High light extraction efficiency concentration gradient fluorescent ceramic, preparation method and application

Abstract

The application discloses high light extraction efficiency concentration gradient fluorescent ceramic, a preparation method and application, and aims to solve the problems of low light extraction efficiency and poor heat conduction performance in the prior art. The fluorescent ceramic adopts a three-layer composite structure design, and is sequentially provided with a fluorescent ceramic layer, a heat-conducting silica gel layer and a silicon carbide composite ceramic layer from inside to outside. The uniform gradient distribution of the rare earth ion concentration in the fluorescent ceramic layer can reduce the use of the rare earth ions, efficiently utilize the light beam intensity of an excitation source, make the laser output more uniform, and reduce the thermal effect. The heat-conducting silica gel layer effectively improves the light extraction efficiency and reduces internal reflection loss of light through scattering of titanium oxide and graphite powder particles. The silicon carbide composite ceramic layer has high thermal conductivity. The application has excellent optical and thermal properties, the internal quantum efficiency reaches 70-80%, the external quantum efficiency reaches 30-35%, and the luminescent efficiency can reach 96-99% at room temperature under the condition of 473K, and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the fields of laser illumination and near-infrared detection, specifically to a high light extraction efficiency concentration gradient fluorescent ceramic, its preparation method, and its application. Background Technology

[0002] In recent years, near-infrared (NIR) fluorescent materials have been widely used in plant growth lighting, night vision, biomedical imaging, near-infrared detection, photobiology, and information encryption due to their tunable red-to-near-infrared (650-1300nm) emission characteristics. When NIR phosphors are encapsulated in commercial InGaN blue LED chips, the operating temperature can reach approximately 150°C due to heat accumulation in the chip. Meanwhile, the photoluminescence (PL) intensity of fluorescent ceramics typically decreases with increasing temperature due to enhanced non-radiative processes. Therefore, the key lies in developing methods for producing fluorescent ceramics with excellent PL thermal stability.

[0003] The literature (Journal of the American Ceramic Society, 2023, 106(4): 2309-2316.) describes the design and fabrication of multi-level gradient-doped Yb:YAG laser ceramics using a tape casting method to improve the pump absorption efficiency and smooth the temperature gradient of the laser medium, thereby achieving more efficient high-power solid-state laser output. Although existing research has demonstrated the importance of composite gain media for improving thermal management and laser performance, current technologies still have some limitations, making it difficult to completely avoid interface fractures. While maintaining efficient energy conversion, it is necessary to further reduce optical loss centers and improve overall optical quality.

[0004] Invention patent CN107253854A discloses a method for preparing chromium-containing luminescent central ions using slip casting combined with vacuum sintering. 3+ 、Nd 3+ Yb 3+ The matrix is ​​Y3Al5O 12 Or, gradient-doped transparent laser ceramics of Y₂O₃. The concentration of doped ions varies non-uniformly along the radial or axial direction of the ceramic, and the number of types of slurry is the same as the number of gradients. Essentially, this patent utilizes slurry casting, vacuum sintering, and non-uniform gradient to change the ion concentration to improve the slope efficiency and output power of transparent laser ceramics.

[0005] Invention patent CN117209275A describes the preparation of a Lu3Al5O matrix using a gelation method with Isobam as the monomer and vacuum sintering. 12 This patent describes a laser-transparent ceramic. It introduces Yb or Nd as the luminescent element non-uniformly in the Z-direction (radial direction) of the ceramic. Essentially, this patent utilizes the high doping concentration of ions at the beginning of the ceramic end face to absorb the pump light, thus preventing damage to the ceramic.

[0006] Invention patent CN116857594A describes the fabrication of a white-emitting hollow fluorescent ceramic optical fiber via extrusion molding. This invention aims to increase the heat dissipation area through a hollow structure and utilize total internal reflection of light within the air and ceramic to achieve long-distance light propagation.

[0007] Invention patent CN112759396A describes a fluorescent ceramic rod prepared by gel casting, which exhibits low optical spread and can be used for high-power laser illumination. The core of this patent lies in using gel casting for one-time molding and reducing concentration quenching by lowering the rare-earth ion doping concentration to improve luminous efficiency.

[0008] Invention patent CN114394822B describes a face-centered ceramic structure prepared by dry pressing. This face-centered structure coats the fluorescent ceramic surface with an alumina thermally conductive layer, aiming to reduce the impact of a large thermally conductive layer proportion on luminescence.

[0009] Invention patent CN111018512A utilizes tape casting to prepare fluorescent ceramics by stacking fluorescent ceramics with different refractive indices according to their refractive index values. This patent achieves a high color rendering index (CRI) by doping red-emitting ions only in the topmost tape layer during the preparation process. By adjusting the refractive index, it mitigates the light loss caused by excessively small light emission angles in the fluorescent ceramics.

[0010] Invention patent CN117658616A describes a three-layer structure prepared by tape casting, using (Re 1-x Ce x )3Al5O 12 It is a yellow-green fluorescent layer, (A1) 1-y Ce y )3(Al 1-z B z )5O 12 The red fluorescent layer (AlN) serves as the heat dissipation layer. This invention achieves high color index and high-efficiency luminescence by stacking different ceramic layers.

[0011] Invention patent CN118879321A describes a near-infrared fluorescent ceramic (Ba) prepared by calcination. 9- x Sr x Sc 1.98 Cr 0.02 Si6O 24 ,2≤ x ≤8) It is characterized by ease of preparation, good stability, and high luminescence intensity. However, at higher temperatures (such as 413 K), its emission intensity drops significantly to 26.83% of the initial intensity. This indicates that the thermal stability of the material needs to be improved.

[0012] In summary, the issues of light extraction rate and thermal stability faced by fluorescent ceramics greatly limit their application, making it essential to explore new design strategies. Summary of the Invention

[0013] To address the aforementioned problems, this invention proposes a concentration gradient fluorescent ceramic with high light extraction efficiency. The fluorescent ceramic layer and the silicon carbide composite ceramic layer are prepared using ink direct writing (DIW) technology. In the fluorescent ceramic layer, rare earth ions exhibit a gradient distribution within the ceramic, and ultraviolet (UV) light is used for assisted curing during the printing process. The near-infrared (NIR) luminescent ceramic used has the chemical formula Y3Sc3Al2O. 12 : x Cr 3+ (YSAO:Cr) 3+ The thermally conductive silicone layer contains uniformly distributed titanium dioxide and graphite powder, which not only helps dissipate heat but also enhances light scattering. Furthermore, the light scattering rate of the thermally conductive silicone layer is higher than that of the fluorescent ceramic layer, thus improving luminous efficiency. To better protect the luminescent ceramic and prevent light leakage, a silicon carbide composite ceramic layer structure with excellent mechanical properties was prepared, achieving a compressive strength of 12.5 MPa.

[0014] One of the objectives of this invention is to effectively utilize the intensity of the excitation source beam to achieve a uniform decrease in the concentration of rare earth ions along the axial radius, thereby improving the uniformity and stability of light emission and enabling more precise control of optical performance.

[0015] The second objective of this invention is to manufacture three-layer composite fluorescent ceramics using a higher-precision additive manufacturing method. This allows for flexible adjustment of the proportions and properties of each layer, simplifying the production process and better adapting to the specific needs of different fields.

[0016] The third objective of this invention is to effectively scatter light using scattering particles with high refractive index. These scattering particles are added to thermally conductive silicone, and the scattering characteristics are adjusted by controlling the particle size and concentration, thereby optimizing the light path. This method allows more photons to be absorbed within the fluorescent ceramic layer and converted into fluorescence or laser emission. Simultaneously, the scattering effect occurs in the region near the fluorescent surface, helping to overcome the total internal reflection condition, enhancing the amount of light escaping from the interior of the fluorescent ceramic, and thus improving light extraction efficiency.

[0017] To achieve the above objectives, the present invention proposes the following technical solution:

[0018] A concentration gradient fluorescent ceramic with high light extraction efficiency is disclosed. The fluorescent ceramic employs a three-layer composite cylindrical structure, consisting of a fluorescent ceramic layer, a thermally conductive silicone layer, and a silicon carbide composite ceramic layer, arranged sequentially from the inside out. The fluorescent ceramic layer is a cylindrical structure with a radius of 3-6 mm and a height of 1-2 cm, and is made of Y3Sc3Al2O3. 12 : x Cr 3+ fluorescent powder, among which x = 1-7 mol%, Cr in the fluorescent ceramic layer 3+ The concentration gradient distribution gradually decreases from the inside to the outside along the axial radius of the cylindrical structure; the silicon carbide composite ceramic layer is a hollow cylindrical structure with a thickness of 1-3 mm and a height of 1-2 cm; after preparing the fluorescent ceramic layer and the silicon carbide composite ceramic layer using 3D printing technology, a thermally conductive silicone layer slurry prepared by hot pressing is applied to the outer surface of the fluorescent ceramic layer and the inner surface of the silicon carbide composite ceramic layer along the circumferential direction, and the silicon carbide composite ceramic layer is assembled to the outside of the fluorescent ceramic layer. After curing, a high light extraction efficiency concentration gradient fluorescent ceramic with a firm bond between the fluorescent ceramic layer, the thermally conductive silicone layer and the silicon carbide composite ceramic layer is obtained, wherein the thickness of the thermally conductive silicone layer is 2-6 mm.

[0019] The fluorescent ceramic layer has a radius of 3-6 mm and a height of 1-2 cm to ensure a uniform distribution of rare earth ion concentration over a large area and to provide sufficient optical interaction. Furthermore, specific regions of the ceramic (such as high-power-density regions) are treated with higher concentrations of Cr. 3+ The ions are concentrated in one region, while other regions maintain a lower concentration, and the ions are distributed in a uniform gradient. This design effectively avoids Cr... 3+ Localized overheating and phase separation caused by ion aggregation optimize the distribution of optical and thermal properties.

[0020] The thermally conductive silicone layer possesses excellent thermal stability and moderate flexibility, effectively maintaining the integrity and stability of the entire structure. The added scattering particles, titanium dioxide and graphite powder, have high refractive indices. When light enters the ceramic material, it is first reflected or scattered in the outer thermally conductive silicone layer, enhancing the interaction between light and the material. In the inner ceramic layer, light is reflected and re-propagated by the scattering particles, extending the propagation path and increasing the light's residence time and utilization efficiency. By adjusting the particle size, morphology, and ratio of the scattering particles to the matrix material, the optical properties of the composite material can be precisely controlled. The thickness of the thermally conductive silicone layer is 2-6 mm.

[0021] The silicon carbide composite ceramic layer, with a thickness of 1-3 mm, provides excellent strength and high-temperature stability, and exhibits high thermal conductivity (400-700 W·m⁻¹·K⁻¹). The microscopic layered wrinkled structure formed between graphene and silicon carbide effectively inhibits oxygen diffusion and enhances the material's high-temperature oxidation resistance. The combination of graphene's flexibility and silicon carbide's high rigidity enhances the composite material's toughness and crack resistance, achieving a tensile strength of 2-3 GPa.

[0022] This invention employs advanced printing technology to manufacture a functional ceramic component with a composite structure. First, a multi-nozzle 3D printer is used to precisely deposit chromium-doped ceramic components of varying concentrations. 3+ Y3Sc3Al2O ions 12 : x Cr 3+ (YSAO:Cr) 3+ The ceramic is formed by creating a ceramic layer with an internal gradient distribution (concentration gradually decreasing from the center to the periphery). Simultaneously, a silicon carbide composite ceramic slurry is prepared and then printed. After the fluorescent ceramic and silicon carbide composite ceramic blanks have naturally dried, they are subjected to high-temperature sintering. After sintering, the surface is cleaned and polished, then a thermally conductive silicone slurry is applied, cleverly and uniformly dispersing one or more scattering particles such as graphite powder, titanium dioxide, and silica. This not only enhances the thermal conductivity of the material but also endows it with excellent optical properties. Finally, a curing process is performed to obtain a high-light-extraction-efficiency concentration-gradient fluorescent ceramic. The specific preparation steps of this invention are as follows:

[0023] (1) Preparation of fluorescent ceramic layer:

[0024] ① Preparation of fluorescent ceramic powder: A series of Y3Sc3Al2O powders were synthesized by high-temperature solid-state method. 12 : x Cr 3+ fluorescent powder, among which x = 1-7 mol% represents Cr 3+ In the synthesis of phosphor Y3Sc3Al2O 12 : x Cr 3+ The molar percentage of each component. Using Y2O3, Sc2O3, Al2O3 and Cr2O3 as raw materials, H3BO3, accounting for 3-5 wt% of the raw materials, is added as a co-solvent. After each component is accurately weighed according to the molar ratio, it is ground in an agate mortar for 30-60 minutes to ensure uniform mixing. Then the mixture is transferred to an alumina crucible and sintered in a muffle furnace at 1500℃ for 15 hours to form a block. After being ground again, fluorescent ceramic powder is obtained.

[0025] ② Slurry preparation: First, under atmospheric pressure, YSAO is mixed at a speed of 2500-2550 r / min using a double asymmetric centrifugal vacuum mixer. x Cr 3+ Ceramic powder was mixed with dispersant BYK-111 at 2.3-2.5% by weight for 10-15 min. Then, under the same conditions, monomers 1,6-hexanediol diacrylate (HDDA) and polyethylene glycol diacrylate (PEGDA, average molecular weight 700) and a non-reactive diluent PPEG-400 mixed with photoinitiator 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO) were added to the slurry. To break up any possible powder agglomerates, 2 mm zirconia grinding balls were added to the slurry, with a grinding ball to powder mass ratio of 4:1. The mixture was then stirred for 10-15 min under a vacuum of 150-200 mbar at a speed of 2500-2550 r / min to obtain a fluorescent ceramic layer slurry with a volume fraction of 51-61 vol%, wherein the dispersant BYK-111 accounted for % of YSAO. x The mass fraction of Cr³⁺ ceramic powder is 2.3-2.5 wt%, and 1,6-hexanediol diacrylate accounts for % of YSAO: x The mass fraction of Cr³⁺ ceramic powder is 4.43-4.50 wt%, and the percentage of polyethylene glycol diacrylate in YSAO is: x The mass fraction of Cr³⁺ ceramic powder is 4.91-5.0 wt%, the mass fraction of photoinitiator 2,4,6-trimethylbenzoyl diphenylphosphine oxide in YSAO:xCr³⁺ ceramic powder is 0.037-0.055 wt%, and the mass fraction of non-reactive diluent PPEG-400 in YSAO:xCr³⁺ ceramic powder is 4.43-4.50 wt%.

[0026] ③ Printing of the fluorescent ceramic layer: The prepared fluorescent ceramic layer slurry is stored in a 10mL light-proof syringe and sprayed through four nozzles. The radius R of the fluorescent ceramic layer cylinder is set to 3-6mm. During the printing process, the movement path of the nozzles is planned using RegenHU Slicing Software. Nozzle 1 is loaded with Y3Sc3Al2O3. 12 7 mol% Cr³⁺ fluorescent ceramic slurry, nozzle 2 loaded with Y₃Sc₃Al₂O 12 5 mol% Cr³⁺ fluorescent ceramic layer slurry, nozzle 3 loaded with Y₃Sc₃Al₂O 12 3 mol%Cr³⁺ fluorescent ceramic layer slurry, nozzle 4 loaded with Y3Sc3Al2O 12 :1 mol% Cr³⁺ fluorescent ceramic layer slurry; Cr at each location in this layer is calculated based on a preset distribution function. 3+Concentration, the movement trajectory of the four nozzles is adjusted in real time according to the concentration distribution curve to achieve Cr 3+ The concentration gradually decreases from the center of the fluorescent ceramic cylinder outwards in an equally spaced gradient distribution, with the radii of each layer from the inside out being R / 4, R / 2, 3R / 4, and R, respectively.

[0027] ④ Before printing, the slurry needs to be centrifuged at 5000-5500 rpm for 2-3 minutes. The printing process is carried out at room temperature using an Ink Direct Write (DIW) 3D printer, with "yellow light" illumination in the laboratory.

[0028] The air pressure inside the syringe is set to 0.25-0.30 mbar, combined with a feed rate of 10-15 mm / s. After each layer is printed, the extruded slurry is scanned across the printed object at a scanning speed of 1-2 mm / s and then UV cured. During the curing process, an LED light source with a nominal wavelength of 365 nm, an output power of 360 mW, and an irradiance of 8.9 μW / mm² is used, and the curing time is 30-35 seconds.

[0029] ⑤ Sintering Process: First, non-reactive diluents and organic polymers are removed by water and thermal degreasing. The sample is immersed in distilled water for 12-24 hours, followed by air drying in an oven at 30-35°C for 12-24 hours. Next, the sample is heated to 180-200°C at room temperature, and then heated to 505-510°C at a low heating rate of 0.5-1.0°C / min, holding for 30-60 minutes. Subsequently, it is heated to 1100-1200°C at a heating rate of 5°C / min for pre-sintering, holding for 1-2 hours. Finally, the sample is heated to 1500-1550°C at a heating rate of 5-10°C / min for sintering, lasting 23-24 hours. The sintered fluorescent ceramic is then wiped and polished with alcohol.

[0030] (2) Preparation of silicon carbide composite ceramic layer:

[0031] ① Powder preparation: Silicon carbide particles (SiCp) and graphene nanosheets (GNPs) were mixed and ball-milled for 6 and 2 hours respectively, with a mass ratio of SiCp to isopropanol of 1:5 and a mass ratio of GNPs to isopropanol of 1:10, to obtain a dispersion. The two were then subjected to pulsed ultrasonic mixing for 1-1.5 hours with an ultrasonic power of 150-200W, and the isopropanol was removed by evaporation to obtain a graphene to silicon carbide mass ratio of 1:4. Subsequently, the powder was milled and sieved to obtain a graphene / silicon carbide composite powder, wherein the silicon carbide particle size was 2.5-3.0 μm and the graphene nanosheet particle size was 8-10 μm.

[0032] ② Preparation of slurry: Polycarbosilane (PCS) solution, graphene / silicon carbide composite powder, and tetramethylammonium hydroxide (TMAH) were ball-milled at a weight ratio of 1:1:34. Each 1g of PCS powder was used to prepare a PCS solution with 2mL of n-hexane. The ball milling speed was 400-450r / min for 2-2.5h. Finally, the mixture was magnetically stirred for 3-4h at a speed of 300-350rpm to obtain a silicon carbide composite ceramic layer slurry. The polycarbosilane (PCS) had a softening point of 180-220℃ and a molecular weight of 1500-1550g / mol. -1 .

[0033] ③ Printing Process: The printing path for the main structure was generated by the RegenHU Slicing Software code generator. The structure was drawn using SolidWorks software. Then, Cura software was used for slicing, path planning, and generating G-code files, which were subsequently imported for printing. A line spacing of 0.5 mm and a layer height of 0.5 mm were used. A 0.6 mm tungsten carbide nozzle was selected and preheated before printing, with the nozzle temperature controlled between 50°C and 70°C. The printing speed was set to 10-15 mm / s, and printing was carried out in a nitrogen atmosphere. Hollow cylindrical silicon carbide composite ceramic layers with a thickness of 1-3 mm and a height of 1-2 cm were printed. The printed samples were placed in a UV curing chamber with a wavelength of 405 nm.

[0034] ④ Sintering Process: After printing, the printed part is placed in a sintering furnace and sintered under a nitrogen atmosphere. The temperature is set to 1800°C-2000°C with a heating rate of 10-15°C / min. It is then held at 1950°C-2000°C for 2-4 hours. During the cooling phase, the temperature is first reduced to approximately 1000°C at a rate of 50-100°C / min, and then further reduced at a rate of 5-10°C / min until room temperature. The sintered silicon carbide composite ceramic is then wiped and polished with alcohol.

[0035] (3) Preparation of thermally conductive silicone layer:

[0036] ① Slurry Composition: Silica gel (SG) and graphite powder (GP) are dried in an oven at 100°C for 5-6 hours to remove residual moisture. The dried SG and GP are then mixed with polyvinyl alcohol (PVA) and titanium dioxide and stirred. Subsequently, the mixture is compressed using a press under a pressure of 10-15 MPa. It is then dried again at 100-150°C for 6-8 hours to obtain the thermally conductive silica gel slurry. The mass fraction of each component is as follows: SG 58-60%, PVA 8-10%, GP 18-20%, and titanium dioxide 13-15%.

[0037] Titanium dioxide particles in the 20-200 nm range are selected to ensure scattering effect without compromising thermal conductivity. Concentration: A concentration of 13-15% optimizes light scattering while maintaining suitable thermal conductivity.

[0038] ② Coating Process: After completing the above steps, due to the certain adsorption capacity of this thermally conductive silicone, use a brush or scraper to evenly coat the prepared thermally conductive silicone slurry onto the outer surface of the fluorescent ceramic and the inner surface of the silicon carbide composite ceramic. Ensure that each layer is evenly covered, avoiding air bubbles or gaps. Perform multiple coatings, allowing each layer to dry completely before applying the next layer.

[0039] ③ Curing Process: After coating, the silicon carbide composite ceramic is assembled onto the outside of the fluorescent ceramic, with both ends aligned. The coated ceramic sample is placed in a drying oven and dried at 60-100°C. The coated thermally conductive silicone layer is then cured, typically at a temperature in the range of 150-200°C, for a sintering time of 2-6 hours. The final thermally conductive silicone layer thickness is 2-6 mm.

[0040] This invention also provides the application of high light extraction efficiency concentration gradient fluorescent ceramics in the fields of laser illumination and near-infrared detection. When the concentration gradient fluorescent ceramics are applied to laser illumination and near-infrared detection, the excitation source is blue light excitation, the internal quantum efficiency (IQE) reaches 70-80%, the external quantum efficiency (EQE) reaches 30-35%, and it can maintain a luminous efficiency of 96-99% at room temperature under 473K.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] (1) In this invention, a higher concentration of Cr is set in specific areas of the ceramic (such as high light power density areas). 3+ The concentration of rare earth ions is high in some areas, while other areas maintain a low concentration, and the ions are distributed in a uniform gradient, achieving effective conservation of rare earth ions. This design not only prevents Cr from being released into the atmosphere, but also ensures the efficient conservation of rare earth ions. 3+ The localized overheating and phase separation caused by ion aggregation reduces the thermal effect and optimizes the energy utilization of the excitation source, making efficient use of the beam intensity of the excitation source.

[0043] (2) The composite structure of the present invention can be used to expand the color gamut. By selecting different doping elements and the particle size of scattering particles, a wider range of color reproduction capabilities can be achieved, thereby providing more diverse optical performance.

[0044] (3) The silicon carbide composite ceramic used in this invention has high thermal conductivity (400-700 W·m). - ¹·K -¹It possesses excellent mechanical properties (tensile strength up to 2.5 GPa). Furthermore, this layer exhibits outstanding 3D printing adaptability and adjustability, enabling it to meet the demands of a wide range of demanding applications.

[0045] (4) The silicon carbide composite ceramic layer of the present invention effectively blocks the penetration of oxygen. The micro-layered wrinkled structure formed between the graphene nanosheets and silicon carbide further inhibits the diffusion of oxygen, delays the oxidation process, and significantly improves the oxidation resistance of the material under high temperature environment. At the same time, the combination of the flexibility of graphene and the high rigidity of silicon carbide enhances the toughness and crack resistance of the composite material, and its tensile strength can reach 2-3 GPa.

[0046] (5) The thermally conductive silicone proposed in this invention has certain elasticity and viscosity, which can effectively buffer and seal. As a carrier matrix, it ensures the uniform distribution of scattering particles in the system and avoids performance inhomogeneity caused by excessively high local concentrations. The added scattering particles, titanium dioxide and graphite powder, have high refractive indices. When light enters the ceramic material, it is first reflected or scattered in the outer thermally conductive silicone, enhancing the interaction between light and the material. In the inner ceramic layer, light is reflected and re-propagated through the scattering particles, extending the propagation path and increasing the residence time and utilization efficiency of light. By adjusting the particle size, morphology, and ratio of the scattering particles to the matrix material, the optical properties of the composite material can be precisely controlled.

[0047] (6) The concentration gradient fluorescent ceramic of this invention achieves an internal quantum efficiency (IQE) of 70-80% and an external quantum efficiency (EQE) of 30-35%, and can maintain a luminescence efficiency of 96-99% at room temperature under 473K conditions. The proposed complex structure ceramic has a luminescence efficiency of 675 S·m. - The high electrical conductivity¹ helps to better regulate the thermal and optical emission characteristics of the material, enhancing the near-infrared optical performance of the ceramic, especially significantly improving the stability of light output under high-temperature conditions. Simultaneously, the ceramic's bulk density reaches 1.49 g·cm³. - ³, which means that the material has stronger radiation resistance in high-radiation environments, can effectively shield external thermal or electromagnetic radiation, and maintain the stability of internal optical properties. Attached Figure Description

[0048] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are 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.

[0049] Figure 1 A schematic diagram of the three-layer near-infrared ceramic light-emitting device of the present invention.

[0050] Figure 2 A schematic diagram of the three-layer near-infrared ceramic structure of this invention. Detailed Implementation

[0051] The present invention will be further described below with reference to specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make some non-essential improvements and adjustments based on the above-described invention.

[0052] Example 1

[0053] like Figure 2 As shown, the high-efficiency concentration gradient fluorescent ceramic of this embodiment adopts a three-layer composite structure design, consisting of a fluorescent ceramic layer, a thermally conductive silicone layer, and a silicon carbide composite ceramic layer from the inside out. The fluorescent ceramic layer has a radius of 3 mm and a height of 1 cm, the thermally conductive silicone layer has a thickness of 2 mm, and the silicon carbide composite ceramic layer has a thickness of 1 mm. The preparation process is as follows:

[0054] (1) Preparation of fluorescent ceramic layer slurry:

[0055] ① Preparation of fluorescent ceramic powder: A series of Y3Sc3Al2O powders were synthesized by high-temperature solid-state method. 12 : x Cr 3+ fluorescent powder, among which x = 1 mol%, 3 mol%, 5 mol%, 7 mol%, using Y2O3, Sc2O3, Al2O3 and Cr2O3 as raw materials, adding H3BO3 at a mass fraction of 3 wt% of the raw materials as a co-solvent; after each component is accurately weighed according to the molar ratio, it is ground in an agate mortar for 30 minutes; then the mixture is transferred to an alumina crucible and sintered in a muffle furnace at 1500℃ for 15 hours to form a block, which is then ground again to obtain fluorescent ceramic powder;

[0056] ② Preparation of fluorescent ceramic layer slurry: First, under atmospheric pressure, Y3Sc3Al2O3 was mixed with Y3Sc3Al2O3 using a double asymmetric centrifugal vacuum mixer at a speed of 2500 r / min. 12 : x Cr 3+ (Abbreviated as YSAO:) x Cr 3+Ceramic powder was mixed with dispersant BYK-111 at 2.3% of powder weight for 10-15 min. Then, under the same conditions, monomers 1,6-hexanediol diacrylate (HDDA) and polyethylene glycol diacrylate (PEGDA, average molecular weight 700) and a non-reactive diluent PPEG-400 mixed with photoinitiator 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO) were added to the slurry. To break up any possible powder agglomerates, 2 mm zirconia grinding balls were added to the slurry at a ball-to-powder mass ratio of 4:1. The mixture was then mixed at 2500 r / min for 10 min under a vacuum of 150 mbar to obtain a fluorescent ceramic layer slurry with a volume fraction of 51 vol%. The dispersant BYK-111 accounted for 2.3% of the total volume of the slurry. x Cr 3+ The ceramic powder has a mass fraction of 2.3 wt%, and 1,6-hexanediol diacrylate accounts for % of YSAO: x Cr 3+ The ceramic powder has a mass fraction of 4.43 wt%, and polyethylene glycol diacrylate accounts for % YSAO: x Cr 3+ The ceramic powder had a mass fraction of 4.91 wt%, and the photoinitiator 2,4,6-trimethylbenzoyldiphenylphosphine oxide accounted for % of YSAO: x Cr 3+ The ceramic powder has a mass fraction of 0.037 wt%, and the non-reactive diluent PPEG-400 accounts for a certain percentage of YSAO. x Cr 3+ The mass fraction of the ceramic powder is 4.43 wt%.

[0057] (2) Preparation of silicon carbide composite ceramic layer slurry:

[0058] ① Powder preparation: Silicon carbide particles (SiCp) and graphene nanosheets (GNPs) were mixed and ball-milled for 6 h and 2 h respectively, with a mass ratio of SiCp to isopropanol of 1:5 and a mass ratio of GNPs to isopropanol of 1:10, at a ball milling rate of 200 rpm to obtain dispersions. The two were then subjected to pulsed ultrasonic mixing for 1 h at an ultrasonic power of 150 W, and isopropanol was removed by evaporation. Subsequently, the mixture was milled and sieved to obtain graphene / silicon carbide composite powder, with a mass ratio of graphene to silicon carbide of 1:4. The silicon carbide particle size was 2.5 μm, and the graphene nanosheet particle size was 8 μm.

[0059] ② Preparation of slurry: Polycarbosilane (PCS) solution, graphene / silicon carbide composite powder, and tetramethylammonium hydroxide (TMAH) were ball-milled at a weight ratio of 1:1:34. Each 1g of PCS powder was used to prepare a PCS solution with 2mL of n-hexane. The ball milling speed was 400r / min for 2h, followed by magnetic stirring for 3h at 300rpm. This yielded a silicon carbide composite ceramic layer slurry. The polycarbosilane (PCS) had a softening point of 180-220℃ and a molecular weight of 1500-1550g / mol. -1 .

[0060] (3) The fluorescent ceramic layer was printed. The fluorescent ceramic layer paste was stored in a 10 mL light-proof syringe and sprayed through four nozzles. The radius of the cylinder was set to 3 mm. During the printing process, the movement path of the nozzles was planned using dedicated RegenHUSlicing Software. Nozzle 1 was loaded with YSAO:7 mol%Cr 3+ Slurry, nozzle 2 loaded with YSAO: 5 mol%Cr 3+ Slurry, nozzle 3 loaded with YSAO: 3mol%Cr 3+ Slurry, nozzle 4 loaded with YSAO:1mol%Cr 3+ Slurry. Calculate the Cr content at each location in this layer according to the preset distribution function. 3+ The concentration of Cr³⁺ is adjusted in real time according to the concentration distribution curve. This achieves a concentration gradient distribution where the Cr³⁺ concentration gradually decreases from the center of the fluorescent ceramic layer cylinder outwards with equal spacing. The spray radii of the four nozzles, from the inside out, are 0.75 mm, 1.5 mm, 2.25 mm, and 3 mm, respectively.

[0061] Before printing, the slurry needs to be centrifuged at 5000 rpm for 2 minutes. The printing process is carried out at room temperature using an ink-to-write (DIW) 3D printer, with "yellow light" illumination in the laboratory.

[0062] The air pressure inside the syringe was set to 0.25 mbar, combined with a feed rate of 10 mm / s. After each layer was printed, the extruded slurry was scanned across the printed object at a scanning speed of 1 mm / s and then UV cured. During the curing process, an LED light source with a nominal wavelength of 365 nm, an output power of 360 mW, and an irradiance of 8.9 μW / mm² was used, with a curing time of 30 seconds, ultimately producing a fluorescent ceramic layer with a radius of 3 mm and a height of 1 cm.

[0063] (4) The silicon carbide composite ceramic layer was printed, and the printing path of its main structure was generated by the RegenHU Slicing Software code generator. The structure was drawn using SolidWorks software. Then, Cura software was used for slicing, path planning, and generating G-code files, which were then imported for printing. The line spacing and layer height were 0.5 mm. A 0.6 mm tungsten carbide nozzle was selected and preheated before printing, with the nozzle temperature controlled at 50°C. The printing speed was set to 10 mm / s, and the printing was carried out in a nitrogen atmosphere. A hollow cylindrical silicon carbide composite ceramic layer with a thickness of 1 mm and a height of 1 cm was obtained, and then placed in a UV curing chamber with a wavelength of 405 nm.

[0064] (5) Degreasing the fluorescent ceramic layer with water and heat. The sample was immersed in distilled water for 12 h, and then dried in air in an oven at 30°C for 12 h. Next, the sample was heated to 180°C at room temperature and then heated to 505°C at a low heating rate of 0.5°C / min, and held for 30 min. Subsequently, it was heated to 1100°C at a heating rate of 5°C / min and pre-sintered for 1 h. Finally, the sample was heated to 1500°C at a heating rate of 5°C / min for sintering treatment for 23 h. The sintered fluorescent ceramic was then wiped with alcohol and polished.

[0065] (6) Sintering of silicon carbide composite ceramic layer: After printing, the printed part is placed in sintering furnace and sintered in nitrogen atmosphere. The temperature is set to 1800°C and the heating rate is 10°C / min. Then it is held at 1950°C for 2 hours. During the cooling stage, the temperature is first reduced to 1000°C at a rate of 50°C / min, and then the temperature is continued to drop to room temperature at a rate of 5°C / min. The sintered silicon carbide composite ceramic is wiped and polished with alcohol.

[0066] (7) Preparation of thermally conductive silicone layer:

[0067] ① Preparation of slurry: SG (silicone slurry) and GP (graphite powder) were dried in an oven at 100°C for 5 hours to remove residual moisture. The dried SG and GP were then mixed with PVA (polyvinyl alcohol) and titanium dioxide, and stirred to ensure uniform mixing. Subsequently, the mixture was compressed under a pressure of 10 MPa using a press, and then dried again at 100°C for 6 hours to obtain thermally conductive silicone slurry. The mass fraction of each component was as follows: SG 59%, PVA 8.8%, GP 18.9%, and titanium dioxide 13.3%.

[0068] ② Coating process: After completing the above steps, clean the prepared ceramic and then apply thermally conductive silicone to the outer surface of the fluorescent ceramic and the inner surface of the silicon carbide composite ceramic. Multiple coatings can be applied. After each coating, allow it to fully cure or dry before applying the next layer.

[0069] (8) Curing of thermally conductive silicone: After coating, the silicon carbide composite ceramic is assembled onto the outside of the fluorescent ceramic, with both ends aligned. The coated ceramic sample is placed in a drying oven and dried at 60°C. Then, it is cured at 150°C for 2 hours. The thickness of the cured thermally conductive silicone is 2 mm, thus obtaining a concentration gradient fluorescent ceramic with high light extraction efficiency.

[0070] The ceramic shell manufactured in this embodiment has a thermal conductivity as high as 400 W·m. - ¹·K - ¹, with a tensile strength up to 2 GPa and a tensile strength of 675 S·m. - ¹ Electrical conductivity, 1.49 g·cm⁻¹ -3 The volumetric density is high. When packaged with a blue LED, the internal quantum efficiency (IQE) reaches 70%, and the external quantum efficiency (EQE) reaches 30%, maintaining a luminous efficiency of 96% at room temperature at 473K. This composite structure is ideal for infrared detection applications, especially in situations requiring high temperature resistance, oxidation resistance, and good thermal conductivity.

[0071] Example 2

[0072] The high light extraction efficiency concentration gradient fluorescent ceramic of this embodiment adopts a three-layer composite structure design, consisting of a fluorescent ceramic layer, a thermally conductive silicone layer, and a silicon carbide composite ceramic layer from the inside out. The fluorescent ceramic layer has a radius of 4.5 mm and a height of 1.5 cm, the thermally conductive silicone layer has a thickness of 4 mm, and the silicon carbide composite ceramic layer has a thickness of 2.5 mm.

[0073] The preparation process is as follows:

[0074] (1) Preparation of fluorescent ceramic layer slurry:

[0075] ① Preparation of fluorescent ceramic powder: A series of Y3Sc3Al2O powders were synthesized by high-temperature solid-state method. 12 : x Cr 3+ fluorescent powder, among which x= 1 mol%, 3 mol%, 5 mol%, 7 mol%, using Y2O3, Sc2O3, Al2O3 and Cr2O3 as raw materials, adding H3BO3 at a mass fraction of 4 wt% of the raw materials as a co-solvent, after each component is accurately weighed according to the molar ratio, it is ground in an agate mortar for 45 minutes to ensure uniform mixing, and then the mixture is transferred to an alumina crucible and sintered in a muffle furnace at 1500℃ for 15 hours to form a block, and then ground again to obtain fluorescent ceramic powder;

[0076] ② Slurry preparation: First, under atmospheric pressure, YSAO is mixed with a double asymmetric centrifugal vacuum mixer at a speed of 2525 r / min. x Cr 3+ Ceramic powder was mixed with 2.4% (by weight) of dispersant BYK-111 for 12.5 min. Then, under the same conditions, monomers 1,6-hexanediol diacrylate (HDDA) and polyethylene glycol diacrylate (PEGDA, average molecular weight 700) and a non-reactive diluent PPEG-400 mixed with photoinitiator 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO) were added to the slurry. Zirconia grinding balls of 2 mm in diameter were added at a ball-to-powder mass ratio of 4:1. The mixture was then stirred for 12.5 min at 2525 r / min under a vacuum of 175 mbar to obtain a fluorescent ceramic layer slurry with a volume fraction of 56 vol%.

[0077] Among them, dispersant BYK-111 accounts for YSAO: x Cr 3+ The ceramic powder has a mass fraction of 2.4 wt%, and 1,6-hexanediol diacrylate accounts for % of YSAO: x Cr 3+ The ceramic powder had a mass fraction of 4.46 wt%, and polyethylene glycol diacrylate accounted for % YSAO: x Cr 3+ The ceramic powder had a mass fraction of 4.95 wt%, and the photoinitiator 2,4,6-trimethylbenzoyldiphenylphosphine oxide accounted for % YSAO: x Cr 3+ The ceramic powder had a mass fraction of 0.046 wt%, and the non-reactive diluent PPEG-400 accounted for % of YSAO. x Cr 3+ The mass fraction of the ceramic powder is 4.46 wt%.

[0078] (2) Preparation of silicon carbide composite ceramic layer slurry:

[0079] ① Powder preparation: Silicon carbide particles (SiCp) and graphene nanosheets (GNPs) were mixed and ball-milled for 6 and 2 hours respectively at a mass ratio of SiCp to isopropanol of 1:5 and GNPs to isopropanol of 1:10, respectively, at a ball milling rate of 210 rpm to obtain dispersions. The two were then subjected to pulsed ultrasonic mixing for 1.25 hours at an ultrasonic power of 175 W, and isopropanol was removed by evaporation. Subsequently, the mixture was milled and sieved to obtain graphene / silicon carbide composite powder with a mass ratio of graphene to silicon carbide of 1:4. The silicon carbide particle size was 2.75 μm, and the graphene nanosheet particle size was 9 μm.

[0080] ② Preparation of slurry: Polycarbosilane (PCS) solution, graphene / silicon carbide composite powder, and tetramethylammonium hydroxide (TMAH) were ball-milled at a weight ratio of 1:1:34. Each 1g of PCS powder was used to prepare a PCS solution with 2mL of n-hexane. The ball milling speed was 425r / min for 2.25h. Finally, the mixture was magnetically stirred for 3.5h at a speed of 325rpm to obtain a silicon carbide composite ceramic layer slurry. The polycarbosilane (PCS) had a softening point of 180-220℃ and a molecular weight of 1500-1550g / mol. -1 .

[0081] (3) Printing process of fluorescent ceramic layer: The prepared paste is stored in a 10mL light-proof syringe and sprayed through four nozzles. The radius of the cylinder is set to 4.5mm. The Cr at each position of the layer is calculated according to the preset distribution function. 3+ Concentration. The working ratio of the four nozzles is adjusted in real time according to the concentration distribution curve. A concentration gradient distribution of Cr³⁺ is achieved, which gradually decreases from the center of the fluorescent ceramic layer cylinder to the surrounding area with equal spacing. The spray radii of the four nozzles from the inside out are 1.125 mm, 2.25 mm, 3.375 mm and 4.5 mm respectively.

[0082] During the printing process, the dedicated RegenHU Slicing Software is used to plan the nozzle's movement path. Nozzle 1 is loaded with YSAO: 7 mol% Cr 3+ Slurry, nozzle 2 loaded with YSAO: 5 mol% Cr 3+ Slurry, nozzle 3 loaded with YSAO: 3 mol% Cr 3+ Slurry, nozzle 4 loaded with YSAO: 1 mol % Cr 3+ Slurry.

[0083] ④ Before printing, the slurry needs to be centrifuged at 5250 rpm for 2.5 minutes. The printing process is carried out at room temperature using an Ink Direct Write (DIW) 3D printer, with "yellow light" illumination in the laboratory.

[0084] The air pressure inside the syringe was set to 0.27 mbar, combined with a feed rate of 12.5 mm / s. After each layer was printed, the extruded slurry was scanned across the printed object at a scanning speed of 1.5 mm / s and then UV cured. During the curing process, an LED light source with a nominal wavelength of 365 nm, an output power of 360 mW, and an irradiance of 8.9 μW / mm² was used, and the curing time was 32.5 seconds. The final product was a fluorescent ceramic layer with a radius of 4.5 mm and a height of 1.5 cm.

[0085] (4) Printing the silicon carbide composite ceramic layer: The printing path of its main structure was generated by the RegenHU Slicing Software code generator. The structure was drawn using SolidWorks software. Then, Cura software was used for slicing, path planning, and generating G-code files, which were then imported for printing. A line spacing of 0.5 mm and a layer height of 0.5 mm were used. A 0.6 mm tungsten carbide nozzle was selected and preheated before printing, with the nozzle temperature controlled at 60°C. The printing speed was set to 12.5 mm / s. Printing was carried out in a nitrogen atmosphere. A hollow cylindrical silicon carbide composite ceramic layer with a thickness of 2 mm and a height of 1.5 cm was printed and placed in a UV curing chamber with a wavelength of 405 nm.

[0086] (5) Sintering of the fluorescent ceramic layer: Non-reactive diluents and organic polymers were removed by water degreasing and thermal degreasing. The sample was immersed in distilled water for 18 h, followed by air drying in an oven at 32.5°C for 18 h. Then, the sample was heated to 210°C at room temperature and then heated to 507°C at a low heating rate of 7.5°C / min, and held for 45 min. Subsequently, it was heated to 1150°C at a heating rate of 5°C / min and pre-sintered for 1.5 h. Finally, the sample was heated to 3050°C at a heating rate of 7.5°C / min for sintering for 23.5 h. The sintered fluorescent ceramic was wiped and polished with alcohol.

[0087] (6) Sintering of the silicon carbide composite ceramic layer: After printing, the printed part is placed in a sintering furnace and sintered under a nitrogen atmosphere. The temperature is set to 1900°C with a heating rate of 12.5°C / min. Then, it is held at 1975°C for 3 hours. During the cooling stage, the temperature is first reduced to about 1000°C at a rate of 75°C / min, and then further reduced at a rate of 75°C / min until room temperature. The sintered silicon carbide composite ceramic is wiped and polished with alcohol.

[0088] (7) Preparation of thermally conductive silicone layer:

[0089] ① Slurry Composition: Silica gel (SG) and graphite powder (GP) were dried in an oven at 100°C for 5.5 hours to remove residual moisture. The dried SG and GP were then mixed with polyvinyl alcohol (PVA) and titanium dioxide and stirred. Subsequently, the mixture was compressed and molded using a press under a pressure of 12.5 MPa. It was then dried again at 125°C for 7 hours to obtain the thermally conductive silicone slurry. The mass fractions of the components were as follows: SG 59%, PVA 8.5%, GP 18.5%, and titanium dioxide 14%.

[0090] ② Coating process: After completing the above steps, clean the prepared ceramic and then apply thermally conductive silicone to the outer surface of the fluorescent ceramic and the inner surface of the silicon carbide composite ceramic. Ensure that each layer is evenly coated and avoid air bubbles or gaps. Multiple coatings can be applied, allowing each layer to dry completely before applying the next layer.

[0091] (8) Curing of thermally conductive silicone: After coating, the silicon carbide composite ceramic is assembled onto the outside of the fluorescent ceramic, with both ends aligned. It is placed in a drying oven and dried at 130°C. Then, it is cured at 175°C for 4 hours. After curing, the thickness of the thermally conductive silicone is 4 mm, thus obtaining a concentration gradient fluorescent ceramic with high light extraction efficiency.

[0092] The silicon carbide ceramic layer prepared in this embodiment has a strength of 550 W·m⁻¹. - ¹·K - It exhibits a thermal conductivity of ¹, a tensile strength of 2.5 GPa, an electrical conductivity of 675 S·m⁻¹, and a bulk density of 1.49 g·cm⁻³. When packaged with a blue LED, it achieves an internal quantum efficiency (IQE) of 75% and an external quantum efficiency (EQE) of 33%, maintaining a luminous efficiency of 98% at room temperature under 473 K conditions.

[0093] Example 3

[0094] The high light extraction efficiency concentration gradient fluorescent ceramic of this embodiment adopts a three-layer composite structure design, consisting of a fluorescent ceramic layer, a thermally conductive silicone layer, and a silicon carbide composite ceramic layer from the inside out. The fluorescent ceramic layer has a radius of 6 mm and a height of 3 cm, the thermally conductive silicone layer has a thickness of 6 mm, and the silicon carbide composite ceramic layer has a thickness of 3 mm.

[0095] The preparation process is as follows:

[0096] (1) Preparation of fluorescent ceramic layer slurry:

[0097] ① Preparation of fluorescent ceramic powder: A series of Y3Sc3Al2O powders were synthesized by high-temperature solid-state method. 12 : x Cr 3+ fluorescent powder, among which x= 1 mol%, 3 mol%, 5 mol%, 7 mol%, using Y2O3, Sc2O3, Al2O3 and Cr2O3 as raw materials, adding H3BO3 at a mass fraction of 5 wt% of the raw materials as a co-solvent, after each component is accurately weighed according to the molar ratio, it is ground in an agate mortar for 60 minutes to ensure uniform mixing, and then the mixture is transferred to an alumina crucible and sintered in a muffle furnace at 1500℃ for 15 hours to form a block, and then ground again to obtain fluorescent ceramic powder;

[0098] ② Slurry preparation: First, under atmospheric pressure, YSAO is mixed at a speed of 2550 r / min using a double asymmetric centrifugal vacuum mixer. x Cr 3+ Ceramic powder was mixed with 2.5% (by weight) of dispersant BYK-111 for 15 min. Then, under the same conditions, monomers 1,6-hexanediol diacrylate (HDDA) and polyethylene glycol diacrylate (PEGDA, average molecular weight 700) were added, along with a non-reactive diluent PPEG-400 containing the photoinitiator 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO). To break up any possible powder agglomerates, 2 mm zirconia grinding balls were added to the slurry at a ball-to-powder mass ratio of 4:1. The mixture was then stirred for 15 min at 2550 r / min under a vacuum of 200 mbar to obtain a fluorescent ceramic layer slurry with a volume fraction of 61 vol%.

[0099] Among them, dispersant BYK-111 accounts for YSAO: x Cr 3+ The ceramic powder has a mass fraction of 2.5 wt%, and 1,6-hexanediol diacrylate accounts for % of YSAO: x Cr 3+ The ceramic powder has a mass fraction of 4.50 wt%, and polyethylene glycol diacrylate accounts for % YSAO: x Cr 3+ The ceramic powder has a mass fraction of 5.0 wt%, and the photoinitiator 2,4,6-trimethylbenzoyldiphenylphosphine oxide accounts for % of YSAO: x Cr 3+ The ceramic powder has a mass fraction of 0.055 wt%, and the non-reactive diluent PPEG-400 accounts for % of YSAO: x Cr 3+ The mass fraction of the ceramic powder is 4.50 wt%.

[0100] (1) Preparation of silicon carbide composite ceramic layer slurry:

[0101] ① Powder preparation: Silicon carbide particles (SiCp) and graphene nanosheets (GNPs) were mixed and ball-milled for 6 and 2 hours respectively at a mass ratio of SiCp to isopropanol of 1:5 and GNPs to isopropanol of 1:10, respectively, at a ball milling rate of 220 rpm to obtain dispersions. The two were then subjected to pulsed ultrasonic mixing for 1.5 hours at an ultrasonic power of 200W, and isopropanol was removed by evaporation. Subsequently, the mixture was milled and sieved to obtain a graphene / silicon carbide composite powder with a mass ratio of graphene to silicon carbide of 1:4, wherein the silicon carbide particle size was 3.0 μm and the graphene nanosheet particle size was 10 μm.

[0102] ② Preparation of slurry: Polycarbosilane (PCS) solution, graphene / silicon carbide composite powder, and tetramethylammonium hydroxide (TMAH) were ball-milled at a weight ratio of 1:1:34. Each 1g of PCS powder was used to prepare a PCS solution with 2mL of n-hexane. The ball milling speed was 450r / min for 2.5h. Finally, the mixture was magnetically stirred for 4h at a speed of 350rpm to obtain a silicon carbide composite ceramic layer slurry. The polycarbosilane (PCS) had a softening point of 180-220℃ and a molecular weight of 1500-1550g / mol. -1 .

[0103] (3) The fluorescent ceramic layer was printed. The prepared slurry was stored in a 10 mL light-proof syringe and sprayed through four nozzles. The radius of the cylinder was set to 6 mm. During the printing process, the movement path of the nozzles was planned using RegenHU Slicing Software. Nozzle 1 was loaded with YSAO: 7 mol% Cr 3+ Slurry, nozzle 2 loaded with YSAO: 5mol% Cr 3+ Slurry, nozzle 3 loaded with YSAO: 3 mol% Cr 3+ Slurry, nozzle 4 loaded with YSAO: 1 mol % Cr 3+ Slurry. Calculate the Cr content at each location in this layer based on the preset distribution function. 3+ Concentration. The working ratio of the four nozzles is adjusted in real time according to the concentration distribution curve to achieve a concentration gradient distribution of rare earth Cr³⁺ that gradually decreases from the center of the fluorescent ceramic layer cylinder to the surrounding area with equal spacing. The spray radii of the four nozzles from the inside out are 1.5mm, 3mm, 4.5mm and 6mm respectively.

[0104] Before printing, the slurry needs to be centrifuged at 5500 rpm for 3 minutes. The printing process is carried out at room temperature using an ink-to-write (DIW) 3D printer, with "yellow light" illumination in the laboratory.

[0105] The air pressure inside the syringe was set to 0.30 mbar, combined with a feed rate of 15 mm / s. After each layer was printed, the extruded slurry was scanned across the printed object at a scanning speed of 2 mm / s and then UV cured. During the curing process, an LED light source with a nominal wavelength of 365 nm, an output power of 360 mW, and an irradiance of 8.9 μW / mm² was used, with a curing time of 35 seconds, ultimately producing a fluorescent ceramic layer with a radius of 6 mm and a height of 3 cm.

[0106] (4) Printing of the silicon carbide composite ceramic layer: The printing path of its main structure was generated by the RegenHU Slicing Software code generator. The structure was drawn using SolidWorks software. Then, Cura software was used for slicing, path planning, and generating G-code files, which were then imported for printing. A line spacing of 0.5 mm and a layer height of 0.5 mm were used. A 0.6 mm tungsten carbide nozzle was selected and preheated before printing. The nozzle temperature was controlled at 70°C, and the printing speed was set to 15 mm / s in a nitrogen atmosphere. A hollow cylindrical silicon carbide composite ceramic structure with a thickness of 3 mm and a height of 2 cm was printed and then placed in a UV curing chamber with a wavelength of 405 nm.

[0107] (5) Degreasing the fluorescent ceramic layer with water and heat. The sample was immersed in distilled water for 24 h, and then dried in air in an oven at 35°C for 24 h. Next, the sample was heated to 200°C at room temperature, and then heated to 510°C at a low heating rate of 1.0°C / min, and held for 60 min. Subsequently, it was heated to 1200°C at a heating rate of 5°C / min and pre-sintered for 2 h. Finally, the sample was heated to 1550°C at a heating rate of 10°C / min for sintering for 24 h. The sintered fluorescent ceramic was wiped and polished with alcohol.

[0108] (6) Sintering of the silicon carbide composite ceramic layer: After printing, the printed part is placed in a sintering furnace and sintered under a nitrogen atmosphere. The temperature is set to 2000°C with a heating rate of 15°C / min. Then, it is held at 2000°C for 4 hours. During the cooling stage, the temperature is first reduced to about 1000°C at a rate of 100°C / min, and then further reduced at a rate of 10°C / min until room temperature. The sintered silicon carbide composite ceramic is wiped and polished with alcohol.

[0109] (7) Preparation of thermally conductive silicone layer:

[0110] ① The composition of the slurry: Silica gel (SG) and graphite powder (GP) were dried in an oven at 100°C for 6 hours. The dried SG and GP were then mixed with polyvinyl alcohol (PVA) and titanium dioxide and stirred. Subsequently, the mixture was compressed under a pressure of 15 MPa using a press and dried again at 150°C for 8 hours to obtain a thermally conductive silica gel slurry. The mass fraction of each component was as follows: SG 59%, PVA 9%, GP 18%, and titanium dioxide 14%.

[0111] ② Coating process: After completing the above steps, clean the prepared ceramic and then apply thermally conductive silicone to the outer surface of the fluorescent ceramic and the inner surface of the silicon carbide composite ceramic. Ensure that each layer is evenly covered and avoid air bubbles or gaps. Multiple coatings can be applied, allowing each layer to fully cure or dry before applying the next layer.

[0112] (8) Curing of thermally conductive silicone: After coating, the coated ceramic sample was placed in a drying oven and dried at 100°C. The coated thermally conductive silicone layer was cured at 200°C for 6 hours. After curing, the thickness of the thermally conductive silicone was 6 mm, thus obtaining a concentration gradient fluorescent ceramic with high light extraction efficiency.

[0113] The silicon carbide ceramic layer prepared in this embodiment has a strength of 700 W·m⁻¹. - ¹·K - ¹ Thermal conductivity, tensile strength of 2.5 GPa, 675 S·m - ¹ Electrical conductivity, 1.49 g·cm⁻¹ -3 The volumetric density is high. When packaged with blue LEDs, the internal quantum efficiency (IQE) reaches 80%, the external quantum efficiency (EQE) reaches 35%, and it can maintain 99% luminous efficiency at room temperature under 473K conditions.

[0114] Comparative Example 1

[0115] The fluorescent ceramic layer in Comparative Example 1 is pure Y3Sc3Al2O 12 :Cr 3+ Phosphor, of which Cr 3+ The doping concentration was 7 mol%, and the printing process used a single nozzle; the remaining steps were the same as in Example 1. The resulting ceramic shell had a thermal conductivity of 400 W·m. - ¹·K - ¹, Tensile strength is 2 GPa, 675 S·m - ¹ Electrical conductivity, 1.49 g·cm⁻¹ -3 The volumetric density is [not specified]. After being packaged with blue LEDs, the internal quantum efficiency (IQE) reaches 60%, the external quantum efficiency (EQE) reaches 25%, and it can maintain a luminous efficiency of 71% at room temperature under 473K conditions.

[0116] The foregoing has shown and described the basic principles and main features of the present invention, as well as its advantages. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A concentration gradient fluorescent ceramic with high light extraction efficiency, characterized in that, The fluorescent ceramic adopts a three-layer composite cylindrical structure, consisting of a fluorescent ceramic layer, a thermally conductive silicone layer, and a silicon carbide composite ceramic layer from the inside out. The fluorescent ceramic layer is a cylindrical structure with a radius of 3-6 mm and a height of 1-2 cm, and is made of Y3Sc3Al2O3. 12 : x Cr 3+ fluorescent powder, among which x = 1-7 mol%, Cr in the fluorescent ceramic layer 3+ The concentration is distributed in a uniform gradient that gradually decreases from the inside to the outside along the axial radius of the cylindrical structure; the silicon carbide composite ceramic layer is a hollow cylindrical structure with a thickness of 1-3 mm and a height of 1-2 cm; after preparing the fluorescent ceramic layer and the silicon carbide composite ceramic layer using 3D printing technology, a thermally conductive silicone layer slurry prepared by hot pressing is applied to the outer surface of the fluorescent ceramic layer and the inner surface of the silicon carbide composite ceramic layer along the circumferential direction; the silicon carbide composite ceramic layer is assembled to the outside of the fluorescent ceramic layer; after curing, a high light extraction efficiency concentration gradient fluorescent ceramic with a firm bond between the fluorescent ceramic layer, the thermally conductive silicone layer and the silicon carbide composite ceramic layer is obtained, wherein the thickness of the thermally conductive silicone layer is 2-6 mm; The thermally conductive silicone layer is composed of silicone SG, polyvinyl alcohol PVA, graphite powder GP, and titanium dioxide. The silicon carbide composite ceramic layer is composed of graphene and silicon carbide.

2. The method for preparing high-light-extraction-efficiency concentration gradient fluorescent ceramics according to claim 1, characterized in that: A fluorescent ceramic layer and a silicon carbide composite ceramic layer were prepared using 3D printing technology, and a thermally conductive silicone layer slurry was prepared using a hot-pressing process. The specific preparation steps are as follows: (1) Preparation of fluorescent ceramic layer slurry; (2) Preparation of silicon carbide composite ceramic layer slurry; (3) Using UV-assisted 3D printing technology to print fluorescent ceramic layers and silicon carbide composite ceramic layers; (4) The fluorescent ceramic layer and the silicon carbide composite ceramic layer are sintered; (5) A thermally conductive silicone slurry is prepared by hot pressing. The thermally conductive silicone slurry is coated on the outer surface of the fluorescent ceramic layer and the inner surface of the silicon carbide composite ceramic layer after the treatment in step (4). After curing, a concentration gradient ceramic with high light extraction efficiency is obtained.

3. The method for preparing high-light-extraction-efficiency concentration gradient fluorescent ceramics according to claim 2, characterized in that... The preparation steps of the fluorescent ceramic layer slurry in (1) are as follows: ① Preparation of fluorescent ceramic powder: A series of Y3Sc3Al2O powders were synthesized by high-temperature solid-state method. 12 : x Cr 3+ fluorescent powder, among which x =1-7 mol%, representing Cr 3+ In the phosphor Y3Sc3Al2O 12 : x Cr 3+ The molar percentage of the components is determined by using Y2O3, Sc2O3, Al2O3 and Cr2O3 as raw materials, and adding H3BO3 at a mass fraction of 3-5 wt% as a co-solvent. After each component is accurately weighed according to the molar ratio, it is ground in an agate mortar for 30-60 minutes. Then the mixture is transferred to an alumina crucible and sintered in a muffle furnace at 1500℃ for 15 hours to form a block. After being ground again, fluorescent ceramic powder is obtained. ② Preparation of fluorescent ceramic layer slurry: First, under atmospheric pressure, fluorescent ceramic powder is mixed with 2.3-2.5% (by weight) of dispersant BYK-111 at a speed of 2500-2550 r / min using a double asymmetric centrifugal vacuum mixer for 10-15 min. Then, under the same speed conditions, monomers 1,6-hexanediol diacrylate (HDDA) and polyethylene glycol diacrylate (PEGDA) with an average molecular weight of 700, as well as a non-reactive diluent PPEG-400 mixed with photoinitiator 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO), are added and mixed at a speed of 2500-2550 r / min under a vacuum of 150-200 mbar for 10-15 min to obtain a fluorescent ceramic layer slurry with a volume fraction of 51-61 vol%. The dispersant BYK-111 accounts for 2.3-2.5% (by weight) of the fluorescent ceramic powder. The fluorescent ceramic powder contains 4.43-4.50 wt% 1,6-hexanediol diacrylate, 4.91-5.0 wt% polyethylene glycol diacrylate, 0.037-0.055 wt% photoinitiator 2,4,6-trimethylbenzoyl diphenylphosphine oxide, and 4.43-4.50 wt% non-reactive diluent PPEG-400.

4. The method for preparing high-light-extraction-efficiency concentration gradient fluorescent ceramics according to claim 2, characterized in that... The preparation steps of the silicon carbide composite ceramic layer slurry in (2) are as follows: ① Preparation of silicon carbide composite ceramic layer powder: Silicon carbide particles (SiCp) and graphene nanosheets (GNPs) were mixed and ball-milled for 6 hours and 2 hours respectively, with a mass ratio of SiCp to isopropanol of 1:5 and a mass ratio of GNPs to isopropanol of 1:10, respectively, at a ball milling rate of 200-220 rpm to obtain silicon carbide dispersion and graphene nanosheet dispersion. The graphene nanosheet dispersion and silicon carbide dispersion were then mixed by pulsed ultrasonication for 1-1.5 hours at a mass ratio of graphene to silicon carbide of 1:4, with an ultrasonic power of 150-200W. Isopropanol was removed by evaporation, followed by milling and sieving to obtain graphene / silicon carbide composite powder, wherein the silicon carbide particle size was 2.5-3.0 μm and the graphene nanosheet particle size was 8-10 μm. ② Preparation of silicon carbide composite ceramic layer slurry: Polycarbosilane (PCS) solution, graphene / silicon carbide composite powder, and tetramethylammonium hydroxide (TMAH) were ball-milled at a weight ratio of 1:1:34 for 2-2.5 hours at a speed of 400-450 r / min. Finally, the mixture was magnetically stirred for 3-4 hours at a speed of 300-350 rpm to obtain the silicon carbide composite ceramic layer slurry. For every 1 g of PCS powder, 2 mL of n-hexane was added to prepare the PCS solution. The polycarbosilane (PCS) had a softening point of 180-220 ℃ and a molecular weight of 1500-1550 g / mol. -1 .

5. The method for preparing high-light-extraction-efficiency concentration gradient fluorescent ceramics according to claim 2, characterized in that... The fluorescent ceramic layer was printed using UV-assisted 3D printing technology, and the steps are as follows: The prepared fluorescent ceramic layer slurry was stored in a 10 mL light-proof syringe and sprayed through four nozzles. The radius R of the fluorescent ceramic layer cylinder was set to 3-6 mm. During the printing process, the movement path of the nozzles was planned using RegenHU Slicing Software. Nozzle 1 was loaded with Y3Sc3Al2O3. 12 7mol%Cr 3+ Fluorescent ceramic layer slurry, nozzle 2 loaded with Y3Sc3Al2O 12 5mol%Cr 3+ Fluorescent ceramic layer slurry, nozzle 3 loaded with Y3Sc3Al2O 12 3 mol%Cr 3+ Fluorescent ceramic layer slurry, nozzle 4 loaded with Y3Sc3Al2O 12 1mol%Cr 3+ Fluorescent ceramic layer slurry; Cr content at various locations in the layer is calculated based on a preset distribution function. 3+ Concentration, the movement trajectory of the four nozzles is adjusted in real time according to the concentration distribution curve to achieve Cr 3+ The concentration gradually decreases from the center of the fluorescent ceramic layer cylinder outwards in an equally spaced gradient distribution. That is, the radii of the four nozzles from the inside out are R / 4, R / 2, 3R / 4 and R, respectively.

6. The method for preparing high-light-extraction-efficiency concentration gradient fluorescent ceramics according to claim 2, characterized in that... The steps for printing silicon carbide composite ceramic layers using UV-assisted 3D printing technology are as follows: Select a 0.6mm tungsten carbide nozzle and preheat it before printing. Control the nozzle temperature at 50°C-70°C, set the printing speed to 10-15mm / s, and print in a nitrogen atmosphere with a line spacing of 0.5mm and a layer height of 0.5mm to obtain a hollow cylindrical silicon carbide composite ceramic layer with a thickness of 1-3mm and a height of 1-2cm. Place the obtained sample in a UV curing chamber with a wavelength of 405nm.

7. The method for preparing high-light-extraction-efficiency concentration gradient fluorescent ceramics according to claim 2, characterized in that... The steps for sintering the fluorescent ceramic layer in step (4) are as follows: First, non-reactive diluents and organic polymers are removed by water degreasing and thermal degreasing. The fluorescent ceramic layer sample after printing is immersed in distilled water for 12-24 hours. Then, it is dried in air in an oven at 30-35°C for 12-24 hours. Next, the sample is heated to 180-200°C at room temperature and heated to 505-510°C at a heating rate of 0.5-1.0°C / min, and held for 30-60 minutes. Then, it is heated to 1100-1200°C at a heating rate of 5°C / min and pre-sintered for 1-2 hours. Finally, the sample is heated to 1500-1550°C at a heating rate of 5-10°C / min and sintered for 23-24 hours. The sintered fluorescent ceramic is then wiped with alcohol and polished. The steps of sintering the silicon carbide composite ceramic layer in step (4) are as follows: the silicon carbide composite ceramic layer print is placed in a sintering furnace and sintered in a nitrogen atmosphere. The temperature is set to 1800°C-2000°C with a heating rate of 10-15°C / min, followed by holding at 1950°C-2000°C for 2-4 hours. During the cooling stage, the temperature is first reduced to 1000°C at a rate of 50-100°C / min, and then further reduced at a rate of 5-10°C / min until room temperature. The sintered silicon carbide composite ceramic is then wiped and polished with alcohol.

8. The method for preparing high-light-extraction-efficiency concentration gradient fluorescent ceramics according to claim 2, characterized in that... The preparation steps of the thermally conductive silicone layer slurry are as follows: SG (silicone slurry) and GP (graphite powder) are dried in an oven at 100°C for 5-6 hours to remove residual moisture. The dried SG and GP are then mixed with PVA (polyvinyl alcohol) and titanium dioxide and stirred to ensure uniform mixing. Subsequently, the mixture is compressed under a pressure of 10-15 MPa using a press to make it more compact and smooth. It is then dried again at 100-150°C for 6-8 hours to obtain a thermally conductive silicone slurry. The mass fraction of each component is as follows: SG 58-60%, PVA 8-10%, GP 18-20%, and titanium dioxide 13-15%.

9. The method for preparing high-light-extraction-efficiency concentration gradient fluorescent ceramics according to claim 2, characterized in that... The preparation method of the concentration gradient fluorescent ceramic with high light extraction efficiency is as follows: ① Coating process: Use a scraper to evenly coat the prepared thermally conductive silicone slurry onto the outer surface of the fluorescent ceramic layer and the inner surface of the silicon carbide composite ceramic layer; ② Curing process: After coating, the silicon carbide composite ceramic is assembled onto the outside of the fluorescent ceramic, with both ends aligned, and placed in a drying oven to dry at 60-100°C. Then, the coated thermally conductive silicone layer is cured at 150-200°C for 2-6 hours. After curing, the thickness of the thermally conductive silicone is 2-6 mm, thus obtaining a concentration gradient fluorescent ceramic with high light extraction efficiency.

10. The application of the high light extraction efficiency concentration gradient fluorescent ceramic of claim 1 in the fields of laser illumination and near-infrared detection, characterized in that: When concentration gradient fluorescent ceramics are used for laser illumination and near-infrared detection, the excitation source is blue light excitation. The internal quantum efficiency (IQE) reaches 70-80%, and the external quantum efficiency (EQE) reaches 30-35%. It can maintain a luminous efficiency of 96-99% at room temperature under 473K.

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