source, and sulfur source (0.8 mmol of selenium powder and 0.9 mmol of sulfur powder dissolved in 1.25 mL of tri-n-octylphosphine) were rapidly injected into the reaction flask and heated to 200 °C for 30 min of continuous mixing; next, the mixture was heated to 250 °C and reacted for 2 h; a second injection of the zinc source (1.0 g of zinc stearate dissolved in 4 mL of octadecene), selenium source, and sulfur source (0.6 mmol of selenium powder and 1.8 mmol of sulfur powder dissolved in 1.5 mL of tri-n-octylphosphine) was then performed. The mixture was first injected with 1.0 g of zinc stearate dissolved in 4 mL of octadecene, and then with selenium and sulfur sources (0.4 mmol selenium powder and 2.7 mmol sulfur powder dissolved in 1.75 mL of tri-n-octylphosphine), and reacted at 270 °C for 2 h. Then, it was injected a third time with zinc source (1.0 g of zinc stearate dissolved in 4 mL of octadecene), and then with selenium and sulfur sources (0.2 mmol selenium powder and 3.6 mmol sulfur powder dissolved in 2 mL of tri-n-octylphosphine), and reacted at 280 °C for 3 h, forming a gradient zinc sulfoselenide shell.

[0050] (4) The temperature was rapidly cooled to 210°C, and a solution of 0.75 mmol aluminum isopropoxide dissolved in 1.5 mL of octyl mercaptan was added. The reaction was carried out at 210°C for 30 min. The temperature was then lowered to 190°C, and a zinc acetate solution (2 mmol of zinc acetate dihydrate dissolved in 2 mL of oleylamine and 10 mL of octadecene) was added. The reaction was carried out at 190°C for 1 h and then cooled to room temperature to obtain core-shell quantum dots. The obtained quantum dots were mixed with anhydrous ethanol at a volume ratio of 1:7, centrifuged to precipitate and purified, and then redispersed in n-hexane.

[0051] Example 3

[0052] The method for synthesizing aluminum-doped indium phosphide quantum dots in this embodiment is the same as that in Example 1, and steps (1) and (2) are the same. The operations of steps (3) and (4) in this embodiment are as follows:

[0053] (3) For the further shell-forming process, aluminum isopropoxide solution (0.5 mmol aluminum isopropoxide dissolved in 0.5 mL oleylamine), zinc source (1.0 g zinc stearate dissolved in 4 mL octadecene), selenium source, and sulfur source (0.8 mmol selenium powder and 0.9 mmol sulfur powder dissolved in 1.25 mL tri-n-octylphosphine) were rapidly injected into the reaction flask and heated to 200 °C and mixed continuously for 30 min; next, the mixture was heated to 250 °C and reacted for 2 h; a second injection of aluminum isopropoxide solution (0.5 mmol aluminum isopropoxide dissolved in 0.5 mL oleylamine), zinc source (1.0 g zinc stearate dissolved in 4 mL octadecene), selenium source, and sulfur source (0.6 mmol selenium powder and 1.8 mmol sulfur powder dissolved in 1.5 mL oleylamine) was injected. The mixture was reacted at 260°C for 2 hours. A third reaction was performed with aluminum isopropoxide solution (0.5 mmol aluminum isopropoxide dissolved in 0.5 mL oleylamine), zinc source (1.0 g zinc stearate dissolved in 4 mL octadecene), selenium source, and sulfur source (0.4 mmol selenium powder and 2.7 mmol sulfur powder dissolved in 1.75 mL tri-n-octylphosphine), and the mixture was reacted at 270°C for 2 hours. A fourth reaction was performed with aluminum isopropoxide solution (0.5 mmol aluminum isopropoxide dissolved in 0.5 mL oleylamine), zinc source (1.0 g zinc stearate dissolved in 4 mL octadecene), selenium source, and sulfur source (0.2 mmol selenium powder and 3.6 mmol sulfur powder dissolved in 2 mL tri-n-octylphosphine), and the mixture was reacted at 280°C for 3 hours, forming a gradient aluminum-doped zinc sulfoselenide shell.

[0054] (4) The temperature was rapidly cooled to 210°C, and a solution of 0.75 mmol aluminum isopropoxide dissolved in 1.5 mL of octyl mercaptan was added. The reaction was carried out at 210°C for 30 min. The temperature was then lowered to 190°C, and a zinc acetate solution (2 mmol of zinc acetate dihydrate dissolved in 2 mL of oleylamine and 10 mL of octadecene) was added. The reaction was carried out at 190°C for 1 h and then cooled to room temperature to obtain core-shell quantum dots. The obtained quantum dots were mixed with anhydrous ethanol at a volume ratio of 1:7, centrifuged to precipitate and purified, and then redispersed in n-hexane.

[0055] Example 4

[0056] The method for synthesizing aluminum-doped indium phosphide quantum dots in this embodiment is the same as that in Example 1, except that step (3) in this embodiment is performed as follows:

[0057] (3) For the further shell-forming process, aluminum isopropoxide solution (0.25 mmol aluminum isopropoxide dissolved in 0.25 mL oleylamine), zinc source (1.0 g zinc stearate dissolved in 4 mL octadecene), selenium source, and sulfur source (0.8 mmol selenium powder and 0.9 mmol sulfur powder dissolved in 1.25 mL tri-n-octylphosphine) were rapidly injected into the reaction flask and heated to 200 °C and mixed continuously for 30 min; next, the mixture was heated to 250 °C and reacted for 2 h; a second injection of aluminum isopropoxide solution (0.25 mmol aluminum isopropoxide dissolved in 0.25 mL oleylamine), zinc source (1.0 g zinc stearate dissolved in 4 mL octadecene), selenium source, and sulfur source (0.6 mmol selenium powder and 1.8 mmol sulfur powder dissolved in 1.5 mL oleylamine) was injected. The mixture was reacted at 260°C for 2 hours. A third reaction was performed with aluminum isopropoxide solution (0.25 mmol aluminum isopropoxide dissolved in 0.25 mL oleylamine), zinc source (1.0 g zinc stearate dissolved in 4 mL octadecene), selenium source, and sulfur source (0.4 mmol selenium powder and 2.7 mmol sulfur powder dissolved in 1.75 mL tri-n-octylphosphine), and the mixture was reacted at 270°C for 2 hours. A fourth reaction was performed with aluminum isopropoxide solution (0.25 mmol aluminum isopropoxide dissolved in 0.25 mL oleylamine), zinc source (1.0 g zinc stearate dissolved in 4 mL octadecene), selenium source, and sulfur source (0.2 mmol selenium powder and 3.6 mmol sulfur powder dissolved in 2 mL tri-n-octylphosphine), and the mixture was reacted at 280°C for 3 hours, forming a gradient aluminum-doped zinc sulfoselenide shell.

[0058] Example 5

[0059] The method for synthesizing aluminum-doped indium phosphide quantum dots in this embodiment is the same as that in Example 1, except that step (3) in this embodiment is performed as follows:

[0060] (3) For the further shell-forming process, aluminum isopropoxide solution (0.75 mmol aluminum isopropoxide dissolved in 0.75 mL oleylamine), zinc source (1.0 g zinc stearate dissolved in 4 mL octadecene), selenium source, and sulfur source (0.8 mmol selenium powder and 0.9 mmol sulfur powder dissolved in 1.25 mL tri-n-octylphosphine) were rapidly injected into the reaction flask and heated to 200 °C and mixed continuously for 30 min; next, the mixture was heated to 250 °C and reacted for 2 h; a second injection of aluminum isopropoxide solution (0.75 mmol aluminum isopropoxide dissolved in 0.75 mL oleylamine), zinc source (1.0 g zinc stearate dissolved in 4 mL octadecene), selenium source, and sulfur source (0.6 mmol selenium powder and 1.8 mmol sulfur powder dissolved in 1.5 mL oleylamine) was injected. The mixture was reacted at 260°C for 2 hours. A third reaction was performed with aluminum isopropoxide solution (0.75 mmol aluminum isopropoxide dissolved in 0.75 mL oleylamine), zinc source (1.0 g zinc stearate dissolved in 4 mL octadecene), selenium source, and sulfur source (0.4 mmol selenium powder and 2.7 mmol sulfur powder dissolved in 1.75 mL tri-n-octylphosphine), and the mixture was reacted at 270°C for 2 hours. A fourth reaction was performed with aluminum isopropoxide solution (0.75 mmol aluminum isopropoxide dissolved in 0.75 mL oleylamine), zinc source (1.0 g zinc stearate dissolved in 4 mL octadecene), selenium source, and sulfur source (0.2 mmol selenium powder and 3.6 mmol sulfur powder dissolved in 2 mL tri-n-octylphosphine), and the mixture was reacted at 280°C for 3 hours, forming a gradient aluminum-doped zinc sulfoselenide shell.

[0061] Example 6

[0062] The method for synthesizing aluminum-doped indium phosphide quantum dots in this embodiment is the same as that in Example 1, except that step (3) in this embodiment is performed as follows:

[0063] (3) For the further shell-forming process, aluminum isopropoxide solution (1 mmol aluminum isopropoxide dissolved in 1 mL oleylamine), zinc source (1.0 g zinc stearate dissolved in 4 mL octadecene), selenium source, and sulfur source (0.8 mmol selenium powder and 0.9 mmol sulfur powder dissolved in 1.25 mL tri-n-octylphosphine) were rapidly injected into the reaction flask and heated to 200 °C and mixed continuously for 30 min; next, the mixture was heated to 250 °C and reacted for 2 h; a second injection of aluminum isopropoxide solution (1 mmol aluminum isopropoxide dissolved in 1 mL oleylamine), zinc source (1.0 g zinc stearate dissolved in 4 mL octadecene), and selenium source and sulfur source (0.6 mmol selenium powder and 1.8 mmol sulfur powder dissolved in 1.5 mL oleylamine) was injected. The mixture was reacted at 260°C for 2 hours. A third reaction was performed with aluminum isopropoxide solution (1 mmol aluminum isopropoxide dissolved in 1 mL oleylamine), zinc source (1.0 g zinc stearate dissolved in 4 mL octadecene), selenium source, and sulfur source (0.4 mmol selenium powder and 2.7 mmol sulfur powder dissolved in 1.75 mL tri-n-octylphosphine), and the mixture was reacted at 270°C for 2 hours. A fourth reaction was performed with aluminum isopropoxide solution (1 mmol aluminum isopropoxide dissolved in 1 mL oleylamine), zinc source (1.0 g zinc stearate dissolved in 4 mL octadecene), selenium source, and sulfur source (0.2 mmol selenium powder and 3.6 mmol sulfur powder dissolved in 2 mL tri-n-octylphosphine), and the mixture was reacted at 280°C for 2 hours, forming a gradient aluminum-doped zinc sulfoselenide shell.

[0064] Comparative Example 1

[0065] The preparation method of undoped core-shell quantum dots includes the following steps:

[0066] (1) Take 0.8920 g of indium triiodide and 0.5998 g of zinc chloride, dissolve them in a 50 mL three-necked flask containing 12 mL of oleylamine, first evacuate for 1 h, add 2 mL of tri-n-octylphosphine (TOP) solution containing 0.7 mL of tri(dimethylamino)phosphine under argon conditions, heat to 180 °C and react for 1 min; during this period, the solution color changes from colorless to orange and then to brown; after 1 min, immediately cool the solution to room temperature, then mix the obtained indium phosphide core with excess anhydrous ethanol, centrifuge at high speed (10000 rpm, 5 min) to collect the precipitate, and then completely dissolve the indium phosphide core with n-hexane;

[0067] (2) Mix 6 mL of oleylamine, 6 mL of octadecene and 0.5998 g of zinc chloride in a 100 mL four-necked flask. First, evacuate the flask at room temperature, and then heat it to 130 °C for 1 h in an argon atmosphere (to keep the whole apparatus in an anhydrous and oxygen-free environment) to completely dissolve the zinc chloride. At this time, add the indium phosphide core solution dissolved in n-hexane into the reaction system and collect the n-hexane vapor through a reflux condenser to passivate the indium phosphide core with ions.

[0068] (3) For the further shell-forming process, the zinc source (1.0 g of zinc stearate dissolved in 4 mL of octadecene), selenium source, and sulfur source (0.8 mmol of selenium powder and 0.9 mmol of sulfur powder dissolved in 1.25 mL of tri-n-octylphosphine) were rapidly injected into the reaction flask and heated to 200 °C for 30 min of continuous mixing; next, the mixture was heated to 250 °C and reacted for 2 h; a second injection of the zinc source (1.0 g of zinc stearate dissolved in 4 mL of octadecene), selenium source, and sulfur source (0.6 mmol of selenium powder and 1.8 mmol of sulfur powder dissolved in 1.5 mL of tri-n-octylphosphine) was then performed. The mixture was first injected with 1.0 g of zinc stearate dissolved in 4 mL of octadecene, and then with selenium and sulfur sources (0.4 mmol selenium powder and 2.7 mmol sulfur powder dissolved in 1.75 mL of tri-n-octylphosphine), and reacted at 270 °C for 2 h. Then, it was injected a third time with zinc source (1.0 g of zinc stearate dissolved in 4 mL of octadecene), and then with selenium and sulfur sources (0.2 mmol selenium powder and 3.6 mmol sulfur powder dissolved in 2 mL of tri-n-octylphosphine), and reacted at 280 °C for 3 h, forming a gradient zinc sulfoselenide shell.

[0069] (4) The temperature was rapidly cooled to 210℃, 1.5 mL of octyl mercaptan was added, and the reaction was carried out at 210℃ for 30 min. The temperature was then lowered to 190℃, and zinc acetate solution (2 mmol of zinc acetate dihydrate dissolved in 2 mL of oleylamine and 10 mL of octadecene) was added. The reaction was carried out at 190℃ for 1 h and then cooled to room temperature to obtain undoped core-shell quantum dots. The obtained quantum dots were mixed with anhydrous ethanol at a volume ratio of 1:7, centrifuged to precipitate and purified, and then redispersed in n-hexane.

[0070] The properties of the products prepared in Examples 1-3 and Comparative Example 1 were characterized using ultraviolet absorption and fluorescence spectra and transmission electron microscopy. The corresponding results are as follows: Figures 1-8 As shown in the figure, the quantum dots prepared in Examples 1-3 have better size uniformity than the undoped quantum dots prepared in Comparative Example 1.

[0071] The UV absorption peak, fluorescence emission peak, full width at half maximum (FWHM), and quantum yield of the quantum dots prepared in the above examples and comparative examples were statistically analyzed and calculated. The FWHM was measured using a Cary Eclipse fluorescence spectrophotometer (Agilent Technologies) at a solution concentration of 0.5 mg / mL. The characterization results of the optical properties of the quantum dots are shown in Table 1.

[0072] Table 1:

[0073]

[0074] As shown in the table above, the fluorescence emission peak of the indium phosphide quantum dots prepared by aluminum doping in Examples 1-6 of this invention remains around 530 nm, exhibiting green light emission. Compared with Comparative Example 1, the addition of a certain proportion of aluminum isopropoxide in Examples 1-6 significantly narrowed the full width at half maximum (FWHM) of the quantum dots, decreasing from 44 nm to 40-38 nm. This indicates that the method provided by this invention can significantly improve the size uniformity of core-shell indium phosphide quantum dots, which is more intuitively apparent from TEM images. Furthermore, compared with the comparative example, the addition of a certain proportion of aluminum isopropoxide in Examples 1-6 significantly improved the quantum yield, increasing from 67% to 85%-96%. This demonstrates that the method provided by this invention can passivate surface defects in core-shell indium phosphide quantum dots, improving the luminescence efficiency and performance of the quantum dots.

[0075] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A two-step method for synthesizing aluminum-doped indium phosphide quantum dots, characterized in that, The steps include the following: (1) The indium source and the phosphorus source react in a solution environment in which zinc halide is present to form an indium phosphide core; The molar ratio of indium source to phosphorus source is 1:2~4; the molar ratio of indium source to zinc halide is 1:2~5; the reaction temperature is 120~220 ℃, and the reaction time is 1~60 min; (2) First, vacuum the system at room temperature, then heat it to 130 °C for 1 h in an argon atmosphere to completely dissolve the zinc halide. At this time, add the indium phosphide core solution dissolved in hexane to the reaction system and collect the hexane vapor through a reflux condenser to obtain the passivated indium phosphide core. The molar ratio of zinc halide to indium source in step (1) is 2~5:1; (3) Using aluminum isopropoxide, zinc source, selenium source and sulfur source as shell material, the shell material is reacted in batches in solution environment to coat the passivated indium phosphide core layer by layer to form a gradient aluminum doped zinc sulfide selenide shell. Based on the molar ratio of raw materials to indium source in step (1), the molar ratio of zinc source to indium source is 1~5:1, the molar ratio of sulfur source to indium source is 0.5~10:1, the molar ratio of selenium source to indium source is 0.5~5:1, and the molar ratio of aluminum isopropoxide to sulfur source in this step is 0.2~3:

1. The shell material was reacted in solution in four batches to progressively coat the passivated indium phosphide core; the first batch was reacted at 250 °C for 2 h; the second batch was reacted at 260 °C for 2 h; the third batch was reacted at 270 °C for 2 h; and the fourth batch was reacted at 280 °C for 3 h. (4) A sulfur source and aluminum isopropoxide react on the surface of a gradient aluminum-doped zinc sulfide shell to form an aluminum-doped zinc sulfide shell; in a solution environment, zinc acetate is reacted to treat the surface to obtain core-shell quantum dots; the molar ratio of aluminum isopropoxide to the sulfur source in this step is 1:2~15, the molar ratio of the sulfur source to the indium source in step (1) is 0.5~10:1, and the molar ratio of zinc acetate to the sulfur source in this step is 1:2~5.

2. The method according to claim 1, characterized in that: In step (1), the indium source includes at least one of indium chloride, indium bromide, indium iodide, and indium acetate; the phosphorus source includes at least one of tris(trimethylsilyl)phosphine, tris(dimethylamino)phosphine, and tris(diethylamino)phosphine; and the zinc halide includes at least one of zinc chloride, zinc bromide, and zinc iodide.

3. The method according to claim 1, characterized in that: In step (2), the zinc halide includes at least one of zinc chloride, zinc bromide, and zinc iodide.

4. The method according to claim 1, characterized in that: In step (3), the zinc source includes at least one of zinc stearate and zinc acetate, the selenium source includes at least one of selenium and selenium oxide, and the sulfur source includes at least one of sulfur, 1-dodecyl mercaptan and octyl mercaptan.

5. The method according to claim 1, characterized in that: In step (4), the sulfur source includes at least one of sulfur, 1-dodecyl mercaptan, and octyl mercaptan.

6. A core-shell quantum dot, characterized in that, It is made by means of any one of claims 1 to 5.

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