阅读说明：本技术 一种具有非线性响应级联放大效应的纳米光子雪崩荧光原理与实现方法 (Nanometer photon avalanche fluorescence principle with nonlinear response cascade amplification effect and implementation method ) 是由 詹求强 梁宇森 朱志旻 乔书倩 郭鑫 王保举 于 2021-08-02 设计创作，主要内容包括：本发明公开了一种具有非线性响应级联放大效应的纳米光子雪崩荧光原理与实现方法,所述的级联放大效应的光子雪崩由光子雪崩纳米引擎与级联离子共同作用实现,光子雪崩纳米引擎由雪崩离子与蓄水离子共掺杂的纳米晶体组成,两种离子都能辐射出高效稳定的光子雪崩荧光,级联离子掺杂在包覆纳米引擎的壳层,通过晶格能量迁移路径可将引擎中光子雪崩能量传递到级联离子。此稀土掺杂荧光纳米材料产生具有级联放大作用的高阶非线性光子雪崩效应,从而用同一激发策略实现纳米体系中多离子光子雪崩荧光辐射。(The invention discloses a nano photon avalanche fluorescence principle with nonlinear response cascade amplification effect and a realization method thereof, wherein photon avalanche of the cascade amplification effect is realized by the combined action of a photon avalanche nano engine and cascade ions, the photon avalanche nano engine consists of an avalanche ion and water storage ion co-doped nano crystal, both ions can radiate high-efficiency and stable photon avalanche fluorescence, the cascade ions are doped in a shell layer covering the nano engine, and photon avalanche energy in the engine can be transmitted to the cascade ions through a lattice energy migration path. The rare earth doped fluorescent nano material generates a high-order nonlinear photon avalanche effect with a cascade amplification effect, so that multi-ion photon avalanche fluorescence radiation in a nano system is realized by using the same excitation strategy.)

1. A realization method of nano-photon avalanche with nonlinear response cascade amplification effect is characterized by comprising the following steps:

s1, constructing a photon avalanche engine with a double-ion structure, wherein one ion is an avalanche ion, the other ion is a water storage ion, under the action of exciting light with a specific wavelength, the avalanche ion carries out energy level transition, under the assistance of the water storage ion, through certain energy cycle conduction, the number of energy level particles of an excited state of the avalanche ion is increased in an avalanche mode, and photon avalanche fluorescence which is efficient and stable and has a high-order nonlinear dependence on the intensity of the exciting light is radiated;

s2, in the energy cycle conduction process, the water storage ions assist the excited state energy level of the avalanche ions to carry out particle number accumulation, and meanwhile, the excited state energy level particle number of the water storage ions also grows along with the avalanche ions, and finally photon avalanche fluorescence is radiated;

s3 the two ions in the photon avalanche engine can transfer the avalanche energy to the third ion cascade ion outside the engine through the lattice energy transfer path, after receiving the avalanche energy, the cascade ion jumps to the radiation energy level step by step to radiate the up-conversion photon avalanche fluorescence, wherein the nonlinear dependence is amplified in the up-conversion process, and the photon avalanche effect of cascade amplification is realized.

2. The method for realizing the cascade amplification photon avalanche effect according to claim 1, wherein a beam of laser with photon energy matching with excited state absorption of avalanche ions is used for excitation, the avalanche ions perform energy level transition through weak ground state absorption and strong excited state absorption, and in combination with efficient energy transfer between the water storage ions and the avalanche ions, energy is circularly conducted between the two ions, when the laser power reaches a certain threshold, the number of particles of multiple energy levels in the avalanche ions and the water storage ions increases in an avalanche manner as the power continues to increase, and the fluorescence radiated by the energy levels has an ultrahigh-order nonlinear response relation to the excitation light.

3. The method of claim 1, wherein the avalanche ion or the water accumulating ion can transfer part of avalanche energy to the cascade ion to realize up-conversion luminescence, and the energy level of the avalanche ion or the water accumulating ion is matched with the existing energy level interval of the avalanche ion or the water accumulating ion.

4. A method for realizing rare earth doped fluorescent nano material with cascade amplification photon avalanche effect is characterized by comprising the following steps:

s1, the photon avalanche engine and the cascade ions are separated in different structural layers by constructing a multilayer core-shell nano structure, so that the cascade ions and the photon avalanche engine are prevented from generating other interactions to influence the photon avalanche generation process, wherein the photon avalanche engine is positioned in a nuclear layer, and the cascade ions are positioned in a shell layer;

s2, constructing a sub-crystalline grid network of avalanche ions or water storage ions in the multilayer core-shell nano structure, so that avalanche energy is transmitted outwards from the photon avalanche engine and is transmitted to the structural layer where cascade ions are located;

s3, the inert nanocrystals are coated on the outermost layer of the nanostructure to compensate the surface lattice defects of the nanostructure and isolate the surface quenchers, so that all internal luminescent ions are protected, avalanche energy is prevented from being transmitted to the defects of the nanoparticles or the surface quenchers, and avalanche energy is prevented from being lost.

5. The method for realizing rare earth doped fluorescent nanomaterial with cascade amplified photon avalanche effect according to claim 4, wherein the photon avalanche engine core structure is formed by avalanche ions Pr³⁺With water-retaining ions Yb³⁺Co-doped in fluoride nanocrystal, and the inner shell structure of cascade ion is composed of cascade ion X³⁺With water-retaining ions Yb³⁺Co-doped in fluoride nano crystal to store water ion Yb³⁺A sublattice network is formed between the core and the inner shell, with the outer shell structure consisting of inert fluoride nanocrystals.

6. The method for realizing rare earth doped fluorescent nanomaterial with cascade amplified photon avalanche effect as claimed in claim 5, wherein the cascade ion X is³⁺Can be Tm³⁺、Ho³⁺、Er³⁺。

7. The method for realizing rare earth doped fluorescent nanomaterial with cascade amplified photon avalanche effect according to claim 4, characterized in that photon avalanche engine core structureIn particular from avalanche ions Pr³⁺With water-retaining ions Yb³⁺Co-doped in fluoride nanocrystal, and the inner shell structure of cascade ion is composed of cascade ion X³⁺And avalanche ion Pr³⁺Co-doped in fluoride nanocrystals, avalanche ion Pr³⁺A sublattice network is formed between the core and the inner shell, with the outer shell structure consisting of inert fluoride nanocrystals.

8. The method for realizing rare earth doped fluorescent nanomaterial with cascade amplified photon avalanche effect as claimed in claim 7, wherein the cascade ion X is³⁺Can be Eu³⁺、Tb³⁺。

Technical Field

The invention belongs to the field of nonlinear optics and nanophotonics, and particularly relates to a nanophotonic avalanche fluorescence principle with nonlinear response cascade amplification effect and an implementation method.

Technical Field

The nonlinear multi-photon effect means that molecules/atoms in a ground state absorb a plurality of photons simultaneously and then jump to an excited state under the excitation of incident light with high photon density, the photons jump to a sub-excited state through a relaxation process, and finally the photons spontaneously radiate back to the ground state to release fluorescence photons with energy slightly less than the sum of the energy of the absorbed photons. Since the first two-photon laser scanning microscope developed by Denk et al in 1990, multiphoton imaging has been widely used in the medical field due to its advantages of low invasiveness, high penetration, strong spatial sectioning capability, high spatial resolution, etc. Meanwhile, other multi-photon technologies based on the nonlinear fluorescence effect are widely applied to the fields of molecular detection, three-dimensional information storage, micromachining and the like, and show wide development prospects.

However, in the conventional nonlinear material, the laser power density is required to be extremely high to realize high-order absorption, and a pulse laser is often adopted as an excitation source, even if the nonlinear order is increased to more than four, the nonlinear order is very difficult to be increased. On the other hand, the excitation mode with high-order nonlinearity and the short-wavelength excitation light are often adopted to improve the resolution of the multi-photon imaging, but in fact, the two have a contradiction relationship and mutually restrict: the excitation wavelength of the multiphoton is usually in the near infrared region, and the higher the order, the longer the wavelength used, which limits the improvement of the multiphoton imaging resolution.

In the field of nonlinear optics, rare earth doped up-conversion nanoparticles are an emerging nonlinear fluorescent probe. The rare earth ions have rich stepped energy levels, the service life of the middle energy level is long, a plurality of photons can be continuously absorbed and jump to the high energy level, low-energy near infrared light is converted into visible light and ultraviolet light, and the method has the advantages of large penetration depth of exciting light, no autofluorescence background, no light bleaching and the like. The photon avalanche phenomenon is an important mechanism for up-conversion of fluorescence, is reported for the first time in 1979, and shows great potential in the aspect of high-order nonlinear fluorescence response. However, most of the reported photon avalanche phenomena are observed in bulk materials or bulk materials and are actually observed under the nanoscalePhoton avalanche fluorescence emission is now very difficult. More importantly, all photon avalanche effect can only be achieved at Pr³⁺、Nd³⁺、Tm³⁺、Er³⁺、Ho³⁺When the fluorescence of single rare earth ions is realized, if the photon avalanche fluorescence of different ions is required to be realized, various complex mechanisms are required, the efficiency is low, and the popularization and the application of the photon avalanche effect in the field of nonlinear optics are hindered.

Disclosure of Invention

The invention aims to overcome the inherent low efficiency of the conventional photon avalanche system, provides a nanoscale cascade photon avalanche system, realizes multi-ion photon avalanche fluorescence radiation in the nano system by using the same excitation strategy, and breaks the principle limitation that photon avalanche only aims at single ion in the traditional research. The inventor provides a novel cascade photon avalanche system with photon avalanche energy capable of being transmitted among different ions from the angle of constructing a photon avalanche engine, so that more rare earth ions which cannot generate photon avalanche effect can realize high-order nonlinear photon avalanche fluorescence radiation.

The invention has another advantage that the up-conversion photon avalanche fluorescence of the cascade ions has cascade amplification effect, the nonlinear order of the nonlinear fluorescence response is further amplified in a superposition manner on the basis of the photon avalanche engine, and N is satisfied after amplification_CPA≤N_PA×N_UC，N_CPAOrder of nonlinear effect, N, representing cascade photon avalanche_PARepresenting the order of the nonlinear effect of a photon avalanche engine, N_UCIndicating the order of the upconversion luminescence inherent to the cascade of ions.

The purpose of the invention is realized by the following technical scheme: a method for realizing rare earth doped fluorescent nano material with cascade amplification photon avalanche effect comprises the following steps:

(1) and constructing a three-layer core-shell nano structure, wherein the core is a photon avalanche engine, the inner shell layer is a layer where cascade ions for expanding photon avalanche fluorescence are located, and the outer shell layer is an inert fluoride nano crystal with a protection effect.

(2) Construction of nanoparticles with double dissociation in the core structureA photon avalanche engine of a substructure, which serves as a core of the photon avalanche fluorescence nanoparticle. Photon avalanche engine composed of avalanche ion Pr³⁺And water-retaining ions Yb³⁺The common components are excited by a continuous near-infrared exciting light beam, and the photon energy of the laser is not completely matched with Pr³⁺From³H₄To¹G₄Is absorbed but perfectly matched to Pr³⁺From¹G₄To³P₀Is absorbed by the excited state of (1). Under the excitation of a certain power of near infrared laser, is in³H₄Is first at least partly excited to¹G₄Is then excited to³P₁And rapidly relax to³P₀，Pr³⁺And Yb³⁺With an efficient energy transfer process in between, Pr³⁺In the middle of³P₀The particles of (a) transfer energy to Yb³⁺Middle ground state energy level²F_7/2Post-particle relaxation of¹G₄Yb of³⁺The particles of ground state energy level are excited to²F_5/2Then, the energy is transferred back to Pr³⁺To make Pr³⁺Excitation of particles in the ground state to¹G₄Thereby realizing¹G₄Multiplication of the number of particles. As the laser power increases, the population and number of cycles of the initial cycle vary with power,¹G₄the number of particles shows avalanche growth, thereby¹G₄Particles excited to other energy levels also undergo avalanche-like growth phenomena, e.g.³P₁、³P₀And¹D₂etc. and also Yb³⁺Excited state energy level of²F_5/2The fluorescence intensity of the radiation at these energy levels also shows avalanche mode increase, indicating that the fluorescence has super high order nonlinear response to the exciting light. The measured response curve (the logarithmic relation curve of the fluorescence intensity and the excitation light intensity) presents an S shape, namely a certain power threshold value exists, when the power reaches the threshold value, the nonlinear effect starts to be sharply enhanced, the photon avalanche fluorescence effect is generated, the power continues to be increased, the fluorescence reaches saturation, and the nonlinear order is reduced.

(3) The inner shell layer containing, in addition to the cascade ion X³⁺And water-retaining ions Yb³⁺Or avalanche ion Pr³⁺So as to form a sub-lattice network between different layers, so that avalanche energy can be transmitted from the dual-ion photon avalanche engine of the nuclear structure to the shell layer and finally transmitted to the cascade ion X³⁺After receiving avalanche energy, the cascade ions are gradually converted upwards to a high energy level, and then the up-conversion photon avalanche fluorescence is radiated. The up-conversion photon avalanche fluorescence has a cascade amplification photon avalanche effect, namely, the up-conversion photon avalanche fluorescence is further amplified in a superposition manner on the basis of the original photon avalanche high-order nonlinear effect, and the amplified photon avalanche fluorescence meets the requirement of N_CPA≤N_PA×N_UC，N_CPAOrder of nonlinear effect, N, representing cascade photon avalanche_PARepresenting the order of the nonlinear effect of a photon avalanche engine, N_UCRepresenting the order of the upconversion luminescence inherent to the cascade ion, e.g. the nonlinear order of the luminescence of a photon avalanche engine reaches 20, the avalanche energy is transferred to the cascade ion to excite its two-photon upconversion process, and the nonlinear order of the cascade ion two-photon luminescence can reach 40.

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

1. compared with the traditional photon avalanche fluorescence, the method can efficiently and stably realize the photon avalanche fluorescence under the nanoscale, and breaks through the limitations of the traditional macroscopic material and the low-temperature condition;

2. compared with the traditional photon avalanche fluorescence, the method can excite various ions to simultaneously generate photon avalanche fluorescence emission only by single beam of continuous near-infrared laser. The traditional photon avalanche fluorescence needs to develop different excitation schemes aiming at different ions, the scheme development needs to be analyzed by combining the energy level structure characteristics of a system, the energy level structure of part of ions cannot meet the conditions required by photon avalanche, and the stability and the high efficiency are difficult to guarantee;

3. compared with the traditional photon avalanche fluorescence, the invention can achieve the ultrahigh-order nonlinear response which cannot be realized by the traditional nonlinear material through the cascade amplification effect.

Drawings

FIG. 1 shows Tm in example 1³⁺Is a schematic diagram of the cascade photon avalanche principle of the cascade ions.

FIG. 2 shows Ho in example 2³⁺Or Er³⁺Is a schematic diagram of the cascade photon avalanche principle of the cascade ions.

FIG. 3 shows Eu as a reference in example 3³⁺Or Tb³⁺Is a schematic diagram of the cascade photon avalanche principle of the cascade ions.

Fig. 4 is a transmission electron micrograph of the cascade photon avalanche nanoparticles of the multilayer core-shell structure in example 4.

FIG. 5 shows the apparatus for measuring multiple ion cascade photon avalanche fluorescence in example 4.

Fig. 6 is a fluorescence spectrum of the multiple ion cascade photon avalanche nanoparticle in example 4.

Fig. 7 is a fluorescence response curve of the multiple ion cascade photon avalanche nanoparticle in example 4.

DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION

The present invention will be further described with reference to the accompanying drawings, and it should be noted that the present embodiment is based on the technical solution, and the detailed implementation and the specific operation process are provided, but the protection scope of the present invention is not limited to the present embodiment.

The invention relates to a method for realizing cascade amplification photon avalanche effect, which comprises the following steps:

s1, constructing a photon avalanche engine with a double-ion structure, wherein one ion is an avalanche ion, the other ion is a water storage ion, under the action of exciting light with a specific wavelength, the avalanche ion carries out energy level transition, under the assistance of the water storage ion, through certain energy cycle conduction, the number of energy level particles of an excited state of the avalanche ion is increased in an avalanche mode, and photon avalanche fluorescence which is efficient and stable and has a high-order nonlinear dependence on the intensity of the exciting light is radiated;

s2, in the energy cycle conduction process, the water storage ions assist the excited state energy level of the avalanche ions to carry out particle number accumulation, and meanwhile, the excited state energy level particle number of the water storage ions also grows along with the avalanche ions, and finally photon avalanche fluorescence is radiated;

s3 the two ions in the photon avalanche engine can transfer the avalanche energy to the third ion cascade ion outside the engine through the lattice energy transfer path, after receiving the avalanche energy, the cascade ion jumps to the radiation energy level step by step to radiate the up-conversion photon avalanche fluorescence, wherein the nonlinear dependence is amplified in the up-conversion process, and the photon avalanche effect of cascade amplification is realized.

It should be noted that, a beam of laser whose photon energy matches with the excited state absorption of the avalanche ion is used for excitation, the avalanche ion performs energy level transition through the weaker ground state absorption and the stronger excited state absorption, and in combination with the efficient energy transfer between the water storage ion and the avalanche ion, the energy is conducted between the two ions in a circulating manner, when the laser power reaches a certain threshold, the number of multiple energy level particles in the avalanche ion and the water storage ion increases in an avalanche manner with the continued increase of the power, and the fluorescence of the energy level radiation has an ultra-high order nonlinear response relationship to the excitation light.

It should be noted that, matching with the existing energy level interval of the avalanche ion or the water storage ion, the avalanche ion or the water storage ion can transfer part of avalanche energy to the cascade ion, thereby realizing up-conversion luminescence.

A method for realizing rare earth doped fluorescent nano material with cascade amplification photon avalanche effect comprises the following steps:

s1, the photon avalanche engine and the cascade ions are separated in different structural layers by constructing a multilayer core-shell nano structure, so that the cascade ions and the photon avalanche engine are prevented from generating other interactions to influence the photon avalanche generation process, wherein the photon avalanche engine is positioned in a nuclear layer, and the cascade ions are positioned in a shell layer;

s2, constructing a sub-crystalline grid network of avalanche ions or water storage ions in the multilayer core-shell nano structure, so that avalanche energy is transmitted outwards from the photon avalanche engine and is transmitted to the structural layer where cascade ions are located;

s3, the inert nanocrystals are coated on the outermost layer of the nanostructure to compensate the surface lattice defects of the nanostructure and isolate the surface quenchers, so that all internal luminescent ions are protected, avalanche energy is prevented from being transmitted to the defects of the nanoparticles or the surface quenchers, and avalanche energy is prevented from being lost.

The photon avalanche engine core structure consists of avalanche ions Pr³⁺With water-retaining ions Yb³⁺Co-doped in fluoride nanocrystal, and the inner shell structure of cascade ion is composed of cascade ion X³⁺With water-retaining ions Yb³⁺Co-doped in fluoride nano crystal to store water ion Yb³⁺A sublattice network is formed between the core and the inner shell, with the outer shell structure consisting of inert fluoride nanocrystals.

Note that the cascade ion X is³⁺Can be Tm³⁺、Ho³⁺、Er³⁺。

It is noted that the photon avalanche engine core structure is specifically composed of avalanche ions Pr³⁺With water-retaining ions Yb³⁺Co-doped in fluoride nanocrystal, and the inner shell structure of cascade ion is composed of cascade ion X³⁺And avalanche ion Pr³⁺Co-doped in fluoride nanocrystals, avalanche ion Pr³⁺A sublattice network is formed between the core and the inner shell, with the outer shell structure consisting of inert fluoride nanocrystals.

Note that the cascade ion X is³⁺Can be Eu³⁺、Tb³⁺。

Example 1

The present embodiment provides a method of using Tm³⁺The method is a method for realizing the rare earth doped fluorescent nano material with cascade ion and cascade amplification photon avalanche effect. In the multilayer core-shell structure upconversion nanoparticles constructed in the embodiment, the core of the nanoparticle is a photon avalanche engine and is composed of water-storage ions Yb³⁺And avalanche ion Pr³⁺Co-doped in NaYF₄Nanocrystal of Yb³⁺The doping concentration is about 15 percent, and Pr³⁺The doping concentration is about 0.5%, and the inner shell layer is made of water-storage ions Yb³⁺And the cascade ion Tm³⁺Co-doped in NaYF₄Composition of nanocrystals of Yb³⁺The doping concentration is about 3 percent, and Tm is³⁺Doping concentrationThe degree is about 4 percent, and the outer shell layer is inert NaYF₄A nanocrystal.

Excited by a continuous near infrared exciting light beam, the photon energy of which is not completely matched with Pr³⁺From³H₄To¹G₄Is absorbed but perfectly matched to Pr³⁺From¹G₄To³P₁Is absorbed by the excited state of (1). Under the excitation of a certain power of near infrared laser, is in³H₄Is first at least partly excited to¹G₄Is then rapidly excited to³P₁And relax to³P₀，Pr³⁺And Yb³⁺With an efficient energy transfer process in between, Pr³⁺In the middle of³P₀The particles of (a) transfer energy to Yb³⁺Middle ground state energy level²F_7/2Post-particle relaxation of¹G₄Yb of³⁺The particles of ground state energy level are excited to²F_5/2Then, the energy is transferred back to Pr³⁺To make Pr³⁺Excitation of particles in the ground state to¹G₄Thereby realizing¹G₄The multiplication of the number of particles, after a number of cycles,¹G₄the number of particles shows avalanche growth, thereby¹G₄Particles excited to other energy levels also undergo avalanche-like growth phenomena, e.g.³P₀、³P₀And¹D₂etc. also include Yb³⁺Excited state energy level of²F_5/2The fluorescence emitted from the energy levels has an ultrahigh-order nonlinear response to the excitation light, the response curve (the logarithmic relation curve of the fluorescence intensity and the excitation light intensity) presents an S shape, and after the power reaches a certain threshold value, the nonlinear effect starts to be sharply enhanced to trigger the photon avalanche engine to generate the photon avalanche fluorescence effect.

Yb between different layers³⁺A sub-crystalline grid network is formed, so that avalanche energy is transmitted outwards from the dual-ion photon avalanche engine and finally transmitted to the cascade ion Tm³⁺The cascade ions receive avalanche energy and are excited by up-conversionThe range radiates the upconversion cascade photon avalanche fluorescence, and the specific energy transfer process is shown in figure 1. Tandem ion Tm³⁺From the ground state energy level³H₆Is excited to³H₅、³F₂、¹G₄、¹D₂And (3) emitting the up-conversion photon avalanche fluorescence with the cascade amplification effect by the excitation state energy level, namely further superposing and amplifying the fluorescence on the basis of the high-order nonlinear effect of the original photon avalanche engine.

Example 2

The present embodiment provides a method to perform HO³⁺Or Er³⁺The method is a method for realizing the rare earth doped fluorescent nano material with cascade ion and cascade amplification photon avalanche effect. In the multilayer core-shell structure upconversion nanoparticles constructed in the embodiment, the core of the nanoparticle is a photon avalanche engine and is composed of water-storage ions Yb³⁺And avalanche ion Pr³⁺Co-doped in NaYF₄Nanocrystal of Yb³⁺The doping concentration is about 15 percent, and Pr³⁺The doping concentration is about 0.5%, and the inner shell layer is made of water-storage ions Yb³⁺And the cascade ion Tm³⁺Co-doped in NaYF₄Composition of nanocrystals of Yb³⁺Doping concentration of about 3%, HO³⁺Or Er³⁺The doping concentration of the metal oxide is about 4 percent, and the shell layer is inert NaYF₄A nanocrystal.

Similar to example 1, a beam of continuous near-infrared excitation light is used for excitation, and after the power reaches a certain threshold, the nonlinear effect starts to be enhanced rapidly, so as to trigger the photon avalanche engine to generate the photon avalanche fluorescence effect. Yb between different layers³⁺A sub-crystalline grid network is formed, so that avalanche energy is transmitted outwards from the dual-ion photon avalanche engine and finally transmitted to the cascade ion Ho³⁺Or Er³⁺After receiving the avalanche energy, the cascade ion radiates the upconversion cascade photon avalanche fluorescence through an upconversion excitation process, and the specific energy transfer process is shown in fig. 1. Cascade ion Ho³⁺From the ground state energy level⁵I₈Is excited to⁵I₆、⁵F₅、⁵S₂、⁵F₂Excited state levels, cascadeIon Er³⁺From the ground state energy level⁴I_15/2Is excited to⁴I_11/2、⁴F_9/2、²H_11/2And (3) emitting the up-conversion photon avalanche fluorescence with the cascade amplification effect by the excitation state energy level, namely further superposing and amplifying the fluorescence on the basis of the high-order nonlinear effect of the original photon avalanche engine.

Example 3

This example provides a method of using Eu³⁺Or Tb³⁺The method is a method for realizing the rare earth doped fluorescent nano material with cascade ion and cascade amplification photon avalanche effect. In the multilayer core-shell structure upconversion nanoparticles constructed in the embodiment, the core of the nanoparticle is a photon avalanche engine and is composed of water-storage ions Yb³⁺And avalanche ion Pr³⁺Co-doped in NaYF₄Nanocrystal of Yb³⁺The doping concentration is about 15 percent, and Pr³⁺The doping concentration is about 0.5%, and the inner shell layer is made of avalanche ions Pr³⁺And cascade ion Eu³⁺Or Tb³⁺Co-doped in NaYF₄Composition of nanocrystals, Pr³⁺The doping concentration is about 3 percent, and Eu³⁺Or Tb³⁺The doping concentration of the metal oxide is about 4 percent, and the shell layer is inert NaYF₄A nanocrystal.

Similar to example 1, a beam of continuous near-infrared excitation light is used for excitation, and after the power reaches a certain threshold, the nonlinear effect starts to be enhanced rapidly, so as to trigger the photon avalanche engine to generate the photon avalanche fluorescence effect. Pr between different layers³⁺A sub-crystalline grid network is formed, so that avalanche energy is transmitted outwards from the dual-ion photon avalanche engine and finally transmitted to the cascade ion Eu³⁺Or Tb³⁺After receiving the avalanche energy, the cascade ion radiates the upconversion cascade photon avalanche fluorescence through an upconversion excitation process, and the specific energy transfer process is shown in fig. 1. Cascade ion Eu³⁺From the ground state energy level⁵1₈Is excited to⁵D₀、⁵D₁Equi-excited state energy level, cascade ion Tb³From the ground state energy level⁴I_15/2Is excited to⁵D₄Excited state energy levels due to Eu³⁺Or Tb³⁺The multi-photon excitation process is not carried out, and the emitted photon avalanche fluorescence does not have the cascade amplification effect.

Example 4

Based on the implementation method of the rare earth doped nanoparticles for radiating multi-ion cascade photon avalanche fluorescence in example 1, this example illustrates specific synthetic steps:

firstly, synthesizing a photon avalanche engine core structure: at room temperature (23-25 deg.C), 5mL of 0.2M Ln (CH) was added to a 100mL round bottom flask₃COO)₃Then, 7.5mL of oleic acid and 17.5mL of 1-octadecene were added to the solution (Ln ═ Y/Yb/Pr) in this order, and the mixture was reacted at 150 ℃ for 40 minutes to obtain a precursor. The heating mantle was removed and the reaction mixture was allowed to cool to 40 ℃ with stirring, and 10mL NH was added quickly₄A mixture of F-methanol solution (0.4M) and 2.5mL of NaOH-methanol solution (1M) was reacted at 40 ℃ for at least 2 hours, followed by reaction at 110 ℃ for 30 minutes under vacuum to remove methanol. After evaporation of the methanol, the temperature was raised to 300 ℃ under an argon atmosphere and reacted at the same temperature for 1.5 hours. Removing the heating jacket, stirring while cooling the reactants to room temperature, adding 10mL of absolute ethyl alcohol, centrifuging at 7500r.p.m. speed for 5 minutes, removing the supernatant, collecting the product, washing with a mixture of ethanol and cyclohexane to obtain the nuclear NaYF of the upconversion nanoparticles₄: Yb/Pr, dispersed in 9mL of cyclohexane. By adjusting Y^{3 +}、Pr³⁺And Yb³⁺The doping component is NaYF₄: Yb/Pr (15/0.5%) nanoparticles.

Then synthesizing and coating an inner shell structure in which the cascade ions are located: at room temperature (23-25 deg.C), 5mL of 0.2M Ln (CH) was added to a 100mL round bottom flask₃COO)₃Solution (Ln ═ Y/Yb/Tm), then 7.5mL oleic acid and 17.5mL 1-octadecene solution were added sequentially and heated to 120 ℃ for 10 minutes to remove water and then reacted at 150 ℃ for 40 minutes to form a precursor, then the solution was cooled to 80 ℃, 3mL nanoparticle core structure solution previously synthesized was added to the flask and stored at this temperature for 30 minutes to remove cyclohexane, and the solution was cooled to 40 ℃ and held at this temperature for at least 2 hours. Followed by reaction at 110 ℃ under vacuum for 30 minutes to remove methanol. After evaporation of the methanol, the temperature was raised to 300 ℃ under an argon atmosphere and the reaction was carried out at this temperature for 1.5 hours at constant temperature. Then, the same operation as the previous operation is carried out, the temperature is reduced to the room temperature, 10mL of absolute ethyl alcohol is added, the centrifugal operation is carried out, the supernatant is discarded, the product is collected, the ethanol cyclohexane mixed solution is used for cleaning, and finally cyclohexane is added for dissolving to obtain the photon avalanche nanoparticle NaYF with the double-layer core-shell structure₄：Yb/Pr(15/0.5％)@NaYF₄：Yb/Tm(3/4％)。

Finally, synthesizing and coating an outer shell structure consisting of inert fluoride nanocrystals: to a 100mL round bottom flask was added 5mL of 0.2M Y (CH)₃COO)₃And adding 7.5mL of oleic acid and 17.5mL of 1-octadecene into the solution in sequence, heating to 120 ℃, reacting for 10 minutes to remove water, reacting for 40 minutes at 150 ℃ to form a precursor, cooling to 80 ℃, adding 3mL of the photon avalanche nanoparticle solution with the double-layer core-shell structure synthesized in the previous step, and keeping for 20 minutes to remove cyclohexane. Cooled to 40 ℃ for at least 2 hours, followed by reaction at 110 ℃ under vacuum for 30 minutes to remove methanol. After evaporation of the methanol, the temperature was raised to 300 ℃ under an argon atmosphere and the reaction was carried out at this temperature for 1.5 hours at constant temperature. Then, the same operation as the previous operation is carried out, the temperature is reduced to the room temperature, 10mL of absolute ethyl alcohol is added, the centrifugal operation is carried out, the supernatant is removed, the product is collected, the ethanol cyclohexane mixed solution is used for cleaning, and finally cyclohexane is added for dissolving to obtain the prepared three-layer nuclear shell structure photon avalanche nano particle NaYF₄：Yb/Pr(15/0.5％)@NaYF₄：Yb/Tm(3/4％)@NaYF₄。

The transmission electron micrograph of the successfully synthesized cascade photon avalanche nanoparticle with the multilayer core-shell structure is shown in figure 2.

Example 5

In order to test rare earth doped nanoparticles based on the radiative multi-ion cascade photon avalanche fluorescence implemented in example 1, the following test apparatus including an excitation light generation module, a multi-photon microscopy module, a photodetection module, as shown in fig. 5, can be used for verification.

The excitation light generation module comprises a near-infrared continuous laser 1, an optical filter 2, a collimation beam expander 3 (including a pinhole filter), a half wave plate 4 and a polaroid 5. The near-infrared laser generates continuous Gaussian laser with the wavelength of 852nm and outputs, the filter filters stray light of other wave bands in the laser, the collimating beam expander enlarges the size of an excitation light spot, the utilization rate of the power of the excitation light is improved, the pinhole filter is arranged at the focus to filter high-frequency stray light, and the half wave plate 4 is arranged on the rotatable mounting seat and matched with the linear polarizer 5 to adjust the power of the laser beam.

The multi-photon microscopic module comprises a high-reflection low-transmission dichroic mirror 7, an optical filter 8, an objective lens 9 and a cascade photon avalanche fluorescence nanometer material 10 arranged on an objective table. The laser beam is further filtered by the optical filter 8, and then the laser is focused by the objective lens to the cascade photon avalanche fluorescence nanometer material arranged on the objective table.

The photoelectric detection module comprises a high-reflection low-transmission dichroic mirror 7, an optical filter 11, a focusing lens 10 and a photoelectric detector 11. Part of cascade photon avalanche fluorescence collected by the objective lens is separated from exciting light through the high-reflection low-transmission dichroic mirror 7, is subjected to filtering processing through the optical filter 11, and is focused by the focusing lens 10 to enter the photoelectric detector to complete receiving.

Cascaded photon avalanche nanoparticles NaYF synthesized in example 4₄：Yb/Pr(15/0.5％)@NaYF₄：Yb/Tm(3/4％)@NaYF₄The fluorescence spectrum test result of (2) is shown in FIG. 6, and the fluorescence response curve test result is shown in FIG. 7.

Various modifications may be made by those skilled in the art based on the above teachings and concepts, and all such modifications are intended to be included within the scope of the present invention as defined in the appended claims.