A rare earth doped photochromic material, and a preparation method and application thereof

Abstract

The application discloses a rare earth doped photochromic material and a preparation method and application thereof, and belongs to the technical field of inorganic photochromic materials. The application solves the problem of the complex process of the organic photochromic material in the prior art, the difficulty in realizing industrial application, and the poor photochromic effect and poor color fading reversibility of nano tungsten trioxide. The photochromic material has a chemical composition as shown in the following formula (1): WO3:xRe,yM formula (1), wherein Re is a rare earth element, M is selected from at least one of redox metal ions, x represents the mole fraction of the Re element, and the value range is 0 < x <= 0.5, and y represents the mole fraction of M, and the value range is 0 <= y <= 0.05. Based on the surface defect construction and the energy transfer between the rare earth luminescent ions and the tungsten trioxide, the photochromic performance of the material is greatly improved. The application has the advantages of fast response speed, high color difference value, and simple and controllable preparation process.

Description

Technical Field

[0001] This invention relates to the field of inorganic photochromic materials technology, and in particular to a rare earth-doped photochromic material, its preparation method, and its application. Background Technology

[0002] Photochromic materials are a class of stimulus-responsive smart materials that undergo reversible photochemical reactions under the stimulation of specific wavelengths of light, resulting in different color changes. They are widely used in anti-counterfeiting encryption, optical sensing, color-changing fibers, and smart windows. Photochromic materials are generally classified into organic and inorganic types based on their chemical composition. Organic photochromic materials are diverse, mainly including diarylethylene, azobenzene, spiropyran, and ursolic anhydride. Their advantages lie in their fast photochromic response and good reversibility. However, organic materials have complex preparation processes, are not heat-resistant, and are prone to photobleaching, making industrial application difficult. In contrast, inorganic photochromic materials have simple preparation processes, good chemical stability, and are not prone to photobleaching, thus attracting market attention and favor.

[0003] Nano-tungsten oxide is a promising inorganic photochromic material. When stimulated by ultraviolet light, the surface of the nanomaterial undergoes a redox reaction, exhibiting photochromic properties. The crystal form and surface defects of nano-tungsten oxide significantly influence its photochromic performance. However, conventional nano-tungsten oxide exhibits a slow response to ultraviolet light, low color difference before and after photochromism, and poor reversibility of fading, severely limiting its practical application. Summary of the Invention

[0004] In view of the above, the present invention aims to provide a rare earth-doped photochromic material and its preparation method and application, so as to solve at least one of the problems existing in the prior art: (1) Traditional organic photochromic materials have complex processes, limited application scenarios and are difficult to realize industrial application; (2) Conventional inorganic photochromic materials, such as nano tungsten oxide, have a slow response to ultraviolet light, and the color difference value of the material before and after photochromism is low, and the fading reversibility is poor, which seriously limits the practical application.

[0005] The objective of this invention is mainly achieved through the following technical solutions:

[0006] The first aspect of this invention provides a rare-earth-doped photochromic material having a chemical composition as shown in formula (1): WO3: xRe, yM (1) Among them, Re is a rare earth element, and M is selected from at least one of redox metal ions; x represents the molar fraction of the Re element in formula (1), and its value range is 0 < x ≤ 0.5, and y represents the molar fraction of M in formula (1), and its value range is 0 ≤ y ≤ 0.05.

[0007] Further, 0.05 ≤ x ≤ 0.3, 0.005 ≤ y ≤ 0.02.

[0008] Further, the rare earth element is selected from at least one of Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0009] Further, the redox metal ion is selected from at least one of Ag, Cr, Cu, Mn, and Fe.

[0010] Further, the rare earth element is selected from at least one of Eu, Tb, Sm, and Ce.

[0011] Further, M is at least one of Cu or Fe.

[0012] The second aspect of the present invention provides a photochromic film, including the photochromic material described in the first aspect.

[0013] Further, the film is used for window glass, building curtain wall glass, or optical anti-counterfeiting elements.

[0014] The third aspect of the present invention provides a method for preparing the photochromic material described in the first aspect, including the following steps: S1. In the presence of a complexing agent, raw materials containing a W source, a Re source, and a M source are mixed in water to form a precursor solution; S2. Under light-shielded conditions, the pH value of the precursor solution is adjusted to 0.5 - 2 to obtain an acidic precursor solution; S3: The acidic precursor solution obtained in step S2 is subjected to a hydrothermal reaction, and the hydrothermal reaction product is separated to obtain the photochromic material.

[0015] Further, the temperature of the hydrothermal reaction is 80 - 300 °C, and the time is 12 - 48 h.

[0016] Further, the W source is selected from at least one of sodium tungstate, ammonium tungstate, and tungsten hexachloride.

[0017] Further, the Re source is selected from compounds containing at least one element of Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0018] Furthermore, the M source is selected from compounds containing at least one element selected from Ag, Cr, Cu, Mn and Fe.

[0019] Furthermore, the complexing agent is selected from at least one of oxalic acid, tartaric acid, and citric acid.

[0020] Furthermore, the W source is selected from sodium tungstate and / or ammonium tungstate.

[0021] Furthermore, the Re source is selected from at least one of europium nitrate, samarium nitrate, or terbium nitrate.

[0022] Furthermore, the M source is selected from ferric chloride and / or copper chloride.

[0023] Furthermore, it also includes: step S4: washing and drying the solid phase after solid-liquid separation of the hydrothermal reaction product to obtain the photochromic material.

[0024] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: (1) This invention introduces rare earth ions into nano-tungsten trioxide, which on the one hand introduces defects on the material surface, which is conducive to the separation of electrons and holes, thereby enhancing the photochromic properties of the material; on the other hand, rare earth ions can absorb light, thereby constructing an energy transfer process from rare earth ions to tungsten trioxide nanoparticles, promoting the generation of electron-hole pairs, and further improving the photochromic properties of nano-tungsten trioxide. For example, after irradiation with 365nm ultraviolet light for 10 minutes, the color difference between the irradiated sample and the sample before irradiation is not less than 25.

[0025] (2) Based on the high color difference value obtained by rare earth doping, this invention further introduces a specific amount of redox metal ions M. The redox metal ions and rare earth ions Re produce a significant synergistic effect, which not only ensures that the obtained photochromic material is still at an excellent level of high color difference value (ΔE>30), but also significantly improves the fading rate and cycle reversibility of the material (24h reflection recovery rate>83%). It successfully overcomes the common performance trade-off problem between color-changing performance and fading reversibility in photochromic materials, and obtains a photochromic material with significantly improved comprehensive performance. Attached Figure Description

[0026] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0027] Figure 1 This is a transmission electron microscope (TEM) image of the photochromic material prepared in Example 1.

[0028] Figure 2Reflection spectra of the photochromic material prepared in Example 1 under different UV irradiation times.

[0029] Figure 3 Reflection spectra of the photochromic material prepared in Example 2 under different UV irradiation times.

[0030] Figure 4 Reflection spectra of the photochromic material prepared in Example 3 under different UV irradiation times.

[0031] Figure 5 Reflection spectra of the photochromic material prepared in Example 4 under different UV irradiation times.

[0032] Figure 6 Color difference values of the photochromic materials prepared in Comparative Example 1 and Examples 1 - 4 after UV irradiation.

[0033] Figure 7 Reflection spectra of the photochromic material prepared in Example 5 under different UV irradiation times.

[0034] Figure 8 Reflection spectra of the photochromic material prepared in Example 6 under different UV irradiation times.

[0035] Figure 9 Graph of reflectance change during natural fading of the photochromic materials prepared in Examples 1, 5, and 6 in a dark environment.

[0036] Figure 10 Transmittance of the film prepared from the photochromic material prepared in Example 1 before and after sunlight irradiation. Detailed implementation manners

[0037] The preferred embodiments of the present invention will be specifically described below in conjunction with the accompanying drawings, where the accompanying drawings form a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention.

[0038] Due to problems such as slow response to ultraviolet light and slow fading rate of conventional inorganic photochromic materials in the prior art, such as nano tungsten oxide, which severely limit practical applications, in the first aspect of the present invention, a rare earth - doped photochromic material is provided, having a chemical composition as shown in formula (1): WO3: xRe, yM Formula (1) Where Re is a rare earth element, M is selected from at least one of Ag, Cr, Cu, Mn, and Fe; x represents the molar fraction of the Re element in formula (1), with a value range of 0 < x ≤ 0.5, and y represents the molar fraction of M in formula (1), with a value range of 0 ≤ y ≤ 0.05.

[0039] In the present invention, by introducing rare earth ions into tungsten trioxide nanomaterials, on the one hand, it is possible to introduce defects on the material surface, which is beneficial to the separation of electrons and holes, thereby enhancing the photochromic performance of the material; on the other hand, rare earth ions can absorb light, thus constructing an energy transfer process from rare earth ions to tungsten trioxide nanoparticles, promoting the generation of electron-hole pairs, and further improving the photochromic performance of tungsten trioxide nanoparticles. In the present invention, under ultraviolet light excitation, the 4f electrons or 5d electrons of some rare earth ions (such as Eu 2+ , Ce 3+ ) of rare earth ions jump to the excited state. Subsequently, through a non-radiative energy transfer process, the excited state energy is transferred to the conduction band or defect energy level of WO3, promoting the generation and separation of electron-hole pairs. This process not only improves the light absorption efficiency of the material, but also further enhances the carrier migration and capture ability through the surface defect states introduced by rare earth doping, thereby increasing the color difference value of the photochromic material before and after color change.

[0040] Furthermore, when the value range of x satisfies 0 < x ≤ 0.5, it can ensure that the introduction amount of rare earth ions is sufficient to form an optimal density of active defect sites on the material surface and in the bulk phase, thereby improving its light excitation and charge separation efficiency on the premise of ensuring the stability of the basic structure of the material. When x is greater than 0.5, excessive rare earth ions are likely to agglomerate in the lattice, reducing the efficiency of energy transfer and the generation of electron-hole pairs; at the same time, too high doping amount will damage the main lattice structure of tungsten trioxide, resulting in a decrease in the crystallinity of the material and a deterioration of the phase stability, thereby damaging its basic photochromic performance and cycle life. If x is 0, the material is undoped pure tungsten trioxide or a system doped only with element M, and it is impossible to construct an energy transfer path from rare earth ions to tungsten trioxide, nor is it possible to introduce unique defect states through rare earth ions, and the photochromic performance of the material will be significantly reduced.

[0041] According to some embodiments of the present invention, 0.05 ≤ x ≤ 0.3, 0.005 ≤ y ≤ 0.02.

[0042] In this invention, the inventors discovered through numerous inventive experiments that when the range of x (mole fraction of Re) is further preferably 0.05≤x≤0.3, and the range of y (mole fraction of M) is further preferably 0.005≤y≤0.02, Re and M can produce a significant synergistic effect. That is, by introducing the above-mentioned specific types and amounts of rare earth ions Re into WO3, an efficient energy transfer and defect structure is constructed. At the same time, a specific amount of redox metal ions M is introduced. The rare earth ions and metal ions are sufficient to form a continuous and effective modification network in the matrix. This allows the final photochromic material to achieve excellent fading reversibility (e.g., 24h reflection recovery rate > 83%) while still maintaining a high color difference value (ΔE > 30), without significantly reducing the color difference value. This ensures an effective balance between the color-changing effect and the natural fading reversibility of the material.

[0043] For example, x can take values ​​of 0.05, 0.08, 0.1, 0.15, 0.2, 0.25, and 0.3, or any two of the above values, preferably 0.05-0.15. y can take values ​​of 0.005, 0.008, 0.01, 0.015, 0.02, or any two of the above values, preferably 0.005-0.015.

[0044] According to some embodiments of the present invention, considering that the rare earth element can participate in the light absorption and energy transfer process through the 4f or 5d energy level to improve the photochromic performance, the rare earth element is selected from at least one of Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. Furthermore, when the rare earth element is selected from at least one of Eu, Tb, Sm and Ce, and M is selected from at least one of Cu or Fe, it can synergistically enhance the photochromic performance with tungsten trioxide.

[0045] It should be noted that the photochromic material provided by this invention will undergo a significant change in appearance color under 300-380nm ultraviolet light irradiation. The appearance color can be reversibly restored by heat treatment or by placing it in the dark. When applied to car windows / window glass films, it can intelligently adjust the brightness of the light inside the car / indoors according to the intensity of sunlight, thereby creating a more comfortable driving environment.

[0046] It is understood that the heat treatment temperature is 80-120℃ and the time is 10-30 minutes.

[0047] A second aspect of the present invention provides a photochromic film, the photochromic film comprising the photochromic material described in the first aspect.

[0048] According to some embodiments of the present invention, the photochromic film can be prepared by the following method: (1) Weigh out polymethyl methacrylate (PMMA) and add it to dichloromethane (DCM), and stir until dissolved and clear; (2) Weigh out the photochromic material, grind it into powder, add it to N,N-dimethylformamide (DMF), and stir until uniform; (3) Mix the two solutions in step (1) and step (2) and stir evenly. Then pour the mixed solution into a mold and dry it at 40-50℃ for 1-2 hours to finally obtain a photochromic film.

[0049] In the mixture of PMMA and DCM, the concentration of PMMA is 0.02-0.15 g / mL, and the amount of photochromic material powder used ensures that the doping amount of photochromic material in the final photochromic film is 5-20 wt%. For example, the amount of polymethyl methacrylate can be 2-6 g, the amount of DCM can be 50-100 mL, and the amount of photochromic material powder can be 0.1-0.5 g. There are no requirements for the amount of DMF, as long as it is enough to dissolve the photochromic material; for example, it can be 1-3 mL.

[0050] In this invention, the thickness of the photochromic film is 0.1-0.3 mm.

[0051] According to some embodiments of the present invention, the film is used in vehicle window glass, building curtain wall glass, or optical anti-counterfeiting elements.

[0052] In this invention, the thin film morphology provides an ordered two-dimensional interface for the photochromic material, promoting efficient energy transfer of rare earth ions (Re) and rapid separation of photogenerated carriers. Simultaneously, the thin film facilitates the use of metal ions (M) as charge mediators to accelerate ion diffusion, thereby achieving a uniform, rapid, and reversible color-changing response at the device level. When applied to vehicle windows or curtain wall glass, the thin film dynamically adjusts light transmittance through light-driven color change, achieving passive intelligent shading and heat insulation. When applied to optical anti-counterfeiting components, its rapid and reversible color-changing characteristics encode visible information, providing dynamic anti-counterfeiting functionality.

[0053] A third aspect of the present invention provides a method for preparing the photochromic material described in the first aspect, comprising the following steps: S1. In the presence of a complexing agent, raw materials containing W source, Re source and M source are mixed in water to form a precursor solution; S2. Under light-protected conditions, adjust the pH value of the precursor solution to 0.5-2 to obtain an acidic precursor solution; S3: The acidic precursor solution obtained in step S2 is subjected to a hydrothermal reaction, and the hydrothermal reaction products are separated to obtain the photochromic material.

[0054] In this invention, the preparation method ensures that the precursor is uniformly mixed at the molecular level in the solution by coexisting W, Re and M sources in a hydrothermal system and using a complexing agent to inhibit premature precipitation of metal ions.

[0055] Furthermore, by precisely adjusting the pH of the precursor solution to a strongly acidic range (0.5-2), the metal ions were made to exist stably in the form of cations. Under subsequent hydrothermal conditions, they were simultaneously hydrolyzed, condensed, and crystallized, achieving in-situ and uniform doping of rare earth ions (Re) and redox metal ions (M) in the WO3 lattice. This directly constructed the energy transfer interface from Re to WO3 and the charge transport channel involving M ions, significantly improving the photochromic performance of the photochromic material.

[0056] According to some embodiments of the present invention, the temperature of the hydrothermal reaction is 80-300°C and the time is 12-48h.

[0057] In this invention, the hydrothermal reaction temperature is controlled between 80-300℃, which promotes the formation and directional growth of WO3 crystal nuclei under sufficient thermodynamic driving force, while ensuring that Re and M ions are effectively incorporated into the WO3 lattice. The reaction time is maintained between 12-48 hours, ensuring that the crystals grow to a suitable size and complete a stable doped structure, thereby obtaining a well-crystallized, uniformly composed photochromic material.

[0058] According to a preferred embodiment of the present invention, the hydrothermal reaction is carried out at a temperature of 120-240°C for a duration of 24-48 hours.

[0059] According to some embodiments of the present invention, considering the reasons of high solubility, few impurities and controllable cost, the W source is selected from at least one of sodium tungstate, ammonium tungstate and tungsten hexachloride.

[0060] According to some embodiments of the present invention, the Re source is selected from compounds containing at least one element selected from Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Considering good solubility and ease of decomposition and removal in subsequent hydrothermal reactions, the Re source can be a nitrate of the above elements, preferably europium nitrate, samarium nitrate, or terbium nitrate.

[0061] According to some embodiments of the present invention, the M source is selected from compounds containing at least one element selected from Ag, Cr, Cu, Mn and Fe. Considering that chloride ions have a complexing effect on some metal ions, which helps to stabilize the precursor and make the reactivity suitable, the M source is selected from chloride salts of the above elements, preferably ferric chloride and / or copper chloride.

[0062] In this invention, the complexing agent is selected from at least one of oxalic acid, tartaric acid, and citric acid.

[0063] In this invention, the complexing agent can not only prevent tungsten from precipitating prematurely in an acidic environment and provide a uniform precursor for the hydrothermal reaction through complexation, but also regulate the nucleation and growth rate of crystals, affecting the particle size and morphology of the final product.

[0064] In this invention, the molar ratio of the complexing agent to the total number of metal ions (W, Re and M) is 0.09-0.1.

[0065] According to some embodiments of the present invention, the method further includes step S4: washing and drying the solid phase after solid-liquid separation of the hydrothermal reaction product to obtain the photochromic material.

[0066] In this invention, residual inorganic ions (such as Na+) in hydrothermal products can be thoroughly removed by washing (e.g., water washing, alcohol washing). + Cl - NO3 - The solvent is removed to remove organic impurities, thus avoiding affecting the intrinsic photochromic properties of the material. The subsequent drying process (e.g., vacuum drying or freeze drying) can remove the solvent while maximally maintaining the porous nanostructure of the material, thereby maintaining its high specific surface area, which is beneficial for light absorption and ion transport, and ultimately ensuring the photochromic properties of the material.

[0067] In this invention, after washing and drying the solid phase, the dried product can be ground by grinding or ball milling to make the dried material particles more uniform and finer, so as to obtain photochromic powder with consistent performance and easier processing and application.

[0068] The advantages of the present invention will be illustrated below through examples.

[0069] In the following embodiments, the morphology of the material was tested using a high-resolution transmission electron microscope (Thermoscientific Talos F200i).

[0070] Diffuse reflectance spectrum and transmittance test: The test was conducted using a UH4150 spectrophotometer.

[0071] Color difference test: The test was conducted using a CS-826 benchtop spectrophotometer.

[0072] Nano-tungsten trioxide: purchased from the Institute of Organic Functional Materials and Application Technology, Yangtze River Delta National Technology Innovation Center.

[0073] The reversibility of natural fading is represented by the ratio of reflectance after 24 hours of natural fading to the initial reflectance.

[0074] Example 1 This example illustrates WO3:0.05Eu 3+ Preparation of photochromic materials S1, according to the chemical formula WO 3 0.05Eu 3+ To determine the stoichiometric ratio of each element, weigh out 10g of sodium tungstate, 0.6762g of europium nitrate, and 0.2729g of oxalic acid and add them to a 250mL conical flask. Add distilled water to dissolve them completely to obtain the precursor solution. S2. Add concentrated hydrochloric acid to the precursor solution to adjust the pH to 1, and stir for 2 hours under dark conditions to obtain an acidic precursor solution. S3. The acidic precursor solution is added to a hydrothermal reactor at a reaction temperature of 120°C for 24 hours. The hydrothermal reaction product is then centrifuged to remove the supernatant. The solid phase is then washed three times with water and three times with alcohol to obtain the photochromic material.

[0075] The microstructure of the photochromic material prepared in Example 1 was tested by TEM. It can be seen that the microstructure of the material is a two-dimensional nanosheet structure, and lattice diffraction fringes can be clearly observed on the surface, indicating that the photochromic material has good crystallinity.

[0076] like Figure 2 As shown, the initial color of the photochromic material powder sample in this embodiment is light yellow. After being irradiated with 365nm ultraviolet light for 10 minutes, the color of the sample turns into dark blue, exhibiting obvious photochromic characteristics. The color difference value before and after irradiation is 35.85.

[0077] Meanwhile, the reflectance spectra before and after ultraviolet light irradiation were tested. The reflectance spectra of the powder samples also changed significantly. In particular, the reflectance of the pale yellow sample decreased significantly in the visible light (400-760nm) and near-infrared bands (760-1400nm), indicating that the photochromic sample has good absorption and blocking efficiency for visible and near-infrared light.

[0078] The reversibility of natural fading after the photochromic material of Example 1 undergoes a color-changing reaction under ultraviolet light irradiation was tested, and the results are shown in Table 1.

[0079] like Figure 10As shown, a photochromic film was prepared by doping the photochromic material of Example 1 into polymethyl methacrylate (PMMA): 4g of PMMA was weighed and added to 50mL of dichloromethane (DCM), and stirred until clear to obtain solution a. 0.3g of photochromic powder was weighed and added to 1.5mL of N,N-dimethylformamide (DMF), and stirred until homogeneous to obtain solution b. Solutions a and b were mixed and stirred evenly, and then the mixed solution was poured into a mold and dried at 40°C for 1 hour to finally obtain a photochromic film (0.2mm). The doping amount of the photochromic material accounted for 8% of the total weight of the photochromic film. The transmittance of the film sample in the visible and near-infrared regions could be maintained above 75%, exhibiting excellent light transmittance. When the film sample was placed under sunlight, with the extension of the illumination time, the film gradually underwent a photochromic reaction under the stimulation of ultraviolet rays in sunlight, and the transmittance of the film also decreased accordingly. After being exposed to sunlight for 30 minutes, the film turns a deep blue color, exhibiting excellent photochromic properties and showing promising application prospects in the field of automotive window films.

[0080] Example 2 This example illustrates WO3:0.05Tb 3+ Preparation of photochromic materials The method is the same as in Example 1, except that europium nitrate in the raw materials is replaced with terbium nitrate.

[0081] The resulting photochromic materials, such as Figure 3 As shown, the powder sample in this embodiment was initially pale yellow. After being irradiated with ultraviolet light for 10 minutes, the sample turned dark blue, exhibiting obvious photochromic properties. Simultaneously, the reflectance spectrum of the powder sample also changed significantly, especially with a substantial decrease in reflectance in the visible and near-infrared bands, indicating that the photochromic sample has good absorption and blocking efficiency for visible and near-infrared light.

[0082] The color difference value and the reversibility of natural fading of the material before and after light exposure were tested, and the results are shown in Table 1.

[0083] Examples 3-4 Examples 3 and 4 in this document are used to illustrate WO3:0.05Ce 3+ and WO3:0.05Sm 3+ Preparation of photochromic materials.

[0084] The method is the same as in Example 1, except that europium nitrate in the raw materials is replaced with cerium nitrate and samarium nitrate, respectively.

[0085] The photochromic material obtained in Example 3 is as follows: Figure 4 As shown, the photochromic material obtained in Example 4 is as follows: Figure 5 As shown, the initial color of the powder samples was pale yellow. After irradiation with ultraviolet light for 10 minutes, the color of the samples all turned dark blue, exhibiting obvious photochromic properties. At the same time, the reflectance spectrum of the powder samples also changed significantly, especially the reflectance in the visible and near-infrared bands decreased significantly, indicating that the photochromic samples have good absorption and blocking efficiency for visible and near-infrared light.

[0086] The color difference value and the reversibility of natural fading of the material before and after light exposure were tested, and the results are shown in Table 1.

[0087] Example 5 This example illustrates WO3:0.05Eu 3+ 0.01Cu 2+ Preparation of photochromic materials S1. Weigh 10g sodium tungstate, 0.6762g europium nitrate, 0.0732g copper nitrate and 0.2729g oxalic acid and add them to a 250mL conical flask. Add distilled water to dissolve them completely to obtain the precursor solution. S2. Add concentrated hydrochloric acid to the precursor solution to adjust the pH to 1, and stir for 2 hours under dark conditions to obtain an acidic precursor solution. S3. The acidic precursor solution is added to a hydrothermal reactor at a reaction temperature of 120°C for 24 hours. The hydrothermal reaction product is then centrifuged to remove the supernatant. The solid phase is then washed three times with water and three times with alcohol to obtain the photochromic material.

[0088] like Figure 7 As shown, the powder sample in this embodiment was initially pale yellow. After irradiation with ultraviolet light for 10 minutes, the sample turned dark blue, exhibiting obvious photochromic properties. The color difference values ​​before and after irradiation are shown in Table 1. Simultaneously, the reflectance spectrum of the powder sample also changed significantly, especially with a substantial decrease in reflectance in the visible and near-infrared bands, indicating that the photochromic sample has good absorption and blocking efficiency for visible and near-infrared light. 2+ The doping in the system acts as a reversible electronic modifier. Although it slightly reduces the color depth (color difference value), it significantly accelerates the fading process by promoting electron reflux, thus achieving an optimal balance between color change intensity and cycle stability. Figure 9 As shown, the reflectivity of the color-changing material gradually increases (at 1320nm) under dark conditions, and the reflectivity can be restored to 83.17% of the initial value after natural fading for 24 hours. Compared with Example 1, the reversibility of photochromism in this example is significantly improved.

[0089] Example 6 This example illustrates WO3:0.05Eu 3+ 0.01Fe3+ Preparation of photochromic materials S1. In the presence of oxalic acid, weigh 10g sodium tungstate, 0.6762g europium nitrate, 0.1225g ferric nitrate and 0.2729g oxalic acid and add them to a 250mL conical flask. Add distilled water to dissolve them completely to obtain the precursor solution. S2. Add concentrated hydrochloric acid to the precursor solution to adjust the pH to 1, and stir for 2 hours under dark conditions to obtain an acidic precursor solution. S3. The acidic precursor solution is added to a hydrothermal reactor at a reaction temperature of 120°C for 24 hours. The hydrothermal reaction product is then centrifuged to remove the supernatant. The solid phase is then washed three times with water and three times with alcohol to obtain the photochromic material.

[0090] like Figure 8 As shown, the initial color of the material powder sample in this embodiment is pale yellow. After irradiation with ultraviolet light for 10 minutes, the sample color turns deep blue, exhibiting obvious photochromic properties. The color difference values ​​before and after irradiation are shown in Table 1. Simultaneously, the reflectance spectrum of the powder sample also changes significantly, especially with a substantial decrease in reflectance in the visible and near-infrared bands, indicating that the photochromic sample has good absorption and blocking efficiency for visible and near-infrared light. Due to Fe... 3+ It has good redox properties and can promote the fading process of WO3, such as... Figure 9 As shown, the reflectivity of the color-changing material gradually increases (at 1320nm) under dark conditions, and the reflectivity can be restored to 75.95% of the initial value after natural fading for 24 hours. Compared with Example 1, the reversibility of photochromism in this example is significantly improved.

[0091] Example 7 The method is the same as in Example 6, except that the amount of europium nitrate is 0.6762 g and the amount of ferric nitrate is 0.0612 g, so that the chemical formula of the photochromic material is WO. 3 0.05Eu 3+ 0.005Fe 3+ The color difference values ​​of the prepared photochromic material before and after irradiation and the reversibility of natural fading are shown in Table 1.

[0092] Example 8 The method is the same as in Example 1, except that the hydrothermal reaction temperature is 250°C and the reaction time is 24 hours.

[0093] The color difference values ​​of the prepared photochromic material before and after irradiation and the reversibility of natural fading are shown in Table 1.

[0094] Comparative Example 1 Following the method of Example 1, except that europium nitrate was not added, a chemical formula WO3: 0.01Cu² was prepared. + The photochromic material was prepared. The color difference values ​​of the photochromic material before and after irradiation and the reversibility of natural fading are shown in Table 1.

[0095] Comparative Example 2 The method was followed in Example 1, except that oxalic acid was not added. The color difference values ​​of the prepared photochromic material before and after irradiation and the reversibility of natural fading are shown in Table 1.

[0096] Comparative Example 3 The method is the same as in Example 1, except that in step S2, the pH value of the precursor solution is adjusted to 2.5. The color difference values ​​of the prepared photochromic material before and after irradiation and the reversibility of natural fading are shown in Table 1.

[0097] Comparative Example 4 The comparison sample is a single WO3, and its color difference values ​​before and after irradiation and the reversibility of natural fading are shown in Table 1.

[0098] Table 1

[0099] Note: Initial reflectance refers to the reflectance of the sample before illumination. As can be seen from the above, the embodiments of the present invention exhibit significant advantages over the comparative examples: In Examples 1-7, the photochromic materials prepared in systems doped only with rare earth elements or co-doped with rare earth elements and redox metals all showed significant color-changing effects after ultraviolet light irradiation, with color difference values ​​(ΔE) generally higher than 20, reaching a maximum of 35.85, which is far superior to the undoped comparative example 1 (ΔE=20.19) and the pure tungsten trioxide comparative example 4 (ΔE=0.51); at the same time, the introduction of redox metal ions (such as Cu) 2+ Fe 3 +After this process, the reversibility of fading in the dark is significantly improved, with the ratio of reflectance after 24 hours of natural fading to the initial reflectance (i.e., the 24-hour reflectance recovery rate) reaching a maximum of 83.17% (Example 5). This indicates that the present invention effectively improves the response speed and color difference of photochromism through rare earth doping, and further optimizes the fading kinetics and cycle reversibility through synergistic doping of redox metal ions, resulting in significantly better overall performance than single-doped or undoped systems. The present invention introduces specific types and amounts of rare earth ions into WO3 to construct efficient energy transfer and defect structures, and then simultaneously introduces specific amounts of redox metal ions, resulting in a significant synergistic effect. As shown in Example 5, this synergistic effect enables the final material to achieve excellent fading reversibility (e.g., 24-hour reflectance recovery rate > 83%) while maintaining a high color difference value (ΔE > 30) comparable to that of excellent rare earth doped systems, without significantly reducing the color difference value.

[0100] from Figure 2 As can be seen, for the photochromic material prepared in Example 1, its reflectivity in the entire visible and near-infrared regions decreased significantly and comprehensively within a very short time after ultraviolet light irradiation began. This indicates that the material's appearance color changes rapidly and significantly in the initial stage of light irradiation. In contrast, pure WO3 in Comparative Example 4 showed almost no obvious color change under the same irradiation conditions. This confirms that the present invention, through rare earth doping, greatly accelerates the material's response speed to ultraviolet light, achieving rapid color change.

[0101] It is worth noting that the reflectance ratio of Comparative Example 4 (pure WO3) is as high as 98.7%. This does not mean that its fading reversibility is good, but rather that the photochromic effect of the undoped material is extremely weak, and the change in reflectance before and after illumination is negligible, resulting in the initial value and the value after fading being very close when calculating the ratio.

[0102] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A rare-earth-doped photochromic material, characterized in that, It has a chemical composition as shown in formula (1): WO3: xRe, yM Formula (1) Where Re is a rare earth element, and M is selected from at least one of redox metal ions; x represents the molar fraction of the Re element in formula (1), with a value range of 0 < x ≤ 0.5, and y represents the molar fraction of M in formula (1), with a value range of 0 ≤ y ≤ 0.

05.

2. The photochromic material according to claim 1, characterized in that, 0.05 ≤ x ≤ 0.3, 0.005 ≤ y ≤ 0.02; And / or, the rare earth element is selected from at least one of Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; And / or, the redox metal ion is selected from at least one of Ag, Cr, Cu, Mn, and Fe.

3. The photochromic material according to claim 1, characterized in that, The rare earth element is selected from at least one of Eu, Tb, Sm, and Ce; And / or, M is at least one of Cu or Fe.

4. A photochromic thin film, characterized in that, It includes the photochromic material described in any one of claims 1 - 3.

5. The photochromic film according to claim 4, characterized in that, The film is used for vehicle window glass, building curtain wall glass, or optical anti-counterfeiting elements.

6. A method for preparing the photochromic material according to any one of claims 1-3, characterized in that, It includes the following steps: S1. In the presence of a complexing agent, raw materials containing a W source, a Re source, and a M source are mixed in water to form a precursor solution; S2. Under light - shielding conditions, the pH value of the precursor solution is adjusted to 0.5 - 2 to obtain an acidic precursor solution; S3: The acidic precursor solution obtained in step S2 is subjected to a hydrothermal reaction, and the hydrothermal reaction product is separated to obtain the photochromic material.

7. The preparation method according to claim 6, characterized in that, The temperature of the hydrothermal reaction is 80 - 250 °C, and the time is 12 - 48 h.

8. The preparation method according to claim 6, characterized in that, The W source is selected from at least one of sodium tungstate, ammonium tungstate, and tungsten hexachloride; And / or, the Re source is selected from compounds containing at least one element of Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; And / or, the M source is selected from compounds containing at least one element of Ag, Cr, Cu, Mn, and Fe; And / or, the complexing agent is selected from at least one of oxalic acid, tartaric acid, and citric acid.

9. The preparation method according to claim 6, characterized in that, The W source is selected from sodium tungstate and / or ammonium tungstate; And / or, the Re source is selected from at least one of europium nitrate, samarium nitrate, or terbium nitrate; And / or, the M source is selected from ferric chloride and / or copper chloride.

10. The method according to any one of claims 6-9, characterized in that, It further includes: Step S4: The solid phase after solid - liquid separation of the hydrothermal reaction product is washed and dried to obtain the photochromic material.

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