WO2017067451A1

WO2017067451A1 - Method for synthesizing high-quality colloidal cadmium-free quantum dots

Info

Publication number: WO2017067451A1
Application number: PCT/CN2016/102486
Authority: WO
Inventors: 陈威; 王恺; 孙小卫; 郝俊杰; 秦静
Original assignee: 广东昭信光电科技有限公司
Priority date: 2015-10-20
Filing date: 2016-10-19
Publication date: 2017-04-27
Also published as: CN105219380B; CN105219380A

Abstract

Disclosed is a method for synthesizing high-quality cadmium-free quantum dots. Dissolving a copper source, an indium source and a sulfur source in liquid paraffin and heating to 100-150°C to obtain a copper indium precursor liquid; applying a vacuum and repeatedly introducing nitrogen; in an atmospheric environment or under the protection of an inert atmosphere, continuing to heat to 180-260°C then maintaining heat to obtain a core quantum dot solution; dissolving a zinc source in liquid paraffin and heating to 100-200°C to obtain a zinc precursor liquid; at that temperature, injecting the zinc precursor liquid into the core quantum dot solution; raising the temperature to 180-260°C then maintaining heat to obtain a core-shell structure quantum dot solution; purifying the core-shell structure quantum dot solution to obtain finished core-shell structure quantum dots. The present invention uses low-cost, non-toxic and chemically stable liquid paraffin as a non-coordinating solvent to manufacture cadmium-free quantum dots. Because of liquid paraffin's stable chemical properties and high effectiveness as a barrier against atmospheric moisture and oxygen, this manufacturing process can be performed in an air environment, greatly reducing vacuum environment costs.

Description

Method for synthesizing high quality colloidal cadmium-free quantum dots

Technical field

The invention relates to the technical field of preparation of semiconductor nano materials, in particular to a method for synthesizing high quality colloidal cadmium-free quantum dots.

Background technique

A quantum dot is an inorganic nanocrystal. Since the size of the nanocrystal is smaller than the exciton Bohr radius of the bulk material, the electrons and holes are quantum confined, and the quasi-continuous band structure becomes a discrete energy level structure. Due to the excitation of external energy, including light, electricity and other rays, the electrons in the quantum dots are excited by the valence band to the conduction band, leaving holes on the valence band, and the electrons on the conduction band and the vacancy on the valence band. The holes form electron-hole pairs (ie, excitons), and the electrons on the conduction band will transition to the valence band. The transition process may be a non-radiative transition, that is, in the form of lattice vibration, the electrons may be returned to the valence band, or may be radiation. The transition, that is, in the process of bringing the price band in the transition, emits photons, that is, illuminates. Since the quantum confinement is related to the size of the nanocrystal, the band gap width of the quantum dot is also affected by the size, that is, the photon energy and the emission wavelength released by the electron transition are all affected by the size of the quantum dot, which is The size effect of quantum dots. The size effect allows the luminescence of quantum dots to be continuously tunable by changing the size of the nanocrystals, and has great applications in the field of illumination and display.

At present, the emission spectrum of cadmium selenide quantum dots composed of II-VI elements is continuously adjustable in the visible range, and the prepared quantum dots have a uniform size distribution, and the half-width of the spectrum is narrow, and the surface is organically and bluntly blunt. After the formation, the high quantum yield and stability have been widely studied and concerned. However, heavy metal cadmium (Cd) is used in cadmium selenide quantum dots, which has certain toxicity and pollution to the human body and the natural environment, which makes it reapplied and receives certain limitations. Therefore, the development of cadmium-free and low-cadmium quantum dots is synthesized. Luminescent materials have great practical significance. In addition, since the cadmium selenide quantum dots have a small Stokes shift, in the application process, a part of the absorption spectrum and the emission spectrum overlap to cause a self-absorption effect, which is limited in the field of display illumination.

The copper indium sulphide and its alloy quantum dots composed of II-III-VI elements are currently widely concerned nano-semiconductor crystal materials. Currently, the main non-coordinating solvent mainly used in the synthesis of copper-indium-sulfur quantum dots in organic phase is octadecene. The compound has high cost, is irritating to human skin, pollutes the environment, is relatively unstable in chemical properties, and is flammable and explosive, so the synthesis process needs to be carried out under the protection of a vacuum atmosphere.

Summary of the invention

The technical problem to be solved by the present invention is a method for synthesizing high quality colloidal cadmium-free quantum dots.

The technical solution adopted by the present invention is:

A method for synthesizing high quality colloidal cadmium-free quantum dots, comprising the steps of:

Dissolving copper source, indium source and sulfur source in liquid paraffin, heating to 100-150 ° C, obtaining copper indium precursor liquid, vacuuming, repeatedly injecting nitrogen, and heating to 180- under atmospheric environment or under inert atmosphere protection 260 ° C, 1-30 min incubation, to obtain a core quantum dot solution;

Dissolving the zinc source in liquid paraffin and heating to 100-200 ° C to obtain a zinc precursor liquid. At this temperature, the zinc precursor liquid is injected into the core quantum dot solution, and the temperature is raised to 180-260 ° C, and the temperature is maintained. Obtaining a core-shell structure quantum dot solution;

The core-shell structure quantum dot solution is purified to obtain a core-shell structured quantum dot product.

Preferably, in the process of preparing the core quantum dot solution, a doping metal source is further added, and the doping metal source is a zinc source or a gallium source.

Preferably, the copper source is cuprous iodide or organic copper.

Preferably, the source of indium is any one of zinc stearate, zinc oleate, and zinc acetate.

Preferably, the sulfur source is any one of dodecanol, H ₂ S, sodium sulfide, and sulfur powder.

Preferably, the ratio of the amount of the copper source and the indium source is 1: (1-10).

Preferably, the specific step of the purification process is: adding an organic solvent to the core-shell structure quantum dot solution for extraction, adding ethanol, and centrifuging to obtain a quantum dot powder.

Further preferably, the purification process is a repeated number of purification processes.

The invention has the beneficial effects that the invention adopts an inexpensive, non-toxic, chemically stable liquid paraffin as a non-coordinating solvent to prepare cadmium-free quantum dots. Due to the stable chemical nature of liquid paraffin, it has a good insulation effect on moisture and oxygen in the air. The preparation process can also be carried out in an air environment, which greatly saves the cost of the vacuum environment.

DRAWINGS

1 is a fluorescence spectrum of CuInS ₂ /ZnS quantum dots prepared in Example 1;

2 is a fluorescence spectrum of CuInS ₂ /ZnS quantum dots prepared in Example 2;

3 is a fluorescence spectrum of a ZnCuInS ₂ /ZnS quantum dot prepared in Example 4;

4 is a fluorescence spectrum of CuGa _0.8 In _0.2 S ₂ /ZnS quantum dots prepared in Example 5.

detailed description

The concept, the specific structure and the technical effects of the present invention will be clearly and completely described in conjunction with the embodiments and the accompanying drawings. It is apparent that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments, based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative efforts belong to The scope of protection of the present invention. In addition, all the coupling/joining relationships involved in the patents are not directly connected to the components, but rather may constitute a better coupling structure by adding or reducing the coupling accessories according to the specific implementation. The various technical features in the creation of the invention can be combined and combined without conflicting conflicts.

Example 1:

1. Preparation of CuInS ₂ core quantum dots

Take 0.25 mmol of cuprous iodide (CuI), 1 mmol of indium acetate (In(Ac) ₂ ), 5 mL of dodecyl mercaptan (DDT) and 10 mL of liquid paraffin in a 50 mL three-necked flask, and stir to 100 ° C with heating. Vacuum and repeated injection of nitrogen for 30 minutes, under the protection of an inert atmosphere, the solution was heated to 230 ° C for 3 minutes to obtain CuInS ₂ core quantum dots.

2. Preparation of CuInS ₂ /ZnS core-shell quantum dots

In a separate three-necked flask system, 16 mmol of zinc stearate (Zn(SA) ₂ ), 8 mL of DDT was added to 16 mL of liquid paraffin, and the mixture was heated to 150 ° C to obtain a transparent liquid. At this temperature, the transparent liquid was rapidly injected into the core quantum dot solution of CuInS ₂ under the protection of an inert atmosphere, and the temperature of the mixed solution was raised to 250 ° C for 2 hours. CuInS ₂ /ZnS core-shell quantum dots were obtained.

3. Purification of CuInS ₂ /ZnS core-shell structure quantum dots

The core-shell quantum dot solution was added to n-hexane/methanol for extraction, and then 5 mL of the quantum dot extract was added to a 10 mL centrifuge tube, and then 5 mL of ethanol was continuously added to the centrifuge tube to obtain a turbid milky white liquid. Centrifugation was carried out at a speed of 8000 rpm or more for 10 minutes to obtain a quantum dot precipitated powder. The n-hexane, and the alcohol were added again, and the centrifugation was repeated, and the second centrifugal quantum dots were dispersed into n-hexane to obtain a final CuInS ₂ /ZnS cadmium-free core-shell quantum dot.

In this example, the CuInS ₂ /ZnS quantum dots were successfully prepared in liquid paraffin under the protection of an inert atmosphere. The fluorescence spectrum of the obtained CuInS ₂ /ZnS quantum dots is shown in Fig. 1. The emission wavelength of the quantum dots is 564 nm, and the absolute quantum yield is obtained. Up to 83%, half width is 98nm. It is a high quality cadmium-free quantum dot for white LED lighting and display technology. The inorganic passivation is completed on the surface of the copper indium-sulfur quantum dots, which has a high quantum yield, a large Stokes shift, and the emission wavelength is continuously adjustable in the visible range, and is based on the quantum dot size effect. On the upper, the ratio of the existing elements is adjustable, that is, the Cu/In ratio adjusts the emission wavelength, and the alloying composition is adjustable, that is, the elements such as Ga and Zn are doped, and the emission peaks of the copper indium-sulfur quantum dots have different degrees of blue shift. And red shift, the emission range is increased to 500 to 900 nm, which not only removes the dependence on the elements of heavy metals from the raw materials, but can be applied to down-conversion light-emitting devices, such as display and illumination devices, which is an ideal light conversion. material.

Example 2:

1. Preparation of CuInS ₂ core quantum dots

0.125 mmol of CuI, 0.5 mmol of In(Ac) ₂ , 2.5 mL of DDT and 10 mL of liquid paraffin were placed in a 50 mL three-necked flask, heated to 100 ° C, vacuumed and repeatedly injected with nitrogen for 30 minutes, and then in an atmosphere. The solution was heated to 230 ° C for 3 minutes to obtain a CuInS ₂ core quantum dot.

2. Preparation of CuInS ₂ /ZnS core-shell quantum dots

In a separate three-necked flask system, 8 mmol of zinc stearate (Zn(SA) ₂ ), 4 mL of DDT was added to 8 mL of liquid paraffin, and the mixture was heated and stirred to 150 ° C to obtain a transparent liquid. At this temperature, the transparent liquid was rapidly injected into the core quantum dot solution of CuInS ₂ under an atmospheric environment, and the temperature of the mixed solution was raised to 250 ° C for 1.5 hours. CuInS ₂ /ZnS core-shell quantum dots were obtained.

3. Purification of CuInS ₂ /ZnS core-shell structure quantum dots

The core-shell quantum dot solution was added to n-hexane/methanol for extraction, and then 5 mL of the quantum dot extract was added to a 10 mL centrifuge tube, and then 5 mL of ethanol was continuously added to the centrifuge tube to obtain a turbid milky white liquid. Centrifugation was carried out at a speed of 8000 rpm or more for 10 minutes to obtain a quantum dot precipitated powder. Re-add n-hexane, and alcohol, repeat centrifugation, and disperse the second centrifuged quantum dots into n-hexane. That is, the final CuInS ₂ /ZnS cadmium-free core-shell structure quantum dots are obtained.

In this embodiment, CuInS ₂ /ZnS quantum dots are successfully prepared in liquid paraffin under atmospheric conditions. The fluorescence spectrum of the obtained CuInS ₂ /ZnS quantum dots is shown in Fig. 2. The emission wavelength of quantum dots is 630 nm, and the fluorescence quantum yield is obtained. It is 60% and the half width is 121 nm. It is a high quality cadmium-free quantum dot that can be applied to white LED lighting and display technology. The invention adopts cheap, non-toxic, chemically stable liquid paraffin as a non-coordinating solvent to prepare cadmium-free quantum dots, and has good isolation effect on moisture and oxygen in the air due to stable chemical properties of liquid paraffin, the preparation process It can also be carried out in an air environment, which greatly saves the cost of the vacuum environment. The method of the present invention can also be carried out under the protection of an inert atmosphere, and the quantum dots generated are quantum dots synthesized in an air environment.

Example 3:

1. Preparation of CuInS ₂ core quantum dots

Take 0.25 mmol of cuprous iodide (CuI), 1 mmol of indium acetate (In(Ac) ₂ ), 5 mL of dodecyl mercaptan (DDT), and 10 mL of liquid paraffin in a 50 mL three-necked flask, and stir to 150 ° C with heating. Vacuum and repeated injection of nitrogen for 30 minutes, the solution was heated to 260 ° C under an inert atmosphere for 3 minutes to obtain CuInS ₂ core quantum dots.

2. Preparation of CuInS ₂ /ZnS core-shell quantum dots

In a separate three-necked flask system, 16 mmol of zinc stearate (Zn(SA) ₂ ), 8 mL of DDT was added to 16 mL of liquid paraffin, and the mixture was heated to 100 ° C to obtain a transparent liquid. At this temperature, the transparent liquid was rapidly injected into the core quantum dot solution of CuInS ₂ under the protection of an inert atmosphere, and the temperature of the mixed solution was raised to 180 ° C for 2.5 hours. CuInS ₂ /ZnS core-shell quantum dots were obtained.

3. Purification of CuInS ₂ /ZnS core-shell structure quantum dots

The core-shell quantum dot solution was added to n-hexane/methanol for extraction, and then 5 mL of the quantum dot extract was added to a 10 mL centrifuge tube, and then 5 mL of ethanol was continuously added to the centrifuge tube to obtain a cloudy milky white liquid. Centrifugation was carried out at a speed of 8000 rpm or more for 10 minutes to obtain a quantum dot precipitated powder. Re-add n-hexane, and alcohol, repeat centrifugation, disperse the second centrifugal quantum dots into n-hexane, and obtain the final CuInS ₂ /ZnS cadmium-free core-shell quantum dots. The resulting quantum dots are high-quality cadmium-free quantum dots. Can be applied to white LED lighting and display technology.

Example 4:

1. Preparation of ZnCuInS ₂ core quantum dots

0.125 mmol of CuI, 0.125 mmol of zinc stearate (Zn(SA) ₂ ), 0.125 mmol of In(Ac) ₂ , 2.5 mL of DDT and 10 mL of liquid paraffin were placed in a 50 mL three-necked flask and heated to 100 ° C. Vacuum and repeated injection of nitrogen for 30 minutes, the solution was heated to 230 ° C under an inert atmosphere for 3 minutes to obtain ZnCuInS ₂ core quantum dots.

2. Preparation of quantum dots of ZnCuInS ₂ /ZnS core-shell structure

In a separate three-necked flask system, 8 mmol of zinc stearate (Zn(SA) ₂ ), 4 mL of DDT was added to 8 mL of liquid paraffin, and the mixture was heated and stirred to 150 ° C to obtain a transparent liquid. At this temperature, the transparent liquid was rapidly injected into the ZnCuInS ₂ core quantum dot solution under the protection of an inert atmosphere, and the temperature of the mixed solution was raised to 250 ° C for 1.5 hours. A quantum dot of ZnCuInS ₂ /ZnS core-shell structure is obtained.

3. Purification of ZnCuInS ₂ /ZnS core-shell structure quantum dots

The core-shell quantum dot solution was added to n-hexane/methanol for extraction, and then 5 mL of the quantum dot extract was added to a 10 mL centrifuge tube, and then 5 mL of ethanol was continuously added to the centrifuge tube to obtain a turbid milky white liquid. Centrifugation was carried out at a speed of 8000 rpm or more for 10 minutes to obtain a quantum dot precipitated powder. Re-add n-hexane, and alcohol, repeat centrifugation, and disperse the second centrifuged quantum dots into n-hexane. That is, the final ZnCuInS ₂ /ZnS cadmium-free core-shell structure quantum dots are obtained.

In this example, the ZnCuInS ₂ /ZnS quantum dots were successfully prepared in liquid paraffin under the protection of an inert atmosphere. The fluorescence spectrum of the obtained ZnCuInS ₂ /ZnS quantum dots is shown in Fig. 3. The emission wavelength of quantum dots is 573 nm. The rate was 68% and the half width was 110 nm. It is a high quality cadmium-free quantum dot that can be applied to white LED lighting and display technology.

Example 5:

1. Preparation of CuGa _0.8 In _0.2 S ₂ core quantum dots

0.125 mmol of CuI, 0.4 mmol of gallium acetylacetonate (Ga(Acac) ₂ ), 0.1 mmol of In(Ac) ₂ , 2.5 mL of DDT and 10 mL of liquid paraffin were placed in a 50 mL three-necked flask, and the mixture was heated and stirred to 100 ° C. Vacuum and repeated injection of nitrogen for 30 minutes, the solution was heated to 230 ° C under an inert atmosphere for 3 minutes to obtain CuGa _0.8 In _0.2 S ₂ core quantum dots.

2. Preparation of CuGa _0.8 In _0.2 S ₂ /ZnS core-shell quantum dots

In a separate three-necked flask system, 8 mmol of zinc stearate and 4 mL of DDT were added to 8 mL of liquid paraffin, and the mixture was heated and stirred to 150 ° C to obtain a transparent liquid. At this temperature, the transparent liquid was rapidly injected into the CuGa _0.8 In _0.2 S ₂ core quantum dot solution under the protection of an inert atmosphere, and the temperature of the mixed solution was raised to 250 ° C for 1.5 hours. A CuGa _0.8 In _0.2 S ₂ /ZnS core-shell quantum dot was obtained.

3. Purification of CuGa _0.8 In _0.2 S ₂ /ZnS core-shell quantum dots

The core-shell quantum dot solution was added to n-hexane/methanol for extraction, and then 5 mL of the quantum dot extract was added to a 10 mL centrifuge tube, and then 5 mL of ethanol was continuously added to the centrifuge tube to obtain a turbid milky white liquid. Centrifugation was carried out at a speed of 8000 rpm or more for 10 minutes to obtain a quantum dot precipitated powder. Re-add n-hexane, and alcohol, repeat centrifugation, and disperse the second centrifuged quantum dots into n-hexane. The final CuGa _0.8 In _0.2 S ₂ /ZnS cadmium-free core-shell quantum dots were obtained.

In this example, the CuGa _0.8 In _0.2 S ₂ /ZnS quantum dots were successfully prepared in liquid paraffin under the protection of an inert atmosphere. The fluorescence spectrum of the obtained CuGa _0.8 In _0.2 S ₂ /ZnS quantum dots is shown in Fig. 4. The emission wavelength was 530 nm, the fluorescence quantum yield was 71%, and the half width was 131 nm. It is a high quality cadmium-free quantum dot that can be applied to white LED lighting and display technology.

Example 6

1. Preparation of CuGa _0.8 In _0.2 S ₂ core quantum dots

0.125 mmol of CuI, 0.4 mmol of gallium acetylacetonate (Ga(Acac) ₂ ), 1.25 mmol of In(Ac) ₂ , 2.5 mL of DDT and 10 mL of liquid paraffin were placed in a 50 mL three-necked flask, and the mixture was heated and stirred to 150 ° C. Vacuum and repeated injection of nitrogen for 30 minutes, under the protection of an inert atmosphere, the solution was heated to 180 ° C for 6 minutes to obtain CuGa _0.8 In _0.2 S ₂ core quantum dots.

2. Preparation of CuGa _0.8 In _0.2 S ₂ /ZnS core-shell quantum dots

In a separate three-necked flask system, 8 mmol of zinc stearate and 4 mL of DDT were added to 8 mL of liquid paraffin, and the mixture was heated and stirred to 200 ° C to obtain a transparent liquid. At this temperature, the transparent liquid was rapidly injected into the CuGa _0.8 In _0.2 S ₂ core quantum dot solution under the protection of an inert atmosphere, and the temperature of the mixed solution was raised to 260 ° C for 1.5 hours. A CuGa _0.8 In _0.2 S ₂ /ZnS core-shell quantum dot was obtained.

3. Purification of CuGa _0.8 In _0.2 S ₂ /ZnS core-shell quantum dots

The core-shell quantum dot solution was added to n-hexane/methanol for extraction, and then 5 mL of the quantum dot extract was added to a 10 mL centrifuge tube, and then 5 mL of ethanol was continuously added to the centrifuge tube to obtain a turbid milky white liquid. Centrifugation was carried out at a speed of 8000 rpm or more for 10 minutes to obtain a quantum dot precipitated powder. Re-add n-hexane, and alcohol, repeat centrifugation, and disperse the second centrifuged quantum dots into n-hexane. The final CuGa _0.8 In _0.2 S ₂ /ZnS cadmium-free core-shell quantum dots are obtained, and the obtained quantum dots are high-quality cadmium-free quantum dots, which can be applied to white LED illumination and display technology.

Claims

A method for synthesizing high quality colloidal cadmium-free quantum dots, comprising the steps of:

Dissolving copper source, indium source and sulfur source in liquid paraffin, heating to 100-150 ° C, obtaining copper indium precursor liquid, vacuuming, repeatedly injecting nitrogen, and heating to 180- under atmospheric environment or under inert atmosphere protection 260 ° C, 1-30 min incubation, to obtain a core quantum dot solution;

Dissolving the zinc source in liquid paraffin and heating to 100-200 ° C to obtain a zinc precursor liquid. At this temperature, the zinc precursor liquid is injected into the core quantum dot solution, and the temperature is raised to 180-260 ° C, and the temperature is maintained. Obtaining a core-shell structure quantum dot solution;

The core-shell structure quantum dot solution is purified to obtain a core-shell structured quantum dot product.
The method for synthesizing high-quality colloidal cadmium-free quantum dots according to claim 1, wherein in the process of preparing the core quantum dot solution, a doping metal source is further added, and the doped metal source is a zinc source or Gallium source.
The method according to claim 1, wherein the copper source is cuprous iodide or organic copper.
The method according to claim 1, wherein the source of indium is any one of zinc stearate, zinc oleate and zinc acetate.
The method for synthesizing high-quality colloidal cadmium-free quantum dots according to claim 1, wherein the sulfur source is any one of dodecanol, H2S, sodium sulfide, and sulfur powder.
The method for synthesizing a high quality colloidal cadmium-free quantum dot according to claim 1, wherein the ratio of the substance of the copper source and the indium source is 1: (1-10).
The method for synthesizing high-quality colloidal cadmium-free quantum dots according to claim 1, wherein the specific step of the purification process comprises: adding an organic solvent to the core-shell structure quantum dot solution for extraction, and then adding Ethanol was centrifuged to obtain a quantum dot powder.
The method for synthesizing high quality colloidal cadmium-free quantum dots according to claim 7, wherein the purification process is a repeated purification process.