Nd < 3 + > single-doped sandwich core-shell structure nanoparticles and preparation method thereof

Abstract

The invention relates to the technical field of photoelectric functional materials, in particular to Nd < 3 + > single-doped sandwich core-shell structure nanoparticles and a preparation method thereof.According to the Nd < 3 + > single-doped sandwich core-shell structure nanoparticles, a rare earth light-emitting ion doped layer is arranged between an inert core and a peripheral inert protection layer, doped ions are limited in a quasi-two-dimensional space, and the rare earth light-emitting ion doped layer is formed; therefore, excited state energy loss is effectively inhibited, and luminous efficiency is improved. The core-shell structure size and the doped ion concentration are synergistically optimized, and the thickness of a luminous ion doped layer is controlled to be 0.1-1 nm, so that the luminous intensity of the sandwich core-shell structure nanoparticles is enhanced by 33 times compared with that of common core-shell nanoparticles, the luminous quantum yield is increased to 28.6%, and the luminous life is prolonged to 295.9 ms; the preparation method disclosed by the invention is simple, the performance of the product is obviously improved, and the preparation method has important value on research and application of rare earth-based nano material photophysics, rare earth-based nano-photon solid-state devices and biological imaging probes.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic functional materials technology, specifically to an Nd... 3+ Single-doped sandwich core-shell structured nanoparticles and their preparation method. Background Technology

[0002] Rare-earth-doped nanocrystals are a class of nanoparticles with unique photophysical properties, possessing significant application value in various fields such as biomedicine, imaging displays, anti-counterfeiting labels, optoelectronic sensing, and information communication. Rare-earth-based nanocrystalline luminescent particles exhibit advantages such as large Stokes shift, high quantum yield, and good photostability. The rare-earth ions in these materials are typically classified into three categories: sensitizers, activators, and matrix ions. Among them, Nd... 3+ Yb 3+ Er 3+ Tm 3+ Pr can be used as a sensitizer that is excited in the near-infrared band; 3+ 、Nd 3+ Ho 3+ Er 3+ Tm 3+ Sc can act as an activator, reaching an excited state by receiving energy from the sensitizer, and then undergoing a radiative transition; 3+ Y 3+ La 3+ Gd 3+ Lu 3+ Rare earth fluorides have relatively stable electronic configurations and are generally difficult to excite. They typically serve as matrix cations to form optically inert lattices and / or participate in crystal field modulation. Rare earth fluorides and their complex salts have the advantages of low lattice phonon energy and high chemical stability, making them ideal matrices for bulk and micro / nano-scale rare earth-based luminescent materials.

[0003] Due to their high specific surface area and associated high surface defect rate, nanoluminescent materials generally exhibit lower luminescence quantum yields compared to bulk luminescent materials of the same composition. To address surface defects, current research typically involves epitaxially growing inert lattices with matching crystal structures to repair the nanocrystal surface, while simultaneously using the inert lattice layer to isolate external quenching factors (molecules capable of resonance). For example, epitaxially growing an inert matrix of rare-earth fluoride nanocrystals doped with sensitizers and activators can significantly improve the luminescence quantum yield of the nanoparticles. Current methods for synthesizing core-shell epitaxial rare-earth nanoparticles include precursor thermal decomposition and ion coprecipitation.

[0004] While the core-shell epitaxial structure alleviates the surface defect problem of rare-earth-doped luminescent nanoparticles, defects still exist in the rare-earth-doped core lattice. The three-dimensional energy transfer network of sensitizer and activator rare-earth ions can also experience quenching when encountering lattice defects. On the other hand, reducing the doping concentration of sensitizer and activator ions to disrupt the energy transfer network will decrease the total number of luminescent dopant ions in the nanoparticles, leading to a decrease in luminescence intensity.

[0005] Therefore, how to limit energy migration and improve the luminescence intensity and quantum yield of nanoparticles based on the design of core-shell epitaxial nanoparticles remains one of the important challenges in the field of rare earth luminescent nanomaterials. Summary of the Invention

[0006] This invention places a rare-earth luminescent ion doped layer between an inert core and an outer inert protective layer, resulting in sandwich-structured rare-earth nanocrystalline luminescent particles. This confines the doped ions within a quasi-two-dimensional space, restricting the pathways and distances of doped ion energy migration, thereby effectively suppressing excited-state energy loss and improving luminescence efficiency. Without reducing the doping concentration, the luminescence efficiency and intensity of the rare-earth doped nanoparticles are ensured.

[0007] In a first aspect, the present invention provides an Nd 3+ Single-doped sandwich core-shell structured nanoparticles, wherein the sandwich structure, from the inside out, consists of: an inert core, a luminescent ion doping layer, and an inert protective layer; the inert core material is β-ALnF4; the luminescent ion doping layer material is β-ALnF4:Nd; and the inert protective layer material is β-ALnF4; wherein A is selected from Li. + Na + K + One of them; Ln is selected from Y 3+ Gd 3+ La 3+ Lu 3+ At least one of the following. Further, the thickness of the luminescent ion doped layer is 0.1-5 nm; or 0.1-3 nm; or 0.1-1 nm; or 0.4-0.9 nm. Further, the luminescent ion doped layer contains rare earth dopant ions Nd... 3+ The doping molar concentration is 1-100%; or 20-100%; or 20-80%; or 20-60%.

[0008] Secondly, the present invention provides an Nd 3+ A method for preparing single-doped sandwich core-shell structured nanoparticles includes the following steps: S1. The matrix rare earth trifluoroacetate and sodium salt were added to a mixed solvent of oleic acid / oleylamine / octadecene, heated and stirred under a nitrogen atmosphere, and the product was collected by centrifugation after the thermal decomposition reaction was completed to obtain α-ALnF4 nanoparticles; α-ALnF4 nanoparticles and sodium salt were added to a mixed solvent of oleic acid / octadecene, heated and stirred under a nitrogen atmosphere, and the product was collected by centrifugation after the thermal decomposition reaction was completed to obtain inert core particles β-ALnF4; S2. The inert core particles β-ALnF4 are mixed with matrix rare earth trifluoroacetate, neodymium trifluoroacetate and sodium trifluoroacetate, and heated and stirred under nitrogen atmosphere to complete the epitaxial growth of the luminescent ion doped layer βALnF4:Nd, and the core-shell epitaxial composite nanoparticles β-ALnF4@ALnF4:Nd are obtained. S3. The core-shell epitaxial composite nanoparticles β-ALnF4@ALnF4:Nd are mixed with rare earth trifluoroacetate and sodium salts of the matrix, and heated and stirred under a nitrogen atmosphere to complete the epitaxial growth of the inert protective layer β-ALnF4, thus obtaining core-shell-shell epitaxial sandwich structure nanoparticles β-ALnF4@ALnF4:Nd@ALnF4.

[0009] Further, in S1, the matrix rare earth trifluoroacetate is selected from at least one of yttrium salt, gadolinium salt, lanthanum salt, and lutetium salt; further, in S1, the sodium salt is selected from one of NaOH, NaF, CF3COONa, and CH3COONa; further, in S1, the molar ratio of the matrix rare earth trifluoroacetate to the sodium salt is 1:(1~2); the molar ratio of α-ALnF4 to the sodium salt is 1:(1~2).

[0010] Further, in S1, the heating reaction conditions are as follows: after evacuating the reaction vessel, nitrogen gas is introduced and stirred, and the mixture is heated to 280-350 ℃, or 280-330 ℃, or 300-320 ℃, or 310 ℃ for reaction; the temperature is maintained for 10-50 min, or 10-40 min, or 20-40 min, or 30 min.

[0011] Further, in step S2, the matrix rare earth trifluoroacetate is selected from at least one of yttrium salt, gadolinium salt, lanthanum salt, and lutetium salt; further, in step S2, the molar ratio of the inert core particle β-ALnF4, the matrix rare earth trifluoroacetate, neodymium trifluoroacetate, and sodium trifluoroacetate is (1-16):(0.1-1):(0.1-1):1.

[0012] Further, in step S2, the heating reaction conditions are as follows: after evacuating the reaction vessel, nitrogen gas is introduced for stirring, and the mixture is heated to 280-350 °C, or 280-330 °C, or 300-320 °C, or 310 °C for reaction; then the temperature is maintained for 10-50 min, or 10-40 min, or 20-40 min, or 30 min. Further, in step S3, the matrix rare earth trifluoroacetate is selected from at least one of yttrium salt, gadolinium salt, lanthanum salt, and lutetium salt; further, in step S3, the sodium salt is selected from one of NaOH, NaF, CF3COONa, and CH3COONa; further, in step S3, the molar ratio of the core-shell epitaxial composite nanoparticles β-ALnF4@ALnF4:Nd, the matrix rare earth trifluoroacetate, and the sodium salt is 1:(1-4):(1-4).

[0013] Further, in S3, the heating reaction conditions are as follows: after evacuating the reaction vessel, nitrogen gas is introduced for stirring, and the mixture is heated to 300-350 ℃, or 300-330 ℃, or 300-320 ℃, or 310 ℃; and maintained for 10-50 min, or 10-40 min, or 20-40 min, or 30 min.

[0014] The sandwich core-shell structured nanoparticles of this invention incorporate rare earth-doped Nd ions. 3+ Confining the domain within a quasi-two-dimensional space restricts the pathways and distances of energy migration of dopant ions, thereby effectively suppressing excited-state Nd. 3+ This invention achieves reduced energy loss and improved luminescence efficiency by synergistically optimizing the core-shell structure size and dopant ion concentration. The thickness of the luminescent ion doped layer is controlled within 0.1-1 nm, resulting in a 33-fold increase in luminescence intensity, a luminescence quantum yield of 28.6%, and a luminescence lifetime of 295.9 ms compared to ordinary core-shell nanoparticles. The preparation method is simple, and the product performance is significantly improved, making it valuable for the research and application of rare-earth-based nanomaterial photophysics, rare-earth-based nanophotonic solid-state devices, and biological imaging probes. Attached Figure Description

[0015] Figure 1 This is a transmission electron microscope image of the inert core β-NaGdF4 nanoparticles of the present invention; Figure 2 Transmission electron microscopy (TEM) images of b-NaGdF4@NaGdF4:60%Nd core-shell epitaxial composite nanoparticles with different doped layer thicknesses in Examples 1-4; where C represents core, S represents shell, and C:S represents the molar ratio of core and shell components. Figure 3Transmission electron microscopy (TEM) images of core-shell-shell epitaxial sandwich nanoparticles with different doped layer thicknesses b-NaGdF4@NaGdF4:60%Nd@NaGdF4 in Examples 1-4; where C represents core, S represents shell, and C:S:S represents the molar ratio of core, shell, and shell components. Figure 4 The luminescence properties of b-NaGdF4@NaGdF4:60%Nd@NaGdF4 core-shell-shell epitaxial sandwich structure nanoparticles with different doped layer thicknesses in Examples 1-4; in, Figure 4 a represents the emission spectrum (excitation wavelength 808 nm) of NaGdF4@NaGdF4:60%Nd@NaGdF4 particles with different doped layer thicknesses. Figure 4 b is the corresponding Figure 4 The integral area of ​​the emission peak of a; Figure 4 c is the photon count decay curve of the 1058 nm emission peak after pulse excitation of the particle; Figure 4 d is the corresponding Figure 4 The fitting results of the luminescence lifetime of c; Figure 5 Transmission electron microscope (TEM) images of b-NaGdF4@NaGdF4:Nd nanoparticles with different doping concentrations in Example 5; Figure 6 The luminescence lifetime of b-NaGdF4@NaGdF4:Nd@NaGdF4 nanoparticles and Nd 3+ The relationship between changes in ion doping concentration; Figure 7 The integral area of ​​the emission spectrum of b-NaGdF4@NaGdF4:Nd@NaGdF4 nanoparticles and Nd 3+ The relationship between changes in ion doping concentration.

[0016] Figure 8 The rare-earth ion-doped sandwich core-shell structured nanoparticles β-ALnF4@ALnF4:Nd of the present invention are @ALnF4 structure diagram. Detailed Implementation

[0017] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be described in detail below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise stated, percentages and parts are by weight. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein can be applied to the present invention. The preferred embodiments and materials described herein are for illustrative purposes only.

[0018] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0019] Please see Figure 8 This invention aims to provide rare-earth ion-doped sandwich core-shell structured nanoparticles. The sandwich structure, from the inside out, consists of an inert core, a luminescent ion doped layer, and an inert protective layer, thereby confining the luminescent ions in a quasi-two-dimensional space. By synergistically optimizing the core-shell structure size and dopant ion concentration, the pathway and distance of dopant ion energy migration are restricted, thereby effectively suppressing excited-state energy loss and improving luminescence efficiency.

[0020] In some specific embodiments, the inert core material of the rare-earth-doped sandwich core-shell structured nanoparticles is β-ALnF4; the luminescent ion doping layer material is β-ALnF4:E; and the inert protective layer material is β-ALnF4; wherein, A is selected from Li + Na + K + One of them; Ln is selected from Y 3+ Gd 3+ La 3+ Lu 3+ At least one of them; E is selected from Nd 3+ Yb 3+ Tm 3+ Er 3+ At least one of them.

[0021] In some preferred embodiments, E is selected from Nd 3+ .

[0022] In some specific embodiments, the thickness of the light-emitting ion doped layer is 0.1-5 nm; for example, 0.1 nm, 0.2 nm, 0.4 nm, 0.6 nm, 0.8 nm, 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm; other specific values ​​within this range can be selected, and will not be described in detail here.

[0023] In some specific embodiments, the molar concentration of rare earth dopant ions E in the luminescent ion doped layer is 10-100%; for example, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%; other specific values ​​within this range can be selected, and will not be described in detail here.

[0024] In other specific embodiments, a method for preparing rare earth-doped sandwich core-shell structured nanoparticles is provided, comprising the following steps: S1. The matrix rare earth trifluoroacetate and sodium salt are added to a mixed solvent of oleic acid / oleylamine / octadecene, heated and stirred under a nitrogen atmosphere. After the thermal decomposition reaction is completed, the mixture is cooled to room temperature, ethanol is added, and the product is collected by centrifugation to obtain α-ALnF4 nanoparticles; α-ALnF4 nanoparticles and sodium salt are added to a mixed solvent of oleic acid / octadecene, heated and stirred under a nitrogen atmosphere. After the thermal decomposition reaction is completed, the mixture is cooled to room temperature, ethanol is added, and the product is collected by centrifugation to obtain inert core particles β-ALnF4; In some embodiments of this implementation, the matrix rare earth trifluoroacetate is selected from at least one of yttrium salts, gadolinium salts, lanthanum salts, and lutetium salts; In a preferred embodiment, the matrix rare earth trifluoroacetate is selected from Gadolinium salt; in some embodiments of this implementation, the sodium salt is selected from one of NaOH, NaF, CF3COONa, and CH3COONa; in a preferred embodiment, the sodium salt is selected from CF3COONa; in some embodiments of this implementation, the molar ratio of the matrix rare earth trifluoroacetate to the sodium salt is 1:(1~2); for example, the molar ratio is 1:1, or the molar ratio is 1:1.2, or the molar ratio is 1:1.5, or the molar ratio is 1:1.8, or the molar ratio is 1:2; other specific values ​​within this range can be selected, and will not be elaborated here; it should be noted that "molar ratio" refers to the molar ratio of the chemical formula of the matrix rare earth trifluoroacetate to the chemical formula of the sodium salt.

[0025] In some embodiments of this implementation, the molar ratio of α-ALnF4 to the sodium salt is 1:1. It should be noted that "molar ratio" refers to the molar ratio of the chemical formulas of α-ALnF4 and the sodium salt.

[0026] In some embodiments of this implementation, after the reaction vessel is evacuated to remove water and oxygen, nitrogen gas is introduced, and the mixture is stirred and heated to 280-350 °C, and the reaction is maintained at this temperature for 10-50 min; for example, heating to 280 °C, 290 °C, 300 °C, 310 °C, 320 °C, 330 °C, 340 °C, and 350 °C; other specific values ​​within this range can be selected, and will not be described in detail here; for example, maintaining the temperature for 10 min, 20 min, 30 min, 40 min, and 50 min; other specific values ​​within this range can be selected, and will not be described in detail here. S2. Inert core particles β-ALnF4 were mixed with matrix rare earth trifluoroacetate, luminescent doped rare earth trifluoroacetate, and sodium trifluoroacetate. The mixture was heated and stirred under a nitrogen atmosphere to complete the epitaxial growth of the doped layer. After the thermal decomposition reaction was completed, the mixture was cooled to room temperature, ethanol was added, and the product was collected by centrifugation to obtain core-shell epitaxial composite nanoparticles β-ALnF4@ALnF4:E. In some embodiments of this implementation, the matrix rare earth trifluoroacetate is selected from at least one of yttrium salts, gadolinium salts, lanthanum salts, and lutetium salts; In a preferred embodiment, the matrix rare earth trifluoroacetate is selected from gadolinium salts or a variety thereof; In some embodiments of this implementation, the luminescent doped rare earth trifluoroacetate is selected from at least one of neodymium salts, ytterbium salts, thulium salts, and erbium salts; In a preferred embodiment of this implementation, the luminescent doped rare-earth trifluoroacetate is selected from neodymium salts; In some embodiments of this implementation, the molar ratio of the inert core particle β-ALnF4, the matrix rare earth trifluoroacetate, the luminescent doped rare earth trifluoroacetate, and sodium trifluoroacetate is (1-16):(0.1-1):(0.1-1):1. For example, the molar ratio is 2:0.9:0.1:1; the molar ratio is 4:0.8:0.2:1; the molar ratio is 6:0.9:0.1:1; the molar ratio is 8:0.55:0.45:1; the molar ratio is 12:0.8:0.2:1; the molar ratio is 16:0.4:0.6:1. Other specific values ​​within this range can be selected and will not be elaborated here. It should be noted that "molar ratio" refers to the molar ratio of the chemical formulas of β-ALnF4, matrix rare earth trifluoroacetate, luminescent doped rare earth trifluoroacetate, and sodium trifluoroacetate.

[0027] In some embodiments of this implementation, the heating reaction conditions are as follows: after the reaction vessel is evacuated to remove water and oxygen, nitrogen gas is introduced, and the temperature is raised to 280-350 °C and maintained for 10-50 min; for example, heating to 280 °C, 290 °C, 300 °C, 310 °C, 320 °C, 330 °C, 340 °C, or 350 °C; other specific values ​​within this range can be selected and will not be described in detail here; for example, maintaining the temperature for 10 min, 20 min, 30 min, 40 min, or 50 min; other specific values ​​within this range can be selected and will not be described in detail here. S3. The core-shell epitaxial composite nanoparticles β-ALnF4@ALnF4:E were mixed with rare earth trifluoroacetate and sodium salts of the matrix, and heated and stirred under a nitrogen atmosphere to complete the epitaxial growth of the inert protective layer. After the thermal decomposition reaction was completed, the mixture was cooled to room temperature, ethanol was added, and the product was collected by centrifugation to obtain the core-shell-shell epitaxial sandwich structure nanoparticles β-ALnF4@ALnF4:E@ALnF4.

[0028] In some embodiments of this implementation, the matrix rare earth trifluoroacetate is selected from at least one of yttrium salts, gadolinium salts, lanthanum salts, and lutetium salts; In a preferred embodiment, the matrix rare earth trifluoroacetate is selected from gadolinium salts; In some embodiments of this implementation, the sodium salt is selected from one of NaOH, NaF, CF3COONa, and CH3COONa; In a preferred embodiment, the sodium salt is selected from CF3COONa; In some embodiments of this implementation, the molar ratio of the core-shell epitaxial composite nanoparticles β-ALnF4@ALnF4:E, the matrix rare earth trifluoroacetate, and the sodium salt is 1:(1-4):(1-4); for example, the molar ratio is 1:1:1; the molar ratio is 1:2:2; the molar ratio is 1:3:3; the molar ratio is 1:4:4; other specific values ​​within this range can be selected, and will not be elaborated here; it should be noted that "molar ratio" refers to the molar ratio of the chemical formulas of β-ALnF4@ALnF4:E, the matrix rare earth trifluoroacetate, and the sodium salt.

[0029] In some embodiments of this implementation, the heating reaction conditions are as follows: after evacuating the reaction vessel to remove water and oxygen, nitrogen gas is introduced, and the mixture is stirred and heated to 300-350 °C, and the reaction is maintained at this temperature for 10-50 min; for example, heating to 300 °C, 310 °C, 320 °C, 330 °C, 340 °C, or 350 °C; other specific values ​​within this range can be selected and will not be described in detail here; for example, maintaining the temperature for 10 min, 20 min, 30 min, 40 min, or 50 min; other specific values ​​within this range can be selected and will not be described in detail here. The technical solution of the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the present invention. Example 1

[0030] Synthesis of β-NaGdF4 inert core particles: 1 mmol CF3COONa, 1 mmol Gd(CF3COO)3, 10 mmol oleic acid (OA), 10 mmol oleylamine (OM), and 20 mmol octadecene (ODE) were transferred to a two-necked flask. The mixture was heated under vacuum for 10 min with stirring to remove moisture and oxygen. After stopping the vacuum, nitrogen gas was introduced and continuously supplied. Once the pressure stabilized, the mixture was heated to 310 °C and maintained for 30 min. After the reaction was complete and cooled, 60 ml ethanol was added, and the α-NaGdF4 nanoparticle precipitate was collected by centrifugation. The α-NaGdF4 nanoparticles were redispersed with a quantitative amount of cyclohexane. Half the volume of the α-NaGdF4 nanoparticle-cyclohexane solution from the above process was transferred to a two-necked flask, and the cyclohexane was dried. 0.5 mmol CF3COONa, 20 mmol OA, and 20 mmol ODE were added, and the vacuum removal, deoxygenation, and nitrogen protection procedures were repeated. The mixture was heated to 310 °C. The reaction was carried out at ℃ for 30 min. After the reaction was completed and cooled, 60 ml of ethanol was added, and the β-NaGdF4 inert core particle precipitate was collected by centrifugation. The nanoparticles were redispersed with a quantitative amount of cyclohexane.

[0031] Synthesis of NaGdF4@NaGdF4:60%Nd core-shell nanoparticles: A cyclohexane solution containing 0.5 mmol of β-NaGdF4 nanoparticles was transferred to a two-necked flask, and the cyclohexane was dried. 0.1 mmol Gd(CF3COO)3, 0.15 mmol Nd(CF3COO)3, 0.25 mmol CF3COONa, 20 mmol OA, and 20 mmol ODE were added. The mixture was stirred and heated under vacuum for 10 min to thoroughly remove moisture and oxygen. After the vacuum was stopped, nitrogen gas was introduced and continuously supplied. Once the gas pressure stabilized, the mixture was heated to 310 °C and maintained for 30 min. After the reaction was complete and cooled, 60 ml of ethanol was added, and the β-NaGdF4@NaGdF4:60%Nd nanoparticle precipitate was collected by centrifugation. The nanoparticles were redispersed with a quantitative amount of cyclohexane. The sample name of this core-shell nanoparticle was labeled 1C-0.5S.

[0032] Synthesis of b-NaGdF4@NaGdF4:60%Nd@NaGdF4 core-shell-shell nanoparticles: A quantitative solution of b-NaGdF4@NaGdF4:60%Nd nanoparticles in cyclohexane was transferred to a two-necked flask, and the cyclohexane was dried. 2 mmol CF3COONa, 2 mmol Gd(CF3COO)3, 20 mmol OA, and 20 mmol ODE were added. The mixture was stirred and heated under vacuum for 10 min to thoroughly remove moisture and oxygen. After the vacuum was stopped, nitrogen gas was introduced and continuously supplied. Once the gas pressure stabilized, the mixture was heated to 310 °C and maintained for 30 min. After the reaction was complete and cooled, 60 ml of ethanol was added, and the b-NaGdF4@NaGdF4:60%Nd@NaGdF4 nanoparticle precipitate was collected by centrifugation. The nanoparticles were redispersed with a quantitative amount of cyclohexane. The sample name of this core-shell-shell nanoparticle was labeled 1C-0.5S-4S.

[0033] The morphology of the nanoparticles prepared in this embodiment was characterized using transmission electron microscopy (TEM). A TEM image of the inert core β-NaGdF4 nanoparticles is shown below. Figure 1 As shown, the particles are spherical with a diameter of approximately 9.4 nm. TEM images of b-NaGdF4@NaGdF4:60%Nd core-shell epitaxial composite nanoparticles with different doping layer thicknesses are shown below. Figure 2 As shown. Taking the core-shell nanoparticle sample 1C-0.5S as an example, the particles have a spherical morphology with a diameter of approximately 11.2 nm. Figure 2 a) The thickness of the epitaxial ion-doped layer is approximately 0.9 nm. TEM images of b-NaGdF4@NaGdF4:60%Nd@NaGdF4 core-shell-shell epitaxial composite nanoparticles with different doping layer thicknesses are shown below. Figure 3As shown, taking the core-shell-shell nanoparticle sample 1C-0.5S-4S as an example, the particles have a spherical morphology with a diameter of approximately 17.1 nm. Figure 3 a), that is, the thickness of the epitaxial inert protective layer is approximately 3.0 nm.

[0034] The luminescence properties of the rare-earth-doped sandwich core-shell structured nanoparticles in this embodiment were tested using a fluorescence spectrophotometer. The raw data and analysis results are as follows: Figure 4 As shown, in order are Figure 4 a. Emission spectrum of nanoparticle solutions with normalized particle concentration Figure 4 b. Statistics on the integral area of ​​the emission spectrum Figure 4 c. Photon count decay curve of normalized initial emission intensity of nanoparticle solution after pulse excitation. Figure 4 d. The fitted luminescence lifetime of the nanoparticles.

[0035] Taking the core-shell-shell nanoparticle sample 1C-0.5S-4S as an example, the integral area of ​​the emission spectrum of the nanoparticle solution after normalizing the particle concentration is 6.16×10⁻⁶. 5 The luminescence lifetime fitted value for au is 69.7 ms. Example 2

[0036] The preparation method is basically the same as in Example 1, but the aim is to control the doping layer thickness of b-NaGdF4@NaGdF4:60%Nd nanoparticles. The specific preparation method differs as follows: After drying the cyclohexane in the two-necked flask containing the β-NaGdF4 nanoparticle solution, 0.05 mmol Gd(CF3COO)3, 0.075 mmol Nd(CF3COO)3, 0.125 mmol CF3COONa, 20 mmol OA, and 20 mmol ODE are added. All other operations are the same as in Example 1. The resulting core-shell nanoparticle sample is named 1C-0.25S, and the core-shell-shell nanoparticle sample is named 1C-0.25S-4S.

[0037] like Figure 2 As shown in b, the morphology of the core-shell nanoparticle sample 1C-0.25S is spherical with a diameter of approximately 10.7 nm, indicating that the thickness of the epitaxial ion-doped layer is approximately 0.7 nm. Figure 3 As shown in b, the core-shell-shell nanoparticle sample 1C-0.25S-4S has a spherical morphology with a diameter of approximately 16.8 nm, which means that the thickness of the epitaxial inert protective layer is approximately 3.0 nm.

[0038] The luminescence properties of the rare-earth ion sandwich core-shell structured nanoparticle sample 1C-0.25S-4S in this embodiment were tested. The integral area of ​​the emission spectrum of the nanoparticle solution after normalizing the particle concentration was 9.83 × 10⁻⁶.5 The fitted value for the luminescence lifetime is 157.8 ms. Example 3

[0039] The preparation method is basically the same as in Example 1, but the aim is to control the thickness of the doped layer of the sandwich core-shell nanoparticles. The specific preparation method is as follows: After drying the cyclohexane in the β-NaGdF4 nanoparticle solution in the two-necked flask, add 0.025 mmol Gd(CF3COO)3, 0.0375 mmol Nd(CF3COO)3, 0.0625 mmol CF3COONa, 20 mmol OA, and 20 mmol ODE. All other operations are the same as in Example 1. The obtained core-shell nanoparticle sample is named 1C-0.125S, and the core-shell-shell nanoparticle sample is named 1C-0.125S-4S.

[0040] like Figure 2 As shown in Figure c, the morphology of the core-shell nanoparticle sample 1C-0.125S is spherical with a diameter of approximately 10.4 nm, indicating that the thickness of the epitaxial ion-doped layer is approximately 0.5 nm. Figure 3 As shown in c, the core-shell-shell nanoparticle sample 1C-0.125S-4S has a spherical morphology with a diameter of approximately 16.4 nm, which means that the thickness of the epitaxial inert protective layer is approximately 3.0 nm.

[0041] The luminescence properties of the rare-earth ion sandwich core-shell structured nanoparticle sample 1C-0.125S-4S in this embodiment were tested. The integral area of ​​the emission spectrum of the nanoparticle solution after normalizing the particle concentration was 8.27 × 10⁻⁶. 5 The fitted value for the luminescence lifetime of au is 232.2 ms. Example 4

[0042] The preparation method is basically the same as in Example 1, but the aim is to control the thickness of the doped layer of the sandwich core-shell nanoparticles. The specific preparation method is as follows: After drying the cyclohexane in the β-NaGdF4 nanoparticle solution in the two-necked flask, add 0.0125 mmol Gd(CF3COO)3, 0.001875 mmol Nd(CF3COO)3, 0.03125 mmol CF3COONa, 20 mmol OA, and 20 mmol ODE. All other operations are the same as in Example 1. The obtained core-shell nanoparticle sample is named 1C-0.0625S, and the core-shell-shell nanoparticle sample is named 1C-0.0625S-4S.

[0043] like Figure 2As shown in Figure d, the core-shell nanoparticle sample 1C-0.0625S exhibits a spherical morphology with a diameter of approximately 10.2 nm, indicating that the thickness of the epitaxial ion-doped layer is approximately 0.4 nm. Figure 3 As shown in d, the core-shell-shell nanoparticle sample 1C-0.0625S-4S has a spherical morphology with a diameter of approximately 16.2 nm, which means that the thickness of the epitaxial inert protective layer is approximately 3.0 nm.

[0044] The luminescence properties of the rare-earth ion sandwich core-shell structured nanoparticle sample 1C-0.0625S-4S in this embodiment were tested. The integral area of ​​the emission spectrum of the nanoparticle solution after normalizing the particle concentration was 5.56 × 10⁻⁶. 5 The fitted value for the luminescence lifetime is 279.6 ms. Example 5

[0045] The preparation method is basically the same as in Example 1, but the aim is to control the Nd ion doping concentration of the sandwich core-shell nanoparticle doped layer. The specific preparation method differs as follows: After drying the cyclohexane in the β-NaGdF4 nanoparticle solution in the two-necked flask, add a total of 0.125 mmol of rare earth trifluoroacetate, 0.125 mmol of CF3COONa, 20 mmol of OA, and 20 mmol of ODE. Nd(CF3COO)3 accounts for X% of the total rare earth trifluoroacetate (X = 20, 40, 60, 80, 100), with the remainder made up by Gd(CF3COO)3. All other operations are the same as in Example 1. Example 6

[0046] The preparation method is basically the same as in Example 1, but the aim is to control the Nd ion doping concentration of the sandwich core-shell nanoparticle doped layer. The specific preparation method differs as follows: After drying the cyclohexane in the β-NaGdF4 nanoparticle solution in the two-necked flask, add a total of 0.0625 mmol of rare earth trifluoroacetate, 0.0625 mmol of CF3COONa, 20 mmol of OA, and 20 mmol of ODE. Nd(CF3COO)3 accounts for X% of the total rare earth trifluoroacetate (X = 20, 40, 60, 80, 100), with the remainder made up by Gd(CF3COO)3. All other operations are the same as in Example 1.

[0047] Test example: (1) Investigate the effect of different doping layer thicknesses on the luminescence properties of sandwich core-shell structured nanoparticles. The nanoparticles prepared in Examples 1-4 were subjected to structural characterization, emission spectroscopy testing, and luminescence lifetime testing.

[0048] Figure 1The TEM image shows an inert core β-NaGdF4 particle with a diameter of approximately 9.4 nm. Figure 2 The sample shown in a is named 1C-0.5S b-NaGdF4@NaGdF4:60%Nd nanoparticles with a diameter of 11.2 nm and a rare earth ion doping layer thickness of 0.9 nm. Figure 2 The sample shown in b is named 1C-0.25S b-NaGdF4@NaGdF4:60%Nd nanoparticles with a diameter of 10.7 nm and a rare earth ion doping layer thickness of 0.7 nm. Figure 2 The sample shown in c is named 1C-0.125S b-NaGdF4@NaGdF4:60%Nd nanoparticles with a diameter of 10.4 nm and a rare earth ion doping layer thickness of 0.5 nm. Figure 2 The sample shown in d is named 1C-0.0625S b-NaGdF4@NaGdF4:60%Nd nanoparticles with a diameter of 10.2 nm and a rare earth ion doping layer thickness of 0.4 nm. In summary, by using the same inert core nanoparticles as the epitaxial growth substrate and adjusting the amount of the thermal decomposition reaction precursor, core-shell nanoparticles corresponding to Nd2O3 can be obtained through epitaxial growth. 3+ The thickness of the ion-doped layer varies, ranging from 0.4 to 0.9 nm.

[0049] Normalized luminescence intensity of b-NaGdF4@NaGdF4:60%Nd@NaGdF4 core-shell-shell nanoparticles with different doped layer thicknesses, as shown in the figure. Figure 4 As shown in Figure a, under 808 nm excitation, the core-shell-shell nanoparticles prepared in Examples 1-4 emit a main peak at 1060 nm, corresponding to... 4 F3 / 2→ 4 I 11 / 2 electric dipole transition. Reference Figure 4 According to the statistical results of the emission peak integrated area of ​​sample b, the core-shell-shell nanoparticle named 1C-0.25S-4S in Example 2 has the largest emission spectrum integrated area value, and its doped layer thickness is 0.7 nm. (Reference) Figure 4Based on the luminescence lifetime fitting results, the core-shell-shell nanoparticles of 1C-0.0625S-4S in Example 4 exhibited the longest luminescence lifetime. This indicates that the thinnest doped layer thickness resulted in the lowest energy loss rate of neodymium ions in the excited state, effectively confining the energy transfer network and maximizing the average luminescence efficiency of the doped ions. However, the luminescence intensity of rare-earth-doped nanoparticles is directly proportional to the product of the total number of doped ions and the average luminescence efficiency of the doped ions. With the same neodymium ion doping concentration of 60%, reducing the doped layer thickness would decrease the total number of neodymium ions. Therefore, the integrated area value of the emission spectrum of sample 1C-0.0625S-4S in Example 4 was not the largest.

[0050] (2) Investigate the effect of rare earth ion doping concentration of the doped layer on the luminescence properties of sandwich core-shell structured nanoparticles. TEM imaging was performed on the b-NaGdF4@NaGdF4:x%Nd (x=20, 40, 60, 80, 100) core-shell nanoparticles prepared in Examples 5 and 6. Figure 5 As shown, the doped layer thickness of the nanoparticles is uniform under different doping concentrations. Therefore, the difference in luminescence properties of the b-NaGdF4@NaGdF4:x%Nd@NaGdF4 (x=20, 40, 60, 80, 100) core-shell-shell nanoparticles prepared in Examples 5 and 6 mainly comes from the different Nd doping concentrations.

[0051] Emission spectroscopy and luminescence lifetime tests were performed on the samples from Examples 5 and 6. The results are as follows: Figure 6 , Figure 7 As shown in Table 1, the structure of the b-NaGdF4@NaGdF4:X%Nd@NaGdF4 core-shell-shell nanoparticles prepared in Example 5 is consistent with that of the sample 1C-0.25S-4S in Example 2. The integrated area of ​​the emission spectrum reaches a maximum when the doping concentration is 40%. The structure of the b-NaGdF4@NaGdF4:X%Nd@NaGdF4 core-shell-shell nanoparticles prepared in Example 6 is consistent with that of the sample 1C-0.125S-4S in Example 3. The integrated area of ​​the emission spectrum reaches a maximum when the doping concentration is 80%. The luminescence lifetime fitting results of the samples in Examples 5 and 6 show that the luminescence lifetime decreases monotonically with increasing Nd:I ion doping concentration, indicating that the average luminescence efficiency of Nd:I ions decreases monotonically with increasing doping concentration. The integrated area of ​​the emission spectrum of rare-earth-doped nanoparticles is proportional to the product of the total number of dopant ions and the average luminescence efficiency of the ions. The performance comparison results of the samples in Examples 5 and 6 demonstrate that the thinner the doped layer, the higher the optimal doping concentration obtained based on luminescence intensity. This verifies that the quasi-two-dimensional thin-layer lattice confined doping method can effectively limit the energy migration network between rare earth ions and reduce harmful energy migration losses.

[0052] Table 1. Rare earth ion doping concentration and luminescence properties of sandwich core-shell structured nanoparticles

[0053] Finally, it should be noted that the above description is only a preferred embodiment of the present invention. Those skilled in the art, under the guidance of the present invention, can make various similar representations without departing from the spirit and claims of the present invention, and such modifications all fall within the protection scope of the present invention.

Claims

1. An Nd 3+ Single-doped sandwich core-shell structured nanoparticles, characterized in that, Core-shell-shell epitaxial composite nanoparticles are formed by an inert core and sequentially epitaxially grown luminescent ion doped layer and inert protective layer; the inert core material is β-ALnF4; the luminescent ion doped layer material is β-ALnF4:Nd; the inert protective layer material is β-ALnF4; wherein, A is selected from Li. + Na + K + One of them; Ln is selected from Y 3+ Gd 3+ La 3+ Lu 3+ At least one of them.

2. The rare-earth ion-doped sandwich core-shell structured nanoparticles according to claim 1, characterized in that, The thickness of the luminescent ion doped layer is 0.1-5 nm; or 0.1-3 nm; or 0.1-1 nm; or 0.4-0.9 nm.

3. The Nd according to claim 1 3+ Single-doped sandwich core-shell structured nanoparticles, characterized in that, Rare earth dopant ions Nd in the luminescent ion doped layer 3+ The doping molar concentration is 1-100%; or 20-100%; or 20-80%; or 20-60%.

4. An Nd 3+ A method for preparing single-doped sandwich core-shell structured nanoparticles, characterized in that, Includes the following steps: S1. The matrix rare earth trifluoroacetate and sodium salt were added to a mixed solvent of oleic acid / oleylamine / octadecene, heated and stirred under a nitrogen atmosphere, and the product was collected by centrifugation after the thermal decomposition reaction was completed to obtain nanoparticles α-ALnF4; α-ALnF4 and sodium salt were added to a mixed solvent of oleic acid / octadecene, heated and stirred under a nitrogen atmosphere, and the product was collected by centrifugation after the thermal decomposition reaction was completed to obtain inert core particles β-ALnF4; S2. Mix β-ALnF4 with matrix rare earth trifluoroacetate, neodymium trifluoroacetate and sodium salt, heat and stir under nitrogen atmosphere to complete the epitaxial growth of luminescent ion doped layer β-ALnF4:Nd, and obtain core-shell epitaxial composite nanoparticles β-ALnF4@ALnF4:Nd; S3. Mix β-ALnF4@ALnF4:Nd with rare earth trifluoroacetate and sodium salts of the matrix, heat and stir under nitrogen atmosphere to complete the epitaxial growth of the inert protective layer β-ALnF4, and obtain core-shell-shell epitaxial sandwich structure nanoparticles β-ALnF4@ALnF4:Nd@ALnF4.

5. The preparation method according to claim 4, characterized in that, In step S1, the matrix rare earth trifluoroacetate is selected from at least one of yttrium salts, gadolinium salts, lanthanum salts, and lutetium salts; and / or, the sodium salt is selected from NaOH, NaF, CF3COONa, and One of CH3COONa; the molar ratio of the matrix rare earth trifluoroacetate salt to the sodium salt is 1:(1~2); and / or, the molar ratio of the α-ALnF4 to the sodium salt is 1:(1~2).

6. The preparation method according to claim 4, characterized in that, In S2, the matrix rare earth trifluoroacetate is selected from at least one of yttrium salt, gadolinium salt, lanthanum salt, and lutetium salt; and / or, the sodium salt is selected from one of NaOH, NaF, CF3COONa, and CH3COONa; the molar ratio of β-ALnF4, matrix rare earth trifluoroacetate, neodymium trifluoroacetate, and sodium salt is (1-16):(0.1-1):(0.01-1):

1.

7. The preparation method according to claim 4, characterized in that, In step S3, the matrix rare earth trifluoroacetate is selected from at least one of yttrium salts, gadolinium salts, lanthanum salts, and lutetium salts; and / or, the sodium salt is selected from NaOH, NaF, CF3COONa, and... One of CH3COONa; the molar ratio of β-ALnF4@ALnF4:Nd, matrix rare earth trifluoroacetate and sodium salt is 1:(1-4):(1-4).

8. The preparation method according to claim 4, characterized in that, In S1, the heating reaction conditions are as follows: after evacuating the reaction vessel to remove water and oxygen, nitrogen gas is introduced, and the mixture is stirred and heated to 280-350 ℃, or 280-330 ℃, or 300-320 ℃, or 310 ℃; and / or, the reaction is maintained at this temperature for 10-50 min, or 10-40 min, or 20-40 min, or 30 min.

9. The preparation method according to claim 4, characterized in that, In S2, the heating reaction conditions are as follows: after evacuating the reaction vessel to remove water and oxygen, nitrogen gas is introduced, and the mixture is stirred and heated to 280-350 ℃, or 280-330 ℃, or 300-320 ℃, or 310 ℃; and / or, the reaction is maintained at this temperature for 10-50 min, or 10-40 min, or 20-40 min, or 30 min.

10. The preparation method according to claim 4, characterized in that, In S3, the heating reaction conditions are as follows: after evacuating the reaction vessel to remove water and oxygen, nitrogen gas is introduced, and the mixture is stirred and heated to 300-350 ℃, or 300-330 ℃, or 300-320 ℃, or 310 ℃; and / or, the reaction is maintained at this temperature for 10-50 min, or 10-40 min, or 20-40 min, or 30 min.

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