Red up-conversion luminescence nanometer material obtained through energy allocation and preparation method and application thereof

Abstract

The invention discloses a red up-conversion luminescence nanometer material obtained through energy allocation and a preparation method and application thereof, and belongs to the technical field of up-conversion luminescence materials.According to the nanometer material, NaYF4 serves as a passivation core and a passivation shell on the outermost layer at the same time, NaErF4 serves as a matrix, NaYF4 serves as a passivation shell on the outermost layer, and NaYF4 serves as a passivation shell on the outermost layer and NaYF4 serves as a passivation shell on the outermost layer. Yb < 3 + > is introduced as a sensitized ion, and an active shell layer and a NaYF4: Yb sublattice shell layer of a Tm < 3 + > energy capture center are introduced. The NaYF4 passivation core and the passivation shell are utilized to effectively reduce energy loss, so that energy is recycled between the first shell layer and the second shell layer as far as possible, and 654 nm high-intensity red up-conversion emission light emitted by Er < 3 + > is finally obtained under the excitation conditions of 980 nm and 1532 nm through energy migration of Yb < 3 + >, energy back transfer of Yb < 3 + > to Er < 3 + > and the energy capture center effect of Tm < 3 + >.

Description

Technical Field

[0001] This invention relates to the field of upconversion luminescent material preparation technology, specifically to a nanomaterial that obtains red upconversion luminescence through energy modulation, its preparation method, and its application. Background Technology

[0002] Rare-earth-doped upconversion luminescent nanomaterials are anti-Stokes radiation materials. These nanomaterials typically use low-phonon-energy materials as the matrix lattice and introduce sensitizers. By absorbing infrared radiation, they convert two or more low-energy near-infrared excited photons into high-energy visible or ultraviolet photons. These nanomaterials can be applied in cutting-edge fields such as optical storage, anti-counterfeiting technology, solar cells, 3D displays, biomonitoring, upconversion lasers, bioimaging, and photodynamic therapy. Studies have shown that compared to short-wavelength green and blue / violet light, long-wavelength red light has superior tissue penetration and imaging resolution, mainly due to its lower tissue scattering and autofluorescence interference, thus exhibiting significant advantages in bioimaging applications.

[0003] Er 3+ Lanthanides are excellent upconversion ions, capable of absorbing 980nm and 1532nm photons and emitting red light. Their excellent resistance to concentration quenching allows them to function as both sensitizers and activators. However, the luminescence efficiency of these nanomaterials is relatively low, as their high specific surface area, numerous surface defects, and low crystallinity exacerbate nonradiative decay and luminescence quenching. Therefore, precisely controlling the spatial distribution of lanthanides in nanostructures and constructing efficient energy transfer pathways are crucial for enhancing luminescence efficiency. 3+ High-intensity red light is a major challenge in the field of luminescent materials technology. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a nanomaterial that achieves red upconversion luminescence through energy modulation. In this structural design, NaYF4 serves as both the passivation core and the outermost passivation shell. Between the two passivation layers, a NaErF4 matrix is ​​sequentially coated, and Yb is introduced. 3+ As a sensitizing ion and Tm 3+ The invention utilizes an active shell at the energy trapping center and a NaYF4:Yb sublattice shell to effectively reduce energy loss by employing a NaYF4 passivated core and passivated shell, allowing energy to be recycled between the first and second shells as much as possible, and through Yb... 3+ Energy transfer, Yb 3+ For Er 3+ Energy return transfer and Tm 3+ The energy capture center plays a central role, ultimately obtaining Er 3+ The 654 nm red upconversion emission light.

[0005] The objective of this invention is achieved through the following technical solution: The first aspect of the present invention is to provide a nanomaterial that obtains red upconversion luminescence through energy modulation, the chemical formula of which is NaYF4@NaErF4:xYb,1%Tm@NaYF4:yYb@NaYF4, and its structural composition is that NaYF4 is used as the core, and NaErF4:xYb,1%Tm shell, NaYF4:yYb shell and NaYF4 outer layer are sequentially coated. Where x is the mole percentage Yb / (Er+Yb+Tm), y is the mole percentage Yb / (Y+Yb), and x and y satisfy 0 ≤ x ≤ 49% and 10% ≤ y ≤ 80%, respectively.

[0006] In some preferred embodiments, x is 49% and y is 80%.

[0007] In some preferred embodiments, the nanomaterial has a particle size of 21.81-23.91 nm.

[0008] A second aspect of the present invention is to provide an application of the nanomaterial that obtains red upconversion luminescence through energy modulation as a luminescent material in the field of bioimaging, wherein the nanomaterial that obtains red upconversion luminescence through energy modulation can emit 654 nm red upconversion emission light under 980 nm light excitation.

[0009] A third aspect of the present invention is to provide a method for preparing the nanomaterial that obtains red upconversion luminescence through energy modulation, comprising the following steps: (1) Yttrium source, erbium source, ytterbium source and thulium source were mixed with oleic acid and octadecene respectively, and heated to react to obtain yttrium-oleic acid chelate, erbium-oleic acid chelate, ytterbium-oleic acid chelate and thulium-oleic acid chelate respectively; (2) Preparation of NaYF4 core layer: After cooling the yttrium-oleic acid chelate, sodium source and fluorine source were added, and the reaction was carried out under an inert atmosphere to obtain NaYF4 nanoparticles; (3) Preparation of NaErF4:xYb,1%Tm shell: Oleic acid, octadecene and erbium-oleic acid chelate, ytterbium-oleic acid chelate, thulium-oleic acid chelate are mixed evenly, and the NaYF4 nanoparticles, sodium source and fluorine source are added. The reaction is carried out under an inert atmosphere to obtain NaYF4@NaErF4:xYb,1%Tm core-shell structured nanoparticles; (4) Preparation of NaYF4:yYb shell: Oleic acid, octadecene and yttrium-oleic acid chelate and ytterbium-oleic acid chelate are mixed evenly, and the NaYF4@NaErF4:xYb,1%Tm core-shell structured nanoparticles, sodium source and fluorine source are added. The reaction is carried out under an inert atmosphere to obtain NaYF4@NaErF4:xYb,1%Tm@NaYF4:yYb core-shell-shell structured nanoparticles; (5) Preparation of the outer layer of NaYF4: The NaYF4@NaErF4:xYb,1%Tm@NaYF4:yYb core-shell-shell structured nanoparticles and yttrium-oleic acid chelate are mixed evenly, sodium source and fluorine source are added, and the reaction is carried out under an inert atmosphere to obtain the red upconversion luminescent nanomaterial with the NaYF4@NaErF4:xYb,1%Tm@NaYF4:yYb@NaYF4 core-shell-shell-shell structure obtained by energy modulation.

[0010] In some preferred embodiments, the yttrium source is yttrium chloride; the erbium source is erbium chloride; the ytterbium source is ytterbium chloride; the thulium source is thulium chloride; the sodium source is sodium hydroxide; and the fluorine source is ammonium fluoride.

[0011] In some preferred embodiments, in one or more steps of steps (2)-(5), the reaction temperature of the heating reaction under an inert atmosphere is 280-305°C and the reaction time is 0.9-1.6h.

[0012] In some preferred embodiments, the reaction temperature for heating the reaction in an inert atmosphere in step (2) is 290°C and the reaction time is 1 h; the reaction temperature for heating the reaction in an inert atmosphere in steps (3)-(5) is 300°C and the reaction time is 1.5 h.

[0013] In some preferred embodiments, the inert atmosphere is a nitrogen atmosphere.

[0014] The beneficial effects of this invention are as follows: (1) The upconversion nanomaterial of the present invention uses NaYF4 as a passivation core layer, and is sequentially coated with a NaErF4:xYb,1%Tm shell layer, a NaYF4:yYb shell layer, and a NaYF4 passivation outer layer. In this structural design, NaYF4 serves as both the passivation core and the outermost passivation shell, so that energy can be recycled between the first and second shell layers as much as possible, and through Yb 3+ Energy transfer, Yb 3+ For Er 3+ Energy return transfer and Tm 3+ The energy capture center plays a central role, ultimately obtaining Er 3+ The 654 nm red upconversion emission light.

[0015] (2) The present invention provides a method for preparing the nanomaterial by co-precipitation reaction of oleic acid, octadecene, rare earth chloride, rare earth element-oleic acid chelate, sodium hydroxide and ammonium fluoride. The preparation process is simple and easy to operate, low in cost and short in cycle, and suitable for mass production. Attached Figure Description

[0016] The present invention will be further described with reference to the accompanying drawings, but the embodiments in the drawings do not constitute any limitation on the present invention. For those skilled in the art, other drawings can be obtained based on the following drawings without creative effort.

[0017] Figure 1 The images show the fluorescence spectra of the NaErF4:1%Tm@NaYF4, NaYF4@NaErF4@NaYF4, NaYF4@NaErF4:1%Tm@NaYF4, and NaYF4@NaErF4:1%Tm upconversion nanoparticles prepared in Examples 1-4 of this invention; wherein, the excitation conditions for (a) and (b) are 980 nm and 1532 nm, respectively. Figure 2 The fluorescence spectra of NaYF4@NaErF4:x%Yb,1%Tm@NaYF4 (where x = 0, 10, 20, 30, 49) nanomaterials prepared in Examples 3 and 5-8 of this invention are shown, where the excitation conditions for (a) and (b) are 980 nm and 1532 nm, respectively. Figure 3 The images show the fluorescence spectra of the NaYF4@NaErF4:49%Yb,1%Tm@NaYF4:x%Yb@NaYF4 (where x = 10, 20, 50, 80, 100) nanomaterials prepared in Examples 9-13 of this invention. The excitation conditions for (a) and (b) are 980 nm and 1532 nm, respectively. Figure 4 These are transmission electron microscope (TEM) images of the nanomaterials prepared in Example 12 of this invention, wherein (a), (b), (c), and (d) correspond to NaYF4, NaYF4@NaErF4:49%Yb,1%Tm, NaYF4@NaErF4:49%Yb,1%Tm@NaYF4:80%Yb, and NaYF4@NaErF4:49%Yb,1%Tm@NaYF4:80%Yb@NaYF4 nanoparticles, respectively. Figure 5 This is the X-ray diffraction pattern of the NaYF4@NaErF4:49%Yb,1%Tm@NaYF4:80%Yb@NaYF4 nanomaterials prepared in Example 12 of this invention, wherein the standard PDF card used is β-NaYF4 (JCPDS: 16-0334); Figure 6 This is the energy level transition diagram of the NaYF4@NaErF4:49%Yb,1%Tm@NaYF4:80%Yb@NaYF4 upconversion nanomaterial prepared in Example 12 of this invention under excitation at 980nm and 1532nm. Detailed Implementation

[0018] The present invention will be further described in conjunction with the following embodiments.

[0019] The embodiments of the present invention relate to a nanomaterial that obtains red upconversion luminescence through energy modulation, with the chemical formula NaYF4@NaErF4:xYb,1%Tm@NaYF4:yYb@NaYF4. Its structural composition is NaYF4 as the core, which is sequentially coated with a NaErF4:xYb,1%Tm shell, a NaYF4:yYb shell, and a NaYF4 outer layer. Where x is the mole percentage Yb / (Er+Yb+Tm), y is the mole percentage Yb / (Y+Yb), and x and y satisfy 0≤ x ≤ 49% and 10% ≤ y ≤ 80%, respectively. In some implementations, x takes the value of 10%, 20%, 30%, or 40%, and y takes the value of 10%, 20%, 40%, 60%, or 80%. More preferably, x takes the value of 49%, and y takes the value of 80%. The method for preparing nanomaterials that achieve red upconversion luminescence through energy modulation includes the following steps: (1) The solutions of yttrium chloride, erbium chloride, ytterbium chloride and thulium chloride were mixed with oleic acid and octadecene respectively, and the water was removed by evaporation under a nitrogen atmosphere. The mixture was then heated at high temperature and cooled to obtain yttrium-oleic acid chelate, erbium-oleic acid chelate, ytterbium-oleic acid chelate and thulium-oleic acid chelate respectively. In some embodiments, the volume ratio of oleic acid to octadecene in step (1) is (0.65-0.75):1, more preferably 0.75:1; In some embodiments, the temperature for evaporating and removing moisture in step (1) is 100-110°C, more preferably 105°C; In some embodiments, the conditions for the high-temperature heating reaction in step (1) are to react at 145-155 °C for 1-1.5 h, more preferably at 150 °C under nitrogen protection for 1.5 h; In some embodiments, when preparing the yttrium-oleic acid chelate in step (1), the concentration of the yttrium chloride solution is 0.85-1.15 mol·L⁻¹. -1 More preferably 1 mol·L -1 ; In some embodiments, when preparing the yttrium-oleic acid chelate in step (1), the volume ratio of oleic acid to the yttrium chloride solution is (2-10):1, more preferably 4:1; In some embodiments, when preparing the erbium-oleic acid chelate in step (1), the concentration of the erbium chloride solution is 0.4-0.6 mol·L⁻¹. -1 More preferably 0.5 mol·L -1 ; In some embodiments, when preparing the erbium-oleic acid chelate in step (1), the volume ratio of the oleic acid to the erbium chloride solution is (2-10):1, more preferably 4:1; In some embodiments, when preparing the ytterbium-oleic acid chelate in step (1), the concentration of the ytterbium chloride solution is (0.2-1) mol·L⁻¹. -1 More preferably 0.5 mol·L -1 ; In some embodiments, when preparing the ytterbium-oleic acid chelate in step (1), the volume ratio of oleic acid to the ytterbium chloride solution is (2-6):1, more preferably 4:1; In some embodiments, when preparing the thulium-oleic acid chelate in step (1), the concentration of the thulium chloride solution is 0.08-0.12 mol·L⁻¹. -1 More preferably 0.1 mol·L⁻¹ -1 ; In some embodiments, when preparing the thulium-oleic acid chelate in step (1), the volume ratio of the oleic acid to the thulium chloride solution is (4-10):1, more preferably 4:1; (2) Mix and stir the yttrium-oleic acid chelate, the methanol solution of sodium hydroxide and the methanol solution of ammonium fluoride, and heat and evaporate the excess methanol in a nitrogen atmosphere to remove it. Then continue to heat and carry out high temperature reaction. Finally, wash and centrifuge the solution after the reaction to obtain a white precipitate, namely the core layer NaYF4 nanoparticles. In some embodiments, the concentration of the yttrium-oleic acid chelate in step (2) is 0.04-0.2 mol·L⁻¹. -1 More preferably 0.2 mol·L⁻¹ -1 ; In some embodiments, the concentration of sodium hydroxide in the methanol solution of sodium hydroxide in step (2) is (0.2-0.8) mol·L⁻¹. -1 More preferably 0.5 mol·L -1 ; In some embodiments, the concentration of ammonium fluoride in the methanol solution of ammonium fluoride in step (2) is 0.5-1 mol·L⁻¹. -1More preferably 0.8 mol·L -1 ; In some embodiments, the volume ratio of the methanol solution of sodium hydroxide and the methanol solution of ammonium fluoride in step (2) is (0.8-1.2):1, more preferably 1:1; In some embodiments, the volume ratio of the yttrium-oleic acid chelate to the methanol solution of sodium hydroxide (or the methanol solution of ammonium fluoride) in step (2) is (0.5-8):1, more preferably 1:1; (3) After mixing and stirring oleic acid, octadecene, erbium-oleic acid chelate, ytterbium-oleic acid chelate and thulium-oleic acid chelate evenly, the core-layer NaYF4 nanoparticles prepared in step (2) are added, followed by the addition of a methanol solution of sodium hydroxide and a methanol solution of ammonium fluoride and stirring. Under the protection of nitrogen, the temperature is raised to evaporate and remove excess methanol. Then, a high-temperature reaction is carried out and the mixture is naturally cooled to obtain NaYF4@NaErF4:xYb,1%Tm core-shell structured nanoparticles. In some embodiments, the volume ratio of oleic acid to octadecene in step (3) is (1.8-2.2):3, more preferably 2:3; In some embodiments, the concentration of the erbium-oleic acid chelate in step (3) is 0.02-0.2 mol·L⁻¹. -1 More preferably 0.2 mol·L⁻¹ -1 ; In some embodiments, the concentration of the ytterbium-oleic acid chelate in step (3) is 0.02-0.2 mol·L⁻¹. -1 More preferably 0.1 mol·L⁻¹ -1 ; In some embodiments, the concentration of the thulium-oleic acid chelate in step (3) is 0.004-0.04 mol·L⁻¹. -1 More preferably 0.04 mol·L -1 ; In some embodiments, the volume ratio of oleic acid and erbium-oleic acid chelate in step (3) is 100:(2.5-4.95), more preferably 100:2.5; In some embodiments, the volume ratio of oleic acid and ytterbium-oleic acid chelate in step (3) is 10:(0.1-0.49), more preferably 10:0.49; In some embodiments, the volume ratio of oleic acid and thulium-oleic acid chelate in step (3) is 10:0.025; In some embodiments, the molar ratio of the NaYF4 nanoparticles to the erbium-oleic acid chelate in step (3) is 1:(0.5-0.99), more preferably 1:0.5; In some embodiments, the molar ratio of the NaYF4 nanoparticles to the ytterbium-oleic acid chelate in step (3) is 1:(0.1-0.49), more preferably 1:0.49; In some embodiments, the molar ratio of the NaYF4 nanoparticles to the thulium-oleic acid chelate in step (3) is 1:0.01; In some embodiments, the volume ratio of the erbium-oleic acid chelate and the methanol solution of sodium hydroxide in step (3) is (2.5-4.95):5, more preferably 2.5:5; In some embodiments, the volume ratio of the ytterbium-oleic acid chelate and the methanol solution of sodium hydroxide in step (3) is (1-4.95):5, more preferably 4.9:5; In some embodiments, the volume ratio of the thulium-oleic acid chelate and the methanol solution of sodium hydroxide in step (3) is 0.25:5; (4) Oleic acid, octadecene and yttrium-oleic acid chelate and ytterbium-oleic acid chelate are mixed evenly, and the NaYF4@NaErF4:xYb,1%Tm core-shell structured nanoparticles are added. Then, a methanol solution of sodium hydroxide and a methanol solution of ammonium fluoride are added and stirred. Under the protection of nitrogen, the temperature is raised to evaporate and remove excess methanol. Then, a high-temperature reaction is carried out and the mixture is naturally cooled to obtain a reaction solution with NaYF4@NaErF4:xYb,1%Tm@NaYF4:yYb core-shell structured nanoparticles. In some embodiments, the concentration of the yttrium-oleic acid chelate in step (4) is 0.04-0.4 mol·L⁻¹. -1 More preferably 0.2 mol·L⁻¹ -1 ; In some embodiments, the concentration of the ytterbium-oleic acid chelate in step (4) is 0.02-0.2 mol·L⁻¹. -1 More preferably 0.1 mol·L⁻¹ -1 ; In some embodiments, the volume ratio of oleic acid and yttrium-oleic acid chelate in step (4) is 10:(0-0.45), more preferably 10:0.1; In some embodiments, the volume ratio of oleic acid and ytterbium-oleic acid chelate in step (4) is 10:(0.05-0.5), more preferably 10:0.4; In some embodiments, the molar ratio of the yttrium-oleic acid chelate to the NaYF4 nanoparticles in step (4) is (0-0.9):1, more preferably 0.2:1; In some embodiments, the molar ratio of the ytterbium-oleic acid chelate to the NaYF4 nanoparticles in step (4) is (0.1-1):1, more preferably 0.8:1; In some embodiments, the volume ratio of the yttrium-oleic acid chelate and the methanol solution of sodium hydroxide in step (4) is (0-4.5):5, more preferably 1:5; In some embodiments, the volume ratio of the ytterbium-oleic acid chelate and the methanol solution of sodium hydroxide in step (4) is (1-10):5, more preferably 8:5; (5) Add the yttrium-oleic acid chelate to the reaction solution prepared in step (4) and mix evenly. Add the methanol solution of sodium hydroxide and the methanol solution of ammonium fluoride and stir. Under the protection of nitrogen, heat up to evaporate and remove excess methanol. Then carry out high temperature reaction. Finally, wash and centrifuge the reaction solution to obtain the red upconversion luminescent nanomaterial with the core-shell-shell-shell structure of NaYF4@NaErF4:xYb,1%Tm@NaYF4:yYb@NaYF4. In some embodiments, the concentration of the yttrium-oleic acid chelate in step (5) is 0.04-0.4 mol·L⁻¹. -1 More preferably 0.2 mol·L⁻¹ -1 ; In some embodiments, the molar ratio of the yttrium-oleic acid chelate to the NaYF4 nanoparticles in step (5) is (0.8-1.2):1, more preferably 1:1; In some embodiments, the volume ratio of the yttrium-oleic acid chelate to the methanol solution of sodium hydroxide in step (5) is (4.5-5.5):5, more preferably 1:1; In some embodiments, the concentration of sodium hydroxide in the methanol solution of sodium hydroxide described in steps (3), (4), and (5) is 0.2-0.8 mol·L⁻¹. -1 More preferably 0.5 mol·L -1 ; In some embodiments, the concentration of ammonium fluoride in the methanol solution of ammonium fluoride described in steps (3), (4), and (5) is 0.5-1 mol·L⁻¹. -1 More preferably 0.8 mol·L -1 ; In some embodiments, the volume ratio of the methanol solution of sodium hydroxide and the methanol solution of ammonium fluoride in steps (2), (3), (4) and (5) is (0.8-1.2):1, more preferably 1:1; In some embodiments, the temperature for heating and evaporating to remove excess methanol in steps (2), (3), (4) and (5) is 85-105 °C, more preferably 90 °C; In some embodiments, the conditions for carrying out the high-temperature reaction under nitrogen protection in step (2) are to react at 280-290 °C for 0.9-1.1 h, more preferably at 290 °C for 1 h; In some embodiments, the high-temperature reaction conditions described in steps (3), (4) and (5) are 1.3-1.6 h at 295-305 °C, more preferably 1.5 h at 300 °C; In some embodiments, the washing method described in steps (2) and (5) is washing with anhydrous ethanol; In some embodiments, the centrifugation conditions described in steps (2) and (5) are centrifugation at 9000-11000 rpm for 8-12 min, for a total of 2-4 times, more preferably centrifugation at 10000 rpm for 10 min, for a total of 2 times.

[0020] Example 1 This embodiment relates to a NaErF4:1%Tm@NaYF4 upconversion nanomaterial, the preparation method of which includes the following steps: (1) Preparation of NaErF4:1%Tm core layer: Take 15 mL of oleic acid and 20 mL of octadecene into a three-necked flask and stir thoroughly until well mixed. Then add 1.98 mL of 0.5 mol·L⁻¹ core layer. -1 Erbium chloride solution and 0.1 mL of 0.1 mol·L⁻¹ -1 A thulium chloride solution was thoroughly stirred and mixed. The mixture was then heated to 105°C to remove water, followed by a high-temperature reaction at 150°C for 1.5 h to generate a rare earth-oleic acid chelate. The mixture was then allowed to cool naturally to room temperature, and 5 mL of a 0.5 mol·L⁻¹ solution was added. -1 A methanol solution of sodium hydroxide and 5 mL of a 0.8 mol·L⁻¹ solution. -1The ammonium fluoride was dissolved in methanol and stirred until homogeneous. The mixture was heated to 90°C for 1 h under nitrogen protection to remove excess methanol. Then, the mixture was reacted at 290°C for 1 h. Finally, the reaction mixture was allowed to cool naturally to room temperature, washed with anhydrous ethanol, and centrifuged twice at 10,000 rpm for 10 min to obtain the precipitate, which was NaErF4:1%Tm nanoparticles. These precipitates were then dispersed and stored in cyclohexane.

[0021] (2) NaYF4 passivation layer coating: Take 10 mL of oleic acid and 15 mL of octadecene in a three-necked flask and stir thoroughly until well mixed. Then take 2.5 mL of 0.04 mol·L⁻¹ solution. -1 The yttrium-oleic acid chelate and 0.1 mmol of the nanoparticles obtained in step (1) were mixed and stirred until homogeneous, and then 0.5 mL of a 0.5 mol·L⁻¹ solution was added. -1 A methanol solution of sodium hydroxide and 0.5 mL of a 0.8 mol·L⁻¹ solution. -1 The ammonium fluoride was dissolved in methanol and stirred. The temperature was raised to 90 °C and maintained for 45 min to remove excess methanol. Then, under nitrogen protection, the mixture was reacted at 300 °C for 1.5 h. Finally, the reaction mixture was naturally cooled to room temperature, washed with anhydrous ethanol, and centrifuged at 10,000 rpm for 10 min twice to obtain the precipitate, which was NaErF4:1%Tm@NaYF4 core-shell structured nanoparticles, which were dispersed and stored in cyclohexane.

[0022] Example 2-3 Examples 2-3 relate to a NaYF4@NaErF4:xTm@NaYF4 upconversion nanomaterial, where x represents 0% and 1% respectively. The preparation method in Example 2 includes the following steps: (1) Preparation of NaYF4 core layer: Take 15 mL of oleic acid and 20 mL of octadecene into a three-necked flask and stir thoroughly until well mixed. Then add 1 mL of 1 mol·L⁻¹ solution. -1 A yttrium chloride solution was thoroughly stirred and mixed. The mixture was then heated to 105°C to evaporate and remove water. A high-temperature reaction was then carried out at 150°C for 1.5 h to generate a yttrium-oleic acid chelate. The mixture was then allowed to cool naturally to room temperature, and 5 mL of a 0.5 mol·L⁻¹ solution was added. -1 A methanol solution of sodium hydroxide and 5 mL of a 0.8 mol·L⁻¹ solution. -1The ammonium fluoride was dissolved in methanol and stirred until homogeneous. The mixture was heated to 90°C and held for 1 hour to remove excess methanol. Then, the mixture was subjected to a high-temperature reaction at 290°C for 1 hour under nitrogen protection. Finally, the reaction mixture was allowed to cool naturally to room temperature, washed with anhydrous ethanol, and centrifuged at 10,000 rpm for 10 minutes. The centrifugation was repeated twice to obtain a white precipitate, namely NaYF4 core nanoparticles, which were dispersed and stored in cyclohexane. (2) NaErF4:0%Tm shell coating: Take 10 mL of oleic acid and 15 mL of octadecene in a three-necked flask and stir thoroughly until well mixed. Then add 0.5 mL of 0.2 mol·L⁻¹. -1 The erbium-oleic acid chelate was mixed and stirred evenly, and 0.1 mmol of the nanoparticles prepared in step (1) was added, followed by 0.5 mL of 0.5 mol·L⁻¹ solution. -1 A methanol solution of sodium hydroxide and 0.5 mL of a 0.8 mol·L⁻¹ solution. -1 The methanol solution of ammonium fluoride was stirred and heated to 90 °C and maintained for 45 min to remove excess methanol. Then, under nitrogen protection, the reaction was carried out at 300 °C for 1.5 h. Finally, the solution of NaYF4@NaErF4:0%Tm core-shell structured nanoparticles was obtained by natural cooling. (3) NaYF4 shell coating: 0.5 mL of 0.2 mol·L⁻¹ NaYF₄@NaErF₄:0%Tm core-shell structured nanoparticles were added to the reaction solution of NaYF₄@NaErF₄:0%Tm core-shell structured nanoparticles obtained after cooling in step (2). -1 The yttrium-oleic acid chelate was mixed and stirred until homogeneous, and then 0.5 mL of a 0.5 mol·L⁻¹ solution was added. -1 A methanol solution of sodium hydroxide and 0.5 mL of a 0.8 mol·L⁻¹ solution. -1 The ammonium fluoride was dissolved in methanol and stirred. The temperature was raised to 90°C and maintained for 45 min to remove excess methanol. Then, under nitrogen protection, the mixture was reacted at 300°C for 1.5 h. Finally, the reaction mixture was naturally cooled to room temperature, washed with anhydrous ethanol, and centrifuged at 10,000 rpm for 10 min twice to obtain the precipitate, which was NaYF4@NaErF4:0%Tm@NaYF4 core-shell structured nanoparticles, which were dispersed and stored in cyclohexane.

[0023] The preparation method of Example 3 is the same as that of Example 2, except that the rare earth-oleic acid chelate added to the mixture of oleic acid and octadecene in step (2) is different. In Example 3, 0.495 mL of a 0.2 mol·L⁻¹ rare earth-oleic acid chelate is added. -1 Erbium-oleic acid chelate and 0.025 mL of 0.04 mol·L⁻¹ -1 Thulium-oleic acid chelate.

[0024] Example 4 This embodiment relates to a NaYF4@NaErF4:1%Tm upconversion nanomaterial, and the preparation method of the upconversion nanomaterial includes the following steps: (1) Preparation of NaYF4 core layer: Take 15 mL of oleic acid and 20 mL of octadecene into a three-necked flask and stir thoroughly until well mixed. Then add 1 mL of 1 mol·L⁻¹ solution. -1 A yttrium chloride solution was thoroughly stirred and mixed. The mixture was then heated to 105 °C to remove water, followed by a high-temperature reaction at 150 °C for 1.5 h to generate a yttrium-oleic acid chelate. The mixture was then allowed to cool naturally to room temperature, and 5 mL of a 0.5 mol·L⁻¹ solution was added. -1 A methanol solution of sodium hydroxide and 5 mL of a 0.8 mol·L⁻¹ solution. -1 A methanol solution of ammonium fluoride was added to the erbium-oleic acid chelate prepared above and stirred until homogeneous. The mixture was heated to 90 °C and held for 1 h to remove excess methanol. Then, the mixture was subjected to a high-temperature reaction at 290 °C for 1 h under nitrogen protection. Finally, the reaction mixture was allowed to cool naturally to room temperature, washed with anhydrous ethanol, and centrifuged at 10,000 rpm for 10 min, and centrifuged twice to obtain a white precipitate, namely NaYF4 core nanoparticles, which were dispersed and stored in cyclohexane. (2) NaErF4:1%Tm shell coating: Take 10 mL of oleic acid and 15 mL of octadecene in a three-necked flask and stir thoroughly until well mixed. Then add 0.495 mL of 0.2 mol·L⁻¹ iodine. -1 Erbium-oleic acid chelate and 0.025 mL of 0.04 mol·L⁻¹ -1 The thulium-oleic acid chelate was mixed and stirred evenly, and 0.1 mmol of the nanoparticles prepared in step (1) was added, followed by 0.5 mL of 0.5 mol·L⁻¹ solution. -1 A methanol solution of sodium hydroxide and 0.5 mL of a 0.8 mol·L⁻¹ solution. -1 An ammonium fluoride solution was prepared in methanol and stirred. The temperature was raised to 90 °C and maintained for 45 min to remove excess methanol. Then, under nitrogen protection, the reaction was carried out at 300 °C for 1.5 h. Finally, the mixture was allowed to cool naturally to obtain a reaction solution of NaYF4@NaErF4:1%Tm core-shell structured nanoparticles. The reaction mixture was then allowed to cool naturally to room temperature, washed with anhydrous ethanol, and centrifuged at 10,000 rpm for 10 min twice to obtain the precipitate, which was the NaYF4@NaErF4:1%Tm core-shell structured nanoparticles, which were dispersed and stored in cyclohexane.

[0025] Examples 5-8 Examples 5-8 involve an upconversion nanomaterial NaYF4@NaErF4:xYb,1%Tm@NaYF4, where x represents 10%, 20%, 30%, and 49%, respectively. The preparation method of the upconversion nanomaterial in Examples 5-8 is the same as in Example 3, except that the rare earth-oleic acid chelate added to the mixture of oleic acid and octadecene in step (2) is different, wherein: Example 5 involves adding 0.445 mL of a 0.2 mol·L⁻¹ solution. -1 Erbium-oleic acid chelate, 0.1 mL, concentration of 0.1 mol·L⁻¹ -1 The ytterbium-oleic acid chelate and 0.025 mL of a 0.04 mol·L⁻¹ solution -1 Thulium-oleic acid chelates; Example 6 involves adding 0.395 mL of a solution with a concentration of 0.2 mol·L⁻¹. -1 Erbium-oleic acid chelate, 0.2 mL, concentration of 0.1 mol·L⁻¹ -1 The ytterbium-oleic acid chelate and 0.025 mL of a 0.04 mol·L⁻¹ solution -1 Thulium-oleic acid chelates; Example 7 involves adding 0.345 mL of a solution with a concentration of 0.2 mol·L⁻¹. -1 Erbium-oleic acid chelate, 0.3 mL, concentration of 0.1 mol·L⁻¹ -1 The ytterbium-oleic acid chelate and 0.025 mL of a 0.04 mol·L⁻¹ solution -1 Thulium-oleic acid chelates; Example 8 involves adding 0.25 mL of a 0.2 mol·L⁻¹ solution. -1 Erbium-oleic acid chelate, 0.49 mL, concentration of 0.1 mol·L⁻¹ -1 The ytterbium-oleic acid chelate and 0.025 mL of a 0.04 mol·L⁻¹ solution -1 Thulium-oleic acid chelate.

[0026] Examples 9-13 Examples 9-13 relate to a NaYF4@NaErF4:49%Yb,1%Tm@NaYF4:xYb@NaYF4 nanomaterial, where x represents 10%, 20%, 50%, 80%, and 100%, respectively. The preparation method in Example 9 includes the following steps: (1) Preparation of NaYF4 core layer: Take 15 mL of oleic acid and 20 mL of octadecene into a three-necked flask and stir thoroughly until well mixed. Then add 1 mL of 1 mol·L⁻¹ solution. -1A yttrium chloride solution was thoroughly stirred and mixed. The mixture was then heated to 105 °C to remove water, followed by a high-temperature reaction at 150 °C for 1.5 h to generate a yttrium-oleic acid chelate. The mixture was then allowed to cool naturally to room temperature, and 5 mL of a 0.5 mol·L⁻¹ solution was added. -1 A methanol solution of sodium hydroxide and 5 mL of a 0.8 mol·L⁻¹ solution. -1 The ammonium fluoride was dissolved in methanol and stirred until homogeneous. The mixture was heated to 90 °C and held for 1 h to remove excess methanol. Then, the mixture was subjected to a high-temperature reaction at 290 °C for 1 h under nitrogen protection. Finally, the reaction mixture was allowed to cool naturally to room temperature, washed with anhydrous ethanol, and centrifuged at 10,000 rpm for 10 min. The centrifugation was repeated twice to obtain a white precipitate, namely NaYF4 core layer nanoparticles, which were dispersed and stored in cyclohexane. (2) NaErF4:49%Yb,1%Tm shell coating: Take 10 mL of oleic acid and 15 mL of octadecene in a three-necked flask and stir thoroughly until well mixed. Then add 0.25 mL of 0.2 mol·L⁻¹ solution. -1 Erbium-oleic acid chelate, 0.49 mL, concentration 0.1 mol·L⁻¹ -1 The ytterbium-oleic acid chelate and 0.025 mL of a 0.04 mol·L⁻¹ solution. -1 The thulium-oleic acid chelate was mixed and stirred evenly, and the nanoparticles prepared in step (1) were added. Then, 0.5 mL of a 0.5 mol·L⁻¹ solution was added. -1 A methanol solution of sodium hydroxide and 0.5 mL of a 0.8 mol·L⁻¹ solution. -1 The methanol solution of ammonium fluoride was stirred and heated to 90 °C and maintained for 45 min to remove excess methanol. Then, under nitrogen protection, the reaction was carried out at 300 °C for 1.5 h. Finally, the reaction solution of NaYF4@NaErF4:49%Yb,1%Tm core-shell structured nanoparticles was obtained by natural cooling. (3) NaYF4:10%Yb shell coating: 0.45 mL of 0.2 mol·L⁻¹ core-shell nanoparticles with a concentration of 49%Yb and 1%Tm were added to the reaction solution of NaYF4@NaErF4:49%Yb,1%Tm core-shell nanoparticles obtained after cooling in step (2). -1 Yttrium-oleic acid chelate and 0.1 mL of 0.1 mol·L⁻¹ -1 The ytterbium-oleic acid chelate was mixed and stirred until homogeneous, and then 0.5 mL of a 0.5 mol·L⁻¹ solution was added. -1 A methanol solution of sodium hydroxide and 0.5 mL of a 0.8 mol·L⁻¹ solution. -1The methanol solution of ammonium fluoride was stirred and heated to 90℃ and maintained for 45 min to remove excess methanol. Then, under nitrogen protection, the reaction was carried out at 300℃ for 1.5 h. Finally, the reaction solution of NaYF4@NaErF4:49%Yb,1%Tm@NaYF4:10%Yb core-shell structured nanoparticles was obtained by natural cooling. (4) NaYF4 passivation layer coating: 0.5 mL of 0.2 mol·L⁻¹ NaYF₄@NaErF₄:49%Yb,1%Tm@NaYF₄:10%Yb core-shell structured nanoparticles obtained after cooling in step (3) were added. -1 The yttrium-oleic acid chelate was mixed and stirred until homogeneous, and then 0.5 mL of a 0.5 mol·L⁻¹ solution was added. -1 A methanol solution of sodium hydroxide and 0.5 mL of a 0.8 mol·L⁻¹ solution. -1 The ammonium fluoride was dissolved in methanol and stirred. The temperature was raised to 90℃ and maintained for 45 min to remove excess methanol. Then, under nitrogen protection, the mixture was reacted at 300℃ for 1.5 h. Finally, the reaction mixture was naturally cooled to room temperature, washed with anhydrous ethanol, and centrifuged at 10000 rpm for 10 min twice to obtain a precipitate, which was NaYF4@NaErF4:49%Yb,1%Tm@NaYF4:10%Yb@NaYF4 core-shell nanoparticles, which were dispersed and stored in cyclohexane.

[0027] The preparation methods of Examples 10-13 are the same as those of Example 9, except that the rare earth-oleic acid chelate added to the mixture of oleic acid and octadecene in step (3) is different, wherein: Example 10 involves adding 0.4 mL of a solution with a concentration of 0.2 mol·L⁻¹. -1 Yttrium-oleic acid chelate and 0.2 mL of 0.1 mol·L⁻¹ -1 Ytterbium-oleic acid chelates; Example 11 involves adding 0.25 mL of a 0.2 mol·L⁻¹ solution. -1 Yttrium-oleic acid chelate and 0.5 mL of 0.1 mol·L⁻¹ -1 Ytterbium-oleic acid chelates; Example 12 involves adding 0.1 mL of a solution with a concentration of 0.2 mol·L⁻¹. -1 Yttrium-oleic acid chelate and 0.8 mL of 0.1 mol·L⁻¹ -1 Ytterbium-oleic acid chelates; Example 13 involves adding 1 mL of a 0.1 mol·L⁻¹ solution. -1 Ytterbium-oleic acid chelate.

[0028] Experimental Example The fluorescence spectra of the upconversion nanomaterials prepared in Example 1 (NaErF4:1%Tm@NaYF4), Example 2 (NaYF4@NaErF4@NaYF4), Example 3 (NaYF4@NaErF4:1%Tm@NaYF4), and Example 4 (NaYF4@NaErF4:1%Tm@NaYF4) under excitation conditions of 980 nm and 1532 nm were compared using a fluorescence analyzer. The results are as follows: Figure 1 As shown in the figure, the fluorescence intensity of NaYF4@NaErF4:1%Tm@NaYF4 is significantly higher than that of NaErF4:1%Tm@NaYF4 and NaYF4@NaErF4:1%Tm, proving that NaYF4 is used as both the core and outermost passivation layer, and a small amount of Tm is also used. 3+ It can significantly improve the red light upconversion emission intensity of materials.

[0029] The NaYF4@NaErF4 prepared in Examples 3 and 5-8 were analyzed using a fluorescence analyzer. x The fluorescence spectra of Yb,1%Tm@NaYF4 upconversion nanomaterials under excitation at 980 nm and 1532 nm were analyzed, where x = 0%, 10%, 20%, 30%, and 49%. The results are as follows: Figure 2 As shown in the figure, when Yb 3+ At a doping concentration of 49%, the sample exhibited the highest red upconversion luminescence intensity, indicating that Yb 3+ Doping can effectively improve the red light emission intensity of a sample.

[0030] The fluorescence spectra of the NaYF4@NaErF4:49%Yb,1%Tm@NaYF4:xYb@NaYF4 upconversion nanomaterials prepared in Examples 9-13 under excitation at 980 nm and 1532 nm were analyzed using a fluorescence analyzer, where x = 10%, 20%, 50%, 80%, and 100%. The results are as follows: Figure 3 As shown in the figure, when Yb 3+ At a doping concentration of 80%, the sample exhibited the highest red upconversion luminescence intensity, indicating that the second shell Yb 3+ Doping can effectively improve the red light emission intensity of a sample.

[0031] The morphology of the NaYF4, NaYF4@NaErF4:49%Yb,1%Tm, NaYF4@NaErF4:49%Yb,1%Tm@NaYF4:80%Yb, and NaYF4@NaErF4:49%Yb,1%Tm@NaYF4:80%Yb@NaYF4 nanomaterials prepared in Example 12 was analyzed using transmission electron microscopy. The results are as follows: Figure 4As shown, the obtained sample exhibits high homogeneity and monodispersity.

[0032] The phase composition of the NaYF4@NaErF4:49%Yb,1%Tm@NaYF4:80%Yb@NaYF4 nanomaterials prepared in Example 12 was analyzed using X-ray diffraction analysis. The results are as follows: Figure 5 As shown in the figure, when the prepared nanoparticles are compared with the standard hexagonal NaYF4, each diffraction peak corresponds to the other, indicating that the prepared nanoparticles belong to the standard hexagonal phase structure. The standard PDF card used is β-NaYF4 (JCPDS: 16-0334).

[0033] Figure 6 The figure shows the energy level transition diagrams of NaYF4@NaErF4:Yb,Tm@NaYF4:Yb@NaYF4 nanomaterials under excitation at 980 nm and 1532 nm. As can be seen from the figure, this nanomaterial uses NaYF4 as both the passivation core and the outermost passivation shell, with NaErF4 as the matrix sequentially coated between the two passivation layers, and Yb introduced into the matrix. 3+ As a sensitizing ion and Tm 3+ The invention utilizes an active shell at the energy trapping center and a NaYF4:Yb sublattice shell to effectively reduce energy loss by employing a NaYF4 passivated core and passivated shell, allowing energy to be recycled between the first and second shells as much as possible, and through Yb... 3+ Energy transfer, Yb 3+ For Er 3+ Energy return transfer and Tm 3+ The energy trapping center acts as an energy-harvesting center, enabling the acquisition of Er under excitation at 980 nm and 1532 nm. 3+ The emitted 654 nm high-intensity red upconversion emission light.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A nanomaterial that achieves red upconversion luminescence through energy modulation, characterized in that, Its chemical formula is NaYF4@NaErF4:xYb,1%Tm@NaYF4:yYb@NaYF4. Its structure consists of a NaYF4 core, which is sequentially coated with a NaErF4:xYb,1%Tm shell, a NaYF4:yYb shell, and a NaYF4 outer layer. Among them, x and y satisfy 0 ≤ x ≤ 49% and 10% ≤ y ≤ 80%, respectively.

2. The nanomaterial for obtaining red upconversion luminescence through energy modulation according to claim 1, characterized in that, The value of x is 49%, and the value of y is 80%.

3. The nanomaterial for obtaining red upconversion luminescence through energy modulation according to claim 1, characterized in that, The nanomaterial has a particle size of 21.81-23.91 nm.

4. The application of the nanomaterial described in claim 1, which obtains red upconversion luminescence through energy modulation, as a luminescent material in the field of bioimaging.

5. A method for preparing nanomaterials that exhibit red upconversion luminescence through energy modulation according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Yttrium source, erbium source, ytterbium source and thulium source were mixed with oleic acid and octadecene respectively, and heated to react to obtain yttrium-oleic acid chelate, erbium-oleic acid chelate, ytterbium-oleic acid chelate and thulium-oleic acid chelate respectively; (2) Preparation of NaYF4 core layer: After cooling the yttrium-oleic acid chelate, sodium source and fluorine source were added, and the reaction was carried out under an inert atmosphere to obtain NaYF4 nanoparticles; (3) Preparation of NaErF4:xYb,1%Tm shell: Oleic acid, octadecene and erbium-oleic acid chelate, ytterbium-oleic acid chelate, thulium-oleic acid chelate are mixed evenly, and the NaYF4 nanoparticles, sodium source and fluorine source are added. The reaction is carried out under an inert atmosphere to obtain NaYF4@NaErF4:xYb,1%Tm core-shell structured nanoparticles; (4) Preparation of NaYF4:yYb shell: Oleic acid, octadecene and yttrium-oleic acid chelate and ytterbium-oleic acid chelate are mixed evenly, and the NaYF4@NaErF4:xYb,1%Tm core-shell structured nanoparticles, sodium source and fluorine source are added. The reaction is carried out under an inert atmosphere to obtain NaYF4@NaErF4:xYb,1%Tm@NaYF4:yYb core-shell-shell structured nanoparticles; (5) Preparation of the outer layer of NaYF4: The NaYF4@NaErF4:xYb,1%Tm@NaYF4:yYb core-shell-shell structured nanoparticles and yttrium-oleic acid chelate are mixed evenly, sodium source and fluorine source are added, and the reaction is carried out under an inert atmosphere to obtain the red upconversion luminescent nanomaterial with the NaYF4@NaErF4:xYb,1%Tm@NaYF4:yYb@NaYF4 core-shell-shell-shell structure obtained by energy modulation.

6. The preparation method according to claim 5, characterized in that, The yttrium source is yttrium chloride; the erbium source is erbium chloride; the ytterbium source is ytterbium chloride; the thulium source is thulium chloride; the sodium source is sodium hydroxide; and the fluorine source is ammonium fluoride.

7. The preparation method according to claim 5, characterized in that, In one or more steps of steps (2)-(5), the reaction temperature for heating the reaction under an inert atmosphere is 280-305℃ and the reaction time is 0.9-1.6h.

8. The preparation method according to claim 5, characterized in that, The inert atmosphere is a nitrogen atmosphere.

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