A cerium-doped calcium hexaaluminate photochromic material and its preparation method

Abstract

This invention discloses a cerium-doped calcium hexaaluminate photochromic material and its preparation method. The chemical formula of the material is Ca. 1‑ x A1 12 O 19 :xCe, where 0.0025≤x≤0.02; and Ce is less than or equal to Ce. 3+ and Ce 4+ The coexistence state exists; during preparation, Al(NO3)3·9H2O, CaCl2, Ce(NO3)3·6H2O, citric acid monohydrate, and water are first mixed and heated to obtain a gel, which is then subjected to heat treatment and calcination. The material of this invention exhibits a significant color change before and after irradiation under a 254nm portable ultraviolet lamp, changing from white to yellow, with a distinct absorption peak at 428nm. The samples before and after photochromism show a large difference in light reflectance. Furthermore, after being subjected to seven alternating ultraviolet irradiations and thermal stimulation, the photochromic performance of this material does not significantly decrease, demonstrating good reversibility.

Description

Technical Field

[0001] This invention belongs to the field of inorganic photochromic materials, and particularly relates to a cerium-doped calcium hexaaluminate photochromic material and its preparation method. Background Technology

[0002] Inorganic photochromic materials are a class of materials that change color when irradiated by a light source. Specifically, under irradiation with light of a specific wavelength, color centers are formed in inorganic photochromic materials. These color centers cause the materials to selectively absorb visible light, resulting in a visible color change. Furthermore, they can be bleached back to their original state by thermal or light stimulation. Utilizing this property, inorganic photochromic materials can be applied in fields such as anti-counterfeiting encryption, information storage, and optical switches.

[0003] Some limitations of common inorganic photochromic materials restrict their large-scale industrial applications in fields such as anti-counterfeiting encryption, information storage, and optical switches. For example, the raw materials required for the preparation of hafnium salts, germanates, tungstates, stannates, tantalates, and gallates are difficult to obtain and expensive, resulting in high production costs. While the raw materials required for the preparation of BaMgSiO4-based photochromic materials are inexpensive, the synthesis process requires the use of reducing gas protection, which increases costs. 7-x Er x Ti4NbO 21 Ceramics require a 405nm blue-violet laser as an irradiation source, making their application cost relatively high. Na 0.5 Bi 2.5 While Nb₂O₉:Er ferroelectric oxide photochromic materials exhibit good reversibility of photochromism, the color change is not significant. Titanium dioxide photochromic materials, although capable of producing noticeable color changes after irradiation and possessing good photochromic properties, suffer from poor reversibility of photochromism.

[0004] The factors mentioned above make existing inorganic photochromic materials unsuitable for large-scale industrial applications. Summary of the Invention

[0005] Purpose of the invention: The technical problem to be solved by the present invention is how to provide a photochromic material and its preparation method that can make the color change obvious, with a clear change from white to yellow, and has excellent reversibility.

[0006] Technical solution: The present invention relates to a cerium-doped calcium hexaaluminate photochromic material, the chemical formula of which is Ca. 1- x A1 12 O 19:xCe, where 0.0025≤x≤0.02; and Ce is less than or equal to Ce. 3+ and Ce 4+ A state of coexistence exists.

[0007] This invention is in CaAl 12 O 19 Medium-doped Ce 3+ Subsequently, Ce was present during the preparation process. 3+ First to Ce 4+ Ce 4+ Then Ce 3+ The conversion process generates oxygen vacancies. The sol-gel method creates a weakly reducing atmosphere during high-temperature calcination, further promoting the oxidation of Ce. 4+ To Ce 3+ The conversion generates more oxygen vacancies. ;and Ce 3+ and Ce 4+ Replace Ca 2+ It produced and Defect, the and Defects and oxygen vacancies All can be prepared in Ca 1-x A1 12 O 19 The xCe material system exists stably, forming defect energy levels with a certain trap depth; and then, under 254nm ultraviolet irradiation, CaAl... 12 O 19 After Ce was applied, the material exhibited a photochromic change from white to yellow, with a significant color change and a distinct absorption peak at 428 nm. The samples before and after the photochromic change showed a large difference in light reflectance. Furthermore, after being subjected to alternating ultraviolet irradiation and thermal stimulation seven times, the photochromic performance did not significantly decrease, demonstrating good reversibility.

[0008] The present invention provides a method for preparing the above-mentioned cerium-doped calcium hexaaluminate photochromic material, comprising the following steps:

[0009] (1) Al(NO3)3·9H2O, CaCl2, Ce(NO3)3·6H2O, citric acid monohydrate and water are mixed and stirred to obtain a sol. Then the sol is heated to obtain a gel.

[0010] (2) The gel was heat-treated and calcined to obtain cerium-doped calcium hexaaluminate photochromic material.

[0011] Furthermore, in step (1) of the preparation method of the present invention, the ratio of the number of moles of citric acid monohydrate to the total number of moles of Al(NO3)3·9H2O, CaCl2 and Ce(NO3)3·6H2O is (0.5-1.5):1.

[0012] Furthermore, in step (1) of the preparation method of the present invention, the process of heating the sol to obtain the gel involves sealing the sol, heating and stirring it under reflux at 80-90°C for 1-2 hours, then unsealing it and continuing to heat and stir to form the gel.

[0013] Furthermore, in step (2) of the preparation method of the present invention, the temperature of the heat treatment is 180-200℃ and the heat treatment time is 2-4h.

[0014] Furthermore, in step (2) of the preparation method of the present invention, the calcination temperature is 1100-1200℃, and the calcination time is 4-6h. Preferably, the calcination atmosphere is air.

[0015] The cerium-doped calcium hexaaluminate photochromic material of the present invention is applied to anti-counterfeiting encryption.

[0016] Beneficial effects: Compared with the prior art, the significant advantages of the present invention are as follows: the cerium-doped calcium hexaaluminate inorganic photochromic material exhibits obvious color changes before and after irradiation under a 254nm portable ultraviolet lamp, changing from white to yellow, with a significant absorption peak at 428nm, and a large difference in light reflectance before and after photochromism; moreover, after being subjected to seven alternating ultraviolet irradiations and thermal stimulation, the photochromic performance of the material does not decrease significantly and has good reversibility, making it applicable to fields such as anti-counterfeiting encryption, information storage, and optical switches. Attached Figure Description

[0017] Figure 1 The X-ray diffraction pattern of the cerium-doped calcium hexaaluminate photochromic material prepared in Example 1 of this invention;

[0018] Figure 2 The X-ray photoelectron spectrum of the cerium-doped calcium hexaaluminate photochromic material prepared in Example 2 of this invention is shown below.

[0019] Figure 3 The diffuse reflectance spectrum and photochromic photograph of the cerium-doped calcium hexaaluminate photochromic material prepared in Example 1 of this invention before and after 15 minutes of 254nm ultraviolet radiation.

[0020] Figure 4 The diffuse reflectance spectrum and photochromic photograph of the cerium-doped calcium hexaaluminate photochromic material prepared in Example 2 of this invention before and after 15 minutes of 254nm ultraviolet radiation.

[0021] Figure 5The diffuse reflectance spectrum and photochromic photograph of the cerium-doped calcium hexaaluminate photochromic material prepared in Example 3 of this invention before and after 15 minutes of 254nm ultraviolet radiation.

[0022] Figure 6 The diffuse reflectance spectrum and photochromic photograph of the cerium-doped calcium hexaaluminate photochromic material prepared in Example 4 of this invention before and after 15 minutes of 254nm ultraviolet radiation.

[0023] Figure 7 The diffuse reflectance spectrum and photochromic photograph of the undoped calcium hexaaluminate material prepared in Comparative Example 1 of this invention before and after 15 min of 254 nm ultraviolet irradiation.

[0024] Figure 8 The diffuse reflectance spectrum and photochromic photograph of the europium-doped calcium hexaaluminate material prepared in Comparative Example 2 of this invention before and after 15 min of 254 nm ultraviolet irradiation.

[0025] Figure 9 The diffuse reflectance spectrum and photochromic photograph of the terbium-doped calcium hexaaluminate material prepared in Comparative Example 3 of this invention before and after 15 min of 254 nm ultraviolet irradiation.

[0026] Figure 10 The diffuse reflectance spectrum and photochromic photograph of the praseodymium-doped calcium hexaaluminate material prepared in Comparative Example 4 of this invention before and after 15 min of 254 nm ultraviolet irradiation.

[0027] Figure 11 The diffuse reflectance spectrum and photochromic photograph of the 3% cerium-doped calcium hexaaluminate material prepared in Comparative Example 5 of this invention before and after 15 min of 254 nm ultraviolet radiation.

[0028] Figure 12 The graph shows the change in diffuse reflectance of the cerium-doped calcium hexaaluminate photochromic material prepared in Example 3 of this invention during the photochromic reversibility test.

[0029] Figure 13 The electron paramagnetic resonance spectra of the cerium-doped calcium hexaaluminate photochromic material prepared in Example 2 of this invention before and after ultraviolet radiation are shown. Detailed Implementation

[0030] This invention provides a cerium-doped calcium hexaaluminate photochromic material, the chemical formula of which is Ca. 1- x A1 12 O 19 :xCe, where 0.0025≤x≤0.02.

[0031] Cerium-doped calcium hexaaluminate photochromic material can produce photochromic phenomena when irradiated under a 254nm portable ultraviolet lamp. The sample before and after photochromic changes show obvious color changes, from white to yellow. It has a significant absorption peak at 428nm and the sample before and after photochromic changes has a large difference in light reflectance. It can be applied to anti-counterfeiting and encryption materials.

[0032] Cerium-doped calcium hexaaluminate photochromic materials have , The defects and numerous oxygen vacancies in the material form defect energy levels with a certain trap depth. After irradiation with 254nm ultraviolet light, the material exhibits photochromism, changing from white to yellow.

[0033] The cerium-doped calcium hexaaluminate photochromic material showed no significant decrease in photochromic performance after being subjected to seven alternating exposures to ultraviolet light and heat stimulation. This indicates that the inorganic photochromic material has good reversibility, thermal stability, and fatigue resistance, and can be applied in the field of anti-counterfeiting and encryption.

[0034] The method for preparing cerium-doped calcium hexaaluminate photochromic material provided in this invention includes:

[0035] Al(NO3)3·9H2O, CaCl2, Ce(NO3)3·6H2O and citric acid monohydrate are weighed according to stoichiometric ratio. In the embodiments of the present invention, the ratio of the number of moles of citric acid monohydrate to the total number of moles of Al(NO3)3·9H2O, CaCl2 and Ce(NO3)3·6H2O is (0.5-1.5):1.

[0036] Al(NO3)3·9H2O, CaCl2, Ce(NO3)3·6H2O and citric acid monohydrate were placed in a beaker, and distilled water was added and stirred until a transparent sol was formed.

[0037] Seal the beaker and reflux it at 80-90℃ on a thermostatic magnetic stirrer for 1-2 hours while stirring. Unseal and continue heating and stirring on the thermostatic magnetic stirrer to evaporate the water until a transparent gel is formed.

[0038] A beaker containing transparent gel was placed in an electrically heated drying oven and heat-treated at 180-200℃ for 2-4 hours to form a fluffy precursor powder. The precursor powder was then calcined in a rapid-heating box furnace at 1100-1200℃ for 4-6 hours in air to obtain cerium-doped calcium hexaaluminate photochromic material. The heating rate of the rapid-heating box furnace had no effect on this experiment, and conventional settings were sufficient.

[0039] The method for preparing cerium-doped calcium hexaaluminate photochromic materials involves low synthesis temperature, convenient and safe operation, and allows for direct preparation of photochromic materials in air. The cerium-doped calcium hexaaluminate photochromic materials prepared by this method have uniform particle size and do not require further ball milling.

[0040] The cerium-doped calcium hexaaluminate photochromic material provided by this invention can achieve photochromism under ultraviolet light excitation and can be used in the field of anti-counterfeiting and encryption.

[0041] The technical solution of the present invention will be further described in detail below through specific embodiments.

[0042] Example 1

[0043] This embodiment provides a cerium-doped calcium hexaaluminate photochromic material with the chemical formula Ca. 0.9975 A1 12 O 19 0.0025Ce, its preparation method is as follows:

[0044] (1) Weigh out CaCl2, Al(NO3)3·9H2O, Ce(NO3)3·6H2O and citric acid monohydrate into beakers, where CaCl2 is 0.4428g, Al(NO3)3·9H2O is 18.0062g, Ce(NO3)3·6H2O is 0.0043g and citric acid monohydrate is 16.3909g; then add distilled water and stir until homogeneous to form a transparent sol;

[0045] (2) Seal the beaker and heat and stir it at 80°C for 1 hour on a constant temperature magnetic stirrer. Then unseal it and continue to heat and stir it on the constant temperature magnetic stirrer to evaporate the water until a transparent gel is formed.

[0046] (3) Place the beaker containing the transparent gel in a 180°C electric heating drying oven for 4 hours to form a fluffy precursor powder;

[0047] (4) The precursor powder was placed in a rapid heating box-type resistance furnace and calcined at 1100℃ for 6 hours in air atmosphere to obtain Ca. 0.9975 A1 12 O 19 0.0025Ce photochromic material.

[0048] Example 2

[0049] This embodiment provides a cerium-doped calcium hexaaluminate photochromic material with the chemical formula Ca. 0.995 A1 12 O 19 0.005Ce, its preparation method is as follows:

[0050] (1) Weigh out CaCl2, Al(NO3)3·9H2O, Ce(NO3)3·6H2O and citric acid monohydrate into beakers, where CaCl2 is 0.4417g, Al(NO3)3·9H2O is 18.0062g, Ce(NO3)3·6H2O is 0.0087g and citric acid monohydrate is 8.1955g; then add distilled water and stir evenly to form a transparent sol;

[0051] (2) Seal the beaker and heat and stir it at 85°C for 1.5 hours on a constant temperature magnetic stirrer. Then unseal it and continue to heat and stir it on the constant temperature magnetic stirrer to evaporate the water until a transparent gel is formed.

[0052] (3) Place the beaker containing the transparent gel in a 180°C electric heating drying oven for 3.5 hours to form a fluffy precursor powder;

[0053] (4) The precursor powder was placed in a rapid heating box-type resistance furnace and calcined at 1100℃ for 5 hours in air atmosphere to obtain Ca. 0.995 A1 12 O 19 0.005Ce photochromic material.

[0054] Example 3

[0055] This embodiment provides a cerium-doped calcium hexaaluminate photochromic material with the chemical formula Ca. 0.99 A1 12 O 19 0.01Ce, its preparation method is as follows:

[0056] (1) Weigh out CaCl2, Al(NO3)3·9H2O, Ce(NO3)3·6H2O and citric acid monohydrate into beakers, where CaCl2 is 0.4395g, Al(NO3)3·9H2O is 18.0062g, Ce(NO3)3·6H2O is 0.0174g and citric acid monohydrate is 10.9273g; then add distilled water and stir until homogeneous to form a transparent sol;

[0057] (2) Seal the beaker and heat and stir it at 90°C for 1.5 hours on a constant temperature magnetic stirrer. Then unseal it and continue to heat and stir it on the constant temperature magnetic stirrer to evaporate the water until a transparent gel is formed.

[0058] (3) Place the beaker containing the transparent gel in a 190°C electric heating drying oven for 3 hours to form a fluffy precursor powder;

[0059] (4) The precursor powder was placed in a rapid heating box-type resistance furnace and calcined at 1150°C for 5 hours in air atmosphere to obtain Ca. 0.99 A1 12 O 19 0.01Ce photochromic material.

[0060] Example 4

[0061] This embodiment provides a cerium-doped calcium hexaaluminate photochromic material with the chemical formula Ca. 0.98 A1 12 O 19 0.02Ce, its preparation method is as follows:

[0062] (1) Weigh out CaCl2, Al(NO3)3·9H2O, Ce(NO3)3·6H2O and citric acid monohydrate into beakers, where CaCl2 is 0.4350g, Al(NO3)3·9H2O is 18.0062g, Ce(NO3)3·6H2O is 0.0347g and citric acid monohydrate is 5.4636g; then add distilled water and stir until homogeneous to form a transparent sol.

[0063] (2) Seal the beaker and heat and stir it at 80°C for 2 hours on a constant temperature magnetic stirrer. Then unseal it and continue to heat and stir it on the constant temperature magnetic stirrer to evaporate the water until a transparent gel is formed.

[0064] (3) Place the beaker containing the transparent gel in a 200℃ electric heating drying oven for 2 hours to form a fluffy precursor powder;

[0065] (4) The precursor powder was placed in a rapid heating box-type resistance furnace and calcined at 1200℃ for 4 hours in air atmosphere to obtain Ca. 0.98 A1 12 O 19 0.02Ce photochromic material.

[0066] Comparative Example 1

[0067] This comparative example provides an undoped calcium hexaaluminate material with the chemical formula CaAl. 12 O 19 The preparation method is as follows:

[0068] (1) Weigh CaCl2, Al(NO3)3 9H2O and citric acid monohydrate into beakers, where CaCl2 is 0.4439g, Al(NO3)3 9H2O is 18.0062g and citric acid monohydrate is 8.1955g; then add distilled water and stir until homogeneous to form a transparent sol.

[0069] (2) Seal the beaker and heat and stir it at 85°C for 1.5 hours on a constant temperature magnetic stirrer. Then unseal it and continue to heat and stir it on the constant temperature magnetic stirrer to evaporate the water until a transparent gel is formed.

[0070] (3) Place the beaker containing the transparent gel in a 180°C electric heating drying oven for 3.5 hours to form a fluffy precursor powder;

[0071] (4) The precursor powder was placed in a rapid heating box-type resistance furnace and calcined at 1100°C for 5 hours in air atmosphere to obtain undoped calcium hexaaluminate material.

[0072] Comparative Example 2

[0073] This comparative example provides a europium-doped calcium hexaaluminate material with the chemical formula Ca. 0.995 A1 12 O 19 0.005Eu, its preparation method is as follows:

[0074] (1) Weigh out CaCl2, Al(NO3)3·9H2O, Eu(NO3)3·6H2O and citric acid monohydrate into beakers, where CaCl2 is 0.4417g, Al(NO3)3·9H2O is 18.0062g, Eu(NO3)3·6H2O is 0.0089g and citric acid monohydrate is 8.1955g; then add distilled water and stir until homogeneous to form a transparent sol;

[0075] (2) Seal the beaker and heat and stir it at 85°C for 1.5 hours on a constant temperature magnetic stirrer. Then unseal it and continue to heat and stir it on the constant temperature magnetic stirrer to evaporate the water until a transparent gel is formed.

[0076] (3) Place the beaker containing the transparent gel in a 180°C electric heating drying oven for 3.5 hours to form a fluffy precursor powder;

[0077] (4) The precursor powder was placed in a rapid heating box-type resistance furnace and calcined at 1100℃ for 5 hours in air atmosphere to obtain Ca. 0.995 A1 12 O 19 0.005Eu material.

[0078] Comparative Example 3

[0079] This comparative example provides a terbium-doped calcium hexaaluminate material with the chemical formula Ca. 0.995 A1 12 O 19 0.005Tb, its preparation method is as follows:

[0080] (1) Weigh out CaCl2, Al(NO3)3·9H2O, Tb(NO3)3·6H2O and citric acid monohydrate into beakers, where CaCl2 is 0.4417g, Al(NO3)3·9H2O is 18.0062g, Tb(NO3)3·6H2O is 0.0091g ​​and citric acid monohydrate is 8.1955g; then add distilled water and stir evenly to form a transparent sol;

[0081] (2) Seal the beaker and heat and stir it at 85°C for 1.5 hours on a constant temperature magnetic stirrer. Then unseal it and continue to heat and stir it on the constant temperature magnetic stirrer to evaporate the water until a transparent gel is formed.

[0082] (3) Place the beaker containing the transparent gel in a 180°C electric heating drying oven for 3.5 hours to form a fluffy precursor powder;

[0083] (4) The precursor powder was placed in a rapid heating box-type resistance furnace and calcined at 1100℃ for 5 hours in air atmosphere to obtain Ca. 0.995 A1 12 O 19 0.005Tb material.

[0084] Comparative Example 4

[0085] This comparative example provides a praseodymium-doped calcium hexaaluminate material with the chemical formula Ca. 0.995 A1 12 O 19 0.005Pr, its preparation method is as follows:

[0086] (1) Weigh CaCl2, Al(NO3)3·9H2O, Pr(NO3)3·6H2O and citric acid monohydrate into beakers respectively, wherein CaCl2 is 0.4417g, Al(NO3)3·9H2O is 18.0062g, Pr(NO3)3·6H2O is 0.0087g and citric acid monohydrate is 8.1955g; then add distilled water and stir evenly to form a transparent sol;

[0087] (2) Seal the beaker and heat and stir it at 85°C for 1.5 hours on a constant temperature magnetic stirrer. Then unseal it and continue to heat and stir it on the constant temperature magnetic stirrer to evaporate the water until a transparent gel is formed.

[0088] (3) Place the beaker containing the transparent gel in a 180°C electric heating drying oven for 3.5 hours to form a fluffy precursor powder;

[0089] (4) The precursor powder was placed in a rapid heating box-type resistance furnace and calcined at 1100℃ for 5 hours in air atmosphere to obtain Ca. 0.995 A1 12 O 19 0.005Pr material.

[0090] Comparative Example 5

[0091] This comparative example provides a 3% cerium-doped calcium hexaaluminate material with the chemical formula Ca. 0.97 A1 12 O 19 0.03Ce, its preparation method is as follows:

[0092] (1) Weigh CaCl2, Al(NO3)3·9H2O, Ce(NO3)3·6H2O and citric acid monohydrate into beakers, where CaCl2 is 0.4306g, Al(NO3)3·9H2O is 18.0062g, Ce(NO3)3·6H2O is 0.0521g and citric acid monohydrate is 8.1955g; then add distilled water and stir evenly to form a transparent sol;

[0093] (2) Seal the beaker and heat and stir it at 85°C for 1.5 hours on a constant temperature magnetic stirrer. Then unseal it and continue to heat and stir it on the constant temperature magnetic stirrer to evaporate the water until a transparent gel is formed.

[0094] (3) Place the beaker containing the transparent gel in a 180°C electric heating drying oven for 3.5 hours to form a fluffy precursor powder;

[0095] (4) The precursor powder was placed in a rapid heating box-type resistance furnace and calcined at 1100℃ for 5 hours in air atmosphere to obtain Ca. 0.97 A1 12 O 19 0.03Ce material.

[0096] Microstructure analysis:

[0097] The Ca prepared in Example 1 was analyzed using an X-ray diffractometer of model X'Pert3Powder. 0.9975 A1 12 O 19 Phase composition analysis of the 0.0025Ce photochromic material was performed, and the results are as follows: Figure 1 As shown. Figure 1 The X-ray diffraction pattern of the cerium-doped calcium hexaaluminate photochromic material prepared in Example 1 of this invention. Figure 1As can be seen, the diffraction peaks are sharp, indicating good crystallization effect. The main crystalline phase is calcium hexaaluminate, which shows that the preparation method of the present invention can successfully prepare calcium hexaaluminate material.

[0098] Ca was studied using an ESCALAB 250Xi X-ray photoelectron spectrometer. 0.995 A1 12 O 19 The elemental composition of the 0.005Ce photochromic material was tested, and the results are shown below. Figure 2 . Figure 2 The image shows the X-ray photoelectron spectrum of the cerium-doped calcium hexaaluminate photochromic material prepared in Example 2 of this invention. Figure 2 As can be seen, the photoelectron spectral peaks corresponding to Al 2p, Ca 2p, O 1s, and Ce 3d indicate that the sample contains Al, Ca, O, and Ce elements, and does not contain other impurity elements, demonstrating that the preparation method of this invention can successfully prepare cerium-doped calcium hexaaluminate materials. From the right figure, it can be observed that the Ce element in the sample exhibits a Ce0 pattern. 3+ and Ce 4+ A state in which two valence states coexist.

[0099] Performance testing:

[0100] 1. Photochromic performance test

[0101] Test materials: cerium-doped calcium hexaaluminate photochromic materials prepared in Examples 1-4, undoped calcium hexaaluminate material prepared in Comparative Example 1, europium, terbium, and praseodymium-doped calcium hexaaluminate materials prepared in Comparative Examples 2-4, and 3% cerium-doped calcium hexaaluminate material prepared in Comparative Example 5.

[0102] Test equipment: UV3600Plus UV-Vis spectrophotometer, 8W 254nm portable UV lamp, and metal plate with a hollowed-out N-shaped pattern.

[0103] Test Method: Appropriate amounts of the cerium-doped calcium hexaaluminate photochromic materials prepared in Examples 1-4, the calcium hexaaluminate material prepared in Comparative Example 1, the europium, terbium, and praseodymium-doped calcium hexaaluminate materials prepared in Comparative Examples 2-4, and the 3% cerium-doped calcium hexaaluminate material prepared in Comparative Example 5 were taken as samples. First, the diffuse reflectance spectrum was measured using a UV-Vis spectrophotometer. Then, each group of samples was irradiated with a portable UV lamp for 15 minutes, and the diffuse reflectance spectrum was measured again using a UV-Vis spectrophotometer. The UV-Vis spectrophotometer's test wavelength range was 200 nm-800 nm.

[0104] Take an appropriate amount of each group of samples to completely fill the mold, cover the sample with a metal plate with a hollowed-out N-shaped pattern, irradiate with a 254nm portable ultraviolet lamp for 15 minutes, remove the metal plate and take a picture of the sample material.

[0105] Analysis of test results: The test results of the photochromic performance of the cerium-doped calcium hexaaluminate photochromic materials prepared in Examples 1-4 are as follows: Figure 3-6 The photochromic performance test results of the undoped calcium hexaaluminate material prepared in Comparative Example 1 are shown in [reference]. Figure 7 The photochromic properties of the europium, terbium, and praseodymium-doped calcium hexaaluminate materials prepared in Comparative Examples 2-4 are shown in the attached table. Figure 8-10 The photochromic performance test results of the 3% cerium-doped calcium hexaaluminate material prepared in Comparative Example 5 are shown in [reference]. Figure 11 .

[0106] from Figure 3-6 As can be seen, compared with before ultraviolet irradiation, after 15 minutes of 254nm ultraviolet irradiation, the absorption of light by the cerium-doped calcium hexaaluminate photochromic materials prepared in Examples 1-4 was significantly enhanced in the visible light range, with a clear absorption peak at 428nm. After 15 minutes of 254nm ultraviolet irradiation, obvious N-shaped patterns appeared on the surface of the cerium-doped calcium hexaaluminate photochromic materials prepared in Examples 1-4, indicating that the test samples underwent significant photochromism. Among them, the area blocked by the mold was white, and the area forming the N-shaped pattern was yellow, indicating that the color of the sample changed from white to yellow after ultraviolet irradiation, and the color change was significant. The cerium-doped calcium hexaaluminate photochromic materials before and after photochromism have a large difference in light reflectance.

[0107] from Figure 7 It can be seen that the undoped calcium hexaaluminate material prepared in Comparative Example 1 also exhibited photochromism, but the color change of the sample after ultraviolet irradiation was not significant, changing from white to gray. After photochromism, the sample showed overall absorption of visible light, and there was no obvious absorption peak in the diffuse reflectance spectrum. The difference in light reflectance before and after photochromism was also small, indicating that the photochromism was not obvious.

[0108] from Figure 8-10 It can be seen that the europium, terbium, and praseodymium-doped calcium hexaaluminate materials prepared in Comparative Examples 2-4 exhibit overall absorption of visible light after photochromism, with no obvious absorption peak in the diffuse reflectance spectrum. The color of the samples changes from white to gray before and after ultraviolet irradiation, showing relatively low contrast. 0.995 A1 12 O 19 :0.005Eu in Eu 2+ and Eu 3+ The coexistence state exists, Ca 0.995 A1 12 O 19 :0.005Tb in Tb 3+ and Tb 4+ The coexistence state exists, Ca0.995 A1 12 O 19 :0.005Pr in Pr 3+ and Pr 4+ The coexistence of europium, terbium, and praseodymium in multiple valence states did not cause the material to exhibit more pronounced photochromic changes.

[0109] And from Figure 11 It can be seen that the 3% cerium-doped calcium hexaaluminate material prepared in Comparative Example 5 hardly exhibited photochromism, and the color change of the sample before and after ultraviolet irradiation was very small, with almost no N-type pattern observed.

[0110] 2. Photochromic reversibility test

[0111] Test material: Ca prepared in Example 3 0.99 A1 12 O 19 0.01Ce photochromic material.

[0112] Test equipment: UV3600Plus UV-Vis spectrophotometer, 8W 254nm portable UV lamp, far-infrared microcrystalline heating plate.

[0113] Test method: First, the Ca prepared in Example 3 was tested and recorded using a UV3600Plus UV-Vis spectrophotometer. 0.99 A1 12 O 19 The original diffuse reflectance spectrum of the 0.01Ce photochromic material was recorded, and Ca was also recorded. 0.99 A1 12 O 19 The reflectance value of the 0.01Ce photochromic material at 428nm.

[0114] Thermal bleaching treatment: Ca was treated with an 8W 254nm portable UV lamp. 0.99 A1 12 O 19 Irradiation of 0.01Ce photochromic material for 15 minutes causes Ca to... 0.99 A1 12 O 19 After the 0.01Ce photochromic material exhibited photochromism, its diffuse reflectance spectrum was measured using a UV-Vis spectrophotometer, and the reflectance value at 428 nm was recorded. The photochromic Ca was then subjected to temperature changes at 440℃ using a far-infrared microcrystalline heating plate. 0.99 A1 12 O 19 0.01Ce material is subjected to thermal stimulation, and the Ca after heat bleaching... 0.99 A1 12 O 19After the 0.01Ce material was cooled to room temperature, its diffuse reflectance spectrum was measured using a UV-Vis spectrophotometer, and the reflectance value at 428 nm was recorded. The Ca prepared in the same Example 3 was also analyzed. 0.99 A1 12 O 19 The 0.01Ce photochromic material was subjected to seven repeated thermal bleaching treatments.

[0115] Test Result Analysis:

[0116] Figure 12 The Ca prepared in Example 3 of this invention 0.99 A1 12 O 19 A graph showing the reflectance change of a 0.01Ce photochromic material during a photochromic reversibility test. (From...) Figure 12 It can be seen that after seven cycles of thermal bleaching, the Ca prepared in Example 3 of this invention... 0.99 A1 12 O 19 The relative reflectance of the 0.01Ce photochromic material did not change significantly after each photochromic change or thermal stimulation. This indicates that the photochromic performance of the cerium-doped calcium hexaaluminate photochromic material prepared in Example 3 of this invention has good reversibility. Furthermore, the cerium-doped calcium hexaaluminate photochromic material exhibits thermal stability and fatigue resistance, eliminating the need for high-power lasers or xenon lamps as bleaching light sources. It can be reused multiple times using thermal bleaching treatment. This further demonstrates that the cerium-doped calcium hexaaluminate photochromic material prepared by the method of this invention possesses good photochromic reversibility and can be applied in fields such as anti-counterfeiting encryption, information storage, and optical switches.

[0117] 3. Test of single-ionized oxygen vacancies in samples before and after photochromism

[0118] Ca was studied using a JES FA200 electron paramagnetic resonance spectrometer manufactured by Nippon Electron Ltd. 0.995 A1 12 O 19 The presence of single-ionized oxygen vacancies in samples of the 0.005Ce photochromic material before and after ultraviolet irradiation was tested, and the results are shown in [the table below]. Figure 13 . Figure 13 The Ca prepared in Example 2 of this invention 0.995 A1 12 O 19 Electron paramagnetic resonance spectra of a 0.005Ce photochromic material before and after ultraviolet radiation. From... Figure 13It can be seen that both the samples before and after ultraviolet irradiation exhibit a distinct electron paramagnetic resonance peak at g = 2.002, proving the presence of single-ionized oxygen vacancies in the material. After ultraviolet irradiation, the intensity of the electron paramagnetic resonance signal peak of the single-ionized oxygen vacancies significantly increases, indicating an increase in the content of single-ionized oxygen vacancies, meaning more oxygen vacancies are converted into single-ionized oxygen vacancies, forming more F-type color centers. This is the main reason for the material's photochromic ability. Furthermore, because cerium-doped calcium hexaaluminate possesses… , Defects can form defect energy levels with a certain trap depth in materials, causing the materials to exhibit photochromism from white to yellow after irradiation with 254nm ultraviolet light, and a significant absorption peak at 428nm.

[0119] In summary, the cerium-doped calcium hexaaluminate photochromic material of this invention exhibits photochromic behavior under irradiation with a 254nm portable ultraviolet lamp. After photochromic transformation, the cerium-doped calcium hexaaluminate photochromic material shows a significant macroscopic color change from white to yellow, with a distinct absorption peak at 428nm. The material also exhibits a large difference in light reflectance before and after photochromic transformation. Furthermore, the cerium-doped calcium hexaaluminate photochromic material of this invention possesses excellent photochromic reversibility. With its superior photochromic performance and reversibility, the cerium-doped calcium hexaaluminate photochromic material can be successfully applied in the field of anti-counterfeiting and encryption materials.

Claims

1. A cerium-doped calcium hexaaluminate photochromic material, characterized in that, The chemical formula of this material is Ca. 1-x Al 12 O 19 :xCe, where 0.0025≤x≤0.02; and Ce is less than or equal to Ce. 3+ and Ce 4+ A state of coexistence exists.

2. A method for preparing the cerium-doped calcium hexaaluminate photochromic material according to claim 1, characterized in that, Includes the following steps: (1) Al(NO3)3·9H2O, CaCl2, Ce(NO3)3·6H2O, citric acid monohydrate and water are mixed and stirred to obtain a sol. Then the sol is heated to obtain a gel. (2) The gel was heat-treated and calcined to obtain cerium-doped calcium hexaaluminate photochromic material.

3. The method according to claim 2, characterized in that, In step (1), the ratio of the number of moles of citric acid monohydrate to the total number of moles of Al(NO3)3·9H2O, CaCl2 and Ce(NO3)3·6H2O is (0.5-1.5):

1.

4. The method according to claim 2, characterized in that, In step (1), the process of heating the sol to obtain the gel involves sealing the sol, heating and stirring it under reflux at 80-90°C for 1-2 hours, then unsealing the sol and continuing to heat and stir it to form the gel.

5. The method according to claim 2, characterized in that, In step (2), the heat treatment temperature is 180-200℃ and the heat treatment time is 2-4h.

6. The method according to claim 2, characterized in that, In step (2), the calcination temperature is 1100-1200℃ and the calcination time is 4-6h.

7. The method according to claim 6, characterized in that, The calcination atmosphere is air.

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