CN111019628A

CN111019628A - Preparation method of core-shell structure nanocrystal

Info

Publication number: CN111019628A
Application number: CN201811171921.9A
Authority: CN
Inventors: 程陆玲; 杨一行
Original assignee: TCL Research America Inc
Current assignee: TCL Corp; TCL Research America Inc
Priority date: 2018-10-09
Filing date: 2018-10-09
Publication date: 2020-04-17

Abstract

The invention provides a preparation method of core-shell structure nanocrystalline, which comprises the following steps: providing a quantum dot core; performing shell layer growth on the surface of the quantum dot core for N times to prepare N shell layers to obtain core-shell structure nanocrystalline, wherein a shell source for shell growth comprises a shell source cation precursor and a shell source anion precursor, and the shell source cation precursor is metal organic carboxylate; adding organic amine into a shell growth reaction system which forms a previous shell for mixing and heating between M adjacent shell growth steps in different orders, and then growing the next shell; wherein N is a positive integer greater than or equal to 2; m is a positive integer, and the value of M satisfies: n/3 is more than or equal to M and less than or equal to N-1; dispersing the core-shell structure nanocrystal in a solution containing an organic acid for heating treatment.

Description

Preparation method of core-shell structure nanocrystal

Technical Field

The invention belongs to the technical field of nanocrystalline material preparation, and particularly relates to a preparation method of core-shell structure nanocrystals.

Background

Nanoscience and nanotechnology are emerging scientific technologies and have potential application value and economic benefits, and thus are receiving attention of scientists worldwide. Nanocrystals (NCs) can exhibit very interesting phenomena with respect to bulk materials, mainly depending on their electrical, optical, magnetic and electrochemical properties (which are not achievable with corresponding bulk materials). Semiconductor nanocrystals, also known as Quantum Dots (QDs), range in size from 1 to 10nm, and when the size of the particle size is varied, the band gap valence band and conduction band of the semiconductor nanocrystal are also altered (quantum size effect), such as absorption and emission of CdSe nanocrystals covering almost the entire visible spectral range, and thus, semiconductor nanocrystals exhibit size-dependent phenomena of photoluminescence. Semiconductor nanocrystals have been used in many areas of technology such as biomarkers, diagnostics, chemical sensors, light emitting diodes, electroluminescent devices, photovoltaic devices, lasers, and electronic transistors, among others. However, different types of semiconductor quantum dots are required to be prepared aiming at the application in different technical fields, and the preparation of high-quality semiconductor quantum dots is a precondition for the effective application of the size effect of the semiconductor quantum dots.

In the past decades, researchers have developed a number of methods to obtain high quality semiconductor nanocrystals. The prior art mainly comprises surface ligand modification and core-shell structure design. In the design of the core-shell structure, the core is made of a narrow-bandgap semiconductor material, and the shell is made of a wide-bandgap material. The synthesis means of the core-shell structure mainly comprises a one-step method, a two-step method and a three-step method. The one-step method refers to that the core-shell quantum dots are subjected to long core and long shell in one reaction vessel. The two-step method means that the preparation of the core-shell quantum dot comprises two steps: and (3) carrying out core growing in a reaction vessel, taking out the quantum dot core, and placing the quantum dot core in another reaction solvent for shell growing. The three-step method refers to that the preparation of the core-shell quantum dot comprises two steps: and one reaction vessel is used for carrying out core growth, the quantum dot cores are taken out and then placed in another reaction solvent for intermediate shell layer growth, and the core-shell quantum dots containing the intermediate shell layers are taken out and placed in a third reaction vessel for outermost shell layer growth. At present, a shell layer growth mode adopted for preparing the core-shell structure nanocrystalline is utilized, whether the shell layer growth mode is a one-step long shell mode, a two-step long shell mode or a three-step long shell mode, generally, continuous injection growth is carried out simply by utilizing a shell source precursor, the method cannot well control the shell layer growth quality, and the method is mainly embodied on the particle seed surface of the final quantum dot nanocrystalline, and has the defects of large lattice stress between atoms and shell layer atoms, poor photo-thermal stability and non-uniform size, and the crystal lattice defect and the low fluorescence intensity of the shell layer surface of epitaxial crystal, so that the finally prepared core-shell quantum dot has poor photo-thermal stability, low fluorescence intensity and poor solubility. Therefore, the research on the growth mode of the shell layer of the core-shell quantum dot and the control of the growth of the shell layer are of great significance.

Disclosure of Invention

The invention aims to provide a preparation method of a core-shell structure nanocrystal, and aims to solve the problems that in the existing preparation method of the core-shell structure nanocrystal, the lattice stress between atoms and shell layer atoms on the particle seed surface of the nanocrystal is large due to a simple mode of continuous injection growth by using a shell source precursor, so that the core-shell structure nanocrystal has poor photo-thermal stability, nonuniform size, and low fluorescence intensity due to lattice defect on the surface of the shell layer of epitaxial crystal.

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

the invention provides a preparation method of core-shell structure nanocrystalline, which comprises the following steps:

providing a quantum dot core;

performing shell layer growth on the surface of the quantum dot core for N times to prepare N shell layers to obtain core-shell structure nanocrystalline, wherein a shell source for shell growth comprises a shell source cation precursor and a shell source anion precursor, and the shell source cation precursor is metal organic carboxylate; adding organic amine into a shell growth reaction system which forms a previous shell for mixing and heating between M adjacent shell growth steps in different orders, and then growing the next shell; wherein N is a positive integer greater than or equal to 2; m is a positive integer, and the value of M satisfies: n/3 is more than or equal to M and less than or equal to N-1;

dispersing the core-shell structure nanocrystal in a solution containing an organic acid for heating treatment.

The preparation method of the core-shell structure nanocrystal provided by the invention takes metal organic carboxylate as a cation precursor of a shell layer, and prepares the core-shell quantum dot with a multilayer shell structure by growing the shell layer for N times. Adding organic amine into a shell growth reaction system which forms a previous shell between M adjacent shell growth steps in different orders, mixing and heating, and then growing the next shell. The organic amine is easier to combine on the surface of the metal atom of the shell layer, and can partially exchange the organic carboxylic acid ligand derived from the shell source on the surface of the former shell layer and fill the cation vacancy of the former shell layer. In the process of the growth of the latter shell, because the binding force between the organic amine and the metal atoms on the surface of the shell is relatively weaker, the organic amine can be desorbed from the metal atoms on the surface of the former shell only by less energy, so that in the process of the growth of the shells in the current sequence, anions in the shell source precursor are more easily combined with the metal ions on the surface of the former shell for epitaxial growth, thereby avoiding the larger lattice stress of the core-shell quantum dots between atoms at the interface of the shells and the shells, reducing the lattice defects existing on the surface of the shell of epitaxial crystallization, further improving the fluorescence intensity, improving the photothermal light qualitative and the film forming property of the quantum dots, and finally improving the current efficiency and the device life of the QLED device.

Further, the core-shell structure nanocrystal is dispersed into a solution containing organic acid for heating treatment. The organic acid can effectively eliminate protonated organic amine (derived from modifier organic amine for eliminating lattice defects in the growth process of the shell layer) connected to the surface of the shell layer of the core-shell structure nanocrystal, reduce organic amine ligands with charges on the surface of the core-shell structure nanocrystal, prevent excitons (electrons) generated by the core-shell structure nanocrystal during luminescence from being captured by the organic amine ligands with charges on the surface, and further prolong the transient fluorescence life of the nanocrystal.

Detailed Description

In order to make the technical problems, technical solutions and advantageous effects to be solved by the present invention more clearly apparent, the present invention is further described in detail below with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

In the description of the present invention, it is to be understood that the terms "first", "second" and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.

The embodiment of the invention provides a preparation method of a core-shell structure nanocrystal, which comprises the following steps:

s01, providing a quantum dot core;

s02, performing shell layer growth on the surface of the quantum dot core for N times, preparing N shell layers, and obtaining core-shell structure nanocrystalline, wherein a shell source for shell growth comprises a shell source cation precursor and a shell source anion precursor, and the shell source cation precursor is metal organic carboxylate; adding organic amine into a shell growth reaction system which forms a previous shell for mixing and heating between M adjacent shell growth steps in different orders, and then growing the next shell; wherein N is a positive integer greater than or equal to 2; m is a positive integer, and the value of M satisfies: n/3 is more than or equal to M and less than or equal to N-1;

s03, dispersing the core-shell structure nanocrystals in a solution containing organic acid for heating treatment.

According to the preparation method of the core-shell structure nanocrystal, provided by the embodiment of the invention, the metal organic carboxylate is used as a cation precursor of a shell layer, and the core-shell quantum dot with the multilayer shell structure is prepared by growing the shell layer for N times. Adding organic amine into a shell growth reaction system which forms a previous shell between M adjacent shell growth steps in different orders, mixing and heating, and then growing the next shell. The organic amine is easier to combine on the surface of the metal atom of the shell layer, and can partially exchange the organic carboxylic acid ligand derived from the shell source on the surface of the former shell layer and fill the cation vacancy of the former shell layer. In the process of the growth of the latter shell, because the binding force between the organic amine and the metal atoms on the surface of the shell is relatively weaker, the organic amine can be desorbed from the metal atoms on the surface of the former shell only by less energy, so that in the process of the growth of the shells in the current sequence, anions in the shell source precursor are more easily combined with the metal ions on the surface of the former shell for epitaxial growth, thereby avoiding the larger lattice stress of the core-shell quantum dots between atoms at the interface of the shells and the shells, reducing the lattice defects existing on the surface of the shell of epitaxial crystallization, further improving the fluorescence intensity, improving the photothermal light qualitative and the film forming property of the quantum dots, and finally improving the current efficiency and the device life of the QLED device.

Specifically, in an embodiment of step S01, since the subsequent long shell method in this embodiment is not limited, the method can be applied to, for example, a one-step method, a two-step method, or a three-step method. Thus, in one particular embodiment, the quantum dot core may be a one-step long shell in-process quantum dot core; in a specific embodiment, the solution containing the quantum dot core can be the quantum dot after the quantum dot core is prepared and purified by washing, and the embodiment is mainly suitable for a two-step method and a three-step method.

The quantum dot core may be selected from at least one of a group II/VI quantum dot core, a group III/V quantum dot core, a group III/VI quantum dot core, and a group II/III/VI quantum dot core, but is not limited thereto. By way of example, the group II/VI quantum dot core may be selected from CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, CdZnSe, CdSSe, ZnSe, ZnCdS, ZnCdSe, zneses, ZnCdTe, ZnCdSSe, ZnCdSeS, and ZnCdTeS, but is not limited thereto; the group III/V quantum dot core may be selected from InAs, InP, GaAs, GaP, GaSb, InSb, AlAs, AlP, AlSb, InGaAs, GaAsP, and InAsP, but is not limited thereto; by way of example, the group III/VI quantum dotsThe core is selected from InS and In₂S₃、InSe、In₂Se₃、In₄Se₃、In₂Se₃、InTe、In₂Se₃、GaS、Ga₂Se₃、GaSe、Ga₂Se₃、GaTe、Ga₂Te₃But are not limited thereto; the group II/III/VI quantum dot core is selected from the group consisting of CuInS, CuInZnS and CuInSeS, but is not limited thereto. Preferably, the quantum dot core may be selected from group II/VI quantum dot cores.

In the embodiment of the invention, the surface ligand is combined on the surface of the quantum dot core. The surface ligand is selected from at least one of organic carboxylic acid ligand, organic phosphonic acid ligand, organic phosphine ligand and phosphine oxide ligand. Specifically, the organic carboxylic acid ligand is preferably selected from at least one of oleic acid, myristic acid and lauric acid; the organic phosphonic acid ligand is preferably selected from at least one of octadecyl phosphonic acid, tetradecyl phosphonic acid and dodecyl; the organophosphine ligand is preferably selected from at least one of, but not limited to, trioctylphosphine and tributylphosphine; the phosphine oxide ligand is preferably selected from at least one of trioctylphosphine oxide and tributylphosphine oxide.

Preferably, before the shell layer is prepared on the surface of the quantum dot core, the quantum dot core is subjected to modification treatment.

As a preferred embodiment, the quantum dot core is dispersed in the solution containing the organic carboxylic acid and subjected to a heating treatment, and the quantum dot core is subjected to a surface modification treatment, so that the organic carboxylic acid is bonded to cations on the surface of the quantum dot core, so as to fill cation vacancies of the quantum dot core, reduce defect states between core-shell interfaces, and provide a good epitaxial interface for the growth of a shell layer. Meanwhile, the organic carboxylic acid can also play a role in passivating the surface of the quantum dot core, so that the quantum dot core cannot be self-cured in the stage of heating to the long shell temperature, and the quantum dot with uniform particle size is obtained.

Preferably, the quantum dot core is dispersed in the solution containing the organic carboxylic acid and heated at a temperature of 80 to 150 ℃ for 20 to 60 min. Under the condition, the organic carboxylic acid is stably combined on the surface of the quantum dot, so that the organic carboxylic acid can fully play a passivation role.

Preferably, the organic carboxylic acid in the solution containing the organic carboxylic acid is selected from organic carboxylic acids with 8-18 carbon atoms, and in this case, the organic carboxylic acid has relatively small steric hindrance, which is beneficial for the passivation treatment of the organic carboxylic acid. Further, the organic carboxylic acid is selected from linear organic carboxylic acids containing one carboxyl group, and the linear organic carboxylic acids are favorable for reducing steric hindrance and promoting passivation. Specifically, the organic carboxylic acid may be at least one selected from oleic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, and octadecanoic acid.

Preferably, in the step of surface-modifying the quantum dot core with an organic carboxylic acid, the quantum dot is dispersed in a solution containing the organic carboxylic acid so that the quantum dot core is surface-modified, with the mass molar ratio of the quantum dot core to the organic carboxylic acid being 10mg (3 to 10 mmol). In order to ensure that the organic carboxylic acid can fully passivate the quantum dot core and reduce the defect state on the surface of the quantum dot core, the organic carboxylic acid can exist in a certain excess amount, but the organic carboxylic acid cannot be excessive, otherwise, the viscosity is too high, the subsequent long shell rate is influenced, and the shell layer is not formed.

As a preferred embodiment, the quantum dot core is dispersed in the solution containing the organic amine and heated, and the surface of the quantum dot core is modified to combine the organic amine with cations on the surface of the quantum dot core, so as to fill the cation vacancy of the quantum dot core and reduce the defect state between the core-shell interfaces. As the binding force between the organic amine and the metal atoms on the surface of the quantum dot core is relatively weaker, the organic amine can be desorbed from the metal atoms on the surface of the previous shell layer only by less energy, and in the subsequent shell layer growth process, anions in the shell source precursor are more easily combined with the metal ions on the surface of the core for epitaxial growth, so that the larger lattice stress between atoms at the interface of the quantum dot core and the shell layer can be avoided, and the lattice defects on the surface of the shell layer of epitaxial crystallization are reduced. In addition, the amino functional group of the organic amine has a dipole effect, so that the shell grows according to the crystal orientation of the quantum dot core when the shell is subjected to epitaxial crystallization, the shell obtained by shell growth is consistent with the crystal form of the quantum dot core, and the lattice defect between the surface atom of the quantum dot core and the shell is further reduced.

Preferably, the quantum dot core is dispersed into the solution containing organic amine and heated for 20-60min at the temperature of 80-150 ℃. Under the condition, the organic amine is stably combined on the surface of the quantum dot, and the organic carboxylic acid is favorably and fully exerted the passivation effect.

Preferably, the organic amine in the solution containing the organic amine is selected from organic amines with the carbon atom number of 8-18, and in this case, the steric hindrance is relatively small, which is beneficial for the organic amine to perform surface modification on the quantum dot core. Further, the organic amine reagent is selected from linear chain organic amine containing one amino group, and the linear chain amine is favorable for reducing steric hindrance and promoting the organic amine to carry out surface modification on the quantum dot core. Specifically, the organic amine reagent can be at least one selected from oleylamine, trioctylamine, dodecylamine, tetradecylamine, hexadecylamine and octadecylamine.

Preferably, in the step of performing surface modification treatment on the quantum dot core by using organic amine, the quantum dot is dispersed into a solution containing the organic amine according to the mass molar ratio of the quantum dot core to the organic amine being 10mg (3-10 mmol), and the quantum dot core is subjected to surface modification treatment. In order to fully passivate the surface of the quantum dot core and reduce the defect state of the surface of the quantum dot core, the organic amine is excessive, but the excessive organic amine reagent has too much viscosity, so that the subsequent shell growing rate is influenced, and the formation of a shell layer is not facilitated.

In the embodiment of the present invention, in the step S02, the shell growth reaction system is a reaction material system and a process system for growing a shell on the surface of the quantum dot core. Such as one-step, two-step and three-step processes (reactive material systems and process systems for the growth shell comprising an intermediate shell and an outermost shell). Specifically, in the embodiment of the present invention, the process system of shell layer growth refers to performing N times of shell layer growth on the surface of the quantum dot core to prepare N layers of shell layers. Here, the relationship between the growth of the N shells and the N shells is: adding a shell source into the quantum dot core solution to perform first shell layer growth to prepare a first shell layer; further, on the basis of the first shell layer, adding a shell source to perform secondary shell layer growth, and preparing a second shell layer on the surface of the first shell layer; and repeating the above steps, and growing the N-th shell layer (forming N shell layers on the surface of the quantum dot core). Wherein, the N layers of shell layers form a shell of the core-shell structure nanocrystal. The material system for shell growth refers to a material system applied in the shell growth process. In a specific embodiment, the method can be a quantum dot core in a one-step shell growing process, and during the growth of a first shell layer, a shell source cation precursor and an anion precursor are added into a product solution for preparing the quantum dot core to perform the growth of the first shell layer; the second shell growth is carried out, namely, a shell source cation precursor and an anion precursor are added into a solution system containing the material after the first shell growth is finished, so as to carry out the second shell growth; and sequentially finishing the growth of the N shells. The different sequence of the growth steps of the M adjacent shells refers to the process gap between the completion of the previous shell and the growth of the next shell. For example, a core-shell structure nanocrystal with three shell layers is prepared, wherein M can be 1 or 2, and a process gap from the growth completion of the first shell layer to the growth of the second shell layer can be formed between the growth steps of M adjacent shell layers in different orders; or the process gap from the growth completion of the second shell layer to the growth of the third shell layer; or the process gap from the growth of the first shell layer to the growth of the second shell layer and the process gap from the growth of the second shell layer to the growth of the third shell layer; in a specific embodiment, the solution containing the quantum dot core may be a quantum dot core prepared by adding the quantum dot core into a solvent again after the quantum dot core is prepared and purified by washing. Dispersing a quantum dot core into a solution when a first shell layer grows, and adding a shell source cation precursor and an anion precursor into the quantum dot core solution to grow the first shell layer; the second shell growth is carried out, namely, a shell source cation precursor and an anion precursor are added into a solution system containing the material after the first shell growth is finished, so as to carry out the second shell growth; and sequentially finishing the growth of the N shells. The different sequence of the growth steps of the M adjacent shells refers to the process gap between the completion of the previous shell and the growth of the next shell. For example, a core-shell structure nanocrystal with three shell layers is prepared, wherein M can be 1 or 2, and a process gap from the growth completion of the first shell layer to the growth of the second shell layer can be formed between the growth steps of M adjacent shell layers in different orders; or the process gap from the growth completion of the second shell layer to the growth of the third shell layer; or the process gap from the growth of the first shell layer to the growth of the second shell layer and the process gap from the growth of the second shell layer to the growth of the third shell layer.

Preferably, in the solution containing the quantum dot core, the ratio of the mass of the quantum dot core to the volume of the solvent is 10mg: (5-15 ml), under the concentration condition, the distance between the quantum dot cores is kept appropriate, good conditions can be provided for shell formation of the shell source precursor by crystallization on the surfaces of the quantum dot cores, and a shell layer with good dispersity and uniform thickness can be obtained.

In the embodiment of the invention, the shell source cation precursor is at least one of organic metal carboxylates formed by reacting oxides or metal salts of metals such as Cd, Zn, Pb, Ag, Hg, Fe, In, Al and the like with organic carboxylic acids. Further, the shell source cation precursor is selected from zinc oleate, lead oleate, silver oleate, mercury oleate, indium oleate, copper oleate, iron oleate, manganese oleate, aluminum oleate, zinc stearate, lead stearate, silver stearate, mercury stearate, indium stearate, copper stearate, iron stearate, manganese stearate, aluminum stearate, zinc myristate, lead myristate, silver myristate, mercury myristate, indium myristate, copper myristate, iron myristate, manganese myristate, aluminum myristate, zinc palmitate, lead palmitate, silver palmitate, mercury palmitate, indium palmitate, copper palmitate, zinc laurate, silver laurate, manganese laurate, aluminum laurate, zinc laurate, manganese laurate, aluminum laurate, zinc laurate, copper laurate, manganese laurate, aluminum laurate, zinc laurate, copper laurate, aluminum laurate, zinc laurate, copper laurate, zinc oleate, zinc, At least one of zinc stearate, lead stearate, silver stearate, mercury stearate, indium stearate, copper stearate, iron stearate, manganese stearate, and aluminum stearate, but not limited thereto.

In the embodiment of the invention, nonmetallic simple substances such as Te, Se, S, P and the like are dispersed into organic molecules to form an anion complex, and then the shell source anion precursor is prepared. When the shell source anion precursor is an anion complex formed by non-metal simple substances such as Te, Se, S, P and the like and organic molecules, the organic molecules are selected from at least one of trioctylphosphine, tributylphosphine, oleic acid and octadecene, but the invention is not limited thereto.

In the embodiment of the present invention, if the anionic precursor is thiol, the organic molecule containing non-metal atoms is an organic molecule containing a mercapto (-HS) functional group with a single functional group (e.g., octadecanethiol, heptadecanethiol, hexadecanethiol, pentadecanethiol, tetradecanethiol, tridecanethiol, dodecanethiol, octanethiol, etc., but not limited thereto).

In the embodiment of the present invention, the choice of the shell source is not limited, and preferably should be satisfied such that the band gap of the obtained shell layer is larger than that of the quantum dot core.

Preferably, in the embodiment of the present invention, the shell source cation precursor is selected from at least one of organometallic carboxylates of Cd, Zn and Pb, and the shell source anion precursor is selected from an anionic complex formed by dispersing Te, Se and S into an organic molecule, or thiol.

In the embodiment of the invention, in the process of shell layer growth, the shell source cation precursor and the shell source anion precursor are dispersed in a solvent to prepare a precursor solution, and then the precursor solution is injected into a shell layer growth reaction system to carry out shell layer growth. Preferably, in the process of shell layer growth, the shell source cation precursor and the shell source anion precursor are dispersed in a solvent to prepare a precursor solution, and then the precursor solution is injected into a shell layer growth reaction system at the temperature of 150-320 ℃ to carry out shell layer growth. Each of the solvents may be selected from, but not limited to, TOP, TBP, OA, ODE and OAm, for example. In the embodiment of the invention, the adding sequence of the shell source cation precursor and the shell source anion precursor is not strictly limited every time the shell source is injected for shell layer growth. For example, the shell source is a mixed precursor solution in which a shell source cation precursor and a shell source anion precursor are dispersed; the method of adding the shell source may be: the shell source cation precursor and the shell source anion precursor are respectively added into a solvent to prepare a cation precursor solution and an anion precursor solution, and the shell source cation precursor solution can be added firstly and then the shell source anion precursor solution can be added. Preferably, in the step of growing the shell layers for N times, when the shell source cation precursor and the shell source anion precursor are respectively added into the solvent to prepare the cation precursor solution and the anion precursor solution, the shell source anion precursor is added into the shell layer growth reaction system, and then the shell source cation precursor is added into the shell layer growth reaction system to perform shell layer growth in the current order. The added anions can be combined with metal ions in the surface of the core more conveniently for epitaxial growth, so that the problem that lattice stress between atoms at the interface of the quantum dot core and the shell is large is avoided, and lattice defects existing on the surface of the shell of epitaxial crystallization are reduced. In the precursor solution, the concentration of the shell source cation precursor is 0.5-1.5 mmol/ml, and the concentration of the shell source anion precursor is 0.5-1.5 mmol/ml. In the preferred concentration, the shell source anion/cation precursor maintains proper concentration and dispersion density, which is beneficial to the uniform combination on the surface of the quantum dot core and the uniform and stable shell layer is formed by crystallization. Preferably, the total shell thickness (sum of the thicknesses of the N shells) is from 5 to 12 nm. Further preferably, in the prepared N layers of shell layers, the thickness of each layer of shell layer is 0.1-2nm, and the value range of N is 6-18. If the thickness of each shell layer is too thick or the number of times of shell layer growth is too small, each shell layer is thick, the organic amine and/or organic phosphine cannot be sufficiently combined to the defect position of the shell layer, and the effect of eliminating the lattice defect cannot be generated. Preferably, in the step of preparing each layer of shell layer, the shell source precursor is added according to the mass ratio of the shell source cation precursor to the quantum dot core (1-1.5 mmol):10mg and the mass ratio of the shell source anion precursor to the quantum dot core (1-1.5 mmol):10mg, so that the shell layer with proper thickness in single-cycle long shell is obtained.

In the embodiment of the invention, between M adjacent shell growth steps in different orders, organic amine is added into a shell growth reaction system which forms a previous shell, mixed and heated, and then the growth of the next shell is carried out. The organic amine is combined on the surface of a metal atom of the previous shell layer, exchanges an organic carboxylic acid ligand derived from a shell source on the surface of the previous shell layer, and fills a cation vacancy of the previous shell layer. In the process of the growth of the latter shell, because the binding force between the organic amine and the metal atoms on the surface of the shell is relatively weaker, the organic amine can be desorbed from the metal atoms on the surface of the former shell only by less energy, so that in the process of the growth of the shells in the current sequence, anions in the shell source precursor are more easily combined with the metal ions on the surface of the former shell for epitaxial growth, the problem that the lattice stress of the core-shell quantum dots between atoms at the interface of the shells and the shell is larger is avoided, the lattice defects existing on the surface of the shell subjected to epitaxial crystallization are reduced, the fluorescence intensity is improved, the photothermal optical quality of the quantum dots is improved, and the current efficiency and the service life of the QLED device are finally improved.

In the embodiment of the invention, if the number of times of modification by organic amine is too small, the concentration of the organic amine in the shell growth reaction system is reduced along with the growth of shells of different layers, so that the organic amine cannot be fully combined on the surface of the previous shell between the growth steps of the adjacent shells. Therefore, between the growth steps of the adjacent shell of M times, no matter the previous shell is modified by independently adopting organic amine, or the obtained previous shell is modified by adopting organic amine and organic phosphine as a modifier, or the previous shell is modified by adopting organic amine and also adopting organic amine and organic phosphine as a modifier, the total number of modification times M is required, and the value of M satisfies the following conditions: n/3 is more than or equal to M and less than or equal to N-1. Preferably, in order to fully exert the effect of organic amine modification, between each adjacent shell growth step in the N-1 times, organic amine is added to the shell growth reaction system in which the former shell is formed, and after mixing and heating, the latter shell is grown, that is, M ═ N-1.

In the step of adding organic amine into a shell growth reaction system which forms a previous shell for mixing and heating and then growing a next shell among M adjacent shell growth steps in different orders, the organic amine is added into the shell growth reaction system which forms the previous shell for mixing and heating according to the mass ratio of the mole of the organic amine to the quantum dot core (0.2-0.9 mmol) of 10 mg.

Preferably, the organic amine is selected from organic amines with the carbon atom number of 8-18, and the organic amine has relatively small steric hindrance and is beneficial to the modification of the organic amine. Specifically, the organic amine may be at least one selected from oleylamine, trioctylamine, dodecylamine, tetradecylamine, hexadecylamine, and octadecylamine. Further preferably, the organic amine is selected from linear organic amines containing only one amino group, and on one hand, the linear amine is beneficial to reducing steric hindrance, so that the organic amine is more easily combined to the surface of the quantum dot; on the other hand, the organic amine containing only one amino group is adopted, because the single binding site has a more ideal exchange effect, and the stability of cyclic modification and exchange reaction is improved.

In the embodiment of the invention, between the adjacent shell layer growth steps in different orders, the organic phosphine can be added into the shell layer growth reaction system which forms the former shell layer, or the organic phosphine and the organic amine are simultaneously added into the shell layer growth reaction system for mixing and heating, and then the growth of the latter shell layer is carried out. And organic phosphine is added between the growth steps of adjacent shell layers, and the organic phosphine can generate a coordination effect with non-metal atoms on the surface of the quantum dot nanocrystalline shell layer, so that the diversity of the nanocrystalline surface modifier is further increased, the surface defects are reduced, and the fluorescence intensity of the final sample is increased.

In an embodiment of adding the organic phosphine, when M is less than N-1, on the basis of adding the organic amine into a shell growth reaction system which forms a previous shell for mixing and heating and then growing a next shell between M adjacent shell growth steps in different orders, the method also comprises a step of independently adding the organic phosphine into the shell growth reaction system which forms the previous shell for mixing and heating and then growing the next shell between S adjacent shell growth steps in different orders. Wherein S is a positive integer, and S is more than or equal to 1 and less than or equal to (N-1) -M, and the growth steps of the adjacent shells are between the growth steps of the adjacent shells, wherein the growth steps of the adjacent shells are between the growth steps of the adjacent shells, and organic amine or organic amine and organic phosphine are not added into a shell growth reaction system which forms a previous shell to modify the previous shell in the current sequence. Adding organic phosphine into a shell layer growth reaction system which forms a previous shell layer between S adjacent shell layer growth steps in different orders, mixing and heating, and then carrying out the growth of the next shell layer, wherein 10mg of organic phosphine is added into the shell layer growth reaction system which forms the previous shell layer according to the mass ratio of the mol of the organic phosphine to the quantum dot core (0.2-0.9 mmol) for mixing and heating.

In an embodiment of adding the organic phosphine, between the M adjacent shell growth steps in different orders, including between L adjacent shell growth steps in different orders, adding the organic amine and the organic phosphine into a shell growth reaction system with a formed previous shell, mixing and heating, and then growing the next shell, wherein L is a positive integer and is less than or equal to M. Preferably, in order to fully exert the effect of organic amine modification, between each adjacent shell growth step in the N-1 times, organic amine is added to the shell growth reaction system in which the previous shell is formed, and after mixing and heating, the subsequent shell is grown, that is, L ═ M ═ N-1. In the step of adding organic amine and organic phosphine into a shell growth reaction system which forms a previous shell for mixing and heating and then growing a subsequent shell between L adjacent shell growth steps in different orders, the organic amine and the organic phosphine are added into the shell growth reaction system which forms the previous shell for mixing and heating according to the mass ratio of the sum of the molar weight of the organic amine and the organic phosphine to the quantum dot core of (0.2-0.9 mmol) of 10 mg.

In the embodiment of the present invention, the organic phosphine is preferably an organic phosphine which is liquid at room temperature. Preferably, the organic phosphine is at least one selected from trioctylphosphine and tributylphosphine. The coordination effect between the preferable organic phosphine and the non-metal atoms on the surface of the quantum dot nanocrystalline shell layer is more remarkable.

It is worth noting that the organic amine and/or organic phosphine and the shell source cation precursor can form a complex to influence the crystallization effect of the shell layer, and the nonmetal atoms thermally decomposed from the shell source anion precursor can generate side reaction with the modifier and also influence the growth of the shell layer. Thus, in the present examples, the organic amine and/or organic phosphine can be added neither simultaneously with the shell-derived anion precursor nor simultaneously with the shell-derived cation precursor.

Preferably, sufficient epitaxial crystallization is carried out for each dropwise addition of the shell source. The time of each shell growth is 5-20min, or the precursor solution is injected into a shell growth reaction system to react for 5-20min, and then organic amine and/or organic phosphine are added to modify the previous shell. Namely: adding a shell source for growing a previous shell in the current sequence into a shell growing system for 5-20min, adding organic amine into the shell growing reaction system with the previous shell formed for mixing and heating between M adjacent shell growing steps in different sequences each time, and then growing a next shell;

or adding a shell source for growing a previous shell in the current sequence into a shell growing system for 5-20min, adding organic amine and organic phosphine into a shell growing reaction system with the previous shell formed for mixing and heating between L adjacent shell growing steps in different sequences each time, and then growing the next shell;

or adding a shell source for growing the previous shell in the current sequence into the shell growing system for 5-20min, adding organic phosphine into the shell growing reaction system with the previous shell formed for mixing and heating between S adjacent shell growing steps in different sequences each time, and then growing the next shell.

Preferably, in order to fully modify the surface of the former shell layer by the organic amine and/or the organic phosphine, after the organic amine and/or the organic phosphine is added into the shell layer growth reaction system for 5-20min, the shell source precursor solution for preparing the latter shell layer is injected into the shell layer growth reaction system for the growth of the latter shell layer. The method for adding the organic amine and/or the organic phosphine to the shell growth reaction system with the formed previous shell is not limited, and the organic amine and/or the organic phosphine can be injected in batches or at one time.

Preferably, between M adjacent shell growth steps in different orders, adding organic amine into a shell growth reaction system with a formed previous shell, mixing and heating at 150-320 ℃ for 5-20min, and then adding a shell source to grow the next shell;

preferably, between L adjacent shell growth steps in different orders, adding organic amine and organic phosphine into a shell growth reaction system with a formed previous shell, mixing and heating at 150-320 ℃ for 5-20min, and then adding a shell source to grow the next shell;

preferably, between S times of adjacent shell layer growth steps in different orders, adding organic phosphine into a shell layer growth reaction system with a formed previous shell layer, mixing and heating at 150-320 ℃ for 5-20min, and then adding a shell source to grow the next shell layer.

Preferably, 10mg of the organic amine and/or the organic phosphine is added into a shell growth reaction system which forms a previous shell according to the mass ratio of the mol of the organic amine and/or the organic phosphine to the quantum dot core (0.2-0.9 mmol), the organic amine and/or the organic phosphine are mixed and heated, the previous shell is modified, and then the next shell is grown. The content of organic amine and/or organic phosphine is too low, and the modification effect is difficult to exert; if the content of the organic amine and/or the organic phosphine is too high, the excessive organic amine and/or the excessive organic phosphine can inhibit the pyrolysis of the shell source cation precursor in the next shell growing process, the organic amine and/or the excessive organic phosphine can form a complex with the shell source cation precursor, and the shell source anion precursor is combined with the organic amine and/or the excessive organic phosphine after being pyrolyzed to form atoms, so that the growth of a shell layer is not facilitated.

Further, a post-treatment reagent can be adopted to modify the core-shell structure nanocrystal. The embodiment of the invention provides three implementation modes for carrying out modification treatment on the core-shell structure nanocrystal.

In one embodiment of modifying the core-shell nanocrystal, the core-shell nanocrystal is modified with an organic phosphine. Specifically, the core-shell structure nanocrystal is dispersed into a solution containing organic phosphine for heating, and is modified, so that the organic phosphine is coordinated and combined with a non-metal atom on the surface of a shell layer of the nanocrystal to fill an anion vacancy of the core-shell structure nanocrystal, reduce a defect state on the surface of the core-shell structure nanocrystal, and further improve the fluorescence intensity of the core-shell structure nanocrystal.

The organic phosphine is used for modifying the core-shell structure nanocrystal, and a good effect can be achieved only by adding a proper amount of organic phosphine in a proper temperature range. Preferably, in the step of dispersing the core-shell structure nanocrystal in a solution containing organic phosphine and modifying the core-shell structure nanocrystal, the core-shell structure nanocrystal is dispersed in the solution containing organic phosphine according to the molar mass ratio of (2-5 mmol) to 10mg of the organic phosphine to the core-shell structure nanocrystal. If the content of the organic phosphine is too low, the effect of passivating the anion vacancy is not obvious, and the fluorescence intensity of the core-shell structure nanocrystal is difficult to be obviously improved. If the content of the organic phosphine is too high, the film forming performance of the core-shell structure nanocrystal in the preparation of the film layer can be influenced. Preferably, in the step of dispersing the core-shell structure nanocrystal in a solution containing organic phosphine and modifying the core-shell structure nanocrystal, the core-shell structure nanocrystal is dispersed in the solution containing organic phosphine and heated at the temperature of 100-320 ℃ for 10-60 min. If the modification treatment temperature and/or time of the organic phosphine to the core-shell structure nanocrystal are too low and/or too short, the effect of passivating the anion vacancy by the organic phosphine is not obvious, even the passivation effect cannot be exerted, and further the fluorescence intensity of the core-shell structure nanocrystal cannot be improved; if the modification treatment temperature of the organic phosphine on the core-shell structure nanocrystal is too high, the organic phosphine is easy to volatilize and affects the modification treatment effect, and the high temperature condition can affect the stability of the core-shell structure nanocrystal structure.

Specifically, the organic phosphine is at least one selected from trioctylphosphine and tributylphosphine.

In a particularly preferred embodiment, the quantum dot core is dispersed in the organic carboxylic acid-containing solution and heated to perform a surface modification treatment on the quantum dot core; then, performing shell growth on the surface of the quantum dot core for multiple times, adding a solution containing organic amine into a shell growth reaction system, mixing and heating the mixture, and then performing the growth of the next shell to prepare the core-shell structure nanocrystal; and finally, dispersing the core-shell structure nanocrystal into a solution containing organic phosphine, and modifying the core-shell structure nanocrystal. The method can improve the fluorescence intensity of the core-shell structure nanocrystal. Specifically, the quantum dot core is modified by organic amine, so that lattice defects formed between the quantum dot core and the first shell layer can be effectively avoided. And adding organic amine into a shell growth reaction system which forms the previous shell between the adjacent shell growth steps for mixing and heating, so that the cation defects on the surface of the core-shell quantum dots can be filled, and the anion defects on the surface of the core-shell nanocrystal have no obvious effect. Based on the method, the prepared core-shell structure nanocrystal is modified by adopting organic phosphine, the organic phosphorus is coordinated and combined with non-metal atoms on the surface of a core-shell structure nanocrystal shell layer, so that anion vacancy on the surface of the core-shell structure nanocrystal shell layer is filled, the defect state of the surface of the core-shell quantum dot nanocrystal is reduced, and the fluorescence intensity of the core-shell structure nanocrystal is further improved.

In another embodiment of modifying the core-shell structure nanocrystal, an organic acid is used to modify the prepared core-shell structure nanocrystal. Specifically, the core-shell structure nanocrystal is dispersed into a solution containing an organic acid for heating, and the core-shell structure nanocrystal is modified. The organic acid can effectively eliminate protonated organic amine (derived from modifier organic amine for eliminating lattice defects in the growth process of the shell layer) connected to the surface of the shell layer of the core-shell structure nanocrystal, reduce organic amine ligands with charges on the surface of the core-shell structure nanocrystal, prevent excitons (electrons) generated by the core-shell structure nanocrystal during luminescence from being captured by the organic amine ligands with charges on the surface, and further prolong the transient fluorescence life of the nanocrystal.

The modification treatment by the organic acid needs to be carried out within a proper temperature range, and a proper amount of the organic acid is added to achieve a good effect. Preferably, in the step of dispersing the core-shell structure nanocrystal in a solution containing an organic acid and modifying the core-shell structure nanocrystal, the core-shell structure nanocrystal is dispersed in the solution containing the organic acid according to a molar mass ratio of the organic acid to the core-shell structure nanocrystal of (5-10 mmol):10 mg. If the content of the organic acid is too low, the effect of eliminating the protonated organic amine connected to the surface of the shell layer of the core-shell structure nanocrystal is not obvious, and the transient fluorescence life of the nanocrystal is difficult to be obviously prolonged. If the content of the organic acid is too high, the film forming performance of the core-shell structure nanocrystal in the preparation of the film layer is affected. Preferably, in the step of dispersing the core-shell structure nanocrystals into a solution containing an organic acid and modifying the core-shell structure nanocrystals, the core-shell structure nanocrystals are dispersed into a solution containing an organic acid and heated at a temperature of 240-320 ℃ for 30-90 min. If the modification treatment temperature and/or time of the organic acid on the core-shell structure nanocrystal is too low and/or too short, the effect of the organic acid on eliminating the protonated organic amine connected to the surface of the core-shell structure nanocrystal shell layer is not obvious, and the transient fluorescence life of the nanocrystal is difficult to be obviously prolonged; if the modification temperature of the organic acid on the core-shell structure nanocrystal is too high, the organic acid is easy to volatilize, the modification treatment effect is influenced, and the stability of the core-shell structure nanocrystal structure can be influenced by the high-temperature condition.

Preferably, the organic acid is selected from organic acids with 8-18 carbon atoms, and in this case, the steric hindrance is relatively small, and the reactivity is high. Further preferably, the organic acid used for modification treatment of the core-shell structure nanocrystal is selected from linear carboxylic acid containing terminal carboxyl, so as to ensure that the organic acid has good reaction activity and obtain a good effect of eliminating protonated organic amine. Specifically, the organic acid agent may be at least one selected from the group consisting of oleic acid, dodecanoic acid, tetradecanoic acid, hexadecanoic acid, and octadecanoic acid.

In another embodiment of modifying the core-shell structure nanocrystal, the reagents for modifying the prepared core-shell structure nanocrystal are organic acid and organic phosphine. Specifically, the core-shell structure nanocrystal is dispersed in a solution containing organic acid and organic phosphine and heated, and the core-shell structure nanocrystal is modified. On one hand, the organic phosphine is coordinated and combined with the non-metal atoms on the surface of the shell layer of the nanocrystalline, so that anion vacancy is further passivated, the defect state of the surface of the nanocrystalline with the core-shell structure is reduced, and the fluorescence intensity of the nanocrystalline with the core-shell structure is improved; on the other hand, the organic acid can effectively eliminate protonated organic amine connected to the surface of the shell layer of the core-shell structure nanocrystal, reduce organic amine ligands with charges on the surface of the core-shell structure nanocrystal, prevent excitons (electrons) generated by the core-shell structure nanocrystal during luminescence from being captured by the organic amine ligands with charges on the surface, and further prolong the transient fluorescence life of the nanocrystal. Dispersing the core-shell structure nanocrystal in a solution containing organic acid and organic phosphine, and when the core-shell structure nanocrystal is modified, forming mutually staggered ligands on the surface of the core-shell structure nanocrystal by the organic acid and the organic phosphine, and combining the mutually staggered ligands with metal and nonmetal atoms on the surface of the nanocrystal, wherein the mutually staggered ligands can further enhance the solubility and stability of the nanocrystal. In addition, the core-shell structure nanocrystal is dispersed in a solution containing organic acid and organic phosphine, and when the core-shell structure nanocrystal is subjected to modification treatment, the organic acid can promote the decomposition of a part of the shell with unstable surface crystallization of the core-shell quantum dot. The metal atom obtained after decomposition and the organic acid can form a metal cation precursor, and the anion obtained after decomposition and the organic phosphine can form an anion precursor. The metal cation precursor and the anion precursor preferentially carry out shell layer growth on the surface of the small-particle core-shell structure nanocrystal with large relative surface and high growth rate, and finally the size uniformity of the core-shell quantum dot is improved.

In this embodiment, the manner of dispersing the core-shell structure nanocrystals in a solution containing an organic acid and an organic phosphine can be flexibly selected. Organic acid and organic phosphine in a certain proportion can be dissolved in a solvent for heating to form a mixed solution, and then the core-shell structure nanocrystal is dispersed in the mixed solution; the organic phosphine may be added to the reaction system in a certain proportion after the core-shell structure nanocrystal is dispersed in the solution containing the organic acid, or the organic acid may be added to the reaction system in a certain proportion after the core-shell structure nanocrystal is dispersed in the solution containing the organic phosphine.

Preferably, in the step of dispersing the core-shell structure nanocrystal in a solution containing an organic acid and an organic phosphine, and modifying the core-shell structure nanocrystal, the core-shell structure nanocrystal is dispersed in a solution containing an organic acid and an organic phosphine, in such a manner that the molar mass ratio of the organic acid to the quantum dot core is (5-10 mmol):10mg, and the molar mass ratio of the organic phosphine to the quantum dot core is (2-5 mmol):10 mg. The effect of the organic acid, the organophosphine content is as described hereinbefore.

Preferably, in the step of dispersing the core-shell structure nanocrystal in a solution containing an organic acid and an organic phosphine, and modifying the core-shell structure nanocrystal, the core-shell structure nanocrystal is dispersed in a solution containing an organic acid and an organic phosphine, and heated at a temperature of 100-320 ℃ for 10-60 min. The effect of the conditions of the modification treatment is as described above.

Dispersing the core-shell structure nanocrystal in a solution containing an organic acid and an organic phosphine, and selecting the organic phosphine and the organic acid for modifying the core-shell structure nanocrystal.

As a specific preferred embodiment, the quantum dot core is dispersed in the solution containing the organic amine and heated, and the surface modification treatment is performed on the quantum dot core; then, performing shell growth on the surface of the quantum dot core for multiple times, adding a solution containing organic amine into a shell growth reaction system, mixing and heating the mixture, and then performing the growth of the next shell to prepare the core-shell structure nanocrystal; and finally, dispersing the core-shell structure nanocrystal into a solution containing organic phosphine and organic acid, and modifying the core-shell structure nanocrystal. The size uniformity of the core-shell structure nanocrystal can be improved. Specifically, organic amine is adopted to carry out pretreatment on a quantum dot core, and between the growth steps of adjacent shells, organic amine is added into a shell growth reaction system which forms the previous shell for mixing and heating, although the crystal form of shell crystallization growth can be consistent with that of the quantum dot core, the size dispersion rate of the final core-shell structure nanocrystal is larger under the influence of reaction conditions (temperature, stirring speed, atmosphere and the like) along with the gradual growth of the shells, so that the size uniformity of the core-shell quantum dot is improved through post-treatment. In the process of modifying the prepared core-shell structure nanocrystal by adopting organic acid and organic phosphine, the organic acid not only can exchange organic amine ligands on the surface of the core-shell structure nanocrystal, but also can decompose part of a shell with unstable crystallization on the surface of the core-shell structure nanocrystal. The metal atom obtained after decomposition and the organic acid can form a metal cation precursor, and the anion obtained after decomposition and the organic phosphine can form an anion precursor. The metal cation precursor and the anion precursor preferentially carry out shell layer growth on the surface of the small-particle core-shell structure nanocrystal with large relative surface and high growth rate, and finally the size uniformity of the core-shell quantum dot is improved.

The embodiment of the invention also provides the core-shell structure nanocrystal prepared by the method.

Further, the embodiment of the invention provides application of the core-shell structure nanocrystal in the fields of optical devices, optical films, core-shell structure nanocrystal ink, glue, biological probes and the like.

Specifically, the optical device includes, but is not limited to, a quantum dot light emitting diode, and a quantum dot sensitized cell.

Specifically, the optical film includes, but is not limited to, quantum dot light-blocking diaphragms, quantum dot light-emitting tubes, and the like.

Specifically, the core-shell structure nanocrystal ink includes, but is not limited to, an ink in which quantum dots and other different chemical solvents are combined according to different proportions.

Specifically, the glue includes, but is not limited to, a glue formed by combining core-shell structure nanocrystals with other different chemical agents according to different viscosity ratios.

The following description will be given with reference to specific examples.

Example 1

A method for preparing core-shell structure nanocrystals by a two-step method comprises the following steps:

1. preparation of cadmium selenide (CdSe) quantum dot cores

11) Preparing a cadmium precursor: 0.25mmol of CdO, 0.5mmol of octadecylphosphonic acid and 3g of trioctylphosphine were taken together and introduced into a 50ml three-neck flask, which was heated to 380 ℃ to dissolve it and to obtain a clear and transparent solution and was held at this temperature.

12) Preparation of Se precursor: 0.5mmol of Se source solution is taken and stirred in 1ml of trioctylphosphine at room temperature until clear for use.

13) Preparation of CdSe quantum dots: injecting 1ml of trioctylphosphine solution into 11), injecting the Se precursor into 12) for reaction for 30s when the temperature of the solution is raised to 380 ℃, then injecting 10ml of octadecyl quenching reaction, cooling to room temperature, and cleaning.

14) And (3) cleaning and purifying the CdSe quantum dots: 30ml of acetone is added into the quantum dot mixed solution to centrifugally separate the quantum dots, and the centrifugally separated CdSe quantum dots are dispersed in 10ml of n-hexane for later use.

2. Processing of cadmium selenide (CdSe) quantum dot cores

21) Dispersing CdSe quantum dot cores: taking 2ml of CdSe quantum dots well prepared and dispersed in n-hexane in the step 1), adding the CdSe quantum dots into 10ml of octadecyl solution, firstly heating the CdSe quantum dot solution to 150 ℃, exhausting for 20min to remove the redundant n-hexane solution in the solution, and then raising the temperature of the CdSe solution to 300 ℃.

Preparation of CdSe/CdS core-shell quantum dots

31) Preparing a CdS shell source: 1mmol of cadmium oleate precursor and 1.5mmol of 1-octadecanethiol are taken to be dispersed in 10ml of octadecane solution, and then the solution is stirred and heated at 80 ℃ to ensure that turbid liquid becomes clear and then is cooled to room temperature for standby.

32) And (3) growing a CdS shell: dripping the CdS shell source prepared in the step 31) into the CdSe quantum dot core solution in the step 2) at the dripping rate of 6ml/h for 10min, stopping injecting, curing for 5min, then injecting the mixed solution of 0.5mmol of tetradecylamine and tributylphosphine into the mixed solution of quantum dots, and curing for 9 min; the circulation is carried out for 9 times according to the mode of injecting the CdS shell source and the mixed solution of the modifier (decatetramine and tributyl phosphine).

33) And cooling the prepared CdSe/CdS quantum dot solution to room temperature without any post-treatment after the circulation reaction is finished.

Purification of CdSe/CdS core-shell quantum dots

41) Adding a proper amount of ethyl acetate and ethanol into the quantum dot mixed solution obtained in the step 3) to carry out centrifugal separation on the CdSe/CdS quantum dot solution, dispersing the CdSe/CdS quantum dot solution obtained by centrifugation into a proper amount of chloroform solution again to disperse the chloroform solution, then adding acetone and methanol into the solution to carry out precipitation and centrifugal separation, and repeating the step once; and finally, carrying out vacuum drying on the obtained CdSe/CdS quantum dots.

According to the CdSe/CdS quantum dot prepared by the method of the embodiment, the generation of shell defects during shell growth is reduced, and the fluorescence intensity of the CdSe/CdS core-shell quantum dot is improved. The Quantum Yield (QY) of the solution at room temperature was measured by an integrating sphere (Edinburgh-FS 5) of a fluorescence spectrometer, where the QY value ranged from 75-85%.

Example 2

1. preparation of cadmium selenide (CdSe) quantum dot cores

2. Processing of cadmium selenide (CdSe) quantum dot cores

Preparation of CdSe/CdS core-shell quantum dots

31) Preparing a CdS shell source: 1mmol of cadmium oleate precursor and 1.5mmol of 1-dodecyl mercaptan are dispersed in 10ml of octadecyl solution, stirred and heated at 80 ℃ to ensure that turbid liquid becomes clear, and then cooled to room temperature for later use.

32) And (3) growing a CdS shell: dripping the CdS shell source prepared in the step 31) into the CdSe quantum dot core solution in the step 2) at the dripping rate of 6ml/h for 10min, stopping injecting, curing for 5min, and then injecting 100 microliters of oleylamine into the quantum dot mixed solution and curing for 5 min; and circulating for 9 times according to a mode of injecting a CdS shell source and a modifier oleylamine.

Purification of CdSe/CdS core-shell quantum dots

According to the CdSe/CdS quantum dot prepared by the method of the embodiment, the generation of shell defects during shell growth is reduced, and the fluorescence intensity of the CdSe/CdS core-shell quantum dot is improved. The Quantum Yield (QY) of the solution at room temperature was measured by an integrating sphere (Edinburgh-FS 5) of a fluorescence spectrometer, where the QY value ranged from 70-80%.

Example 3

A method for preparing core-shell structure nanocrystalline by a one-step method comprises the following steps:

1. preparation of cadmium selenide (CdSe) quantum dot cores

13) Preparation of CdSe quantum dots: 1ml of trioctylphosphine solution is injected into 11), and the Se precursor in 12) is injected for reaction for 30s when the temperature of the solution is raised to 380 ℃.

Preparing CdSe/CdS core-shell quantum dots:

21) preparing a CdS shell source: 1mmol of cadmium oleate precursor and 1.5mmol of 1-dodecyl mercaptan are dispersed in 10ml of octadecyl solution, stirred and heated at 80 ℃ to ensure that turbid liquid becomes clear, and then cooled to room temperature for later use.

22) And (3) growing a CdS shell: dripping the CdS shell source prepared in the step 21) into the CdSe quantum dot core solution in the step 1 at the dripping rate of 6ml/h for 10min, stopping injecting, curing for 5min, and then injecting 500 microliters of oleylamine into the quantum dot mixed solution and curing for 5 min; and then 16 times of circulation by injecting the CdS shell source and the modifier oleylamine.

23) And cooling the prepared CdSe/CdS quantum dot solution to room temperature without any post-treatment after the circulation reaction is finished.

Purification of CdSe/ZnS quantum dots

31) Adding a proper amount of ethyl acetate and ethanol into the quantum dot mixed solution obtained in the step 2) to centrifuge the CdSe/ZnS quantum dot solution, dispersing the centrifuged CdSe/ZnS quantum dot solution in a proper amount of chloroform solution again to disperse the CdSe/ZnS quantum dot solution, then adding acetone and methanol into the solution to precipitate and centrifugally separate, and repeating the step once; and finally, carrying out vacuum drying on the obtained CdSe/ZnS quantum dots.

The CdSe/CdS quantum dots prepared by the method of the embodiment reduce the generation of shell defects during shell growth, and improve the fluorescence intensity of the CdSe/CdS core-shell quantum dots. The Quantum Yield (QY) of the solution at room temperature was measured by an integrating sphere (Edinburgh-FS 5) of a fluorescence spectrometer, where the QY value ranged from 76-85%.

Example 4

A method for preparing core-shell structure nanocrystalline by a three-step method comprises the following steps:

1. the oil-soluble red CdS/CdSe/CdS quantum well quantum dots are prepared as follows:

11) preparation of cadmium oleate { Cd (OA)2} precursor:

adding 1mmol of cadmium oxide (CdO), 4ml of Oleic Acid (OA) and 10ml of Octadecene (ODE) into a three-neck flask, vacuumizing for 30mins at normal temperature, then heating to 180 ℃, discharging argon for 60mins, maintaining the vacuum for 30mins at 180 ℃, and cooling to room temperature for later use.

12) Preparation of selenium (Se) precursor:

10mmol of Se was weighed into 10ml of Trioctylphosphine Oxide (TOP), heated to 170 ℃ for 30min and then cooled to 140 ℃.

13) Preparation of sulfur (S-TOP) precursor:

20mmol of S was weighed into 10ml of Trioctylphosphine Oxide (TOP), heated to 170 ℃ for 30min and then cooled to 140 ℃.

14) Preparation of sulfur (S-ODE) precursor:

5mmol of S was weighed into 10ml of Octadecene (ODE), heated to 110 ℃ for 60min, and then incubated at 110 ℃.

15) Will be provided with11) Cadmium oleate { Cd (OA)₂Heating the precursor to 250 ℃, extracting 14), injecting 2ml of S-ODE precursor into a three-neck flask for reaction for 10min to obtain CdS quantum dot nuclei, and dispersing the prepared CdS quantum dot nuclei in n-hexane through centrifugal separation and drying.

The CdS/CdSe core-shell quantum dots are prepared as follows:

21) preparation of CdSe shell source: 1mmol of cadmium oleate precursor and 1.5mmol of Se-TOP are taken and dispersed in 10ml of octadecyl solution, and then stirred for standby.

22) Dispersing 10mg CdS quantum dot core in 1ml OA and 10ml ODE, exhausting gas at normal temperature for 20min, and heating to 300 deg.C.

23) And (3) growing a CdS shell: dripping the CdS shell source prepared in the step 21) into the CdSe quantum dot core solution in the step 1 at the dripping rate of 6ml/h for 10min, stopping injecting, curing for 5min, and then injecting 500 microliters of oleylamine into the quantum dot mixed solution and curing for 5 min; circulating 8 times according to the mode of injecting CdS shell source and modifier oleylamine.

24) Adding a precipitator into the CdS/CdSe core-shell quantum dot mixed solution, and dispersing the prepared CdS/CdSe quantum dot core in n-hexane through centrifugal separation and drying.

The CdS/CdSe/CdS core-shell quantum dots are prepared as follows:

32) Dispersing 10mg CdS/CdSe quantum dots in 1ml OA and 10ml ODE, exhausting gas at normal temperature for 20min, heating to 300 deg.C,

33) and (3) growing a CdS shell: dripping the CdS shell source prepared in the step 31) into the CdSe quantum dot core solution in the step 1 at a dripping rate of 6ml/h for 10min, stopping injecting, curing for 5min, and then injecting 100 microliters of oleylamine into the quantum dot mixed solution and curing for 5 min; and then circulating for 12 times in a mode of injecting a CdS shell source and a modifier oleylamine.

34) And cooling the prepared CdS/CdSe/CdS quantum dot solution to room temperature without any post-treatment after the circulation reaction is finished.

Purification of CdS/CdSe/CdS quantum well quantum dots

41) Adding a proper amount of ethyl acetate and ethanol into the quantum dot mixed solution in the step 3) to carry out centrifugal separation on the CdS/CdSe/Cd quantum well quantum dot solution, dispersing the CdS/CdSe/CdS quantum well quantum dot solution obtained by centrifugation into a proper amount of chloroform solution again to disperse the solution, then adding acetone and methanol into the solution to carry out precipitation centrifugal separation, and repeating the step once; and finally, carrying out vacuum drying on the CdS/CdSe/CdS quantum well quantum dots.

The CdS/CdSe/CdS quantum dots prepared by the method of the embodiment reduce the generation of shell defects during shell growth, and improve the fluorescence intensity of the CdS/CdSe/CdS core-shell quantum dots. The Quantum Yield (QY) of the solution at room temperature was measured by an integrating sphere of fluorescence spectrometer (Edinburgh-FS 5), with the QY value ranging from 73-82%.

Example 5

A preparation method of core-shell structure nanocrystal comprises the following steps:

1. preparation of cadmium selenide (CdSe) quantum dot cores

2. Processing of cadmium selenide (CdSe) quantum dot cores

21) Dispersing CdSe quantum dot cores: taking 2ml of CdSe quantum dots well prepared and dispersed in n-hexane in the step 1), adding the CdSe quantum dots into 10ml of octadecyl solution, firstly heating the CdSe quantum dot solution to 150 ℃, exhausting gas for 20min to remove the redundant n-hexane solution in the solution, and then raising the temperature of the CdSe solution to 300 ℃.

Preparation of CdSe/CdS core-shell quantum dots

32) And (3) growing a CdS shell: dripping the CdS shell source prepared in the step 31) into the CdSe quantum dot core solution in the step 2) at the dripping rate of 6ml/h for 10min, stopping injecting, curing for 5min, and then injecting 100 microliters of oleylamine into the quantum dot mixed solution and curing for 5 min; and then circulating for 9 times in a mode of injecting a CdS shell source and a modifier oleylamine.

33) After the growth of the shell is finished, adding 5mmol of mixed solution of oleic acid and trioctylphosphine into the mixed solution, and curing for 60min at 300 ℃.

34) And cooling the prepared CdSe/CdS quantum dot solution to room temperature after the aftertreatment by utilizing the oleic acid and the trioctylphosphine modifier is finished.

Purification of CdSe/CdS core-shell quantum dots

The CdSe/CdS quantum dot prepared by the method not only reduces the generation of shell defects when the shell grows, but also enhances the solubility and stability of the CdSe/CdS core-shell quantum dot, and the Quantum Yield (QY) of a CdSe/CdS solution is tested by an integrating sphere (Edinburgh-FS 5) of a fluorescence spectrometer after the CdSe/CdS quantum dot is placed for 30 days at room temperature, wherein the range of the QY value is 75-81%; and testing the absorbance of the CdSe/CdS solution (with the concentration of 0.05mg/ml) by using an ultraviolet visible fluorescence spectrum, wherein the absorbance value ranges from 0.9 to 1.5.

Example 6

1. preparation of cadmium selenide (CdSe) quantum dot cores

2. Processing of cadmium selenide (CdSe) quantum dot cores

Preparation of CdSe/CdS core-shell quantum dots

33) After the growth of the shell is finished, 5mmol of oleic acid is added into the mixed solution to be aged for 60min at 300 ℃.

34) And cooling the prepared CdSe/CdS quantum dot solution to room temperature after the post-treatment by using the oleic acid modifier is finished.

Purification of CdSe/CdS core-shell quantum dots

The CdSe/CdS quantum dot prepared by the method of the embodiment not only reduces the generation of shell defects when the shell grows, but also reduces the defect state of the surface of the CdSe/CdS core-shell quantum dot, further enhances the fluorescence intensity of the CdSe/CdS core-shell quantum dot, and prolongs the transient fluorescence life of the CdSe/CdS core-shell quantum dot. The Quantum Yield (QY) of the solution at room temperature and the transient life of the CdSe/CdS core-shell quantum dot are tested through an integrating sphere (Edinburgh-FS 5) of a fluorescence spectrometer, wherein the range of the QY value is 80-89%, and the life value is 25-30 ns.

Example 7

1. preparation of cadmium selenide (CdSe) quantum dot cores

2. Processing of cadmium selenide (CdSe) quantum dot cores

Preparation of CdSe/CdS core-shell quantum dots

32) And (3) growing a CdS shell: dropwise adding the CdS shell source prepared in the step 31) into the CdSe quantum dot core solution in the step 2) at the dropwise adding rate of 6ml/h for 10min, stopping injecting, curing for 5min, and then injecting 0.5mmol of mixed solution of tetradecylamine and tributylphosphine into the mixed solution of quantum dots; and then circulating for 9 times in a mode of injecting a mixed solution of the CdS shell source and a modifier decatetramine and tributyl phosphine.

33) After the growth of the shell is finished, adding 2mmol of tributylphosphine mixed solution into the mixed solution, and curing for 60min at 300 ℃.

34) And cooling the prepared CdSe/CdS quantum dot solution to room temperature after the aftertreatment by utilizing the tributyl phosphine modifier is finished.

Purification of CdSe/CdS core-shell quantum dots

The CdSe/CdS quantum dot prepared by the method of the embodiment not only reduces the generation of shell defects when the shell grows, but also reduces the defect state of the surface of the CdSe/CdS core-shell quantum dot, and further enhances the fluorescence intensity of the CdSe/CdS core-shell quantum dot. The Quantum Yield (QY) of the solution at room temperature was measured by an integrating sphere (Edinburgh-FS 5) of a fluorescence spectrometer with the QY value ranging from 82 to 91%.

Example 8

1. preparation of cadmium selenide (CdSe) quantum dot cores

2. Processing of cadmium selenide (CdSe) quantum dot cores

21) Dispersing CdSe quantum dot cores: taking 2ml of CdSe quantum dots prepared and dispersed in n-hexane in the step 1) and 1ml of oleylamine, adding the CdSe quantum dots into 10ml of octadecene solution, firstly heating the CdSe quantum dots solution to 150 ℃, exhausting gas for 20min to remove the redundant n-hexane solution in the solution, and then raising the temperature of the CdSe solution to 300 ℃.

Preparation of CdSe/CdS core-shell quantum dots

Purification of CdSe/CdS core-shell quantum dots

The CdSe/CdS quantum dots prepared by the method of the embodiment reduce the generation of defect states between core-shell interfaces, reduce the generation of shell defects during shell growth, and further improve the fluorescence intensity of the CdSe/CdS core-shell quantum dots. The Quantum Yield (QY) of the solution at room temperature was measured by an integrating sphere (Edinburgh-FS 5) of a fluorescence spectrometer, where the QY values ranged from 78-92%.

Example 9

1. preparation of cadmium selenide (CdSe) quantum dot cores

2. Processing of cadmium selenide (CdSe) quantum dot cores

21) Dispersing CdSe quantum dot cores: 2ml of CdSe quantum dots prepared and dispersed in n-hexane in the step 1) and 1ml of oleic acid are added into 10ml of octadecylene solution, the CdSe quantum dot solution is heated to 150 ℃ and exhausted for 20min to remove the redundant n-hexane solution in the solution, and then the temperature of the CdSe solution is raised to 300 ℃.

Preparation of CdSe/CdS core-shell quantum dots

32) And (3) growing a CdS shell: dropwise adding the CdS shell source prepared in the step 31) into the CdSe quantum dot core solution in the step 2) at the dropwise adding rate of 6ml/h for 10min, stopping injecting, curing for 5min, then injecting 0.5mmol of mixed solution of oleylamine and tributylphosphine into the mixed solution of quantum dots, and curing for 5 min; and then the cycle is 9 times in the way of injecting CdS shell source and modifier oleylamine and tributylphosphine.

Purification of CdSe/CdS core-shell quantum dots

The CdSe/CdS quantum dot prepared by the method reduces the generation of shell defects during shell growth and enhances the transient fluorescence lifetime of the core-shell quantum dot, and the Quantum Yield (QY) of a solution at room temperature and the transient lifetime of the CdSe/CdS core-shell quantum dot are tested by an integrating sphere (Edinburgh-FS 5) of a fluorescence spectrometer, wherein the range of the QY value is 75-90%, and the lifetime value is 28-32 ns.

Example 10

1. preparation of cadmium selenide (CdSe) quantum dot cores

2. Processing of cadmium selenide (CdSe) quantum dot cores

Preparation of CdSe/CdS core-shell quantum dots

33) And after the circulation reaction is finished, adding 3mmol of tributyl phosphine modifier into the quantum dot mixed solution, and continuously heating and stirring for 30min at the temperature of 300 ℃.

Purification of CdSe/CdS core-shell quantum dots

The CdSe/CdS quantum dot prepared by the method of the embodiment not only reduces the generation of shell defects when the shell grows, but also enhances the stability of the core-shell quantum dot. The Quantum Yield (QY) of the solution at room temperature was measured by an integrating sphere of a fluorescence spectrometer (Edinburgh-FS 5) with a value ranging from 75 to 90%, and the Quantum Yield (QY) of the CdSe/CdS solution after being left for 30 days at room temperature was measured by an integrating sphere of a fluorescence spectrometer (Edinburgh-FS 5) with a value ranging from 76 to 80%.

Example 11

1. preparation of cadmium selenide (CdSe) quantum dot cores

2. Processing of cadmium selenide (CdSe) quantum dot cores

Preparation of CdSe/CdS core-shell quantum dots

33) After the circulation reaction is finished, 1ml of OA and 3mmol of tributyl phosphine modifier are added into the quantum dot mixed solution, and the mixture is continuously heated and stirred for 30min at 300 ℃.

Purification of CdSe/CdS core-shell quantum dots

The CdSe/CdS quantum dot prepared by the method reduces the generation of shell defects during shell growth and enhances the size uniformity of the core-shell quantum dot, the Quantum Yield (QY) of a solution at room temperature is tested by an integrating sphere (Edinburgh-FS 5) of a fluorescence spectrometer, wherein the range of a QY value is 75-85%, and the range of a dispersion value of the size dispersion rate of the CdSe/CdS core-shell quantum dot is 3-10% when the size dispersion rate is tested by a scanning transmission electron microscope.

Example 12

1. preparation of cadmium selenide (CdSe) quantum dot cores

2. Processing of cadmium selenide (CdSe) quantum dot cores

Preparation of CdSe/CdS core-shell quantum dots

Purification of CdSe/CdS core-shell quantum dots

The CdSe/CdS quantum dots prepared by the method of the embodiment not only reduce the generation of shell defects when the shell grows, but also further enhance the fluorescence intensity of the core-shell quantum dots. The Quantum Yield (QY) of the solution at room temperature was measured by an integrating sphere (Edinburgh-FS 5) of a fluorescence spectrometer, where the QY value ranged from 85-95%.

Example 13

1. preparation of cadmium selenide (CdSe) quantum dot cores

2. Processing of cadmium selenide (CdSe) quantum dot cores

Preparation of CdSe/CdS core-shell quantum dots

Purification of CdSe/CdS core-shell quantum dots

The CdSe/CdS quantum dots prepared by the method of the embodiment not only reduce the generation of shell defects when the shell grows, but also further enhance the solubility and the film forming property of the core-shell quantum dots. The Quantum Yield (QY) of the solution at room temperature is tested by an integrating sphere (Edinburgh-FS 5) of a fluorescence spectrometer, wherein the range of the QY value is 85-95%, the absorbance of the CdSe/CdS solution (with the concentration of 0.05mg/ml) is tested by an ultraviolet visible fluorescence spectrum, the range of the absorbance value is 0.9-1.5, and the flatness of the CdSe/CdS core-shell quantum dots is 70-89% tested by AFM.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims

1. A preparation method of core-shell structure nanocrystalline is characterized by comprising the following steps:

providing a quantum dot core;

2. The method for producing core-shell nanocrystals according to claim 1, wherein in the step of dispersing the core-shell nanocrystals in a solution containing an organic acid and heating the dispersion, the core-shell nanocrystals are dispersed in a solution containing an organic acid in such an amount that the molar mass ratio of the organic acid to the quantum dot core is (5 to 10mmol):10 mg.

3. The method for preparing core-shell structured nanocrystals according to claim 2, wherein in the step of dispersing the core-shell structured nanocrystals in a solution containing an organic acid for heat treatment, the core-shell structured nanocrystals are dispersed in a solution containing an organic acid and heat-treated at a temperature of 240-320 ℃ for 30-90 min.

4. The method for producing core-shell structured nanocrystals according to claim 1, wherein the core-shell structured nanocrystals are dispersed in a solution containing an organic acid and an organic phosphine and subjected to a heat treatment.

5. The method for producing core-shell nanocrystals according to claim 4, wherein in the step of dispersing the core-shell nanocrystals in a solution containing an organic acid and an organic phosphine and heating the dispersion, the core-shell nanocrystals are dispersed in a solution containing an organic acid and an organic phosphine such that the molar mass ratio of the organic acid to the quantum dot core is (5 to 10mmol):10mg and the molar mass ratio of the organic phosphine to the quantum dot core is (2 to 5mmol):10 mg.

6. The method for preparing core-shell structured nanocrystal, according to claim 4, wherein in the step of dispersing the core-shell structured nanocrystal in a solution containing organic acid and organic phosphine for heat treatment, the core-shell structured nanocrystal is dispersed in a solution containing organic acid and organic phosphine and heated at a temperature of 100-320 ℃ for 10-60 min.

7. The method for preparing core-shell structured nanocrystals according to any of claims 1 to 6, wherein the organic acid is selected from linear carboxylic acids containing a terminal carboxyl group.

8. The method for preparing core-shell structured nanocrystals according to claim 4, wherein the organic phosphine is at least one selected from trioctylphosphine and tributylphosphine.

9. The method for preparing core-shell structured nanocrystals according to any of claims 1 to 6, wherein M is N-1.

10. The method for preparing the nanocrystal with the core-shell structure according to claim 1, wherein between the M adjacent shell growth steps in different orders, including between the L adjacent shell growth steps in different orders, the organic amine and the organic phosphine are added into the shell growth reaction system in which the previous shell is formed, mixed and heated, and then the subsequent shell is grown, wherein L is a positive integer and is not more than M.

11. The method of claim 10, wherein L ═ M ═ N-1.

12. The method for preparing core-shell structure nanocrystals according to claim 1, wherein when M < N-1, the method further comprises the step of adding, mixing and then growing the subsequent shell between the growth steps of S adjacent shells in different order, wherein the step between the growth steps of S adjacent shells means the step between the growth steps of adjacent shells in which the organic amine or the organic amine and the organic phosphine are not added to the growth reaction system of the previous shell, and the step is mixing and heating, wherein S is a positive integer and S is not less than 1 and not more than (N-1) -M.

13. The method for preparing the core-shell structure nanocrystal according to any one of claims 1 to 6, wherein in the prepared N layers of shell layers, the thickness of each layer of shell layer is 0.1-2nm, and the value range of N is 6-18.

14. The method for preparing a core-shell nanocrystal, according to any of claims 1, 10 or 12, wherein after adding the shell source for growing the previous shell in the current order to the shell growth system for 5-20min, between each of the M adjacent shell growth steps in different orders, adding organic amine to the shell growth reaction system having formed the previous shell, mixing and heating, and then growing the next shell;

15. The method for preparing the core-shell structure nanocrystal, according to any one of claims 1, 10 or 12, wherein, between M adjacent shell growth steps in different orders, organic amine is added to a shell growth reaction system in which a previous shell is formed, and after mixing and heating at 150-320 ℃ for 5-20min, a shell source is added to perform the growth of the next shell;

or, adding organic amine and organic phosphine into a shell growth reaction system forming a previous shell between L adjacent shell growth steps in different orders, mixing and heating at 150-320 ℃ for 5-20min, and then adding a shell source to grow the next shell;

or, adding organic phosphine into a shell growth reaction system with a formed previous shell between S adjacent shell growth steps in different orders, mixing and heating at 150-320 ℃ for 5-20min, and then adding a shell source to grow the next shell.