CN113698931A

CN113698931A - Nanocrystalline/alumina core-shell structure luminescent material and preparation method thereof

Info

Publication number: CN113698931A
Application number: CN202111001987.5A
Authority: CN
Inventors: 徐庶; 张璐璐; 耿翀
Original assignee: Hebei University of Technology
Current assignee: Hebei University of Technology
Priority date: 2021-08-30
Filing date: 2021-08-30
Publication date: 2021-11-26
Anticipated expiration: 2041-08-30
Also published as: CN113698931B

Abstract

The invention relates to a luminescent material with a nanocrystalline/alumina core-shell structure and a preparation method thereof. The interactive interface of the nanocrystal core and the alumina shell in the nanocrystal/alumina core-shell structure luminescent material has a Type-I heterostructure, and the luminescent material simultaneously has the following properties: the LED device packaged by the prepared material has no fluorescence attenuation phenomenon after running for 1000 hours under the drive of 5mA current. The preparation method comprises the steps of inducing the surface of a nanocrystal modified by an organic acid ligand to react with metal organic aluminum in an anhydrous system, introducing a weak oxidant to control the reaction speed, realizing the low-temperature liquid-phase growth of a crystalline alumina coating layer which is difficult to realize by the traditional method, and preparing the monodisperse nanocrystal/alumina core-shell structure nanoparticles.

Description

Nanocrystalline/alumina core-shell structure luminescent material and preparation method thereof

Technical Field

The invention relates to a high-efficiency stable nanocrystalline/alumina core-shell structure luminescent material and a preparation method thereof, which are applied to the technical field of semiconductor photoelectric materials.

Background

The colloidal semiconductor nanocrystal has the excellent optical and photoelectric characteristics of adjustable spectrum, high luminous efficiency, high solution dispersibility and the like, and has wide application prospect, so that the colloidal semiconductor nanocrystal is attracted by attention. However, the surface of the material is extremely sensitive to moisture, oxygen, temperature, illumination and the like in the environment, so that unstable luminescence performances such as fluorescence quenching and the like occur. Therefore, obtaining good stability while maintaining its excellent performance is one of the major challenges in practical application of semiconductor nanocrystals. At present, oxide coating is considered to be one of the most effective methods for improving perovskite nanocrystals, but at present, there is no report on improving stability by coating crystalline alumina on the surface of the nanocrystals.

Disclosure of Invention

The invention provides a nanocrystalline/alumina core-shell structure luminescent material with high luminescent efficiency and stable performance and a preparation method thereof. The luminescent material is formed by wrapping the nanocrystalline by the crystalline alumina, the stability of the nanocrystalline is greatly improved due to the surface passivation and the water-oxygen barrier property of the crystalline alumina, and meanwhile, the nanocrystalline uniformly wrapped by the alumina still keeps good colloid dispersion property in a solution. The preparation method comprises the steps of inducing the surface of a nanocrystal modified by an organic acid ligand to react with metal organic aluminum in an anhydrous system, introducing a weak oxidant to control the reaction speed, realizing the low-temperature liquid-phase growth of a crystalline alumina coating layer which is difficult to realize by the traditional method, and preparing the monodisperse nanocrystal/alumina core-shell structure nanoparticles. Due to the ultra-wide forbidden band width of the crystalline alumina, an I-type semiconductor heterostructure can be formed by the crystalline alumina and the nanocrystal coated by the crystalline alumina, so that exciton confinement can be effectively in a nanocrystal core, and the luminous quantum efficiency of the nanocrystal is remarkably improved.

The invention adopts the following technical scheme:

the invention provides a nanocrystal/alumina core-shell structure luminescent material with high luminescent efficiency and good stability, which comprises a nanocrystal core and a crystalline alumina shell layer coated on the surface of the nanocrystal.

The interactive interface of the nanocrystal core and the alumina shell in the nanocrystal/alumina core-shell structure luminescent material has a Type-I heterostructure, and the luminescent material simultaneously has the following properties: good water oxygen and environmental tolerance, for example, no fluorescence attenuation phenomenon appears after soaking in ethanol for 30 days; good photochemical stability, such as illumination for 1000 hours at 80 ℃ and under a 405nm blue light continuous excitation aging test, still maintains 100% of the initial fluorescence intensity; and the good stability of the light-emitting device, such as an LED device packaged based on the prepared material, does not generate the phenomenon of fluorescence attenuation after running for 1000 hours under the drive of 5mA current.

The preparation method of the nanocrystalline/alumina core-shell structure luminescent material comprises the following steps: the method comprises the steps of epitaxially growing crystalline aluminum oxide on the surface of a nanocrystal for modifying an organic carboxylate ligand, reacting an organic aluminum precursor with the carboxylate on the surface of the nanocrystal to generate an aluminum oxide thin layer on the surface of the nanocrystal, and subsequently combining with an oxygen source to induce the aluminum oxide thin layer to continuously grow a homogeneous crystalline aluminum oxide shell layer on the thin layer.

The nanocrystal comprises a chalcogenide simple structure, a core-shell structure nanocrystal, a III-V compound simple structure, a core-shell structure nanocrystal, an all-inorganic halide perovskite simple structure and a core-shell structure nanocrystal.

The chalcogenide simple-structure nanocrystal comprises binary, ternary or quaternary simple-structure nanocrystals including CdSe, CdS, CdTe, ZnSe, ZnTe, ZnS, ZnSeS, ZnSeTe, ZnSTe, CdZnS, CdSeS, CdSeTe, CdSTe, PbS, PbSeS, GaP, AgS, AgSe, CuInS₂、CuInSe₂CdZnSeS, CdZnSeTe, CdZnSTe or CuInSSe, wherein the elements in the ternary or quaternary material are similar without proportion limitation;

the shell layer of the chalcogenide core-shell structure nanocrystal is made of CdS, ZnS, ZnSe, ZnTe, ZnO, ZnSeS, ZnSeTe, ZnSTe, CdZnS or CdZnSeS; wherein, the elements of the ternary or quaternary material are not limited by proportion;

the III-V compound simple structure nanocrystalline contains InP, GaP, GaAs and InAs; the shell layer of the III-V compound core-shell structure nanocrystal is made of GaP, ZnS, ZnSe and ZnO.

The all-inorganic halide perovskite simple structure nanocrystal comprises a simple perovskite structure and a perovskite structure containing a doping element.

The perovskite structure is A_xB_yX_zWherein A is one or more of cesium, rubidium and potassium; b is one or more of lead, iron, chromium, tin, copper, antimony, bismuth, silver, fluorine, titanium, tellurium and zirconium; x is halogen anion, and comprises one or more of chlorine, bromine or iodine.

The perovskite structure is preferably AB₂X₃Or A₃B₂X₅Wherein A is monovalent cation and comprises one or more of cesium, rubidium and potassium; b is a monovalent cation and comprises one or more of copper and silver; x is a halogen anion and comprises one or more of chlorine and bromine.

The perovskite structure is preferably ABX₃、A₂BX₄Or A₄BX₆Wherein A is monovalent cation and comprises one or more of cesium, rubidium and potassium; b is divalent cation, and contains one or more of lead, tin, chromium, copper and iron; x is a halogen anion and comprises one or more of chlorine and bromine.

The perovskite structure is preferably A₃B₂X₉Or A₂BX₅Wherein A is monovalent cation and comprises one or more of cesium, rubidium and potassium; b is trivalent cation, comprising one or more of antimony and bismuth; x is a halogen anion and comprises one or more of chlorine and bromine.

The perovskite structure is preferably A₂BX₆Wherein A is monovalent cation and comprises one or more of cesium, rubidium and potassium; b is a quadrivalent cation containing one or more of zirconium, tin, fluorine, tellurium, lead and titanium; x is halogen anion and contains one or more of chlorine and bromine。

The doping element is one or more of manganese, zinc, aluminum, strontium, tin, cobalt, cadmium, europium, samarium, neodymium, erbium, ytterbium, bismuth, iron, nickel, copper, gallium, germanium, arsenic, technetium, ruthenium, rhodium, silver, copper, antimony, rhenium, iridium, platinum, cerium, terbium or dysprosium.

The perovskite core-shell structure is formed by adding a shell layer structure on the basis of the perovskite core structure (the core-shell structure is a lead halide perovskite structure). The lead-halogen perovskite/lead-halogen/perovskite/lead-halogen/lead, or lead-halogen/lead-perovskite/lead-halogen/lead-lead perovskite/lead, or lead-lead perovskite/lead-lead.

The three-dimensional lead-halogen perovskite structure/two-dimensional lead-halogen perovskite structure is preferably CsPbX₃/CsPb₂X₅And X is halogen anion and contains one or more of chlorine, bromine or iodine.

The three-dimensional lead-halogen perovskite structure/zero-dimensional lead-halogen perovskite structure is preferably CsPbX₃/Cs₄PbX₆And X is halogen anion and contains one or more of chlorine, bromine or iodine.

The perovskite core-shell structure is formed by adding a shell layer structure on the basis of the perovskite core structure. The core-shell structure is a chalcogenide or an oxide, such as CdS, ZnS, PbS, ZnO, etc.

The surface of the nanocrystal is modified with carboxylate ligands. Preferably, the carbon chain length of the carboxylate ligand is 4-22, such as oleate, stearate, butyrate, cinnamate, acrylate, phenylpropionate and the like.

The organoaluminum precursor is a compound having the following structural formula: r₃Al、R₂AlZ、RAlZ₂Wherein R is hydrocarbyl, Z is H, F, Cl, Br, OR, SR, NH₂、NHR、NR₂、PR₂And the like. Further, the organoaluminum is preferably an alkylaluminum and a halide thereof, such as trimethylaluminum, triisobutylaluminum, diethylaluminum chloride and the like.

The thickness of the aluminum oxide is 0.5 nm-10 nm, and the aluminum oxide is in a crystalline state in the nanocrystal.

The oxygen source comprises oxygen source gas or oxygen source solution, and the oxygen source gas is oxygen/inert gas mixed gas such as oxygen/nitrogen mixed gas; the oxygen source solution takes a non-polar solvent as a solvent, a solid or liquid oxygen source as a solute, the solute is phosphine oxide or organic peroxide, the phosphine oxide is preferably at least one of trioctylphosphine oxide, tributylphosphine oxide or triphenylphosphine oxide, and the organic peroxide is preferably at least one of tert-butyl perbenzoate or benzoperoxide; the nonpolar solvent is toluene, xylene, n-hexane or n-octane.

The second aspect of the invention provides a preparation method of a luminescent material with a nanocrystalline/alumina core-shell structure, which comprises the following steps:

a: preparing nanocrystalline/alumina core-shell structure nanocrystalline:

the raw materials (nanocrystalline solution, alumina precursor, ligand and the like) and the reaction solvent are subjected to anhydrous or water-removing treatment to remove trace water, so that amorphous alumina or aluminum hydroxide impurities caused by introduction of water molecules in the reaction process are avoided.

Placing the nanocrystalline solution, the nonpolar organic solvent and the amine ligand solution in a three-neck flask, stirring, vacuumizing to ensure that no bubbles are generated in the mixed solution, introducing nitrogen, and keeping stirring and nitrogen atmosphere to obtain the mixed solution; heating to a temperature below the boiling point of the nonpolar organic solvent, slowly injecting an organic aluminum precursor solution (in the organic aluminum precursor solution, the nonpolar solvent such as toluene, xylene, normal hexane and n-octane is used as the solvent, and the organic aluminum is used as the solute), then slowly injecting oxygen source gas or solution, and reacting for 5-120 minutes to obtain the nanocrystal raw solution with the nanocrystal/alumina core-shell structure.

b: cleaning and collecting the nanocrystalline/alumina core-shell structure nanocrystalline:

and c, cleaning and centrifuging the nanocrystalline raw solution with the nanocrystalline/alumina core-shell structure prepared in the step a, taking solid precipitate, and dissolving the solid precipitate in a nonpolar organic solvent to obtain the nanocrystalline/alumina core-shell structure nanocrystalline luminescent material.

The nonpolar organic solvent in the step a is one or more of toluene, n-hexane, n-octane, xylene, tetradecane, octadecane or octadecene.

The amine ligand in the step a is selected from organic amine with a carbon chain length of 4-22;

preferably, the amine ligand in step a is one or more of n-butylamine, hexylamine, octylamine, dodecylamine, tetradecylamine, hexadecylamine, octadecylamine, aniline, amphetamine, phentermine, 1, 4-butanediamine, octadecylamine or oleylamine, etc.

The molar ratio of the nanocrystalline molecules to the amine ligand in the step a is 1:1-1: 8; the molar ratio of the nanocrystalline molecules to the organic aluminum is 4:1-1: 8.

The molar ratio of the organic aluminum to the oxygen source in step a is 1:1 to 1:50, preferably 1:2 to 1: 5.

The organic aluminum in step a is preferably an organic aluminum compound such as trimethylaluminum or triethylaluminum which does not react with the nonpolar organic solvent, and the nonpolar organic solvent in the preparation of the organic aluminum precursor solution may be the same as or different from the nonpolar organic solvent in step a.

The oxygen source described in step a includes an oxygen/inert gas mixed gas such as an oxygen/nitrogen mixed gas, a phosphine oxide such as trioctylphosphine oxide, tributylphosphine oxide or triphenylphosphine oxide, an organic peroxide such as t-butyl perbenzoate and benzoic peroxide, and the like. The non-polar organic solvent in the oxygen source preparation solution may be the same as or different from the non-polar organic solvent in step a.

The temperature of the nonpolar organic solvent is controlled below the boiling point temperature in the step a, namely the reaction temperature is controlled between 10 and 140 ℃.

The cleaning solvent in the step b is one or more of ethyl acetate, ethanol or propanol; the centrifugal rotation speed is 2000-12000 revolutions. The rate of addition of the organoaluminum precursor solution is 20-1000 microliters, preferably 25-200 microliters, per minute. The oxygen source solution is added at a rate of 20 to 1000 microliters, preferably 25 to 200 microliters, per minute.

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

the invention provides a luminescent material with a nanocrystalline/alumina core-shell structure, which comprises a nanocrystalline core and a crystalline alumina shell layer which is coated and grown on the surface of the nanocrystalline core. The prepared core-shell structure nanocrystal has good dispersibility, high luminous efficiency and high stability. Crystalline alumina and nanocrystalline form an I-type semiconductor heterostructure, which can confine excitons in a nanocrystal core and improve radiative recombination efficiency. Crystalline alumina provides a compact barrier layer for the nanocrystal, can effectively prevent the erosion of water vapor, oxygen and light to the nanocrystal, thereby greatly improving the stability of the nanocrystal, having better stability in a polar solvent, and being applied to the field of photoelectric devices.

The invention further provides a preparation method for liquid phase epitaxial growth of crystalline alumina on the surface of a nanocrystal, which comprises the steps of firstly reacting an organic aluminum precursor with carboxylate radicals on the surface of the nanocrystal to generate an alumina thin layer on the surface of the perovskite nanocrystal, and then continuing to grow a homogeneous alumina shell layer on the thin layer by combining with an oxygen source, wherein the whole process is carried out in an anhydrous environment. The preparation method realizes the epitaxial growth of the crystalline alumina on the nanocrystal on the surface of the modified organic carboxylate radical ligand at low temperature, avoids the damage of the crystalline alumina synthesized at high temperature to the nanocrystal at present, improves the quantum efficiency and stability of the nanocrystal, and simultaneously keeps the colloidal dispersion characteristic of the nanocrystal. The preparation method is simple to operate, the synthesis temperature is low, and the quantum efficiency of the perovskite nanocrystal can be greatly improved.

Furthermore, the method can also be used as a general method for epitaxial growth of crystalline oxide on the surface of the nanocrystal, can be used for growth of alumina, and can also be used for low-temperature liquid phase epitaxial growth of oxides such as titanium oxide, zirconium oxide, nickel oxide, indium oxide, gallium oxide and the like, and can be popularized as a universal scheme.

The invention can prepare crystalline alumina coating and has three characteristics or advantages of I-type semiconductor structure, water-oxygen barrier improvement stability and good colloid dispersion maintenance. The water is removed before the reaction to eliminate the influence of water molecules, the adding speed of the organic aluminum precursor solution is controlled to enable the surface reaction to be more controllable, meanwhile, weak oxidants such as trioctylphosphine oxide, anhydrous mixed gas and the like are used as oxidants, the reaction process is controlled to realize slow and controllable reaction, the organic carboxylate radical on the surface of the nanocrystal reacts with the organic aluminum to enable the growth of the aluminum oxide to be controllable, and the phenomenon that the aluminum oxide or the aluminum hydroxide is easily grown into amorphous state in the air (when the oxygen content is higher) or under the condition of containing water molecules is avoided.

The preparation method of the invention overcomes the following problems:

1. the problems that alumina and other oxides grow on the surface of the nanocrystal by generally adopting a metal organic precursor hydrolysis, alcoholysis or air oxidation method in the prior art, the growth controllability is poor, the obtained oxides are not firmly combined with the surface of the nanocrystal, and most of the oxides are coated by amorphous alumina or aluminum hydroxide composite coating are solved. The above problems result in insufficient densification of the surface-grown oxide, surface pores exist and thus fail to provide a dense air barrier, resulting in O₂/H₂O has a high permeability, thereby reducing the protective effect and making it difficult to sufficiently improve quantum efficiency.

2. Annealing inorganic metal oxides at high temperatures above 800c can promote the transition of the alumina from the amorphous to the crystalline state. However, high-temperature annealing needs to be performed in a powder state, so that the colloid dispersion characteristic of the semiconductor nanocrystal is damaged, and high-temperature calcination induces severe fluorescence quenching and decomposition of the nanocrystal, so that a core-shell structure for coating the nanocrystal cannot be formed.

3. The alumina deposited by adopting the modes of vapor deposition (ALD) and the like can only cover colloidal nanocrystals which can not act on dispersion on the surface of the nanocrystals, can not generate uniform coating layers on the surface of the nanocrystals, and is difficult to form a heterostructure to realize exciton confinement.

Drawings

FIG. 1 shows CsPbBr prepared in example 1 of the present invention₃A reaction mechanism diagram of nanocrystalline/alumina core-shell structure nanocrystalline; wherein trimethylaluminum (Me)₃Al) and CsPbBr₃Carboxylate radical on the surface of the nanocrystal and an oxygen source react to grow the nanocrystal/alumina I-type heterostructure semiconductor material.

FIG. 2 shows CsPbBr as a starting material prepared in example 1 of the present invention₃Perovskite nanocrystals and CsPbBr₃Quantum efficiency contrast (left panel) of nanocrystal/alumina core-shell structured nanocrystals and corresponding on-dayPhoto of solution under the light (middle picture) and ultraviolet light (right picture) lamps;

FIG. 3 shows CsPbBr as a starting material prepared in example 1 of the present invention₃Perovskite nanocrystals and CsPbBr₃Infrared spectroscopy (FTIR) of nanocrystalline/alumina core-shell structured nanocrystals;

FIG. 4 shows CsPbBr prepared in example 1 of the present invention₃Transmission Electron Microscope (TEM) image of nanocrystal/alumina core-shell structure nanocrystal, wherein a is CsPbBr prepared in example 1₃TEM image of nanocrystalline/alumina core-shell structure nanocrystalline, inset is prepared CsPbBr₃The size distribution of the nanocrystal/alumina core-shell structure nanocrystal, b is CsPbBr prepared in example 1₃TEM image under single-particle high power lens of nanocrystalline/alumina core-shell structure nanocrystalline;

FIG. 5 is a drawing of the initial CsPbBr prepared in example 1 of the present invention₃Perovskite nanocrystals, CsPbBr₃X-ray diffraction (XRD) patterns of nanocrystals/alumina core-shell structured nanocrystals and their corresponding standard cards;

FIG. 6 is an initial CsPbBr prepared in example 1 of the present invention₃Perovskite nanocrystals and CsPbBr₃The ethanol stability of the nanocrystalline/alumina core-shell structure nanocrystalline is compared; wherein a is the initial CsPbBr prepared in example 1₃Perovskite nanocrystals and CsPbBr₃Comparative optical photograph of nanocrystals/alumina heterostructure nanocrystals immersed in 1 ml of ethanol solution for 30 days, b is the initial CsPbBr prepared in example 1₃Perovskite nanocrystals and CsPbBr₃A fluorescence intensity change diagram of the nanocrystal/alumina core-shell structure nanocrystal soaked in 1 ml of ethanol solution for 30 days;

FIG. 7 shows initial CsPbBr prepared in example 1 of the present invention under the aging test of continuous excitation of blue light at 80 deg.C, 30% humidity and 405nm₃Perovskite nanocrystals and CsPbBr₃A stability contrast diagram of the nanocrystalline/alumina core-shell structure nanocrystalline;

FIG. 8 is a graph of initial CsPbBr prepared in example 1 of the present invention in a 5mA current light aging test₃Perovskite nanocrystals and CsPbBr₃A stability contrast diagram of the nanocrystalline/alumina core-shell structure nanocrystalline;

FIG. 9 shows CsPbBr prepared in example 4 of the present invention₃Transmission Electron Microscope (TEM) images of nanocrystalline/alumina core-shell structured nanocrystalline with different alumina shell layer thicknesses;

FIG. 10 shows CsPbBr prepared in example 5 of the present invention₃Optical picture of nanocrystalline/alumina core-shell structure nanocrystalline powder.

Detailed Description

The invention is further described with reference to the following figures and detailed description. The specific examples are only for illustrating the present invention in further detail and do not limit the scope of protection of the present application.

The preparation method of the nanocrystalline/alumina core-shell structure nanocrystalline comprises the following steps:

a. preparing nanocrystalline/alumina core-shell structure nanocrystalline:

and S1, carrying out anhydrous or water removal treatment on the raw material to remove trace water. Placing the treated nanocrystalline solution, the nonpolar organic solvent and the amine ligand solution in a three-neck flask, stirring, vacuumizing to ensure that no bubbles are generated in the mixed solution, introducing nitrogen, and keeping stirring and nitrogen atmosphere to obtain the mixed solution; carboxylate ions are enriched on the surface of the nanocrystal;

s2, heating to a temperature below the boiling point temperature of the nonpolar organic solvent, and then slowly injecting an organic aluminum precursor solution into the mixed solution to react aluminum ions with carboxylate ions on the surface of the perovskite to generate an alumina thin layer;

and S3, injecting an oxygen source, reacting for 5-120 minutes, and inducing to continue to grow a homogeneous alumina shell layer on the thin layer by combining the oxygen source, thereby finally obtaining the nanocrystal raw solution with the nanocrystal/alumina core-shell structure.

b. Cleaning and collecting the nanocrystalline/alumina core-shell structure nanocrystalline:

and c, cleaning and centrifuging the nanocrystalline/alumina core-shell structure nanocrystalline stock solution prepared in the step a, taking solid precipitate, and dissolving the solid precipitate in a nonpolar organic solvent to obtain the nanocrystalline/alumina core-shell structure luminescent material.

The nanocrystalline comprises a chalcogenide simple structure, core-shell structure nanocrystalline, a III-V compound simple structure, core-shell structure nanocrystalline, a full-inorganic halide perovskite simple structure and core-shell structure nanocrystalline;

the perovskite is halide perovskite nanocrystalline, and the perovskite structure is preferably ABX₃Wherein A is monovalent cation including one or more of cesium, rubidium and potassium; b is divalent cation, including one or more of lead, tin, copper, bismuth and silver; x is halogen anion, and comprises one or more of chlorine, bromine or iodine.

The nonpolar organic solvent in the step a is one or more of toluene, n-hexane, n-octane, xylene, tetradecane, octadecane or octadecene. More preferably toluene or xylene.

The molar ratio of the organic aluminum to the oxygen source in step a is 1:5 to 1: 50.

The organic aluminum in step a is preferably an organic aluminum compound such as trimethylaluminum or triethylaluminum which does not react with the nonpolar organic solvent, and the nonpolar organic solvent in the preparation of the organic aluminum precursor solution may be the same as or different from the nonpolar organic solvent in the first step.

The oxygen source described in step a includes an oxygen/inert gas mixed gas such as an oxygen/nitrogen mixed gas, a phosphine oxide such as trioctylphosphine oxide, tributylphosphine oxide or triphenylphosphine oxide, an organic peroxide such as t-butyl perbenzoate and benzoic peroxide, and the like.

The cleaning solvent in the step b is one or more of ethyl acetate, ethanol or propanol; wherein the volume ratio of the material solution to the ethyl acetate solution is 1:1-1: 5; the volume ratio of the material solution to the ethanol solution is 5:1-1: 2; the centrifugal rotation speed is 2000-12000 revolutions.

Example 1

CsPbBr₃/Al₂O₃Preparing a core-shell structure luminescent material:

all raw materials were subjected to dehydration treatment. 5 ml of 0.01M CsPbBr were added at room temperature₃The toluene solution, 75 microliters of octylamine and 5 milliliters of toluene are placed in a 25 milliliter three-neck flask, the stirring speed is 500 revolutions per minute, the vacuum is pumped for 2 to 5 minutes until no bubbles are generated in the mixed solution, and nitrogen is introduced. The temperature was raised to 60 ℃ in 2 minutes, at which 0.7 ml of a 0.1M trimethylaluminum toluene solution was added to the above mixed solution at a rate of 50. mu.l/min to start the reaction, followed by injection of 0.7 ml of a 1M tri-n-octylphosphorus oxide toluene solution, stirring the reaction for further 30 minutes, and the solution was cooled to room temperature.

And mixing the obtained material solution with ethyl acetate according to the volume ratio of 1:3, putting the mixture into a centrifugal tube, centrifugally cleaning the mixture at the speed of 8000 rpm for 10 minutes, removing the upper-layer impurity solution after all the nanocrystalline/alumina core-shell structure nanocrystalline is precipitated, re-dispersing the precipitated material into toluene for storage, and finally obtaining the nanocrystalline/alumina core-shell structure nanocrystalline luminescent material.

FIG. 1 is a schematic diagram of the surface reaction mechanism of the material of the present invention obtained in example 1 and the band structure formed by the two materials, trimethylaluminum (Me)₃Al) is firstly combined with organic carboxylate ligands on the surface of perovskite to form an alumina thin layer, then combined with oxygen sources to gradually grow to form a thicker alumina shell layer, and finally the amine ligand modified CsPbBr is prepared₃Nanocrystal/alumina core-shell structure nanocrystal; according to the energy band positions of the perovskite and the aluminum oxide material, the aluminum oxide is a perovskite nuclear layer coating material, and the energy band of the aluminum oxide material is largeIn the materials of the core layer, the two materials finally form a Type-I core-shell structure, so that exciton confinement can be effectively in the perovskite nanocrystal core, environmental influence is resisted, and stability and efficiency are improved.

FIG. 2 shows CsPbBr obtained in example 1₃Perovskite nanocrystals and CsPbBr₃A comparison graph (left graph) of fluorescence quantum efficiency of the nanocrystal with the nanocrystal/alumina core-shell structure (adopting an ocean optics QEpro quantum efficiency test system, the excitation light source is 450nm) and a photo (right graph) of two samples under the excitation of a fluorescent lamp (middle graph) and an ultraviolet lamp (365nm) correspondingly. It can be seen from the figure that the quantum efficiency of the nanocrystals/alumina is greatly improved (from 58.26% to 98.69%) compared to the original perovskite nanocrystals due to the surface passivation and carrier confinement of alumina. This difference can also be seen in the picture given in the figure (middle panel), where the perovskite nanocrystal solution is yellow in color and the nanocrystal/alumina nanocrystal solution is green in color (although the color is not visible in the figure for grey scale reasons).

FIG. 3 is an infrared spectrum test of the nanocrystal/alumina core-shell structure nanocrystal and the original perovskite nanocrystal obtained in example 1, and it can be seen from the infrared spectrum that the nanocrystal/alumina core-shell structure nanocrystal prepared by the invention has the advantages that compared with the original perovskite, O-C ═ O bonds disappear and the thickness is 800cm^-1The stretching vibration of Al-O bonds appears, and N-H functional groups are added, so that the fact that aluminum ions grow on the surface of the perovskite through the combination of carboxylate radicals on the surface of the perovskite is proved, and finally the amine ligand modified nanocrystalline/alumina nanocrystalline is formed.

FIG. 4 is a transmission electron microscope topography of the nanocrystal/alumina core-shell structured nanocrystal prepared in example 1. From the TEM image, it can be seen that the size distribution of the nanocrystal/alumina core-shell structure nanocrystal is uniform, and the average particle size is about 18.69 nm (shown as a in FIG. 4); in fig. 4, b is an image of a single-particle core-shell structure of the nanocrystal/alumina nanocrystal prepared in example 1, and it can be seen that the nanocrystal/alumina core-shell structure nanocrystal has a crystal structure with distinct grain boundaries.

Fig. 5 is an XRD pattern of the nanocrystal/alumina core-shell structure nanocrystal prepared in example 1, from which it can be known that the original perovskite nanocrystal exhibits a cubic phase structure (PDF card corresponds to JCPDS 54-0752). Compared with the original perovskite, the nanocrystalline/alumina core-shell structure nanocrystalline has an alumina diffraction peak (PDF card corresponding to JCPDS 35-0121), which indicates that alumina grows on the surface of the perovskite.

FIG. 6 is a comparison of ethanol stability over time for the nanocrystalline/alumina core-shell structured nanocrystals prepared in example 1 and the original perovskite nanocrystals (control) under 365nm blue light excitation; wherein, a in fig. 6 is the solution change condition of the material of the present invention and the original perovskite material respectively soaked in ethanol for 30 days. In fig. 6, b is a comparison graph of fluorescence attenuation of the material of the invention and the original perovskite nano-crystal in ethanol corresponding to a, and it can be seen from the graph that the material of the invention has no fluorescence attenuation phenomenon in 30 days, while the fluorescence intensity of the original perovskite nano-crystal is attenuated to 5% in day 2, and the structural form of the invention obviously enhances the ethanol stability.

FIG. 7 is a graph of the stability of the nanocrystalline/alumina core-shell structured nanocrystals prepared in example 1 and the initial perovskite nanocrystals (control) in the 80 deg.C, 30% relative humidity and 405nm blue light continuous excitation aging test; as can be seen from the figure, the material of the invention still keeps 100 percent of the initial fluorescence intensity after being heated and irradiated for 1000 hours under the condition, and shows excellent light-resistant and heat-resistant properties. The fluorescence intensity of the original perovskite nanocrystal decays very fast, and the decay is 0% by 200 hours.

Fig. 8 is a stability curve of the nanocrystalline/alumina core-shell structured nanocrystalline and the initial perovskite nanocrystalline (comparative sample) prepared in example 1 driven by a current of 5mA, and it can be seen that the nanocrystalline/alumina core-shell structured nanocrystalline has no fluorescence decay phenomenon after aging for 700 hours. The fluorescence intensity of the perovskite nanocrystals (control) decreased linearly to 20% within 240 hours and the fluorescence completely attenuated from 240 hours to 700 hours, further demonstrating the excellent stability of the nanocrystal/alumina nanocrystals prepared in example 1.

Example 2

CsPbClBr₂/Al₂O₃Preparing a core-shell structure luminescent material:

all raw materials were subjected to dehydration treatment.

In a glove box, 5 ml of 0.01M CsPbClBr after water removal was added under room temperature₂The toluene solution, 150. mu.l oleylamine, was placed in a 25 ml three-neck flask with a stirring speed of 500 revolutions per minute. The solution was warmed to 60 ℃ over 2 minutes, at which temperature 0.2 ml of triethylaluminum solution was added to the above mixed solution at a rate of 50. mu.l/min, followed by injection of 0.5 ml of 1M toluene solution of tri-n-octylphosphine oxide, stirring was continued for 30 minutes, and the solution was cooled to room temperature.

And mixing the obtained material solution with ethyl acetate according to the volume ratio of 1:3, putting the mixture into a centrifugal tube, centrifugally cleaning the mixture at the speed of 8000 rpm for 10 minutes, removing the upper-layer impurity solution after all the nanocrystalline/alumina core-shell structure nanocrystalline is precipitated, re-dispersing the precipitated material into a toluene solution, and storing to finally obtain the perovskite/alumina core-shell structure luminescent material.

Example 3

CsPbBrI₂/Al₂O₃Preparing a core-shell structure luminescent material:

in this example, 5 ml of 0.01M CsPbBrI was added at room temperature₂The toluene solution and 5 ml of toluene are put into a 25 ml three-neck flask, the stirring speed is 500 r/min, the vacuum is pumped for 2-5 min until no bubble is generated in the mixed solution, and nitrogen is introduced. The remaining steps were the same as in example 2.

Example 4

CsPbBr₃/Al₂O₃Preparing a core-shell structure luminescent material:

the procedure of this example was the same as example 1 except that 0.25 ml, 0.5 ml, 0.75 ml and 0.1 ml of 0.1M trimethylaluminum toluene solution was added to the above mixed solution at a rate of 50. mu.l/min at 60 ℃ followed by injection of 0.25 ml, 0.5 ml, 0.75 ml and 0.1 ml of 1M tri-n-octylphosphorus oxide toluene solution, stirring was continued for 30 minutes and the solution was cooled to room temperature to obtain alumina shells having different thicknesses.

FIG. 9 is a transmission electron microscope topography of the nanocrystal/alumina core-shell structured nanocrystal prepared in example 4. As can be seen from the figure, the thickness of the alumina shell corresponds to the amount of the different aluminum precursors injected during the reaction process, which is 0.91 nm, 1.52 nm, 2.86 nm and 3.33 nm, respectively.

Example 5

CsPbBr₃/Al₂O₃Preparing a core-shell structure luminescent material:

the procedure of this example is the same as example 1 except that 0.7 ml of a 1M toluene solution of tributyl phosphonium oxide is injected.

FIG. 10 is a photograph of the nanocrystal/alumina core-shell structure nanocrystal solid powder prepared in example 5 under the irradiation of a fluorescent lamp (left drawing) and an ultraviolet lamp (right drawing). The photograph under the fluorescent lamp was green powder and the photograph under the ultraviolet lamp showed bright green light. (although the colors are not visible in figure 10 for grayscale photographs).

Crystalline alumina is wrapped outside the nanocrystalline luminescent material obtained in the embodiment, the crystalline alumina is an ultra-wideband gap semiconductor and can be compounded with semiconductor nanocrystals to form an I-type semiconductor heterostructure, excitons are effectively confined in the nanocrystals, quantum efficiency is fully improved, the crystalline alumina has excellent water-oxygen blocking capability, and the nanocrystals can be effectively protected.

Example 6

In this example, an InP/ZnS nanocrystal/alumina core-shell structure is prepared using an InP/ZnS nanocrystal as a raw material, and all the raw materials are dehydrated in the same manner as in example 1, and alumina is grown using a 2% oxygen/nitrogen mixed gas as a weak oxygen source. Obtaining the core-shell structure of the InP/ZnS nanocrystalline wrapped by the crystalline alumina.

Example 7

Organic carboxylate ligand modification is carried out on the surface of the CdSe/ZnS nanocrystal, organic zirconium is used as a zirconium source, epitaxial growth is carried out according to the mode of embodiment 1, and a CdSe/ZnS nanocrystal/crystalline zirconia core-shell structure is obtained by combining an oxygen source.

Example 8

The steps of this example are the same as example 1, except that the raw materials were used without being dehydrated.

The nanocrystal raw materials are all nanocrystals modified by organic carboxylate ligands.

The invention is not the best known technology.

Claims

1. The luminescent material with the nanocrystalline/alumina core-shell structure is characterized by comprising a nanocrystalline core and a crystalline alumina shell layer coated on the surface of the nanocrystalline.

2. The luminescent material as claimed in claim 1, wherein the interface between the nanocrystal core and the alumina shell in the nanocrystal/alumina core-shell structure luminescent material has a Type-I heterostructure, and the luminescent material has the following properties: the water-oxygen and environment tolerance is good, and the phenomenon of fluorescence attenuation does not occur after the glass is soaked in ethanol for 30 days; good photochemical stability, and the initial fluorescence intensity is still kept at 100 percent under the conditions of illumination for 1000 hours at 80 ℃ and a 405nm blue light continuous excitation aging test; and the LED device packaged by the prepared material has good stability, and does not have the phenomenon of fluorescence attenuation after running for 1000 hours under the drive of 5mA current.

3. The luminescent material according to claim 1, wherein the luminescent material is prepared by: the method comprises the steps of epitaxially growing crystalline aluminum oxide on the surface of a nanocrystal for modifying an organic carboxylate ligand, reacting an organic aluminum precursor with the carboxylate on the surface of the nanocrystal to generate an aluminum oxide thin layer on the surface of the nanocrystal, and subsequently combining with an oxygen source to induce the aluminum oxide thin layer to continuously grow a homogeneous crystalline aluminum oxide shell layer on the thin layer.

4. The luminescent material according to claim 1, wherein the nanocrystals comprise chalcogenide simple structures and core-shell structured nanocrystals, group III-V compound simple structures and core-shell structured nanocrystals, all-inorganic halide perovskite simple structures and core-shell structured nanocrystals;

the chalcogenide core-shell structure nanocrystal comprises a shell layer made of CdS, ZnS, ZnSe, ZnTe, ZnO, ZnSeS, ZnSeTe, ZnSTe, CdZnS or CdZnSeS; wherein, the elements of the ternary or quaternary material are not limited by proportion;

the III-V compound simple structure nanocrystalline contains InP, GaP, GaAs and InAs; the shell layer of the III-V compound core-shell structure nanocrystal comprises GaP, ZnS, ZnSe and ZnO;

the all-inorganic halide perovskite simple structure comprises a simple perovskite structure and a perovskite structure containing a doping element;

the perovskite structure is A_xB_yX_zWherein A is one or more of cesium, rubidium and potassium; b is one or more of lead, iron, chromium, tin, copper, antimony, bismuth, silver, fluorine, titanium, tellurium and zirconium; x is halogen anion, and comprises one or more of chlorine, bromine or iodine;

the perovskite structure is preferably AB₂X₃Or A₃B₂X₅Wherein A is monovalent cation and comprises one or more of cesium, rubidium and potassium; b is a monovalent cation and comprises one or more of copper and silver; x is a halogen anion and comprises one or more of chlorine and bromine;

the perovskite structure is preferably ABX₃、A₂BX₄Or A₄BX₆Wherein A is monovalent cation and comprises one or more of cesium, rubidium and potassium; b is divalent cation, and contains one or more of lead, tin, chromium, copper and iron; x is halogen anionIons comprising one or more of chlorine and bromine;

the perovskite structure is preferably A₃B₂X₉Or A₂BX₅Wherein A is monovalent cation and comprises one or more of cesium, rubidium and potassium; b is trivalent cation, comprising one or more of antimony and bismuth; x is a halogen anion and comprises one or more of chlorine and bromine;

the perovskite structure is preferably A₂BX₆Wherein A is monovalent cation and comprises one or more of cesium, rubidium and potassium; b is a quadrivalent cation containing one or more of zirconium, tin, fluorine, tellurium, lead and titanium; x is a halogen anion and comprises one or more of chlorine and bromine;

the doping element is one or more of manganese, zinc, aluminum, strontium, tin, cobalt, cadmium, europium, samarium, neodymium, erbium, ytterbium, bismuth, iron, nickel, copper, gallium, germanium, arsenic, technetium, ruthenium, rhodium, silver, copper, antimony, rhenium, iridium, platinum, cerium, terbium or dysprosium;

the perovskite core-shell structure is formed by adding a shell layer structure on the basis of a perovskite core structure, and the core-shell structure is a lead-halogen perovskite structure and comprises a three-dimensional lead-halogen perovskite structure/a two-dimensional lead-halogen perovskite structure and a three-dimensional lead-halogen perovskite structure/a zero-dimensional lead-halogen perovskite structure.

The three-dimensional lead-halogen perovskite structure/two-dimensional lead-halogen perovskite structure is preferably CsPbX₃/CsPb₂X₅X is a halogen anion containing one or more of chlorine, bromine or iodine;

the three-dimensional lead-halogen perovskite structure/zero-dimensional lead-halogen perovskite structure is preferably CsPbX₃/Cs₄PbX₆X is a halogen anion containing one or more of chlorine, bromine or iodine;

5. The nanocrystal of claim 3, wherein the nanocrystal is characterized by comprisingModifying a carboxylate ligand on the crystal surface, preferably selecting a carboxylate ligand with a carbon chain length of 4-22, such as an oleate, a stearate, a butyrate, a cinnamate, an acrylate and a phenylpropionate; the organoaluminum precursor has a compound of the formula: r₃Al、R₂AlZ、RAlZ₂Wherein R is hydrocarbyl, Z is H, F, Cl, Br, OR, SR, NH₂、NHR、NR₂、PR₂Etc.; further, the organoaluminum is preferably an alkylaluminum and a halide thereof, such as trimethylaluminum, triisobutylaluminum, diethylaluminum chloride and the like.

6. The luminescent material according to claim 1, wherein the alumina has a thickness of 0.5nm to 10nm, and the alumina is crystalline in the nanocrystal.

7. A method for preparing the nanocrystalline/alumina core-shell structure luminescent material according to claim 1, which comprises the following steps:

a: preparing nanocrystalline/alumina core-shell structure nanocrystalline:

the raw materials are treated in an anhydrous or water-removing way to remove trace water,

placing the treated nanocrystalline solution, the nonpolar organic solvent and the amine ligand solution in a three-neck flask, stirring, vacuumizing to ensure that no bubbles are generated in the mixed solution, introducing nitrogen, and keeping stirring and nitrogen atmosphere to obtain the mixed solution; heating to a temperature below the boiling point of the nonpolar organic solvent, slowly injecting an organic aluminum precursor solution into the mixed solution, then injecting a weak oxidant oxygen source, and reacting for 5-120 minutes to obtain a nanocrystal raw solution with a nanocrystal/alumina core-shell structure;

b, cleaning and centrifuging the nanocrystalline/alumina core-shell structure nanocrystalline stock solution prepared in the step a, then taking a solid precipitate, and dissolving the solid precipitate in a nonpolar organic solvent to obtain the nanocrystalline/alumina core-shell structure luminescent material;

in the step a, the amine ligand solution and the organic aluminum precursor solution are mixed firstly, and then the mixture is added into the mixed solution of the nanocrystal solution and the nonpolar solvent.

8. The preparation method according to claim 7, wherein the organic aluminum precursor solution contains a nonpolar solvent as a solvent and organic aluminum as a solute, and the nonpolar solvent is toluene, xylene, n-hexane or n-octane; the organic aluminum is an organic aluminum compound which does not react with the non-polar organic solvent, and the molar ratio of the organic aluminum to the oxygen source is 1:1-1:50, preferably 1:2-1: 5;

the amine ligand is selected from organic amine with a carbon chain length of 4-22; the amine ligand is one or more of n-butylamine, hexylamine, octylamine, dodecylamine, tetradecylamine, hexadecylamine, octadecylamine, aniline, amphetamine, phentermine, 1, 4-butanediamine, octadecylamine or oleylamine; the molar ratio of the nanocrystalline molecules to the amine ligand in the step a is 1:1-1: 8; the molar ratio of the nanocrystalline molecules to the organic aluminum is 4:1-1: 8;

The boiling temperature of the nonpolar organic solvent in the step a is controlled to be below 10-140 ℃, namely the reaction temperature is controlled to be below; the cleaning solvent in the step b is one or more of ethyl acetate, ethanol or propanol; the centrifugal rotating speed is 2000-12000 turns; the adding speed of the organic aluminum precursor solution is 20-1000 microliter per minute, preferably 25-100 microliter; the oxygen source solution is added at a rate of 20 to 1000 microliters per minute, preferably 25 to 100 microliters.

9. Use of a luminescent material according to any one of claims 1 to 6 or obtained by a method according to any one of claims 7 to 8 in an optoelectronic device.

10. A nanocrystalline epitaxial growth method is characterized in that crystalline oxide is epitaxially grown on the surface of a nanocrystal for modifying an organic carboxylate radical ligand, and an oxygen source is combined to induce the nanocrystalline oxide to continuously grow a homogeneous crystalline oxide shell layer on the crystalline oxide, wherein the crystalline oxide shell layer is a crystalline titanium oxide shell layer, a crystalline zirconium oxide shell layer, a crystalline nickel oxide shell layer, a crystalline indium oxide shell layer or a crystalline gallium oxide shell layer.