CuInS2/In2S3/ZnS fluorescent quantum dot with double-layer core-shell structure and preparation method thereof

Abstract

The present invention provides a CuInS.sub.2/In.sub.2S.sub.3/ZnS fluorescent quantum dot with a double-layer core-shell structure, aiming to overcome the defects of the existing CuInS.sub.2 quantum dots. CuInS.sub.2 serves as a core, In.sub.2S.sub.3 serves as a first shell for cladding the core, and ZnS serves as a second shell for cladding the first shell. The present invention further provides a preparation method for the CuInS.sub.2/In.sub.2S.sub.3/ZnS fluorescent quantum dot with a double-layer core-shell structure. The CuInS.sub.2 quantum dot is synthesized using two stabilizers, and indium thiophosphate serves as a monomolecular precursor of the In.sub.2S.sub.3 shell.

Claims

1. A CuInS.sub.2/In.sub.2S.sub.3/ZnS fluorescent quantum dot with double-layer core-shell structure, comprising a core formed of CuInS.sub.2, a first shell formed of In.sub.2S.sub.3 cladding the core, and a second shell formed of ZnS cladding the first shell.

2. The CuInS.sub.2/In.sub.2S.sub.3/ZnS fluorescent quantum dot with double-layer core-shell structure of claim 1, wherein a molar ratio of CuInS.sub.2 to In.sub.2S.sub.3 is 1:0.5-5, and a molar ratio of CuInS.sub.2 to ZnS is 1:1-4.

3. A preparation method of the CuInS.sub.2/In.sub.2S.sub.3/ZnS fluorescent quantum dot with double-layer core-shell structure of claim 1, comprising the following steps: step (1): uniformly mixing a copper source, an indium source, an alkyl amine, an alkyl mercaptan and a non-polar solvent to obtain a solution, wherein, a molar ratio of the alkyl mercaptan to the alkyl amine is 8-10:1, a concentration of the copper source is 0.01-0.1 mol/L, and the copper source, the indium source and the alkyl mercaptan are in such proportion that a molar ratio of Cu:In:S is 1:1-1.5:25-250; keeping the solution at 200-230 C. for 5-60 minutes for reaction, and then cooling the solution to terminate the reaction; performing a centrifugal purification to obtain a precipitate, then dissolving the precipitate in the non-polar solvent to obtain a CuInS.sub.2 quantum dot solution having a concentration of 0.005-0.02 mol/L; step (2): uniformly mixing an indium thiophosphate, an alkyl mercaptan and a non-polar solvent to obtain an In.sub.2S.sub.3 precursor solution, wherein, the indium thiophosphate is indium dialkyldithiophosphate or indium dicresyl dithiophosphate, a concentration of the indium thiophosphate is 0.005-0.02 mol/L, and a molar ratio of the indium thiophosphate to the alkyl mercaptan is 1:10-50; adding the In.sub.2S.sub.3 precursor solution dropwise into the CuInS.sub.2 quantum dot solution obtained in step (1) at 220-240 C., maintaining the temperature for 30-60 minutes for reaction, and then cooling the solution to terminate the reaction; performing a centrifugal purification to obtain a precipitate, then dissolving the precipitate in the non-polar solvent to obtain a CuInS.sub.2/In.sub.2S.sub.3 quantum dot solution having a concentration of 0.005-0.02 mol/L; step (3): uniformly mixing a zinc diethyldithiocarbamate, an alkyl mercaptan and a non-polar solvent to obtain a ZnS precursor solution, wherein, a concentration of the zinc diethyldithiocarbamate is 0.005-0.02 mol/L, and a molar ratio of the zinc diethyldithiocarbamate to the alkyl mercaptan is 1:10-50; adding the ZnS precursor solution dropwise into the CuInS.sub.2/In.sub.2S.sub.3 quantum dot solution obtained in step (2) at 220-240 C., maintaining the temperature for 30-60 minutes for reaction, and then cooling the solution to terminate the reaction and thereby a CuInS.sub.2/In.sub.2S.sub.3/ZnS quantum dot solution is obtained; step (4): adding ethanol or acetone into the CuInS.sub.2/In.sub.2S.sub.3/ZnS quantum dot solution obtained in step (3), subjecting the solution to centrifugation to obtain the fluorescent quantum dot with double-layer core-shell structure.

4. The preparation method of the CuInS.sub.2/In.sub.2S.sub.3/ZnS fluorescent quantum dot with double-layer core-shell structure of claim 3, wherein in step (2), the CuInS.sub.2 quantum dot solution and the In.sub.2S.sub.3 precursor solution are in such proportion that a molar ratio of Cu:In is 1:1-10; in step (3), the CuInS.sub.2/In.sub.2S.sub.3 quantum dot solution and the ZnS precursor solution are in such proportion that a molar ratio of Cu:Zn is 1:1-4.

5. The preparation method of the CuInS.sub.2/In.sub.2S.sub.3/ZnS fluorescent quantum dot with double-layer core-shell structure of claim 3, wherein in step (2), the indium dialkyldithiophosphate is selected from the group consisting of indium diethyldithiophosphate, indium diisopropyl dithiophosphate, indium diisobutyl dithiophosphate, indium di-sec-butyl dithiophosphate and indium diisopentyl dithiophosphate.

6. The preparation method of the CuInS.sub.2/In.sub.2S.sub.3/ZnS fluorescent quantum dot with double-layer core-shell structure of claim 3, wherein the non-polar solvent is an alkyl mercaptan or an aliphatic olefin.

7. The preparation method of the CuInS.sub.2/In.sub.2S.sub.3/ZnS fluorescent quantum dot with double-layer core-shell structure of claim 6, wherein the aliphatic olefin is hexadecylene or octadecylene.

8. The preparation method of the CuInS.sub.2/In.sub.2S.sub.3/ZnS fluorescent quantum dot with double-layer core-shell structure of claim 3, wherein the copper source is selected from the group consisting of cuprous chloride, cuprous iodide and cuprous acetate; and the indium source is selected from the group consisting of indium acetate, indium nitrate, and indium chloride.

9. The preparation method of the CuInS.sub.2/In.sub.2S.sub.3/ZnS fluorescent quantum dot with double-layer core-shell structure of claim 3, wherein the alkyl mercaptan is dodecyl mercaptan or hexadecyl mercaptan; and the alkyl amine is selected from the group consisting of oleylamine, dodecyl amine and hexadecyl amine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic view of a CuInS.sub.2/In.sub.2S.sub.3/ZnS fluorescent quantum dot with double-layer core-shell structure according to the present invention;

(2) FIG. 2 shows the energy levels in the CuInS.sub.2/In.sub.2S.sub.3/ZnS fluorescent quantum dot with double-layer core-shell structure according to the present invention.

(3) Reference characters in the drawings: 1: ZnS shell; 2: In.sub.2S.sub.3 shell; and 3: CuInS.sub.2 core.

DETAILED DESCRIPTION OF THE INVENTION

Embodiment 1

(4) Step (1): adding 0.1 mmol of cuprous iodide and 0.1 mmol of indium acetate into a mixed solution consisting of 25 mmol of dodecyl mercaptan (serving as a sulfur source and a stabilizer), 2.5 mmol of oleylamine, and octadecylene (serving as solvent), in such proportion that the concentration of cuprous iodide is 0.01 mol/L; evacuating and purging with nitrogen for three times under stirring, and then keeping the solution at 100 C. under a nitrogen atmosphere until the solution becomes clear; then bringing and keeping the solution at 230 C. for 5 minutes for reaction, and then cooling the solution to terminate the reaction; subjecting the solution to centrifugation to obtain a precipitate, and dissolving the precipitate in octadecylene to obtain a CuInS.sub.2 quantum dot solution having a concentration of 0.01 mol/L.

(5) Step (2): adding 1.0 mmol of indium diethyldithiophosphate and 20 mmol of dodecyl mercaptan into octadecylene to obtain an In.sub.2S.sub.3 precursor solution (wherein a concentration of the indium diethyldithiophosphate is 0.01 mol/L); adding the In.sub.2S.sub.3 precursor solution dropwise into the CuInS.sub.2 quantum dot solution obtained in step (1) at 230 C., maintaining the temperature for 45 minutes for reaction under a nitrogen atmosphere, and then cooling the solution to terminate the reaction; subjecting the solution to centrifugation to obtain a precipitate, and dissolving the precipitate in octadecylene to obtain a CuInS.sub.2/In.sub.2S.sub.3 quantum dot solution having a concentration of 0.01 mol/L;

(6) Step (3): adding 0.4 mmol of zinc diethyldithiocarbamate and 8 mmol of dodecyl mercaptan into octadecylene to obtain a ZnS precursor solution (wherein a concentration of the zinc diethyldithiocarbamate solution is 0.01 mol/L); adding the ZnS precursor solution dropwise into the CuInS.sub.2/In.sub.2S.sub.3 quantum dot solution obtained in step (2) at 230 C., maintaining the temperature for 45 minutes for reaction, and then cooling the solution to terminate the reaction and thereby obtain a CuInS.sub.2/In.sub.2S.sub.3/ZnS quantum dot solution;

(7) Step (4): adding ethanol into the CuInS.sub.2/In.sub.2S.sub.3/ZnS quantum dot solution obtained in step (3), wherein volume of the ethanol is five times of that of the CuInS.sub.2/In.sub.2S.sub.3/ZnS quantum dot solution; subjecting the solution to centrifugation to obtain the fluorescent quantum dot with double-layer core-shell structure.

Embodiment 2

(8) The process in this embodiment is generally identical to that in embodiment 1, except for the following aspects:

(9) In step (1), 0.5 mmol of cuprous iodide and 0.625 mmol of indium acetate are added into a mixed solution consisting of 25 mmol of dodecyl mercaptan (serving as a sulfur source and a stabilizer), 2.5 mmol of oleylamine, and octadecylene (serving as solvent), in such proportion that the concentration of cuprous iodide is 0.05 mol/L, and concentration of the resulting CuInS.sub.2 quantum dot solution is controlled to be 0.005 mol/L.

(10) In Step (2), 5.0 mmol of indium diethyldithiophosphate and 250 mmol of dodecyl mercaptan are added into octadecylene to obtain an In.sub.2S.sub.3 precursor solution (wherein a concentration of the indium diethyldithiophosphate is 0.005 mol/L); the In.sub.2S.sub.3 precursor solution is added dropwise into the CuInS.sub.2 quantum dot solution obtained in step (1) at 220 C., followed by maintaining the temperature for 60 minutes for reaction under a nitrogen atmosphere; and concentration of the resulting CuInS.sub.2/In.sub.2S.sub.3 quantum dot solution is controlled to be 0.005 mol/L.

(11) In step (3), 2 mmol of zinc diethyldithiocarbamate and 100 mmol of dodecyl mercaptan are added into octadecylene to obtain a ZnS precursor solution (wherein a concentration of the zinc diethyldithiocarbamate is 0.005 mol/L); the ZnS precursor solution is added dropwise into the CuInS.sub.2/In.sub.2S.sub.3 quantum dot solution obtained in step (2) at 220 C., followed by maintaining the temperature for 60 minutes for reaction.

(12) In step (4), acetone is added into the CuInS.sub.2/In.sub.2S.sub.3/ZnS quantum dot solution, wherein volume of the acetone is five times of that of the CuInS.sub.2/In.sub.2S.sub.3/ZnS quantum dot solution.

Embodiment 3

(13) The process in this embodiment is generally identical to that in embodiment 1, except for the following aspects:

(14) In step (1), 1 mmol of cuprous iodide and 1.5 mmol of indium acetate are added into a mixed solution consisting of 25 mmol of dodecyl mercaptan (serving as a sulfur source and a stabilizer), 2.5 mmol of oleylamine, and octadecylene (serving as solvent), in such proportion that the concentration of cuprous iodide is 0.1 mol/L, and concentration of the resulting CuInS.sub.2 quantum dot solution is controlled to be 0.02 mol/L.

(15) In Step (2), 10.0 mmol of indium diethyldithiophosphate and 100 mmol of dodecyl mercaptan are added into octadecylene to obtain an In.sub.2S.sub.3 precursor solution (wherein a concentration of the indium diethyldithiophosphate is 0.02 mol/L); the In.sub.2S.sub.3 precursor solution is added dropwise into the CuInS.sub.2 quantum dot solution obtained in step (1) at 220 C., followed by maintaining the temperature for 60 minutes for reaction under a nitrogen atmosphere; and concentration of the resulting CuInS.sub.2/In.sub.2S.sub.3 quantum dot solution is controlled to be 0.02 mol/L.

(16) In step (3), 4 mmol of zinc diethyldithiocarbamate and 40 mmol of dodecyl mercaptan are added into octadecylene to obtain a ZnS precursor solution (wherein a concentration of the zinc diethyldithiocarbamate is 0.02 mol/L); the ZnS precursor solution is added dropwise into the CuInS.sub.2/In.sub.2S.sub.3 quantum dot solution obtained in step (2) at 220 C., followed by maintaining the temperature for 60 minutes for reaction.

Embodiment 4

(17) The process in this embodiment is generally identical to that in embodiment 1, except for the following aspects:

(18) In step (2), 0.5 mmol of indium diethyldithiophosphate and 10 mmol of dodecyl mercaptan are added into octadecylene to obtain an In.sub.2S.sub.3 precursor solution (wherein a concentration of the indium diethyldithiophosphate is 0.01 mol/L), and the reaction is controlled to take place at 240 C. for 30 minutes.

(19) In step (3), 0.2 mmol of zinc diethyldithiocarbamate and 4 mmol of dodecyl mercaptan are added into octadecylene to obtain a ZnS precursor solution (wherein a concentration of the zinc diethyldithiocarbamate is 0.01 mol/L), and the reaction is controlled to take place at 240 C. for 30 minutes.

Embodiment 5

(20) The process in this embodiment is generally identical to that in embodiment 1, except for the following aspects:

(21) In step (2), 0.1 mmol of indium diethyldithiophosphate and 2 mmol of dodecyl mercaptan are added into octadecylene to obtain an In.sub.2S.sub.3 precursor solution (wherein a concentration of the indium diethyldithiophosphate is 0.01 mol/L).

(22) In step (3), 0.1 mmol of zinc diethyldithiocarbamate and 2 mmol of dodecyl mercaptan are added into octadecylene to obtain a ZnS precursor solution (wherein a concentration of the zinc diethyldithiocarbamate is 0.01 mol/L).

Embodiment 6

(23) The process in this embodiment is generally identical to that in embodiment 1, except for that the molar ratio of dodecyl mercaptan to oleylamine is 8:1.

Embodiment 7

(24) The process in this embodiment is generally identical to that in embodiment 1, except for that the molar ratio of dodecyl mercaptan to oleylamine is 9:1.

Embodiment 8

(25) The process in this embodiment is generally identical to that in embodiment 1, except for that the non-polar solvent in step (1) is dodecyl mercaptan.

Embodiment 9

(26) The process in this embodiment is generally identical to that in embodiment 1, except for that the non-polar solvent in step (1) is hexadecyl mercaptan.

Embodiment 10

(27) The process in this embodiment is generally identical to that in embodiment 1, except for that the copper source is cuprous chloride.

Embodiment 11

(28) The process in this embodiment is generally identical to that in embodiment 1, except for that the copper source is cuprous acetate.

Embodiment 12

(29) The process in this embodiment is generally identical to that in embodiment 1, except for that the indium source is indium nitrate.

Embodiment 13

(30) The process in this embodiment is generally identical to that in embodiment 1, except for that the indium source is indium chloride.

Embodiment 14

(31) The process in this embodiment is generally identical to that in embodiment 1, except for that the mercaptan is hexadecyl mercaptan.

Embodiment 15

(32) The process in this embodiment is generally identical to that in embodiment 1, except for that the alkyl amine is hexadecyl amine.

Embodiment 16

(33) The process in this embodiment is generally identical to that in embodiment 1, except for that the alkyl amine is dodecyl amine.

Embodiment 17

(34) The process in this embodiment is generally identical to that in embodiment 1, except for that the non-polar solvent is hexadecylene.

Embodiment 18

(35) The process in this embodiment is generally identical to that in embodiment 1, except for that the reaction in step (1) takes place for 15 minutes.

Embodiment 19

(36) The process in this embodiment is generally identical to that in embodiment 1, except for that the reaction in step (1) takes place for 30 minutes.

Embodiment 20

(37) The process in this embodiment is generally identical to that in embodiment 1, except for that the reaction in step (1) takes place for 60 minutes.

Embodiment 21

(38) The process in this embodiment is generally identical to that in embodiment 1, except for that the reaction in step (1) takes place at 215 C.

Embodiment 22

(39) The process in this embodiment is generally identical to that in embodiment 1, except for that the reaction in step (1) takes place at 200 C.

Embodiment 23

(40) The process in this embodiment is generally identical to that in embodiment 1, except for that the indium thiophosphate in step (2) is indium diisopropyl dithiophosphate.

Embodiment 24

(41) The process in this embodiment is generally identical to that in embodiment 1, except for that the indium thiophosphate in step (2) is indium diisobutyl dithiophosphate.

Embodiment 25

(42) The process in this embodiment is generally identical to that in embodiment 1, except for that the indium thiophosphate in step (2) is indium di-sec-butyl dithiophosphate.

Embodiment 26

(43) The process in this embodiment is generally identical to that in embodiment 1, except for that the indium thiophosphate in step (2) is indium diisopentyl dithiophosphate.

Embodiment 27

(44) The process in this embodiment is generally identical to that in embodiment 1, except for that the indium thiophosphate in step (2) is indium dicresyl dithiophosphate.

Comparative Example 1

(45) The process in this embodiment is generally identical to that in embodiment 1, except for that the precursor of In.sub.2S.sub.3 in step (2) is indium acetate.

Comparative Example 2

(46) The process in this embodiment is generally identical to that in embodiment 1, except for that oleylamine is not added in step (1).

(47) Table 1 shows the fluorescence emission peak position and the corresponding fluorescence quantum yield of the CuInS.sub.2/In.sub.2S.sub.3/ZnS fluorescent quantum dot prepared in each embodiment and comparative example.

(48) The fluorescence quantum yields are obtained by the following method.

(49) With the aid of a fluorescence spectrophotometer and an ultraviolet-visible spectrophotometer, the fluorescence quantum yields are measured by the reference method in dilute solution, comprising the following steps: (1) measuring the absorbance of each of the CuInS.sub.2/In.sub.2S.sub.3/ZnS samples and the standard example at a certain wavelength; (2) measuring the fluorescence emission spectrum of the CuInS.sub.2/In.sub.2S.sub.3/ZnS samples and the standard example, under a same excitation condition at a certain wavelength; (3) the fluorescence quantum yields of the CuInS.sub.2/In.sub.2S.sub.3/ZnS samples are obtained by the following equation:

(50) ${}_U=\frac{A_S{I}_U{n}_U^2}{A_U{I}_S{n}_S^2}{}_S=\frac{I_u/A_u}{I_s/A_s}\frac{n_u^2}{n_s^2}{}_s$

(51) .sub.U and .sub.S are respectively the quantum yields of the CuInS.sub.2/In.sub.2S.sub.3/ZnS sample and the standard sample, I.sub.U and I.sub.S are respectively the integrated fluorescence intensity of the CuInS.sub.2/In.sub.2S.sub.3/ZnS sample and the standard sample, A.sub.U and A.sub.S are respectively the absorbance of the CuInS.sub.2/In.sub.2S.sub.3/ZnS sample and the standard sample at the corresponding excitation wavelength, which are both less than 0.05, and n.sub.u and n.sub.s are respectively the refractive indexes of the solvent in the CuInS.sub.2/In.sub.2S.sub.3/ZnS sample and that in the standard sample. The solvent in the CuInS.sub.2/In.sub.2S.sub.3/ZnS sample is n-hexane (n.sub.u=1.388), and the solvent in the standard sample is ethanol (n.sub.s=1.3614). The reference standard is Rhodamine 6G (Rh-6G).

(52) As shown in the comparative example 1, when using indium acetate as the precursor of In.sub.2S.sub.3, the fluorescence wavelength is 570 nm, indicating a significant blueshift that affects the quantum yield in red region. When using indium dialkyldithiophosphate or indium dicresyl dithiophosphate, the fluorescence wavelength is greater than 630 nm, resulting in a greater quantum yield in red region.

(53) As shown in the comparative example 2, when using only alkyl mercaptan without alkyl amine, the resulting quantum yield is lower, which is only 72%.

(54) TABLE-US-00001 TABLE 1 Details of the embodiments Step Step (1) Step (2) (3) Performance Cu Cu:In:S Mercaptan:amine Cu:In Indium Cu:Zn Quantum Fluorescence concentration molar molar Temperature Time molar concentration molar yield wavelength (mol/L) ratio ratio ( C.) (min) ratio (mol/L) ratio (%) (nm) 1 0.01 1:1:250 10:1 230 5 1:10 0.01 1:4 82 630 2 0.05 1:1.25:50 10:1 230 5 1:10 0.005 1:4 83 630 3 0.1 1:1.5:25 10:1 230 5 1:10 0.02 1:4 85 630 4 0.01 1:1:250 10:1 230 5 1:5 0.01 1:2 75 630 5 0.01 1:1:250 10:1 230 5 1:1 0.01 1:1 70 630 6 0.01 1:1:250 8:1 230 5 1:10 0.01 1:4 82 630 7 0.01 1:1:250 9:1 230 5 1:10 0.01 1:4 82 630 8 Identical with embodiment 1 except for that the non-polar solvent in step (1) is 80 630 dodecyl mercaptan. 9 Identical with embodiment 1 except for that the non-polar solvent in step (1) is 80 630 hexadecyl mercaptan. 10 Identical with embodiment 1 except for that the copper source is cuprous 75 630 chloride. 11 Identical with embodiment 1 except for that the copper source is cuprous 80 630 acetate. 12 Identical with embodiment 1 except for that the indium source is indium 80 630 nitrate. 13 Identical with embodiment 1 except for that the indium source is indium 80 630 chloride. 14 Identical with embodiment 1 except for that the mercaptan is hexadecyl 80 630 mercaptan. 15 Identical with embodiment 1 except for that the alkyl amine is hexadecyl 75 630 amine 16 Identical with embodiment 1 except for that the alkyl amine is dodecyl amine. 75 630 17 Identical with embodiment 1 except for that the non-polar solvent is 78 630 hexadecylene. 18 0.01 1:1:250 10:1 230 15 1:10 0.01 1:4 80 670 19 0.01 1:1:250 10:1 230 30 1:10 0.01 1:4 80 705 20 0.01 1:1:250 10:1 230 60 1:10 0.01 1:4 80 775 21 0.01 1:1:250 10:1 215 15 1:10 0.01 1:4 80 720 22 0.01 1:1:250 10:1 200 15 1:10 0.01 1:4 80 690 23 Identical with embodiment 1 except for that the indium thiophosphate is 82 630 indium diisopropyl dithiophosphate. 24 Identical with embodiment 1 except for that the indium thiophosphate is 82 630 indium diisobutyl dithiophosphate. 25 Identical with embodiment 1 except for that the indium thiophosphate is 82 630 indium di-sec-butyl dithiophosphate. 26 Identical with embodiment 1 except for that the indium thiophosphate is 82 630 indium diisopentyl dithiophosphate. 27 Identical with embodiment 1 except for that the indium thiophosphate is 82 630 indium dicresyl dithiophosphate. C1 Identical with embodiment 1 except for that the precursor of In.sub.2S.sub.3 is indium 82 570 acetate. C2 Identical with embodiment 1 except for that oleylamine is not added in step (1). 72 630