CN117126659A

CN117126659A - Core-shell structure indium phosphide quantum dot based on tripyrrolidine and preparation method and application thereof

Info

Publication number: CN117126659A
Application number: CN202311097989.8A
Authority: CN
Inventors: 蔡培庆; 薛淇文; 董前民; 刘祖刚
Original assignee: China Jiliang University
Current assignee: China Jiliang University
Priority date: 2023-08-29
Filing date: 2023-08-29
Publication date: 2023-11-28

Abstract

The invention relates to the technical field of quantum dot luminescent materials, and discloses a core-shell structure indium phosphide quantum dot based on triphenylphosphine and a preparation method and application thereof. And taking the tripyrrolidine phosphine as a brand new phosphorus source, firstly preparing an indium phosphide inner core, coating a zinc selenium sulfur intermediate shell layer, finally adding a zinc precursor solution and an n-dodecyl mercaptan solution to react to obtain a quantum dot solution, and purifying to obtain the indium phosphide quantum dot with the core-shell structure. According to the method, the safe and environment-friendly tripyrrolidine phosphine is adopted as a phosphorus source, the phosphorus source has lower reactivity than the traditional phosphorus source, the nucleation and growth of the indium phosphide quantum dot can be better controlled, the particle size distribution of the quantum dot is more uniform, the indium phosphide quantum dot with the core-shell structure and the narrow half-peak width and high quantum efficiency is obtained, and the luminescence performance of the indium phosphide quantum dot with the core-shell structure is optimized. The preparation method has simple process, safety and environmental protection, and can realize large-scale preparation.

Description

Core-shell structure indium phosphide quantum dot based on tripyrrolidine and preparation method and application thereof

Technical Field

The invention relates to the technical field of quantum dot luminescent materials, in particular to a core-shell structure indium phosphide quantum dot based on triphenylphosphine and a preparation method and application thereof.

Background

Quantum dots have been widely used in the fields of display, illumination, biology, etc. due to their unique photoelectric properties. Currently, the quantum dots are mainly classified into the following three types: cd-based quantum dots (CdSe, cdS, etc.), cadmium-free quantum dots (InP, cuInS ₂ Etc.) and perovskite quantum dots (CsPbX) ₃ X is halogen such as: cl, br, I). The development of Cd-based quantum dots and perovskite quantum dots is particularly outstanding, but the Cd-based quantum dots and perovskite quantum dots contain heavy metal elements such as Cd, pb and the like, so that the Cd-based quantum dots and the perovskite quantum dots have great harm to human health and environmental protection, and further development of the Cd-based quantum dots and the perovskite quantum dots is limited. The indium phosphide quantum dot has the advantages of adjustable light-emitting band gap in the whole visible light range, environmental friendliness and the like, and becomes a powerful substitute for Cd-based and Pb-based perovskite quantum dots.

In 1994, micic et al used tris (trimethylsilyl) phosphine as a phosphorus source and reacted with trioctylphosphine-dissolved indium chloride and oxalic acid for three days to successfully synthesize indium phosphide nanocrystals, but the luminescent properties of indium phosphide nanocrystals were severely affected by the presence of a large number of defects on the surface of the indium phosphide nanocrystals, nano Lett, 2002,2 (9): 1027-1030. Among them, trioctylphosphine oxide has a high boiling point as a complexing solvent, thereby causing the reaction to be carried out at a high temperature, making the reaction very slow, requiring a long time. In order to solve the problem, zhejiang university Peng Xiaogang et al synthesizes high-quality indium phosphide nanocrystalline by adopting a non-coordinating solvent 1-octadecene to replace trioctylphosphine oxide in the presence of fatty acid, shortens the reaction time from a few days to a few hours, and greatly saves the time cost.

Compared with cadmium selenide quantum dots, the indium phosphide quantum dots are most outstanding in that the indium phosphide quantum dots have higher covalency, so that the indium phosphide quantum dots show higher carrier mobility and better stability. But at the same time presents difficulties that are difficult to overcome, in the synthesis process, the reaction is usually required to be kept at a higher temperature for a longer time, and researchers find that the tris (trimethylsilyl) phosphine is high in reactivity, and the phosphorus precursor is consumed very quickly, so that insufficient supply of phosphorus monomer in nucleation and subsequent growth processes is caused, and the monomer required in the growth stage can only be obtained through an ostwald ripening process, but the quality of the prepared indium phosphide quantum dot is poor along with the increase of polydispersity. Meanwhile, as tris (trimethylsilyl) phosphine is expensive, flammable and inconvenient to transport, certain dangers and uncontrollable reactions exist. Therefore, it is urgent to find a suitable phosphorus source.

In the process of searching a phosphorus source, researchers try to synthesize indium phosphide nanocrystalline by using phosphine gas generated by zinc phosphide, phosphorus trichloride, calcium phosphide, white phosphorus and the like, but no great result is obtained. In 2013 Heesun Yan group uses cheap, safe and environment-friendly tri (dimethylamino) phosphine as phosphorus source to synthesize indium phosphide quantum dot for the first time, and InP/ZnS core/shell quantum dot J.Nanopart.Res.,2013,15 (6): 1-10, with quantum efficiency of 51% -53% and half-width of 60nm-64nm, is obtained by coating ZnS shell.

In recent years, with continuous optimization of researchers, the performance of indium phosphide quantum dots based on tris (dimethylamino) phosphine as a phosphorus source is almost comparable to ACS appl. However, tris (dimethylamino) phosphine is still classified as flammable liquid and vapor according to the global chemical uniform classification and labeling system, endangering the health of human bodies, and possibly causing genetic defects and carcinogenesis, which hinders its practical application. 2021 patent document No. CN112143496A discloses a novel phosphorus source M- (O-C≡P) _n . Wherein M is a metal element, and the red light indium phosphide nanocrystalline with fluorescence peak value of 580-670 nm, fluorescence emission peak width of less than 50nm and quantum yield of higher than 80% is synthesized by utilizing a phosphorus source, and good effect is obtained by utilizing the phosphorus source, but the synthesis condition of the phosphorus source is relatively harsh, the purchase is difficult, and the large-scale preparation is relatively difficult.

Disclosure of Invention

Aiming at the problem that the quantum dots prepared by taking tri (trimethylsilyl) phosphine or tri (dimethylamino) phosphine as a phosphorus source in the prior art have great harm to human bodies, the invention provides the core-shell structure indium phosphide quantum dots prepared by taking the tripyrrolidine phosphine as a novel phosphorus source, which have small harm to human bodies and the environment, greatly reduce potential safety hazards and can realize large-scale preparation.

In order to achieve the above purpose, the invention adopts the following technical scheme:

a preparation method of a core-shell structure indium phosphide quantum dot based on triphenylphosphine comprises the following steps:

step 1, respectively dissolving a zinc source, a selenium source and a sulfur source in a solvent to form a zinc precursor solution, a selenium precursor solution and a sulfur precursor solution; dissolving a tripyrrolidine phosphine in a solvent to form a phosphorus precursor solution;

step 2, dissolving and mixing indium halide and zinc halide, heating to a first temperature for reaction, heating to a second temperature, and adding a phosphorus precursor solution for reaction to obtain an indium phosphide core solution;

step 3, continuously adding a zinc precursor solution, a selenium precursor solution and a sulfur precursor solution into the indium phosphide core solution in the step 2, and heating to a third temperature to react to obtain an indium phosphide solution coated with a zinc-selenium-sulfur intermediate shell layer;

and step 4, heating the solution in the step 3 to a fourth temperature, adding a zinc precursor solution and an n-dodecyl mercaptan solution to react to obtain a quantum dot solution, and purifying to obtain the core-shell structure indium phosphide quantum dot.

According to the invention, the safe and environment-friendly tripyrrolidine is adopted as a phosphorus source, the nucleation and growth processes of the indium phosphide quantum dots are controlled more accurately by utilizing the characteristic of relatively low reactivity, the particle size distribution of the obtained core-shell structure quantum dots is more uniform, the core-shell structure quantum dots have very narrow half-width (FWHM=37 nm) and high quantum efficiency (PLQY=82.3%), the potential safety hazard is greatly reduced, and the luminescent performance of the core-shell structure indium phosphide quantum dots can be optimized.

The solvent used in the zinc precursor solution comprises any one or more of octadecene, oleylamine, oleic acid, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene and 1-eicosene;

the solvent adopted by the selenium precursor solution and the sulfur precursor solution is independently selected from any one or more of trioctylphosphine, octadecene and oleylamine;

the solvent adopted by the phosphorus precursor solution comprises any one or more of oleylamine, ethylenediamine, 1, 2-propylenediamine, 1, 3-propylenediamine and 1, 4-butylenediamine;

the precursor solution in the step 1 is prepared by heating and dissolving raw materials in a solvent; the heating energy can more effectively fully dissolve the raw materials, and the heating temperature of the zinc precursor solution is 100-150 ℃; the heating temperature of the selenium precursor solution and the sulfur precursor solution is 60-90 ℃; the heating temperature of the phosphorus precursor solution is 30-70 ℃.

The zinc source comprises any one or more of zinc stearate, zinc acetate, zinc oxide, zinc chloride, zinc bromide and zinc iodide;

the selenium source comprises any one or more of selenium powder, diselenide, selenium tetrachloride, phenylselenium chloride, selenol and diselenide;

the sulfur source comprises any one or more of sulfur powder, dodecyl mercaptan and octyl mercaptan.

The concentration of the precursor solution is suitable for the raw materials to be fully dissolved, dispersed and uniformly deposited; preferably, the molar ratio of the zinc source to the solvent is 1:5-10; the molar ratio of the selenium powder to the solvent is 0.5-2:1; the molar ratio of the sulfur powder to the solvent is 0.5:1-2:1; the molar ratio of the tripyrrolidine phosphine to the solvent is 1:0.5-2.5.

The indium halide comprises any one or more of indium iodide, indium bromide and indium chloride;

the zinc halide comprises any one or more of zinc bromide, zinc iodide and zinc chloride;

in the step 2, the reaction solvent comprises one or more of oleylamine, dodecane, hexadecane, hexadecylamine, octadecylamine, octylamine, oleic acid and octadecene;

in the step 2, the mol ratio of the indium halide to the zinc halide to the tripyrrolidine phosphine is 1 (4.5-5.5): 3.4-5; the triphenylphosphine refers to the content of the triphenylphosphine in the phosphorus precursor solution. The ratio can lead the crystallization quality and crystal seed morphology of the synthesized indium phosphide core to be more excellent, and the particle size of the indium phosphide quantum dots to be more uniform.

In the step 2, the first temperature is 120-140 ℃, and the second temperature is 190-200 ℃; when the temperature is kept at 120-140 ℃ at the first temperature, redundant residual steam and oxygen are generated in the reaction system, and in order to avoid the influence on the surface of the indium phosphide quantum dot, harmful gas generated in the reaction system is taken away by vacuumizing when the temperature is heated to 120-140 ℃. The temperature is 190-200 ℃ at the second temperature, and the phosphorus precursor is added to the reaction mixture to be related to the reaction activity; the slow reaction activity is shown in that the reaction time is adjusted, compared with the faster reaction time (6-10 min) of the tri (dimethylamino) phosphine, the reaction time of the tripyrrolidine phosphine is longer than that of the tri (dimethylamino) phosphine by 10-20 min, and the longer reaction time is used for uniformly and slowly nucleating the indium phosphide quantum dots, so that the surface defects are reduced, the non-radiative recombination probability of lattice internal stress and excitons is inhibited, and the quantum yield is improved.

The reaction time is 30-60 min at the first temperature in the step 2; adding a phosphorus precursor solution for reaction for 10-20 min; the reaction is carried out for 30 to 60 minutes at the first temperature, so that the redundant vapor and oxygen generated in the reaction process can be removed; after the phosphorus precursor solution is added, the reaction is carried out for 10 to 20 minutes, so that the indium phosphide quantum dots can be stably nucleated, and the uniformity of size distribution is ensured.

In the step 3, the molar ratio of the zinc source in the zinc precursor solution, the selenium source in the selenium precursor solution and the sulfur source to the indium halide in the sulfur precursor solution is (9-12.5): 2.5-5.5): 1;

in the step 3, the third temperature is 260-280 ℃ and the reaction time is 90-120 min; the growth of the ZnSeS shell passivates the defects on the surface of the indium phosphide core, relieves the lattice mismatch between the indium phosphide core and the ZnS shell, and reduces interface defects.

In the step 4, the mole ratio of the zinc source, n-dodecyl mercaptan and indium halide in the zinc precursor solution is (2.5-5.5): 9-19): 1; the quantum yield of the quantum dot obtained by using the component proportion is higher.

In the step 4, the fourth temperature is 290-300 ℃ and the reaction is carried out for 60-80min. ZnS is a wide-bandgap semiconductor material, the escape of excitons to the outer shell layer is further restrained by wrapping the ZnS outer shell layer, the direct contact of external water, oxygen and indium phosphide quantum dots is avoided, and the luminous performance of the quantum dots is improved.

The whole process of the preparation method of the core-shell structure indium phosphide quantum dot is carried out under the protection of inert gas atmosphere, wherein the inert gas adopts at least one of nitrogen and argon.

Compared with the traditional tri (dimethylamino) phosphine nucleation time (6-10 min), the phosphorus source nucleation time (10-20 min) adopted in the invention is longer, which shows that the phosphorus source has lower reactivity, has enough monomer supply in the process of quantum dot nucleation and growth, and does not enter an Ostwald ripening stage prematurely, so that the particle size distribution is uniform, the spectrum is reflected to be narrower half-peak width, and the obtained quantum dot has more excellent performance.

Preferably, in step 3, the selenium precursor solution and the sulfur precursor solution are added into the reaction solution at a speed of 0.5-2 ml/h, respectively, and in the process of growing the ZnSeS shell, in order to obtain a uniform and compact ZnSeS shell, the selenium precursor solution and the sulfur precursor solution are uniformly dripped into the reaction solution.

Preferably, in step 4, n-dodecyl mercaptan is added into the reaction solution at a rate of 1-3 ml/hr, and during the growth of ZnS shell, we drop n-dodecyl mercaptan into the reaction solution at a uniform rate in order to obtain a uniform and dense ZnS shell.

Preferably, the purification in step 4 comprises the steps of: and adding the reaction solution into a nonpolar solvent for dissolution and centrifugation, then adding the nonpolar solvent to separate out precipitate, and filtering to obtain the core-shell structure indium phosphide quantum dot.

The nonpolar solvent comprises any one or more of n-octane, n-hexane and toluene;

the polar solvent comprises any one or more of ethanol, acetone and methanol.

The volume ratio of the nonpolar solvent to the polar solvent is 1-2:1-3.

The invention also provides the indium phosphide quantum dot with the core-shell structure, which is prepared by the preparation method, has the advantages of safe raw materials, less harm to human bodies and environment, excellent luminescence performance, narrow half-peak width, high quantum efficiency and quantum efficiency of more than 50 percent.

Based on the excellent environmental protection and luminous performance of the quantum dot, the invention also provides the application of the core-shell structure indium phosphide quantum dot in the photoelectric field, and the quantum dot has great potential for replacing the indium phosphide quantum dot prepared by the prior phosphorus source.

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

(1) The method adopts safe and environment-friendly tripyrrolidine as the phosphorus source, has lower reactivity than the traditional phosphorus source, can better control the nucleation and growth of the indium phosphide quantum dots, ensures that the particle size distribution of the quantum dots is more uniform, has simple process, easy purchase and less harm to human bodies and environment, greatly reduces potential safety hazard, and can realize large-scale preparation.

(2) According to the method, the amount of Zn sources added during ZnS growth is regulated, the extension of excitons to a shell layer is limited, radiation recombination is enhanced, the core-shell structure indium phosphide quantum dot with narrow half-width (minimum FWHM=37 nm) and high quantum efficiency (maximum PLQY=82.3%) is obtained, and the luminescence performance of the core-shell structure indium phosphide quantum dot is optimized.

Drawings

Fig. 1 is a preparation flow chart of the indium phosphide quantum dot with the core-shell structure.

Fig. 2 is an ultraviolet absorption spectrum picture of the indium phosphide quantum dot with the core-shell structure prepared in example 1.

Fig. 3 is a fluorescent emission spectrum picture of the indium phosphide quantum dot with core-shell structure prepared in example 1.

Fig. 4 is a graph of lifetime decay curve of indium phosphide quantum dots with core-shell structure prepared in example 1.

Fig. 5 is a TEM photograph of the core-shell structure indium phosphide quantum dot prepared in example 1.

Fig. 6 is an ultraviolet absorption spectrum picture of the indium phosphide quantum dot with the core-shell structure prepared in example 2.

Fig. 7 is a fluorescent emission spectrum picture of the indium phosphide quantum dot with core-shell structure prepared in example 2.

Fig. 8 is a graph of lifetime decay curve of indium phosphide quantum dots with core-shell structure prepared in example 2.

Fig. 9 is a TEM photograph of the core-shell structure indium phosphide quantum dot prepared in example 2.

Fig. 10 is an ultraviolet absorption spectrum picture of the indium phosphide quantum dot with the core-shell structure prepared in example 3.

Fig. 11 is a fluorescence emission spectrum picture of the indium phosphide quantum dot with the core-shell structure prepared in example 3.

Fig. 12 is a graph of lifetime decay curve of indium phosphide quantum dots with core-shell structure prepared in example 3.

Fig. 13 is a TEM photograph of the core-shell structure indium phosphide quantum dot prepared in example 3.

Fig. 14 is an ultraviolet absorption spectrum picture of the core indium phosphide quantum dot prepared in comparative example 1.

Fig. 15 is a graph of fluorescence emission spectra of the core indium phosphide quantum dots prepared in comparative example 1.

Fig. 16 is a graph of the lifetime decay curve of the core indium phosphide quantum dots prepared in comparative example 1.

Fig. 17 is a TEM photograph of the core indium phosphide quantum dot prepared in comparative example 1.

Fig. 18 is an ultraviolet absorption spectrum picture of the core-shell structure indium phosphide quantum dot prepared in comparative example 2.

Fig. 19 is a fluorescent emission spectrum picture of the core-shell structure indium phosphide quantum dot prepared in comparative example 2.

Fig. 20 is a graph of lifetime decay curves of the core-shell structure indium phosphide quantum dots prepared in comparative example 2.

Fig. 21 is a TEM photograph of the core-shell structure indium phosphide quantum dot prepared in comparative example 2.

Fig. 22 is an XRD pattern of indium phosphide quantum dots of the core-shell structures of the examples and comparative examples.

Detailed Description

The present invention will be described in further detail with reference to the following examples in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention. Modifications and equivalents will occur to those skilled in the art upon understanding the present teachings without departing from the spirit and scope of the present teachings.

The preparation process of the core-shell structure indium phosphide quantum dot based on the triphenylphosphine is shown in figure 1, and specifically:

step 1, preparing a zinc, selenium, sulfur and phosphorus precursor solution:

preparation of zinc precursor solution: mixing and dissolving a zinc source and a non-coordination solvent in a molar ratio of 1:5-10 in a three-neck flask, heating and stirring at 100-150 ℃ and a rotating speed of 300-1000 revolutions under a nitrogen atmosphere until the solution is clear and transparent, and obtaining the zinc precursor solution;

preparing a selenium precursor solution: mixing selenium powder and trioctylphosphine in a sample bottle in a nitrogen atmosphere, and heating and stirring for 10-60 minutes at the temperature of 60-90 ℃ and the rotating speed of 300-1000 revolutions to obtain a selenium precursor solution;

preparation of a sulfur precursor solution: mixing sulfur powder and trioctylphosphine in a sample bottle in a nitrogen atmosphere, and heating and stirring for 10-60 minutes at the temperature of 60-90 ℃ and the rotating speed of 300-1000 revolutions to obtain a sulfur precursor solution;

preparation of phosphorus precursor solution: adopting tripyrrolidine phosphine as a novel phosphorus source, mixing the tripyrrolidine phosphine with the molar ratio of 1:0.5-2.5 and organic amine in a sample bottle under the nitrogen atmosphere, heating and stirring for 10-60 minutes at the temperature of 30-70 ℃ and the rotating speed of 300-1000 revolutions, and obtaining a phosphorus precursor solution;

step 2, preparing indium phosphide core solution:

mixing and dissolving indium halide, zinc halide and an organic solvent in a three-neck flask, stirring and heating under the nitrogen atmosphere at the rotating speed of 300-1000 r, vacuumizing for 30-90 minutes after the temperature is increased to 120-140 ℃, backfilling nitrogen, continuously increasing the temperature to 190-200 ℃ under the nitrogen atmosphere, injecting a phosphorus precursor solution, and maintaining for 10-20 minutes to finish the preparation of the indium phosphide core solution. Wherein the molar ratio of the phosphorus source in the indium halide, the zinc halide, the organic solvent and the phosphorus precursor is 1:4.1-4.8:30.6-47.6:3.4-5;

step 3, coating a zinc-selenium-sulfur intermediate shell layer:

and (3) injecting a zinc precursor solution into the indium phosphide core solution at the temperature of 190-200 ℃, simultaneously injecting a selenium precursor solution and a sulfur precursor solution at the rate of 0.5 ml/h-2 ml/h, raising the temperature to 260-280 ℃, and keeping for 90-120 minutes to finish the coating of the zinc-selenium-sulfur intermediate shell layer. Wherein, the molar ratio of the zinc source in the zinc precursor, the selenium powder in the selenium precursor and the sulfur powder in the sulfur precursor to the indium halide is 9-12.5:2.5-5.5:2.5-5.5:1;

step 4, coating of a zinc sulfide outer shell layer:

after finishing the coating of the zinc selenium sulfur intermediate shell layer, continuously increasing the temperature to be stable within the range of 290-300 ℃, injecting a zinc precursor solution, and injecting n-dodecyl mercaptan solution at the rate of 1-3 ml/h for 60-80 minutes, thereby finishing the coating of the zinc sulfide intermediate shell layer, wherein the molar ratio of a zinc source, n-dodecyl mercaptan and indium halide in the zinc precursor is 2.6-5.4:9.4-19:1;

step 5, purifying to obtain a product:

after the coating of the zinc sulfide crust layer is completed, naturally cooling the temperature to room temperature, adding a nonpolar solvent n-octane for dissolution, centrifuging for 3-8 minutes at a rotation speed of 5000-12000 r, and then adding a polar solvent ethanol for precipitation. Wherein the volume ratio of the nonpolar solvent to the polar solvent is 1-2:1-3, and the preparation of the core-shell structure indium phosphide quantum dot is completed.

The starting materials used in the following embodiments are all purchased from commercial reagents.

Example 1

Preparation of core-shell structure indium phosphide quantum dots based on tripyrrolidine phosphine as phosphorus source:

step 1, preparing a zinc, selenium, sulfur and phosphorus precursor solution:

preparation of zinc precursor solution: 6 g of zinc stearate (9.48 mmol) and 24 ml of octadecene are mixed in a three-neck flask, and heated at 150 ℃ under nitrogen atmosphere at a rotation speed of 900 revolutions until the solution is clear and transparent, so as to obtain the zinc precursor solution.

And (3) preparing a selenium precursor solution, namely mixing 2.4 mmol of selenium powder and 1ml of trioctylphosphine in a sample bottle under the nitrogen atmosphere, and heating and stirring at 80 ℃ and 600 r for 30 minutes to obtain the selenium precursor.

Preparation of sulfur precursor: 2.4 mmol of sulfur powder and 1ml of trioctylphosphine are mixed in a sample bottle under nitrogen atmosphere, heated and stirred at 80 ℃ and 600 r for 30 minutes to obtain the sulfur precursor.

Preparation of phosphorus precursor solution: 1.96 mmol of tripyrrolidine and 3 mmol (1 mL,2.99 mmol) of oleylamine were mixed in a sample bottle under nitrogen atmosphere, heated at 50deg.C for 30 min at 600 rpm, to give 1.45 mL of the phosphorus precursor.

Step 2, preparing indium phosphide core solution:

mixing 0.44 mmol of indium iodide, 2.2 mmol of zinc bromide and 5mL of oleylamine in a three-neck flask, stirring and heating under nitrogen atmosphere at the rotation speed of 700 turns, vacuumizing for 60 minutes when the temperature is increased to 130 ℃, backfilling nitrogen, continuously increasing the temperature to 200 ℃ under nitrogen atmosphere, injecting 1.45 mL (1 mL of oleylamine+0.45 mL of phosphorus source) of phosphorus precursor solution, and keeping for 20 minutes to complete the preparation of the indium phosphide core solution.

Step 3, coating a zinc-selenium-sulfur intermediate shell layer:

and (2) at the temperature of 200 ℃, 4.74mmol of zinc source zinc precursor solution (12 ml) is injected into the indium phosphide core solution obtained in the step (2), 1ml of selenium and sulfur precursor solution are sequentially injected at the speed of 1 ml/h, the temperature is increased to 270 ℃, and the temperature is kept for 120 minutes, so that the coating of the zinc-selenium-sulfur intermediate shell layer is completed.

Step 4, coating of a zinc sulfide outer shell layer:

on the basis of step 3, the temperature was continuously raised to a temperature stabilized at 290 ℃,3 ml of zinc precursor solution (0.75 g,1.18mmol zinc source) was injected, and 1.5 ml (6.26 mmol) of n-dodecyl mercaptan solution was injected at a rate of 3 ml/hr, and the mixture was kept for 70 minutes, thereby completing the coating of the zinc sulfide crust layer.

And 5, cooling and purifying to obtain the indium phosphide quantum dot with the core-shell structure:

and (3) naturally cooling the temperature to room temperature on the basis of the step (4), adding 10 ml of normal hexane into the solution cooled to room temperature, centrifuging at 10000 revolutions for 4 minutes, removing impurities, mixing the obtained supernatant with ethanol at 1:1, centrifuging at 10000 revolutions for 4 minutes, dissolving the obtained precipitate with 2 ml of normal hexane, continuing to add 2 ml of ethanol for precipitation, centrifuging at 10000 revolutions for 3 minutes, discarding the supernatant, and collecting the precipitate to complete the preparation of the indium phosphide quantum dot with the core-shell structure.

Fig. 2 is an ultraviolet absorption spectrum picture of the core-shell structure indium phosphide quantum dot prepared in this example. Fig. 3 is a fluorescence emission spectrum picture of the indium phosphide quantum dot with the core-shell structure prepared in this example, and it can be seen that the fluorescence emission peak position of the indium phosphide quantum dot with the core-shell structure prepared in this example is 510nm, the half-width is 52nm, and the quantum efficiency is about 58%.

FIG. 4 is a graph of decay of fluorescence lifetime for a quantum dot prepared in this example, where the decay lifetime is double-exponentially fitted to determine that the average fluorescence lifetime of the quantum dot is around 76ns, where the fluorescence lifetime is shorter, the radiation rate is faster, and the fluorescence lifetime is matched with the higher fluorescence quantum yield of the quantum dot. Fig. 5 is a TEM image of the indium phosphide quantum dot with core-shell structure prepared in this example, and it can be seen that the particle size distribution of the quantum dot is relatively uniform, the average particle size is about 8.6nm, and the advantage of uniform particle size of the quantum dot is also matched with a narrower emission spectrum.

Example 2

step 1, preparing a zinc, selenium, sulfur and phosphorus precursor solution:

Preparation of phosphorus precursor solution: 1.96 mmole of tripyrrolidine phosphine and 3 mmole of oleylamine were mixed in a sample bottle under nitrogen atmosphere, heated at 55 degrees celsius at 600 revolutions and stirred for 30 minutes to give 1.45 ml of the phosphorus precursor.

Step 2, preparing indium phosphide core solution:

mixing 0.44 mmol of indium iodide, 2.2 mmol of zinc bromide and 5ml of oleylamine in a three-neck flask, stirring and heating under nitrogen atmosphere at the rotation speed of 700 revolutions, vacuumizing for 60 minutes when the temperature is increased to 130 ℃, backfilling nitrogen, continuously increasing the temperature to 200 ℃ under nitrogen atmosphere, injecting 1.45 ml of phosphorus precursor solution, and keeping for 20 minutes to complete the preparation of the indium phosphide core solution.

Step 3, coating a zinc-selenium-sulfur intermediate shell layer:

and (2) at the temperature of 200 ℃, injecting 12 milliliters of zinc precursor solution into the indium phosphide core solution obtained in the step (2), simultaneously sequentially injecting 1 milliliter of selenium and sulfur precursor solution at the speed of 1 milliliter/hour, raising the temperature to 270 ℃, and keeping for 120 minutes to finish the coating of the zinc-selenium-sulfur intermediate shell layer.

Step 4, coating of a zinc sulfide outer shell layer:

on the basis of step 3, the temperature was continuously raised to a temperature stabilized at 290 ℃, 5ml of zinc precursor solution (1.25 g zinc source, 1.97 mmol) was injected, and 1.5 ml of n-dodecyl mercaptan solution was injected at a rate of 3 ml/hr, and maintained for 70 minutes, completing the coating of the zinc sulfide crust layer.

Fig. 6 is an ultraviolet absorption spectrum picture of the core-shell structure indium phosphide quantum dot prepared in this example. Fig. 7 is a fluorescence emission spectrum picture of the indium phosphide quantum dot with the core-shell structure prepared in this example, and it can be seen that the fluorescence emission peak position of the indium phosphide quantum dot with the core-shell structure prepared in this example is 525nm, the half-peak width is 37nm, and the quantum efficiency is 82.3%. Fig. 8 is a life decay graph of this embodiment. FIG. 9 is a TEM image of the indium phosphide quantum dot having the core-shell structure prepared in this example, and it can be seen that the quantum dot has a uniform particle size distribution and an average particle size of about 5.5 nm.

Example 3

step 1, preparing a zinc, selenium, sulfur and phosphorus precursor solution:

Step 2, preparing indium phosphide core solution:

Step 3, coating a zinc-selenium-sulfur intermediate shell layer:

Step 4, coating of a zinc sulfide outer shell layer:

on the basis of the step 3, the temperature is continuously increased to be stable at 290 ℃, 6 milliliters (1.5 g,2.37mmol of zinc source) of zinc precursor solution is injected, 1.5 milliliters of n-dodecyl mercaptan solution is injected at the speed of 3 milliliters/hour, and the mixture is kept for 70 minutes, so that the coating of the zinc sulfide crust layer is completed.

Fig. 10 is an ultraviolet absorption spectrum picture of the core-shell structure indium phosphide quantum dot prepared in this example. Fig. 11 is a fluorescence emission spectrum picture of the indium phosphide quantum dot with the core-shell structure prepared in this example, and it can be seen that the fluorescence emission peak position of the indium phosphide quantum dot with the core-shell structure prepared in this example is 541nm, the half-peak width is 48nm, and the quantum efficiency is about 51.6%. Fig. 12 is a life decay graph of this embodiment. Fig. 13 is a TEM image of the core-shell indium phosphide quantum dot prepared in this example, and it can be seen that the quantum dot distribution is relatively uniform and the average particle size thereof is about 7.2nm.

Comparative example 1

Preparation of core indium phosphide quantum dot based on tripyrrolidine phosphine as phosphorus source

Step 1, preparing a phosphorus precursor solution:

1.96 mmole of tripyrrolidine phosphine and 3 mmole of oleylamine were mixed in a sample bottle under nitrogen atmosphere, heated at 55 degrees celsius at 600 revolutions and stirred for 30 minutes to give 1.45 ml of the phosphorus precursor.

Step 2, preparing indium phosphide core solution:

Step 3, cooling and purifying to obtain the core indium phosphide quantum dot:

and (3) naturally cooling the temperature to room temperature on the basis of the step (2), adding 5ml of normal hexane into the solution cooled to room temperature, centrifuging at 10000 revolutions for 4 minutes, removing impurities, mixing the obtained supernatant with ethanol at 1:1, centrifuging at 10000 revolutions for 4 minutes, dissolving the obtained precipitate with 2 ml of normal hexane, continuing to add 2 ml of ethanol for precipitation, centrifuging at 10000 revolutions for 3 minutes, discarding the supernatant, and collecting the precipitate to complete the preparation of the inner core indium phosphide quantum dot.

Fig. 14 is an ultraviolet absorption spectrum picture of the core indium phosphide quantum dot prepared in this comparative example. Fig. 15 is a fluorescence emission spectrum picture of the core indium phosphide quantum dot prepared in this comparative example, and it can be seen that the fluorescence emission peak position of the quantum dot is 512nm, the half-width is 55nm, and the quantum efficiency is about 6.2%, and is poorer than that of the quantum dot of the core-shell structure. Fig. 16 is a graph of lifetime decay of the quantum dot. FIG. 17 is a TEM image of the core indium phosphide quantum dot prepared in this comparative example, and it can be seen that the quantum dot distribution is relatively uniform and the average particle diameter thereof is about 5.2nm.

Comparative example 2

Preparation of core-shell structure indium phosphide quantum dot based on tris (dimethylamino) phosphine as phosphorus source

Step 1, preparing a zinc, selenium, sulfur and phosphorus precursor solution:

Preparation of phosphorus precursor solution: 2.48 mmole of tris (dimethylamino) phosphine and 3 mmole of oleylamine were mixed in a sample bottle under nitrogen atmosphere, heated at 50 degrees celsius at 600 revolutions and stirred for 30 minutes to give 1.45 ml of the phosphorus precursor.

Step 2, preparing indium phosphide core solution:

mixing 0.44 mmol of indium iodide, 2.2 mmol of zinc bromide and 5ml of oleylamine in a three-neck flask, stirring and heating under nitrogen atmosphere at the rotation speed of 700 revolutions, vacuumizing for 60 minutes when the temperature is increased to 130 ℃, backfilling nitrogen, continuously increasing the temperature to 200 ℃ under nitrogen atmosphere, injecting 1.45 ml of phosphorus precursor solution, and maintaining for 6-10 minutes to complete the preparation of the indium phosphide core solution. Step 3, coating a zinc-selenium-sulfur intermediate shell layer:

Step 4, coating of a zinc sulfide outer shell layer:

on the basis of the step 3, the temperature is continuously increased to be stable at 290 ℃, 5ml of zinc precursor solution is injected, 1.5 ml of n-dodecyl mercaptan solution is injected at the rate of 3 ml/h, and the coating of the zinc sulfide crust layer is completed after the solution is kept for 70 minutes.

Fig. 18 is an ultraviolet absorption spectrum picture of the core-shell structure indium phosphide quantum dot prepared in this comparative example. FIG. 19 is a fluorescence emission spectrum picture of the core-shell structure indium phosphide quantum dot prepared in the comparative example, and it can be seen that the fluorescence emission peak position of the core-shell structure indium phosphide quantum dot prepared in the comparative example is 527nm, the half-width is 57nm, and the quantum efficiency is about 42%; compared with the same amount of the example 2, the quantum efficiency of the example 2 is 82.3%, the half-peak width is only 37nm, and the quantum dots prepared by adopting the traditional phosphorus source have quite different effects.

Fig. 20 is a life decay graph of comparative example 2. Fig. 21 is a TEM image of the core-shell indium phosphide quantum dot prepared in this comparative example, and it can be seen that the quantum dot has poor uniformity in distribution and an average particle diameter of about 6.6nm.

Fig. 22 is an XRD pattern of the quantum dots prepared in examples and comparative examples, in which the quantum dots prepared in examples 1 to 3 can be seen to have (111) plane, (220) plane, (311) plane, three significant sphalerite characteristic peaks, and no other impurity peaks, and the higher XRD peak obtained in example 2 can be seen by comparison, indicating that the quantum dot obtained in example 2 is better in crystallinity.

The properties of the quantum dots prepared in examples and comparative examples are summarized in table 1, and it can be seen from examples 1,2 and 3 that the emission peak position of the quantum dot is red shifted with the increase of the Zn source content, the half-width thereof is the narrowest and 37nm when the amount of Zn source injected is 5ml at the time of ZnS growth, as shown in fig. 7, and the particle size distribution of the quantum dot is uniform and the fluorescence quantum yield thereof is as high as 82.3% as seen from the TEM image of fig. 9. The method shows that the increase of Zn source quantity is helpful to grow thicker ZnS shell layer when ZnS is grown, thereby restricting the extension of excitons to the shell layer and enhancing the quantum efficiency of the indium phosphide quantum dot with the core-shell structure.

Further increasing the amount of Zn source, it can be seen that when the amount of Zn source reaches 6 ml, its half-width becomes wider and quantum efficiency decreases, probably due to the fact that ZnS shell layers are too thick, resulting in an increase in strain between the shell layers, thereby resulting in an increase in defects between the shell layers, an increase in non-radiative recombination, and a decrease in quantum dot light emission performance, but overall is still better than the comparative example.

By comparing the embodiment with the comparative example 1, the indium phosphide core quantum dot based on the indium phosphide quantum dot with the tripyrrolidine as the phosphorus source and without the cladding shell has poor luminous performance, the quantum efficiency is only 6.2%, and the half-peak width indicates that the cladding shell is beneficial to reducing defects, enhancing the radiation recombination efficiency and improving the luminous performance of the indium phosphide quantum dot;

compared with the comparative example 2, the half-width of the comparative example is wider and the luminous efficiency is lower, so that the indium phosphide quantum dot with the core-shell structure, which is synthesized by taking the tripyrrolidine as a phosphorus source, can be obtained, compared with the indium phosphide quantum dot with the core-shell structure, which is synthesized by taking the tripyrrolidine as a phosphorus source, the indium phosphide quantum dot with the core-shell structure, which is excellent in luminous performance based on the tripyrrolidine as the phosphorus source, can be obtained by optimizing.

Table 1 summary of luminescent properties of quantum dots prepared in examples and comparative examples

Sequence number	Fluorescence emission peak position	Half width of peak	Quantum efficiency
				Example 1	510nm	52nm	58％
Example 2	525nm	37nm	82.3％
				Example 3	541nm	48nm	51.6％
Comparative example 1	512nm	55nm	6.2％
				Comparative example 2	527nm	57nm	42％

Claims

1. The preparation method of the core-shell structure indium phosphide quantum dot based on the tripyrrolidine phosphine is characterized by comprising the following steps:

2. The preparation method of the triphenylphosphine-based core-shell structured indium phosphide quantum dot according to claim 1, wherein the solvent used in the zinc precursor solution comprises any one or more of octadecene, oleylamine, oleic acid, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, and 1-eicosene;

the solvent used for the phosphorus precursor solution comprises any one or more of oleylamine, ethylenediamine, 1, 2-propylenediamine, 1, 3-propylenediamine and 1, 4-butylenediamine.

3. The preparation method of the triphenylphosphine-based core-shell structure indium phosphide quantum dot according to claim 1, wherein the precursor solution in step 1 is prepared by heating and dissolving a raw material in a solvent;

the heating temperature of the zinc precursor solution is 100-150 ℃;

the heating temperature of the selenium precursor solution and the sulfur precursor solution is 60-90 ℃;

the heating temperature of the phosphorus precursor solution is 30-70 ℃.

4. The preparation method of the triphenylphosphine-based core-shell structured indium phosphide quantum dot according to claim 1, wherein the zinc source comprises any one or more of zinc stearate, zinc acetate, zinc oxide, zinc chloride, zinc bromide and zinc iodide;

5. The preparation method of the triphenylphosphine-based core-shell structure indium phosphide quantum dot according to claim 1, wherein the indium halide comprises any one or more of indium iodide, indium bromide and indium chloride; the zinc halide comprises any one or more of zinc bromide, zinc iodide and zinc chloride;

the reaction solvent adopted in the step 2 comprises any one or more of oleylamine, dodecane, hexadecane, hexadecylamine, octadecylamine, octylamine, oleic acid and octadecene.

6. The preparation method of the core-shell structure indium phosphide quantum dot based on the tripyrrolidine according to claim 1 is characterized in that the molar ratio of indium halide, zinc halide and tripyrrolidine in the step 2 is 1 (4.5-5.5): 3.4-5);

the first temperature is 120-140 ℃, and the second temperature is 190-200 ℃;

the reaction time is 30-60 min at the first temperature; and adding the phosphorus precursor solution for reaction for 10-20 min.

7. The preparation method of the triphenylphosphine-based core-shell structure indium phosphide quantum dot according to claim 1, wherein in the step 3, the molar ratio of the zinc source in the zinc precursor solution, the selenium source in the selenium precursor solution, the sulfur source in the sulfur precursor solution and the indium halide is (9-12.5): (2.5-5.5): 1;

the third temperature is 260-280 ℃ and the reaction time is 90-120 min.

8. The preparation method of the core-shell structure indium phosphide quantum dot based on the tripyrrolidine according to claim 1, wherein in the step 4, the molar ratio of zinc source, n-dodecyl mercaptan and indium halide in the zinc precursor solution is (2.5-5.5): (9-19): 1;

the fourth temperature is 290-300 ℃ and the reaction is carried out for 60-80min.

9. A core-shell structured indium phosphide quantum dot prepared according to the preparation method of any one of claims 1-8.

10. The use of the core-shell structured indium phosphide quantum dot as set forth in claim 9 in the photovoltaic field.