CN111303882B - Cadmium-free quantum dot and preparation method thereof - Google Patents

Cadmium-free quantum dot and preparation method thereof Download PDF

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CN111303882B
CN111303882B CN201811508090.XA CN201811508090A CN111303882B CN 111303882 B CN111303882 B CN 111303882B CN 201811508090 A CN201811508090 A CN 201811508090A CN 111303882 B CN111303882 B CN 111303882B
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quantum dot
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cadmium
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CN111303882A (en
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高静
余文华
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Najing Technology Corp Ltd
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    • C09K11/88—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing selenium, tellurium or unspecified chalcogen elements
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Abstract

The invention provides a cadmium-free quantum dot and a preparation method thereof. The preparation method comprises the following steps: s1, mixing a first precursor, a first ligand and a solvent, and heating to a first temperature to obtain a first mixed solution; s2, mixing a second precursor, a second ligand and a solvent, and adding the first mixed solution at a second temperature to prepare a second mixed solution; s3, heating the second mixed solution to a third temperature for a first time period, and keeping the temperature constant for a second time period at the third temperature; and S4, heating the third time to a fourth temperature, and keeping constant temperature at the fourth temperature for a fourth time to obtain the quantum dot core. According to the method, the nucleation and growth uniformity of the quantum dots are controlled by a multi-gradient heating technology, so that the half-peak width of the cadmium-free quantum dot nuclei and the half-peak width of the quantum dots are reduced, and the luminous efficiency of the cadmium-free quantum dots is improved.

Description

Cadmium-free quantum dot and preparation method thereof
Technical Field
The invention relates to the technical field of semiconductors, in particular to a cadmium-free quantum dot and a preparation method thereof.
Background
The quantum dot is also called as semiconductor nanocrystalline, and has the advantages of adjustable luminescence wavelength, high luminescence efficiency, good stability and the like, thereby having wide application in the fields of display, illumination, biology, solar cells and the like. In recent years, research on II-VI group quantum dot materials containing CdSe, cdS and the like has greatly progressed, and the performances of luminous efficiency, half-peak width, stability and the like are greatly improved, and the material is applied to the fields of display, biology and the like. However, since Cd is a toxic heavy metal, strict regulations on Cd content in goods entering the market of the Cd are all made by the european union "regulations on registration, evaluation, licensing and limitation of chemicals" (abbreviated as "REACH"), and the wide application of the Cd is limited to a certain extent, so that the research on environment-friendly cadmium-free quantum dots has never been abandoned. How to improve the performance of cadmium-free quantum dots has been the key point and difficulty of research. Among the cadmium-free quantum dots, III-V InP-based quantum dots become hot spots for research, and are expected to replace Cd-containing quantum dots.
In recent years, the development of cadmium-free quantum dots has also advanced greatly, and commercial applications are now available. However, the performance ratio of the quantum dot containing cadmium is different from that of the quantum dot containing cadmium, and the quantum dot containing cadmium is mainly characterized by wide half-peak width, low luminous efficiency and the like. The current preparation methods of quantum dot cores mainly comprise two types: one is a hot injection method and one is a heating method. The thermal injection method is to heat one precursor to a certain temperature and then inject the other precursor at a high temperature to generate quantum dot nuclei. This approach can separate nucleation and growth but is not easily scaled up. The heating method is to mix two or more reaction precursors and then directly heat the mixture to a set temperature to generate quantum dot nuclei. The method is simple to operate, is suitable for large-scale production, but can not separate nucleation and growth, and generally can only obtain high-quality quantum dots at a relatively proper rate of nucleation and growth. Therefore, a new preparation technology is developed, the half-peak width of the cadmium-free quantum dot is reduced, and the fluorescent efficiency of the cadmium-free quantum dot is improved.
Disclosure of Invention
The invention mainly aims to provide a cadmium-free quantum dot and a preparation method thereof, which are used for solving the problems of low luminous efficiency and large luminous half-peak width of the cadmium-free quantum dot in the prior art.
In order to achieve the above object, according to one aspect of the present invention, there is provided a method for preparing cadmium-free quantum dots, comprising the steps of: s1, mixing a first precursor, a first ligand and a solvent, and heating to a first temperature to obtain a first mixed solution; s2, mixing a second precursor, a second ligand and a solvent, and adding the first mixed solution at a second temperature to prepare a second mixed solution; s3, heating the second mixed solution to a third temperature for a first time period, and keeping the temperature at the third temperature for a second time period; and S4, heating the third time to a fourth temperature, and keeping the temperature constant at the fourth temperature for a fourth time to obtain the quantum dot core.
Further, the heating rate of the heating reaction in the step S3 and the step S4 is independently selected from 1 to 150 ℃/min, preferably 5 to 100 ℃/min.
Further, the third temperature and the fourth temperature are 30 to 310 ℃, respectively, and the fourth temperature is higher than the third temperature.
Further, the second time period and the fourth time period are each 1min to 2h.
Further, the heating process in the above step S3 may be a gradient heating process, preferably a multi-gradient heating process.
Further, the step S3 includes the following steps: s31, heating the second mixed solution to a fifth temperature for a fifth time period, and keeping the temperature at the fifth temperature for a sixth time period; s32, repeating the operation of the step S31 for one to three times to obtain the second mixed solution with the final temperature of the third temperature; wherein, the heating rate of the heating reaction in the step S31 is the same as or different from that in the step S32, and the time length of the constant temperature reaction in the step S31 is the same as or different from that in the step S32.
Further, the third temperature is not higher than 150 ℃, the heating rate of the heating reaction in the step S3 is independently selected from 5 to 75 ℃/min, and the heating rate of the heating reaction in the step S4 is selected from 50 to 100 ℃/min.
Further, the molar ratio of the first precursor to the second precursor is 50:1 to 1:50, preferably 10:1 to 1:10.
Further, the first precursor is a group iii element precursor, and the second precursor is a group v element precursor.
Further, the first precursor may be selected from one or more of Zn, mg, ca, sr, al, zr, fe, sc, ti, cr, si and Ni element precursors.
Further, after the step S4, the preparation method further includes a step S5, where the quantum dot core coats the shell layer.
According to another aspect of the invention, a cadmium-free quantum dot is provided and is prepared by the preparation method.
According to another aspect of the invention, a photoelectric device is provided, which comprises the cadmium-free quantum dot prepared by the preparation method.
By applying the technical scheme of the invention, the preparation method of the cadmium-free quantum dot is provided, the nucleation and growth uniformity of the quantum dot is controlled by using a multi-gradient heating technology, the half-peak width of the cadmium-free quantum dot core and the half-peak width of the quantum dot are reduced, and the luminous efficiency of the cadmium-free quantum dot is improved.
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The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention. In the drawings:
FIG. 1 shows a schematic flow chart of a method for preparing cadmium-free quantum dots;
fig. 2 shows the uv-vis absorption spectrum of InP quantum dot cores in example 1 of the present application.
Detailed Description
It should be noted that, without conflict, the embodiments of the present invention and features of the embodiments may be combined with each other. The invention will be described in detail below with reference to the drawings in connection with embodiments.
In order that those skilled in the art will better understand the present invention, a technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in which it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.
It should be noted that the terms "first," "second," and the like in the description and the claims of the present invention and the above figures are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate in order to describe the embodiments of the invention herein. 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.
As described in the background art, the cadmium-free quantum dots in the prior art have lower luminous efficiency and larger luminous half-width. In order to solve the technical problems, the invention provides a preparation method of cadmium-free quantum dots, as shown in fig. 1, comprising the following steps: s1, mixing a first precursor, a first ligand and a solvent, and heating to a first temperature to obtain a first mixed solution; s2, mixing a second precursor, a second ligand and a solvent, and adding the first mixed solution at a second temperature to prepare a second mixed solution; s3, heating the second mixed solution to a third temperature for a first time period, and keeping the temperature constant for a second time period at the third temperature; and S4, heating the third time to a fourth temperature, and keeping constant temperature at the fourth temperature for a fourth time to obtain the quantum dot core.
Step S1, mixing a first precursor, a first ligand and a solvent, and heating to a first temperature to enable the first precursor and the first ligand to be fully dissolved in the solvent to form a first mixed solution. Wherein the first ligand is selected from one or more of octanoic acid, dodecanoic acid, hexadecanoic acid, octadecanoic acid and oleic acid, but not limited thereto.
And S2, mixing a second precursor, a second ligand and a solvent, and adding the first mixed solution at a second temperature to prepare a second mixed solution. Wherein the second ligand is selected from phosphine ligands (such as trioctylphosphine, tributylphosphine) and/or amine ligands (such as n-hexylamine, octaamine, dodecylamine and dipropylamine, trioctylamine), but is not limited thereto. It will be appreciated by those skilled in the art that the first temperature in step S1 may be controlled within a range that the first precursor and the first ligand are sufficiently dissolved in the solvent, and natural cooling or physical cooling (e.g., cooling with cold oil) may be selected to the second temperature after the first mixed solution is formed. In some embodiments, the second temperature is not higher than the first temperature, preferably the second temperature is room temperature.
Step S3, heating the second mixed solution to a third temperature for a first time period, and keeping the temperature constant for a second time period at the third temperature; and S4, heating the third time to a fourth temperature, and keeping constant temperature at the fourth temperature for a fourth time to obtain the quantum dot core.
According to the preparation method of the cadmium-free quantum dot, the nucleation and growth uniformity of the quantum dot is controlled by a multi-gradient heating technology, so that the half-peak width of the cadmium-free quantum dot core and the half-peak width of the quantum dot are reduced, and the luminous efficiency of the cadmium-free quantum dot is improved.
In one or more embodiments, the heating rate of the heating reactions of step S3 and step S4 is independently selected from the range of 1 to 150 ℃/min, preferably from 5 to 100 ℃/min.
In one or more embodiments, in step S3 and step S4, the third temperature and the fourth temperature are 30 to 310 ℃, respectively, and it is understood that the fourth temperature is higher than the third temperature.
In one or more embodiments, the second time length and the fourth time length are respectively 1min to 2h, and the second time length may be selected to be greater than, equal to, or less than the fourth time length.
In one or more embodiments, the heating process in step S3 is a gradient heating process, that is, the second mixed solution is warmed up from the second temperature to a certain temperature and then kept at a constant temperature for a period of time, is warmed up again to a certain temperature and then kept at a constant temperature for a period of time, reaches the third temperature after undergoing the above warming up and keeping at the third temperature for a second period of time. The heating rate of each heating in the heating process is independently selected from 1 to 150 ℃/min, preferably 5 to 100 ℃/min, and more preferably 5 to 75 ℃/min. The rate of temperature rise may be the same or different for each time. When the temperature rising rates of the multiple temperature rising are different, the heating process in the step S3 is a multi-gradient heating process. The length of each constant temperature time in the heating process is 1 min-2 h, and the constant temperature time can be the same or different according to specific quantum dots.
In a preferred embodiment, step S3 comprises the steps of: s31, heating the second mixed solution to a fifth temperature for a fifth time period, and keeping the temperature at the fifth temperature for a sixth time period; s32, repeating the operation of the step S31 for one to three times to obtain a second mixed solution with the final temperature of a third temperature; wherein the heating rate of the heating reaction in step S31 is the same as or different from that in step S32, and the time length of the constant temperature reaction in step S31 is the same as or different from that in step S32.
In a more preferred embodiment, the third temperature is not higher than 150 ℃, the heating rate of the heating reaction in step S3 is independently selected from 5 to 75 ℃/min, the heating rate of the heating reaction in step S4 is selected from 50 to 100 ℃/min, where step S4 is a direct rapid heating process, and when the temperature of the second mixed solution is raised to the third temperature, then the heating rate is raised in the heating reaction in step S4 to facilitate the formation of uniform quantum dot nuclei.
In the prior art, the preparation of InP quantum dots is often performed by a phosphorus precursor (e.g., P (SiMe 3 ) 3 ) The reactivity of InP quantum dots is too high and the reaction time at high temperature is only a few seconds, which results in insufficient P monomer supply during the growth phase, so that InP quantum dots grow prematurely into the Ostwald ripening phase, resulting in polydispersity of the quantum dot size. The preparation method of the cadmium-free quantum dot adopted by the invention controls the nucleation and growth uniformity of the quantum dot by using a multi-gradient heating technology, reduces the half-peak width of the cadmium-free quantum dot core and the half-peak width of the quantum dot, and improves the luminous efficiency of the cadmium-free quantum dot.
In the above preparation method of the present invention, the molar ratio of the first precursor to the second precursor is preferably 50:1 to 1:50, more preferably 10:1 to 1:10.
In one or more embodiments, the first precursor is a group iii element precursor and the second precursor is a group v element precursor, forming a group iii-v quantum dot; preferably, the above III-V group quantum dots are InP quantum dots, inAs quantum dots, doped InP quantum dots, or doped InAs quantum dots, but are not limited thereto.
In one or more embodiments, the first precursor is selected from one or more of Zn, mg, ca, sr, al, zr, fe, sc, ti, cr, si and a Ni element precursor.
In a preferred embodiment, after the step S4, the preparation method of the present invention further includes a step S5 of coating the quantum dot core with a shell layer; preferably, the shell layer is a II-VI compound shell layer, and the shell layer can improve the stability of the cadmium-free quantum dot. In one or more embodiments, the quantum dot core is coated with two shells of II-VI compound, which greatly improves the stability of the cadmium-free quantum dot, wherein the first shell and the second shell are of the same or different types. The first shell layer or the second shell layer may include a plurality of single shell layers.
After the step S4, the reaction system is heated or cooled to the initial reaction temperature of the step S5. In some embodiments, the initial reaction temperature of step S5 is 100 to 310 ℃.
According to another aspect of the application, a cadmium-free quantum dot is provided, and the cadmium-free quantum dot is prepared by the preparation method. According to the preparation method, the nucleation and growth uniformity of the quantum dots are controlled by a multi-gradient heating technology, so that the half-peak width of the cadmium-free quantum dot nuclei and the half-peak width of the quantum dots are reduced, and the luminous efficiency of the cadmium-free quantum dots is improved.
The cadmium-free quantum dot provided by the application can be applied to preparation of a quantum dot composition, and the composition comprises the cadmium-free quantum dot prepared by the preparation method. When the composition is used for specific application, the cadmium-free quantum dot not only has a narrower half-peak width, but also has higher luminous efficiency, so that the composition also has the application advantages.
According to another aspect of the present application, an optoelectronic device is provided that includes cadmium-free quantum dots as an electroluminescent material or photoluminescent material. In particular, the optoelectronic device may be an electroluminescent display device, a photoluminescent display device, an image sensor, or a solar cell, but is not limited thereto.
The invention is described in further detail below in connection with specific examples which are not to be construed as limiting the scope of the invention as claimed.
[ example 1 ]
The preparation method of the embodiment comprises the following steps:
first, 0.2mmol of In (Ac) was weighed out 3 (indium acetate), 0.6mmol of OA (oleic acid), 5.0g of ODE (octadecene) were put into a 100mL three-necked flask, N 2 Heating to 170 ℃ in the exhaust state for dissolution, and then cooling to room temperature.
Then, a mixture of 0.1mmol TMS-P (tris (trimethylsilyl) phosphine), 0.5mL TOP, and 0.5mL ODE (octadecene) was added to the above solution at room temperature.
Then, heating to 150 ℃ from room temperature (25 ℃) for 5min, and keeping the constant temperature for 2min; heating to 300 ℃ for 5min, and reacting at constant temperature for 2min to obtain InP core solution.
Finally, the reaction temperature was reduced to 150℃and 1.5mmol of ZnAc was added 2 (Zinc acetate), exhausting for 30min, heating to 280 ℃, adding 1mL Se-TOP (0.1 mmol/mL) (selenium-trioctylphosphine) for reaction for 20min, and adding 0.8mL S-TOP (1 mmol/mL) (sulfur-trioctylphosphine) for reaction for 20min. And after the reaction is finished, cooling to room temperature, extracting with methanol for three times, precipitating and centrifuging with acetone, and dissolving the precipitate in toluene to obtain the InP/ZnSe/ZnS quantum dot solution.
[ example 2 ]
The preparation method of the embodiment comprises the following steps:
first, 0.2mmol of In (Ac) was weighed out 3 (indium acetate), 0.6mmol of OA (oleic acid), 5.0g of ODE (octadecene) were put into a 100mL three-necked flask, N 2 Heating to 170 ℃ in the exhaust state for dissolution, and then cooling to room temperature.
Then, a mixture of 0.1mmol TMS-P (tris (trimethylsilyl) phosphine), 0.5mL TOP, and 0.5mL ODE (octadecene) was added to the above solution at room temperature.
Then, heating to 85 ℃ from room temperature for 10min, and keeping the temperature constant for 5min; heating to 150 ℃ for 10min, heating to 300 ℃ for 5min, and reacting at constant temperature for 2min to obtain InP core solution.
Finally, the reaction temperature was reduced to 150℃and 1.5mmol of ZnAc was added 2 (Zinc acetate), exhausting for 30min, heating to 280 ℃, adding 1mL Se-TOP (0.1 mmol/mL) (selenium-trioctylphosphine) for reaction for 20min, and adding 0.8mL S-TOP (1 mmol/mL) (sulfur-trioctylphosphine) for reaction for 20min. And after the reaction is finished, cooling to room temperature, extracting with methanol for three times, precipitating and centrifuging with acetone, and dissolving the precipitate in toluene to obtain the InP/ZnSe/ZnS quantum dot solution.
[ example 3 ]
The preparation method of the embodiment comprises the following steps:
first, 0.2mmol of In (Ac) was weighed out 3 (indium acetate), 0.6mmol of OA (oleic acid), 5.0g of ODE (octadecene) were put into a 100mL three-necked flask, N 2 Heating to 170deg.C for dissolution in the exhaust state, and cooling to roomTemperature.
Then, a mixture of 0.1mmol TMS-P (tris (trimethylsilyl) phosphine), 0.5mL TOP, and 0.5mL ODE (octadecene) was added to the above solution at room temperature.
Then, the temperature is heated to 50 ℃ at a rate of 5 ℃/min for 5min from room temperature, and the temperature is kept constant for 5min; heating to 75deg.C at a rate of 5deg.C/min for 5min, and keeping the temperature constant for 5min; heating to 125 deg.C at a rate of 10deg.C/min for 5min, and maintaining the temperature for 2min; heating to 300 ℃ for 5min, and reacting at constant temperature for 2min to obtain InP core solution.
Finally, the reaction temperature was reduced to 150℃and 1.5mmol of ZnAc was added 2 (Zinc acetate), exhausting for 30min, heating to 280 ℃, adding 1mL Se-TOP (0.1 mmol/mL) (selenium-trioctylphosphine) for reaction for 20min, and adding 0.8mL S-TOP (1 mmol/mL) (sulfur-trioctylphosphine) for reaction for 20min. And after the reaction is finished, cooling to room temperature, extracting with methanol for three times, precipitating and centrifuging with acetone, and dissolving the precipitate in toluene to obtain the InP/ZnSe/ZnS quantum dot solution.
[ example 4 ]
The preparation method of the embodiment comprises the following steps:
first, 0.2mmol of In (Ac) was weighed out 3 (indium acetate), 0.6mmol of OA (oleic acid), 5.0g of ODE (octadecene) were put into a 100mL three-necked flask, N 2 Heating to 170 ℃ in the exhaust state for dissolution, and then cooling to room temperature.
Then, a mixture of 0.1mmol TMS-P (tris (trimethylsilyl) phosphine), 0.5mL TOP, and 0.5mL ODE (octadecene) was added to the above solution at room temperature.
Then, the temperature is heated to 125 ℃ at a rate of 50 ℃/min for 2min from room temperature, and the temperature is kept constant for 5min; and heating to 285 ℃ at a speed of 80 ℃/min for 2min to obtain InP core solution.
Finally, the reaction temperature was reduced to 150℃and 1.5mmol of ZnAc was added 2 (Zinc acetate), exhausting for 30min, heating to 280 ℃, adding 1mL Se-TOP (0.1 mmol/mL) (selenium-trioctylphosphine) for reaction for 20min, and adding 0.8mL S-TOP (1 mmol/mL) (sulfur-trioctylphosphine) for reaction for 20min. Cooling to room temperature after the reaction is finished, extracting with methanol for three times, precipitating with acetone, centrifuging,and dissolving the precipitate in toluene to obtain InP/ZnSe/ZnS quantum dot solution.
[ example 5 ]
The preparation method of the embodiment comprises the following steps:
first, 0.2mmol of In (Ac) was weighed out 3 (indium acetate), 0.6mmol of OA (oleic acid), 5.0g of ODE (octadecene) were put into a 100mL three-necked flask, N 2 Heating to 170 ℃ in the exhaust state for dissolution, and then cooling to room temperature.
Then, a mixture of 0.1mmol TMS-P (tris (trimethylsilyl) phosphine), 0.5mL TOP, and 0.5mL ODE (octadecene) was added to the above solution at room temperature.
Then, the temperature is heated to 30 ℃ at a rate of 1 ℃/min for 5min after the time from room temperature, and the temperature is kept constant for 5min; heating to 150deg.C for 10min, and keeping the temperature for 3min; and heating to 300 ℃ at a speed of 20 ℃/min for 5min, and reacting at constant temperature for 2min to obtain the InP core solution.
Finally, the reaction temperature was reduced to 150℃and 1.5mmol of ZnAc was added 2 (Zinc acetate), exhausting for 30min, heating to 280 ℃, adding 1mL Se-TOP (0.1 mmol/mL) (selenium-trioctylphosphine) for reaction for 20min, and adding 0.8mL S-TOP (1 mmol/mL) (sulfur-trioctylphosphine) for reaction for 20min. And after the reaction is finished, cooling to room temperature, extracting with methanol for three times, precipitating and centrifuging with acetone, and dissolving the precipitate in toluene to obtain the InP/ZnSe/ZnS quantum dot solution.
[ example 6 ]
The preparation method of the embodiment comprises the following steps:
first, 0.2mmol of In (Ac) was weighed out 3 (indium acetate), 0.6mmol of OA (oleic acid), 5.0g of ODE (octadecene) were put into a 100mL three-necked flask, N 2 Heating to 170 ℃ in the exhaust state for dissolution, and then cooling to room temperature.
Then, a mixture of 0.1mmol TMS-P (tris (trimethylsilyl) phosphine), 0.5mL TOP, and 0.5mL ODE (octadecene) was added to the above solution at room temperature.
Then, the temperature is heated to 100 ℃ at a speed of 15 ℃/min for 5min from room temperature, and the temperature is kept constant for 10min; heating to 300 ℃ at a speed of 100 ℃/min for 2min, and reacting at constant temperature for 5min to obtain InP core solution.
Finally, the reaction temperature was reduced to 150℃and 1.5mmol of ZnAc was added 2 (Zinc acetate), exhausting for 30min, heating to 280 ℃, adding 1mL Se-TOP (0.1 mmol/mL) (selenium-trioctylphosphine) for reaction for 20min, and adding 0.8mL S-TOP (1 mmol/mL) (sulfur-trioctylphosphine) for reaction for 20min. And after the reaction is finished, cooling to room temperature, extracting with methanol for three times, precipitating and centrifuging with acetone, and dissolving the precipitate in toluene to obtain the InP/ZnSe/ZnS quantum dot solution.
[ example 7 ]
The preparation method of the embodiment comprises the following steps:
first, 0.2mmol of In (Ac) was weighed out 3 (indium acetate), 0.6mmol of OA (oleic acid), 5.0g of ODE (octadecene) were put into a 100mL three-necked flask, N 2 Heating to 170 ℃ in the exhaust state for dissolution, and then cooling to room temperature.
Then, a mixture of 0.1mmol TMS-P (tris (trimethylsilyl) phosphine), 0.5mL TOP, and 0.5mL ODE (octadecene) was added to the above solution at room temperature.
Then, the temperature is heated to 150 ℃ at a rate of 25 ℃/min for 5min from room temperature, and the temperature is kept constant for 10min; heating to 300 ℃ at the speed of 150 ℃/min for 1min, and reacting at constant temperature for 2h to obtain InP core solution.
Finally, the reaction temperature was reduced to 150℃and 1.5mmol of ZnAc was added 2 (Zinc acetate), exhausting for 30min, heating to 280 ℃, adding 1mL Se-TOP (0.1 mmol/mL) (selenium-trioctylphosphine) for reaction for 20min, and adding 0.8mL S-TOP (1 mmol/mL) (sulfur-trioctylphosphine) for reaction for 20min. And after the reaction is finished, cooling to room temperature, extracting with methanol for three times, precipitating and centrifuging with acetone, and dissolving the precipitate in toluene to obtain the InP/ZnSe/ZnS quantum dot solution.
[ example 8 ]
The preparation method of this example differs from that of example 1 in that:
In(Ac) 3 the amount of (indium acetate) was 0.2mmol and the amount of TMS-P (tris (trimethylsilyl) phosphine) was 0.02mmol.
[ example 9 ]
The preparation method of this example differs from that of example 1 in that:
In(Ac) 3 the amount of (indium acetate) was 0.2mmol and the amount of TMS-P (tris (trimethylsilyl) phosphine) was 2mmol.
Comparative example 1
The method for preparing the heat injection method comprises the following steps:
weigh 0.2mmol In (Ac) 3 (indium acetate), 0.6mmol of OA (oleic acid), 5.0g of ODE (octadecene) were put into a 100mL three-necked flask, N 2 Heating to 280 ℃ in the exhaust state and keeping constant temperature. A mixture of 0.1mmol TMS-P (tris (trimethylsilyl) phosphine), 0.5mL TOP, and 0.5mL ODE (octadecene) was rapidly injected and reacted for 10min to give an InP core solution.
The reaction temperature was reduced to 150℃and 1.5mmol of ZnAc was added 2 (Zinc acetate), exhausting for 30min, heating to 280 ℃, adding 1mL Se-TOP (0.1 mmol/mL) (selenium-trioctylphosphine) for reaction for 20min, and adding 0.8mL S-TOP (1 mmol/mL) (sulfur-trioctylphosphine) for reaction for 20min. And after the reaction is finished, cooling to room temperature, extracting with methanol for three times, precipitating and centrifuging with acetone, and dissolving the precipitate in toluene to obtain the InP/ZnSe/ZnS quantum dot solution.
Comparative example 2
The heating method comprises the following steps:
weigh 0.2mmol In (Ac) 3 (indium acetate), 0.6mmol of OA (oleic acid), 5.0g of ODE (octadecene) were put into a 100mL three-necked flask, N 2 Heating to 170 ℃ in the exhaust state for dissolution, and then cooling to room temperature. Then, 0.1mmol TMS-P (tris (trimethylsilyl) phosphine), 0.5mL TOP and 0.5mL ODE (octadecene) were added to the above solution, and the temperature was directly raised to 280℃and the reaction was carried out at constant temperature for 10min to obtain an InP core solution.
The reaction temperature was reduced to 150℃and 1.5mmol of ZnAc was added 2 (Zinc acetate), exhausting for 30min, heating to 280 ℃, adding 1mL Se-TOP (0.1 mmol/mL) (selenium-trioctylphosphine), reacting for 20min, adding 0.8mL S-TOP (1 mmol/mL) (sulfur-trioctylphosphine), and reacting for 20min. And cooling to room temperature after the reaction is finished, extracting for three times by using methanol, precipitating and centrifuging by using acetone, and dissolving the precipitate in toluene to obtain the InP/ZnSe/ZnS quantum dot solution.
Carrying out ultraviolet absorption test on the InP core solutions prepared in the examples 1-9 and the comparative examples 1 and 2 to obtain half-width of ultraviolet absorption peak of the InP core; the InP/ZnSe/ZnS quantum dot solution was subjected to a fluorescence emission performance test to obtain the Photoluminescence (PL) spectrum emission peak position and emission peak half-width of the InP/ZnSe/ZnS quantum dot, and the quantum yield of the InP/ZnSe/ZnS quantum dot was tested by using an integrating sphere, and the results are shown in table 1.
TABLE 1
Figure BDA0001900007760000091
The quality of the synthesis of the core can be judged according to the half-peak width data of the InP core, and the narrower the half-peak width is, the better the uniformity of the core is. As can be seen from comparative examples 1-9 and comparative examples 1 and 2, the cadmium-free quantum dots produced by the preparation method of the invention have better core uniformity, the half-peak width of the obtained cadmium-free quantum dots is relatively narrow, and the quantum efficiency is greatly improved.
From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:
according to the preparation method, the nucleation and growth uniformity of the quantum dots are controlled by a multi-gradient heating technology, so that the half-peak width of the cadmium-free quantum dot nuclei and the half-peak width of the quantum dots are reduced, and the luminous efficiency of the cadmium-free quantum dots is improved.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (4)

1. The preparation method of the cadmium-free quantum dot is characterized by comprising the following steps of:
s1, mixing a first precursor, a first ligand and a solvent, heating to a first temperature to obtain a first mixed solution, wherein the first precursor is an indium precursor, the first ligand is one or more of octanoic acid, dodecanoic acid, hexadecanoic acid, octadecanoic acid and oleic acid, the solvent is octadecene, and the first temperature is 170 ℃;
s2, mixing a second precursor, a second ligand and a solvent, adding the first mixed solution at a second temperature to prepare a second mixed solution, wherein the second precursor is a phosphorus element precursor, the second ligand is one or more of trioctylphosphine, tributylphosphine, n-hexylamine, octaamine, dodecylamine, dipropylamine and trioctylamine, the solvent is octadecene, and the second temperature is room temperature;
s3, heating the second mixed solution to a third temperature, and keeping the temperature at the third temperature for a second time length;
s4, heating to a fourth temperature, and keeping constant temperature at the fourth temperature for a fourth time length to obtain a quantum dot core;
the third temperature is 30-150 ℃, the fourth temperature is 285 or 300 ℃, the heating rate of the heating reaction in the step S3 is selected from 5-75 ℃/min, the heating rate of the heating reaction in the step S4 is selected from 50-100 ℃/min, the fourth temperature is higher than the third temperature, the second time length and the fourth time length are respectively 1 min-2 h, the heating process in the step S3 is a gradient heating process, after the step S4, the preparation method further comprises a step S5, and the quantum dot core cladding shell layer is a ZnSe/ZnS shell layer.
2. The method of claim 1, wherein the heating process in step S3 is a multi-gradient heating process.
3. The method of claim 1, wherein the molar ratio of the first precursor to the second precursor is 50:1 to 1:50.
4. The method of claim 1, wherein the molar ratio of the first precursor to the second precursor is 10:1 to 1:10.
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