A method for preparing quantum dots

Abstract

The application relates to a quantum dot preparation method and belongs to the technical field of quantum dot materials. The quantum dot preparation method comprises the following steps: dispersing original core quantum dots in a nonpolar solvent I to obtain original core quantum dot suspension I; mixing the original core quantum dot suspension I with a polar solvent containing doped cations to transfer the original core quantum dots to the polar solvent to obtain original core quantum dot suspension II; adding nonpolar solvent II and ligand solvent into the original core quantum dot suspension II to transfer the original core quantum dots to the nonpolar solvent II to obtain ligand-exchanged original core quantum dot suspension III; and mixing dispersing solvent, doped cation precursor solution and the original core quantum dot suspension III to perform cation exchange. The application cooperates the pretreatment process of ligand exchange with the liquid-phase cation exchange process, and tunes the optical performance of the core quantum dots.

Description

Technical Field

[0001] This invention belongs to the field of quantum dot materials technology, and specifically relates to a method for preparing quantum dots. Background Technology

[0002] Quantum dots (QDs) are a class of semiconductor nanocrystals with a significant three-dimensional quantum confinement effect. Their optical and electrical properties can be designed in a highly controllable manner by adjusting their size, crystal localization, chemical composition, and surface state. Therefore, they have broad application prospects in display devices, lighting sources, photodetectors, solar cells, and bioimaging.

[0003] In existing technologies, liquid-phase cation exchange (LCE) is a commonly used method for controlling and doping the composition of quantum dots. This method introduces specific dopant cations into the liquid phase, allowing them to diffuse from the solution to the surface of the quantum dot and enter the crystal lattice, thereby altering the chemical composition and band structure of the quantum dot. This process can achieve a blue-shift or red-shift of the first exciton absorption peak of the quantum dot, modulate the emission wavelength, and introduce new photoelectric functions. For example, in III–V group semiconductor quantum dots, InP quantum dots doped with Ga... 3+ This can effectively increase the band gap of quantum dots, causing a blue shift in the emission wavelength and meeting the requirements for high-purity blue light emission. It has significant application value in blue QLED (quantum dot light-emitting diode) and high-resolution display fields. Another example is ZnSe quantum dots doped with Cd, which are part of group II–VI quantum dots. 2+ It can reduce the band gap of the material, causing the emission wavelength to shift towards longer wavelengths (redshift), thus achieving wide color gamut coverage. At the same time, it can also adjust the lattice constant to match the subsequent shell (such as ZnS, CdS), thereby optimizing the optical performance and stability of the core-shell structure.

[0004] However, the doping efficiency of traditional liquid-phase cation exchange processes is significantly affected by the organic ligands on the quantum dot surface. When the surface ligand binding force is strong or the ligand coverage density is high, the mass transfer rate of the doped cations decreases significantly, leading to insufficient doping and uneven composition distribution. The tunable range of the exciton absorption peak after doping is limited, which is not conducive to the design of core-shell quantum dots with wide wavelength tunability. In addition, to improve doping efficiency, solid-phase cation exchange technology often requires the exchange reaction to be carried out at higher temperatures, but high temperatures can easily cause problems such as the formation of quantum dot lattice defects, deterioration of optical properties, and quantum dot ripening. Furthermore, quantum dots based on solid-phase cation exchange have poor optical properties, manifested in low quantum yield and broad fluorescence peaks.

[0005] Therefore, under the premise of ensuring the stability of quantum dot structure and optical performance, how to improve the introduction efficiency of doped cations in quantum dot lattice and expand the tunable range of the first exciton absorption peak in liquid phase cation exchange process has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing quantum dots, which solves the technical problem of low cation doping degree in traditional liquid-phase cation exchange doping by combining ligand exchange pretreatment process with liquid-phase cation exchange process.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing quantum dots includes the following steps:

[0009] S1: Primitive nuclear quantum dots: A suspension of primitive nuclear quantum dots is obtained by dispersing primitive nuclear quantum dots in a nonpolar solvent.

[0010] S2: Ligand exchange: The original quantum dot suspension 1 is mixed with a polar solvent containing doped cations, and the mixture is stirred to transfer the original quantum dots to the polar solvent to obtain the original quantum dot suspension 2; nonpolar solvent 2 and ligand solvent are added to the original quantum dot suspension 2, and the mixture is stirred to transfer the original quantum dots to the nonpolar solvent 2 to obtain the ligand-exchanged original quantum dot suspension 3;

[0011] S3: Cation exchange: The dispersion solvent, the doped cation precursor solution, and the suspension of the original nuclear quantum dots are mixed and heated to carry out cation exchange.

[0012] Furthermore, the atomic nucleus quantum dots mentioned in S1 are IIIA-VA group quantum dots or IIB-VIA group quantum dots, and the metal precursor used to synthesize the atomic nucleus quantum dots contains metal carboxylates;

[0013] Furthermore, the original nuclear quantum dot mentioned in S1 is an InP quantum dot;

[0014] Furthermore, both nonpolar solvent one and nonpolar solvent two in S1 and S2 are one or more of the following: alkanes, toluene, chloroform, liquid paraffin, carbon tetrachloride, dichloromethane, petroleum ether, and carbon tetrachloride.

[0015] Furthermore, the polar solvent in S2 containing doped cations is one or more of N,N-dimethylformamide, dimethyl sulfoxide, formamide, methanol, ethanol, methyl acetate, and acetone.

[0016] Furthermore, the doped cations mentioned in S2 and S3 are one or more of Group IIIA cations, Group IIB cations, and Group V cations.

[0017] Furthermore, the ligand solvent mentioned in S2 is a long-chain amine with 8-22 carbon atoms.

[0018] Furthermore, in S2, the stirring temperature for transferring the original nuclear quantum dots to a polar solvent to obtain a second suspension of the original nuclear quantum dots is 25-125 °C, and the stirring time is 5 min-48 h.

[0019] Furthermore, in the ligand exchange of S2, the volume ratio of the suspension of the original nuclear quantum dots to the polar solvent containing doped cations is 10:1 to 1:10; the concentration of the polar solvent containing doped cations is 0.1-1 M, and the concentration of the suspension of the original nuclear quantum dots is 0.001-1 M.

[0020] Furthermore, the dispersing solvent mentioned in S3 is one or more of an alkene with 8-22 carbon atoms, petroleum ether, and a long-chain amine with 8-22 carbon atoms.

[0021] Furthermore, the cation exchange step described in S3 includes: mixing the suspension of the original nuclear quantum dots with a dispersion solvent and heating it to 50-250 °C under an inert gas, then adding the doped cation precursor solution and heating it to 100-300 °C, and reacting for 30 min-24 h.

[0022] Furthermore, the concentration of the cation-doped precursor solution in S3 is 0.01-1 M; the volume ratio of the original nuclear quantum dot suspension to the cation-doped precursor solution is 1:10-10:1; and the volume ratio of the cation-doped precursor solution to the dispersion solvent is 1:10-10:1.

[0023] Furthermore, it also includes coating the surface of quantum dots prepared in S3 with a shell.

[0024] The beneficial effects of this invention are:

[0025] This invention improves the efficiency of introducing doped cations into the quantum dot lattice by combining a ligand exchange pretreatment process with a liquid-phase cation exchange process, expands the tunable range of the first exciton absorption peak, and successfully tunes the emission wavelength of InGaP / ZnS core-shell quantum dots based on this process to a bluer region with a half-width of 42 nm and a quantum yield greater than 50%.

[0026] As can be seen from the embodiments and comparative examples of the present invention, the fluorescence peak wavelength of InGaP / ZnS prepared only after cation exchange did not reach the target 460-470 nm blue light region. This may be because the carboxylate ligands on the surface of InP quantum dots react with Ga... 3+ The strong coordination ability of the ions hinders the Ga ionization process to some extent. 3+ To mitigate the diffusion of Ga, ligand exchange is performed before cation exchange. This replaces the carboxylic acid ligands on the InP quantum dot surface with ligands that have weaker coordination ability, and reduces the surface ligand density, which is beneficial for Ga. 3+ Further diffusion yields InGaP quantum dots with higher Ga content and larger band gap, and finally, after being coated with ZnS, quantum dots with shorter fluorescence peak wavelengths are obtained. Attached Figure Description

[0027] Figure 1 For InP 431 Absorption spectrum of primitive nuclear quantum dots;

[0028] Figure 2 The absorption spectrum of InGaP quantum dots in Comparative Example 1 is shown.

[0029] Figure 3 This is a schematic diagram of the ligand exchange process;

[0030] Figure 4 The absorption spectrum of the first exciton absorption peak during the ligand exchange synergistic cation exchange process;

[0031] Figure 5 The diagram shows the peak position changes of the first exciton absorption peak during the ligand exchange synergistic cation exchange process.

[0032] Figure 6 The image shows the optical performance of the quantum dot in Comparative Example 3.

[0033] Figure 7 The image shows the optical performance of the quantum dot in Comparative Example 2.

[0034] Figure 8 The image shows the optical properties of the quantum dots in Example 2.

[0035] Figure 9 Comparative figures show the optical performance comparison of Example 2, Comparative Example 2, and Comparative Example 3;

[0036] Figure 10 This is a flowchart of the quantum dot manufacturing process. Detailed Implementation

[0037] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0038] Volume-to-diameter ratio (VD value) = 1 - Value波谷 / Value 波峰 .

[0039] Oleylamine and 1-octadecene were degassed at 120 °C for 1 h and stored in a glove box filled with nitrogen.

[0040] Indium acetate (99.99%), zinc chloride (99%), palmitic acid (99%), 1-dodecyl mercaptan (98.5%), and oleylamine (80-90%) were all purchased from Sigma-Aldrich. Zinc acetate (99.99%), ethanol (99.5%, ultra-dry), hexane (97.5%, ultra-dry), octane (99%, ultra-dry), and 1-octadecene (ODE, 90%) were all purchased from J&K Scientific. Trioctylphosphine (97%) was purchased from Strem Chemicals. Oleic acid (99%) was purchased from Psaitong. Gallium(III) iodide (99.999%) was purchased from Bide Pharma. Toluene (99.5%) was purchased from Sinopharm Chemical Reagent.

[0041] In the diagram, CE represents cation exchange and LE represents ligand exchange.

[0042] Example 1

[0043] Example 1 Quantum dots are prepared using a cation exchange process synergistic with ligand exchange pretreatment, specifically including the following steps:

[0044] S1: InP 431 InP quantum dots were synthesized at high temperature using indium carboxylate and phosphine precursors until the first exciton absorption peak of the InP quantum dots reached 431 nm, yielding a stock solution of InP quantum dots. The InP quantum dots were then precipitated and purified using ethanol and toluene, and redispersed in 5 mL of hexane to obtain a suspension of InP quantum dots with a concentration of 0.1 M. In Example 1, the original InP quantum dots were denoted as InP. 431 The phosphine precursor is a precursor containing tris(trimethylsilyl)phosphine;

[0045] S2: Ligand Exchange: Take 3 mL of N,N-dimethylformamide (DMF), add 1.5 mL of the InP quantum dot suspension I from S1 and 1.5 mL of 0.2 M gallium triiodide DMF solution sequentially, and stir vigorously at room temperature for 5 min to completely transfer the InP quantum dots into the DMF phase. Remove the supernatant. At this time, the carboxylate ligands on the surface of the InP quantum dots are transformed into inorganic ligands. Add toluene to the lower layer solution to precipitate the InP quantum dots in the DMF phase to form a yellow colloidal suspension. Separate the precipitate and redisperse it in 5 mL of DMF to obtain the InP quantum dot suspension II. Then add 3 mL of hexane and add oleylamine (OAm) to completely transfer the InP quantum dots to the upper hexane layer to obtain the ligand-exchanged InP suspension III.

[0046] S3: Cation Exchange: 405 mg of gallium triiodide was dissolved in 3 mL of OAM in a nitrogen-filled glove box to obtain a 0.3 M gallium triiodide precursor solution. 1.5 mL of InP suspension and 9 mL of OAM were mixed in a three-necked flask. The flask was heated to 180 °C under a nitrogen flow, and the gallium triiodide precursor solution was rapidly injected with vigorous stirring. The mixture was heated to 240 °C and held for 30 min, then cooled to room temperature to obtain the desired product. The quantum dot stock solution was precipitated and purified using ethanol and toluene. quantum dots, The quantum dot is the same as the quantum dot in Example 1.

[0047] Example 2

[0048] Example 2 is ZnS shell ZnS quantum dots, specifically prepared using the following methods:

[0049] Example 1 The quantum dots were redispersed in 5 mL of hexane to obtain A quantum dot solution was prepared by adding 0.314 g of zinc chloride (ZnCl2), 3.5 mL of OAm, 1.5 mL of TOP, and 2 mL of ODE to a three-necked flask under vacuum and degassing at 120 °C for 1 h. Then, under a nitrogen flow, 0.75 mL of... The quantum dot solution was then heated to 240 °C over 15 min, and 0.2 mL of 1-dodecylthiol (DDT) was added dropwise to initiate ZnS shell growth. This was maintained for 30 min, followed by heating the flask to 280 °C over 10 min, then adding 0.4 mL of DDT. The mixture was maintained at 280 °C for 1 h and cooled to room temperature to obtain the quantum dots of Example 2, named... / ZnS, will / ZnS was precipitated and purified using ethanol and hexane.

[0050] Comparative Example 1

[0051] Comparative Example 1 Quantum dots are prepared using a traditional cation exchange process, and the specific preparation method includes the following steps:

[0052] S1: Prepare InP according to the steps in S1 of Example 1. 431 Quantum dot suspension 1;

[0053] S2: Synthesis Quantum dots, specifically, are prepared by dissolving 405 mg of gallium triiodide in 3 mL of OAM in a nitrogen-filled glove box to obtain a 0.3 M gallium triiodide precursor solution. Then, 1.5 mL of SiO2-InP... 431 Quantum dot suspension 1: 9 mL of OAM was mixed in a three-necked flask. The flask was heated to 180 °C under nitrogen atmosphere. A gallium triiodide precursor solution was rapidly injected with vigorous stirring. The mixture was then heated to 240 °C and held for 30 min, followed by cooling to room temperature to obtain Comparative Example 1. Quantum dots will Quantum dots were precipitated and purified using ethanol and toluene.

[0054] Comparative Example 2

[0055] Comparative Example 2 is The specific preparation method for ZnS quantum dots includes the following steps:

[0056] Comparative Example 1 Quantum dots were redispersed in 5 mL of hexane. Under vacuum, 0.314 g of ZnCl2, 3.5 mL of OAm, 1.5 mL of TOP, and 2 mL of ODE were added to a three-necked flask. The mixture was degassed at 120 °C for 1 h. Under flowing nitrogen, [the following was added] The quantum dot solution was then heated to 240 °C over 15 min, and 0.2 mL of DDT was added dropwise to initiate ZnS shell growth. This was maintained for 30 min, followed by heating the flask to 280 °C over 10 min, then adding 0.4 mL of DDT dropwise. The mixture was maintained at 280 °C for 1 h and then cooled to room temperature to obtain Comparative Example 2. / ZnS quantum dots, / ZnS was purified using ethanol and hexane.

[0057] Comparative Example 3

[0058] Comparative Example 3 did not involve ligand exchange or cation exchange; InP was directly applied. 431 Quantum dot-coated ZnS shell, InP 431The preparation method of ZnS quantum dots includes the following steps:

[0059] S1: Prepare InP according to the steps in S1 of Example 1. 431 Quantum dot suspension 1;

[0060] S2: Synthesis of InP 431 The specific steps for obtaining InP quantum dots (ZnS) are as follows: Under vacuum conditions, 0.314 g of ZnCl2, 3.5 mL of OAm, 1.5 mL of TOP, and 2 mL of ODE are added to a three-necked flask. The flask is degassed at 120 °C for 1 h. Under flowing nitrogen, a suspension of InP quantum dots is added, followed by heating to 240 °C over 15 min. 0.2 mL of DDT is added dropwise to initiate ZnS shell growth, which is maintained for 30 min. The flask is then heated to 280 °C over 10 min, followed by the addition of 0.4 mL of DDT. The flask is maintained at 280 °C for 1 h and cooled to room temperature to obtain InP (Comparative Example 3). 431 / ZnS, will InP 431 / ZnS was purified using ethanol and hexane.

[0061] from Figure 1 It can be seen that InP 431 The first exciton absorption peak of the quantum dot is at 431 nm, with a VD value of 0.34 nm. From Figure 2 , Figure 4 and Figure 5 It can be seen that ligand exchange did not occur. The first exciton absorption peak of quantum dots is at 423 nm, indicating that ligand exchange occurs first, followed by cation exchange. The first exciton absorption peak of the quantum dots blue-shifted to 410 nm. This indicates that replacing the carboxylic acid ligands on the InP quantum dot surface with non-carboxylic acid ligands can yield InGaP quantum dots with higher Ga content under the same conditions. Figures 6-9 It can be seen that directly in InP 431 After the surface is coated with a ZnS shell, InP 431 The fluorescence peak of the ZnS quantum dots is located at 490 nm. After cation exchange... The fluorescence peak of ZnS is located at 475 nm, with a full width at half maximum (FWHM) of 41 nm. Example 2 The fluorescence peak of the ZnS quantum dot is located at 464 nm, with a full width at half maximum (FWHM) of 42 nm. This invention, through a ligand exchange pretreatment process combined with a liquid-phase cation exchange process, effectively increases the doping degree of the doped cation in the nuclear quantum dot, tunes the first exciton absorption peak of the nuclear quantum dot, and optimizes the emission wavelength of the core-shell structure quantum dot based on this nuclear quantum dot.

[0062] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This disclosure is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the claims.

[0063] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. The scope of patent protection of the present invention shall be determined by the claims. Similarly, any equivalent structural changes made based on the content of the present invention's specification shall also be included within the scope of protection of the present invention.

Claims

1. A method for preparing quantum dots, characterized in that, Includes the following steps: S1: Primitive nuclear quantum dots: A suspension of primitive nuclear quantum dots is obtained by dispersing primitive nuclear quantum dots in a nonpolar solvent. S2: Ligand Exchange: The suspension of the original nuclear quantum dots (SQDs) is mixed with a polar solvent containing doped cations, and stirred to transfer the original nuclear quantum dots to the polar solvent, resulting in a second suspension of the original nuclear quantum dots. A second nonpolar solvent and a ligand solvent are added to the second suspension of the original nuclear quantum dots, and the mixture is stirred to transfer the original nuclear quantum dots to the second nonpolar solvent, resulting in a third suspension of the original nuclear quantum dots after ligand exchange. The ligand solvent is a long-chain amine with 8-22 carbon atoms. S3: Cation exchange: The dispersion solvent, the doped cation precursor solution and the suspension of the original nuclear quantum dots are mixed and heated to 240 °C for 30 min to carry out cation exchange. Then, the quantum dots are obtained by coating with a shell. The original nuclear quantum dot is an InP quantum dot, and the first exciton absorption peak of the original nuclear quantum dot is 431 nm. The cations in the polar solvent containing doped cations in S2 and the cation-doped precursor solution in S3 are both gallium ions. The quantum dot has a full width at half maximum (FWHM) of 42 nm.

2. The method for preparing quantum dots according to claim 1, characterized in that, In both S1 and S2, the nonpolar solvent one and the nonpolar solvent two are one or more of toluene, chloroform, liquid paraffin, dichloromethane, petroleum ether, and carbon tetrachloride.

3. The method for preparing quantum dots according to claim 1, characterized in that, The polar solvent in S2 containing doped cations is one or more of N,N-dimethylformamide, dimethyl sulfoxide, formamide, methanol, ethanol, methyl acetate, and acetone.

4. The method for preparing quantum dots according to claim 1, characterized in that, The stirring in S2 transfers the original nuclear quantum dots into a polar solvent to obtain a suspension of the original nuclear quantum dots. The stirring temperature is 25-125 °C, and the stirring time is 5 min-48 h.

5. The method for preparing quantum dots according to claim 1, characterized in that, The dispersing solvent described in S3 is one or more of an alkene with 8-22 carbon atoms, petroleum ether, and a long-chain amine with 8-22 carbon atoms.

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