CN110129054B

CN110129054B - Core-shell quantum dot, preparation method thereof and quantum dot photoelectric device

Info

Publication number: CN110129054B
Application number: CN201910284571.5A
Authority: CN
Inventors: 周健海; 邵蕾; 余世荣
Original assignee: Najing Technology Corp Ltd
Current assignee: Najing Technology Corp Ltd
Priority date: 2019-04-10
Filing date: 2019-04-10
Publication date: 2022-01-18
Anticipated expiration: 2039-04-10
Also published as: CN110129054A

Abstract

The invention discloses a core-shell quantum dot, a preparation method thereof and a quantum dot photoelectric device. The preparation method of the core-shell quantum dot comprises the following steps: s1, providing a quantum dot core, mixing the solution containing the quantum dot core with a zinc precursor in a reaction vessel; s2, after step S1 is completed, adding a sulfur precursor and a transition layer precursor to the reaction vessel in multiple times, the sulfur precursor and the transition layer precursor being not added simultaneously, the sulfur precursor reacting with the zinc precursor to form a plurality of ZnS layers, the transition layer precursor reacting with at least the zinc precursor to form a plurality of transition layers, wherein the band gap width of the transition layers is smaller than that of the ZnS layers, and the single addition of the transition layer precursor is controlled so that the thickness of the transition layers does not exceed 1 layer; s3, after the step S2 is completed, adding a sulfur precursor into the reaction vessel, reacting the zinc precursor with the sulfur precursor to generate a ZnS layer, and obtaining the system containing the core-shell quantum dots after the reaction.

Description

Core-shell quantum dot, preparation method thereof and quantum dot photoelectric device

Technical Field

The invention relates to a quantum dot material, in particular to a core-shell quantum dot, a preparation method thereof and a quantum dot photoelectric device.

Background

Over the past two decades, quantum dot synthesis chemistry has focused primarily on monodisperse control of size morphology and how to improve fluorescence quantum yield. However, in order to make quantum dots as a class of excellent luminescent and optoelectronic materials, it is an important synthetic goal to reduce the influence of the environment, especially water and oxygen, on the optical, electrical, etc. properties of quantum dots as much as possible, which has a great driving effect on the academia and application research of quantum dots.

To obtain stable quantum dots, the simplest method is to coat the surface of the quantum dot with a shell material with a larger band gap width, and the shell thickness is thicker to isolate the contact between excitons and the environment. For example, the issue group of the teacher in Penghao in 2014 reports that the CdSe/CdS core-shell quantum dots with good optical and chemical stability are obtained after the surfaces of the small-size CdSe (3nm) quantum dots are coated with 10-16 layers of CdS. However, the quantum dots have too large size, so that the application of the quantum dots in the fields of biological labeling, imaging and the like is limited, and the cost is high.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide the core-shell quantum dot with lower cost and good stability and the preparation method thereof.

According to one aspect of the present invention, there is provided a method for preparing a core-shell quantum dot, comprising the steps of:

s1, providing a quantum dot core, and mixing a solution containing the quantum dot core with a zinc precursor in a reaction vessel;

s2, after the step S1 is completed, adding a sulfur precursor and a transition layer precursor to the reaction vessel in multiple portions, wherein the sulfur precursor is not added simultaneously with the transition layer precursor, the sulfur precursor reacts with the zinc precursor to form a plurality of ZnS layers, the transition layer precursor reacts with at least the zinc precursor to form a plurality of transition layers, wherein the band gap width of the transition layers is smaller than that of the ZnS layers, and the amount of the transition layer precursor added in a single portion is controlled so that the thickness of the transition layers does not exceed 1 layer;

s3, after the step S2 is completed, adding a sulfur precursor into the reaction vessel, reacting the zinc precursor with the sulfur precursor to form a ZnS layer, and obtaining a system containing core-shell quantum dots;

in each step, the kind and the amount of the sulfur precursor added are the same or different for each time, and the kind and the amount of the transition layer precursor added are the same or different for each time.

Further, the quantum dot core of the step S1 is selected from one of: CdZnSeS, CdZnSe, CdZnS, CdSe, CdS, CdSeS, InP.

Further, the transition layer precursor includes a precursor of at least one anion and/or cation in the quantum dot core, and preferably, the transition layer precursor includes one or more of the following: cadmium precursor, zinc precursor, selenium precursor, sulfur precursor, phosphorus precursor.

Further, in the step S2, the amount of the sulfur precursor added when forming the ZnS layer is recorded as M₁The amount of the transition precursor added when the transition layer adjacent to the ZnS layer is formed is represented as M₂，M₁:M₂＝(5～100):1。

According to another aspect of the present invention, there is provided a core-shell quantum dot including a quantum dot core and a ZnS shell layer covering an outermost side of the quantum dot core, wherein the ZnS shell layer has a thickness of more than 9 layers, the ZnS shell layer includes a plurality of transition layers spaced apart in a radial direction, the plurality of transition layers partition the ZnS shell layer into a plurality of ZnS layers, a band gap width of each of the transition layers is smaller than a band gap width of the ZnS layer, and a thickness of the transition layer is not more than 1 layer.

Further, the thickness of the ZnS shell layer is 30 layers or less.

Further, the quantum dot core is selected from one of CdSe, CdZnSeS, CdZnSe, CdZnS, CdSe, CdS, CdSeS and InP.

Further, the fluorescence efficiency of the core-shell quantum dot is more than 80%.

Further, each of the transition layers may be the same or different, the transition layer may have at least one of the same elements as the quantum dot core, and the transition layer may have at least one of the same elements as the ZnS layer.

According to still another aspect of the present invention, there is provided a quantum dot photoelectric device, including a quantum dot prepared by the method for preparing a core-shell quantum dot according to the present invention or the core-shell quantum dot according to the present invention.

Compared with the prior art, the invention has the beneficial effects that: according to the invention, a thick ZnS shell layer is coated outside a quantum dot core to obtain the core-shell quantum dot with excellent optical property and good anti-water-oxygen performance; the preparation method of the core-shell quantum dots provided by the invention has good universality and is suitable for epitaxial growth of ZnS shells of different types of quantum dots.

Drawings

FIG. 1 illustrates the effect of a thinner transition layer on the energy band of a ZnS shell;

FIG. 2 illustrates the effect of a thicker transition layer on the energy band of a ZnS shell;

FIG. 3 shows an electron micrograph of a CdZnSeS quantum dot prepared in example 1 of the present application;

FIG. 4 shows an electron display mirror photograph of the CdZnSeS/ZnS core-shell quantum dots prepared in example 1 of the present application.

Detailed Description

The present invention is further described below with reference to specific embodiments, and it should be noted that, without conflict, any combination between the embodiments or technical features described below may form a new embodiment.

It is noted that the terms first, second and the like in the description and in the claims of the present application are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It should be understood that the data so used may be interchanged under appropriate circumstances such that embodiments of the application described herein may be used. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus. The definition of "layer" (monolayer, english) is the same as well known in the art, and the number of layers is calculated by thickness back-stepping.

The ZnS shell layer with a large energy band is coated outside the quantum dot core, so that the contact between an exciton and the environment is favorably isolated, however, the lattice mismatching degree between the ZnS shell layer and the core is often large, the ZnS shell layer cannot be thickly coated, the existing method for coating the ZnS shell layer at one time only can coat a very thin layer number (generally less than 3 layers), the defects in the shell layer can be increased along with the increase of the thickness of the ZnS shell layer, and meanwhile, along with the reduction of the yield of the fluorescent quantum dots, the half-peak width of the fluorescence is widened, and the monodispersity of the size and the appearance is poor. In the prior art, some methods coat ZnSe, ZnSeS s or CdZnS with a certain thickness between a core and a ZnS shell layer as a transition layer to reduce lattice mismatching, but the problem of internal defect increase caused by shell layer thickness increase still exists in the subsequent process of coating the ZnS shell layer, and the coated transition layer also affects the energy level and stability of quantum dots. Based on the existing problems, the invention provides a preparation method of the core-shell quantum dot, which solves the problem that a ZnS shell layer cannot be thickened and can also reduce the defects in the ZnS shell layer.

The preparation method of the core-shell quantum dot comprises the following steps:

s1, providing a quantum dot core, mixing the solution containing the quantum dot core with a zinc precursor in a reaction vessel;

s2, after step S1 is completed, adding a sulfur precursor and a transition layer precursor into the reaction vessel a plurality of times, the sulfur precursor and the transition layer precursor being not added simultaneously, the sulfur precursor reacting with the zinc precursor to form a plurality of ZnS layers, the transition layer precursor reacting with at least the zinc precursor to form a plurality of transition layers, wherein the band gap width of the transition layers is smaller than that of the ZnS layers, and the single addition amount of the transition layer precursor is controlled so that the thickness of the transition layers does not exceed 1 layer;

s3, after the step S2 is completed, adding a sulfur precursor into the reaction vessel, reacting the zinc precursor with the sulfur precursor to generate a ZnS layer, and obtaining a system containing the core-shell quantum dots after reaction;

wherein, the type and the amount of the sulfur precursor added in each time are the same or different, and the type and the amount of the transition layer precursor added in each time are the same or different.

The band gap width of the transition layer is small, and the thickness of the transition layer is not more than 1 layer, so that the influence of the transition layer on the energy band continuity and the structure continuity between the ZnS layers can be basically ignored.

The ZnS shell layer of the core-shell quantum dot prepared by the method provided by the invention has the thickness of more than 9 layers, and the fluorescence efficiency of the core-shell quantum dot is more than 80%.

In some embodiments, the quantum dot core of step S1 is a quantum dot core without a shell layer, and the quantum dot core may be selected from one of: CdZnSeS, CdZnSe, CdZnS, CdSe, CdS, CdSeS, InP.

In some embodiments, the transition layer precursor comprises a precursor of at least one anion and/or cation in the quantum dot core, and thus the transition layer has at least one element in common with the quantum dot core. In other words, the transition layer precursor may include only a precursor of one kind of cation or a precursor of one kind of anion in the quantum dot core, may also include precursors of a plurality of kinds of cations or a plurality of kinds of anions in the quantum dot core, and may also include precursors of several kinds of cations and precursors of several kinds of anions in the quantum dot core at the same time.

Preferably, the transition layer precursor comprises one or more of a cadmium precursor, a zinc precursor, a selenium precursor, a sulfur precursor, a phosphorous precursor. According to a specific embodiment, the transition layer precursor is a selenium precursor. According to another specific embodiment, the transition layer precursor is a cadmium precursor. According to another specific embodiment, the transition layer precursor includes a cadmium precursor and a sulfur precursor. According to another specific embodiment, the transition layer precursor includes a cadmium precursor and a selenium-sulfur hybrid precursor (which can be understood to include both a sulfur precursor and a selenium precursor).

In some embodiments, in step S2, the amount of sulfur precursor species added to form a ZnS layer is recorded as M₁The amount of the transition precursor added when forming the transition layer adjacent to the ZnS layer is recorded as M₂，M₁:M₂And (5-100) 1. The "transition layer" in the above-mentioned "generation of a transition layer adjacent to the ZnS layer" includes not only a transition layer on the outer side of the ZnS but also a transition layer on the inner side of the ZnS. In some cases, the formation of a ZnS layer may be formed by reaction of adding a sulfur precursor a plurality of times, and the amount of the substance of the sulfur precursor added when forming the ZnS layer is the total amount of the sulfur precursor added a plurality of times. The thickness of the transition layer is controlled by controlling the addition amount of the precursor of the transition layerThe number of the transition layers is not more than 1, the defects in the ZnS shell layer can be effectively eliminated by the transition layers, and the band structure of the ZnS shell layer is basically not influenced, so that the prepared core-shell quantum dots have high fluorescence quantum yield, good anti-water-oxygen performance and high stability.

The whole synthesis process of the core-shell quantum dot is simple, few in influencing factors and good in repeatability, and is suitable for epitaxial growth of ZnS shells of various types of quantum dots.

The zinc precursor of the present invention can be but is not limited to zinc carboxylate, the cadmium precursor can be but is not limited to cadmium carboxylate, the sulfur precursor can be but is not limited to S-ODE solution, trialkylphosphine sulfur and thiol, and the selenium precursor can be but is not limited to Se-ODE suspension, Se-ODE solution and trialkylphosphine selenium.

The invention also provides a core-shell quantum dot, which comprises a quantum dot core and a ZnS shell layer coated on the outermost side of the quantum dot core, wherein the thickness of the ZnS shell layer is more than 9 layers, a plurality of transition layers are arranged on the ZnS shell layer at intervals along the radial direction, namely the plurality of transition layers divide the ZnS shell layer into a plurality of ZnS layers, the thicknesses of the ZnS layers can be the same or different, the band gap width of each transition layer is smaller than that of the ZnS layer, and the thickness of the transition layer is not more than 1 layer, so that the energy band structures of the front ZnS layer and the rear ZnS layer of the transition layer are basically continuous, namely the ZnS shell layer outside the quantum dot core is a shell layer with a basically continuous energy band structure.

The ZnS shell layer coated on the outermost side of the quantum dot core means that: the core-shell quantum dots are not coated with other shell layers outside the ZnS shell layer.

The ZnS shell layer is thicker than 9 layers, which means that the ZnS shell layer has more than 9 ZnS monomolecular layers. The thickness of the monolayer is generally calculated according to the bond length of the chemical bond, and also according to the unit cell parameters, and the thickness of one layer is about 0.3 to 0.35 nm.

Compared with a CdS shell material, the ZnS shell material has a larger energy band, can bring better results on the optical and chemical stability of quantum dots, and is also favorable for reducing the cost of the shell. The ZnS shell layer of the core-shell quantum dot provided by the invention has the thickness of more than 9 layers, and the ZnS shell layer can well isolate the contact between excitons and the environment.

Further, the thickness of the ZnS shell layer is 30 layers or less. The thickness of the shell layer is not suitable to be too thick, and the too thick shell layer can limit the application of the core-shell quantum dot in the fields of biological marking, imaging and the like.

It is worth mentioning that the transition layer may not completely cover the previous ZnS layer, and thus the aforementioned "transition layer separates the ZnS shell into a plurality of ZnS layers" does not strictly completely separate but also includes the case of partial separation. The thickness of the transition layer can be controlled by controlling the addition amount of reactants for forming the transition layer, and the thickness of the transition layer is ensured not to exceed one layer.

In some embodiments, the transition layer comprises at least one anion and/or cation in the quantum dot core, the transition layer further comprising a Zn element and/or an S element. In other words, the transition layer has at least one of the same elements as the quantum dot core, and the transition layer has at least one of the same elements as the ZnS layer. The transition layer is used for eliminating internal defects generated by increasing the thickness of the shell layer, so that the thickness of the ZnS shell layer can be increased, and the stability of the core-shell quantum dots can be improved. The materials of the transition layers may be the same or different.

Fig. 1 is a schematic diagram of a plurality of transition layers with thicknesses not exceeding 1 layer in a ZnS shell layer, when the thickness of the transition layers is thin enough, the transition layers have small influence on energy bands of the ZnS shell layer, the energy bands of the ZnS layers are basically continuous, and the transition layers have no influence on an energy level structure of the core-shell quantum dots.

Fig. 2 is a schematic view of the presence of multiple thick transition layers within the ZnS shell layer, i.e. the transition layers have a thickness of more than 1 layer. When the transition layer is thick, the transition layer has a large influence on the energy band of the ZnS shell layer, which may cause the energy band of each ZnS layer to be discontinuous, and at this time, the transition layer may have an influence on the energy level structure of the core-shell quantum dot.

Fig. 3 is an electron display mirror photograph of the CdZnSeS quantum dot prepared in example 1 of the present application, and the average particle size of the CdZnSeS quantum dot is 7.5 nm.

Fig. 4 is an electron display mirror photograph of the CdZnSeS/ZnS core-shell quantum dot obtained by coating the ZnS shell layer on the CdZnSeS quantum dot in fig. 3 by the method of embodiment 1, where the average particle size of the CdZnSeS/ZnS core-shell quantum dot is 16nm, and the thickness of the ZnS shell layer of the present application is significantly higher than that of the prior art.

In some embodiments, the quantum dot core is selected from one of CdSe, CdZnSeS, CdZnSe, CdZnS, CdSe, CdS, CdSeS; each transition layer is independently selected from one or more of: ZnSe, ZnSeS, CdZnS, CdZnSeS, CdZnSe.

In some embodiments, the quantum dot core is InP and each transition layer is independently selected from one or more of: InZnS, InZnSe, InZnSeS, ZnPSe, ZnPS.

The invention also provides a quantum dot photoelectric device which comprises the core-shell quantum dot prepared by the preparation method, or comprises the core-shell quantum dot. The quantum dot optoelectronic device may be, but is not limited to, a photo/electro display device, a photo/electro lighting device, a sensor, and the like.

Preparation of Se-S-TOP solution (Se: S ═ 3: 2): 0.64g S g and 1.58g Se were placed in a 20mL glass vial with a rubber stopper and sealed, the atmosphere was purged with inert gas, 10mL TOP was injected, and the mixture was sonicated repeatedly until Se and S were fully dissolved. The Se-S-TOP solution with other concentration can be prepared by only changing the amount of Se and S.

Preparation of 2mmol/mL S-TOP solution: 0.64g S was placed in a 20mL glass vial with a rubber stopper and sealed, the atmosphere was purged with inert gas, 10mL TOP was injected, and the mixture was sonicated repeatedly until S was sufficiently dissolved.

Preparation of 1mmol/mL selenium powder suspension (Se-SUS): selenium powder (0.8g, 10mmol, 100 mesh or 200 mesh) was dispersed in 10mL ODE and sonicated for 5 min to prepare a suspension of 0.5 mmol/mL. The preparation of selenium powder suspension liquid with other concentrations is similar to that of the suspension liquid, and the amount of the selenium powder is only required to be changed; can be used by shaking with hand.

Preparing 0.2mmol/mL cadmium oleate solution: 0.2560g of cadmium oxide (CdO), 5mmol of oleic acid and 10mL of ODE are weighed in a three-neck flask, inert gas is introduced for exhausting for 10 minutes, the temperature is raised to 280 ℃ to obtain a clear solution, and the reaction is stopped for standby.

Preparation of 0.5mmol/mL S-TOP solution: 2.5mL of S-TOP solution with a concentration of 2mmol/mL was added to 7.5mL of ODE and mixed well.

The purification method comprises the following steps: taking 10mL of stock solution into a 50mL centrifuge tube, adding 40mL of acetone, heating to about 50 ℃, then carrying out high-speed centrifugal precipitation at 8000 rpm for 3 minutes, taking out, pouring out supernatant, and dissolving precipitate into a certain amount of toluene.

[ example 1 ]

Synthesizing CdZnSeS alloy quantum dots: 4mmol of zinc acetate, 0.4mmol of cadmium acetate and 20g of ODE are put in a 100mL three-necked flask, inert gas is introduced into the flask at the temperature of 200 ℃ for exhausting for 30 minutes, the temperature is raised to 300 ℃, 1mL of Se-S-TOP solution (Se: S is 3:2) is injected into the flask, the reaction is continued for 20 minutes, the reaction is stopped, and the purified CdZnSeS alloy quantum dots are dissolved in a small amount of ODE.

Synthesizing CdZnSeS/ZnS core-shell quantum dots:

(1) putting 4mmol of zinc acetate, 4.2g of oleic acid and 10mL of ODE into a 100mL three-necked flask, introducing inert gas at 200 ℃ for exhausting for 30 minutes, raising the temperature to 300 ℃, and injecting the purified CdZnSeS alloy quantum dots;

(2) dropping 2mL S-TOP solution with concentration of 0.5mmol/mL at the speed of 6mL/h, then injecting 0.1mL Se-TBP solution with concentration of 2mmol/mL, and reacting for 5 minutes;

(3) after repeating the operation of step (2) five times, 4mL of an S-TOP solution having a concentration of 0.5mmol/mL was added dropwise at a rate of 6mL/h again to stop the reaction.

[ example 2 ]

Example 2 is different from example 1 in that in the process of synthesizing the CdZnSeS/ZnS core-shell quantum dot, the step (2) is as follows: 2mL of S-TOP solution having a concentration of 0.5mmol/mL was added dropwise at a rate of 6mL/h, and then 0.1mL of Se-S-TOP solution (Se: S ═ 1.3:2) was added thereto, followed by reaction for 5 minutes.

[ example 3 ]

Example 3 is different from example 1 in that in the process of synthesizing the CdZnSeS/ZnS core-shell quantum dot, the step (2) is as follows: 2mL of S-TOP solution having a concentration of 0.5mmol/mL was added dropwise at a rate of 6mL/h, and then 0.1mL of Se-S-TOP solution (Se: S ═ 2.5:1.5) was added thereto, followed by reaction for 5 minutes.

[ example 4 ]

Example 4 differs from example 1 in that step (2) and step (3) are replaced by the following steps during the synthesis of CdZnSeS/ZnS core-shell quantum dots: 10mL of S-TOP solution with the concentration of 0.5mmol/mL is dripped at the speed of 6mL/h, 0.1mL of cadmium oleate solution with the concentration of 0.2mmol/mL is injected into each 2mL of S-TOP solution, and finally 4mL of S-TOP solution with the concentration of 0.5mmol/mL is dripped at the speed of 6mL/h to stop the reaction.

[ example 5 ]

Example 5 is different from example 1 in that in the process of synthesizing the CdZnSeS/ZnS core-shell quantum dot, the step (2) is as follows: 2mL of S-TOP solution with a concentration of 0.5mmol/mL was added dropwise at a rate of 6mL/h, and then a mixed solution of 0.1mL of S-TOP with a concentration of 2mmol/mL and 0.1mL of cadmium oleate with a concentration of 0.2mmol/mL was added dropwise at the same rate.

[ example 6 ]

Example 6 is different from example 1 in that in the process of synthesizing the CdZnSeS/ZnS core-shell quantum dot, the step (2) is as follows: 2mL of S-TOP solution having a concentration of 0.5mmol/mL was added dropwise at a rate of 6mL/h, and then a mixed solution of 0.1mL of Se-S-TOP solution (Se: S ═ 1.3:2) and 0.1mL of cadmium oleate having a concentration of 0.2mmol/mL was added dropwise at the same rate.

[ example 7 ]

Example 7 is different from example 1 in that in the process of synthesizing the CdZnSeS/ZnS core-shell quantum dot, the step (2) is as follows: 2mL of S-TOP solution with a concentration of 0.5mmol/mL was added dropwise at a rate of 6mL/h, followed by 0.1mL of a mixed solution of Se-TBP with a concentration of 2mmol/mL and 0.1mL of cadmium oleate with a concentration of 0.2mmol/mL at the same rate.

[ example 8 ]

Synthesis of CdSe quantum dots (first exciton absorption peak 550nm, absorbance 50, particle size 3.3nm, spherical): placing CdO (0.0256g, 0.2mmol), stearic acid HSt (0.1420g, 0.5mmol) and ODE (4mL) into a 25mL three-necked bottle, stirring and introducing air (argon) for 10 minutes, heating to 280 ℃ to obtain a clear solution, cooling to 250 ℃, quickly injecting 1mL of selenium powder suspension with the concentration of 0.1mmol/mL into the three-necked bottle, controlling the reaction temperature at 250 ℃, reacting for 7 minutes, quickly injecting 0.05mL of selenium powder suspension with the concentration of 0.1mmol/mL every 2-3 minutes until the size of the quantum dot reaches a target size (in the reaction process, injecting a certain amount of reaction solution into a quartz cuvette containing 1-2mL of toluene, measuring an ultraviolet visible absorption spectrum and a fluorescence spectrum), immediately stopping heating, and dissolving the purified CdSe quantum dot into a small amount of ODE.

Synthesizing CdSe/ZnS core-shell quantum dots:

(1) putting 4mmol of zinc acetate, 4.2g of oleic acid and 10mLODE in a 100mL three-necked flask, introducing inert gas at 200 ℃ for exhausting for 30 minutes, raising the temperature to 300 ℃, and injecting CdSe quantum dot solution;

(2) dripping 2mL of S-TOP solution with the concentration of 0.5mmol/mL at the speed of 6mL/h, then injecting 0.1mL of Se-TBP solution with the concentration of 2mmol/mL, and reacting for 5 minutes;

(3) after repeating the operation (2) three times, 4mL of S-TOP solution having a concentration of 0.5mmol/mL was added dropwise at a rate of 6mL/h again to stop the reaction.

[ example 9 ]

And (3) synthesizing the CdZnSe quantum dots: weighing basic zinc carbonate (0.66g, 1.2mmol), oleic acid (4.2g, 15mmol) and 10g ODE in a 100mL three-neck flask, exhausting gas for 10 minutes by using inert gas, raising the temperature to 280 ℃ to obtain a clear solution, reducing the temperature to 200 ℃, injecting 1mL TOP, controlling the temperature to 200 ℃, injecting 0.5mL Se-ODE suspension with the concentration of 1mmol/mL, reacting for 10 minutes, then injecting 1.5mL cadmium oleate solution with the concentration of 0.2mmol/mL, directly raising the reaction temperature to 310 ℃, continuing to react for 20 minutes (in the reaction process, injecting a certain amount of reaction solution into a quartz cuvette containing 1-2mL toluene, measuring an ultraviolet visible absorption spectrum and a fluorescence spectrum), and purifying the prepared CdZnSe quantum dots and a small amount of ODE.

Synthesizing CdZnSe/ZnS core-shell quantum dots:

(1) putting 4mmol of zinc acetate, 4.2g of oleic acid and 10mL of ODE into a 100mL three-necked flask, introducing inert gas at 200 ℃ to exhaust for 30 minutes, raising the temperature to 300 ℃, and injecting CdZnSe quantum dot solution;

[ example 10 ]

And (3) synthesis of InP/ZnS core-shell quantum dots:

(1) 0.15mmol (0.043g) of indium acetate, 0.45mmol (0.1036g) of tetradecanoic acid and 10mL of ODE were weighed into a 50mL three-necked flask, the temperature was raised to 180 ℃ and the gas was discharged for 30 minutes, the temperature was lowered to room temperature, and 0.1mmol (TMS) was injected₃Raising the temperature of a mixed solution of P and 1mL of TOP to 260 ℃, reacting for 5 minutes, then lowering the temperature to 180 ℃, injecting a trioctylphosphine oxide solution, then injecting 5mL of zinc stearate-octadecene solution with the concentration of 1mmol/mL, and raising the temperature to 260 ℃;

(2) dropping 1mL of S-TOP solution with the concentration of 0.5mmol/mL at the speed of 6mL/h, then injecting 0.1mL of Se-TBP solution with the concentration of 1mmol/mL, and reacting for 5 minutes;

(3) after repeating the operation (2) twice, 4mL of S-TOP solution having a concentration of 0.5mmol/mL was added dropwise at a rate of 6mL/h again to stop the reaction.

Comparative example 1

The difference between the comparative example 1 and the example 1 is that in the process of synthesizing the CdZnSeS/ZnS core-shell quantum dot, the step (2) is as follows: 2mL of S-TOP solution with a concentration of 0.5mmol/mL was added dropwise at a rate of 6mL/h, followed by injection of 0.5mL of Se-TBP solution with a concentration of 2mmol/mL, and the reaction was carried out for 5 minutes.

Comparative example 2

Comparative example 1 is different from example 1 in that step (2) and step (3) are replaced by the following steps during the synthesis of the CdZnSeS/ZnS core-shell quantum dots: 14mL of S-TOP solution having a concentration of 0.5mmol/mL was added dropwise at a rate of 6mL/h, and the reaction was stopped after the addition.

Table 1 lists the fluorescence peak position, half-peak width, and fluorescence efficiency for each example and comparative example. The detection method of the quantum dot light efficiency comprises the following steps: the 450nm blue LED lamp is used as a backlight spectrum, the integrating sphere is used for respectively testing the blue backlight spectrum and the spectrum penetrating through the quantum dot composite material, and the quantum dot luminous efficiency is calculated by using the integral area of a spectrogram. Quantum dot light efficiency ═ 100% for (quantum dot emission peak area)/(blue backlight peak area-blue light peak area not absorbed through the quantum dot composite).

TABLE 1

Comparing the experimental results of example 1 with comparative example 1, it can be found that: when the shell layer is coated, if the addition amount of the transition layer precursor is too large, the transition layer is too thick, and the fluorescence efficiency of the prepared core-shell quantum dot is low. Comparing the experimental results of example 1 and comparative example 2, it can be found that: when the shell layer is coated, if a transition layer precursor is not added (namely, no transition layer exists in the shell layer), the prepared core-shell quantum dot has larger fluorescence half-peak width and lower fluorescence efficiency. Therefore, the transition layer with proper thickness is added in the shell layer of the core-shell quantum dot, so that the core-shell quantum dot with narrow half-peak width and high fluorescence efficiency can be obtained.

In order to further detect the stability of the core-shell quantum dots, quantum dot films were prepared from the core-shell quantum dots prepared in each example and comparative example, and the aging stability of the quantum dot films was detected (aging condition, 65 ℃/95% humidity), and the quantum dot light efficiency before and after aging was recorded in table 2.

TABLE 2

Comparing the experimental results of example 1 with comparative example 1, it can be found that: when the shell layer is coated, if the addition amount of the transition layer precursor is too large, the transition layer is too thick, and the stability of the prepared core-shell quantum dot is poor. Comparing the experimental results of example 1 and comparative example 2, it can be found that: when the shell layer is coated, if the transition layer precursor is not added (namely, no transition layer exists in the shell layer), the stability of the prepared core-shell quantum dot is poor. Therefore, the transition layer with proper thickness is added in the shell layer of the core-shell quantum dot, so that the core-shell quantum dot with good stability can be obtained.

The above embodiments are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited thereby, and any insubstantial changes and substitutions made by those skilled in the art based on the present invention are within the protection scope of the present invention.

Claims

1. The preparation method of the core-shell quantum dot is characterized by comprising the following steps:

s1, providing a quantum dot core, mixing a solution containing the quantum dot core with a zinc precursor in a reaction vessel;

s2, after the step S1 is completed, adding a sulfur precursor and a transition layer precursor to the reaction vessel in multiple portions, the sulfur precursor being added at a different time from the transition layer precursor, the sulfur precursor reacting with the zinc precursor to form a plurality of ZnS layers, the transition layer precursor reacting with at least the zinc precursor to form a plurality of transition layers, wherein the transition layers have a band gap width smaller than that of the ZnS layers, the single addition of the transition layer precursor being controlled so that the thickness of each of the transition layers does not exceed 1 layer, and the plurality of transition layers separating the plurality of ZnS layers;

s3, after the step S2 is completed, adding a sulfur precursor into the reaction vessel, reacting the zinc precursor with the sulfur precursor to generate a ZnS layer, and obtaining a system containing the core-shell quantum dots after the reaction;

in each step, the kind and the addition amount of the sulfur precursor are the same or different for each time, and the kind and the addition amount of the transition layer precursor are the same or different for each time.

2. The method for preparing the core-shell quantum dot according to claim 1, wherein the quantum dot core of the step S1 is selected from one of the following: CdZnSeS, CdZnSe, CdZnS, CdSe, CdS, CdSeS, InP.

3. The method of preparing core-shell quantum dots according to claim 1, wherein the transition layer precursor comprises a precursor of at least one anion and/or cation in the quantum dot core.

4. The method of preparing a core-shell quantum dot according to claim 3, wherein the transition layer precursor comprises one or more of: cadmium precursor, zinc precursor, selenium precursor, sulfur precursor, phosphorus precursor.

5. The method for producing core-shell quantum dots according to any of claims 1 to 4, wherein the amount of the sulfur precursor added when forming the ZnS layer in step S2 is expressed as M₁The amount of the substance added to the transition layer precursor when the transition layer adjacent to the ZnS layer is formed is recorded as M₂，M₁:M₂=(5~100):1。

6. The core-shell quantum dot is characterized by comprising a quantum dot core and a ZnS shell layer coated on the outermost side of the quantum dot core, wherein the thickness of the ZnS shell layer is larger than 9 layers, a plurality of transition layers are arranged on the ZnS shell layer at intervals along the radial direction, the transition layers divide the ZnS shell layer into a plurality of ZnS layers, the band gap width of each transition layer is smaller than that of the ZnS layer, and the thickness of each transition layer is not more than 1 layer.

7. The core-shell quantum dot of claim 6, wherein the ZnS shell layer has a thickness of 30 layers or less.

8. The core-shell quantum dot of claim 6, wherein the quantum dot core is selected from one of CdSe, CdZnSeS, CdZnSe, CdZnS, CdS, CdSeS, InP.

9. The core-shell quantum dot according to any one of claims 6 to 8, wherein the fluorescence efficiency of the core-shell quantum dot is greater than 80%.

10. A core-shell quantum dot according to any of claims 6-8, wherein each of the transition layers is the same or different, the transition layer has at least one element in common with the quantum dot core, and the transition layer has at least one element in common with the ZnS layer.

11. A quantum dot optoelectronic device, comprising: a quantum dot prepared by the method for preparing a core-shell quantum dot according to any one of claims 1 to 5, or a core-shell quantum dot according to any one of claims 6 to 10.