Preparation method and application of terbium-doped gadolinium oxysulfide luminescent material

Abstract

The invention relates to a preparation method of a terbium-doped gadolinium oxysulfide fluorescent material. The performance of the material is remarkably improved through an optimized high-temperature solid-phase method. According to the process, firstly, polyvinylpyrrolidone (PVP) and dopamine hydrochloride are used as a dispersing agent and a coating agent to prepare uniformly dispersed Gd2O3 and Tb4O7 oxide precursors, then through a fluxing agent system with the synergistic effect of boric acid and lithium carbonate and in combination with a low-temperature pre-sintering-medium-temperature vulcanization-high-temperature crystallization three-stage sintering process, grain aggregation and abnormal growth are effectively inhibited, and the Gd2O3 / Tb4O7 composite material is obtained. And finally, annealing in air to remove carbon impurities to obtain the superfine fluorescent powder with small particle size and narrow distribution. Experiments show that the particle size D50 of the fluorescent powder in the embodiment is 496-678 nm, the fluorescence decay life exceeds 1100 microseconds, the luminous intensity is high, the stability is excellent, and the fluorescent powder has wide application prospects in the fields of liquid crystal display, biomedicine and the like.

Description

Technical Field

[0001] This invention relates to the field of fluorescent materials technology, specifically to a method for preparing and applying a terbium-doped gadolinium oxide luminescent material, which possesses properties such as small particle size, narrow distribution, high luminescence intensity, and excellent stability. Background Technology

[0002] In modern science and industry, luminescent materials play a crucial role. With the rapid development of display technology, the demand for high-definition displays and flexible displays is constantly increasing, leading to a growing need for high-performance luminescent materials. In the lighting field, there is a strong focus on efficient, energy-saving luminescent materials with good color reproduction to meet the lighting needs of various scenarios. Meanwhile, in the biomedical field, fluorescent labeling materials require specific luminescent properties to achieve accurate detection and diagnosis.

[0003] Gadolinium oxysulfide is an excellent luminescent matrix, characterized by narrow spectral bands, high color purity, high light absorption and conversion efficiency, and good physical and chemical stability, making it crucial for applications in information, lighting, and imaging. Ideal luminescent materials should have a narrow particle size distribution, be free of agglomeration, and ideally have a spherical structure. This facilitates the production of high-quality device coatings, thereby improving luminous efficiency and lifespan. The small particle size of gadolinium oxysulfide offers numerous advantages: in medical imaging and industrial flaw detection, small particle size improves imaging resolution, more accurately capturing fine structures and lesion information, ensuring product quality; simultaneously, small particle size enhances luminescence uniformity, resulting in more uniform emitted light and improved display effects in flat panel displays. Furthermore, its larger specific surface area enhances its bonding ability and reactivity with other materials, facilitating the preparation of composite materials or devices and increasing binding sites in fluorescent labeling and bioimaging. Small particle size also reduces afterglow effects, improves imaging temporal resolution, and facilitates processing and application, making it easier to disperse and mold, suitable for the fabrication of miniaturized devices. Currently, the main method for preparing rare-earth sulfur oxide luminescent materials is the high-temperature solid-state method (1000℃~1500℃), which has the advantages of simple preparation process, good particle filling, and easy industrialization. However, it also has some disadvantages, such as high reaction temperature, high energy consumption, uneven product size and irregular morphology, and the vapor generated by solid sulfur at high temperatures polluting the environment. Therefore, the future development direction of the high-temperature solid-state method is to improve the preparation process, reduce reaction temperature and environmental pollution, shorten synthesis time, and achieve controllable product morphology and structure, while ensuring excellent material performance. On the basis of ensuring complete reaction, lowering the sintering temperature and shortening the holding time as much as possible will effectively inhibit grain growth, thereby obtaining more uniform and regular products.

[0004] Terbium-doped gadolinium oxysulfate (Gd₂O₂S:xTe) luminescent materials have been widely used in various fields due to their excellent luminescent properties. They possess advantages such as high luminous efficiency, good color purity, and short afterglow, making them highly favored in medical imaging, display technology, lighting, and industrial inspection. However, this material also has some drawbacks. For example, the high-temperature processing required during preparation leads to high energy consumption and makes it difficult to control particle size and morphology. Furthermore, the elemental sulfur used can easily generate polluting vapors at high temperatures, causing some environmental impact. In addition, it faces challenges such as high cost and the need for further improvement in stability in certain applications. Nevertheless, terbium-doped gadolinium oxysulfate luminescent materials, with their unique advantages, remain an important component of the field of luminescent materials, and there is still broad research and development potential for further performance optimization and application expansion.

[0005] The quality of Gd₂O₂S:xTe phosphors primarily depends on their luminescent properties (such as brightness, intensity, and color) and powder characteristics (such as particle size and morphology distribution), all of which require precise control during synthesis. To address this, this invention utilizes a high-temperature solid-state method to prepare terbium-doped gadolinium oxysulfate phosphors through continuous optimization and improvement of the preparation process. This process effectively yields phosphors with smaller particle sizes, narrower particle distributions, and higher luminescence intensity, thereby significantly improving the overall quality of the phosphor and further expanding its application areas. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art. This invention provides a method for preparing terbium-doped gadolinium oxide luminescent materials. It uses a wet chemical method to prepare uniformly distributed Gd2O3 and Tb4O7 oxides as precursors, and then obtains Gd2O2S:xTe fluorescent materials through a high-temperature solid-state reaction. The materials have the characteristics of small particle size, narrow particle size distribution, and high luminescence intensity, which improves the quality of luminescent materials and expands their application fields.

[0007] This invention relates to a luminescent material with the chemical formula Gd2O2S:xTe, where x is the mole fraction and the value of x ranges from 0.01 to 0.1, preferably from 0.01 to 0.03.

[0008] The preparation method of the Gd2O2S:xTe luminescent material of the present invention is carried out according to the following steps:

[0009] (1) Gd2O3 and Tb4O7 were added to an ethanol aqueous solution in a certain stoichiometric ratio and ball-milled for 0.5-2 hours. Polyvinylpyrrolidone and dopamine hydrochloride were added and ball-milled for another 0.5-2 hours. Tris(hydroxymethyl)aminomethane buffer solution was added and ball-milled for 1-2 hours. The mixture was filtered, washed, and dried to obtain coated Gd2O3 / Tb4O7 composite powder.

[0010] (2) The composite powder, sublimed sulfur and flux are mixed and ground, and reacted in a reducing gas. Specifically, the temperature is increased to 400-500℃ at 5-10℃ / min and held for 0.5-1h; the temperature is increased to 700-900℃ at 10-20℃ / min and held for 2-3h; the temperature is further increased to 1000-1100℃ at 10-20℃ / min and held for 1-3h. After cooling in the furnace, the powder is taken out, crushed and sieved to obtain calcined powder.

[0011] (3) Wash with hydrochloric acid solution with pH ≤ 2 to remove residual sulfides and salts, and wash with water until pH is neutral; add to a ball mill and ball mill for 1-4 hours, dry, and anneal in air at 400-600℃ for 0.5-2 hours to obtain the desired Gd2O2S:xTb 3+ Ultrafine fluorescent materials.

[0012] Preferably, in step (1), the concentration of polyvinylpyrrolidone in the solution is 5-10 wt%, the concentration of dopamine hydrochloride in the solution is 1-5 wt%, and the molar ratio of Gd2O3 and Tb4O7 is 1:0.01-0.05.

[0013] Preferably, the ball milling media in step (1) is zirconium oxide, the ball-to-material ratio is 5:1 to 10:1, and the rotation speed is 300 to 400 rpm.

[0014] Preferably, the number-average molecular weight of the polyvinylpyrrolidone is 1-10w.

[0015] Preferably, the volume concentration of ethanol in the aqueous ethanol solution in step (1) is 40-60%.

[0016] Preferably, the drying temperature in step (1) is 70-90℃ and the drying time is 1-3h.

[0017] Preferably, the molar amount of sublimed sulfur in step (2) is 3-8 times that of Gd2O3.

[0018] Preferably, the amount of co-solvent used in step (2) is 0.1-3 wt% of the total mass of Gd2O3 and Tb4O7.

[0019] Preferably, the reducing gas in step (2) is a mixture of hydrogen and nitrogen, wherein the volume percentage of hydrogen is 5-20%.

[0020] Preferably, the flux in step (2) is H3BO3 and Li2CO3, wherein the molar ratio of H3BO3 to Li2CO3 is 1:0.5-3; more preferably, the molar ratio of H3BO3 to Li2CO3 is 1:1-1.5.

[0021] Preferably, the drying in step (3) is carried out in a vacuum at a temperature of 80-90°C for 2-5 hours.

[0022] Preferably, the present invention also relates to a luminescent material, which is prepared by the preparation method of the present invention.

[0023] Preferably, the present invention also provides an application of the luminescent material, specifically in the fields of liquid crystal display, biomedicine, security detection, and optical communication.

[0024] This invention uses polyvinylpyrrolidone (PVP) as a dispersant in ball milling to avoid introducing defects and lattice distortion during ball milling. Dopamine hydrochloride polymerizes to form polydopamine (PDA), which forms a coating layer on the surface of Gd₂O₃ / Tb₄O₇ particles, reducing powder agglomeration. The long-chain molecules of PVP are adsorbed onto the surface of Gd₂O₃ / Tb₄O₇ particles through pyrrolidone groups, providing steric hindrance during ball milling to prevent particle collision and agglomeration, laying the foundation for subsequent uniform polydopamine coating. On one hand, the uniform coating of polydopamine on the oxide surface forms a nanoscale protective layer, preventing uneven dispersion or agglomeration of Gd₂O₃ / Tb₄O₇ powder. On the other hand, the high-temperature carbonization of polydopamine generates a thin carbon layer, which further inhibits grain growth during calcination (similar to carbothermal reduction), resulting in smaller particle size and narrower particle size distribution of the Gd₂O₂S:xTe fluorescent material, further improving the luminescence performance of the fluorescent material.

[0025] This invention uses a mixture of boric acid and lithium carbonate in a specific molar ratio as a flux. Boric acid decomposes into B₂O₃ at high temperatures (above 300°C), making it a strong flux; however, the borate melt formed when boric acid is used alone typically has a high viscosity. The addition of Li₂CO₃ provides Li⁺ ions through Li₂O. On the one hand, because Li… + With a smaller radius, it can easily penetrate into the crystal lattice, which is beneficial to improving the solubility and dispersion of rare earth ions. On the other hand, B2O3 and Li2O react at high temperatures to form low-melting-point lithium borate. At a temperature much lower than that of either of the co-solvents used alone, a sufficient amount of fluid molten phase can be formed, which is beneficial to reducing the formation temperature of the liquid phase and grain growth, and forming powder materials with small particle size and uniform distribution.

[0026] Regarding the amount of flux, an appropriate amount of flux can promote the reaction and uniform grain growth, but an excessive amount can lead to abnormal grain growth or the formation of bulk sintered bodies. The amount of flux used in this invention is 0.1-3 wt% of the total mass of Gd2O3 and Tb4O7, and the molar ratio of H3BO3 to Li2CO3 is 1:0.5-3, which is beneficial to uniform grain growth and the formation of fluorescent materials with more uniform particle size.

[0027] The high-temperature calcination process of this invention is divided into three stages. The first stage is low-temperature pre-calcination, where the temperature is increased to 400-500℃ at a low rate in the low-temperature range (<500℃). This facilitates the pyrolysis of PDA to generate an amorphous carbon layer, which is loaded onto the particle surface and acts as a physical barrier between adjacent grains. The second stage is medium-temperature sulfidation, where the carbon layer acts as a diffusion barrier in the medium-temperature range (700-900℃), delaying the growth of Gd. 3 + / Tb 3 The increased ion migration rate restricts grain growth kinetics, resulting in a narrow particle size distribution. The third stage, high-temperature crystallization, involves heating at 10-20℃ / min to 1000-1100℃. At this temperature range, small grains preferentially dissolve while large grains grow slowly, which is beneficial for grain maturation, repairing surface defects, improving crystal integrity, and narrowing the size distribution. This three-stage sintering process—low-temperature pre-firing, medium-temperature sulfidation, and high-temperature crystallization—effectively solves the problem of grain agglomeration, interrupts the continuous grain growth process, yields finer and more uniform powder, and simultaneously improves the luminescent properties of the fluorescent material.

[0028] In Gd2O2S:xTb 3 During the preparation of fluorescent materials, residual carbon impurities may remain on the surface or inside the material. These impurities not only affect the optical properties of the material but may also lead to an increase in surface defects and reduce structural stability. This invention anneals the fluorescent material in air, effectively removing carbon impurities and repairing surface defects, thereby optimizing the material's optical properties and stability.

[0029] The advantages or beneficial effects of the method for preparing a terbium-doped gadolinium oxide luminescent material of the present invention include at least the following: The present invention improves the performance of the luminescent material by optimizing the process. First, polyvinylpyrrolidone (PVP) is used as a ball milling dispersant, which effectively avoids the introduction of lattice defects during ball milling. Simultaneously, polydopamine (PDA) formed by the polymerization of dopamine hydrochloride reduces powder agglomeration, and the carbon layer generated after carbonization further inhibits grain growth, thereby achieving smaller and narrower particle sizes. Furthermore, the synergistic effect of boric acid and lithium carbonate lowers the temperature of the molten liquid phase. Combined with a three-stage sintering process of "low-temperature pre-calcination - medium-temperature sulfidation - high-temperature crystallization," the continuous growth of grains is effectively delayed, resulting in finer and more uniform powder, while significantly improving the luminescent performance of the fluorescent material. Finally, annealing in air effectively removes carbon impurities and repairs surface defects, further optimizing the optical properties and luminescence intensity stability of the material. Detailed Implementation

[0030] To more clearly illustrate the purpose, technical solution, and advantages of this invention, the technical solution of this invention will be described in detail below through specific embodiments. It should be noted that these embodiments are only for illustrating this invention and not for limiting its scope of protection; the actual scope of protection of this invention should be determined by the claims.

[0031] Unless otherwise specified, the materials and reagents used in the following examples and comparative examples are commercially available. Unless otherwise specified, the amount of each component in the following examples is 1 g per part by weight.

[0032] 1. The main raw materials used in the examples and comparative examples are as follows:

[0033] Gadolinium trioxide: Molecular formula, Gd2O3; Purity 99.9%, purchased from Aladdin Reagent Co., Ltd.

[0034] Terbium heptaoxide: molecular formula, Tb4O7; purity 99.9%, purchased from Sinopharm Chemical Reagent Co., Ltd.

[0035] Polyvinylpyrrolidone: number average molecular weight 40000 g / mol, purchased from Shanghai Kema New Materials Co., Ltd.

[0036] Dopamine hydrochloride: analytical grade, purchased from Guangzhou Jinshi Biotechnology Co., Ltd.

[0037] Tris(hydroxymethyl)aminomethane: analytical grade, purchased from Guangdong Wengjiang Chemical Reagent Co., Ltd.

[0038] Sublimed sulfur: analytical grade, purchased from Aladdin Reagent Co., Ltd.

[0039] Boric acid: molecular formula, H3BO3; purity 99.9%, purchased from Shanghai Maclean Co., Ltd.

[0040] Lithium carbonate: molecular formula, Li2CO3; purity 99.9%, purchased from Sinopharm Chemical Reagent Co., Ltd.

[0041] Other reagents, such as ethanol, were commercially available, and the water used in the experiments was deionized water.

[0042] 2. Specific Implementation Methods of the Examples and Comparative Examples

[0043] Example 1

[0044] A luminescent material with the chemical formula Gd₂O₂S: 0.01Te is prepared by the following steps:

[0045] (1) Add 98.72g Gd2O3 and 1.25g Tb4O7 to 400g ethanol aqueous solution (ethanol:water = 1:1), ball mill for 1h (zirconia balls, ball-to-material ratio 8:1, 350rpm), add 30g polyvinylpyrrolidone and 10g dopamine hydrochloride, continue ball milling for 1.0h, then add 50mL tris(hydroxymethyl)aminomethane buffer solution (pH = 8.5), ball mill for 1.5h, filter, wash 3 times with ethanol, dry at 80℃ for 2h to obtain composite powder.

[0046] (2) Mix and grind 100g of composite powder, 30g of sublimed sulfur, 0.5g of boric acid and 0.5g of lithium carbonate for 30min, react in 5% H2 / 95% N2 (flow rate 100mL / min), heat to 400℃ at 5℃ / min and hold for 1.0h; heat to 700℃ at 15℃ / min and hold for 2h; continue to heat to 1000℃ at 15℃ / min and hold for 2h, cool with the furnace and take out, crush and pass through a 400-mesh sieve to obtain calcined powder.

[0047] (3) The calcined powder was soaked in 1.0 mol / L hydrochloric acid solution to remove residual sulfides and salts, and washed with water until the pH was neutral. The powder was then ball-milled for 3 hours using zirconia balls (ball-to-powder ratio 5:1, speed 300 rpm), vacuum dried at 85℃ for 3 hours, and annealed in air at 400℃ for 1 hour to obtain the desired Gd2O2S: 0.01Tb. 3+ Ultrafine luminescent materials.

[0048] Example 2

[0049] A luminescent material with the chemical formula Gd₂O₂S:0.02Te is prepared by the following steps:

[0050] (1) Add 97.88g Gd2O3 and 2.12g Tb4O7 to 300g ethanol aqueous solution (ethanol:water = 1:1), ball mill for 0.5h (zirconia balls, ball-to-material ratio 6:1, 400rpm), add 32g polyvinylpyrrolidone and 8g dopamine hydrochloride, continue ball milling for 1.0h, then add 50mL tris(hydroxymethyl)aminomethane buffer solution (pH = 8.5), ball mill for 1h, filter, wash 3 times with ethanol, dry at 90℃ for 1.5h to obtain composite powder.

[0051] (2) Mix and grind 100g of composite powder, 40g of sublimed sulfur, 0.2g of boric acid and 0.3g of lithium carbonate for 30min, react in 5% H2 / 95% N2 (flow rate 100mL / min), heat to 450℃ at 10℃ / min and hold for 0.5h; heat to 800℃ at 15℃ / min and hold for 2.5h; continue to heat to 1050℃ at 15℃ / min and hold for 1.5h, cool with the furnace and take out, crush and pass through a 400-mesh sieve to obtain calcined powder.

[0052] (3) The calcined powder was soaked in 1.0 mol / L hydrochloric acid solution to remove residual sulfides and salts, and washed with water until the pH was neutral. The powder was then ball-milled for 3 h using zirconia balls (ball-to-powder ratio 6:1, speed 300 rpm), vacuum dried at 90℃ for 2.5 h, and annealed in air at 450℃ for 0.5 h to obtain the desired Gd2O2S: 0.02Tb.3+ Ultrafine luminescent materials.

[0053] Example 3

[0054] A luminescent material with the chemical formula Gd₂O₂S:0.03Te is prepared by the following steps:

[0055] (1) Add 96.85g Gd2O3 and 3.15g Tb4O7 to 400g ethanol aqueous solution (ethanol:water = 1:1), ball mill for 1.0h (zirconia balls, ball-to-material ratio 7:1, 400rpm), add 27g polyvinylpyrrolidone and 12g dopamine hydrochloride, continue ball milling for 1.0h, then add 50mL tris(hydroxymethyl)aminomethane buffer solution (pH = 8.5), ball mill for 1h, filter, wash 3 times with ethanol, dry at 90℃ for 1.5h to obtain composite powder.

[0056] (2) Mix and grind 100g of composite powder, 60g of sublimed sulfur, 0.8g of boric acid and 1.2g of lithium carbonate for 40min, react in 5% H2 / 95% N2 (flow rate 100mL / min), heat to 500℃ at 10℃ / min and hold for 0.5h; heat to 900℃ at 15℃ / min and hold for 2.0h; continue to heat to 1100℃ at 15℃ / min and hold for 2.0h, cool with the furnace and take out, crush and pass through a 400-mesh sieve to obtain calcined powder.

[0057] (3) The calcined powder was soaked in 1.0 mol / L hydrochloric acid solution to remove residual sulfides and salts, and washed with water until the pH was neutral. The powder was then ball-milled for 3.5 h using a ball mill (zirconia balls, ball-to-material ratio 6:1, speed 350 rpm), vacuum dried at 80℃ for 4.0 h, and annealed in air at 500℃ for 1.0 h to obtain the desired Gd2O2S: 0.03Tb. 3+ Ultrafine luminescent materials.

[0058] Example 4

[0059] A luminescent material with the chemical formula Gd₂O₂S:0.06Te is prepared by the following steps:

[0060] (1) 93.82g Gd2O3 and 6.18g Tb4O7 were added to 400g of ethanol aqueous solution (ethanol:water = 1:1) and ball-milled for 1.5h (zirconia balls, ball-to-material ratio 8:1, 350rpm). 45g polyvinylpyrrolidone and 15g dopamine hydrochloride were added and ball-milled for another 0.5h. Then 50mL of tris(hydroxymethyl)aminomethane buffer solution (pH = 8.5) was added and ball-milled for another 1.5h. The mixture was filtered, washed three times with ethanol, and dried at 85℃ for 2.0h to obtain composite powder.

[0061] (2) Mix and grind 100g of composite powder, 55g of sublimed sulfur, 0.7g of boric acid and 0.8g of lithium carbonate for 50min, react in 5% H2 / 95% N2 (flow rate 100mL / min), heat to 400℃ at 8℃ / min and hold for 0.5h; heat to 700℃ at 10℃ / min and hold for 2.0h; continue to heat to 1000℃ at 15℃ / min and hold for 1.5h, cool with the furnace and take out, crush and pass through a 400-mesh sieve to obtain calcined powder.

[0062] (3) The calcined powder was soaked in 1.0 mol / L hydrochloric acid solution to remove residual sulfides and salts, and washed with water until the pH was neutral. The powder was then ball-milled for 2.0 h using a ball mill (zirconia balls, ball-to-material ratio 7:1, speed 350 rpm), vacuum dried at 80℃ for 4.0 h, and annealed in air at 400℃ for 0.5 h to obtain the desired Gd2O2S: 0.06Tb. 3+ Ultrafine luminescent materials.

[0063] Example 5

[0064] A luminescent material with the chemical formula Gd₂O₂S:0.08Te is prepared by the following steps:

[0065] (1) Add 92.60g Gd2O3 and 7.40g Tb4O7 to 400g ethanol aqueous solution (ethanol:water = 1:1), ball mill for 1.0h (zirconia balls, ball-to-material ratio 8:1, 350rpm), add 35g polyvinylpyrrolidone and 18g dopamine hydrochloride, continue ball milling for 0.5h, then add 50mL tris(hydroxymethyl)aminomethane buffer solution (pH = 8.5), ball mill for 2.0h, filter, wash 3 times with ethanol, dry at 85℃ for 3.0h to obtain composite powder.

[0066] (2) Mix and grind 100g of composite powder, 62g of sublimed sulfur, 0.5g of boric acid and 0.7g of lithium carbonate for 50min, react in 5% H2 / 95% N2 (flow rate 100mL / min), heat to 450℃ at 8℃ / min and hold for 0.5h; heat to 700℃ at 15℃ / min and hold for 2.0h; continue to heat to 1000℃ at 15℃ / min and hold for 2.0h, cool with the furnace and take out, crush and pass through a 400-mesh sieve to obtain calcined powder.

[0067] (3) The calcined powder was soaked in 1.0 mol / L hydrochloric acid solution to remove residual sulfides and salts, and washed with water until the pH was neutral. The powder was then ball-milled for 1.0 h using a ball mill (zirconia balls, ball-to-material ratio 8:1, speed 400 rpm), vacuum dried at 85℃ for 3.0 h, and annealed in air at 450℃ for 0.5 h to obtain the desired Gd2O2S: 0.08Tb.3+ Ultrafine luminescent materials.

[0068] Comparative Example 1

[0069] The difference from Example 1 is that polyvinylpyrrolidone is not added in step (1), but otherwise it is the same as Example 1.

[0070] Comparative Example 2

[0071] The difference from Example 1 is that dopamine hydrochloride is not added in step (1), but otherwise it is the same as Example 1.

[0072] Comparative Example 3

[0073] The difference from Example 1 is that in step (2), an equal amount of boric acid is used instead of lithium carbonate, that is, the amount of boric acid is 1g and the amount of lithium carbonate is 0g, and the rest is the same as in Example 1.

[0074] Comparative Example 4

[0075] The difference from Example 1 is that in step (2), an equal amount of lithium carbonate is used instead of boric acid, that is, the amount of lithium carbonate is 1g and the amount of boric acid is 0g, and the rest is the same as in Example 1.

[0076] Comparative Example 5

[0077] The difference from Example 1 is that the sintering process in step (2) is as follows: the temperature is raised to 1000℃ at 25℃ / min and held for 5.0h; after cooling in the furnace, it is taken out, crushed and passed through a 400-mesh sieve to obtain calcined powder, and the rest is the same as in Example 1.

[0078] Comparative Example 6

[0079] The difference from Example 1 is that the sintering process in step (2) is as follows: the temperature is increased to 700℃ at 15℃ / min and held for 3 hours; the temperature is increased to 1000℃ at 25℃ / min and held for 2 hours. After cooling in the furnace, the powder is taken out, crushed and passed through a 400-mesh sieve to obtain calcined powder. The rest is the same as in Example 1.

[0080] Comparative Example 7

[0081] The difference from Example 1 is that the sintering process in step (2) is as follows: the temperature is increased to 400℃ at 5℃ / min and held for 1.0h; the temperature is increased to 1000℃ at 25℃ / min and held for 4h. After cooling in the furnace, the powder is taken out, crushed and passed through a 400-mesh sieve to obtain calcined powder. The rest is the same as in Example 1.

[0082] Comparative Example 8

[0083] The difference from Example 1 is that the sintering process in step (3) is as follows: the calcined powder is soaked in 1.0 mol / L hydrochloric acid solution to remove residual sulfides and salts, and washed with water until the pH is neutral; the powder is then ball-milled for 3 hours using a ball mill (zirconia balls, ball-to-material ratio 5:1, speed 300 rpm), and vacuum dried at 85℃ for 3 hours to obtain the desired Gd2O2S: 0.01Tb. 3+ Ultrafine luminescent material. The annealing process was omitted; otherwise, it was the same as in Example 1.

[0084] Comparative Example 9

[0085] Gd₂O₂S: 0.01Tb was prepared using a conventional high-temperature solid-state method. 3+ Fluorescent materials specifically include the following steps:

[0086] (1) Mix and grind 98.72g Gd2O3, 1.25g Tb4O7, 30g sublimed sulfur, 0.5g boric acid and 0.5g lithium carbonate for 30min, react in 5% H2 / 95% N2 (flow rate 100mL / min), heat to 1100℃ at 25℃ / min, keep warm for 5h, cool with furnace and take out, crush and pass through 400 mesh sieve to obtain calcined powder.

[0087] (2) The calcined powder was soaked in 1.0 mol / L hydrochloric acid solution to remove residual sulfides and salts, and washed with water until the pH was neutral. The powder was then ball-milled for 3 h using zirconia balls (ball-to-powder ratio 5:1, speed 300 rpm) and vacuum dried at 85℃ for 3 h to obtain the desired Gd2O2S: 0.01Tb. 3+ Luminescent materials.

[0088] 3. Performance Evaluation:

[0089] The terbium-doped gadolinium oxide luminescent materials prepared in the examples and comparative examples were subjected to relevant performance tests. The specific test methods are as follows:

[0090] (1) Particle size distribution

[0091] Particle size distribution: The particle size of the luminescent materials in the examples and comparative examples was determined using a laser particle size analyzer. The D50 particle size, D10 and D90 are shown in Table 1.

[0092] (2) Stability analysis

[0093] The stability of the luminescent material was characterized by testing the changes in its photoelectric parameters under high temperature and high humidity conditions. Specifically, this included stability under high temperature and high humidity conditions: high temperature treatment referred to aging at 150℃ for 240 hours, and high humidity treatment referred to accelerated aging of the luminescent material at 100℃ and 85% RH for 240 hours, with the rate of change in luminescent properties being measured. The luminescence intensity of Gd₂O₂S:Tb was measured using a FLSP-920 fluorescence spectrometer with an excitation wavelength of 295 nm. The test results of the luminescence intensity are shown in Table 1.

[0094] (3) Fluorescence decay lifetime

[0095] The fluorescence decay lifetime of the luminescent material Gd₂O₂S:Tb was measured using a Delta flex fluorescence lifetime meter, with an excitation wavelength of λ. ex The emission wavelength is 280nm, λ em The fluorescence lifetime is 544nm ± 5nm, used to characterize luminescence efficiency and stability. A long fluorescence decay lifetime indicates that the excited-state fluorescent molecules can remain in the excited state for a relatively long time after excitation, and are not easily quenched by external environmental factors (such as temperature, solvent polarity, oxygen, etc.); at the same time, it can effectively convert absorbed energy into visible light output, resulting in high luminescence efficiency. The test results are shown in Table 1.

[0096] Table 1: Performance tests of the fluorescent materials in the examples and comparative examples are as follows:

[0097]

[0098]

[0099] According to the test results in Table 1, the particle size of the luminescent materials in Examples 1-5 is mainly distributed between 200-900 nm, and the D50 is between 496-678 nm, exhibiting a relatively concentrated particle size distribution and small particle size. The fluorescence decay lifetime is greater than 1100 μs, and the luminescence intensity at 540-550 nm shows good stability, significantly improving the quality of the fluorescent materials and expanding their application fields. Analysis of the preparation process shows that since polyvinylpyrrolidone and dopamine were added during the wet preparation of the oxide precursor and removed during the pre-calcination stage and annealing treatment, they did not affect the particle size distribution of the samples.

[0100] A comparison of Comparative Examples 1-2 with Example 1 shows that in Example 1, the addition of polyvinylpyrrolidone (PVP) as a ball milling dispersant in the preparation of Gd₂O₃ and Tb₄O₇ oxide precursors effectively avoided lattice defects generated during ball milling. The polydopamine (PDA) formed by the polymerization of dopamine hydrochloride was loaded onto the precursor surface, reducing powder agglomeration. The carbon layer generated after carbonization further inhibited grain growth, resulting in smaller and narrower particle sizes, effectively improving the fluorescence decay lifetime and luminescence intensity of the fluorescent material. Comparative Example 1 omitted the ball milling dispersant, potentially leading to lattice defects. In Comparative Example 2, precursor powder agglomeration occurred, and grain growth continued during carbonization, ultimately resulting in an uneven particle size distribution and reduced luminescence performance in the prepared fluorescent material.

[0101] A comparison of Comparative Examples 3-4 with Example 1 shows that the use of a mixture of boric acid and lithium carbonate in a specific molar ratio as a flux in the embodiments of the present invention can synergistically lower the liquid phase formation temperature, which is beneficial for uniform grain growth and the formation of fluorescent materials with more uniform particle size, thus improving the luminescence performance of the fluorescent materials. Comparative Examples 3-4, using only boric acid or lithium carbonate as a flux, did not form low-melting-point lithium borate at high temperatures, which is detrimental to grain growth, leading to abnormal grain growth and the formation of large sintered bodies, resulting in a decrease in the luminescence intensity and stability of the fluorescent materials.

[0102] A comparison of Comparative Examples 5-9 with Example 1 shows that the three-stage sintering process of "low-temperature pre-calcination - medium-temperature sulfidation - high-temperature crystallization" used in this invention effectively slows down the continuous growth of grains, resulting in finer and more uniform powder, which is beneficial for improving the luminescence intensity and other properties of the fluorescent material. Comparative Examples 5-6 omitted the low-temperature pre-calcination and medium-temperature sulfidation, and were calcined at a rapid heating rate to 1100℃. Comparative Example 7 did not undergo medium-temperature sulfidation, resulting in a fluorescent material with a wide particle size distribution, shorter fluorescence decay lifetime, and poorer luminescence intensity and stability.

[0103] Comparative Example 8 omitted the annealing process, leaving trace amounts of unremoved carbon impurities on or inside the fluorescent material. This leads to increased surface defects, reduced structural stability, and decreased optical performance of the fluorescent material. Comparative Example 9 used a traditional high-temperature solid-state method to prepare terbium-doped gadolinium oxysulfate fluorescent material. The particle size was uneven, with a D90 of 1918 nm. Furthermore, the luminescence intensity and stability of the fluorescent material also decreased significantly.

[0104] The above embodiments are merely examples to illustrate the present invention and are not intended to limit the possible implementations of the invention. Based on the disclosure of this invention, those skilled in the art can make various modifications and adjustments. It is neither possible nor necessary to list all possible implementations. Any modifications, equivalent substitutions, or improvements made within the basic principles and scope of this invention should be considered to fall within the protection scope of this invention.

Claims

1. A method for preparing a terbium-doped gadolinium oxide luminescent material, characterized in that, Includes the following steps: (1) Gd2O3 and Tb4O7 were added to an ethanol aqueous solution in a certain stoichiometric ratio and ball-milled for 0.5-2 hours. Polyvinylpyrrolidone and dopamine hydrochloride were added and ball-milled for another 0.5-2 hours. Tris(hydroxymethyl)aminomethane buffer solution was added and ball-milled for 1-2 hours. The mixture was filtered, washed, and dried to obtain coated Gd2O3 / Tb4O7 composite powder. (2) Mix and grind the composite powder, sublimed sulfur and flux, and heat it to 400-500℃ in a reducing gas at 5-10℃ / min, and keep it at that temperature for 0.5-1h; Heat the material to 700-900℃ at a rate of 10-20℃ / min and hold for 2-3 hours; continue heating the material to 1000-1100℃ at a rate of 10-20℃ / min and hold for 1-3 hours. After cooling in the furnace, remove the material, crush it, and sieve it to obtain calcined powder. (3) Wash with hydrochloric acid solution with pH≤2, then wash with water until pH is neutral; add to a ball mill and ball mill the powder for 1-4 hours, dry, and anneal in air at a temperature of 400-600℃ for 0.5-2 hours to obtain the desired luminescent material. The flux in step (2) is H3BO3 and Li2CO3, wherein the molar ratio of H3BO3 to Li2CO3 is 1:0.5-3.

2. The method for preparing terbium-doped gadolinium oxide luminescent material as described in claim 1, characterized in that, In step (1), the concentration of polyvinylpyrrolidone in the solution is 5-10 wt%, and the concentration of dopamine hydrochloride in the solution is 1-5 wt%; the molar ratio of Gd2O3 and Tb4O7 is 1:0.01-0.

05.

3. The method for preparing terbium-doped gadolinium oxide luminescent material as described in claim 1, characterized in that, In step (1), the ball milling medium is zirconium oxide, the ball-to-material ratio is 5:1 to 10:1, and the rotation speed is 300 to 400 rpm.

4. The method for preparing terbium-doped gadolinium oxide luminescent material as described in claim 1, characterized in that, The number-average molecular weight of the polyvinylpyrrolidone is 1-10w.

5. The method for preparing terbium-doped gadolinium oxide luminescent material as described in claim 1, characterized in that, The volume concentration of ethanol in the aqueous ethanol solution in step (1) is 40-60%; the drying temperature in step (1) is 70-90℃ and the drying time is 1-3h.

6. The method for preparing terbium-doped gadolinium oxide luminescent material as described in claim 1, characterized in that, In step (2), the molar amount of sublimed sulfur is 3-8 times that of Gd2O3; in step (2), the amount of flux is 0.1-3 wt% of the total mass of Gd2O3 and Tb4O7.

7. The method for preparing terbium-doped gadolinium oxide luminescent material as described in claim 1, characterized in that, In step (2), the reducing gas is a mixture of hydrogen and nitrogen, wherein the volume percentage of hydrogen is 5-20%.

8. The method for preparing terbium-doped gadolinium oxide luminescent material as described in claim 1, characterized in that, The drying in step (3) is carried out in a vacuum at a temperature of 80-90°C for 2-5 hours.

9. A terbium-doped gadolinium oxide luminescent material prepared by any one of claims 1-8, characterized in that, The chemical formula of the luminescent material is Gd2O2S:xTe, where x is the mole fraction and the value of x is in the range of 0.01≤x≤0.

1.

10. An application of the luminescent material as described in claim 9, characterized in that, Specifically, it has applications in the fields of liquid crystal displays, biomedicine, security testing, and optical communication.

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