CN109294585B - CdZnSeS alloy quantum dot and preparation method thereof - Google Patents
CdZnSeS alloy quantum dot and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a CdZnSeS alloy quantum dot and a preparation method thereof. The preparation method of the CdZnSeS alloy quantum dots comprises the following steps: s1, heating the zinc precursor solution to a first temperature; s2, adding an anion precursor into the zinc precursor solution, and reacting to obtain a mixed solution containing small-size particles, wherein the anion precursor is a selenium precursor, a sulfur precursor or a selenium-sulfur mixed precursor; s3, when the anion precursor added in the step S2 is the sulfur precursor, adding the cadmium precursor and the selenium precursor into the mixed solution for reaction; when the anion precursor added in the step S2 is a selenium precursor, adding a cadmium precursor and a sulfur precursor to the mixed solution to react; when the anion precursor added in step S2 is a selenium-sulfur mixed precursor, a cadmium precursor is added to the mixed solution to perform a reaction. The CdZnSeS alloy quantum dots prepared by the preparation method have the advantages of good size and appearance monodispersity, uniform components, high yield of fluorescent quantum dots and narrow half-peak width.
Description
Technical Field
The invention relates to the technical field of quantum dots, in particular to a CdZnSeS alloy quantum dot and a preparation method thereof.
Background
At present, solution semiconductor nanocrystals (solution quantum dots) with sizes within the quantum confinement range are receiving wide attention in the fields of biological imaging and marking, display, solar cells, light emitting diodes, single photon sources and the like due to the unique optical properties of the nanocrystals. In the fields of biological marking and imaging, light emitting diodes, lasers, quantum dot photovoltaic devices and the like, quantum dot research has become one of the hot spots in each field. In the fields of display (quantum dot backlight television), illumination and the like which affect the daily life of people, quantum dots have already been primarily and practically applied.
Different from the traditional binary quantum dots (such as CdSe and CdS), the energy level structure of the quantum dots can be controlled only by adjusting the size and the shape, and the energy level structure of the quantum dots can be adjusted by adjusting the proportion of components besides the size of the quantum dots with the alloy structure, so that the research on photoelectric devices is facilitated. The blue light core-shell quantum dots obtained by coating CdZnSe alloy quantum dots with ZnS are subject to the professor Lilinsong of Henan university, and the efficiency of the light-emitting diode device can reach 16.2%. Compared with binary quantum dots with single components, the stability and efficiency of the alloy quantum dots are higher, in other words, the defect states are less.
Compared with ternary alloy quantum dots (such as CdZnSe and CdZnS), the CdZnSeS of the quaternary alloy quantum dots is more complex in composition structure and more in adjustable energy band structure. So far, the traditional CdZnSeS alloy quantum dots are synthesized by injecting a selenium-sulfur precursor into a cadmium-zinc precursor at a high temperature for reaction together, or injecting a cadmium-zinc precursor into a selenium-sulfur precursor solution at a high temperature. However, as the reaction time progressed, the fluorescence half-width became gradually wider (more than 30 nm).
Disclosure of Invention
In order to overcome the defects of the prior art, the invention aims to provide the CdZnSeS alloy quantum dot and the preparation method thereof.
According to one aspect of the invention, a preparation method of CdZnSeS alloy quantum dots is provided, which comprises the following steps:
s1, heating the zinc precursor solution to a first temperature;
s2, adding an anion precursor into the zinc precursor solution, and reacting to obtain a mixed solution containing small-size particles, wherein the anion precursor is a selenium precursor, a sulfur precursor or a selenium-sulfur mixed precursor;
s3, adding cadmium precursor and selenium precursor into the mixture to react when the anion precursor added in the step S2 is sulfur precursor; when the anion precursor added in the step S2 is a selenium precursor, adding a cadmium precursor and a sulfur precursor to the mixture solution to react; when the anion precursor added in the step S2 is a selenium-sulfur mixed precursor, a cadmium precursor is added to the mixed solution to perform a reaction.
Further, the first temperature is 250 to 310 ℃.
Further, the small-sized particles have a diameter of 0.1 to 3nm, preferably 0.5 to 2 nm.
Further, in the step S2, the ratio of the amount of the substance of the anion in the anion precursor to the amount of the substance of the zinc ion in the zinc precursor is 1:6 to 1: 1.
Further, in the steps S2 and S3, the ratio of the amount of cadmium ions in the cadmium precursor to the amount of zinc ions in the zinc precursor is 1:400 to 1: 10.
Further, in the steps S2 and S3, the ratio of the amount of the selenium to the amount of the sulfur is 1:7 to 7: 1.
In the step S2, the zinc precursor is selected from zinc carboxylates having a carbon chain length of 8 to 22, and the cadmium precursor is selected from cadmium carboxylates having a carbon chain length of 1 to 22 in the step S3.
According to a preferred embodiment of the first aspect of the present invention, in the step S3, when the anion precursor added in the step S2 is a sulfur precursor, a cadmium precursor is added to the mixed solution, and then a selenium precursor is added to the mixed solution to perform a reaction, or a selenium precursor is added to the mixed solution, and then a cadmium precursor is added to the mixed solution to perform a reaction.
According to another preferred embodiment of the first aspect of the present invention, in the step S3, when the anion precursor added in the step S2 is a selenium precursor, a cadmium precursor is added to the mixed solution, and then a sulfur precursor is added to the mixed solution to perform a reaction, or a sulfur precursor is added to the mixed solution, and then a cadmium precursor is added to the mixed solution to perform a reaction.
According to another preferred embodiment of the first aspect of the present invention, in the step S3, when the anion precursor added in the step S2 is a selenium-sulfur mixed precursor, a cadmium precursor is added to the mixed solution to react for a certain period of time, and then one or more of the selenium precursor, the sulfur precursor, or the selenium-sulfur mixed precursor is added again.
And further, adding the cadmium precursor into the mixed solution, reacting for a period of time, and then adding the selenium-sulfur mixed precursor with different molar ratios of selenium-sulfur elements for multiple times.
According to another aspect of the invention, the CdZnSeS alloy quantum dot is prepared by the preparation method.
Furthermore, the wavelength of fluorescence emitted by the CdZnSeS alloy quantum dots is 500-570 nm, the half-peak width of the fluorescence is 18-25 nm, and the fluorescence quantum yield is more than 80%.
According to another aspect of the present invention, there is provided a CdZnSeS/ZnS core-shell quantum dot obtained by adding the purified CdZnSeS alloy quantum into a zinc precursor solution, and then adding a sulfur precursor for reaction.
According to another aspect of the present invention, there is provided an electronic device comprising the above CdZnSeS alloy quantum dots of the present invention.
Compared with the prior art, the invention has the beneficial effects that: the preparation method of the CdZnSeS alloy quantum dot comprises the steps of taking small-size particles formed in the initial nucleation stage as a substrate, adding a cadmium precursor for cation exchange to form cadmium-containing small-size particles, then growing the quantum dot on the basis, and gradually diffusing cadmium atoms to the whole particle in the growing process, so that the CdZnSeS alloy quantum dot with uniform components and relatively complete alloying and high quantum efficiency and narrow half-peak width is obtained; the preparation method of the CdZnSeS alloy quantum dot can reduce the self-nucleation phenomenon of the quantum dot with binary structures such as CdSe and CdS in the growth process; the preparation method of the invention can also adjust the energy band structure of the CdZnSeS alloy quantum dots by adjusting the addition amount or the addition time of different precursors.
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.
The invention provides a preparation method of CdZnSeS alloy quantum dots, which comprises the following steps:
s1, heating the zinc precursor solution to a first temperature;
s2, adding an anion precursor into the zinc precursor solution, and reacting to obtain a mixed solution containing small-size particles, wherein the anion precursor is a selenium precursor, a sulfur precursor or a selenium-sulfur mixed precursor;
s3, adding cadmium precursor and selenium precursor into the mixture to react when the anion precursor added in the step S2 is sulfur precursor; when the anion precursor added in the step S2 is a selenium precursor, adding a cadmium precursor and a sulfur precursor to the mixture to react; when the anion precursor added in the step S2 is a selenium-sulfur mixed precursor, a cadmium precursor is added to the mixed solution to perform a reaction.
In step S2, the anion precursor reacts with the zinc precursor to obtain small-sized particles, which may be ZnSe or ZnS or ZnSeS S, depending on the kind of the anion precursor. The small-sized particles refer to clusters formed by ZnSe or ZnS or ZnSeS at the initial stage of nucleation or quantum dots having a relatively small size, and the process proceeds to step S3 immediately after the small-sized particles are formed. In some embodiments, the cadmium precursor is rapidly injected in step S3, the cadmium precursor diffuses into the small-sized particles through a rapid and sufficient cation exchange reaction, and in addition, the selenium precursor or the sulfur precursor added in step S3 also participates in the growth process of the quantum dots, thereby obtaining the CdZnSeS alloy quantum dots. In other embodiments, in step S3, changing the peak position of the alloy quantum dots is achieved by changing the addition time of the cadmium precursor; and on the premise of ensuring that the adding amount of the cadmium precursor is the same, the longer the adding time interval is, the smaller the peak position is.
In the growth process of the CdZnSeS alloy quantum dots, firstly, cadmium-free small-size particles are formed, the control of the appearance and the component uniformity of the small-size particles is facilitated, then, a cadmium precursor is added for cation exchange, and cadmium atoms are gradually diffused to the whole quantum dots in the continuous coating process of the ZnSeS, so that the CdZnSeS quantum dots with uniform size appearance and uniform components are finally obtained. The method basically does not generate the self-nucleation phenomenon of the CdSe and CdS binary structure quantum dots in the whole growth process, thereby being beneficial to obtaining the CdZnSeS alloy quantum dots with uniform size, appearance and components. In addition, the band structure of the CdZnSeS alloy quantum dots can be adjusted by adjusting the time interval between the step S3 and the step S2.
In some embodiments, the first temperature is 250-310 ℃, that is, the zinc precursor solution is heated first, and then the selenium precursor, the sulfur precursor or the selenium-sulfur mixed precursor is added at a high temperature, so as to form cadmium-free small-size particles, which is beneficial to controlling the morphology and the uniformity of the components of the small-size particles.
In some embodiments, the small-sized particles have a width of 0.1 to 3 nm. The small-sized particles according to the present invention are not necessarily spheres, but may be clusters, and the width of the small-sized particles is: the maximum width of one face of the three-dimensional structure of the small-sized particles when observed by a microscope.
Preferably, the width of the small-sized particles is 0.5 to 2 nm.
In some embodiments, the zinc precursor is selected from zinc carboxylates having a carbon chain length of 8 to 22. It should be noted that, in the present invention, the zinc precursor may be a zinc carboxylate prepared in advance, or may be a zinc carboxylate formed in a solution before the reaction in step S1, for example, a zinc precursor solution is obtained by mixing basic zinc carbonate and oleic acid in a solution and reacting them. The cadmium precursor is selected from cadmium carboxylate with the carbon chain length of 1-22.
The types of sulfur precursors, selenium precursors, and selenium-sulfur mixed precursors and methods of preparation are within the skill of the art and will not be described in detail herein.
In some embodiments, in step S2, the ratio of the amount of species of anions in the anion precursor to zinc ions in the zinc precursor is 1:6 to 1: 1.
In some embodiments, the ratio of the amount of species of cadmium ions in the cadmium precursor to zinc ions in the zinc precursor is 1:400 to 1:10 in steps S2 and S3. The cadmium ion and the zinc ion referred to herein mean: cadmium ions and zinc ions are added in the whole preparation process.
In some embodiments, the ratio of the amount of the selenium to the sulfur added in steps S2 and S3 is 1:7 to 7: 1. The elemental selenium and elemental sulfur referred to herein are: in the whole preparation process, selenium and sulfur are added.
In some embodiments, in step S3, when the anion precursor added in step S2 is a sulfur precursor, the cadmium precursor is added to the mixed solution and then the selenium precursor is added to react, or the selenium precursor is added to the mixed solution and then the cadmium precursor is added to react. Namely, when the quantum dots continue to grow on the basis of the small-size particle ZnS, the cadmium precursor and the selenium precursor are added separately, so that the self-nucleation phenomenon of the CdSe binary quantum dots can be further reduced, and meanwhile, the added cadmium precursor and zinc atoms in the ZnS perform cation exchange, so that the size and appearance monodispersity and the component uniformity of the obtained CdZnSeS alloy quantum dots are improved.
In some embodiments, in step S3, when the anion precursor added in step S2 is a selenium precursor, a cadmium precursor is added to the mixed solution and then a sulfur precursor is added to the mixed solution for reaction, or a sulfur precursor is added to the mixed solution and then a cadmium precursor is added to the mixed solution for reaction. Namely, when the quantum dots continue to grow on the basis of the small-size particle ZnSe, the cadmium precursor and the sulfur precursor are added separately, so that the self-nucleation phenomenon of the CdS binary quantum dots is further reduced, and meanwhile, the added cadmium precursor and zinc atoms in the ZnSe perform cation exchange, so that the size, appearance and monodispersity of the obtained CdZnSeS alloy quantum dots and the uniformity of the components are improved.
In some embodiments, in step S3, when the anion precursor added in step S2 is a selenium-sulfur mixed precursor, a cadmium precursor is added to the mixed solution to react for a certain period of time, and then one or more of a selenium precursor, a sulfur precursor, or a selenium-sulfur mixed precursor is added again, or selenium-sulfur mixed precursors with different molar ratios of selenium-sulfur elements are added in multiple times. Namely, when quantum dots continue to grow on the basis of small-size particle ZnSeS, cadmium precursor is added firstly to react for a period of time to obtain CdZnSeS cluster, then selenium precursor, sulfur precursor or selenium-sulfur mixed precursor are added to further coat the ZnSeS, and cadmium atoms are continuously diffused to a shell layer in the coating process, so that the size and appearance monodispersity and the component uniformity of the CdZnSeS alloy quantum dots are improved, and the fluorescence peak position of the CdZnSeS alloy quantum dots is adjusted.
The CdZnSeS alloy quantum dot prepared by the method has the advantages that the emitted fluorescence wavelength is 500-570 nm, the fluorescence half-peak width is 18-25 nm, and the fluorescence quantum yield is more than 80%.
In addition, after the CdZnSeS alloy quantum dot prepared by the method is purified, a ZnS shell layer can be continuously coated to improve the stability of the quantum dot.
The method for coating the ZnS shell layer outside the CdZnSeS alloy quantum dots comprises the following steps: adding the purified CdZnSeS alloy quantum dots into a zinc precursor solution, and then adding a sulfur precursor for reaction to obtain the catalyst.
The invention also provides an electronic device comprising the CdZnSeS alloy quantum dot. The electronic device may be, but is not limited to, an electroluminescent diode (QLED), an Organic Light Emitting Diode (OLED), a Light Emitting Diode (LED), various displays such as a Liquid Crystal Display (LCD), a solar cell, a sensor, a hybrid compound, a biomarker, or an imaging sensor, a security ink, various lighting devices, and the like.
Preparation of a reaction precursor:
preparation of 2mmol/mL S-TOP solution: 0.64g S was weighed, sealed in a 20mL glass vial with a rubber stopper, and the atmosphere was purged with inert gas. 10mL of TOP was injected and the mixture was sonicated repeatedly until S was fully dissolved.
Preparation of 0.5mmol/mL S-TOP solution: 2.5mL of 2mmol/mL S-TOP solution was taken and mixed well with 7.5mL ODE.
Preparation of 2mmol/mL Se-TOP solution: 1.58g Se was weighed, placed in a 20mL glass vial with a rubber stopper, sealed, purged of air with inert gas, and injected with 10mL TOP, and the mixture was sonicated repeatedly until Se was sufficiently dissolved.
Preparation of Se-S-TOP solution (Se: S ═ 2.5: 1.5): 0.48g S g Se and 1.97g Se are weighed and placed in a glass bottle with a 20mL rubber plug for sealing, the air in the glass bottle is exhausted by inert gas, 10mL TOP is injected, the mixture is repeatedly oscillated and ultrasonically treated until the Se and the S are fully dissolved, and the preparation of other concentrations only needs to change the amount of the Se and the S.
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.
The quantum dot purification method comprises the following steps: 10mL of the stock solution was put into a 50mL centrifuge tube, 40mL of acetone was added, the mixture was heated to about 50 ℃ and then centrifuged at 8000 rpm for 3 minutes, and the supernatant was removed. The precipitate was dissolved in a certain amount of toluene.
[ example 1 ]
Synthesis of CdZnSeS quantum dots: taking 0.66g of basic zinc carbonate (1.2mmol), 4.2g of oleic acid and 10g of ODE in a 100mL three-necked flask, introducing inert gas, exhausting for 10 minutes, and raising the temperature to 300 ℃ to obtain a clear solution; the temperature was then lowered to 250 ℃ and 1mL of Se-S-TOP solution (Se: S ═ 2.5:1.5) was injected, followed by 2mL of 0.2mmol/mL cadmium oleate solution injected rapidly, the temperature was raised to 300 ℃ and the reaction was continued for 20min, stopping the reaction.
[ example 2 ]
Synthesizing CdZnSeS/ZnS quantum dots: taking 0.66g of basic zinc carbonate (1.2mmol), 4.2g of oleic acid and 10g of ODE in a 100mL three-necked flask, introducing inert gas, exhausting for 10 minutes, and raising the temperature to 300 ℃ to obtain a clear solution; the temperature was lowered to 250 ℃, 1mL Se-S-TOP solution was injected (Se: S ═ 2.5:1.5), followed by 2mL 0.2mmol/mL cadmium oleate solution injected rapidly, the temperature was raised to 300 ℃, the reaction was continued for 20 minutes, stopped, brought to room temperature, purified and dissolved in 1mL ODE.
Weighing basic zinc carbonate (0.66g, 1.2mmol), 2.8g oleic acid and 5g ODE in a 100mL three-necked flask, and exhausting for 10 minutes by using inert gas; raising the temperature to 300 ℃ to obtain a clear solution; injecting the purified CdZnSeS quantum dots, dropwise adding 10mL of 0.5mmol/mL S-TOP solution at the speed of 5mL/h, and stopping the reaction after the dropwise adding is finished.
[ example 3 ]
Synthesis of CdZnSeS quantum dots: taking 0.66g of basic zinc carbonate (1.2mmol), 4.2g of oleic acid and 10g of ODE in a 100mL three-necked flask, introducing inert gas, exhausting for 10 minutes, and raising the temperature to 300 ℃ to obtain a clear solution; the temperature was lowered to 250 ℃, 1mL of Se-S-TOP solution (Se: S ═ 2.5:1.5) was injected and the reaction was allowed to react for 1 minute, 2mL of 0.2mmol/mL cadmium oleate solution was injected, the temperature was raised to 300 ℃, the reaction was continued for 20 minutes, and the reaction was stopped.
[ example 4 ]
Synthesis of CdZnSeS quantum dots: taking 0.66g of basic zinc carbonate (1.2mmol), 4.2g of oleic acid and 10g of ODE in a 100mL three-necked flask, introducing inert gas, exhausting for 10 minutes, and raising the temperature to 300 ℃ to obtain a clear solution; the temperature was lowered to 250 ℃ and 1mL Se-S-TOP solution was injected (Se: S ═ 2.5:1.5), followed by 2mL of 0.2mmol/mL cadmium oleate solution injected rapidly for 1min, 0.25mL of 2mmol/mL Se-TOP solution was injected, the temperature was raised to 300 ℃ and the reaction was continued for 20min, stopping the reaction.
[ example 5 ]
Synthesis of CdZnSeS quantum dots: taking 0.66g of basic zinc carbonate (1.2mmol), 4.2g of oleic acid and 10g of ODE in a 100mL three-necked flask, introducing inert gas, exhausting for 10 minutes, and raising the temperature to 300 ℃ to obtain a clear solution; the temperature was lowered to 250 ℃ and 1mL of Se-S-TOP solution (Se: S ═ 2.5:1.5) was injected followed by 2mL of 0.2mmol/mL cadmium oleate solution injected rapidly for 1min of reaction and 0.25mL of 2mmol/mL S-TOP solution injected, the temperature was raised to 300 ℃ and the reaction was continued for 20min and stopped.
[ example 6 ]
Synthesis of CdZnSeS quantum dots: taking 0.66g of basic zinc carbonate (1.2mmol), 4.2g of oleic acid and 10g of ODE in a 100mL three-necked flask, introducing inert gas, exhausting for 10 minutes, and raising the temperature to 300 ℃ to obtain a clear solution; the temperature was lowered to 250 ℃ and 1mL of Se-S-TOP solution (Se: S ═ 2.5:1.5) was injected followed by 2mL of 0.2mmol/mL cadmium oleate solution injected rapidly for 1min, 0.25mL of Se-S-TOP solution of the same concentration was injected, the temperature was raised to 300 ℃ and the reaction was continued for 20min, stopping the reaction.
[ example 7 ]
Synthesis of CdZnSeS quantum dots: taking 0.66g of basic zinc carbonate (1.2mmol), 4.2g of oleic acid and 10g of ODE in a 100mL three-necked flask, introducing inert gas, exhausting for 10 minutes, and raising the temperature to 300 ℃ to obtain a clear solution; the temperature was lowered to 250 ℃ and 1mL of a 2mmol/mL Se-TOP solution was injected followed by a rapid injection of 2mL of a 0.2mmol/mL cadmium oleate solution followed by a rapid injection of 1mL of a 2mmol/mL S-TOP solution, the temperature was raised to 300 ℃ and the reaction was continued for 20 minutes, stopping the reaction.
[ example 8 ]
Synthesis of CdZnSeS quantum dots: taking 0.66g of basic zinc carbonate (1.2mmol), 4.2g of oleic acid and 10g of ODE in a 100mL three-necked flask, introducing inert gas, exhausting for 10 minutes, and raising the temperature to 300 ℃ to obtain a clear solution; the temperature was lowered to 250 ℃ and 1mL of a 2mmol/mL S-TOP solution was injected followed by a rapid injection of 2mL of a 0.2mmol/mL cadmium oleate solution followed by a rapid injection of 1mL of a 2mmol/mL Se-TOP solution, the temperature was raised to 300 ℃ and the reaction was continued for 20 minutes, stopping the reaction.
[ example 9 ]
Synthesis of CdZnSeS quantum dots: taking 0.66g of basic zinc carbonate (1.2mmol), 4.2g of oleic acid and 10g of ODE in a 100mL three-necked flask, introducing inert gas, exhausting for 10 minutes, and raising the temperature to 300 ℃ to obtain a clear solution; the temperature was lowered to 250 ℃ and 1mL of a 2mmol/mL Se-TOP solution was injected followed by a rapid injection of 1mL of a 2mmol/mL S-TOP solution followed by a rapid injection of 2mL of a 0.2mmol/mL cadmium oleate solution, the temperature was raised to 300 ℃ and the reaction was continued for 20 minutes, stopping the reaction.
[ example 10 ]
Synthesis of CdZnSeS quantum dots: taking 0.66g of basic zinc carbonate (1.2mmol), 4.2g of oleic acid and 10g of ODE in a 100mL three-necked flask, introducing inert gas, exhausting for 10 minutes, and raising the temperature to 300 ℃ to obtain a clear solution; the temperature was then lowered to 250 ℃ and 1mL of Se-S-TOP solution (Se: S ═ 2.5:1.5) was injected, followed by 1mL of 0.2mmol/mL cadmium oleate solution injected rapidly, the temperature was raised to 300 ℃ and the reaction was continued for 20min, stopping the reaction.
[ example 11 ]
Synthesis of CdZnSeS quantum dots: taking 0.66g of basic zinc carbonate (1.2mmol), 4.2g of oleic acid and 10g of ODE in a 100mL three-necked flask, introducing inert gas, exhausting for 10 minutes, and raising the temperature to 300 ℃ to obtain a clear solution; the temperature was then lowered to 250 ℃ and 2mL of Se-S-TOP solution (Se: S ═ 2.5:1.5) was injected, followed by 1mL of 0.2mmol/mL cadmium oleate solution injected rapidly, the temperature was raised to 300 ℃ and the reaction was continued for 20min, stopping the reaction.
[ example 12 ]
Synthesis of CdZnSeS quantum dots: taking 0.66g of basic zinc carbonate (1.2mmol), 4.2g of oleic acid and 10g of ODE in a 100mL three-necked flask, introducing inert gas, exhausting for 10 minutes, and raising the temperature to 300 ℃ to obtain a clear solution; the temperature was then lowered to 250 ℃ and 1mL of Se-S-TOP solution (Se: S ═ 1.3:2) was injected, followed by 1mL of 0.2mmol/mL cadmium oleate solution injected rapidly, the temperature was raised to 300 ℃ and the reaction was continued for 20min, stopping the reaction.
[ example 13 ]
Synthesis of CdZnSeS quantum dots: taking 0.66g of basic zinc carbonate (1.2mmol), 4.2g of oleic acid and 10g of ODE in a 100mL three-necked flask, introducing inert gas, exhausting for 10 minutes, and raising the temperature to 300 ℃ to obtain a clear solution; then, the temperature was lowered to 250 ℃, 0.5mL of Se-S-TOP solution (Se: S ═ 3.5:0.5) was injected, followed by rapid injection of 2mL of 0.2mmol/mL cadmium oleate solution, the temperature was raised to 300 ℃, reaction was carried out for 5min, 0.5mL of Se-S-TOP solution (Se: S ═ 2.5:1.5) was injected again, reaction was carried out for 5min, 0.5mL of Se-S-TOP solution (Se: S ═ 1.5:2.5) was injected again, reaction was carried out for 10min, and the reaction was stopped.
Comparative example 1
Adding 8mmol of zinc acetate, 0.2mmol of selenium powder, 5.2mL of oleic acid and 15mL of octadecene into a three-neck flask with a condenser and a thermometer, vacuumizing for 20min at 150 ℃, charging nitrogen, heating to 280 ℃, then dropwise adding 0.1mmol/mL of cadmium oleate 1-octadecene solution, monitoring the wavelength of a fluorescence emission peak of a product, when the wavelength of the light emission peak is reached, continuously dropwise adding 3mL of trioctylamine solution with the concentration of 4 mol/L1-octanethiol, and controlling the dropwise adding to be finished within 50 min. The reaction was continued at 280 ℃ for 30 min. And cooling to room temperature.
Comparative example 2
0.4mmol of CdO, 4mmol of zinc acetate, 17.6mmol of oleic acid and 20mL of octadecene were weighed into a 100mL three-necked flask. Introducing inert gas at 150 ℃ for exhausting for 30 minutes, and raising the temperature to 300 ℃ to obtain a clear solution; then, the temperature was raised to 310 ℃ and 1mL of Se-S-TOP solution (Se: S ═ 2.5:1.5) was injected, and the reaction was continued for 20min to stop.
Comparative example 3
0.4mmol of CdO, 4mmol of zinc acetate, 17.6mmol of oleic acid and 20mL of octadecene were weighed into a 100mL three-necked flask. Introducing inert gas at 150 ℃ for exhausting for 30 minutes, and raising the temperature to 300 ℃ to obtain a clear solution; then, the temperature was raised to 310 ℃ and 1mL of Se-S-TOP solution (Se: S ═ 2.5:1.5) was injected, and the reaction was continued for 20min, and the reaction was stopped and purified.
Weighing basic zinc carbonate (0.66g, 1.2mmol), 2.8g oleic acid and 5g ODE in a 100mL three-necked flask, and exhausting for 10 minutes by using inert gas; raising the temperature to 300 ℃ to obtain a clear solution; injecting the purified CdZnSeS quantum dots, dropwise adding 10mL of 0.5mmol/mL S-TOP solution at the speed of 5mL/h, and stopping the reaction after the dropwise adding is finished.
Comparative example 4
0.8mmol of CdO, 8mmol of zinc acetate, 35.2mmol of oleic acid and 10mL of octadecene were weighed into a 100mL three-necked flask. Introducing inert gas at 150 ℃ for exhausting for 30 minutes, raising the temperature to 300 ℃ to obtain a clear solution, and cooling to 200 ℃ for later use;
weighing 2.5mmol Se powder, 1.5mmol S powder, 15mL ODE and 100mL three-neck flask, introducing inert gas, exhausting for 10min, and raising the temperature to 280 ℃.5mL of the above cation precursor solution was injected and reacted for 20min, and the reaction was stopped.
The quantum dots finally obtained in the above examples and comparative examples were detected, and the emission peak and half-peak width thereof were measured by a fluorescence emission spectrometer, and the fluorescence efficiency thereof was measured by an integrating sphere, and the detection results are shown in table 1.
TABLE 1
As can be seen from the data of examples 1 to 13 and comparative examples 1 to 4 in Table 1, various CdZnSeS quantum dots or CdZnSeS/ZnS quantum dots obtained by the preparation method of the present invention have narrower half-peak widths and higher fluorescence efficiencies.
It is worth noting that in comparative example 1 (prior art), the temperature is raised after the selenium source and the zinc source are uniformly mixed, and the ZnSe nano particles are obtained firstly, the nano particles obtained by the growth method have uneven size and wider half-peak width; then slowly dripping cadmium salt to perform partial cation exchange to obtain ZnSe/CdZnSe core-shell quantum dots, and then continuously and slowly dripping a sulfur source or a mixed solution of the sulfur source and a zinc source to coat ZnS. Thus the structure obtained by the preparation method of comparative example 1 is actually a ZnSe/CdZnSe/ZnS core-shell quantum dot, not a CdZnSeS alloy quantum dot. In addition, although the cadmium source was slowly added to carry out the cation exchange in comparative example 1, the cadmium atomic composition of the quantum dots obtained as a result of this exchange was not uniform, some quantum dots were more numerous and some quantum dots were less numerous, so that it was observed that the obtained quantum dots had a wide half-peak width. Moreover, from the band angle, the energy band of ZnSe is wider than that of CdZnSe, which is not favorable for protecting excitons.
The preparation method of the CdZnSeS alloy quantum dot comprises the steps of taking small-size particles formed in the initial nucleation stage as a substrate, adding a cadmium precursor for cation exchange to form cadmium-containing small-size particles, then growing the quantum dot on the basis, and gradually diffusing cadmium atoms to the whole particle in the growing process, so that the CdZnSeS alloy quantum dot with uniform components and relatively complete alloying and high quantum efficiency and narrow half-peak width is obtained; according to the preparation method disclosed by the invention, the energy band structure of the CdZnSeS alloy quantum dot can be adjusted by adjusting the addition amount or the addition time of different precursors.
In order to further test the stability of the quantum dots of the present invention, quantum dot films were prepared from the quantum dots prepared in example 2 and comparative example 3, respectively, and the aging stability of the quantum dot films was tested, and the test results (60 ℃, 50mA under high temperature and high light intensity) are shown in table 2.
TABLE 2
| Quantum dot luminous efficiency (initial) | Quantum dot luminous efficiency (aging 500h) | |
| Example 2 | 60％ | 55％ |
| Comparative example 3 | 45％ | 36％ |
The data in table 2 show that the quantum dot light efficiency of the quantum dot prepared in example 2 is reduced by 5% after high-temperature high-light-intensity aging for 500 hours, and the quantum dot light efficiency of the quantum dot prepared in comparative example 3 is reduced by 9% after high-temperature high-light-intensity aging for 500 hours, which indicates that the alloy quantum dot prepared by the preparation method of the CdZnSeS alloy quantum dot has high stability, and has a great promotion effect on the application of the alloy quantum dot and the research on the intrinsic optical properties.
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 (14)
1. A preparation method of CdZnSeS alloy quantum dots is characterized by comprising the following steps:
s1, heating the zinc precursor solution to a first temperature;
s2, adding an anion precursor into the zinc precursor solution, and reacting to obtain a mixed solution containing small-size particles with the diameter of 0.1-3 nm, wherein the anion precursor is a selenium precursor, a sulfur precursor or a selenium-sulfur mixed precursor;
s3, when the anion precursor added in the step S2 is a sulfur precursor, adding a cadmium precursor and a selenium precursor to the mixed solution to react; when the anion precursor added in the step S2 is a selenium precursor, adding a cadmium precursor and a sulfur precursor to the mixed solution to react; when the anion precursor added in the step S2 is a selenium-sulfur mixed precursor, a cadmium precursor is added to the mixed solution to perform a reaction.
2. The preparation method of the CdZnSeS alloy quantum dot as claimed in claim 1, wherein the first temperature is 250-310 ℃.
3. The preparation method of the CdZnSeS alloy quantum dot as claimed in claim 1, wherein the diameter of the small-sized particle is 0.5-2 nm.
4. The method for preparing CdZnSeS alloy quantum dots according to claim 1, wherein in step S2, the ratio of the amount of substance of anions in the anion precursor to the amount of substance of zinc ions in the zinc precursor is 1:6 to 1: 1.
5. The method for preparing CdZnSeS alloy quantum dots according to claim 1, wherein in the steps S2 and S3, the ratio of the amount of the cadmium ions in the cadmium precursor to the amount of the zinc ions in the zinc precursor is 1:400 to 1: 10.
6. The method for preparing CdZnSeS alloy quantum dots according to claim 1, wherein in steps S2 and S3, the ratio of the amount of the selenium to the amount of the sulfur is 1:7 to 7: 1.
7. The preparation method of the CdZnSeS alloy quantum dot as claimed in claim 1, wherein in step S2, the zinc precursor is selected from zinc carboxylates with carbon chain length of 8-22, and in step S3, the cadmium precursor is selected from cadmium carboxylates with carbon chain length of 1-22.
8. The method for preparing the CdZnSeS alloy quantum dot as claimed in any one of claims 1 to 7, wherein in the step S3, when the anion precursor added in the step S2 is a sulfur precursor, a cadmium precursor is added to the mixture and then a selenium precursor is added to the mixture to perform the reaction, or a selenium precursor is added to the mixture and then a cadmium precursor is added to perform the reaction.
9. The method for preparing CdZnSeS alloy quantum dots according to any one of claims 1 to 7, wherein in step S3, when the anion precursor added in step S2 is selenium precursor, cadmium precursor is added to the mixture and then sulfur precursor is added to the mixture for reaction, or sulfur precursor is added to the mixture and then cadmium precursor is added to the mixture for reaction.
10. The method for preparing the CdZnSeS alloy quantum dot as claimed in any one of claims 1 to 7, wherein in the step S3, when the anion precursor added in the step S2 is a selenium-sulfur mixed precursor, the cadmium precursor is added to the mixed solution to react for a certain period of time, and then one or more of the selenium precursor, the sulfur precursor or the selenium-sulfur mixed precursor is added again.
11. The method for preparing the CdZnSeS alloy quantum dot as claimed in claim 10, wherein the cadmium precursor is added to the mixture solution and reacted for a period of time, and then the selenium-sulfur mixture precursor with different molar ratios of elemental selenium and sulfur is added in multiple times.
12. A CdZnSeS alloy quantum dot, wherein the CdZnSeS alloy quantum dot is prepared by the method of any one of claims 1 to 11.
13. The CdZnSeS alloy quantum dot of claim 12, wherein the CdZnSeS alloy quantum dot emits fluorescence with a wavelength of 500-570 nm, a half-peak width of 18-25 nm and a fluorescence quantum yield of more than 80%.
14. An electronic device, characterized in that the electronic device comprises a quantum dot according to any of claims 12-13.
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