Self-recovery photochromic material and preparation method thereof

Abstract

This invention discloses a self-restoring photochromic material and its preparation method. The material is synthesized using a solvothermal-high-temperature solid-state method and has a composition of WO3@ m TiO2: x RE 3+ , m and x TiO2 and RE respectively 3+ The molar ratio with WO3, 0 < m ≤14, 0≤ x <0.5, RE 3+ Selected from Pr 3+ 、Sm 3+ Eu 3+ One of them. After being irradiated with ultraviolet light, the material's body color changed from its initial color to blue; after the ultraviolet light was removed and the material was left to stand naturally for 6 hours, the body color returned to its initial color. When x When the value is not zero, the material exhibits both photochromic and photoluminescent properties, especially RE. 3+ For Eu 3+ When the material exhibits photochromic and luminescence modulation synergistic control functions, it possesses excellent cycle stability and can be used as a rewritable medium or intelligent photothermal modulation coating for applications in information storage, smart windows, and smart greenhouses.

Description

Technical Field

[0001] This invention belongs to the field of inorganic photochromic materials technology, specifically relating to a WO3@TiO2-based self-healing photochromic material and its preparation method. Background Technology

[0002] Photochromic materials refer to functional materials that can change color and undergo related physicochemical changes under the irradiation of light of a specific wavelength. Under photoexcitation, the material will trigger photochemical or photophysical processes, which will lead to changes in molecular configuration, chemical bond connection mode and electron distribution. These microstructure evolutions change the absorption and reflection characteristics of the material to different wavelengths of light, thus manifesting as color change on a macroscopic scale. At present, photochromic materials are mainly divided into two categories: organic and inorganic. Organic photochromic materials have advantages such as diverse structures and flexible regulation, but they generally have problems such as insufficient stability, easy degradation and potential environmental toxicity. In contrast, inorganic photochromic materials usually have better stability, durability and environmental friendliness, and have received widespread attention and research. Inorganic photochromic materials mainly include three categories: (1) Transition metal oxides. These materials include oxides of Ti, V, Mo, W, Nb, Ni and Co. Because the color change process involves changes in the oxidation state of metal elements, most of them face problems such as slow fading and poor self-recovery performance. (2) Rigid network structure oxides. For example, Yang et al. reported Ba3MgSi2O8:Mn 2+ Photochromic phosphors change from white to orange under X-ray irradiation and can fade after 14 minutes of irradiation with 254 nm ultraviolet light [ACS Energy Lett. 2023, 8, 2232-2240]. However, such photochromic materials usually require external photothermal stimulation to return to their initial state and do not have self-recovery capabilities. (3) Ferroelectric materials. For example, Poelman et al. proposed a new strategy to achieve high photochromic performance by constructing deep-level traps in ferroelectric ceramics. The prepared K 0.5 Na 0.5 NbO3-Eu ceramics can undergo a yellow-to-gray color transition under alternating exposure to 420 nm light and 450 °C heat [Laser Photonics Rev. 2021, 15, 2000525]. Similarly, the fading behavior of ferroelectric materials is also highly dependent on photothermal stimulation.

[0003] It is evident that most inorganic photochromic materials currently face the problem of not being able to spontaneously fade. Their fading process largely relies on continuous light exposure, heat treatment, or other external stimuli, requiring additional energy input and resulting in complex application system structures. In contrast, publicly available reports on photochromic materials that can spontaneously recover their color after light exposure ceases without additional external stimuli, relying solely on the material itself, are still relatively limited, and research on related material systems and their applications needs further expansion. Summary of the Invention

[0004] The technical problem to be solved by this invention is to overcome the limitations mentioned in the background section above, and to provide a self-recovering photochromic material without external stimulation and its preparation method, and to apply it to information storage and photothermal modulation. To solve the above technical problem, the technical solution proposed by this invention is as follows.

[0005] A self-healing photochromic material, the composition of which can be represented as WO3@ m TiO2: x RE 3+ , m The molar ratio of TiO2 to WO3 is given, where 0 < 0. m ≤14; RE 3+ Selected from Sm 3+ Pr 3+ Eu 3+ One of them; x For RE 3+ The molar ratio relative to WO3 is 0 ≤ x <0.5. This material possesses a differentiated initial body color; when 0 < m When 4 < 4, the initial body color of the material is light yellow; when 4 ≤ m When the concentration is ≤14, the initial body color of the material is white. After irradiation with commercial ultraviolet light sources at wavelengths of 254 nm, 265 nm, 295 nm, 305 nm, 365 nm, and 395 nm, the self-restoring photochromic materials all exhibited significant photochromism. Ultraviolet-visible-near-infrared diffuse reflectance spectroscopy tests showed a decrease in reflectance in the 400–1400 nm wavelength range, and the material's body color changed from the initial color to blue. After the ultraviolet irradiation was removed, the material spontaneously recovered to its initial color within 6 hours of being left to stand at room temperature. The 365 nm ultraviolet light source is the most common, therefore, 365 nm is preferred as the irradiation source for testing the photochromic performance. The photochromic performance was tested using an ultraviolet-visible-near-infrared spectrophotometer with a test wavelength range of 200–1400 nm. The color-changing contrast was calculated as the difference in reflectance at the wavelength with the largest change before and after the color change.

[0006] Preferably, when 0 < x < 0.5, the self-restoring photochromic material WO3@m TiO2: x RE 3+ It exhibits both photochromic and photoluminescent properties. In the dark, the material emits red light when irradiated with ultraviolet or blue light. In the bright field, the material changes color from its initial color to blue after being irradiated with ultraviolet light; after the ultraviolet light is removed, the material returns to its initial color within 6 hours when left to stand at room temperature.

[0007] Preferably, when RE 3+ For Eu 3+ The self-restoring photochromic material described above, when 0 < x < 0.5, exhibits synergistic regulation of photochromism and photoluminescence. In its initial state, the material can be excited by blue light to produce Eu. 3+ Characteristic red light emission spectrum; Eu in the material under continuous ultraviolet irradiation. 3+ The red light emission intensity decreased with increasing irradiation time, and the decrease in luminescence intensity was strongly correlated with the increase in color contrast. After the ultraviolet irradiation was removed, the material was left to stand naturally at room temperature for 6 hours. Its luminescence intensity and the material color also returned to their initial state. The luminescence self-recovery process was synchronized with the photochromic self-recovery process of the material.

[0008] The self-healing photochromic material WO3@ m TiO2: x RE 3+ The preparation method of [the substance] is characterized by employing a two-step method of solvothermal method and high-temperature solid-state method, comprising the following steps: (1) Preparation of precursor by solvothermal method: WO3 was dispersed in ethanol and prepared according to... m Add titanium source in proportion and mix thoroughly; add water to the system to adjust the volume ratio of water to ethanol to 1:50–1:60; then transfer the reaction system to a reaction vessel and place it in an oven at 160–200 °C for 6–10 h; after the reaction is complete, centrifuge to obtain WO3@ m TiO2 precursor; (2) Photochromic materials were prepared by high-temperature solid-state method: The precursor obtained in step (1) was mixed with a rare earth compound containing RE according to the following steps. x The mixtures were mixed in the specified proportions, thoroughly ground, and then placed in a crucible. The mixture was calcined at 400–700 °C for 2–6 h, cooled, and then ground again to obtain WO3@. m TiO2: x RE 3+ Photochromic materials.

[0009] Preferably, the titanium source is selected from one of tetrabutyl titanate, tetraisopropyl titanate, or titanium tetrachloride.

[0010] Preferably, the rare earth compound containing RE is one of the oxides, oxalates, acetates, nitrates, or chlorides of Pr, Sm, or Eu.

[0011] Preferably, the reaction atmosphere during the high-temperature solid-phase reaction is air.

[0012] Preferably, in the solvothermal reaction process m The ratio and calcination temperature during the high-temperature solid-phase reaction process can adjust the color contrast and color-recovery bleaching rate of the self-restoring photochromic material.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Excellent self-recovery performance: The discolored materials can spontaneously recover their color under natural conditions without external stimulation, and the discoloration and self-recovery bleaching rate of the materials can be adjusted.

[0014] 2. Clear functional zoning: Rare earth-doped self-restorative photochromic materials possess both photochromic and photoluminescent functions, especially Eu... 3+ The doped system can achieve synergistic control of photochromism and luminescence modulation.

[0015] 3. Good cycle stability: After multiple cycles, the material does not show significant decay in color change or luminescence performance, and has a long service life.

[0016] 4. Wide range of applications: It can be applied to multiple fields such as information storage and intelligent photothermal modulation. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 The ultraviolet-visible-near-infrared diffuse reflectance spectrum of the self-restoring photochromic material described in Example 1; Figure 2 The ultraviolet-visible-near-infrared diffuse reflectance spectrum of the self-restoring photochromic material described in Example 2; Figure 3 Example 2: Photochromic fatigue resistance test of the self-restoring photochromic material; Figure 4 The ultraviolet-visible-near-infrared transmission spectrum of the photothermal modulation film described in Example 2; Figure 5The ultraviolet-visible-near-infrared diffuse reflectance spectrum of the self-restoring photochromic material described in Example 3; Figure 6 The ultraviolet-visible-near-infrared diffuse reflectance spectrum of the information storage film described in Example 3; Figure 7 The ultraviolet-visible-near-infrared diffuse reflectance spectrum of the self-restoring photochromic material described in Example 4; Figure 8 The ultraviolet-visible-near-infrared diffuse reflectance spectrum of the self-restoring photochromic material described in Example 5; Figure 9 The ultraviolet-visible-near-infrared diffuse reflectance spectrum of the self-restoring photochromic material described in Example 6; Figure 10 The ultraviolet-visible-near-infrared diffuse reflectance spectrum of the self-restoring photochromic material described in Example 7; Figure 11 The ultraviolet-visible-near-infrared diffuse reflectance spectrum of the self-restoring photochromic material described in Example 8; Figure 12 Fluorescence spectrum of the self-restoring photochromic material described in Example 9; Figure 13 The ultraviolet-visible-near-infrared diffuse reflectance spectrum of the self-restoring photochromic material described in Example 9; Figure 14 Example 9: Luminescence modulation fatigue resistance test of the self-restoring photochromic material described in Example 9; Figure 15 Example 9: Photochromic fatigue resistance test of the self-restoring photochromic material; Figure 16 The ultraviolet-visible-near-infrared transmission spectrum of the photothermal modulation film described in Example 9. Detailed Implementation

[0019] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and representative embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0020] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0021] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0022] Example 1: WO3@1.7TiO2 self-healing photochromic material The material in this embodiment was prepared using a two-step solvothermal-high-temperature solid-state method. The specific preparation steps are as follows: 0.20 g of WO3 was accurately weighed and dispersed in 40 mL of ethanol. 0.5 mL of tetrabutyl titanate was added to the dispersion and stirred for 10 min to ensure uniform mixing of the reactants. Separately, 10 mL of ethanol and 1 mL of deionized water were mixed thoroughly. This mixture was then added to the above reaction system and stirred until fully homogeneous. The mixture was then transferred to a reaction vessel and placed in a programmed temperature oven at 180 °C for 8 h. After the reaction, the reaction vessel was allowed to cool naturally to room temperature. The product was collected by centrifugation and washed three times with anhydrous ethanol. The washed product was dried and ground, then placed in a corundum crucible and calcined in a muffle furnace at 500 °C for 4 h. After the muffle furnace cooled naturally to room temperature, the product was removed and ground again to obtain the WO3@1.7TiO2 self-restoring photochromic material.

[0023] The WO3@1.7TiO2 prepared in this embodiment is a self-restoring photochromic material. The material initially appears light yellow under natural light. After irradiating the sample with 365 nm ultraviolet light for 30 seconds at room temperature, the light yellow matrix of the sample deepens in color, gradually changing towards blue. The diffuse reflectance spectra of the sample before and after the color change are shown below. Figure 1 As shown, after irradiation, the reflectivity of the sample decreased in the 400-1400 nm range, exhibiting significant light absorption. The color contrast at 1400 nm was 27%. After the ultraviolet light source was removed, without the need for additional external stimuli such as light, heat, or electricity, the sample could spontaneously undergo a fading reaction. Within 2 minutes of standing, it could basically recover to its initial light yellow body color, demonstrating excellent self-healing photochromic properties.

[0024] Example 2: WO3@5.1TiO2 self-restoring photochromic material The material in this embodiment was prepared using a two-step solvothermal-high-temperature solid-state method. The specific preparation steps are as follows: 0.20 g of WO3 was accurately weighed and dispersed in 40 mL of ethanol. 1.5 mL of tetrabutyl titanate was added to the dispersion and stirred for 10 min to ensure uniform mixing of the reactants. 20 mL of ethanol and 1 mL of deionized water were mixed thoroughly and added to the above reaction system. After thorough mixing, the mixture was transferred to a reaction vessel and placed in a programmed temperature oven at 160 °C for 10 h. After the reaction, the reaction vessel was allowed to cool naturally to room temperature. The product was collected by centrifugation and washed three times with anhydrous ethanol. The washed product was dried and ground, then placed in a corundum crucible and calcined in a muffle furnace at 500 °C for 5 h. After the muffle furnace cooled naturally to room temperature, the product was removed and ground again to obtain the WO3@5.1TiO2 self-restoring photochromic material.

[0025] The WO3@5.1TiO2 prepared in this embodiment is a self-restoring photochromic material, initially white under natural light. After irradiating the sample with 365 nm ultraviolet light for 30 seconds at room temperature, the sample changed from its initial color to blue. The diffuse reflectance spectra of the sample before and after the color change are as follows: Figure 2 As shown, after irradiation, the reflectance of the sample decreased in the 400-1400 nm range, exhibiting significant light absorption. The color-changing contrast at 1369 nm was 40%. After removing the ultraviolet light source, without additional external stimulation such as light, heat, or electricity, the sample spontaneously underwent a fading reaction, essentially recovering to its initial color within 10 minutes of rest. Another sample, irradiated with 365 nm ultraviolet light for 14 minutes, changed from its initial color to blue, with a color-changing contrast of 71% at 1358 nm. After removing the ultraviolet light source, the sample spontaneously underwent a fading reaction, essentially recovering to its initial color within 1 hour of rest, demonstrating stable self-recovery color-changing performance. Simultaneously, fatigue cycle stability tests were conducted on this sample. During the test, reflectance data were collected at a wavelength of 650 nm for both the colored and bleached states of the material. The test results are shown below. Figure 3 As shown, the material's color-changing and fading process can be repeated multiple times without significant performance degradation, exhibiting excellent fatigue resistance and cyclic stability.

[0026] Benefiting from the reversible color change and broad-spectrum light absorption characteristics of the self-restoring photochromic material WO3@5.1TiO2, it can realize dynamic photothermal modulation applications. To verify the practical application effect of this material in photothermal modulation films, polydimethylsiloxane and WO3@5.1TiO2 were mixed at a mass ratio of 50:2, followed by the addition of 10% by mass of curing agent. After mixing thoroughly again, a 100 μm thick film was prepared using a four-sided molding machine and cured at 80 ℃ for 3 h to obtain the film. After irradiating the film with 365 nm ultraviolet light for 90 s at room temperature, the transmission spectrum of the film is as follows: Figure 4 As shown, the transmittance of the film decreased in the 400-1400 nm range after irradiation. After removing the ultraviolet light source, without additional external stimulation such as light, heat, or electricity, the sample spontaneously underwent a fading reaction, and the initial transmittance was essentially restored within 3 hours of standing, demonstrating good self-recovery performance. This film can be used in smart windows and greenhouses, reducing solar transmittance and lowering indoor or greenhouse temperatures under strong light, while maintaining high solar transmittance under weak light, achieving dynamic photothermal regulation in light response. Covering a simulated greenhouse with this film has a cooling effect under strong summer light and a warming effect under weak winter light.

[0027] Example 3: WO3@10.2TiO2 self-restoring photochromic material The material in this embodiment was prepared using a two-step solvothermal-high-temperature solid-state method. The specific preparation steps are as follows: 0.20 g of WO3 was accurately weighed and dispersed in 40 mL of ethanol. 3 mL of tetrabutyl titanate was added to the dispersion and stirred for 10 min to ensure uniform mixing of the reactants. Separately, 15 mL of ethanol and 1 mL of deionized water were mixed thoroughly. This mixture was added to the above reaction system and stirred until fully homogeneous. The mixture was then transferred to a reaction vessel and placed in a programmed temperature oven at 180 °C for 10 h. After the reaction, the reaction vessel was allowed to cool naturally to room temperature. The product was collected by centrifugation and washed three times with anhydrous ethanol. The washed product was dried and ground, then placed in a corundum crucible and calcined in a muffle furnace at 500 °C for 6 h. After the muffle furnace cooled naturally to room temperature, the product was removed and ground again to obtain the WO3@10.2TiO2 self-restoring photochromic material.

[0028] The WO3@10.2TiO2 prepared in this embodiment is a self-restoring photochromic material, initially white under natural light. After irradiating the sample with 365 nm ultraviolet light for 30 seconds at room temperature, the sample changed from its initial color to blue. The diffuse reflectance spectra of the sample before and after the color change are shown below. Figure 5As shown, after irradiation, the reflectivity of the sample decreased in the range of 400-1400 nm, and obvious light absorption was observed. The color contrast at 1369 nm was 53%. After the ultraviolet light source was removed, the sample could spontaneously undergo a fading reaction without the need for additional external stimuli such as light, heat, or electricity. It could basically recover to its initial white body color within 2 hours of standing, demonstrating good self-recovery performance.

[0029] This WO3@10.2TiO2 self-restoring photochromic material exhibits reversible color development triggered by ultraviolet light, showing potential application in the field of visible-near-infrared information storage media. Based on this, an information storage film was prepared, and application verification experiments were conducted. Polydimethylsiloxane and WO3@10.2TiO2 were thoroughly mixed at a mass ratio of 3:1, followed by the addition of 10% (by mass) of curing agent, and stirring was continued until the materials were uniformly mixed. A 200 μm thick film was prepared using a four-sided film-forming apparatus and cured at 80℃ for 3 h to obtain the information storage film. The reflectance spectra of the obtained film during the coloring and bleaching processes are shown below. Figure 6 As shown, after irradiation with 365 nm ultraviolet light for 60 s, the reflectivity of the film in the 400-1400 nm range decreased significantly. After the ultraviolet excitation source was removed, the film could fade autonomously without any external stimulation, and the information recording state could be stably maintained. After being left to stand for 21 days, the film could gradually recover to its initial state, demonstrating the advantages of long-term information retention and reversible rewriting in optical storage applications.

[0030] Example 4: Preparation of WO3@5.1TiO2 self-restoring photochromic material by calcination at 400 ℃ The material in this embodiment was prepared using a two-step solvothermal-high-temperature solid-state method. The specific preparation steps are as follows: 0.20 g of WO3 was accurately weighed and dispersed in 40 mL of ethanol. 1.5 mL of tetrabutyl titanate was added to the dispersion and stirred for 10 min to ensure uniform mixing of the reactants. Separately, 10 mL of ethanol and 1 mL of deionized water were mixed thoroughly. This mixture was then added to the above reaction system and stirred until fully homogeneous. The mixture was then transferred to a reaction vessel and placed in a programmed temperature oven at 180 °C for 8 h. After the reaction, the reaction vessel was allowed to cool naturally to room temperature. The product was collected by centrifugation and washed three times with anhydrous ethanol. The washed product was dried and ground, then placed in a corundum crucible and calcined in a muffle furnace at 400 °C for 5 h. After the muffle furnace cooled naturally to room temperature, the product was removed and ground again to obtain the WO3@5.1TiO2 self-restoring photochromic material.

[0031] The WO3@5.1TiO2 prepared in this embodiment is a self-restoring photochromic material, initially white under natural light. At room temperature, after irradiating the sample with 365 nm ultraviolet light for 30 seconds, the sample color slightly deepened and exhibited a faint blue tint, with light absorption occurring in the 400-1400 nm range. The diffuse reflectance spectrum before and after the color change showed a contrast of 9% at 1374 nm. After removing the ultraviolet light source, without additional external stimulation such as light, heat, or electricity, the sample spontaneously underwent a fading reaction, returning to its initial color after standing for 2 minutes. Another sample was irradiated with 365 nm ultraviolet light for 14 minutes; the sample changed from its initial color to blue. The diffuse reflectance spectra of the sample before and after the color change are shown below. Figure 7 As shown, the contrast ratio at 1264 nm is 65%; after the ultraviolet light source is removed, the sample can spontaneously undergo a fading reaction and recover to its initial body color after standing for 4 hours, demonstrating good self-recovery performance.

[0032] Example 5: Preparation of WO3@5.1TiO2 self-restoring photochromic material by calcination at 600 ℃ The material in this embodiment was prepared using a two-step solvothermal-high-temperature solid-state method. The specific preparation steps are as follows: 0.20 g of WO3 was accurately weighed and dispersed in 40 mL of ethanol. 1.5 mL of tetrabutyl titanate was added to the dispersion and stirred for 10 min to ensure uniform mixing of the reactants. 20 mL of ethanol and 1 mL of deionized water were mixed thoroughly and added to the above reaction system. After thorough mixing, the mixture was transferred to a reaction vessel and placed in a programmed temperature oven. The reaction temperature was set to 180 °C, and the reaction was carried out for 10 h. After the reaction, the reaction vessel was allowed to cool naturally to room temperature. The product was collected by centrifugation and washed three times with anhydrous ethanol. The washed product was dried and ground, then placed in a corundum crucible and calcined in a muffle furnace at 600 °C for 5 h. After calcination, the product was allowed to cool naturally to room temperature, removed, and ground again to obtain the WO3@5.1TiO2 self-restoring photochromic material.

[0033] The WO3@5.1TiO2 prepared in this embodiment is a self-restoring photochromic material, initially white under natural light. After irradiating the sample with 365 nm ultraviolet light for 30 seconds at room temperature, the sample color changes to blue. The diffuse reflectance spectra of the sample before and after the color change are as follows: Figure 8As shown, significant light absorption occurs in the 400-1400 nm range, with a contrast ratio of 42% at 1395 nm. After removing the ultraviolet light source, the sample spontaneously undergoes a fading reaction without requiring additional external stimuli such as light, heat, or electricity, and essentially recovers to its initial body color within 10 minutes of standing. Another sample, irradiated with 365 nm ultraviolet light for 14 minutes, changed from its initial color to blue, with a color change contrast ratio of 69% at 1266 nm. After removing the ultraviolet light source, the sample spontaneously fading reacted, and essentially recovered to its initial body color within 4 hours of standing, demonstrating stable self-recovery color-changing performance. The self-recovery performance is excellent.

[0034] Example 6: Preparation of WO3@5.1TiO2 self-restoring photochromic material by calcination at 700 ℃ The material in this embodiment was prepared using a two-step solvothermal-high-temperature solid-state method. The specific preparation steps are as follows: 0.20 g of WO3 was accurately weighed and dispersed in 40 mL of ethanol. 1.5 mL of tetrabutyl titanate was added to the dispersion and stirred for 10 min to ensure uniform mixing of the reactants. Separately, 10 mL of ethanol and 1 mL of deionized water were mixed thoroughly. This mixture was added to the above reaction system and stirred thoroughly. The mixture was then transferred to a reaction vessel and placed in a programmed temperature oven at 180 °C for 10 h. After the reaction, the reaction vessel was allowed to cool naturally to room temperature. The product was collected by centrifugation and washed three times with anhydrous ethanol. The washed product was dried and ground, then placed in a corundum crucible and calcined in a muffle furnace at 700 °C for 5 h. After calcination, the product was allowed to cool naturally to room temperature, removed, and ground again to obtain the WO3@5.1TiO2 self-restoring photochromic material.

[0035] The WO3@5.1TiO2 prepared in this embodiment is a self-restoring photochromic material. The material is initially white under natural light. After irradiating the sample with 365 nm ultraviolet light for 30 seconds at room temperature, the sample color changes to blue. The diffuse reflectance spectra before and after the color change are as follows: Figure 9 As shown, after irradiation, the reflectivity of the sample decreased in the range of 400-1400 nm, and obvious light absorption was observed. The color contrast at 1381 nm was 36%. After the ultraviolet light source was removed, the sample could spontaneously undergo a fading reaction without the need for additional external stimuli such as light, heat, or electricity. After standing for about 100 minutes, it could basically recover to its initial white body color, demonstrating good self-recovery performance.

[0036] Example 7: WO3@5.1TiO2: 0.18Sm 3+ Self-restoring photochromic material The material in this embodiment was prepared using a solvothermal-high-temperature solid-state method. The specific preparation steps are as follows: 0.20 g of WO3 was accurately weighed and dispersed in 40 mL of ethanol. 1.5 mL of tetrabutyl titanate was added and stirred for 10 min. 10 mL of ethanol and 1 mL of deionized water were mixed and then added dropwise to the above dispersion. After stirring evenly, the mixture was transferred to a reaction vessel and placed in a programmed temperature oven at 180 ℃ for 10 h. After the reaction was completed, the mixture was allowed to cool naturally. The product was collected by centrifugation, washed three times with anhydrous ethanol, dried, and ground to obtain the WO3@5.1TiO2 precursor. 0.0690 g of Sm(NO3)3 was weighed... . Mix 6H2O with the obtained WO3@5.1TiO2 precursor, grind thoroughly in a mortar for 30 min, place the mixed powder into an alumina crucible, calcine at 500 ℃ in a muffle furnace for 6 h, cool and grind to obtain WO3@5.1TiO2: 0.18Sm 3+ Self-restoring photochromic materials.

[0037] The WO3@5.1TiO2 prepared in this embodiment has a thickness of 0.18Sm. 3+ This is a self-restoring photochromic material. Initially white under natural light, it exhibits photoluminescence. Under bright field conditions, after 8 minutes of 365 nm ultraviolet irradiation at room temperature, the sample changes color to blue. The diffuse reflectance spectra before and after the color change are as follows: Figure 10 As shown, after irradiation, the reflectivity of the sample decreased in the 400-1400 nm range, exhibiting significant light absorption. The color contrast at 1308 nm was 78%. After removing the ultraviolet light source, without additional external stimulation such as light, heat, or electricity, the sample spontaneously underwent a fading reaction and essentially recovered to its initial white body color within 5 hours, demonstrating excellent self-recovery performance. Under dark conditions and a 254 nm ultraviolet lamp, the material emitted red light.

[0038] Example 8: WO3@5.1TiO2: 0.33Pr 3+ Self-restoring photochromic material The material in this embodiment was prepared using a solvothermal-high-temperature solid-state method. The specific preparation steps are as follows: 0.20 g of WO3 was accurately weighed and dispersed in 40 mL of ethanol. 1.5 mL of tetrabutyl titanate was added and stirred for 10 min. 20 mL of ethanol and 1 mL of deionized water were mixed and then added dropwise to the above dispersion. After stirring evenly, the mixture was transferred to a reaction vessel and placed in a programmed temperature oven at 160 ℃ for 10 h. After the reaction was completed, the mixture was allowed to cool naturally. The product was collected by centrifugation and washed three times with anhydrous ethanol. After drying and grinding, the WO3@5.1TiO2 precursor was obtained. 0.0704 g of PrCl3 was weighed and mixed with the obtained WO3@5.1TiO2 precursor. The mixture was ground thoroughly in a mortar for 30 min. The mixed powder was placed in a corundum crucible and calcined in a muffle furnace at 600 ℃ for 5 h. After cooling and grinding, WO3@5.1TiO2:0.33PrCl3 was obtained. 3+ Self-restoring photochromic materials.

[0039] The WO3@5.1TiO2 prepared in this embodiment has a composition of 0.33Pr. 3+ This is a self-restoring photochromic material. Initially white under natural light, it exhibits photoluminescence. Under bright field conditions, after 8 minutes of 365 nm ultraviolet irradiation at room temperature, the sample changes color to blue. The diffuse reflectance spectra before and after the color change are as follows: Figure 11 As shown, after irradiation, the reflectivity of the sample decreased in the 400-1400 nm range, exhibiting significant light absorption, with a contrast ratio of 74% at 1276 nm. After removing the ultraviolet light source, without additional external stimulation such as light, heat, or electricity, the sample spontaneously underwent a fading reaction, essentially recovering to its initial white body color within 5 hours of standing, demonstrating excellent self-recovery performance. Under dark conditions and a 254 nm ultraviolet lamp, the material emitted red light.

[0040] Example 9: WO3@5.1TiO2: 0.34Eu 3+ Self-restoring photochromic material The material in this embodiment was prepared by a solvothermal-high-temperature solid-state method. The specific preparation steps are as follows: 0.20 g of WO3 was accurately weighed and dispersed in 40 mL of ethanol. 1.5 mL of tetrabutyl titanate was added and stirred for 10 min. 15 mL of ethanol and 1 mL of deionized water were mixed and then added dropwise to the above dispersion. After stirring evenly, the mixture was transferred to a reaction vessel and placed in a programmed temperature oven at 180 ℃ for 8 h. After the reaction was completed, the mixture was allowed to cool naturally. The product was collected by centrifugation and washed three times with anhydrous ethanol. After drying and grinding, the WO3@5.1TiO2 precursor was obtained. 0.1308 g of Eu(NO3)3•6H2O was weighed and mixed with the obtained WO3@5.1TiO2 precursor. The mixture was ground thoroughly in a mortar for 30 min. The mixed powder was placed in a corundum crucible and calcined in a muffle furnace at 500 ℃ for 5 h. After cooling and grinding, WO3@5.1TiO2: 0.34Eu was obtained. 3+ Self-restoring photochromic materials.

[0041] The WO3@5.1TiO2 prepared in this embodiment has a content of 0.34Eu. 3+ This is a self-restoring photochromic material. Under natural light, the material is initially white and exhibits photoluminescence properties, demonstrating a synergistic control function between photochromism and luminescence modulation. The fluorescence emission spectrum of the sample is as follows: Figure 12 As shown, under 466 nm blue light excitation, typical Eu appears in the visible light region. 3 ⁺ Characteristic emission spectrum. The emission peak at approximately 590 nm can be attributed to Eu. 3 ⁺ 5 D0→ 7 The F1 transition, with a strong emission peak at 615 nm, is 5 D0→ 7 F2, in addition, a weaker one can be observed at approximately 650 nm. 5 D0→ 7 F3 transition. The diffuse reflectance spectra of the sample before and after the color change are as follows: Figure 13 As shown, after irradiation with 365 nm ultraviolet light for 8 min, the sample exhibited significant light absorption in the 400-1400 nm range, and the material's bulk color changed from white to blue, with a contrast ratio of 64% at 1284 nm; simultaneously, Eu... 3+ The characteristic emission intensity is significantly reduced ( Figure 12 After the ultraviolet light source is removed, without the need for additional external stimuli such as light, heat, or electricity, the sample can spontaneously undergo a fading reaction. Within 5 hours of standing, it can essentially recover to its initial white body color, demonstrating good self-recovery performance; its diffuse reflectance spectrum and Eu... 3 The characteristic emission intensity also recovered to the initial level simultaneously.

[0042] The material underwent luminescence cycling stability and color-changing cycling stability tests. The luminescence cycling test collected fluorescence intensity at the characteristic emission wavelength of 615 nm, while the color-changing cycling test collected reflectance in the colored and bleached states at a wavelength of 650 nm. The test results are as follows: Figure 14 and Figure 15 As shown in the figure. The results show that after repeated cycles, the difference between the fluorescence emission intensity at 615 nm and the reflectance at 650 nm did not decrease significantly. The fluorescence emission behavior and the reversible color change process can be stably repeated without significant performance degradation, demonstrating both excellent luminescence cycle stability and photochromic cycle durability.

[0043] The WO3@5.1TiO2 content is 0.34Eu. 3+ Self-restoring photochromic materials possess reversible ultraviolet color change and synergistic emission-color change response characteristics, making them suitable for photothermal control applications. Based on this, application verification was conducted using polydimethylsiloxane and WO3@5.1TiO2: 0.34Eu. 3+ The film was mixed at a mass ratio of 50:2, followed by the addition of 10% curing agent. After thorough mixing, a 100 μm thick film was prepared using a four-sided molding machine and cured at 80 ℃ for 3 h to obtain a photothermal modulation film. After irradiating the film with 365 nm ultraviolet light for 90 s at room temperature, the transmission spectrum of the film is as follows... Figure 16 As shown, the transmittance of the film decreased in the 400-1400 nm range after irradiation. After removing the ultraviolet light source, without additional external stimulation such as light, heat, or electricity, the sample spontaneously underwent a fading reaction, and the initial transmittance was essentially restored within 3 hours of standing, demonstrating good self-recovery performance. Covering the film with a simulated greenhouse resulted in cooling under strong sunlight in summer and warming under weak sunlight in winter.

Claims

1. A self-restoring photochromic material, characterized in that, The expression is WO3@ m TiO2: x RE 3+ ;in, m The molar ratio of TiO2 to WO3, 0 < m ≤14; RE 3+ Selected from Sm 3+ Pr 3+ Eu 3+ One of them; x For RE 3+ The molar ratio relative to WO3 is 0 ≤ x <0.

5.

2. The self-restoring photochromic material according to claim 1, characterized in that, After being irradiated with ultraviolet light, the material's body color changed from its initial color to blue; Where, when 0 < m When 4 < 4, the initial color is light yellow; when 4 ≤ 4, the initial color is light yellow. m When the UV light intensity is ≤14, the initial color is white; after removing the UV light, the material color will return to the initial color within 6 hours when placed at room temperature.

3. The self-restoring photochromic material according to claim 1 or 2, characterized in that, When 0 < x When the value is <0.5, the material exhibits both photochromic and photoluminescent properties: (1) In the dark, the material emits red light when irradiated with ultraviolet or blue light; (2) Under bright field, the material’s body color changed from the initial color to blue after being irradiated with ultraviolet light; after the ultraviolet light was removed, the material’s body color returned to the initial color within 6 hours when it was placed at room temperature.

4. The self-restoring photochromic material according to claim 1 or 2, characterized in that, When RE 3+ For Eu 3+ 0 < x When the photochromic intensity is less than 0.5, the material exhibits both photochromic and photoluminescent properties, and also possesses a synergistic control function for photochromic and photoluminescence modulation. (1) In the initial state, the material emits red light with the main peak at 615 nm when excited at 466 nm; (2) After being irradiated with ultraviolet light, the material's body color changes from the initial color to blue, and the intensity of red light emission decreases; (3) After the ultraviolet light was removed, the material was placed at room temperature for 6 hours. The body color returned to the initial color and the luminescence returned to the initial level.

5. A method for preparing a self-restoring photochromic material as described in any one of claims 1-4, characterized in that, The two-step method, namely the solvothermal method and the high-temperature solid-state method, includes the following steps: (1) Preparation of precursor by solvothermal method: WO3 was dispersed in ethanol and prepared according to... m Add titanium source in proportion and mix thoroughly; add water to the system to adjust the volume ratio of water to ethanol to 1:50–1:60; then transfer the reaction system to a reaction vessel and place it in an oven at 160–200 °C for 6–10 h; after the reaction is complete, centrifuge to obtain WO3@ m TiO2 precursor; (2) Photochromic materials were prepared by high-temperature solid-state method: WO3@ obtained in step (1) was used to prepare the photochromic materials. m TiO2 precursor and RE-containing rare earth compound according to x The mixtures were mixed in the specified proportions, thoroughly ground, and then placed in a crucible. The mixture was calcined at 400–700 °C for 2–6 h, cooled, and then ground again to obtain WO3@. m TiO2: x RE 3+ Photochromic materials.

6. The method for preparing the self-restoring photochromic material according to claim 5, characterized in that, The titanium source is selected from one of tetrabutyl titanate, tetraisopropyl titanate, or titanium tetrachloride; the rare earth compound containing RE is one of the oxides, oxalates, acetates, nitrates, or chlorides of Pr, Sm, or Eu.

7. The method for preparing the self-restoring photochromic material according to claim 5 or 6, characterized in that, Solvothermal reaction process m The proportions and calcination temperature during the high-temperature solid-state reaction process can adjust the color contrast, color change rate, and self-recovering bleaching rate of the self-recovering photochromic material.

8. The application of a self-restoring photochromic material as described in any one of claims 1-4 or a self-restoring photochromic material prepared by the method described in any one of claims 5-7, characterized in that, By utilizing the photoresponse properties of the material, it can be prepared as a rewritable medium or a photothermal modulation coating for application in the field of information storage; or it can be prepared as an ultraviolet light-responsive color-changing film for use as a smart photothermal modulation material in the fields of smart windows or smart greenhouses.

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