CN110699066A - Multi-component gradient energy level core-shell structure quantum dot and preparation method thereof - Google Patents

Abstract

The invention belongs to the field of optoelectronic materials, and discloses a multi-component gradient energy level core-shell structure quantum dot and a preparation method thereof. The multi-component gradient energy level core-shell structure quantum dots are CdS/Cd _x Zn _{1- x} S/ZnS, CdS _y Se _1-y /CdS/Cd _x Zn _1-x S/ZnS or CdSe/CdS _y Se _1‑y /CdS/Cd _x Zn _1‑x S/ZnS, 0≤x≤1, 0≤y≤1. The photoluminescence spectra of the above three quantum dots are respectively located between 400-480 nm, 480-560 nm and 560-660 nm, and the maximum crystal particle size of each quantum dot does not exceed 20 nm. The preparation method of the multi-component gradient energy level core-shell structure quantum dot of the invention is simple and low in cost, and is an effective method for preparing the core-shell structure quantum dot with strong photoluminescence intensity.

Description

A kind of multi-component gradient energy level core-shell structure quantum dot and preparation method thereof

technical field

The invention belongs to the field of optoelectronic materials, in particular to a multi-component gradient energy level core-shell structure quantum dot and a preparation method thereof.

Background technique

Due to the remarkable quantum confinement effect, nanocrystals (quantum dots) can exhibit tunable absorption spectrum and photoluminescence spectrum by adjusting the size, composition and structure, etc.

It has the advantages of narrow spectrum, strong luminescence intensity, and long fluorescence lifetime, and has shown great advantages in applications such as optoelectronic devices and biomarkers.

For example, displays using quantum dots as light-emitting layers on the market have been widely recognized. Home appliance companies such as Samsung Electronics and TCL use blue light as the backlight source, and similar LCD TVs with red quantum dots and green quantum dots as light-emitting layers have formed a fierce competition with OLED displays. At the same time, quantum dots are gradually transitioning from the laboratory to human life as biological cell markers and rapid diagnosis. However, the lifetime and stability of quantum dot-based optoelectronic devices and the stability of rapid diagnostic reagents have always been the biggest obstacles restricting quantum dot products to the market. As a kind of nanomaterials, the instability caused by the large specific surface area has always been a problem to be solved in synthetic chemistry.

SUMMARY OF THE INVENTION

In view of the above shortcomings and deficiencies of the prior art, the primary purpose of the present invention is to provide a multi-component gradient energy level core-shell structure quantum dot.

Another object of the present invention is to provide a method for preparing the above-mentioned multi-component gradient energy level core-shell structure quantum dots.

The object of the present invention is achieved through the following technical solutions:

A multi-component gradient energy level core-shell structure quantum dot, the multi-component gradient energy level core-shell structure quantum dot is CdS/Cd _x Zn _1-x S/ZnS, CdS _y Se _1-y /CdS/Cd _x Zn _1-x S/ZnS or CdSe/CdS _y Se _1-y /CdS/Cd _x Zn _1-x S/ZnS, wherein 0≤x≤1, 0≤y≤1.

Further, the photoluminescence range of the CdS/Cd _x Zn _1-x S/ZnS is 400-480 nm; the photoluminescence range of the CdS _y Se _1-y /CdS/Cd _x Zn _1-x S/ZnS is 480～560nm; the photoluminescence range of CdSe/CdSySe1 _{-y /} CdS/ _{CdxZn1 -xS} /ZnS is 560～660nm.

Further, the average particle size of the multi-component gradient energy level core-shell structure quantum dots is 2-20 nm. It can be adjusted according to the nanocrystal seed size and shell thickness.

Further, in the CdS/Cd _x Zn _1-x S/ZnS quantum dots, the grain size of the seed crystal CdS does not exceed 4 nm, the thickness of the shell layer Cd _x Zn _1-x S does not exceed 15 nm, and the thickness of ZnS does not exceed 15 nm. 4nm; in CdS _y Se _1-y /CdS/Cd _x Zn _1-x S/ZnS quantum dots, the grain size of seed crystal CdS _y Se _1-y does not exceed 5 nm, the thickness of shell CdS does not exceed 2 nm, Cd The thickness of _x Zn _1-x S does not exceed 20 nm, and the thickness of ZnS does not exceed 4 nm; in CdSe/CdS _y Se _1-y /CdS/Cd _x Zn _1-x S/ZnS quantum dots, the seed crystal CdSe grain size The thickness of the shell layer CdS _y Se _1-y does not exceed 2 nm, the thickness of CdS does not exceed 1.5 nm, the thickness of Cd _x Zn _{1- x} S does not exceed 20 nm, and the thickness of ZnS does not exceed 4 nm.

Further, in the CdS/Cd _x Zn _1-x S/ZnS quantum dots, the photoluminescence range of the seed crystal CdS is 375-435 nm; in CdS _y Se _1-y /CdS/Cd _x Zn _1-x S In the /ZnS quantum dots, the photoluminescence range of the seed crystal CdS _y Se _1-y is 430-500 nm; in the CdSe/CdS _y Se _1-y /CdS/Cd _x Zn _1-x S/ZnS quantum dots, the seed crystal The photoluminescence range of crystalline CdSe is 520-580 nm.

The preparation method of the above-mentioned multi-component gradient energy level core-shell structure quantum dots comprises the following preparation steps:

(1) The multi-component gradient energy level core-shell structure quantum dot is CdS/Cd _x Zn _1-x S/ZnS, and its preparation method is as follows:

a) Synthesis of CdS seed crystals: After mixing Cd source and organic solvent, inert gas is introduced to remove air, and after heating, S source is injected to form nanocrystalline nuclei, and the temperature is kept at 180-300 °C to promote the growth of the nuclei to the desired size. required size to obtain CdS seed nanocrystals;

b) Take CdS seed nanocrystals and put them into the reaction device, add organic solvent, pass in inert gas to remove air and water vapor, add Cd source and Zn source after heating, then drop S source to react to obtain Cd _x Zn _1-x S shell;

c) adding Zn source to the reaction system in step b), and then adding S source dropwise to react, to obtain multi-component gradient energy level core-shell structure quantum dots CdS/Cd _x Zn _1-x S/ZnS;

(2) The multi-component gradient energy level core-shell quantum dots are CdS _y Se _1-y /CdS/Cd _x Zn _1-x S/ZnS, and the preparation method is as follows:

a) Synthesis of CdS _y Se _1-y seed crystals: After mixing Cd source and organic solvent, inert gas is introduced to remove air, and after heating, S source and Se source are injected to form nanocrystalline nuclei, and the temperature is maintained at 180-300 ℃, to promote the growth of the crystal nucleus to the desired size to obtain CdS _y Se _1-y seed nanocrystals;

b) adding CdS _y Se _1-y seed nanocrystals and an organic solvent into the reaction device, feeding an inert gas to remove air and water vapor, adding a Cd source after heating, and then adding an S source to react to obtain a CdS shell;

c) After the reaction in step b), the Cd source and the Zn source are added again after heating, and then the S source is added dropwise to react to obtain a Cd _x Zn _1-x S shell layer;

d) adding Zn source to the reaction system of step c), and then adding S source dropwise to react, to obtain multi-component gradient energy level core-shell structure quantum dots CdS _y Se _1-y /CdS/Cd _x Zn _1-x S/ZnS;

(3) The multi-component gradient energy level core-shell structure quantum dot is CdSe/CdS _y Se _1-y /CdS/Cd _x Zn _1-x S/ZnS, and its preparation method is as follows:

a) Synthesis of CdSe seed crystals: Cd precursor fatty acid cadmium and organic solvent are mixed, and then inert gas is introduced to remove air, and after heating, Se source is added to form nanocrystal nuclei, and the temperature is kept at 180-300 °C to promote the nucleation. growing to a desired size to obtain CdSe seed nanocrystals;

b) Add CdSe seed nanocrystals and organic solvent into the reaction device, pass in inert gas to remove air and water vapor, add Cd source after heating, then drop S source and Se source to react to obtain CdS _y Se _1-y shell layer ;

c) After the reaction in step b), add the Cd source after heating, and then drop the S source to react to obtain a CdS shell layer;

d) After the reaction in step c), the Cd source and the Zn source are added again after heating, and then the S source is added dropwise to react to obtain a Cd _x Zn _1-x S shell layer;

e) adding Zn source to the reaction system in step d), and then adding S source dropwise to react, to obtain multi-component gradient energy level core-shell structure quantum dots CdSe/CdS _y Se _1-y /CdS/Cd _x Zn _{1 -x} S/ZnS.

Further, the Cd source described in (1) to (3) refers to fatty acid cadmium, preferably cadmium acetate, cadmium octoate, cadmium decarate, cadmium dodecanoate, cadmium myristate, cadmium hexadecate, cadmium oleate Or cadmium stearate; Described S source refers to the sulfur dissolved in organic solvent or organic phosphorus TOP, TBP, DDP, or organic mercaptan; Described Zn source refers to fatty acid zinc, preferably zinc acetate, zinc octoate, Zinc decanoate, zinc dodecanoate, zinc myristate, zinc hexadecate, zinc oleate or zinc stearate; the Se source refers to selenium dissolved in an organic solvent or organic phosphorus TOP, TBP, DDP.

Further, the organic solvent in (1) to (3) refers to octadecene, hexadecene, tetradecene, tetradecane, dodecane, decane or octane.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

(1) In the multi-component gradient energy level core-shell structure quantum dot of the present invention, the core composition is different from the shell surrounding the core composition. If the band shift of the core-shell structure is type 1, and the shell semiconductor has a larger band gap than the core material, the photon-generated electrons and holes within the nanocrystal are mainly confined within the core. Type 1 band offset as used herein refers to a core-shell electronic structure in which the conduction and valence bands of the shell semiconductor are both higher or lower than the conduction and valence bands of the core semiconductor. Therefore, core-shell nanocrystals can exhibit high photoluminescence and electroluminescence efficiencies, and can be more stable against photo-oxidation compared to "simple core" semiconductor nanocrystals comprising a single material, as long as the band gap of the core semiconductor is smaller than that of the shell semiconductor. Bandgap.

(2) In the multi-component gradient energy level core-shell structure quantum dots of the present invention, with the formation of the shell layer, the surface defects of the seed nanocrystals gradually decrease until they are small to the smallest. The photoluminescence efficiency of the core-shell quantum dots with multi-component gradient energy level gradually increases (in the same concentration, the photoluminescence spectral intensity is increasing), until the fluorescence efficiency is close to 100%.

(3) The multi-component gradient energy level core-shell structure quantum dots of the present invention can be used in organic solvents such as octadecene, hexadecene, tetradecene, tetradecane, dodecane, decane, octane, n-hexane, and tridecane. The photoluminescence quantum efficiency (PLQY) in chloromethane, dichloromethane, carbon tetrachloride, toluene and other solvents is greater than 90%, and can maintain long-term stability in the air environment.

Description of drawings

FIG. 1 is a photoluminescence spectrum of the CdS seed nanocrystals obtained in Example 1. FIG.

FIG. 2 is a schematic diagram of the energy bands of the multi-component gradient energy level core-shell structure quantum dots CdS/Cd _x Zn _1-x S/ZnS obtained in Example 1. FIG.

FIG. 3 is a graph of the morphology and size of the multi-component gradient energy level core-shell quantum dots CdS/Cd _x Zn _1-x S/ZnS obtained in Example 1 under a high magnification electron microscope.

FIG. 4 is a photoluminescence spectrum of the CdS _y Se _1-y seed nanocrystals obtained in Example 2. FIG.

5 is a schematic diagram of the energy bands of the multi-component gradient energy level core-shell quantum dots CdS _y Se _1-y /CdS/Cd _x Zn _1-x S/ZnS obtained in Example 2.

6 is a graph of the morphology and size of the multi-component gradient energy level core-shell quantum dots CdS _y Se _1-y /CdS/Cd _x Zn _1-x S/ZnS obtained in Example 2 under a high magnification electron microscope.

7 is a schematic diagram of the energy bands of the multi-component gradient energy level core-shell quantum dots CdS _y Se _1-y /CdS/Cd _x Zn _1-x S/ZnS obtained in Example 3.

8 is the absorption and fluorescence spectra of the multi-component gradient energy level core-shell quantum dots CdS _y Se _1-y /CdS/Cd _x Zn _1-x S/ZnS obtained in Example 3.

9 is a graph of the morphology and size of the multi-component gradient core-shell structure quantum dots CdSe/CdS _y Se _1-y /CdS/Cd _x Zn _{1- x} S/ZnS obtained in Example 3 under a high magnification electron microscope.

Detailed ways

The present invention will be described in further detail below with reference to the embodiments and the accompanying drawings, but the embodiments of the present invention are not limited thereto.

Example 1

A method for synthesizing multi-component gradient energy level core-shell structure quantum dots CdS/Cd _x Zn _1-x S/ZnS in this embodiment includes:

1) Synthesis of CdS seed crystals. Mix 1mmol of Cd precursor cadmium oleate and 10ml of solvent octadecene, exhaust air and fill with nitrogen, heat to 180℃～300℃, quickly inject sulfur source (1mmol elemental sulfur and dissolve in 10ml octadecene) to form nanocrystals The crystal nucleus is maintained, and the temperature is kept in the temperature range of 180°C to 300°C to promote the growth of the crystal nucleus. During the incubation period of 30 seconds to 20 minutes, samples were taken to test the absorption spectrum for judging the size of the nanocrystals. When the nuclei grow to within the range of 1.5 nanometers to 5 nanometers, the heating device is removed, the temperature is lowered to room temperature, and CdS seed nanocrystals are obtained after purification. The photoluminescence spectra of the obtained CdS seeded nanocrystals are shown in Figure 1.

2) Add 0.1 g of purified CdS seed nanocrystals and 5 ml of solvent octadecene into the reaction device, remove air and water vapor, and fill in inert gas. The CdS seed nanocrystals and the solvent in an inert gas environment were heated to 200 ° C to 320 ° C, 0.5 mmol of cadmium oleate and 1.5 mmol of zinc oleate were added, and 2 mmol of dodecanethiol was added at a drop rate of 1 ml per minute. Add dropwise into the reaction device for reaction. The addition of cadmium oleate and zinc oleate and the dropwise addition of thiol were repeated 4 times, and each reaction time was within the range of 2 hours to form multilayer gradient CdS/Cd _x Zn _1-x S quantum dots. Among them, the Cd _x Zn _1-x S is a stepwise gradient layer structure, and the Cd _x Zn _1-x S layer structure is due to the Zn element diffusing at different rates with the reaction time and temperature, resulting in Cd and Zn elements in each layer. The ratio of x is constantly changing, and the value range of x in each layer structure is 0≤x≤1.

3) adding 4mol of zinc oleate to the reaction system, then adding the sulfur source (4mmol elemental sulfur is dissolved in 2ml organophosphorus TOP) dropwise into the reaction device at a dropping speed of 1ml per minute, and then the core-shell nanocrystal CdS can be obtained. /Cd _x Zn _1-x S/ZnS. Remove the heating device, cool down to room temperature, and then purify.

The schematic diagram of the energy band of the multi-component gradient energy level core-shell structure quantum dot CdS/Cd _x Zn _1-x S/ZnS obtained in this example is shown in FIG. 2 .

Figure 3 shows the morphology and size of the multi-component gradient energy level core-shell structure quantum dots CdS/Cd _x Zn _1-x S/ZnS obtained in this example under a high magnification electron microscope.

Example 2

A method for synthesizing multi-component gradient energy level core-shell quantum dots CdS _y Se _1-y /CdS/Cd _x Zn _1-x S/ZnS in this embodiment includes:

1) Synthesis of CdS _y Se _1-y seed crystals. Mix 1mmol of Cd precursor cadmium acetate and 10ml of solvent octane, exhaust air and fill with nitrogen, heat to 180℃～300℃, quickly inject sulfur source (0.5mmol elemental sulfur dissolved in 5ml octadecene) and selenium source 0.5mmol Elemental selenium powder was dissolved in 5ml of octadecene) to form nanocrystalline nuclei. Among them, the element ratio of S and Se is 1:1. In the range of 180°C to 300°C, the temperature is kept for 30 seconds to 20 minutes for the growth of crystal nuclei. According to different reaction times and temperatures, samples were taken to test the absorption to determine the size of the nanocrystal seeds. When the growth of the nanocrystal seeds in the reaction system reaches 3 nm, the heating device is removed, the temperature is lowered to room temperature, and CdS _y Se _1-y seed nanocrystals are obtained after purification. The CdS _y Se _1-y seed nanocrystals are Due to different temperatures and reaction rates of anions, the proportion of non-seed nanocrystals is constantly changing, forming a CdS _y Se _1-y stepwise gradient layer structure. The value of y in each layer structure ranges from 0≤y≤1. The photoluminescence spectra of the obtained CdS _y Se _1-y seed nanocrystals are shown in Fig. 4 .

2) Add 0.1 g of CdS _y Se _1-y seed nanocrystals and 10 ml of organic solvent hexadecene into the reaction device, remove air and water vapor, and then fill in inert gas. The entire reaction device was heated to 200°C to 310°C, 0.5 mol of Cd precursor cadmium oleate was added, and 0.5 mmol of dodecanethiol was added dropwise into the reaction system at a rate of 1 ml per minute. After the dropwise addition, the reaction system was kept for 30 minutes to 2 hours to obtain a CdS shell layer.

3) after above-mentioned reaction finishes, further increase the temperature to within the scope of 300 ℃～320 ℃, add the cadmium oleate of 1mmol and the zinc oleate of 4mmol, then with the dripping speed of 1ml per minute, 2.5mmol dodecanethiol is added dropwise into. reaction device. Repeat the process of adding cadmium oleate and zinc oleate and dropping thiol three times, each time within the range of about 2 hours, to obtain core-shell nanocrystals CdS _y Se _1-y /CdS/Cd _x Zn _1-x S, Among them, the Cd _x Zn _1-x S is a stepwise gradient layer structure, and the Cd _x Zn _1-x S layer structure is due to the Zn element diffusing at different rates with the reaction time and temperature, resulting in Cd and Zn elements in each layer. The ratio of x is constantly changing, and the value range of x in each layer structure is 0≤x≤1.

4) adding the Zn source zinc oleate of 4mmol in the reaction system, then adding the sulfur source (4mmol elemental sulfur is dissolved in 2ml organophosphorus TOP) dropwise into the reaction device at a dripping speed of 1ml per minute and entering the reaction device, the core-shell nanocrystals can be obtained. CdS _y Se _1-y /CdS/Cd _x Zn _1-x S/ZnS. Remove the heating device, cool down to room temperature, and then purify. Remove the heating device, cool down to room temperature, and then purify.

The schematic diagram of the energy band of the multi-component gradient energy level core-shell structure quantum dot CdS _y Se _1-y /CdS/Cd _x Zn _1-x S/ZnS obtained in this example is shown in FIG. 5 .

Figure 6 shows the morphology and size of the multi-component gradient core-shell structure quantum dots CdS _y Se _1-y /CdS/Cd _x Zn _1-x S/ZnS obtained in this example under a high magnification electron microscope.

Example 3

A method for synthesizing a multi-component gradient energy level core-shell structure quantum dot CdSe/CdS _y Se _1-y /CdS/Cd _x Zn _1-x S/ZnS of this embodiment includes:

1) Synthesis of CdSe seed crystals. Mix 1mmol of Cd predecessor body cadmium octanoate and 10ml of organic solvent dodecane, exhaust air and fill with nitrogen, heat to 180℃～300℃, inject 1mmol of selenium source (1mol of selenium is dissolved in 1ml of organic phosphorus TOP), keep the temperature for 30 Seconds to 20 minutes in the temperature range of 180°C to 300°C. Then, the heating device is removed, the temperature is lowered to room temperature, and CdSe seed nanocrystals are obtained after purification.

2) Add 0.1 g of CdSe seed nanocrystals and 10 ml of organic solvent dodecane into the reaction device, remove air and water vapor, and fill in inert gas. Put 1mmol of Cd predecessor body cadmium dodecanoate and 2ml of organic solvent dodecane, exhaust air and fill in inert gas, heat to 180℃～250℃, drop in S source (0.5mmol elemental sulfur dissolved in 1ml per minute) In 1ml of organophosphorus TOP) and Se source (0.5mol selenium dissolved in 1ml of organophosphorus TOP), the mixture was added dropwise within 2 hours, and then incubated for 20 minutes to promote growth, forming CdSe/CdS _y Se _1-y core-shell structure, in which the CdS _y Se _1-y layer is constantly changing due to the different temperatures during the reaction process and the reaction rate of anions, etc., resulting in the constant change of the proportion of non-seed nanocrystals, forming a CdS _y Se _1-y stepwise gradient layer structure, each The value range of y in the layer structure is 0≤y≤1.

3) Heating the entire reaction device to 200°C to 310°C, adding 2mmol of Cd precursor cadmium oleate, and then adding 2mmol of dodecanethiol dropwise into the reaction system at a rate of 1ml per minute. After the dropwise addition, the reaction system was kept for 2 hours to form a CdSe/CdS _y Se _1-y /CdS core-shell structure.

4) after above-mentioned reaction finishes, further increase the temperature to within the scope of 300 ℃～320 ℃, add the cadmium oleate of 2mmol and the zinc oleate of 2mmol, then 4mmol dodecyl mercaptan is added dropwise to the reaction with the dripping speed of 1ml per minute device. Repeat the process of adding cadmium oleate and zinc oleate and adding thiol dropwise three times, each time within the range of about 2 hours, to obtain core-shell nanocrystals CdSe/CdS _y Se _1-y /CdS/Cd _x Zn _1-x S, among which, Cd _x Zn _1-x S is a stepwise gradient layer structure, and the Cd _x Zn _1-x S layer structure is due to the Zn element diffusing at different rates with the reaction time and temperature, resulting in each layer of Cd and The ratio of Zn elements is constantly changing, and the value of x in each layer structure is in the range of 0≤x≤1.

5) 4mmol Zn source zinc oleate is added in the reaction system, and the sulfur source (4mol elemental sulfur is dissolved in the organophosphorus TOP) is added dropwise at the dripping speed of 1ml per minute and enters the reaction device to react, and the core-shell nanocrystals can be obtained. CdSe/CdS _y Se _1-y /CdS/Cd _x Zn _1-x S/ZnS. Remove the heating device, cool down to room temperature, and then purify.

The schematic diagram of the energy band of the multi-component gradient energy level core-shell structure quantum dots CdSe/CdS _y Se _1-y /CdS/Cd _x Zn _1-x S/ZnS obtained in this example is shown in FIG. 7 . Its absorption and fluorescence spectra are shown in Figure 8. Its morphology and size under high magnification electron microscope are shown in Figure 9.

The above-mentioned embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above-mentioned embodiments, and any other changes, modifications, substitutions, combinations, The simplification should be equivalent replacement manners, which are all included in the protection scope of the present invention.

Claims (8)

1. A multi-component gradient energy level core-shell structure quantum dot is characterized in that: the multi-component gradient level core-shell structure quantum dot is CdS/Cd_xZn_1-xS/ZnS、CdS_ySe_1-y/CdS/Cd_xZn_1-xS/ZnS or CdSe/CdS_ySe_1-y/CdS/Cd_xZn_1-xS/ZnS, wherein x is more than or equal to 0 and less than or equal to 1, and y is more than or equal to 0 and less than or equal to 1.

2. The quantum dot with the multi-component gradient energy level core-shell structure according to claim 1, wherein: the CdS/Cd_xZn_1-xThe photoluminescence range of S/ZnS is 400-480 nm; CdS_ySe_1-y/CdS/Cd_xZn_1-xThe photoluminescence range of S/ZnS is 480-560 nm; CdSe/CdS_ySe_1-y/CdS/Cd_xZn_1-xThe photoluminescence range of the S/ZnS is 560-660 nm.

3. The quantum dot with the multi-component gradient energy level core-shell structure according to claim 1, wherein: the average particle size of the multi-component gradient energy level core-shell structure quantum dot is 2-20 nm.

4. The quantum dot with the multi-component gradient energy level core-shell structure according to claim 1, wherein: the CdS/Cd_xZn_1-xIn the S/ZnS quantum dot, the CdS crystal grain size of the seed crystal is not more than 4nm, and the Cd of the shell layer_xZn_1-xThe thickness of S is not more than 15nm, and the thickness of ZnS is not more than 4 nm; in CdS_ySe_1-y/CdS/Cd_xZn_1-xSeed crystal CdS in S/ZnS quantum dots_ySe_1-yCrystal grain size is not more than 5nm, shell CdS thickness is not more than 2nm, Cd_xZn_1-xThe thickness of S is not more than 20nm, and the thickness of ZnS is not more than 4 nm; in CdSe/CdS_ySe_1-y/CdS/Cd_xZn_1-xIn the S/ZnS quantum dot, the CdSe crystal grain size of the seed crystal is not more than 5nm, and CdS is in the shell layer_ySe_1-yHas a thickness of 2nm or less, CdS has a thickness of 1.5nm or less, and Cd_xZn_1-xThe thickness of S is not more than 20nm, and the thickness of ZnS is not more than 4 nm.

5. The quantum dot with the multi-component gradient energy level core-shell structure according to claim 1, wherein: the CdS/Cd_xZn_1-xIn the S/ZnS quantum dots, the photoluminescence range of the seed crystal CdS is 375-435 nm; in CdS_ySe_1-y/CdS/Cd_xZn_1-xSeed crystal CdS in S/ZnS quantum dots_ySe_1-yThe photoluminescence range of (a) is 430-500 nm; in CdSe/CdS_ySe_1-y/CdS/Cd_xZn_1-xIn the S/ZnS quantum dot, the photoluminescence range of the seed crystal CdSe is 520-580 nm.

6. The preparation method of the multi-component gradient energy level core-shell structure quantum dot in claim 1 is characterized by comprising the following preparation steps:

(1) the multi-component gradient level core-shell structure quantum dot is CdS/Cd_xZn_1-xThe preparation method of the S/ZnS comprises the following steps:

a) synthesizing CdS seed crystals: mixing a Cd source and an organic solvent, introducing inert gas to remove air, heating, injecting an S source to form a nanocrystal nucleus, keeping the temperature at 180-300 ℃, and promoting the nucleus to grow to a required size to obtain CdS seed nanocrystals;

b) putting CdS seed nanocrystals into a reaction device, adding an organic solvent, introducing inert gas to remove air and water vapor, heating, adding a Cd source and a Zn source, and dropwise adding an S source for reaction to obtain Cd_xZn_1-xS, a shell layer;

c) adding a Zn source into the reaction system in the step b), and then dropwise adding an S source for reaction to obtain the multi-component gradient level core-shell structure quantum dot CdS/Cd_xZn_1-xS/ZnS；

(2) The multi-component gradient energy level core-shell structure quantum dot is CdS_ySe_1-y/CdS/Cd_xZn_1-xThe preparation method of the S/ZnS comprises the following steps:

a) synthesis of CdS_ySe_1-ySeed crystal: mixing a Cd source and an organic solvent, introducing inert gas to remove air, heating, injecting an S source and a Se source to form a nanocrystal nucleus, keeping the temperature at 180-300 ℃, and promoting the nucleus to grow to a required size to obtain CdS_ySe_1-ySeed nanocrystals;

b) CdS (cadmium sulfide)_ySe_1-yAdding the seed nanocrystal and an organic solvent into a reaction device, introducing inert gas to remove air and water vapor, heating, adding a Cd source, and then dropwise adding an S source to react to obtain a CdS shell;

c) after the reaction in the step b) is finished, heating, adding a Cd source and a Zn source again, and then dropwise adding an S source for reaction to obtain Cd_xZn_1-xS, a shell layer;

d) adding a Zn source into the reaction system in the step c), and then dropwise adding an S source for reaction to obtain the quantum dot CdS with the multi-component gradient energy level core-shell structure_ySe_1-y/CdS/Cd_xZn_1-xS/ZnS；

(3) The multi-component gradient level core-shell structure quantum dot is CdSe/CdS_ySe_1-y/CdS/Cd_xZn_1-xThe preparation method of the S/ZnS comprises the following steps:

a) synthesizing CdSe seed crystal: mixing Cd precursor fatty acid cadmium and an organic solvent, introducing inert gas to remove air, heating, adding a Se source to form a nanocrystal nucleus, keeping the temperature at 180-300 ℃, and promoting the nucleus to grow to a required size to obtain CdSe seed nanocrystals;

b) adding CdSe seed nanocrystals and organic solvent into a reaction device, introducing inert gas to remove air and water vapor, heating, adding Cd source, dropwise adding S source and Se source, and reacting to obtain CdS_ySe_1-yA shell layer;

c) after the reaction in the step b) is finished, heating, adding a Cd source, and then dropwise adding an S source for reaction to obtain a CdS shell;

d) after the reaction in the step c) is finished, heating, adding a Cd source and a Zn source again, and then dropwise adding an S source for reaction to obtain Cd_xZn_1-xS, a shell layer;

e) adding a Zn source into the reaction system of the step d), and then dropwise adding an S source for reaction to obtain the multi-component gradient level core-shell structure quantum dot CdSe/CdS_ySe_1-y/CdS/Cd_xZn_1-xS/ZnS。

7. The preparation method of the multi-component gradient energy level core-shell structure quantum dot according to claim 6, characterized in that: (1) the Cd source in the (3) to (3) is cadmium acetate, cadmium octanoate, cadmium decate, cadmium laurate, cadmium tetradecanoate, cadmium hexadecanoate, cadmium oleate or cadmium stearate; the S source is sulfur dissolved in an organic solvent or organophosphorus TOP, TBP and DDP, or organic mercaptan; the Zn source is zinc acetate, zinc caprylate, zinc caprate, zinc laurate, zinc myristate, zinc palmitate, zinc oleate or zinc stearate; the Se source is selenium dissolved in organic solvent or organophosphorus TOP, TBP and DDP.

8. The preparation method of the multi-component gradient energy level core-shell structure quantum dot according to claim 6, characterized in that: (1) the organic solvent in (1) to (3) is octadecene, hexadecene, tetradecene, tetradecane, dodecane, decaalkane or octane.

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