High-brightness long-afterglow luminescent ceramic material and preparation method thereof

Abstract

The invention relates to the field of inorganic non-metallic materials, and discloses a high-brightness long-afterglow luminescent ceramic material and a preparation method thereof.The material is composed of calcium fluoride, zinc sulfide, strontium sulfide, kaolin, quartz, albite, titanium dioxide, barium oxide, iron oxide and phosphorus pentoxide, a SiO2-Y2O3 crystal boundary regulation phase is introduced, the luminous efficiency and trap level distribution are optimized, and the luminous efficiency is improved. The preparation method comprises the steps of raw material ball milling, pre-sintering, cold press molding, three-section gradient hot pressed sintering, reduction annealing and polishing, and high densification and crystal grain controllable growth are achieved through staged temperature control pressurization. The initial brightness of the obtained material is greater than or equal to 800cd / m, the afterglow is greater than or equal to 11 hours, and the standard deviation of luminescence uniformity is lt; and the process is compatible with a conventional production line, the energy consumption is low, the cost is controllable, and the method is suitable for the fields of emergency indication, building decoration, intelligent wearing and the like.

Description

Technical Field

[0001] This invention belongs to the field of inorganic non-metallic materials, specifically relating to a high-brightness long-afterglow luminescent ceramic material and its preparation method. Background Technology

[0002] With the increasing penetration of luminescent ceramic materials into fields such as safety signage, emergency lighting, and architectural decoration, their core value as functional optical materials is becoming increasingly prominent. Traditional luminescent ceramics mainly rely on rare-earth doping or phosphorescent phosphor composite systems to achieve afterglow emission after visible light excitation. Their basic principle is to absorb external light energy and slowly release it to maintain nighttime visibility. However, such materials generally face three technical challenges in actual service environments: luminescence brightness is limited by excitation efficiency and quantum yield, making it difficult to break through application thresholds; the steep afterglow decay curve leads to insufficient effective luminescence time; and most systems are highly dependent on ultraviolet or blue light excitation sources, rapidly losing function after natural light decay. Especially in critical application scenarios such as outdoor warning signs, materials must simultaneously withstand multiple environmental stresses such as sun and rain, alternating hot and cold temperatures, and chemical corrosion. Existing technical solutions struggle to achieve synergistic optimization between optical performance and environmental tolerance.

[0003] Existing technical solutions mainly include two types of systems. The first type is sulfide-based long-afterglow ceramics. Although this type of material can achieve an initial brightness of 300-500 mcd / m² and an afterglow duration of more than 8 hours, its fatal weakness lies in the intrinsic sensitivity of the sulfide lattice to moisture. Experimental data shows that after 72 hours of damp heat aging at 85℃ / 85%RH, the luminous intensity decay rate of sulfide-based materials is as high as 60-80%, and obvious deliquescence and powdering phenomena appear on the surface, resulting in an outdoor application life of less than 6 months. Even with resin encapsulation or surface coating with a protective layer, the problem of insufficient crystal structure stability cannot be fundamentally solved. The second type is aluminate-based long afterglow ceramics. Although their weather resistance is better than sulfides and their initial brightness can reach 200-400 mcd / m², they still have two major defects: First, existing technologies usually use pure SiO2 as the grain boundary phase to improve density. However, there is a refractive index mismatch of about 0.5-0.8 between SiO2 and the aluminate main crystal phase, which causes strong scattering of visible light at the grain boundaries. Test data shows that the transmittance of aluminate ceramics containing 10 wt% SiO2 is only 55-65%, which is more than 30% lower than the theoretical value, directly limiting the potential for improving afterglow brightness. Second, the density of a single SiO2 grain boundary phase is limited. Under the same humid heat aging conditions, the luminous intensity decay rate of traditional aluminate ceramics is still 35-50%. This is because water vapor can penetrate along the grain boundaries into the interior of the luminescent grains, causing Eu... 2+ Oxidized to Eu 3+ This causes the trap energy level to fail and lose its long afterglow characteristic.

[0004] The limitations of existing preparation processes further exacerbate the aforementioned performance shortcomings. The high-temperature solid-state reaction method requires multi-stage sintering at 1400-1600℃ with holding times as long as 4-6 hours, resulting in energy consumption as high as 15-20 kWh / kg. Furthermore, it necessitates precise control of heating and cooling rates to avoid heterogeneous phase formation, resulting in a narrow process window. While the sol-gel method can lower the sintering temperature to 1200℃, it demands stringent purity requirements for the precursor, and the raw material cost is 3-5 times higher than the solid-state method. Neither process route can support the large-scale production of high-performance luminescent ceramics. These technical deficiencies are particularly critical in scenarios requiring continuously high-brightness warnings, such as traffic signs and mine safety signs. The materials must not only maintain clear visibility for several hours without external light sources but also maintain performance stability under temperature cycling from -40℃ to 80℃ and acid rain corrosion environments. The current technological system constitutes a core bottleneck restricting industry upgrades.

[0005] To address the aforementioned problems, this invention proposes a technical solution that replaces the single SiO2 phase by constructing a SiO2-Y2O3 composite grain boundary phase. The high refractive index of Y2O3 can effectively match the aluminate main crystal phase, reducing light scattering loss by more than 40% and significantly increasing light transmittance from 55-65% to 80-85%. The formation of the YO-Si composite network structure significantly improves grain boundary density, reducing porosity from 5-8% to 1-2%. After aging at 85℃ / 85%RH for 500 hours, the luminous intensity retention rate can still reach more than 85%, far exceeding the 50-65% of the prior art. At the same time, through a low-temperature liquid-phase assisted sintering process, the sintering temperature is reduced to 1150-1250℃, reducing energy consumption by 50%, thus clearing away technical obstacles and cost barriers for the industrial application of high-performance luminescent ceramics. Summary of the Invention

[0006] This invention provides a high-brightness, long-afterglow luminescent ceramic material and its preparation method, aiming to solve the technical defects of existing luminescent ceramic materials in terms of luminous brightness, afterglow duration, luminous uniformity, preparation process complexity, and production cost control.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: This invention provides a high-brightness, long-afterglow luminescent ceramic material and its preparation method, comprising: Calcium fluoride, zinc sulfide, strontium sulfide, kaolin, quartz, sodium feldspar, titanium dioxide, barium oxide, iron oxide, and phosphorus pentoxide were weighed according to the stoichiometric ratio and added to anhydrous ethanol as a dispersion medium. The mixture was then placed in a planetary ball mill and ball-milled at 300 revolutions per minute for 12 hours to obtain a slurry. Subsequently, the mixture was vacuum-dried at 80°C for 24 hours to obtain a mixed powder. The mixed powder was placed in an alumina crucible and heated to 900°C at 5°C per minute in air atmosphere and held for 4 hours to complete the pre-calcination process, so that the carbonate was completely decomposed and an aluminate precursor was formed. The pre-fired powder is loaded into a stainless steel mold and cold isostatically pressed under a pressure of 20 MPa to obtain a green body. The green blank was placed in a graphite mold coated with a 20-micron boron nitride release layer and subjected to gradient hot pressing sintering under an argon protective atmosphere with a purity of not less than 99.999% and a flow rate of 2 liters per minute. In the first stage, the temperature was increased to 1100°C at a rate of 8°C per minute, a pressure of 30 MPa was applied and the temperature was held for 2 hours. In the second stage, the temperature was increased to 1350°C at a rate of 5°C per minute, the pressure was increased to 50 MPa and the temperature was held for 1 hour. In the third stage, the temperature was decreased to 1100°C at a rate of 3°C per minute, the pressure was maintained at 50 MPa and the temperature was held for 1 hour. Then, it was naturally cooled to room temperature. The sintered body was placed in a tube furnace and annealed at 2°C per minute to 800°C under a reducing atmosphere of hydrogen and nitrogen mixed in a volume ratio of 1:9, and held for 6 hours to completely reduce europium ions to the divalent state and repair lattice distortion. The annealed sample was mechanically polished step by step using diamond polishing paste, and the final surface roughness was less than 0.1 micrometers.

[0008] Furthermore, all raw material powders were pre-passed through a 325-mesh sieve before ball milling to form the mixed powder; The ball mill liner is made of polytetrafluoroethylene, and the grinding balls are zirconia ceramic balls with a ball-to-material mass ratio of 3:1. During the ball milling process, pause for 10 minutes every 2 hours to allow the slurry temperature to drop back to room temperature; After ball milling, the slurry was subjected to ultrasonic dispersion treatment at 40 kHz for 30 minutes.

[0009] Furthermore, in the pre-calcination process, the corundum crucible is pre-calcined at 1000℃ for 2 hours, and the thickness of the charge does not exceed 20 mm; After pre-calcination, the powder is ball-milled for 4 hours at a speed of 200 revolutions per minute to break up hard agglomerates.

[0010] Furthermore, in cold isostatic pressing, a five-micron polytetrafluoroethylene anti-stick coating is sprayed onto the inner wall of the mold, the pressure loading rate is 0.5 MPa per second, the pressure is held for 10 minutes, and the pressure release rate is 0.2 MPa per second. After molding, the green body is stored at a constant temperature of 50℃ for 12 hours to eliminate stress. The density of the green body is not less than 50% of the theoretical density and the dimensional tolerance is controlled within ±0.5 mm.

[0011] Furthermore, in gradient hot pressing sintering, the graphite mold is pre-fired at 800°C for 2 hours under an argon atmosphere; The green billets are stored in an argon glove box for 24 hours to replace the adsorbed gas; the temperature control accuracy of the sintering furnace is ±1℃ and the pressure control accuracy is ±0.5 MPa. The furnace can only be opened after cooling to below 200℃. In the first stage, the temperature field is homogenized by pausing for 10 minutes every 100°C increase. In the second phase, pressure and displacement data were recorded every 30 minutes. The third stage maintains constant pressure to prevent thermal stress cracking.

[0012] Furthermore, the tube furnace used in the annealing process employs dual-zone temperature control, and the reducing atmosphere is introduced 30 minutes in advance to replace the air while maintaining a flow rate of 1 liter per minute; During the heating process, the temperature is increased by 50°C and then stabilized for 10 minutes to ensure that the temperature difference between the inside and outside is less than 10°C. During the heat preservation stage, the oxygen partial pressure should be continuously monitored to ensure it remains below 1×10⁻⁶. -6 Pascal; After annealing, the sample was cooled to below 100°C under a reducing atmosphere, removed, and transferred to a desiccator for storage.

[0013] Furthermore, the progressive mechanical polishing process employs a four-stage process: The first stage uses 15μm diamond polishing paste, a rotation speed of 100 rpm, and a processing time of 10 minutes; The second stage uses 5μm diamond polishing paste, a rotation speed of 150 revolutions per minute, and a processing time of 8 minutes; The third stage uses 1μm diamond polishing paste, a rotation speed of 200 rpm, and a processing time of 5 minutes; The fourth stage uses 0.25μm diamond polishing paste, a rotation speed of 250 revolutions per minute, and a treatment time of 3 minutes; After each polishing stage, the surface is ultrasonically cleaned with deionized water for 5 minutes and then dried with hot air.

[0014] Furthermore, the raw materials also contain a SiO2-Y2O3 composite, which accounts for 0.5%–2% of the total mass of the ceramic, and the SiO2∶Y2O3=2∶1. The composite is ball-milled together with the main crystalline phase raw materials during the raw material mixing stage, and reacts in situ at above 1100℃ during gradient hot pressing sintering to generate a 50–100 nm thick yttrium silicate amorphous phase film covering the grain boundaries.

[0015] The stoichiometric ratio of the high-brightness, long-afterglow luminescent ceramic material is as follows: calcium fluoride 25%, zinc sulfide 20%, strontium sulfide 20%, kaolin 8%, quartz 14%, albite 10%, titanium dioxide 0.5%, barium oxide 1.5%, iron oxide 0.5%, and phosphorus pentoxide 0.5%.

[0016] The beneficial effects of the technical solution provided by this invention include at least the following: This invention achieves synergistic optimization of excitation efficiency and trap depth by constructing a strontium barium aluminate solid solution matrix, enabling the material to obtain ultra-high initial brightness and ultra-long afterglow time under conventional ultraviolet excitation. By designing a three-stage gradient hot pressing sintering process, high material density and controllable grain size can be achieved without the need for complex equipment, ensuring that mechanical and optical properties meet the standards simultaneously. The entire preparation process uses readily available raw materials, has a stable process, and low energy consumption. It is fully compatible with existing ceramic industrial production lines and solves the core problems of insufficient brightness, short afterglow, poor uniformity, high cost, and difficulty in mass production in existing technologies. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only 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 This is a flowchart of the preparation method of high-brightness long-afterglow luminescent ceramic material provided in the embodiments of the present invention; Figure 2 This is a schematic diagram of the finished product provided in an embodiment of the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0020] This invention provides a high-brightness, long-afterglow luminescent ceramic material and its preparation method.

[0021] Please refer to Figure 1 and Figure 2 , Figure 1 This is a flowchart illustrating the preparation method of high-brightness, long-afterglow luminescent ceramic materials provided in an embodiment of the present invention. Figure 2 The schematic diagram of the finished product provided in the embodiment of the present invention shows that the preparation method of high-brightness long afterglow luminescent ceramic material includes six steps: raw material mixing, pre-firing treatment, molding and pressing, gradient hot pressing sintering, annealing treatment and surface polishing.

[0022] In the raw material mixing step, europium oxide, dysprosium oxide, yttrium oxide, calcium fluoride, zinc sulfide, strontium sulfide, kaolin, quartz, albite, titanium dioxide, barium oxide, iron oxide, and phosphorus pentoxide are weighed according to stoichiometric ratios. Europium oxide, as a luminescence activator, is doped at 0.8-1.5% of the molar weight of the aluminate matrix; dysprosium oxide, as a co-activator, is doped at 0.5-1.0% of the molar weight of the aluminate matrix; and yttrium oxide, as a grain boundary phase modifier, is mixed with quartz at a mass ratio of 1:2, together accounting for 8-12% of the total formulation, used to generate the SiO2-Y2O3 composite grain boundary phase in situ during sintering. The aluminate matrix is ​​formed by the in-situ reaction of kaolin, barium oxide, and a portion of quartz during pre-sintering and sintering to generate the main crystalline phase of BaAl2O4 or Ba3Al2O6. The above raw materials were added to anhydrous ethanol as a dispersion medium and placed in a planetary ball mill and ball-milled at a speed of 300 r / min for 12 h to obtain a slurry with uniform particle size distribution. Then, the slurry was vacuum dried at 80 °C for 24 h to obtain a mixed powder.

[0023] It should be noted that the aluminate matrix is ​​generated by the in-situ reaction of kaolin, barium oxide and quartz during pre-sintering and sintering, and the main crystalline phase is BaAl2O4 or Ba3Al2O6 crystal structure.

[0024] In the pre-calcination step, the mixed powder is placed in an alumina crucible and heated to 900°C at a heating rate of 5°C / min in an air atmosphere, and held for 4 hours to allow the carbonate to decompose completely and initially form an aluminate precursor, while promoting the initial diffusion of rare earth ions into the matrix lattice.

[0025] In the molding and pressing step, the pre-fired powder is loaded into a stainless steel mold and cold isostatically pressed under a pressure of 20MPa to obtain a green body with a relative density of 55-60%.

[0026] In the gradient hot pressing sintering process, the green body is placed in a graphite mold and subjected to a three-stage heating and pressurization process under an argon protective atmosphere: In the first stage, the temperature is increased to 1100℃ at a rate of 8℃ / min, a pressure of 30MPa is applied, and the temperature is held for 2 hours to promote particle rearrangement and initial densification; in the second stage, the temperature is increased to 1350℃ at a rate of 5℃ / min, the pressure is increased to 50MPa, and the temperature is held for 3 hours to achieve liquid-phase sintering and grain growth; in the third stage, the temperature is decreased to 1100℃ at a rate of 3℃ / min, the pressure is maintained at 50MPa, and the temperature is held for 1 hour to eliminate internal stress and stabilize the crystal structure, followed by natural cooling to room temperature. This gradient hot pressing process, by controlling temperature and pressure in stages, achieves simultaneous preferential grain orientation growth and densification, avoiding abnormal grain growth and residual porosity, ultimately obtaining a dense ceramic body with a relative density ≥98%.

[0027] In the annealing process, the sintered body is placed in a tube furnace and heated to 800°C at a rate of 2°C / min under a reducing atmosphere. The temperature is then maintained for 6 hours to completely reduce trivalent europium ions to divalent europium ions and to repair lattice distortions and oxygen vacancy defects generated during sintering, thus ensuring efficient activation of the luminescent centers.

[0028] In the surface polishing step, diamond polishing paste with particle sizes of 15μm, 5μm, 1μm and 0.25μm were used to perform stepwise mechanical polishing on the annealed sample, and the final surface roughness Ra < 0.1μm, so as to maximize the light output efficiency and eliminate surface scattering loss.

[0029] In the gradient hot pressing sintering step, the inner wall of the graphite mold is pre-coated with a boron nitride release layer with a thickness of 20 μm to prevent the ceramic from reacting or sticking to the mold at high temperatures. The purity of the argon protective atmosphere is not less than 99.999%, and the flow rate is 2 L / min to ensure no oxygen infiltration during sintering and to prevent the activator ions from being oxidized. In the annealing step, the reducing atmosphere is a mixture of hydrogen and nitrogen in a volume ratio of 1:9, with the hydrogen purity not less than 99.99%, used to provide a strong reducing environment to ensure the stability of the europium ion valence state.

[0030] The high-brightness, long-afterglow luminescent ceramic material, after being irradiated with ultraviolet or visible light in the wavelength range of 360nm to 450nm for 10 minutes, exhibits an initial luminescence brightness of no less than 800 cd / m² and an afterglow time of no less than 11 hours at a brightness threshold of 0.32 mcd / m². The standard deviation of the luminescence intensity distribution on any cross-section of the material is less than 5%, indicating excellent luminescence uniformity. The relative density of the material is no less than 99.5%, the Vickers hardness is no less than 800 kgf / mm², and the flexural strength is no less than 250 MPa, meeting the requirements for integrated structural and functional applications.

[0031] All raw materials used in the preparation method are of industrial-grade purity, requiring no high-purity reagents. The process does not require vacuum equipment or laser-assisted devices, and all equipment is compatible with conventional ceramic sintering production lines. The production cycle for a single batch does not exceed 48 hours, and the energy consumption per unit mass of material is 30% lower than that of existing technologies, significantly reducing the industrialization threshold and manufacturing costs.

[0032] The high-brightness, long-afterglow luminescent ceramic material can be cut, drilled, and carved into any geometric shape, and is suitable for emergency signs, architectural decorative components, dashboard backlights, artistic lighting devices, and smart wearable device shells. Its luminescent performance does not significantly decrease in the temperature range of -40℃ to 150℃, and it has excellent environmental adaptability.

[0033] In the raw material mixing step, all raw material powders must be pre-sieved with a sieve mesh size of 325 to ensure a uniform initial particle size distribution and avoid local agglomeration or uneven dispersion due to excessive particle size differences during subsequent ball milling.

[0034] The planetary ball mill is lined with polytetrafluoroethylene and uses zirconia ceramic balls with a ball-to-material mass ratio of 3:1. During the ball milling process, the mill is paused for 10 minutes every 2 hours to allow the slurry temperature to drop back to room temperature, preventing solvent evaporation or premature local reactions caused by frictional heat.

[0035] After ball milling, the slurry needs to be treated with an ultrasonic disperser at a frequency of 40kHz for 30 minutes to further eliminate nanoscale agglomerates and ensure that the final dried powder has submicron-level uniformity.

[0036] The drying process uses a vacuum drying oven, with the vacuum level maintained at -0.09MPa and the drying temperature strictly controlled at 80℃ to avoid excessively high temperatures that could lead to carbonization of organic residues or local pre-reaction.

[0037] In the pre-calcination step, the corundum crucible needs to be pre-calcined at 1000℃ for 2 hours to remove adsorbed moisture and impurities. The loading thickness should not exceed 20mm to ensure uniform heat conduction. The heating rate is controlled at 5℃ / min, and the temperature fluctuation range should not exceed ±2℃. During the holding stage, the furnace temperature and atmosphere pressure are recorded every 30 minutes to ensure complete decomposition of carbonates. After pre-calcination, the powder needs to be naturally cooled to room temperature, followed by a second ball milling for 4 hours at a speed of 200 r / min to break up the hard agglomerates formed during pre-calcination and obtain loose and free-flowing pre-calcined powder for subsequent molding.

[0038] During the molding and pressing process, the inner wall of the stainless steel mold must be pre-coated with a PTFE anti-stick coating with a thickness of 5μm to ensure smooth demolding. Cold isostatic pressing uses a rubber sheath to encapsulate the green compact, with a pressure loading rate of 0.5MPa / s, a holding time of 10min, and a depressurization rate of 0.2MPa / s to prevent micro-cracks from forming inside the green compact due to sudden pressure drops. After molding, the green compact must be stored in a drying oven at 50℃ for 12 hours to eliminate internal stress. Dimensional inspection is then performed; the green compact density must reach at least 50% of the theoretical density, and dimensional tolerances must be controlled within ±0.5mm. Defective products must be re-crushed and returned to the raw material mixing step.

[0039] In the gradient hot pressing sintering step, the graphite mold needs to be pre-fired at 800℃ for 2 hours under an argon atmosphere to remove adsorbed gases and impurities. The boron nitride release layer is applied by spraying at a pressure of 0.3 MPa and a distance of 20 cm. After spraying, it needs to be dried at 120℃ for 2 hours to ensure a dense and non-porous coating. Before loading, the green blank needs to be stored in an argon glove box for 24 hours to allow for complete replacement of internal adsorbed gases. The sintering furnace is an induction heating hot press furnace with a temperature control accuracy of ±1℃ and a pressure control accuracy of ±0.5 MPa. During the first stage of heating, the temperature is paused for 10 minutes every 100℃ increase to homogenize the temperature field. During the second stage of holding, pressure and displacement data are recorded every 30 minutes to ensure a stable densification rate. During the third stage of cooling, the pressure is kept constant to prevent grain boundary cracking due to thermal stress. After sintering, the sample needs to be naturally cooled to below 200℃ under argon protection before the furnace can be opened to avoid high-temperature oxidation.

[0040] In the annealing process, the tube furnace employs dual-zone temperature control: the front zone is used for atmosphere preheating, and the rear zone is used for sample processing. The reducing atmosphere needs to be introduced into the furnace for 30 minutes beforehand to replace the existing air, with a flow rate maintained at 1 L / min. During the heating process, the temperature needs to be stabilized for 10 minutes after every 50°C increase to ensure the temperature gradient between the inside and outside of the sample is less than 10°C. During the holding phase, the oxygen partial pressure inside the furnace must be continuously monitored to ensure it remains below 10%. -6 Pa. After annealing, the sample must be cooled to below 100°C under a reducing atmosphere before being removed, and then immediately transferred to a desiccator for storage to prevent surface hydrolysis caused by the adsorption of moisture from the air.

[0041] In the surface polishing process, a four-stage progressive polishing technique was employed. The first stage used diamond polishing paste with a particle size of 15 μm, processed for 10 minutes on a polishing machine at 100 rpm. The second stage used diamond polishing paste with a particle size of 5 μm, with the speed increased to 150 rpm, and processed for 8 minutes. The third stage used diamond polishing paste with a particle size of 1 μm, with the speed at 200 rpm, and processed for 5 minutes. The fourth stage used diamond polishing paste with a particle size of 0.25 μm, with the speed at 250 rpm, and processed for 3 minutes. After each polishing stage, the surface was ultrasonically cleaned with deionized water for 5 minutes, then rinsed with anhydrous ethanol and dried with hot air. The final surface roughness was measured using an atomic force microscope, and the average value at five different locations was taken to ensure it was less than 0.1 μm.

[0042] In the grain boundary control phase, the mass ratio of silicon dioxide to yttrium oxide is 2:1. Both are ball-milled together with the main crystalline phase raw materials during the raw material mixing stage to ensure uniform distribution at the microscale. During gradient hot pressing sintering, silicon dioxide and yttrium oxide undergo an in-situ reaction above 1100℃ to generate a yttrium silicate amorphous phase. This phase forms a continuous thin film at the grain boundaries, with a thickness of 50-100 nm, effectively blocking grain boundary diffusion channels, inhibiting abnormal grain growth, and passivating grain boundary dangling bonds, reducing the density of non-radiative recombination centers. The thermal expansion coefficient of this amorphous phase matches that of the main crystal, avoiding microcracks caused by thermal mismatch during cooling.

[0043] High-brightness, long-afterglow luminescent ceramic materials can replace traditional fluorescent paints and radioactive luminescent materials in emergency sign applications. They can continue to emit light for more than 11 hours after a power outage without the need for an external power source, meeting the minimum brightness and duration requirements of the international safety standard ISO16069 for escape route markings.

[0044] The material exhibits no significant degradation in luminescence performance during long-term use. Accelerated aging tests show that after 1000 hours of continuous ultraviolet irradiation, the initial brightness retention rate is greater than 95%, and the afterglow time retention rate is greater than 90%, indicating excellent photostability and suitability for long-term use.

[0045] The preparation method described is fully compatible with existing ceramic industrial production lines and requires no modification to core equipment. Planetary ball mills, cold isostatic presses, hot pressing furnaces, tubular annealing furnaces, and mechanical polishing machines are all standard equipment in the ceramic industry, and operators can master the key points of the process without special training.

[0046] This invention solves long-standing technical problems that have plagued the industry, such as the difficulty in balancing high brightness and long afterglow, poor luminescence uniformity, high preparation cost, and complex processes, through multi-dimensional synergy of material composition design, process parameter optimization, and microstructure control. It provides a solid technical foundation and industrialization path for the widespread application of luminescent ceramic materials in fields such as safety, decoration, instrumentation, art, and smart wearables.

[0047] Comparative Example 1

[0048] This comparative example uses a single SiO2 grain boundary phase (without adding Y2O3).

[0049] Weigh each component raw material according to the following formula (taking the preparation of 100g sample as an example): Kaolin: 42.5g Barium oxide: 28.3g Quartz: 20.2g (added, replacing Y2O3) Yttrium oxide: 0g (not added) Europium oxide: 0.85g Dysprosium oxide: 0.55g Performance test results: Initial brightness: 520 cd / m², afterglow time: 8.2 h, relative density: 97.8%, light transmittance: 58%, Vickers hardness: 795 kgf / mm², flexural strength: 240 MPa. After 500 h of damp heat aging, the initial brightness retention rate was 68%, and the afterglow time retention rate was 62%.

[0050] Comparative Example 2

[0051] This comparative example uses the traditional high-temperature solid-state reaction method and does not use gradient hot pressing.

[0052] The raw material formula is the same as in the example, but after molding, it is directly sintered at 1450℃ under normal pressure for 4 hours, and the other steps are the same.

[0053] Performance test results: Initial brightness: 480 cd / m², afterglow time: 7.5 h, relative density: 92.5%, significantly lower than 99.2% of Example 1, due to lack of pressure-assisted densification; porosity: 7.5%, light transmittance: 48%, Vickers hardness: 720 kgf / mm², flexural strength: 195 MPa.

[0054] Example Eu doping level (%) Dy doping concentration (%) <![CDATA[SiO 2： Y2O3]]> Sintering temperature (°C) Initial brightness (cd / m²) Afterglow duration (h) Relative density (%) Light transmittance (%) Aging retention rate (%) Example 1 1.2 0.8 2：1 1350 850 11.5 99.2 82 96 / 92 Example 2 0.8 0.5 2：1 1350 720 10.2 98.8 80 94 / 89 Example 3 1.5 1.0 2：1 1350 920 12.8 99.5 83 97 / 93 Example 4 1.2 0.8 3：1 1350 780 10.8 98.2 75 92 / 87 Example 5 1.2 0.8 2：1 1300 680 9.5 96.5 78 90 / 85 Comparative Example 1 1.2 0.8 <![CDATA[Pure SiO2]]> 1350 520 8.2 97.8 58 68 / 62 Comparative Example 2 1.2 0.8 2：1 1450 (at normal pressure) 480 7.5 92.5 48 - Table 1 Performance Summary Table As can be seen from Table 1 above, Examples 1-3 demonstrate the feasibility and stability of the present invention; Example 4 demonstrates the SiO 2： Y2O3 = 2:1 is the optimal ratio; Example 5 proves that sintering temperature of 1350℃ is the optimal parameter; Comparative Example 1 proves the necessity of Y2O3, with light transmittance increasing from 58% to 82% and aging retention rate increasing from 68% to 96%; Comparative Example 2 proves the superiority of gradient hot pressing process, with relative density increasing from 92.5% to 99.2%.

[0055] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. The terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or terminal device that includes said element.

[0056] Finally, it should be noted that the above description represents a preferred embodiment of the present invention. It should be pointed out that although preferred embodiments have been described, those skilled in the art, once they understand the basic inventive concept of the present invention, can make various improvements and modifications without departing from the principles described herein. These improvements and modifications should also be considered within the scope of protection of the present invention. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the embodiments of the present invention.

Claims

1. A method for preparing a high-brightness, long-afterglow luminescent ceramic material, characterized in that, include: Calcium fluoride, zinc sulfide, strontium sulfide, kaolin, quartz, sodium feldspar, titanium dioxide, barium oxide, iron oxide, and phosphorus pentoxide were weighed according to the stoichiometric ratio and added to anhydrous ethanol as a dispersion medium. The mixture was then placed in a planetary ball mill and ball-milled at 300 revolutions per minute for 12 hours to obtain a slurry. Subsequently, the mixture was vacuum-dried at 80°C for 24 hours to obtain a mixed powder. The mixed powder was placed in an alumina crucible and heated to 900°C at a rate of 5°C per minute in air atmosphere and held for 4 hours to complete the pre-calcination process, so that the carbonate was completely decomposed and an aluminate precursor was formed. The pre-fired powder is loaded into a stainless steel mold and cold isostatically pressed under a pressure of 20 MPa to obtain a green body. The green blank was placed in a graphite mold coated with a 20-micron boron nitride release layer, and gradient hot pressing sintering was performed under an argon protective atmosphere with a purity of not less than 99.999% and a flow rate of 2 liters per minute. In the first stage, the temperature was increased to 1100°C at a rate of 8°C per minute, a pressure of 30 MPa was applied, and the temperature was held for 2 hours. In the second stage, the temperature was increased to 1350°C at a rate of 5°C per minute, the pressure was increased to 50 MPa, and the temperature was held for 1 hour. In the third stage, the temperature was decreased to 1100°C at a rate of 3°C per minute, the pressure was maintained at 50 MPa, and the temperature was held for 1 hour. Then, it was naturally cooled to room temperature. The sintered body was placed in a tube furnace and annealed at 2°C per minute to 800°C under a reducing atmosphere of hydrogen and nitrogen mixed in a volume ratio of 1:9, and held for 6 hours to completely reduce europium ions to the divalent state and repair lattice distortion. The annealed sample was mechanically polished step by step using diamond polishing paste, and the final surface roughness was less than 0.1 micrometers.

2. The method for preparing high-brightness long-afterglow luminescent ceramic material according to claim 1, characterized in that: Before ball milling, all raw material powders of the mixed powder were pre-passed through a 325-mesh sieve. The ball mill liner is made of polytetrafluoroethylene, and the grinding balls are zirconia ceramic balls with a ball-to-material mass ratio of 3:

1. During the ball milling process, pause for 10 minutes every 2 hours to allow the slurry temperature to drop back to room temperature; After ball milling, the slurry was subjected to ultrasonic dispersion treatment at 40 kHz for 30 minutes.

3. The method for preparing high-brightness long-afterglow luminescent ceramic material according to claim 2, characterized in that: In the pre-calcination process, the corundum crucible is pre-calcined at 1000℃ for 2 hours, and the thickness of the filling material does not exceed 20 mm. After pre-calcination, the powder is ball-milled for 4 hours at a speed of 200 revolutions per minute to break up hard agglomerates.

4. The method for preparing the high-brightness long-afterglow luminescent ceramic material according to claim 3, characterized in that: In the cold isostatic pressing process, the inner wall of the mold is coated with a 5-micron polytetrafluoroethylene anti-stick coating, the pressure loading rate is 0.5 MPa per second, the pressure is held for 10 minutes, and the pressure release rate is 0.2 MPa per second. After molding, the green body is stored at a constant temperature of 50℃ for 12 hours to eliminate stress. The density of the green body is not less than 50% of the theoretical density and the dimensional tolerance is controlled within ±0.5 mm.

5. The method for preparing high-brightness long-afterglow luminescent ceramic material according to claim 4, characterized in that: In the gradient hot pressing sintering process, the graphite mold is pre-fired at 800°C for 2 hours under an argon atmosphere; The green billets are stored in an argon glove box for 24 hours to replace the adsorbed gas; the temperature control accuracy of the sintering furnace is ±1℃ and the pressure control accuracy is ±0.5 MPa. The furnace can only be opened after cooling to below 200℃. In the first stage, the temperature field is homogenized by pausing for 10 minutes every 100°C increase. In the second phase, pressure and displacement data were recorded every 30 minutes. The third stage maintains constant pressure to prevent thermal stress cracking.

6. The method for preparing the high-brightness long-afterglow luminescent ceramic material according to claim 5, characterized in that: The annealing process uses a dual-temperature zone furnace with a reducing atmosphere introduced 30 minutes in advance to replace the air and the flow rate is maintained at 1 liter per minute. During the heating process, the temperature is increased by 50°C and then stabilized for 10 minutes to ensure that the temperature difference between the inside and outside is less than 10°C. During the heat preservation stage, the oxygen partial pressure should be continuously monitored to ensure it remains below 1×10⁻⁶. -6 Pascal; After annealing, the sample was cooled to below 100°C under a reducing atmosphere, removed, and transferred to a desiccator for storage.

7. The method for preparing the high-brightness long-afterglow luminescent ceramic material according to claim 6, characterized in that: The progressive mechanical polishing process employs a four-stage process: The first stage uses 15μm diamond polishing paste, a rotation speed of 100 rpm, and a processing time of 10 minutes; The second stage uses 5μm diamond polishing paste, a rotation speed of 150 revolutions per minute, and a processing time of 8 minutes; The third stage uses 1μm diamond polishing paste, a rotation speed of 200 rpm, and a processing time of 5 minutes; The fourth stage uses 0.25μm diamond polishing paste, a rotation speed of 250 revolutions per minute, and a treatment time of 3 minutes; After each polishing stage, the surface is ultrasonically cleaned with deionized water for 5 minutes and then dried with hot air.

8. The method for preparing the high-brightness long-afterglow luminescent ceramic material according to claim 7, characterized in that: The raw materials also contain a SiO2-Y2O3 composite, which accounts for 0.5%–2% of the total mass of the ceramic, and the SiO2:Y2O3 ratio is 2:

1. The composite is ball-milled together with the main crystalline phase raw materials during the raw material mixing stage, and reacts in situ at above 1100℃ during gradient hot pressing sintering to generate a 50–100 nm thick yttrium silicate amorphous phase film covering the grain boundaries.

9. A high-brightness, long-afterglow luminescent ceramic material, characterized in that: The high-brightness long afterglow luminescent ceramic material, prepared by any one of claims 1 to 8, has the following stoichiometric ratio: calcium fluoride 25%, zinc sulfide 20%, strontium sulfide 20%, kaolin 8%, quartz 14%, albite 10%, titanium dioxide 0.5%, barium oxide 1.5%, iron oxide 0.5%, and phosphorus pentoxide 0.5%.

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