Up-conversion material for improving fluorescence intensity through neutron irradiation as well as preparation method and application of up-conversion material

Abstract

The invention relates to the field of luminescent materials, in particular to an up-conversion material for improving fluorescence intensity through neutron irradiation and a preparation method and application of the up-conversion material. The chemical expression of the up-conversion material is NaLuF4: xYb, yTm, wherein the molar ratio of Lu to Yb to Tm is 50: 49: 1, x is equal to 0.49, and y is equal to 0.01. The neutron irradiation technology is introduced into a NaLuF4: 49% Yb, 1% Tm up-conversion material system, so that the luminescence property is remarkably enhanced, and the radiation resistance is greatly improved. After neutron irradiation, blue, purple and near-infrared multiband up-conversion luminescence of the material is obviously enhanced, and after the material bears a hundred-year accumulated irradiation dose equivalent to a space station, the optical performance is improved instead of being reduced, so that the material has important breakthrough significance.

Description

Technical Field

[0001] This invention relates to the field of luminescent materials, specifically to an upconversion material whose fluorescence intensity is enhanced by neutron irradiation, its preparation method, and its application. Background Technology

[0002] Upconversion luminescence is an anti-Stokes luminescence process, referring to the process by which a material, under excitation by low-energy photons (such as near-infrared light), emits high-energy photons with wavelengths shorter than the excitation light wavelength through multiphoton absorption. Currently, the main material systems for achieving efficient upconversion luminescence are rare-earth ions (such as Er₂O₃). 3+ Tm 3+ Ho 3+ Inorganic compounds doped with (etc.). Due to their unique 4f electron transition characteristics, these materials have advantages such as long fluorescence lifetime, high photochemical stability, strong resistance to photobleaching, and good biocompatibility, and have been widely used in solid-state lasers, photovoltaic devices, three-dimensional displays, biofluorescent labeling and imaging, and other fields.

[0003] Currently, near-infrared lasers with a wavelength of 980 nm are commonly used as excitation sources to achieve deep tissue imaging and reduce photothermal damage. However, typical rare-earth upconversion luminescent materials (such as Er) 3+ Tm 3+ The activated system often produces multiple emission bands after excitation, covering the ultraviolet, visible and near-infrared regions, and the luminescence intensity is usually weak.

[0004] In recent years, high-energy particle irradiation (such as X-rays, gamma rays, and neutron beams) has been used to modulate the microstructure and optical properties of materials. Neutron irradiation, due to its neutrality, large mass, and strong penetrating power, can induce uniform lattice expansion, defects, or stress fields within materials, thereby altering the local crystal field environment, energy transfer paths, and nonradiative transition probabilities at the luminescence center. However, there are currently no reports on upconversion luminescent materials that can withstand extremely high flux neutron irradiation with significantly enhanced luminescence performance, especially with neutron fluxes above 10⁻⁶. 12 n / cm 2 Under these conditions, a system capable of achieving a more than 50-fold increase in the intensity of the 803 nm emission peak can be developed. Currently, there is a particular lack of stable materials whose luminescence intensity not only does not decrease but actually increases significantly after irradiation with doses equivalent to long-term space radiation (such as the equivalent neutron flux of a century in low Earth orbit). Such materials with an "irradiation-enhanced" effect can significantly improve their reliability in extreme radiation environments, meeting the stringent application requirements of aerospace (such as spacecraft displays, spaceborne optical systems, and space navigation terminals) and nuclear facilities (such as radiation dose detection). Therefore, developing a novel rare-earth-doped upconversion luminescent material that can maintain or even significantly increase its luminescence intensity after strong neutron irradiation has significant scientific and application value. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, the primary objective of this invention is to provide an upconversion material whose fluorescence intensity can be enhanced by neutron irradiation. After high-dose neutron irradiation, the near-infrared emission intensity of this material not only remains stable but also experiences a significant increase, thereby solving the problems of impure luminescence and insufficient intensity in existing upconversion materials.

[0006] The objective of this invention is achieved through the following technical solution: In a first aspect, the present invention provides an upconversion material for improving fluorescence intensity through neutron irradiation, the chemical formula of which is NaLuF4: xYb, yTm (x=0.49, y=0.01), wherein NaLuF4 is the matrix, and Yb... 3+ As a sensitizing ion, Tm 3+ To activate ions.

[0007] The molar ratio of Lu, Yb, and Tm is 50:49:1.

[0008] Preferably, the upconversion material is subjected to 10×10 12 n / cm 2 After neutron fluence irradiation, under 980 nm laser excitation, the intensity of its 803 nm emission peak can be increased by more than 50 times, and the blue-violet light emission is also enhanced.

[0009] Secondly, the present invention provides a method for preparing an upconversion material with enhanced fluorescence intensity through neutron irradiation, comprising the following steps: (1) Mix citric acid solution, sodium hydroxide solution and water evenly, add lutetium nitrate solution, ytterbium nitrate solution and thulium nitrate solution, mix evenly, then add sodium fluoride solution and water, mix evenly to form a turbid liquid; (2) The turbid liquid is subjected to hydrothermal reaction, and the turbid liquid after reaction is centrifuged to obtain a white precipitate. The white precipitate is washed and dried. At the same time, the sample is irradiated by neutron irradiation experiment to obtain the upconversion material with improved fluorescence intensity by neutron irradiation.

[0010] Preferably, the concentration of the citric acid solution is 1~3 mol·L⁻¹. -1 More preferably 2 mol·L -1 .

[0011] Preferably, the concentration of the sodium hydroxide solution is 3-5 mol·L⁻¹. -1 More preferably 4 mol·L -1 .

[0012] Preferably, the volume ratio of citric acid solution, sodium hydroxide solution and water is 1.5:1.25:17.5.

[0013] Citric acid is used as a chelating agent, and sodium hydroxide is used to adjust the pH of the solution.

[0014] Preferably, the preparation process of lutetium nitrate solution involves dissolving lutetium oxide (99.99%) in 30% dilute nitric acid; the preparation process of ytterbium nitrate solution involves dissolving ytterbium oxide (99.99%) in 30% dilute nitric acid; and the preparation process of thulium nitrate solution involves dissolving thulium oxide (99.99%) in 30% dilute nitric acid.

[0015] Preferably, the concentration of the lutetium nitrate solution is 1 mol·L⁻¹. -1 The concentration of the ytterbium nitrate solution is 0.5 mol·L⁻¹. -1 The concentration of the thulium nitrate solution is 0.1 mol·L⁻¹. -1 The volume ratio of lutetium nitrate solution, ytterbium nitrate solution, and thulium nitrate solution is 25:49:5. Preferably, the concentration of the sodium fluoride solution is 1 mol·L⁻¹. -1 .

[0016] Preferably, the volume ratio of lutetium nitrate solution, ytterbium nitrate solution, sodium fluoride solution and water is 25:49:400:875.

[0017] Preferably, the cumulative absorbed neutron flux of the sample reaches 6 × 10⁻⁶. 12 n / cm 2 8×10 12 n / cm 2 10×10 12 n / cm 2 and 12×10 12 n / cm 2 .

[0018] Preferably, the optimal cumulative absorbed neutron flux of the sample is 10 × 10⁻⁶. 12 n / cm 2 .

[0019] Preferably, the water is deionized water.

[0020] Preferably, the hydrothermal reaction is carried out at 200 °C for 10 h.

[0021] Preferably, the centrifugation is performed at 10,000 rpm for 5 minutes, the washing method is to wash with deionized water and alcohol in sequence, and the drying method is preferably to dry at 60 °C for 24 hours.

[0022] Preferably, the neutron flux rate is set to 1×10⁻⁶. 8 n / cm2 ·s.

[0023] Preferably, the neutron irradiation time is 6 × 10⁻⁶ times. 4 seconds, 8×10 4 seconds, 10×10 4 seconds and 12×10 4 Irradiation experiments of different durations per second.

[0024] Preferably, the neutron irradiation flux is 6 × 10⁻⁶. 12 ~ 12×10 12 n / cm 2 .

[0025] Thirdly, this invention provides an application of an upconversion material that enhances fluorescence intensity through neutron irradiation in solar cells, aerospace, and nuclear facilities.

[0026] For example, materials with "irradiation-enhanced" properties can significantly improve their reliability in extreme radiation environments, meeting the stringent application requirements in the aerospace field (such as spacecraft displays, spaceborne optical systems, and space navigation terminals) and inside nuclear facilities (such as radiation dose detection).

[0027] The beneficial effects of this invention are as follows: 1. This invention introduces neutron irradiation technology into the NaLuF4:49%Yb,1%Tm upconversion material system, achieving a significant enhancement in luminescence performance and a substantial improvement in radiation resistance. After neutron irradiation, the material exhibits markedly enhanced upconversion luminescence in multiple bands, including blue, violet, and near-infrared. Furthermore, after enduring an irradiation dose equivalent to a century of cumulative radiation exposure on a space station, its optical performance does not decrease but rather increases, representing a significant breakthrough.

[0028] 2. The preparation process of this invention is simple, employing a hydrothermal synthesis method. Citric acid is used as a chelating agent, and sodium hydroxide is used to adjust the pH. High-performance phosphors can be obtained by controlling the ion ratio. This method has low equipment cost, is easy to operate, environmentally friendly, and has a short cycle time, making it suitable for large-scale production.

[0029] 3. The material of this invention emits high-intensity near-infrared light and blue-violet light under 980 nm excitation, and can be used in optical devices in extreme radiation environments such as spacecraft displays, spaceborne optical systems, and space navigation terminals.

[0030] 4. The material of this invention exhibits excellent neutron radiation stability; after being exposed to radiation equivalent to a century's cumulative dose from a space station, its luminescence performance does not decrease but rather increases significantly. This invention is applicable to radiation stability display and communication in the aerospace field, as well as radiation detection and monitoring in nuclear facilities. Attached Figure Description

[0031] 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.

[0032] Figure 1 The upconversion spectra of the upconversion phosphors prepared in Examples 1-5 under 980 nm laser excitation are shown in thumbnail (magnified fluorescence spectra in the 420-520 nm range).

[0033] Figure 2 The integral intensity of the near-infrared emission band under 980 nm excitation varies with neutron irradiation dose, and is normalized with the pre-irradiation intensity as a reference (relative intensity = 1).

[0034] Figure 3 Comparison of UV-Vis absorption spectra of Examples 1 and 4.

[0035] Figure 4 X-ray diffraction patterns of the upconversion phosphors prepared in Examples 1-5.

[0036] Figure 5 The main diffraction peaks of the upconversion phosphors prepared in Examples 1-5 are shown; the black vertical lines represent the standard diffraction peaks of β-NaLuF4 (JCPDS 27-0726).

[0037] Figure 6 The X-ray photoelectron spectra are those of Examples 1 and 4.

[0038] Figure 7 Scanning electron microscope images of the upconversion phosphors prepared in Examples 1-5; (a) Example 1; (b) Example 2; (c) Example 3; (d) Example 4; (e) Example 5.

[0039] Figure 8 In the diagram, (a) and (b) are schematic diagrams of lattice expansion caused by neutron irradiation; (c) is a diagram of Yb 3+ and Tm 3+ Energy level diagram and schematic diagram of upconversion luminescence mechanism under 980 nm excitation. Detailed Implementation

[0040] The technical solution of the present invention is illustrated below through specific examples. It should be understood that the one or more method steps mentioned in the present invention do not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps; it should also be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention. Furthermore, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or defining the scope of the present invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the present invention.

[0041] To better understand the above technical solutions, exemplary embodiments of the present invention are described in more detail below. While exemplary embodiments of the present invention are shown, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the invention to those skilled in the art.

[0042] The present invention will be further described below with reference to the following embodiments.

[0043] Example 1 A rare-earth-doped upconversion luminescent material, the preparation process of which includes: 1.5 mL of 2 mol·L⁻¹ -1 Citric acid solution, 1.25 mL, concentration 4 mol·L⁻¹ -1 Mix sodium hydroxide solution and 5 mL of deionized water, stir for 30 minutes, and then add 0.5 mL of 1 mol·L⁻¹ sodium hydroxide solution sequentially. -1 A lutetium nitrate solution, 0.98 mL, concentration 0.5 mol·L⁻¹ -1 A ytterbium nitrate solution, 0.1 mL of which has a concentration of 0.1 mol·L⁻¹ -1 A thulium nitrate solution was stirred for 30 minutes, and then 8 mL of a 1 mol·L⁻¹ solution was added. -1 A sodium fluoride solution and 12.5 mL of deionized water were mixed and stirred for 30 minutes to form a milky white turbid liquid. The turbid liquid was transferred to the white liner of a stainless steel reactor, sealed, and placed in an oven for hydrothermal reaction at 200°C for 10 hours. The resulting turbid liquid was centrifuged at 10,000 rpm for 5 minutes to obtain a white precipitate. The white precipitate was washed successively with deionized water and alcohol, and dried at 60°C for 24 hours to obtain the upconversion phosphor (unirradiated sample).

[0044] Example 2 An upconversion material whose fluorescence intensity is enhanced by neutron irradiation, the preparation process of which includes: 1.5 mL of 2 mol·L⁻¹ -1 Citric acid solution, 1.25 mL, concentration 4 mol·L⁻¹ -1 Mix sodium hydroxide solution and 5 mL of deionized water, stir for 30 minutes, and then add 0.5 mL of 1 mol·L⁻¹ sodium hydroxide solution sequentially. -1 A lutetium nitrate solution, 0.98 mL, concentration 0.5 mol·L⁻¹ -1 A ytterbium nitrate solution, 0.1 mL of which has a concentration of 0.1 mol·L⁻¹ -1 A thulium nitrate solution was stirred for 30 minutes, and then 8 mL of a 1 mol·L⁻¹ solution was added. -1 A sodium fluoride solution and 12.5 mL of deionized water were mixed and stirred for 30 minutes to form a milky white turbid liquid. The turbid liquid was transferred to the white liner of a stainless steel reactor, sealed, and placed in an oven for hydrothermal reaction at 200°C for 10 hours. The resulting turbid liquid was centrifuged at 10,000 rpm for 5 minutes to obtain a white precipitate. The white precipitate was washed sequentially with deionized water and alcohol, and dried at 60°C for 24 hours to obtain the upconversion phosphor. The neutron flux was set to 1 × 10⁻⁶. 8 n / cm 2 ·s, performed 6×10 4 The experiment with irradiation duration of s yielded a total neutron fluence of 6 × 10⁻⁶ for the samples. 12 n / cm 2 This yields an upconversion material (6×10⁻⁶) whose fluorescence intensity is enhanced by neutron irradiation. 12 n / cm 2 ).

[0045] Example 3 An upconversion material whose fluorescence intensity is enhanced by neutron irradiation, the preparation process of which includes: 1.5 mL of 2 mol·L⁻¹ -1 Citric acid solution, 1.25 mL, concentration 4 mol·L⁻¹ -1 Mix sodium hydroxide solution and 5 mL of deionized water, stir for 30 minutes, and then add 0.5 mL of 1 mol·L⁻¹ sodium hydroxide solution sequentially. -1 A lutetium nitrate solution, 0.98 mL, concentration 0.5 mol·L⁻¹ -1 A ytterbium nitrate solution, 0.1 mL of which has a concentration of 0.1 mol·L⁻¹ -1 A thulium nitrate solution was stirred for 30 minutes, and then 8 mL of a 1 mol·L⁻¹ solution was added. -1A sodium fluoride solution and 12.5 mL of deionized water were mixed and stirred for 30 minutes to form a milky white turbid liquid. The turbid liquid was transferred to the white liner of a stainless steel reactor, sealed, and placed in an oven for hydrothermal reaction at 200°C for 10 hours. The resulting turbid liquid was centrifuged at 10,000 rpm for 5 minutes to obtain a white precipitate. The white precipitate was washed sequentially with deionized water and alcohol, and dried at 60°C for 24 hours to obtain the upconversion phosphor. The neutron flux was set to 1 × 10⁻⁶. 8 n / cm 2 ·s, performed 8×10 4 The experiment with irradiation duration of s yielded a total neutron fluence of 8 × 10⁻⁶ for the samples. 12 n / cm 2 This yields an upconversion material (8×10⁻⁶) whose fluorescence intensity is enhanced by neutron irradiation. 12 n / cm 2 ).

[0046] Example 4 An upconversion material whose fluorescence intensity is enhanced by neutron irradiation, the preparation process of which includes: 1.5 mL of 2 mol·L⁻¹ -1 Citric acid solution, 1.25 mL, concentration 4 mol·L⁻¹ -1 Mix sodium hydroxide solution and 5 mL of deionized water, stir for 30 minutes, and then add 0.5 mL of 1 mol·L⁻¹ sodium hydroxide solution sequentially. -1 A lutetium nitrate solution, 0.98 mL, concentration 0.5 mol·L⁻¹ -1 A ytterbium nitrate solution, 0.1 mL of which has a concentration of 0.1 mol·L⁻¹ -1 A thulium nitrate solution was stirred for 30 minutes, and then 8 mL of a 1 mol·L⁻¹ solution was added. -1 A sodium fluoride solution and 12.5 mL of deionized water were mixed and stirred for 30 minutes to form a milky white turbid liquid. The turbid liquid was transferred to the white liner of a stainless steel reactor, sealed, and placed in an oven for hydrothermal reaction at 200°C for 10 hours. The resulting turbid liquid was centrifuged at 10,000 rpm for 5 minutes to obtain a white precipitate. The white precipitate was washed sequentially with deionized water and alcohol, and dried at 60°C for 24 hours to obtain the upconversion phosphor. The neutron flux was set to 1 × 10⁻⁶. 8 n / cm 2 ·s, performed 10×10 4 The experiment with irradiation duration of s yielded a total neutron fluence of 10 × 10⁻⁶ for the samples. 12 n / cm 2 This yields an upconversion material (10 × 10⁻⁶) whose fluorescence intensity is enhanced by neutron irradiation. 12 n / cm2 ).

[0047] Example 5 An upconversion material whose fluorescence intensity is enhanced by neutron irradiation, the preparation process of which includes: 1.5 mL of 2 mol·L⁻¹ -1 Citric acid solution, 1.25 mL, concentration 4 mol·L⁻¹ -1 Mix sodium hydroxide solution and 5 mL of deionized water, stir for 30 minutes, and then add 0.5 mL of 1 mol·L⁻¹ sodium hydroxide solution sequentially. -1 A lutetium nitrate solution, 0.98 mL, concentration 0.5 mol·L⁻¹ -1 A ytterbium nitrate solution, 0.1 mL of which has a concentration of 0.1 mol·L⁻¹ -1 A thulium nitrate solution was stirred for 30 minutes, and then 8 mL of a 1 mol·L⁻¹ solution was added. -1 A sodium fluoride solution and 12.5 mL of deionized water were mixed and stirred for 30 minutes to form a milky white turbid liquid. The turbid liquid was transferred to the white liner of a stainless steel reactor, sealed, and placed in an oven for hydrothermal reaction at 200°C for 10 hours. The resulting turbid liquid was centrifuged at 10,000 rpm for 5 minutes to obtain a white precipitate. The white precipitate was washed sequentially with deionized water and alcohol, and dried at 60°C for 24 hours to obtain the upconversion phosphor. The neutron flux was set to 1 × 10⁻⁶. 8 n / cm 2 ·s, performed 12×10 4 The experiment with irradiation duration of s yielded a total neutron fluence of 12 × 10⁻⁶ for the samples. 12 n / cm 2 This yields an upconversion material (12×10⁻⁶) whose fluorescence intensity is enhanced by neutron irradiation. 12 n / cm 2 ).

[0048] Experimental Analysis: The fluorescence intensity of the rare earth-doped upconversion luminescent materials prepared in Examples 1-5 under 980 nm excitation was analyzed using a fluorescence spectrometer (the thumbnail shows the magnified fluorescence spectrum range of 420-520 nm). Figure 2 This is a comparison of the relative fluorescence intensity enhancement of the rare-earth-doped upconversion luminescent materials in Examples 1-5. Figure 3 The UV-Vis absorption spectra of Experimental Examples 1 and 4 are shown, and the results are as follows: Figure 1 , 2 As shown in Figure 3, the 803 nm emission band exhibits a significant dose-dependent evolution with increasing neutron flux. Specifically, as the neutron flux increases from 0 to 10 × 10⁻⁶, the emission band changes with increasing neutron flux. 12 n / cm 2(Example 4) At that time, the fluorescence intensity of the 803 nm peak showed a monotonically increasing trend, and at 10 × 10 12 n / cm 2 It reached its maximum value, approximately 52 times stronger than before irradiation. When the flux was further increased to 12 × 10⁻⁶... 12 n / cm 2 (Example 5) shows that the fluorescence intensity at 803 nm is higher than that at 10 × 10⁻⁶. 12 n / cm 2 The peak value decreased, dropping to a relative intensity of about 50. Figure 3 The absorption spectra of Examples 1 and 4 in the wavelength range of 700-1700 nm are shown. The results indicate that in the region near 980 nm, the absorbance of the rare-earth-doped upconversion luminescent material of Example 4 is significantly stronger than that of the unirradiated upconversion luminescent material of Example 1, which corresponds to the photoluminescence (PL) spectrum. Figure 1 Consistent.

[0049] The phase composition of the rare-earth-doped upconversion luminescent materials prepared in Examples 1–5 was analyzed by X-ray diffraction (XRD), and the chemical states and composition of the upconversion luminescent materials in Examples 1 and 4 were further analyzed by X-ray photoelectron spectroscopy (XPS). The results are as follows: Figure 4-6 As shown. Figure 4 The diffraction peaks of Examples 1-5 are sharp and free of impurity peaks, indicating that the samples have high crystallinity, excellent structural integrity, and no other phases or impurities have been introduced (the diffraction peak characteristics perfectly match those of pure β-NaLuF4, eliminating the interference of multiphase mixing). The X-ray diffraction patterns are consistent with the standard card of hexagonal NaLuF4 (β-NaLuF4), indicating that the material has a hexagonal phase structure. Figure 5 The leftward shift of the diffraction peaks observed by XRD directly proves that the cell parameters systematically increase with increasing irradiation dose, i.e., lattice expansion has occurred. Figure 6 The results in the figure show that, after neutron irradiation, the 4d spectra of Yb and Lu in the upconversion luminescent material of Example 4 show that, in the 4d spectra of Yb, the 4d spectra of Lu are... 5 / 2 (186.38 eV) and Lu 4d 3 / 2 The binding energy of (207.58 eV) is compared to that of the unirradiated sample (Yb 4d) in Example 1. 5 / 2 185.88 eV; Lu 4d 3 / 2 206.98 eV) shows a positive shift ( Figure 6 The XPS peaks of the Yb and Lu 4d orbitals shift towards higher binding energies, with a maximum shift of 0.6 eV. This indicates that Yb 3+ and Lu 3 +The decrease in local electron density of ions confirms the change in local electronic environment and the reduction in crystal field symmetry. The uniform lattice distortion reduces the crystal field symmetry around rare earth ions, thereby partially lifting the transition ban and effectively improving the upconversion luminescence intensity.

[0050] The morphology of the upconversion materials prepared in Examples 1-5 was analyzed using transmission electron microscopy, and the results are as follows: Figure 7 As shown in the image, scanning electron microscopy (SEM) images reveal that the synthesized powder consists of micron-sized particles with uniform elemental distribution. In Examples 1-5, the materials maintained a consistent short hexagonal prism morphology, and the average particle size and thickness did not change significantly under different irradiation doses. Specifically, the unirradiated sample had an average particle size of 3.27 μm and a thickness of 0.95 μm; after a neutron flux of 6 × 10⁻⁶, the sample was... 12 n / cm 2 The irradiated upconversion luminescent material has an average particle size of 3.28 μm and a thickness of 0.91 μm; at a flux of 8 × 10⁻⁶ μm... 12 n / cm 2 At this point, the average particle size of the corresponding sample was 3.44 μm, and the thickness was 0.97 μm; at the optimal injection rate of 10 × 10⁻⁶, 12 n / cm 2 Under these conditions, the average particle size of the material increased to 3.76 μm, and the thickness was 0.89 μm; even at the highest injection rate of 12 × 10⁻⁶ μm, the average particle size of the material increased to 3.76 μm, and the thickness was 0.89 μm. 12 n / cm 2 Under these conditions, the material size remained stable, with an average particle size of 3.55 μm and a thickness of 0.83 μm. Comprehensive analysis confirmed that neutron irradiation did not cause significant morphological changes in the material, demonstrating its good structural stability and radiation resistance.

[0051] Figure 8 (a) and (b) are schematic diagrams of neutron irradiation-induced lattice expansion drawn based on the above experimental results. Figure 8 (c) Upconversion energy level transition diagrams of NaLuF4:49%Yb,1%Tm prepared in Examples 1-5 under 980 nm excitation. Figure 8 As shown in (a) and (b), neutron irradiation provides an effective way to induce controllable lattice distortion. Neutron irradiation has excellent penetrating power and can induce uniform lattice distortion. Under neutron irradiation, the increased interatomic distance leads to the weakening of covalent / ionic bonds, while the shielding effect of valence electrons on the atomic nucleus is weakened, thus forming an asymmetric coordination environment. The uniform lattice distortion reduces the symmetry of the crystal field around rare earth ions, thereby breaking the transition forbidden zone and effectively enhancing the upconversion luminescence intensity. Figure 8 (c) Demonstrates Yb under 980 nm excitation 3+ With Tm 3+ Energy level distribution, energy transfer pathways, and characteristic emission transition mechanisms of ions. Yb3+ The ion first absorbs a 980 nm photon, from its ground state. 2 F 7 / 2 Energy level transition to excited state 2 F 5 / 2 Energy level; then, energy is transferred to Tm through a three-step continuous energy transfer (ET) process. 3+ Ions, causing them to be excited sequentially to 3 H5 3 F 2,3 and 1 G4 and other high-energy levels. Tm 3+ Ions produce characteristic emission through radiative transitions: from 1 G4 level to ground state 3 The H6 energy level transition corresponds to blue light emission at 475 nm; from 1 D2 level towards 3 The F4 energy level transition produces 450 nm emission; from 3 H4 energy level towards 3 The H6 level transition induces near-infrared (NIR) emission at 803 nm.

[0052] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. The illustrative expressions of the above terms in this specification should not be construed as necessarily referring to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0053] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. An upconversion material whose fluorescence intensity is enhanced by neutron irradiation, characterized in that, The chemical formula for the upconversion material is NaLuF4:xYb,yTm; where the molar ratio of Lu, Yb, and Tm is 50:49:1, x=0.49, and y=0.

01.

2. The upconversion material for improving fluorescence intensity by neutron irradiation according to claim 1, characterized in that, The upconversion material is subjected to 10×10 12 n / cm 2 After neutron fluence irradiation, the intensity of its 803 nm emission peak can be increased by more than 50 times under 980 nm laser excitation.

3. A method for preparing an upconversion material with enhanced fluorescence intensity via neutron irradiation as described in claim 1, characterized in that, Includes the following steps: (1) Mix citric acid solution, sodium hydroxide solution and water evenly, add lutetium nitrate solution, ytterbium nitrate solution and thulium nitrate solution, mix evenly, then add sodium fluoride solution and water, mix evenly to form a turbid liquid; (2) The turbid liquid is subjected to hydrothermal reaction, and the turbid liquid after reaction is centrifuged to obtain a white precipitate. The white precipitate is washed and dried. At the same time, the sample is irradiated by neutron irradiation experiment to obtain the upconversion material with improved fluorescence intensity by neutron irradiation.

4. The method for preparing upconversion materials with enhanced fluorescence intensity via neutron irradiation according to claim 3, characterized in that, The concentration of the citric acid solution is 1~3 mol·L⁻¹ -1 The concentration of the sodium hydroxide solution is 3-5 mol·L⁻¹. -1 The volume ratio of citric acid solution, sodium hydroxide solution, and water is 1.5:1.25:17.

5.

5. The method for preparing upconversion materials with enhanced fluorescence intensity by neutron irradiation according to claim 3, characterized in that, The preparation process of lutetium nitrate solution involves dissolving lutetium oxide in 30% dilute nitric acid; the preparation process of ytterbium nitrate solution involves dissolving ytterbium oxide in 30% dilute nitric acid; the preparation process of thulium nitrate solution involves dissolving thulium oxide in 30% dilute nitric acid.

6. The method for preparing upconversion materials with enhanced fluorescence intensity via neutron irradiation according to claim 3, characterized in that, The concentration of the lutetium nitrate solution is 1 mol·L⁻¹. -1 The concentration of the ytterbium nitrate solution is 0.5 mol·L⁻¹. -1 The concentration of the thulium nitrate solution is 0.1 mol·L⁻¹. -1 The volume ratio of lutetium nitrate solution, ytterbium nitrate solution, and thulium nitrate solution is 25:49:

5.

7. The method for preparing upconversion materials with enhanced fluorescence intensity via neutron irradiation according to claim 3, characterized in that, The concentration of the sodium fluoride solution is 1 mol·L⁻¹. -1 The volume ratio of lutetium nitrate solution, ytterbium nitrate solution, sodium fluoride solution, and water is 25:49:400:

875.

8. The method for preparing upconversion materials with enhanced fluorescence intensity by neutron irradiation according to claim 3, characterized in that, The cumulative absorbed neutron fluence of the samples reached 6 × 10⁻⁶. 12 n / cm 2 8×10 12 n / cm 2 10×10 12 n / cm 2 and 12×10 12 n / cm 2 The neutron flux rate is set to 1×10⁸ n / cm²·s.

9. The method for preparing an upconversion material with enhanced fluorescence intensity via neutron irradiation according to claim 3, characterized in that, The preferred conditions for the hydrothermal reaction are 200 °C for 10 h.

10. The application of the upconversion material of claim 1, which enhances fluorescence intensity through neutron irradiation, in solar cells, aerospace, and nuclear facilities.

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