Ligand selection and exchange method of quantum dots

Abstract

The invention discloses a quantum dot ligand selection and exchange method which comprises the following steps: S1, dissolving an oil-soluble quantum dot synthesized by an organic phase in a non-polar solvent to obtain a quantum dot solution; s2, a sulfydryl ligand is dissolved in a propylene glycol monomethyl ether acetate solvent, and a sulfydryl ligand solution is obtained; s3, the quantum dot solution and the sulfydryl ligand solution are mixed according to the volume ratio of 0.1-1, stirring is conducted after mixing, and ligand exchange is conducted; and S4, after ligand exchange, adding a non-polar solvent, and carrying out centrifugal separation to obtain the quantum dots stably dispersed in the propylene glycol monomethyl ether acetate solvent. According to the ligand selection and exchange method of the quantum dots, the sulfydryl ligand is selected to perform ligand exchange on the original ligand on the surfaces of the quantum dots, so that the quantum dots with high quantum yield are stably dispersed in a green industrial propylene glycol monomethyl ether acetate (PGMEA) solvent.

Description

Technical Field

[0001] The invention belongs to the technical field of quantum dots, and in particular relates to a ligand selection and exchange method for quantum dots. Background Art

[0002] A quantum dot is a semiconductor nanostructure that binds excitons in three spatial directions. Sometimes called "artificial atoms" or "quantum dot atoms", it is a new concept proposed in the 1990s. This confinement can be attributed to electrostatic potential (generated by external electrodes, doping, strain, impurities), the interface of two different semiconductor materials (for example: in self-assembled quantum dots), the surface of a semiconductor (for example: semiconductor nanocrystals), or a combination of the above three. Quantum dots have separate quantized energy spectra. The corresponding wave functions are spatially located in the quantum dot, but extend over several lattice periods. A quantum dot has a small number (1-100) of integer electrons, holes, or hole-electron pairs, that is, the charge it carries is an integer multiple of the elementary charge.

[0003] The particle size of quantum dots is close to or smaller than the Bohr radius of the exciton, and the luminescent color can be precisely adjusted in the entire visible light range by adjusting the size and the ratio of elements. In addition, it has the advantages of wide color gamut, pure color, and solution processing, and is a promising luminescent material in the fields of display, laser, photovoltaics, and bio-markers.

[0004] Solution-processable colloidal quantum dots 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 quantum dots in green industrial solvents such as PGMEA has a wide range of applications in optoelectronic devices. However, colloidal quantum dots with high photoluminescence quantum yield (PLQY) are usually synthesized in an organic phase and can be well dispersed in toxic non-polar solvents, but will aggregate and even undergo fluorescence quenching in the polar solvent PGMEA. Therefore, it is a huge challenge to make colloidal quantum dots stably dispersed and efficiently emit light in PGMEA solvent.

[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 of quantum dots, selecting thiol ligands to exchange ligands of original ligands on the surface of quantum dots, thereby achieving stable dispersion of quantum dots with high quantum yield in green industrial propylene glycol monomethyl ether acetate (PGMEA) solvent.

[0007] To achieve the above object, the present invention provides a method for selecting and exchanging ligands of quantum dots, comprising the following steps: Step S1, dissolving the oil-soluble quantum dots synthesized in the organic phase in a non-polar solvent to obtain a quantum dot solution; Step S2, dissolving the thiol ligand in propylene glycol monomethyl ether acetate solvent to obtain a thiol ligand solution; 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; Step S4: After the ligand exchange, a non-polar solvent is added and centrifuged to obtain quantum dots stably dispersed in the propylene glycol monomethyl ether acetate solvent.

[0008] 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 several organic amines or organic acids; the organic amines or organic acids include oleylamine, oleic acid, stearic acid and the like.

[0009] 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 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-XTe / ZnS、PbSe X S 1-X / ZnS, etc.

[0010] 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.

[0011] Preferably, in step S2, the thiol ligand is a ligand containing a thiol group, including but not limited to 2-phenylethanethiol, 3-mercaptopropionic acid butyl ester, bis(3-mercaptopropionic acid) glycol ester, 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.

[0012] Preferably, in step S2, the concentration of the thiol ligand solution is 0.1-10 mol / l.

[0013] Preferably, in step S3, the temperature of ligand exchange is 20-90° C. and the time is 5-90 min.

[0014] The present invention adopts the above-mentioned quantum dot ligand selection and exchange method, and the beneficial effects are as follows: The present invention selects thiol ligands to carry out ligand exchange on 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 at the same time achieves a high degree of dispersibility. The obtained indium phosphide quantum dots have a concentration of 600 mg / ml and a fluorescence quantum yield (PLQY) of more than 95%.

[0015] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A flowchart of an embodiment of a method for selecting and exchanging ligands of quantum dots according to the present invention; 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; Figure 3 This is a test diagram 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 of the present invention; Figure 4 The quantum dots modified with thiol ligands prepared in Example 2 of the method for selecting and exchanging ligands of quantum dots of the present invention; Figure 5This is a test diagram 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 of the present invention; Figure 6 This is a UV absorption spectrum 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; Figure 7 This is a UV absorption spectrum of the thiol ligand-modified quantum dots prepared in Example 2 of a method for selecting and exchanging ligands of quantum dots of the present invention before and after exchange; Figure 8 The fluorescence spectra of the thiol ligand-modified quantum dots prepared in Example 1 of the ligand selection and exchange method of quantum dots of the present invention before and after exchange; Fig. 9 This is a fluorescence spectrum diagram of the thiol ligand-modified quantum dots before and after exchange prepared in Example 2 of a method for selecting and exchanging ligands of quantum dots of the present invention. DETAILED DESCRIPTION

[0017] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0018] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0019] A method for selecting and exchanging ligands of quantum dots, such as Figure 1 As shown, the following steps are included: Step S1, dissolving the oil-soluble quantum dots synthesized in the organic phase in a non-polar solvent to obtain a quantum dot solution.

[0020] 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 include oleylamine, oleic acid, stearic acid, etc. That is, the quantum dots containing one or more of the above ligands are suitable for exchange by the ligand exchange method of the present invention.

[0021] 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 Cd1-X Te、PbSe X S 1-X 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.

[0022] Non-polar solvents include, but are not limited to, n-hexane and toluene.

[0023] Wherein, the concentration of the quantum dot solution is 20 mg / ml.

[0024] Step S2, dissolving the thiol ligand in propylene glycol monomethyl ether acetate solvent to obtain a thiol ligand solution.

[0025] 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, dithiol, mercapto alcohol, mercapto acid, 2-mercaptoacetic acid, 3-mercaptopropionic acid, 4-mercaptobutyric acid, mercaptosuccinic acid, 6-mercaptohexanoic acid, and 4-mercaptobenzoic acid.

[0026] Wherein, the concentration of the thiol ligand solution is 0.1-10 mol / l.

[0027] 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.

[0028] The temperature of ligand exchange is 20-90°C and the time is 5-90 min.

[0029] Step S4: After the ligand exchange, a non-polar solvent is added and centrifuged to obtain quantum dots stably dispersed in the propylene glycol monomethyl ether acetate solvent.

[0030] Embodiment 1 The quantum dots were prepared by ligand exchange of 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.

[0031] A method for selecting and exchanging ligands of quantum dots, the specific steps are as follows: Step S1, providing a first quantum dot solution containing an organic acid ligand, the first quantum dot solution is an InP / ZnSe / ZnS quantum dot stock solution with a luminescence peak wavelength of 620nm and a peak width of 40nm, a volume of 20ml, and a concentration of 20mg / ml. The organic acid ligand of the quantum dot is oleic acid.

[0032] Purification treatment: For the above quantum dots, add 40 ml of ethanol, centrifuge at 5000 rpm for 5 min, discard the supernatant, and 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 min, discard the supernatant, and 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.

[0033] Step S2: Take 60 mmol of 2-phenylethanethiol ligand, add 10 ml of PGMEA solvent to prepare a thiol ligand solution with a concentration of 6 mmol / ml.

[0034] Step S3, ligand exchange: the above hexane quantum dots were mixed with the thiol ligand solution, and reacted at 25° C. and 1500 rpm in air for 30 min.

[0035] Step S4: After ligand exchange, ten times the volume of hexane was added to the mixed solution for purification, and the mixture was centrifuged at 5000 rpm for 5 min. The supernatant was discarded and the precipitate was dispersed in a PGMEA solution to obtain thiol ligand-modified quantum dots.

[0036] like Figure 2 As shown, stably dispersed quantum dots (concentration of 600 mg / ml) were obtained after ligand exchange.

[0037] like Figure 3 As shown, the fluorescence quantum yield of quantum dots is higher after ligand exchange.

[0038] Embodiment 2 The quantum dots are prepared by ligand exchange of a quantum dot solution of InP / ZnSe / ZnS with a luminescent 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 are InP / ZnSe / ZnS quantum dots.

[0039] A method for selecting and exchanging ligands of quantum dots, the specific steps are as follows: Step S1, providing a first quantum dot solution containing an organic acid ligand and an organic amine ligand, wherein the first quantum dot solution is an InP / ZnSe / ZnS quantum dot stock solution with a luminescence peak wavelength of 620nm and a peak width of 40nm, a volume of 20ml, and a concentration of 20mg / ml. The organic acid ligand of the quantum dot is oleic acid, and the organic amine ligand is oleylamine.

[0040] Purification treatment: For the above quantum dots, add 40 ml of ethanol, centrifuge at 5000 rpm for 5 min, discard the supernatant, and 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 min, discard the supernatant, and 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.

[0041] Step S2: Take 60 mmol of 2-phenylethanethiol ligand, add 10 ml of PGMEA solvent to prepare a thiol ligand solution with a concentration of 6 mmol / ml.

[0042] Step S3, ligand exchange: the above hexane quantum dots were mixed with the thiol ligand solution, and reacted at 25° C. and 1500 rpm in air for 30 min.

[0043] Step S4: After ligand exchange, ten times the volume of hexane was added to the mixed solution for purification, and the mixture was centrifuged at 5000 rpm for 5 min. The supernatant was discarded and the precipitate was dispersed in a PGMEA solution to obtain thiol ligand-modified quantum dots.

[0044] like Figure 4 As shown, stably dispersed quantum dots (concentration of 600 mg / ml) were obtained after ligand exchange.

[0045] like Figure 5 As shown, the fluorescence quantum yield of quantum dots is higher after ligand exchange.

[0046] The quantum dots modified with thiol ligands obtained in Example 1 and Example 2 were tested for ultraviolet light absorption and fluorescence intensity, respectively.

[0047] 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.

[0048] 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 green industrial propylene glycol monomethyl ether acetate (PGMEA) solvent.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. 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 solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution 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 the oil-soluble quantum dots synthesized in the organic phase in a non-polar solvent to obtain a quantum dot solution; Step S2, dissolving the thiol ligand in propylene glycol monomethyl ether acetate solvent to obtain a thiol ligand solution; 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; Step S4: After the 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. A method for selecting and exchanging ligands of quantum dots according to claim 1, characterized in that: 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; the organic amines or organic acids include oleylamine, oleic acid, and stearic acid.

3. A method for selecting and exchanging ligands of quantum dots according to claim 2, characterized in that: In step S1, the quantum dots include binary phase, ternary phase, and quaternary phase quantum dots; The binary phase quantum dots include CdS, CdSe, CdTe, InP, InAs, InSb, AgS, PbS, PbSe, HgS, 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 , 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.

4. A method for selecting and exchanging ligands of quantum dots according to claim 3, characterized in that: In step S1, the non-polar solvent includes but is not limited to n-hexane and toluene; the concentration of the quantum dot solution is 20 mg / ml.

5. The method for selecting and exchanging ligands of quantum dots according to claim 1, characterized in that: In step S2, the thiol ligand is a ligand containing a thiol group, including but not limited to 2-phenylethanethiol, 3-mercaptopropionic acid butyl ester, 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.

6. A method for selecting and exchanging ligands of quantum dots according to claim 5, characterized in that: In step S2, the concentration of the thiol ligand solution is 0.1-10 mol / l.

7. The method for selecting and exchanging ligands of quantum dots according to claim 1, characterized in that: In step S3, the temperature of ligand exchange is 20-90° C. and the time is 5-90 min.

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