A quantum dot ligand selection and exchange method

Abstract

The present invention discloses a method for selecting and exchanging ligands for quantum dots. The method comprises the following steps: Step S1, dissolving oil-soluble quantum dots synthesized in an organic phase in a nonpolar solvent to obtain a quantum dot solution; Step S2, dissolving a thiol ligand in a propylene glycol monomethyl ether acetate solvent to obtain a thiol ligand solution; Step S3, mixing the quantum dot solution and the thiol ligand solution in a volume ratio of 0.1-1, stirring the mixture, and performing ligand exchange; Step S4, adding a nonpolar solvent after ligand exchange, and centrifuging to obtain quantum dots stably dispersed in the propylene glycol monomethyl ether acetate solvent. The present invention utilizes the aforementioned method for selecting and exchanging ligands for quantum dots, selecting thiol ligands to exchange existing ligands on the quantum dot surface, thereby achieving stable dispersion of quantum dots with high quantum yield in the green industrial propylene glycol monomethyl ether acetate (PGMEA) solvent.

Description

Technical Field

[0001] The present invention belongs to the technical field of quantum dots, and in particular relates to a method for selecting and exchanging ligands of quantum dots. Background Art

[0002] A quantum dot is a semiconductor nanostructure that confines excitons in three spatial dimensions. Sometimes called an "artificial atom" or "quantum dot atom," it is a novel concept proposed in the 1990s. This confinement can be attributed to an electrostatic potential (created by external electrodes, doping, strain, or impurities), the interface between two dissimilar semiconductor materials (for example, in self-assembled quantum dots), the surface of a semiconductor (for example, in semiconductor nanocrystals), or a combination of these. Quantum dots possess a discrete, quantized energy spectrum. The corresponding wave functions are spatially localized within the quantum dot but extend across several lattice periods. A quantum dot possesses a small number (1-100) of electrons, holes, or hole-electron pairs, meaning that the charge carried by the dot is an integer multiple of the elementary charge.

[0003] Quantum dots, with particle sizes close to or smaller than the exciton Bohr radius, can precisely tune the luminescence color across the entire visible light range by manipulating their size and element ratios. Furthermore, their wide color gamut, pure color, and solution processability make them promising luminescent materials for applications in display, lasers, photovoltaics, and biomarkers.

[0004] Solution-processable colloidal quantum dots (QDs) are often used in advanced optoelectronic devices, which are processed using carcinogenic or neurotoxic organic solvents such as n-hexane during production. Propylene glycol monomethyl ether acetate (PGMEA) is a non-polluting green solvent, and the stable dispersion of QDs in green industrial solvents such as PGMEA has wide applications in optoelectronic devices. However, high-photoluminescence quantum yield (PLQY) CQDs are typically synthesized in organic phases and can be well dispersed in toxic non-polar solvents, but can aggregate and even experience fluorescence quenching in the polar solvent PGMEA. Therefore, ensuring that CQDs can be stably dispersed and efficiently emit light in PGMEA solvent is a significant challenge.

[0005] Therefore, there is a need in the art to develop a method for selecting and exchanging ligands of quantum dots that can effectively solve the above problems. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for selecting and exchanging ligands for quantum dots, selecting thiol ligands to exchange the original ligands on the surface of quantum dots, and thereby achieving stable dispersion of quantum dots with high quantum yield in the green industrial propylene glycol monomethyl ether acetate (PGMEA) solvent.

[0007] To achieve the above objectives, the present invention provides a method for selecting and exchanging ligands of quantum dots, comprising the following steps:

[0008] Step S1, dissolving oil-soluble quantum dots synthesized in an organic phase in a non-polar solvent to obtain a quantum dot solution;

[0009] Step S2, dissolving the thiol ligand in propylene glycol monomethyl ether acetate solvent to obtain a thiol ligand solution;

[0010] Step S3, mixing the quantum dot solution and the thiol ligand solution in a volume ratio of 0.1-1, stirring after mixing and performing ligand exchange;

[0011] Step S4: After ligand exchange, a non-polar solvent is added and centrifuged to obtain quantum dots stably dispersed in the propylene glycol monomethyl ether acetate solvent.

[0012] Preferably, in step S1, the original ligand on the surface of the oil-soluble quantum dots synthesized in the organic phase is one or a combination of organic amines or organic acids; organic amines or organic acids include oleylamine, oleic acid, stearic acid, etc.

[0013] Preferably, in step S1, the quantum dots include binary phase, ternary phase, and quaternary phase quantum dots; wherein the binary phase quantum dots include CdS, CdSe, CdTe, InP, InAs, InSb, AgS, PbS, PbSe, HgS, etc., and the ternary phase quantum dots include InGaP, InGaAs, InGaSb, Zn X Cd 1-X S, Cu X In 1-X S, Zn X Cd 1-X Se, Zn X Se 1-X S, Zn X Cd 1-X Te, PbSe X S 1-X etc. Quaternary phase quantum dots include InP / ZnSe / ZnS, CdSe / ZnSe / ZnS, InGaPAs, Zn X Cd 1-X S / ZnSe、Cu X In 1-X S / ZnS、Zn X Cd 1-XSe / ZnS, CuInSeS, Zn X Cd 1-X Te / ZnS、PbSe X S 1-X / ZnS, etc.

[0014] Preferably, in step S1, the non-polar solvent includes but is not limited to n-hexane and toluene; and the concentration of the quantum dot solution is 20 mg / ml.

[0015] Preferably, in step S2, the thiol ligand is a ligand containing a thiol group, including but not limited to 2-phenylethanethiol, butyl 3-mercaptopropionate, bis(3-mercaptopropionic acid)ethylene glycol, pentaerythritol tetramercaptoacetate, 3-methoxybutyl 3-mercaptopropionate, 2-mercaptoethanol, 3-mercapto-1-propanol, 4-mercapto-1-butanol, 5-mercapto-1-pentanol, 6-mercapto-1-hexanol, dithiol, mercapto alcohol, mercapto acid, 2-mercaptoacetic acid, 3-mercaptopropionic acid, 4-mercaptobutyric acid, mercaptosuccinic acid, 6-mercaptohexanoic acid, and 4-mercaptobenzoic acid.

[0016] Preferably, in step S2, the concentration of the thiol ligand solution is 0.1-10 mol / l.

[0017] Preferably, in step S3, the temperature of the ligand exchange is 20-90° C., and the time is 5-90 min.

[0018] The present invention adopts the above-mentioned quantum dot ligand selection and exchange method, and the beneficial effects are as follows:

[0019] The present invention selects thiol ligands to exchange the original ligands on the surface of quantum dots, transfers the oil-soluble quantum dots to a propylene glycol monomethyl ether acetate (PGMEA) solvent compatible with the photolithography process, and simultaneously achieves a high degree of dispersion. The resulting indium phosphide quantum dots have a concentration of 600 mg / ml and a fluorescence quantum yield (PLQY) of over 95%.

[0020] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A flowchart of an embodiment of a method for selecting and exchanging ligands for quantum dots according to the present invention;

[0022] Figure 2 The quantum dots modified with thiol ligands prepared in Example 1 of the method for selecting and exchanging ligands of quantum dots of the present invention;

[0023] Figure 3 This is a test graph of the fluorescence quantum yield of quantum dots after ligand exchange in Example 1 of a method for selecting and exchanging ligands of quantum dots according to the present invention;

[0024] Figure 4 The quantum dots modified with thiol ligands prepared in Example 2 of the method for selecting and exchanging ligands for quantum dots of the present invention;

[0025] Figure 5 This is a test graph of the fluorescence quantum yield of quantum dots after ligand exchange, in Example 2 of a method for selecting and exchanging ligands of quantum dots according to the present invention;

[0026] Figure 6 This is a graph showing the ultraviolet absorption spectra of the thiol ligand-modified quantum dots prepared in Example 1 of a method for selecting and exchanging ligands of quantum dots of the present invention before and after exchange;

[0027] Figure 7 This is a graph showing the ultraviolet absorption spectra of the thiol ligand-modified quantum dots prepared in Example 2 of the method for selecting and exchanging ligands of quantum dots of the present invention before and after exchange;

[0028] Figure 8 This is a fluorescence spectrum of thiol ligand-modified quantum dots prepared in Example 1 of a method for selecting and exchanging ligands of quantum dots of the present invention before and after exchange;

[0029] Figure 9 This is a fluorescence spectrum of thiol ligand-modified quantum dots before and after exchange, prepared in Example 2 of a ligand selection and exchange method for quantum dots of the present invention. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0031] Unless otherwise defined, technical or scientific terms used in the present invention shall have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0032] A method for selecting and exchanging ligands of quantum dots, such as Figure 1 As shown, the following steps are included:

[0033] Step S1: dissolving the oil-soluble quantum dots synthesized in the organic phase in a non-polar solvent to obtain a quantum dot solution.

[0034] The original ligands on the surface of oil-soluble quantum dots synthesized in an organic phase are one or a combination of organic amines or organic acids. Organic amines or organic acids include oleylamine, oleic acid, stearic acid, and the like. Quantum dots containing one or more of these ligands are suitable for ligand exchange using the ligand exchange method of the present invention.

[0035] Quantum dots include binary, ternary and quaternary phase quantum dots. Binary phase quantum dots include CdS, CdSe, CdTe, InP, InAs, InSb, AgS, PbS, PbSe, HgS, etc. Ternary phase quantum dots include InGaP, InGaAs, InGaSb, Zn X Cd 1-X S, Cu X In 1-X S, Zn X Cd 1-X Se, Zn X Se 1-X S, Zn X Cd 1-X Te, PbSe X S 1-X etc. Quaternary phase quantum dots include InP / ZnSe / ZnS, CdSe / ZnSe / ZnS, InGaPAs, Zn X Cd 1-X S / ZnSe、Cu X In 1-X S / ZnS、Zn X Cd 1-X Se / ZnS, CuInSeS, Zn X Cd 1-X Te / ZnS、PbSe X S 1-X / ZnS, etc. The present invention does not limit the preparation method of quantum dots, as long as the ligand requirements of the original quantum dots can be met.

[0036] Non-polar solvents include, but are not limited to, n-hexane and toluene.

[0037] Wherein, the concentration of the quantum dot solution is 20 mg / ml.

[0038] Step S2: dissolving the thiol ligand in propylene glycol monomethyl ether acetate solvent to obtain a thiol ligand solution.

[0039] The thiol ligand is a ligand containing a thiol group, which includes but is not limited to 2-phenylethanethiol, butyl 3-mercaptopropionate, bis(3-mercaptopropionic acid)ethylene glycol, pentaerythritol tetramercaptoacetate, 3-methoxybutyl 3-mercaptopropionate, 2-mercaptoethanol, 3-mercapto-1-propanol, 4-mercapto-1-butanol, 5-mercapto-1-pentanol, 6-mercapto-1-hexanol, dithiols, mercaptoalcohols, mercapto acids, 2-mercaptoacetic acid, 3-mercaptopropionic acid, 4-mercaptobutyric acid, mercaptosuccinic acid, 6-mercaptohexanoic acid, and 4-mercaptobenzoic acid.

[0040] Wherein, the concentration of the thiol ligand solution is 0.1-10 mol / l.

[0041] Step S3: mixing the quantum dot solution and the thiol ligand solution at a volume ratio of 0.1-1, stirring after mixing, and performing ligand exchange.

[0042] The temperature of ligand exchange is 20-90°C and the time is 5-90 min.

[0043] Step S4: After ligand exchange, a non-polar solvent is added and centrifuged to obtain quantum dots stably dispersed in the propylene glycol monomethyl ether acetate solvent.

[0044] Example 1

[0045] The quantum dots were prepared by ligand exchange in a quantum dot solution of InP / ZnSe / ZnS with a luminescence peak wavelength of 620 nm and a peak width of 40 nm and an original ligand of oleic acid. In this embodiment, the quantum dots were InP / ZnSe / ZnS quantum dots.

[0046] A method for selecting and exchanging ligands of quantum dots, comprising the following steps:

[0047] Step S1: Provide a first quantum dot solution containing an organic acid ligand. The first quantum dot solution is a 20 ml InP / ZnSe / ZnS quantum dot stock solution with a luminescence peak wavelength of 620 nm and a peak width of 40 nm. The volume of the first quantum dot solution is 20 mg / ml and the concentration is 20 mg / ml. The organic acid ligand of the quantum dots is oleic acid.

[0048] Purification: Add 40 ml of ethanol to the quantum dots, centrifuge at 5000 rpm for 5 minutes, and discard the supernatant to obtain a first precipitate. Add 10 ml of n-hexane and 6 ml of ethanol to the first precipitate, centrifuge at 5000 rpm for 5 minutes, and discard the supernatant to obtain a second precipitate. Add 10 ml of n-hexane to the second precipitate to obtain InP / ZnSe / ZnS quantum dots dispersed in n-hexane.

[0049] Step S2: 60 mmol of 2-phenylethanethiol ligand was added to 10 ml of PGMEA solvent to prepare a thiol ligand solution with a concentration of 6 mmol / ml.

[0050] Step S3, ligand exchange: the hexane quantum dots and the thiol ligand solution were mixed and reacted at 25° C. and 1500 rpm in air for 30 min.

[0051] Step S4: After ligand exchange, ten times the volume of hexane of the mixed solution was added for purification, and the mixture was centrifuged at 5000 rpm for 5 min. The supernatant was discarded and the precipitate was dispersed in PGMEA solution to obtain thiol ligand-modified quantum dots.

[0052] like Figure 2As shown, stably dispersed quantum dots (concentration of 600 mg / ml) were obtained after ligand exchange.

[0053] like Figure 3 As shown in Figure 3, the fluorescence quantum yield of quantum dots is higher after ligand exchange.

[0054] Example 2

[0055] The quantum dots were prepared by ligand exchange in a quantum dot solution of InP / ZnSe / ZnS with a luminescence peak wavelength of 620 nm and a peak width of 40 nm and original ligands of oleic acid and oleylamine. In this embodiment, the quantum dots were InP / ZnSe / ZnS quantum dots.

[0056] A method for selecting and exchanging ligands of quantum dots, comprising the following steps:

[0057] Step S1: Providing a first quantum dot solution containing an organic acid ligand and an organic amine ligand. The first quantum dot solution is a 20 ml stock solution of InP / ZnSe / ZnS quantum dots with a peak emission wavelength of 620 nm and a peak width of 40 nm. The volume of the first quantum dot solution is 20 mg / ml and the concentration is 20 mg / ml. The organic acid ligand of the quantum dots is oleic acid, and the organic amine ligand is oleylamine.

[0058] Purification: Add 40 ml of ethanol to the quantum dots, centrifuge at 5000 rpm for 5 minutes, and discard the supernatant to obtain a first precipitate. Add 10 ml of n-hexane and 6 ml of ethanol to the first precipitate, centrifuge at 5000 rpm for 5 minutes, and discard the supernatant to obtain a second precipitate. Add 10 ml of n-hexane to the second precipitate to obtain InP / ZnSe / ZnS quantum dots dispersed in n-hexane.

[0059] Step S2: 60 mmol of 2-phenylethanethiol ligand was added to 10 ml of PGMEA solvent to prepare a thiol ligand solution with a concentration of 6 mmol / ml.

[0060] Step S3, ligand exchange: the hexane quantum dots and the thiol ligand solution were mixed and reacted at 25° C. and 1500 rpm in air for 30 min.

[0061] Step S4: After ligand exchange, ten times the volume of hexane of the mixed solution was added for purification, and the mixture was centrifuged at 5000 rpm for 5 min. The supernatant was discarded and the precipitate was dispersed in PGMEA solution to obtain thiol ligand-modified quantum dots.

[0062] like Figure 4 As shown, stably dispersed quantum dots (concentration of 600 mg / ml) were obtained after ligand exchange.

[0063] like Figure 5 As shown in Figure 3, the fluorescence quantum yield of quantum dots is higher after ligand exchange.

[0064] The quantum dots modified with thiol ligands obtained in Example 1 and Example 2 were subjected to ultraviolet light absorption and fluorescence intensity tests respectively.

[0065] like Figure 6-Figure 9 As shown, the positions and half-peak widths of the absorption and emission peaks of the thiol ligand-modified quantum dots obtained in Example 1 and Example 2 remain substantially unchanged before and after the exchange.

[0066] Therefore, the present invention adopts the above-mentioned quantum dot ligand selection and exchange method, selects thiol ligands to exchange the original ligands on the surface of quantum dots, and thus achieves stable dispersion of quantum dots with high quantum yield in the green industrial propylene glycol monomethyl ether acetate (PGMEA) solvent.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for selecting and exchanging ligands of quantum dots, characterized in that: The following steps are involved: Step S1, dissolving oil-soluble quantum dots synthesized in an organic phase in a non-polar solvent to obtain a quantum dot solution; The original ligand on the surface of the oil-soluble quantum dots synthesized in the organic phase is one or a combination of organic amines or organic acids; the organic amines or organic acids are oleylamine, oleic acid, and stearic acid; Step S2, dissolving the thiol ligand in propylene glycol monomethyl ether acetate solvent to obtain a thiol ligand solution; The concentration of the thiol ligand solution is 0.1-10 mol / l; The thiol ligand is 2-phenylethanethiol; Step S3, mixing the quantum dot solution and the thiol ligand solution in a volume ratio of 0.1-1, stirring after mixing and performing ligand exchange; The temperature for ligand exchange is 20-90°C and the time is 5-90 min; Step S4: After ligand exchange, a non-polar solvent is added and centrifuged to obtain quantum dots stably dispersed in the propylene glycol monomethyl ether acetate solvent.

2. The method for selecting and exchanging ligands of quantum dots according to claim 1, wherein: In step S1, the quantum dots include CdS, CdSe, CdTe, InP, InAs, InSb, AgS, PbS, PbSe, HgS, InGaP, InGaAs, InGaSb, Zn X Cd 1-X S, Cu X In 1-X S, Zn X Cd 1-X Se, Zn X Se 1-X S, Zn X Cd 1-X Te, PbSe X S 1-X , InP / ZnSe / ZnS, CdSe / ZnSe / ZnS, InGaPAs, Zn X Cd 1-X S / ZnSe, Cu X In 1-X S / ZnS, Zn X Cd 1-X Se / ZnS, CuInSeS, Zn X Cd 1-X Te / ZnS, PbSe X S 1-X / ZnS.

3. The method for selecting and exchanging quantum dot ligands according to claim 2, wherein: In step S1, the non-polar solvent includes n-hexane and toluene; and the concentration of the quantum dot solution is 20 mg / ml.

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