A neodymium-sensitized rare earth luminescent multilayer core-shell structure material, preparation method and application thereof

Abstract

The present invention discloses a neodymium-sensitized rare earth luminescent multilayer core-shell structure material, a preparation method and application thereof, wherein the particles thereof have a core-multi-shell heterogeneous structure, the core layer as the luminescent center is a rare earth upconversion nanoparticle, the energy transfer layer is the first shell; the energy capture layer is the second shell; the energy protection layer is the third shell, forming a four-layer structure of an upconversion luminescent material of a core-shell-shell-shell structure. The preparation method of the present invention includes the steps of preparing a precursor of a rare earth salt and preparing a rare earth luminescent multilayer core-shell structure material. The problem to be solved by the present invention is that the luminescent efficiency of the upconversion nanoparticles in the ultraviolet region is low, and the shortest luminescent wavelength is limited to 290nm, while expanding the application range of the upconversion luminescent nanoparticles so that they can be more widely used in materials fields such as biological imaging / detection, photodynamics / photothermal therapy, optogenetics, lithography, anti-counterfeiting, analysis and detection. The preparation method of the present invention is simple to operate, easy to control and the prepared product is stable.

Description

Technical Field

[0001] The present invention relates to the technical field of optoelectronic functional materials, and specifically to a method for simply and efficiently preparing a rare earth up-conversion nanomaterial with a heterogeneous core-shell structure. The heterogeneous up-conversion nanomaterial prepared by the method has a core-shell-shell-shell four-layer structure. The heterogeneous up-conversion nanomaterial can enhance up-conversion emission in the ultraviolet region. Background Art

[0002] Rare earth doped upconversion nanocrystals are a new type of functional material that can convert near-infrared light into ultraviolet-visible light. Rare earth doped upconversion nanocrystals have excellent optical properties, making them widely used in various fields. In recent years, many researchers have used the characteristics of rare earth doped upconversion nanocrystals absorbing near-infrared light and emitting ultraviolet visible light to apply them in biomedicine, environment and industry. In particular, upconversion ultraviolet emission can be used in cutting-edge fields such as photocatalysts, ultraviolet solid-state lasers, and biomedicine.

[0003] However, most rare earth element-doped upconversion nanoluminescent materials are excited at 980nm. Since water has strong absorption at 980nm, water molecules absorb 980nm light and convert it into heat. Therefore, the use of 980nm excitation light source will inevitably cause a strong thermal effect, thereby causing damage to normal biological tissues. At the same time, the absorption of water molecules at 980nm will also reduce the tissue penetration ability of near-infrared light, limiting the application of rare earth element-doped upconversion nanoluminescent materials in the biomedical field.

[0004] In recent years, Nd 3+ Neodymium ion-doped upconversion nanoparticles have a unique advantage in that they can absorb 808nm excitation light, successfully avoiding the shortcomings of 980nm excitation. And because the strong concentration quenching effect between the sensitizer ions and the luminescent ions will greatly reduce the fluorescence intensity of the material, the researchers used a core-multishell structure to sensitize the sensitizer Nd 3+ Ions and luminescent ions are doped in different regions of the nanostructure to reduce the cross relaxation between the sensitizer and the luminescent ions, thereby increasing the fluorescence intensity of the material. 3+ Ion-doped upconversion nanomaterials emit light in the ultraviolet region, which is of great significance. Summary of the invention

[0005] In order to solve the problems of the prior art, the purpose of the present invention is to overcome the shortcomings of the existing technology, provide a neodymium-sensitized rare earth luminescent multilayer core-shell structure material, its preparation method and application, can controllably synthesize the preparation method of up-conversion nanoparticles with heterogeneous core-multi-shell structure, and realize its up-conversion luminescence enhancement in the ultraviolet region. The method is simple to operate, the morphology of the prepared up-conversion nanoparticles has good uniformity, under the excitation of 808nm and 980nm, the shortest luminescent wavelength can reach 253nm, and its up-conversion luminescence in the ultraviolet region is stronger than the nanoparticles reported before. Therefore, the problem to be solved by the present invention is that the luminescent efficiency of the up-conversion nanoparticles in the ultraviolet region is low, and the shortest luminescent wavelength is limited to 290nm. At the same time, the application range of the up-conversion luminescent nanoparticles is expanded, so that it can be more widely used in the fields of biological imaging / detection, photodynamics / photothermal therapy, optogenetics, lithography, anti-counterfeiting, analysis and detection.

[0006] In order to achieve the above object, the present invention adopts the following technical scheme:

[0007] A neodymium-sensitized rare earth luminescent multilayer core-shell structure material, wherein the particles have a core-multi-shell heterogeneous structure, wherein the core layer as the luminescent center is a rare earth upconversion nanoparticle, the energy transfer layer is a first shell coated on the core nanoparticle, forming an upconversion luminescent material with a core-shell structure; the energy capture layer is a second shell coated on the energy transfer layer, forming an upconversion luminescent material with a core-shell-shell structure; the energy protection layer is a third shell coated on the energy capture layer, forming a four-layer structure of an upconversion luminescent material with a core-shell-shell-shell structure; the luminescent ions and the sensitizing ions are evenly distributed in the core layer and each shell layer;

[0008] NaGdF4:Yb / Tm is used as the core of the multilayer core-shell structure, the doping molar fraction of Yb ions is not more than 60%, and the doping molar fraction of Tm is not more than 15%;

[0009] The material of the energy transfer layer includes at least one of NaLuF4, NaYF4, CaF2 and YF3, wherein the molar fraction of Yb ion doping is 10-80%;

[0010] The doping molar concentration of Yb ions in the energy capture layer is 1-90%, and the doping molar concentration of Nd ions is 1-90%; the material of the protective layer includes at least any one of NaGdF4, NaLuF4, NaYF4, CaF2 and YF3.

[0011] Preferably, the luminescent ion combination adopts at least one of Yb / Tm, Yb / Tm / Tb, Yb / Tm / Eu, Yb / Tm / Dy, Yb / Tm / Sm, Yb / Tm / Mn, Yb / Tb, Yb / Eu, Yb / Dy and Yb / Sm.

[0012] Preferably, the wavelength of the excitation light of the rare earth luminescent multilayer core-shell structure material of the present invention is 745nm, 793nm, 808nm and 980nm.

[0013] A method for preparing a neodymium-sensitized rare earth luminescent multilayer core-shell structure material, the steps of which are:

[0014] a. Preparation of rare earth salt precursors:

[0015] dissolving at least one of gadolinium salt, ytterbium salt, thulium salt, lutetium salt, yttrium salt, neodymium salt, terbium salt, europium salt, dysprosium salt, samarium salt, calcium salt and manganese salt in a mixed solvent of oleic acid and octadecene, and reacting to obtain a precursor of a rare earth salt;

[0016] b. Preparation of rare earth luminescent multilayer core-shell structure materials:

[0017] The core material is mixed with the precursor of the rare earth salt prepared in step a to obtain a reaction mixture, and the reaction mixture is reacted in the presence of a sodium source and a fluorine source to coat the core material particles with a shell layer, and then the reaction product is washed and dissolved in cyclohexane to obtain a rare earth luminescent multilayer core-shell structure material solution.

[0018] Preferably, in step b, the synthesis conditions of the rare earth salt precursor are: reacting at 140-170° C. for 1-3 hours to obtain the rare earth salt precursor.

[0019] Preferably, in step a, the gadolinium salt is at least one of GdCl3, Gd(NO3)3, Gd(CH3CO2)3, Gd(TFA)3, and Gd(ACAC)3.

[0020] Preferably, in step a, the ytterbium salt is at least one of YbCl3, Yb(NO3)3, Yb(CH3CO2)3, Yb(TFA)3, and Yb(ACAC)3.

[0021] Preferably, in step a, the thulium salt is at least one of TmCl3, Tm(NO3)3, Tm(CH3CO2)3, Tm(TFA)3, and Tm(ACAC)3.

[0022] Preferably, in step a, the lutetium salt is at least one of LuCl3, Lu(NO3)3, Lu(CH3CO2)3, Lu(TFA)3, and Lu(ACAC)3.

[0023] Preferably, in step a, the yttrium salt is at least one of YCl3, Y(NO3)3, Y(CH3CO2)3, Y(TFA)3, and Y(ACAC)3.

[0024] Preferably, in step a, the neodymium salt is at least one of NdCl3, Nd(NO3)3, Nd(CH3CO2)3, Nd(TFA)3, and Nd(ACAC)3.

[0025] Preferably, in step a, the terbium salt is at least one of TbCl3, Tb(NO3)3, Tb(CH3CO2)3, Tb(TFA)3, and Tb(ACAC)3.

[0026] Preferably, in step a, the europium salt is at least one of EuCl3, Eu(NO3)3, Eu(CH3CO2)3, Eu(TFA)3, and Eu(ACAC)3.

[0027] Preferably, in step a, the dysprosium salt is at least one of DyCl3, Dy(NO3), Dy(CH3CO2)3, Dy(TFA)3, and Dy(ACAC)3.

[0028] Preferably, in step a, the samarium salt is at least one of SmCl3, Sm(NO3), Sm(CH3CO2)3, Sm(TFA)3, and Sm(ACAC)3.

[0029] Preferably, in step a, the calcium salt is at least one of CaCl2, Ca(NO3)2, Ca(CO3)2, Ca(TFA)2, and Ca(ACAC)2.

[0030] Preferably, in step a, the manganese salt is at least one of MnCl2, Mn(NO3)2, Mn(CH3CO2)2, Mn(TFA)2, and Mn(ACAC)2.

[0031] Preferably, in the step b, the synthesis conditions of the neodymium-sensitized rare earth luminescent multilayer core-shell structure material are: reacting at 200-330° C. for 0.5-3 h to coat the core material particles with a shell layer.

[0032] Preferably, in step b, the sodium source is at least one of NaOH, NaF and NaTFA.

[0033] Preferably, in step b, the fluorine source is any one of NH4F and NaF.

[0034] Preferably, in the step b, when preparing the rare earth luminescent multilayer core-shell structure material, a rare earth upconversion nanomaterial with a heterogeneous core-multi-shell structure is prepared in steps, comprising the following steps:

[0035] b-1. The core layer upconversion nanoparticles are coated with an energy transfer layer to obtain core-shell structure upconversion nanoparticles, wherein the transfer layer has a thickness of 2-5nm;

[0036] b-2. The core-shell structure upconversion nanoparticles prepared in step b-1 are coated with an energy capture layer to obtain core-shell-shell structure upconversion nanoparticles, wherein the capture layer has a thickness of 2-5 nm;

[0037] b-3. The core-shell-shell structured upconversion nanoparticles prepared in step b-2 are coated with an energy protection layer to obtain core-shell-shell-shell-shell structured upconversion nanoparticles, wherein the thickness of the protection layer is 2-5 nm.

[0038] Preferably, core layer nanoparticles doped with luminescent ions are prepared, and the core layer nanoparticles doped with luminescent ions are up-conversion luminescent nanomaterials. An energy transfer layer is coated on the core nanoparticles to obtain an up-conversion luminescent material with a core-shell structure, and then an energy capture layer is coated on the core-shell structure nanoparticles to obtain an up-conversion luminescent material with a core-shell-shell structure, and then an energy protection layer is coated on the core-shell-shell structure nanoparticles to obtain an up-conversion luminescent material with a core-shell-shell structure.

[0039] Preferably, by introducing a core-shell structure, the luminescent central ion and the sensitizer Nd 3+ They are distributed in the core layer and the energy capture shell layer respectively, which effectively suppresses the concentration quenching caused by the cross relaxation between the luminescent ions and the sensitizing ions, and can improve the sensitizer Nd 3+ ion doping concentration to increase the material's absorption of 808nm; the introduction of Yb 3+ Ions act as a bridge for energy transfer between sensitizing ions and luminescent ions, ensuring efficient energy transfer. The matrix material of the first shell is composed of Gd 3+ Ion replacement with inert matrix Y 3+ Ions can effectively prevent the excitation light energy from reaching the shell Gd 3+ The lattice defects inside the ions are transmitted and the energy capture by the lattice defects is effectively suppressed, thereby enhancing the upconversion emission under 808nm excitation; by coating the outermost layer with an energy protection layer, the energy capture by the surface quenching molecules can be effectively suppressed, further enhancing the upconversion emission. At the same time, by increasing the size of the core layer, on the one hand, the internal defects of the core-shell structure can be reduced; on the other hand, due to the increase in the size of the core layer, the shell layer becomes thinner, and the thickness of each shell is about 2.5nm, which reduces the distance between ions and increases the Nd 3+ Ions and Yb 3+ Ion, Yb 3+ ions and luminescent ions (Tm 3+ ), luminescent ions (Tm 3+ ) and Gd3+ The efficiency of energy transfer between ions is ultimately reflected in the enhanced upconversion luminescence.

[0040] Application of the neodymium-sensitized rare earth luminescent multilayer core-shell structure material of the present invention in catalysis, anti-counterfeiting, solar energy, bio-marker, drug release, and 3D printing materials.

[0041] Compared with the prior art, the present invention has the following obvious outstanding substantive features and significant advantages:

[0042] 1. The present invention realizes the six-photon process of upconversion luminescence through fine synthesis of multi-layer heterostructures, achieves the purpose of ultraviolet upconversion luminescence enhancement, and breaks the deadlock that neodymium-sensitized upconversion nanomaterials cannot achieve upconversion luminescence in the deep ultraviolet band; the heterogeneous upconversion nanomaterial prepared by this method has a core-shell-shell-shell four-layer structure, and this heterogeneous upconversion nanomaterial can enhance upconversion emission in the ultraviolet region;

[0043] 2. The present invention controls the shell thickness to 2.5nm through structural design and rare earth doping concentration optimization, realizes efficient energy transfer, and enhances upconversion luminescence in the ultraviolet region;

[0044] 3. The present invention uses an inert matrix Y in the energy transfer layer, i.e., the first shell. 3+ Ion replacement matrix Gd 3+ ions, effectively preventing the excitation light energy from reaching the shell Gd 3+ The lattice defects inside the ions are transmitted and the energy capture by the lattice defects is effectively suppressed, thereby enhancing the up-conversion emission in the ultraviolet region under near-infrared light excitation; the preparation method of the present invention is simple to operate, easy to control and the prepared products are stable, and the prepared heterogeneous up-conversion nanomaterials can be applied in cutting-edge fields such as ultraviolet solid-state laser preparation, photocatalysts, and optical information storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 NaGdF4:Yb / Tm@NaYF4:20%Yb@NaGdF4:10%Yb50%Nd@ in Example 1 of the present invention

[0046] Transmission electron microscopy image of NaGdF4 upconversion nanoparticles.

[0047] Figure 2 This is a high-angle annular dark field scanning transmission electron microscopy image (HAADF-STEM) of the heterogeneous core-multi-shell upconversion luminescent nanomaterial in Example 1 of the present invention.

[0048] Figure 3 This is a high-magnification transmission electron microscopy image of the heterogeneous core-multi-shell upconversion luminescent nanomaterial in Example 1 of the present invention.

[0049] Figure 4 This is the X-ray diffraction (XRD) diagram of the heterogeneous core-multi-shell upconversion luminescent nanomaterial in Example 1 of the present invention.

[0050] Figure 5 This is the fluorescence emission diagram of the heterogeneous core-multi-shell upconversion luminescent nanomaterial in Example 1 of the present invention under excitation at 980nm and 808nm.

[0051] Figure 6 The fluorescence emission spectra of the heterogeneous core-multi-shell upconversion luminescent nanomaterials in Example 1 of the present invention synthesized in different batches under 808nm excitation.

[0052] Figure 7 Double logarithmic coordinate diagram of the excitation power intensity and the fluorescence intensity of the heterogeneous core-multi-shell upconversion luminescent nanomaterial in Example 1 of the present invention at (a) 253 nm, (b) 276 nm and (c) 311 nm under 808 nm excitation.

[0053] Figure 8 Statistical graph of particle size distribution of the intermediate material and final material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0054] The above scheme is further described below in conjunction with specific implementation examples. The preferred embodiments of the present invention are described in detail as follows:

[0055] Example 1

[0056] In this embodiment, a method for preparing a neodymium-sensitized rare earth luminescent multilayer core-shell structure material is described. 3 + ,Yb 3+ Taking the NaGdF4 core layer as an example, the steps are:

[0057] (1) First, the doping molar concentration ratio is Tm 3+ :Yb 3+ :Gd 3+=1:49:50 Take a total of 0.4 mmol of Tm(CH3CO2)3·xH2O, Yb(CH3CO2)3·xH2O, and Gd(CH3CO2)3·xH2O aqueous solution in a fixed ratio and add it into a 50 mL three-necked flask, add 5 mL of oleic acid and 5 mL 1-octadecene liquid is heated to 140-160°C and stirred for 30-60min to form a uniform rare earth complex; secondly, when the temperature drops to 50°C, 5mL of methanol solution containing 1mmolNaOH and 1.36mmolNH4F is quickly added and stirred for 30min; finally, the mixed solution is heated to 100°C, vacuumed for 5min and then filled with nitrogen for 1min to remove methanol and oxygen in the reaction system three times, and the temperature is raised to 300°C and reacted under the protection of nitrogen for 1.5h, then cooled to room temperature, washed with anhydrous ethanol and cyclohexane, and the obtained nuclear upconversion nanoparticle luminescent material is dispersed in 4mL of cyclohexane, that is, the nuclear upconversion nanoparticle NaGdF4:Yb / Tm with a diameter of 17nm is obtained; Figure 8 (a)

[0058] (2) First, the doping molar concentration ratio is Yb 3+ :Y 3+ =20:80, add 0.4 mmol of Yb(CH3CO2)3·xH2O and Y(CH3CO2)3xH2O aqueous solution in a fixed ratio into a 50 mL three-necked flask, add 5 mL of oleic acid and 5 mL of 1-octadecene liquid, heat to 140-160° C., and stir for 30-60 min to form a uniform rare earth complex; secondly, when the temperature drops to 80° C., add the core-conversion nanoparticles dispersed in 4 mL of cyclohexane obtained in step (1), stir for 30 min to remove cyclohexane in the system, and when the temperature drops to 50° C., quickly add 5 mL of 1 mmol NaOH and 1.36 mmol NH4F methanol solution, and stirred for 30 minutes; finally, the mixed solution was heated to 100 ° C, vacuumed for 5 minutes, and then filled with nitrogen for 1 minute to remove methanol and oxygen in the reaction system three times, and the temperature was raised to 300 ° C for 1.5 hours under the protection of nitrogen, and then cooled to room temperature, washed with anhydrous ethanol and cyclohexane, and the obtained core-conversion nanoparticle luminescent material was dispersed in 4 mL of cyclohexane to obtain a core-shell conversion nano NaGdF4:Yb / Tm@NaYF4:Yb with a diameter of about 21 nm; Figure 8 (b)

[0059] (3) First, the doping molar concentration ratio is Nd 3+ :Yb 3+ :Gd 3+=50:10:40 Take a total of 0.4mmol of Nd(CH3CO2)3·xH2O, Yb(CH3CO2)3·xH2O, and Gd(CH3CO2)3·xH2O aqueous solution in a fixed ratio and add it into a 50mL three-necked flask, add 5mL of oleic acid and 5mL 1-octadecene liquid is heated to 140-160°C and stirred for 30-60min to form a uniform rare earth complex; secondly, when the temperature drops to 80°C, the core-shell up-conversion nanoparticles dispersed in 4mL of cyclohexane obtained in step (2) are added and stirred for 30min to remove the cyclohexane in the system; when the temperature drops to 50°C, 5mL of a methanol solution containing 1mmol NaOH and 1.36mmol NH4F is quickly added and stirred for 30min; finally, the mixed solution is heated to 100°C, evacuated for 5min, and then filled with nitrogen for 1min to remove methanol and oxygen in the reaction system three times, and the temperature is raised to 300°C and reacted under the protection of nitrogen for 1.5h, then cooled to room temperature, washed with anhydrous ethanol and cyclohexane, and the obtained core-up-conversion nanoparticle luminescent material is dispersed in 4mL of cyclohexane to obtain a core-shell-shell up-conversion nanoparticle luminescent material with a diameter of 26nm.

[0060] NaGdF4:Yb / Tm@NaYF4:Yb@NaGdF4:10%Yb50%Nd; such as Figure 8 (c)

[0061] (4) First, take 0.4 mmol of Gd(CH3CO2)3·xH2O aqueous solution of a certain ratio and add it into a 50 mL three-necked flask, then add 5 mL of oleic acid and 5 mL of 1-octadecene liquid is heated to 140-160°C and stirred for 30-60min to form a uniform rare earth complex; secondly, when the temperature drops to 80°C, the core-shell-shell up-conversion nanoparticles dispersed in 4mL of cyclohexane obtained by (3) are added and stirred for 30min to remove the cyclohexane in the system; when the temperature drops to 50°C, 5mL of a methanol solution containing 1mmol NaOH and 1.36mmol NH4F is quickly added and stirred for 30min; finally, the mixed solution is heated to 100°C, evacuated for 5min, and then filled with nitrogen for 1min to remove methanol and oxygen in the reaction system three times, and the temperature is raised to 300°C and reacted under the protection of nitrogen for 1.5h, then cooled to room temperature, washed with anhydrous ethanol and cyclohexane, and the obtained core-shell-shell-shell up-conversion nanoparticle luminescent material is dispersed in 4mL of cyclohexane to obtain a core-shell-shell-shell-shell up-conversion nanoparticle with a diameter of 29nm.

[0062] NaGdF4:Yb / Tm@NaYF4:Yb@NaGdF4:10%Yb50%Nd@NaGdF4; such as Figure 8 (d) as shown.

[0063] Figure 1 It is shown that the upconversion luminescent nanomaterial with a heterogeneous core-multi-shell structure synthesized according to this embodiment has uniform morphology and appropriate size. Figure 2 It is explained that the upconversion luminescent nanomaterial with a heterogeneous core-multi-shell structure synthesized according to this embodiment is a core-multi-shell structure, in which the bright areas correspond to heavy elements (Gd, Yb and Nd), and the dark areas correspond to light elements (Y). Figure 3 It is explained that the up-conversion luminescent nanomaterial with a heterogeneous core-multi-shell structure synthesized according to this embodiment is a single crystal structure. Figure 4 This indicates that the upconversion luminescent nanomaterial with a heterogeneous core-multi-shell structure synthesized according to this embodiment is a hexagonal phase. Figure 5 It can be seen that the upconversion luminescent nanomaterial with heterogeneous core-multi-shell structure synthesized according to this embodiment has strong upconversion emission in the ultraviolet region regardless of whether it is excited at 808nm or 980nm. Y S2S3 represents the material NaGdF4:Yb / Tm@NaYF4:20%Yb@NaGdF4:10%Yb50%Nd@NaGdF4. Figure 6 It can be seen that the fluorescence emission of different batches of upconversion luminescent nanomaterials with heterogeneous core-multi-shell structures is basically unchanged. The upconversion luminescent nanomaterials with heterogeneous core-multi-shell structures designed and synthesized in this embodiment emit strong ultraviolet light with repeatability. Y S2S3 represents the material NaGdF4:Yb / Tm@NaYF4:20%Yb@NaGdF4:10%Yb50%Nd@NaGdF4. Figure 7 As shown in (a), using this formula I f ∝P n (Physical Review B, 2000, 61(5):3337.), by fitting the fluorescence intensity I f The Log-Log logarithmic coordinate graph of the laser excitation power intensity P can be used to calculate Gd 3+ ion at 253 nm is 6.29, indicating that six photons of 808 nm excitation light are required to convert Gd 3+ Ion excitation 6 D J state, thus producing a six-photon upconversion process. Figure 5 As shown in (b) and (c), Gd 3+ The n values ​​of the ions at 276 nm and 311 nm are 5.27 and 4.94, respectively, indicating that Gd 3+ Five 808nm excitation light photons are required for the ions to emit 276nm and 311nm UV light.

[0064] This embodiment Nd3+ The invention discloses a method for preparing an upconversion luminescent nanomaterial doped with a heterogeneous core-multi-shell structure, which comprises a four-layer structure, a core layer upconversion nanoparticle as a luminescent center; a first shell layer as an energy transfer layer; a second shell layer as an energy capture layer; and a third shell layer as a protective layer. In this embodiment, by introducing a core-shell structure, the luminescent ions and the sensitizer ions are evenly distributed in the core layer and the shell layer, respectively, which effectively suppresses the concentration quenching of the luminescent ions and the sensitizer ions and increases the doping concentration of the sensitizer; at the same time, Yb is introduced. 3+ (Ytterbium) ions serve as a bridge for energy transfer between sensitizing ions and luminescent ions. In the energy transfer layer, an inert matrix Y 3+ (Yttrium) ions replace the matrix Gd 3+ (gadolinium) ions effectively prevent energy transfer to internal energy traps, thereby enhancing upconversion luminescence in the ultraviolet region under near-infrared excitation. The difference between the present invention and other upconversion nanoparticles is that: through structural design and optimization of rare earth doping concentration, the shell thickness is controlled to about 2.5nm, efficient energy transfer is achieved, and upconversion luminescence in the ultraviolet region is enhanced; by using an inert matrix Y in the energy transfer layer, i.e., shell 1, 3+ Ion replacement matrix Gd 3+ ions, effectively preventing the excitation light energy from reaching the shell Gd 3+ The lattice defects inside the ions are transmitted and the energy capture by the lattice defects is effectively suppressed, thereby enhancing the upconversion emission in the ultraviolet region under near-infrared light excitation; the preparation method is simple to operate, easy to control and the prepared products are stable. The prepared heterogeneous upconversion nanomaterials can be used in cutting-edge fields such as ultraviolet solid-state laser preparation, photocatalysts, and optical information storage.

[0065] Example 2

[0066] This embodiment is basically the same as the first embodiment, except that:

[0067] In this embodiment, a neodymium-sensitized rare earth luminescent multilayer core-shell structure material, whose particles have a core-multi-shell heterogeneous structure, the core layer as the luminescent center is a rare earth upconversion nanoparticle, the energy transfer layer is a first shell coated on the core nanoparticle, forming an upconversion luminescent material with a core-shell structure; the energy capture layer is a second shell coated on the energy transfer layer, forming an upconversion luminescent material with a core-shell-shell structure; the energy protection layer is a third shell coated on the energy capture layer, forming a four-layer structure of an upconversion luminescent material with a core-shell-shell-shell structure; the luminescent ions and the sensitizing ions are evenly distributed in the core layer and each shell layer;

[0068] NaGdF4:Yb / Tm is used as the core of the multi-layer core-shell structure, the doping molar fraction of Yb ions is 60%, and the doping molar fraction of Tm is 15%; the material of the energy transfer layer includes at least one of NaLuF4, NaYF4, CaF2 and YF3, wherein the doping molar fraction of Yb ions is 80%; the doping molar concentration of Yb ions in the energy capture layer is 90%, and the doping molar concentration of Nd ions is 90%; the material of the protective layer includes at least one of NaGdF4, NaLuF4, NaYF4, CaF2 and YF3.

[0069] In this embodiment, a method for upconversion luminescent nanomaterials having a heterogeneous core-multi-shell structure comprises the following steps:

[0070] Step 1: Preparation of Tm 3+ The ions are core layer upconversion nanoparticles doped with luminescent ions;

[0071] Step 2: Prepare the 3+ The ion-doped core layer upconversion nanoparticles are coated with an energy transfer layer to obtain core-shell structure upconversion nanoparticles, wherein the transfer layer has a thickness of 2.5 nm;

[0072] Step 3: coating the core-shell structure upconversion nanoparticles prepared in step 2 with an energy capture layer to obtain core-shell-shell structure upconversion nanoparticles, wherein the capture layer has a thickness of 2.5 nm;

[0073] Step 4: The core-shell-shell structure upconversion nanoparticles prepared in step 2 are coated with an energy protection layer to obtain core-shell-shell-shell structure upconversion nanoparticles, wherein the thickness of the protection layer is 2.5 nm.

[0074] In this embodiment, the core nanoparticles are coated with an energy transfer layer with a thickness of 2.5 nm to obtain a core-shell structured upconversion luminescent material, and then the core-shell structured nanoparticles are coated with an energy capture layer with a thickness of 2.5 nm to obtain a core-shell-shell structured upconversion luminescent material, and then the core-shell-shell structured nanoparticles are coated with an energy protection layer with a thickness of 2.5 nm to obtain a core-shell-shell-shell structured upconversion luminescent material. In this embodiment, the luminescent center ion and the sensitizer Nd are introduced into the core-shell structure. 3+ They are distributed in the core layer and the energy capture shell layer respectively, which effectively suppresses the concentration quenching caused by the cross relaxation between the luminescent ions and the sensitizing ions, and can improve the sensitizer Nd 3+ ion doping concentration to increase the material's absorption of 808nm; the introduction of Yb 3+ Ions act as a bridge for energy transfer between sensitizing ions and luminescent ions, ensuring efficient energy transfer. The matrix material of the first shell is composed of Gd 3+Ion replacement with inert matrix Y 3+ Ions can effectively prevent the excitation light energy from reaching the shell Gd 3+ The lattice defects inside the ions are transmitted and the energy capture by the lattice defects is effectively suppressed, thereby enhancing the upconversion emission under 808nm excitation; by coating the outermost layer with an energy protection layer, the energy capture by the surface quenching molecules can be effectively suppressed, further enhancing the upconversion emission. At the same time, by increasing the size of the core layer, on the one hand, the internal defects of the core-shell structure can be reduced; on the other hand, due to the increase in the size of the core layer, the shell layer becomes thinner, and the thickness of each shell is 2.5nm, which reduces the distance between ions and increases the Nd 3+ Ions and Yb 3+ Ion, Yb 3+ ions and luminescent ions (Tm 3+ ), luminescent ions (Tm 3+ ) and Gd 3+ The energy transfer efficiency between ions is ultimately reflected in the enhanced upconversion luminescence. This embodiment can effectively prevent the excitation light energy from transferring to the shell Gd 3+ The lattice defects within the ions are transferred and the energy capture by the lattice defects is effectively suppressed, thereby enhancing the upconversion emission in the ultraviolet region under near-infrared light excitation.

[0075] Example 3

[0076] This embodiment is basically the same as the above embodiment, with the following features:

[0077] In this embodiment, NaGdF4:Yb / Tm is used as the core of the multilayer core-shell structure, the doping molar fraction of Yb ions is 60%, and the doping molar fraction of Tm is 15%; in the energy transfer layer with a thickness of 5nm, the doping molar fraction of Yb ions is 10%; in the energy capture layer with a thickness of 5nm, the doping molar concentration of Yb ions is 1%, and the doping molar concentration of Nd ions is 1%. An energy protection layer with a thickness of 5nm is coated on the above core-shell-shell structure nanoparticles. This embodiment can effectively prevent the excitation light energy from reaching the shell Gd 3+ The lattice defects within the ions are transferred and the energy capture by the lattice defects is effectively suppressed, thereby enhancing the upconversion emission in the ultraviolet region under near-infrared light excitation.

[0078] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. Various changes can be made according to the purpose of the invention of the present invention. Any changes, modifications, substitutions, combinations or simplifications made according to the spirit and principle of the technical solution of the present invention should be equivalent replacement methods. As long as they meet the purpose of the invention of the present invention and do not deviate from the technical principles and inventive concepts of the present invention, they belong to the protection scope of the present invention.

Claims

1. A neodymium-sensitized deep ultraviolet emitting rare earth luminescent multilayer core-shell structure material, characterized in that: The particles have a core-multi-shell heterogeneous structure, wherein the core layer as the luminescent center is a rare earth up-conversion nanoparticle, the energy transfer layer is a first shell coated on the core nanoparticle, forming an up-conversion luminescent material with a core-shell structure; the energy capture layer is a second shell coated on the energy transfer layer, forming an up-conversion luminescent material with a core-shell-shell structure; the energy protection layer is a third shell coated on the energy capture layer, forming a four-layer structure of an up-conversion luminescent material with a core-shell-shell-shell structure; the luminescent ions and the sensitizing ions are uniformly distributed in the core layer and each shell layer; the rare earth luminescent multi-layer core-shell structure material is a multi-layer core-shell structure, so that the Gd element can emit deep ultraviolet light at 253 nm under excitation at 793 nm, 808 nm and 980 nm; The rare earth luminescent multilayer core-shell structure material is NaGdF4:Yb / Tm@NaYF4:Yb@NaGdF4:Yb / Nd@NaGdF4, with NaGdF4:Yb / Tm as the core of the multilayer core-shell structure, the doping molar fraction of Yb ions is 40%-60%, and the doping molar fraction of Tm is 0.5-2%; In the first shell, the molar fraction of Yb ion doping is 10-80%, the first shell is based on an inert material, and the matrix material of the first shell is NaYF4, thereby obtaining deep ultraviolet emission of the Gd element at 253 nm under excitation at 793 nm, 808 nm, and 980 nm; The doping molar concentration of Yb ions in the second shell is 1 to 90%, and the doping molar concentration of Nd ions is 1 to 90%; The matrix material of the third shell is NaGdF4.

2. The neodymium-sensitized deep ultraviolet emitting rare earth luminescent multilayer core-shell structure material according to claim 1, characterized in that: In applications in catalysis, anti-counterfeiting, solar energy, bio-marking, and 3D printing, the rare earth luminescent multilayer core-shell structure material is used to emit light in the ultraviolet region.

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