Fluorescent ceramic with high light extraction efficiency and concentration gradient as well as preparation method and application of fluorescent ceramic

Abstract

The invention discloses high-light extraction efficiency concentration gradient fluorescent ceramic as well as a preparation method and application thereof, 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 sequentially comprises a fluorescent ceramic layer, a heat-conducting silica gel layer and a silicon carbide composite ceramic layer from inside to outside, and the uniform gradient distribution of the concentration of rare earth ions in the fluorescent ceramic layer can reduce the use of the rare earth ions and can efficiently utilize the light beam intensity of an excitation source, so that the laser output is more uniform, and the heat effect is reduced; the heat-conducting silica gel layer effectively improves the light extraction efficiency through scattering of titanium oxide and graphite powder particles, and internal reflection loss of light is reduced; the silicon carbide composite ceramic layer has high thermal conductivity. The organic light-emitting diode has excellent optical and thermal properties, the internal quantum efficiency reaches 70-80%, the external quantum efficiency reaches 30-35%, the light-emitting efficiency of 96-99% at room temperature can be kept under the condition of 473 K, and the organic light-emitting diode has wide application prospects.

Description

Technical Field

[0001] The invention relates to the fields of laser lighting and near-infrared detection, and in particular to a high-light extraction efficiency concentration gradient fluorescent ceramic, a preparation method and an application thereof. Background Art

[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, information encryption and other fields 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 up to about 150°C due to the thermal accumulation of the chip. At the same time, the photoluminescence (PL) intensity of fluorescent ceramics usually decreases with increasing temperature due to enhanced non-radiative processes. Therefore, the key is to develop methods to produce fluorescent ceramics with excellent PL thermal stability.

[0003] The literature (Journal of the American Ceramic Society, 2023, 106(4): 2309-2316.) designs and prepares multi-level gradient-doped Yb:YAG laser ceramics by tape casting to improve the pump absorption efficiency and smooth the temperature gradient of the laser medium, so as to achieve more efficient high-power solid laser output. Although existing studies have demonstrated the importance of composite structure gain media for improving thermal management and laser performance, the existing technology still has some limitations and it is difficult to completely avoid interface fracture. While maintaining efficient energy conversion, it is necessary to further reduce the optical loss center and improve the overall optical quality.

[0004] Invention patent CN107253854A discloses a method for preparing a luminescent central ion Cr by using a slip casting method combined with a vacuum sintering method. 3+ 、Nd 3+ , Yb 3+ , the matrix is ​​Y3Al5O 12 Or gradient doped transparent laser ceramics of Y2O3. The doping ion concentration varies in a non-uniform gradient along the radial or axial direction of the ceramic, and the number of types of slurry for grouting is the same as the number of gradients; the patent essentially uses slurry injection molding, 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 uses a monomer Isobam gel method and vacuum sintering to prepare a matrix of Lu3Al5O 12 Laser transparent ceramics. This patent introduces the luminescent element Yb or Nd non-uniformly in the Z direction (radial direction) of the ceramic; this patent essentially uses the high doping concentration ions at the beginning of the ceramic end face to absorb the pump light to avoid damage to the ceramic.

[0006] Invention patent CN116857594A prepares a hollow fluorescent ceramic optical fiber that emits white light by extrusion molding. The invention aims to increase the heat dissipation area by using a hollow structure and realize long-distance propagation of light by total internal reflection of light in air and ceramics.

[0007] Invention patent CN112759396A uses gel injection molding to prepare fluorescent ceramic rods, which have a low optical expansion and can be used for high-power laser lighting. The core of this patent is to use gel injection molding to form in one step and reduce concentration quenching by reducing the rare earth ion doping concentration to improve the luminous efficiency.

[0008] Invention patent CN114394822B prepares a face-centered structure ceramic by dry pressing. The face-centered structure coats the surface of the fluorescent ceramic with an alumina thermal conductive layer, aiming to reduce the problem of the thermal conductive layer occupying a large proportion and affecting the luminescence.

[0009] Invention patent CN111018512A uses tape casting to stack fluorescent ceramics with different gradient refractive indices according to the size of the refractive index to prepare fluorescent ceramics. This patent achieves high CRI by doping only the topmost tape casting layer with red light emitting ions during the preparation process. By adjusting the refractive index, the loss of fluorescent ceramics caused by too small light emission angle can be achieved.

[0010] Invention patent CN117658616A is a three-layer structure prepared by tape casting, with (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 AlN is the red fluorescent layer and the heat dissipation layer. This invention patent achieves high CRI and high efficiency luminescence by stacking different ceramic layers.

[0011] Invention patent CN118879321A is a near-infrared fluorescent ceramic (Ba 9- x Sr x Sc 1.98 Cr 0.02 SiO 24 , 2≤ x ≤8) has the characteristics of easy 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 light extraction rate and thermal stability problems faced by fluorescent ceramics greatly limit the application of fluorescent ceramics, so it is very necessary to explore new design strategies. Summary of the invention

[0013] In view of the above problems, the present 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 by ink direct writing (DIW) technology. In the fluorescent ceramic layer, the rare earth ions are distributed in a gradient in the ceramic, and ultraviolet light (UV) is used to assist curing during the printing process. The chemical formula of the near-infrared (NIR) luminescent ceramic used is Y3Sc3Al2O 12 : x Cr 3+ (YSAO:Cr 3+ ). Titanium dioxide and graphite powder are evenly distributed in the thermally conductive silicone layer, which not only helps to dissipate heat, but also enhances the scattering of light. In addition, the light scattering rate of the thermally conductive silicone layer is higher than that of the fluorescent ceramic layer, which is beneficial to improve the light effect. In order to better protect the luminescent ceramics and prevent light overflow, a silicon carbide composite ceramic layer structure with excellent mechanical properties was prepared, and the compressive strength reached 12.5 MPa.

[0014] One of the purposes of the present invention is to effectively utilize the intensity of the excitation source beam to achieve a uniform decrease in the rare earth ion concentration along the axial radial direction, thereby improving the uniformity and stability of luminescence and achieving more precise optical performance regulation.

[0015] The second purpose of the present invention is to use a more precise additive manufacturing method to manufacture three-layer composite structure fluorescent ceramics, flexibly adjust the proportions and characteristics of each layer, simplify the production process, and thus better meet the special needs of different fields.

[0016] The third purpose of the present invention is to effectively scatter light by using scattering particles with a high refractive index. Such scattering particles are added to the thermally conductive silica gel, and the scattering properties are adjusted by controlling the size and concentration of the particles to optimize the light path. This method allows more photons to be absorbed in the fluorescent ceramic layer and converted into fluorescence or laser emission. At the same time, the scattering effect occurs in the area close to the fluorescent surface, which helps to break through the total internal reflection condition and enhance the amount of light escaping from the inside of the fluorescent ceramic, thereby improving the light extraction efficiency.

[0017] To achieve the above objectives, the present invention proposes the following technical solutions: A concentration gradient fluorescent ceramic with high light extraction efficiency, the fluorescent ceramic adopts a cylindrical structure with a three-layer composite structure design, which includes a fluorescent ceramic layer, a thermal conductive silicone layer and a silicon carbide composite ceramic layer from the inside to the outside. The fluorescent ceramic layer is a cylindrical structure with a radius of 3-6 mm and a height of 1-2 cm. The fluorescent ceramic layer adopts Y3Sc3Al2O 12: x Cr 3+ Phosphor, including x = 1-7 mol%, Cr in fluorescent ceramic layer 3+ The concentration is distributed in a gradient that gradually decreases from the inside to the outside along the axial radius direction 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 by using 3D printing technology, a thermal conductive silicone layer slurry prepared by a hot pressing process is applied on 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 concentration gradient fluorescent ceramic with high light extraction efficiency in which the fluorescent ceramic layer, the thermal conductive silicone layer and the silicon carbide composite ceramic layer are firmly combined is obtained, wherein the thickness of the thermal conductive silicone layer is 2-6 mm.

[0018] The radius of the fluorescent ceramic layer is set to 3-6 mm and the height is 1-2 cm to ensure that the rare earth ion concentration is evenly distributed in a large area and provide sufficient optical interaction. In addition, a higher concentration of Cr is set in a specific area of ​​the ceramic (such as a high light power density area). 3+ ions, while other areas maintain a lower concentration, and the ions are evenly distributed. This design effectively avoids Cr 3+ Local overheating and phase separation caused by ion aggregation optimize the distribution of optical and thermal properties.

[0019] The thermally conductive silicone layer has excellent thermal stability and moderate flexibility, effectively maintaining the integrity and stability of the entire structure. The added scattering particles of titanium dioxide and graphite powder have a high refractive index. When light enters the ceramic material, it is first reflected or scattered in the outer layer of thermally conductive silicone, enhancing the interaction between light and the material. In the inner ceramic layer, the light is reflected and re-transmitted by the scattering particles, extending the propagation path and increasing the residence time and utilization efficiency of the 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. The thickness of the thermally conductive silicone layer is 2-6 mm.

[0020] The silicon carbide composite ceramic layer has a thickness of 1-3 mm, provides excellent strength and high temperature stability, and has a high thermal conductivity (400-700 W·m⁻¹·K⁻¹). The microscopic layered wrinkle structure formed between graphene and silicon carbide effectively inhibits the diffusion of oxygen and improves the material's high-temperature oxidation resistance. The combination of the flexible properties 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.

[0021] The present invention adopts advanced printing technology to manufacture a functional ceramic component with a composite structure. First, a multi-nozzle 3D printer is used to accurately deposit Cr doped with different concentrations. 3+ Ion Y3Sc3Al2O 12 : x Cr 3+ (YSAO:Cr 3+ ) ceramics to form a ceramic layer with a gradient distribution inside (the concentration gradually decreases from the center to the surrounding areas). At the same time, a silicon carbide composite ceramic slurry is prepared and then printed. After the fluorescent ceramics and silicon carbide composite ceramic blanks are naturally dried, they are sintered at high temperature. After sintering, they are cleaned and polished, and then coated with thermally conductive silicone slurry, and one or more scattering particles such as graphite powder, titanium dioxide, and silicon dioxide are cleverly dispersed evenly therein. This not only enhances the thermal conductivity of the material, but also gives it excellent optical properties. Finally, a curing treatment is carried out to obtain a high light extraction efficiency concentration gradient fluorescent ceramic. The specific preparation steps of the present invention are as follows: (1) Preparation of fluorescent ceramic layer: ① Preparation of fluorescent ceramic powder: A series of Y3Sc3Al2O 12 : x Cr 3+ Phosphor, including x = 1-7 mol% means Cr 3+ In the synthesized phosphor Y3Sc3Al2O 12 : x Cr 3+ The molar percentage of Y2O3, Sc2O3, Al2O3 and Cr2O3 is taken as raw materials, H3BO3 accounting for 3-5 wt% of the raw materials is added as a co-solvent, each component is accurately weighed according to the molar ratio, and ground in an agate mortar for 30-60 minutes to ensure uniform mixing, and then the mixture is transferred to an alumina crucible, and sintered into a block at 1500°C in a muffle furnace for 15 hours, and then ground again to obtain a fluorescent ceramic powder; ② Preparation of slurry: First, at atmospheric pressure, use a dual asymmetric centrifugal vacuum mixer at a speed of 2500-2550r / min to mix YSAO: x Cr 3+The ceramic powder was mixed with a dispersant BYK-111 accounting for 2.3-2.5% of the powder weight for 10-15 minutes; then, monomers 1,6 hexanediol diacrylate (HDDA) and polyethylene glycol diacrylate (PEGDA, average molecular weight 700) and a non-reactive diluent PPEG-400 mixed with a photoinitiator 2,4,6-trimethylbenzoyldiphenylphosphine oxide (TPO) were added under the same conditions. In order to break up the possible powder agglomerates, 2 mm zirconium oxide grinding balls were added to the slurry, and the mass ratio of grinding balls to powder was 4:1. The mixture was mixed at a speed of 2500-2550 r / min for 10-15 minutes under a vacuum environment of 150-200 mbar to obtain a fluorescent ceramic layer slurry with a volume fraction of 51-61 vol%, wherein the dispersant BYK-111 accounted for YSAO: x The mass fraction of Cr³⁺ ceramic powder is 2.3-2.5 wt%, and 1,6-hexanediol diacrylate accounts for YSAO: x The mass fraction of Cr³⁺ ceramic powder is 4.43-4.50 wt%, polyethylene glycol diacrylate accounts for YSAO: x The mass fraction of Cr³⁺ ceramic powder is 4.91-5.0 wt%, the mass fraction of photoinitiator 2,4,6-trimethylbenzoyldiphenylphosphine 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%.

[0022] ③ Printing of fluorescent ceramic layer: 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 nozzle was planned using the RegenHU Slicing Software. Nozzle 1 was loaded with Y3Sc3Al2O 12 :7 mol % Cr³⁺ fluorescent ceramic layer 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 :1mol% Cr³⁺ fluorescent ceramic layer slurry; calculate the Cr at each position of the layer according to the preset distribution function 3+ concentration, adjust the motion trajectory of the four nozzles 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 to the surrounding areas and is distributed in an equidistant concentration gradient. The radius of each layer from the inside to the outside is R / 4, R / 2, 3R / 4 and R respectively.

[0023] ④ Before printing, the slurry needs to be centrifuged at a speed of 5000-5500rpm for 2-3min. The printing process is carried out at room temperature using a direct ink writing (DIW) 3D printer, and "yellow light" is used in the laboratory.

[0024] The air pressure in the syringe was set to 0.25-0.30 mbar, combined with a feed speed of 10-15 mm / s. After each layer was printed, the extruded slurry was scanned over the printed object at a scanning speed of 1-2 mm / s and 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 30-35 seconds.

[0025] ⑤ Sintering process: First, remove non-reactive diluents and organic polymers by water degreasing and thermal degreasing. Soak the sample in distilled water for 12-24 hours, and then dry it in air in an oven at 30-35°C for 12-24 hours. Next, heat the sample to 180-200°C at room temperature, and heat it to 505-510°C at a lower heating rate of 0.5-1.0°C / min, and keep it for 30-60min. Subsequently, heat it to 1100-1200°C at a heating rate of 5°C / min, and pre-sinter it for 1-2h. Finally, heat the sample to 1500-1550°C at a heating rate of 5-10°C / min, and sinter it for 23-24h. Wipe and polish the fired fluorescent ceramics with alcohol.

[0026] (2) Preparation of silicon carbide composite ceramic layer: ① Preparation of powder: Silicon carbide particles (SiCp) and graphene nanosheets (GNPs) are mixed and ball-milled for 6 and 2 hours at a ball-milling rate of 200-220 rpm at a mass ratio of SiCp to isopropanol of 1:5 and a mass ratio of GNPs to isopropanol of 1:10, respectively, to obtain a dispersion; the two are mixed by pulsed ultrasound for 1-1.5 hours at an ultrasonic power of 150-200 W and the isopropanol is removed by evaporation to obtain a graphene to silicon carbide mass ratio of 1:4; then the powder is ground and sieved to obtain a graphene / silicon carbide composite powder, wherein the silicon carbide particle size is 2.5-3.0 μm and the graphene nanosheet particle size is 8-10 μm; ② Preparation of slurry: Polycarbosilane (PCS) solution, graphene / silicon carbide composite powder, and tetramethylammonium hydroxide (TMAH) are ball-milled in a weight ratio of 1:1:34, wherein 1g PCS powder corresponds to 2mL n-hexane to prepare PCS solution, the ball-milling speed is 400-450r / min for 2-2.5h, and finally magnetic stirring is performed for 3-4h at a magnetic stirring speed of 300-350rpm to obtain a silicon carbide composite ceramic layer slurry, wherein the softening point of polycarbosilane (PCS) is 180-220℃ and the molecular weight is 1500-1550g / mol -1 .

[0027] ③Printing process: The printing path of its main structure is generated by the RegenHU Slicing Software code generator. The structure is drawn using SolidWorks software. Then Cura software is used for slicing, path planning and G-code files, which are then imported for printing. It is carried out with a line spacing of 0.5mm and a layer height of 0.5mm. A 0.6mm tungsten steel nozzle is selected and preheated before printing. The nozzle temperature is controlled at 50°C-70°C, the printing speed is set to 10-15mm / s, and the printing is carried out in a nitrogen atmosphere. A hollow cylindrical structure of silicon carbide composite ceramic layer with a thickness of 1-3 mm and a height of 1-2cm is obtained by printing. The printed sample is placed in a UV light curing box with a wavelength of 405 nanometers.

[0028] ④ Sintering process: After printing, put the printed part into the sintering furnace and sinter it in a nitrogen atmosphere. The temperature is set to 1800°C-2000°C, with a heating rate of 10-15°C / min. Then keep it at 1950°C-2000°C for 2-4h. In the cooling stage, first drop to about 1000°C at a rate of 50-100°C / min, and then continue to cool down at 5-10°C / min until room temperature. Wipe and polish the fired silicon carbide composite ceramic with alcohol.

[0029] (3) Preparation of thermal conductive silicone layer: ① Composition of slurry Silica gel SG and graphite powder GP are dried in a furnace at 100°C for 5-6 hours to remove residual moisture. The dried SG and GP are mixed with polyvinyl alcohol PVA and titanium dioxide and stirred. Subsequently, the mixture is compressed by a punch at a pressure of 10-15MPa. Dry again at 100-150°C for 6-8 hours to obtain thermally conductive silica gel slurry, in which the mass fraction of each component is as follows: SG 58-60%, PVA 8-10%, GP 18-20%, titanium dioxide 13-15%.

[0030] Titanium dioxide particles in the range of 20-200 nm can ensure the scattering effect without affecting the thermal conductivity. Concentration: A concentration of 13-15% can optimize the light scattering effect while maintaining appropriate thermal conductivity.

[0031] ②Coating process: After completing the above steps, since this thermally conductive silicone has a certain adsorption capacity, use a brush or scraping tool to evenly apply the prepared thermally conductive silicone slurry on the outer surface of the fluorescent ceramic and the inner surface of the silicon carbide composite ceramic. Ensure that each layer is evenly covered to avoid bubbles or gaps. Apply multiple times, let it dry completely after each coating, and then apply the next layer.

[0032] ③ Curing process: After coating, the silicon carbide composite ceramic is assembled to 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 cured, and the temperature is usually in the range of 150-200°C, and the sintering time is 2-6h. The final thermally conductive silicone layer is 2-6mm thick.

[0033] The present invention also provides applications of concentration gradient fluorescent ceramics with high light extraction efficiency in the fields of laser lighting and near-infrared detection. When the concentration gradient fluorescent ceramics are applied to laser lighting 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 the luminous efficiency can be maintained at 96-99% at room temperature under 473K conditions.

[0034] Compared with the prior art, the present invention has the following beneficial effects: (1) In the present invention, a higher concentration of Cr is set in a specific area of ​​the ceramic (such as a high light power density area) 3+ ions, while other areas maintain a lower concentration, and the ions are evenly distributed in a gradient, achieving effective conservation of rare earth ions. This design not only prevents Cr 3+ The local overheating and phase separation caused by ion aggregation reduce the thermal effect, optimize the energy utilization of the excitation light source, and efficiently utilize the beam intensity of the excitation source.

[0035] (2) The composite structure of the present invention can be used to expand the color gamut. By selecting different doping elements and particle sizes of scattering particles, a wider range of color reproduction capabilities can be achieved, thereby providing more diverse optical performances.

[0036] (3) The silicon carbide composite ceramic used in the present invention has high thermal conductivity (400-700 W·m - ¹·K -¹) and good mechanical properties (tensile strength can be as high as 2.5 GPa). In addition, this layer has excellent 3D printing adaptability and adjustability to meet the needs of various demanding applications.

[0037] (4) The silicon carbide composite ceramic layer of the present invention effectively blocks the penetration of oxygen. The microscopic layered wrinkle structure formed between the graphene nanosheets and silicon carbide further inhibits the diffusion of oxygen, delays the oxidation process, and significantly improves the material's antioxidant properties in high temperature environments. At the same time, the flexibility of graphene combined with 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.

[0038] (5) The thermally conductive silicone rubber proposed in the present invention has certain elasticity and viscosity, and can effectively buffer and seal. As a carrier matrix, it ensures the uniform distribution of the scattering particles in the system, avoiding uneven performance due to excessive local concentration. The added scattering particles of titanium dioxide and graphite powder have a high refractive index. When light enters the ceramic material, it is first reflected or scattered in the outer layer of thermally conductive silicone rubber, enhancing the interaction between light and the material. In the inner ceramic layer, the light is reflected and re-transmitted by the scattering particles, extending the propagation path and increasing the residence time and utilization efficiency of the 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.

[0039] (6) The internal quantum efficiency (IQE) of the concentration gradient fluorescent ceramic of the present invention reaches 70-80%, the external quantum efficiency (EQE) reaches 30-35%, and the luminous efficiency at room temperature can be maintained at 96-99% under 473K conditions. The complex structure ceramic proposed has 675S·m - The conductivity of the ceramic can better adjust the thermal emission and light emission characteristics of the material, enhance the near-infrared optical performance of the ceramic, and significantly improve the stability of light output under high temperature conditions. At the same time, the bulk density of the ceramic reaches 1.49 g·cm - ³, which means that the material has stronger radiation resistance in high-radiation environments, can effectively shield external thermal radiation or electromagnetic radiation, and maintain the stability of internal optical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0041] Figure 1 Schematic diagram of the three-layer near-infrared ceramic light-emitting device of the present invention.

[0042] Figure 2 Schematic diagram of the three-layer near-infrared ceramic structure of the present invention. DETAILED DESCRIPTION

[0043] The present invention will be further described below in conjunction with specific embodiments. It should be understood that the following embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention, and those skilled in the art in this field can make some non-essential improvements and adjustments based on the content of the above invention.

[0044] Example 1 like Figure 2 As shown, the concentration gradient fluorescent ceramic with high light extraction efficiency of this embodiment adopts a three-layer composite structure design, which is a fluorescent ceramic layer, a thermal conductive silicone layer and a silicon carbide composite ceramic layer from the inside to the outside, wherein the radius of the fluorescent ceramic layer is 3mm and the height is 1cm, the thickness of the thermal conductive silicone layer is 2mm, and the thickness of the silicon carbide composite ceramic layer is 1mm. The preparation process is as follows: (1) Preparation of fluorescent ceramic layer slurry: ① Preparation of fluorescent ceramic powder: A series of Y3Sc3Al2O 12 : x Cr 3+ Phosphor, including x = 1 mol%, 3 mol%, 5 mol%, 7 mol%, Y2O3, Sc2O3, Al2O3 and Cr2O3 are used as raw materials, and H3BO3 accounting for 3 wt% of the raw materials is added as a co-solvent; each component is accurately weighed according to the molar ratio and ground in an agate mortar for 30 minutes; then the mixture is transferred to an alumina crucible, and sintered into a block at 1500°C in a muffle furnace for 15 hours, and then ground again to obtain a fluorescent ceramic powder; ② Preparation of fluorescent ceramic layer slurry: First, Y3Sc3Al2O 12 : x Cr 3+ (abbreviated as YSAO: x Cr 3+) ceramic powder was mixed with dispersant BYK-111 accounting for 2.3% of the powder weight for 10-15min; then, monomers 1,6 hexanediol diacrylate (HDDA) and polyethylene glycol diacrylate (PEGDA, average molecular weight 700) and non-reactive diluent PPEG-400 mixed with photoinitiator 2,4,6-trimethylbenzoyldiphenylphosphine oxide (TPO) were added under the same conditions. In order to break up the possible powder agglomerates, 2mm zirconium oxide grinding balls were added to the slurry with a ball-to-material mass ratio of 4:1, and mixed at a speed of 2500r / min for 10min under a vacuum environment of 150mbar to obtain a fluorescent ceramic layer slurry with a volume fraction of 51vol%, in which the dispersant BYK-111 accounted for: YSAO: x Cr 3+ The mass fraction of ceramic powder is 2.3 wt%, and 1,6-hexanediol diacrylate accounts for YSAO: x Cr 3+ The mass fraction of ceramic powder is 4.43wt%, polyethylene glycol diacrylate accounts for YSAO: x Cr 3+ The mass fraction of ceramic powder is 4.91wt%, and the photoinitiator 2,4,6-trimethylbenzoyldiphenylphosphine oxide accounts for YSAO: x Cr 3+ The mass fraction of ceramic powder is 0.037wt%, and the non-reactive diluent PPEG-400 accounts for YSAO: x Cr 3+ The mass fraction of ceramic powder is 4.43wt%.

[0045] (2) Preparation of silicon carbide composite ceramic layer slurry: ① Preparation of powder: Silicon carbide particles (SiCp) and graphene nanosheets (GNPs) were mixed and ball-milled for 6 h and 2 h at 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 rpm to obtain a dispersion; the two were mixed by pulse ultrasonication for 1 h at an ultrasonic power of 150 W and isopropanol was removed by evaporation, followed by grinding and sieving to obtain a graphene / silicon carbide composite powder, with a mass ratio of graphene to silicon carbide of 1:4. The particle size of silicon carbide is 2.5 μm, and the particle size of graphene nanosheets is 8 μm; 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, where 1g of PCS powder corresponded to 2mL of n-hexane to prepare PCS solution. The ball-milling speed was 400r / min for 2h, and finally magnetic stirring was performed for 3h at a magnetic stirring speed of 300rpm to obtain a silicon carbide composite ceramic layer slurry, where the softening point of polycarbosilane (PCS) was 180-220℃ and the molecular weight was 1500-1550g / mol -1 .

[0046] (3) Printing the fluorescent ceramic layer. The fluorescent ceramic layer slurry is stored in a 10 mL light-proof syringe and sprayed through four nozzles. The radius of the cylinder is set to 3 mm. During the printing process, the movement path of the nozzle is planned using the dedicated RegenHUSlicing Software. 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:3mol%Cr 3+ Slurry, nozzle 4 loaded with YSAO:1mol%Cr 3+ According to the preset distribution function, the Cr at each position of the layer is calculated. 3+ The working ratio of the four nozzles is adjusted in real time according to the concentration distribution curve. The concentration of Cr³⁺ gradually decreases from the center of the fluorescent ceramic layer cylinder to the surrounding area and is evenly spaced. The radii of the four nozzles for spraying are 0.75mm, 1.5mm, 2.25mm and 3mm from the inside to the outside.

[0047] Before printing, the slurry needs to be centrifuged at 5000rpm for 2min. The printing process is carried out at room temperature using a direct ink writing (DIW) 3D printer, using "yellow light" lighting in the laboratory.

[0048] The air pressure in the syringe was set to 0.25 mbar, combined with a feed speed of 10 mm / s. After each layer was printed, the extruded slurry was scanned through the printed object at a scanning speed of 1 mm / s and 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. The curing time was 30 seconds, and a fluorescent ceramic layer with a radius of 3 mm and a height of 1 cm was finally obtained.

[0049] (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. Cura software was then used for slicing, path planning and G-code file generation, which were then imported for printing. This was done with a line spacing of 0.5 mm and a layer height of 0.5 mm. A 0.6 mm tungsten steel nozzle was selected and preheated before printing, with the nozzle temperature controlled at 50 °C. The printing speed was set to 10 mm / s 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, which was then placed in a UV light curing box with a wavelength of 405 nm.

[0050] (5) Water degreasing and thermal degreasing of the fluorescent ceramic layer. The sample was soaked 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 lower heating rate of 0.5 °C / min and maintained 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 and sintered for 23 h. The fired fluorescent ceramic was wiped with alcohol and polished.

[0051] (6) For the sintering of the silicon carbide composite ceramic layer, after printing is completed, the printed part is placed in a sintering furnace and sintered in a nitrogen atmosphere. The temperature is set to 1800°C, with a heating rate of 10°C / min, and then kept at 1950°C for 2h. During the cooling stage, the temperature is first reduced to 1000°C at a rate of 50°C / min, and then continued to decrease at 5°C / min until it reaches room temperature. The fired silicon carbide composite ceramic is wiped with alcohol and polished.

[0052] (7) Preparation of thermal conductive silicone layer: ① Preparation of slurry: Silica gel SG and graphite powder GP were dried in a furnace at 100°C for 5h to remove residual moisture, and the dried SG and GP were mixed with polyvinyl alcohol PVA and titanium dioxide, and stirred to ensure uniform mixing to obtain a mixture. Subsequently, the mixture was compressed by a punch at a pressure of 10MPa, and dried again at 100°C for 6h to obtain a thermally conductive silica gel slurry, wherein the mass fraction of each component is as follows: SG 59%, PVA 8.8%, GP 18.9%, titanium dioxide 13.3%; ②Coating process: After completing the above steps, clean the prepared ceramic and then apply the thermal conductive silicone to the outer surface of the fluorescent ceramic and the inner surface of the silicon carbide composite ceramic. Multiple coatings can be performed. After each coating, let it completely cure or dry before applying the next layer.

[0053] (8) Curing of thermally conductive silicone: After coating, the silicon carbide composite ceramic is assembled to 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. It is then cured at 150°C for 2 hours. The thickness of the cured thermally conductive silicone is 2 mm, thereby obtaining a concentration gradient fluorescent ceramic with high light extraction efficiency.

[0054] The thermal conductivity of the ceramic shell produced in this embodiment is as high as 400 W·m - ¹·K - ¹, tensile strength up to 2GPa, with 675S·m - Conductivity of ¹, 1.49 g·cm -3 After packaging with blue LED, the internal quantum efficiency (IQE) reaches 70%, the external quantum efficiency (EQE) reaches 30%, and the luminous efficiency at room temperature can be maintained at 96% under 473K. This composite structure is very suitable for applications in infrared detection, especially in situations where high temperature resistance, oxidation resistance, and good thermal conductivity are required.

[0055] Example 2 The concentration gradient fluorescent ceramic with high light extraction efficiency in this embodiment adopts a three-layer composite structure design, which includes a fluorescent ceramic layer, a thermal conductive silicone layer and a silicon carbide composite ceramic layer from the inside to the outside. The radius of the fluorescent ceramic layer is 4.5 mm and the height is 1.5 cm. The thickness of the thermal conductive silicone layer is 4 mm and the thickness of the silicon carbide composite ceramic layer is 2.5 mm.

[0056] The preparation process is as follows: (1) Preparation of fluorescent ceramic layer slurry: ① Preparation of fluorescent ceramic powder: A series of Y3Sc3Al2O 12 : x Cr 3+ Phosphor, including x = 1 mol%, 3 mol%, 5 mol%, 7mol%, Y2O3, Sc2O3, Al2O3 and Cr2O3 are used as raw materials, H3BO3 accounting for 4wt% of the raw materials is added as a co-solvent, each component is accurately weighed according to the molar ratio, ground in an agate mortar for 45 minutes to ensure uniform mixing, and then the mixture is transferred to an alumina crucible, sintered in a muffle furnace at 1500°C for 15 hours to form a block, and then ground again to obtain a fluorescent ceramic powder; ② Preparation of slurry: First, YSAO: x Cr 3+ The ceramic powder was mixed with a dispersant BYK-111 accounting for 2.4% of the powder weight for 12.5 minutes; 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 a photoinitiator 2,4,6-trimethylbenzoyldiphenylphosphine oxide (TPO) were added. 2mm zirconium oxide grinding balls were added to the slurry, and the ball-to-material mass ratio was 4:1. The mixture was mixed at a speed of 2525r / min for 12.5 minutes under a vacuum environment of 175mbar to obtain a fluorescent ceramic layer slurry with a volume fraction of 56vol%. Among them, dispersant BYK-111 accounts for YSAO: x Cr 3+ The mass fraction of ceramic powder is 2.4 wt%, and 1,6-hexanediol diacrylate accounts for YSAO: x Cr 3+ The mass fraction of ceramic powder is 4.46 wt%, polyethylene glycol diacrylate accounts for YSAO: x Cr 3+ The mass fraction of ceramic powder is 4.95 wt%, and the photoinitiator 2,4,6-trimethylbenzoyldiphenylphosphine oxide accounts for 1.3% of YSAO: x Cr 3+ The mass fraction of ceramic powder is 0.046 wt%, and the non-reactive diluent PPEG-400 accounts for YSAO: x Cr 3+ The mass fraction of ceramic powder is 4.46 wt%.

[0057] (2) Preparation of silicon carbide composite ceramic layer slurry: ① Preparation of powder: Silicon carbide particles (SiCp) and graphene nanosheets (GNPs) were mixed and ball-milled for 6 and 2 h at 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 210 rpm to obtain a dispersion; the two were mixed by pulse ultrasonication for 1.25 h at an ultrasonic power of 175 W and isopropanol was removed by evaporation, followed by grinding and sieving to obtain a graphene / silicon carbide composite powder with a mass ratio of graphene to silicon carbide of 1:4; the particle size of silicon carbide was 2.75 μm, and the particle size of graphene nanosheets was 9 μm; ② Preparation of slurry: Polycarbosilane (PCS) solution, graphene / silicon carbide composite powder, and tetramethylammonium hydroxide (TMAH) were ball-milled in a weight ratio of 1:1:34, where 1g PCS powder corresponded to 2mL n-hexane to prepare PCS solution, the ball-milling speed was 425r / min and the time was 2.25h, and finally magnetic stirring was performed for 3.5h at a magnetic stirring speed of 325rpm to obtain a silicon carbide composite ceramic layer slurry, where the softening point of polycarbosilane (PCS) was 180-220℃ and the molecular weight was 1500-1550g / mol -1 .

[0058] (3) Printing process of fluorescent ceramic layer: The prepared slurry is stored in a 10 mL light-proof syringe and sprayed through four nozzles. The radius of the cylinder is set to 4.5 mm. 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. The concentration of Cr³⁺ is gradually reduced from the center of the fluorescent ceramic layer cylinder to the surrounding area with equal spacing. The radii of the four nozzles for spraying are 1.125mm, 2.25mm, 3.375mm and 4.5mm from the inside to the outside.

[0059] During the printing process, the movement path of the nozzle is planned using the dedicated RegenHU Slicing Software. 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.

[0060] ④ Before printing, the slurry needs to be centrifuged at 5250rpm for 2.5min. The printing process is carried out at room temperature using a direct ink writing (DIW) 3D printer, and "yellow light" is used in the laboratory.

[0061] The air pressure in the syringe was set to 0.27 mbar, combined with a feed speed of 12.5 mm / s. After each layer was printed, the extruded slurry was scanned over the printed object at a scanning speed of 1.5 mm / s and 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. Finally, a fluorescent ceramic layer with a radius of 4.5 mm and a height of 1.5 cm was obtained.

[0062] (4) Printing of the silicon carbide composite ceramic layer: The printing path of its main structure is generated by the RegenHU Slicing Software code generator. The structure is drawn using SolidWorks software. Cura software is then used for slicing, path planning and generation of G-code files, which are then imported for printing. This is done with a line spacing of 0.5 mm and a layer height of 0.5 mm. A 0.6 mm tungsten steel nozzle is selected and preheated before printing. The nozzle temperature is controlled at 60 ° C and the printing speed is set to 12.5 mm / s. Printing is carried out in a nitrogen atmosphere. The hollow cylindrical structure of the silicon carbide composite ceramic layer with a thickness of 2 mm and a height of 1.5 cm is printed and placed in a UV light curing box with a wavelength of 405 nm.

[0063] (5) Sintering the fluorescent ceramic layer: Remove non-reactive diluents and organic polymers by water degreasing and thermal degreasing. Soak the sample in distilled water for 18 hours and then dry it in air in an oven at 32.5°C for 18 hours. Then, heat the sample to 210°C at room temperature and heat it to 507°C at a lower heating rate of 7.5°C / min and keep it for 45 minutes. Then, heat it to 1150°C at a heating rate of 5°C / min and pre-sinter it for 1.5 hours. Finally, heat the sample to 3050°C at a heating rate of 7.5°C / min and sinter it for 23.5 hours. Wipe the fired fluorescent ceramic with alcohol and polish it.

[0064] (6) Sintering the silicon carbide composite ceramic layer: After printing, the printed part is placed in a sintering furnace and sintered in a nitrogen atmosphere. The temperature is set to 1900°C with a heating rate of 12.5°C / min. Then, it is kept 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 continued to be reduced at 75°C / min until it reaches room temperature. The fired silicon carbide composite ceramic is wiped with alcohol and polished.

[0065] (7) Preparation of thermal conductive silicone layer: ① Composition of slurry Silica gel SG and graphite powder GP were dried in a furnace at 100°C for 5.5 hours to remove residual moisture. The dried SG and GP were mixed with polyvinyl alcohol PVA and titanium dioxide and stirred. Subsequently, the mixture was compressed and molded by a punch at a pressure of 12.5MPa. The thermally conductive silica gel slurry was dried again at 125°C for 7 hours to obtain the following mass fraction composition of each component: SG 59%, PVA 8.5%, GP 18.5%, titanium dioxide 14%.

[0066] ②Coating process: After completing the above steps, clean the prepared ceramic and then apply the thermal 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 to avoid bubbles or gaps. Multiple coatings can be performed, and after each coating, let it dry completely before applying the next layer.

[0067] (8) Curing of thermally conductive silicone: After coating, the silicon carbide composite ceramic is assembled to the outside of the fluorescent ceramic with both ends aligned. It is placed in a drying oven and dried at 130°C. It is then cured at a temperature of 175°C for 4 hours. After curing, the thickness of the thermally conductive silicone is 4 mm, thereby obtaining a concentration gradient fluorescent ceramic with high light extraction efficiency.

[0068] The silicon carbide ceramic layer prepared in this embodiment has a power of 550 W·m - ¹·K - ¹ thermal conductivity, 2.5Gpa tensile strength, 675 S·m-¹ electrical conductivity, 1.49 g·cm-3 bulk density. After packaging with a blue LED, the internal quantum efficiency (IQE) reaches 75%, the external quantum efficiency (EQE) reaches 33%, and it can maintain 98% of the room temperature luminous efficiency at 473K.

[0069] Example 3 The concentration gradient fluorescent ceramic with high light extraction efficiency in this embodiment adopts a three-layer composite structure design, which includes a fluorescent ceramic layer, a thermal conductive silicone layer and a silicon carbide composite ceramic layer from the inside to the outside. The radius of the fluorescent ceramic layer is 6 mm and the height is 3 cm. The thickness of the thermal conductive silicone layer is 6 mm and the thickness of the silicon carbide composite ceramic layer is 3 mm.

[0070] The preparation process is as follows: (1) Preparation of fluorescent ceramic layer slurry: ① Preparation of fluorescent ceramic powder: A series of Y3Sc3Al2O 12 : x Cr 3+ Phosphor, including x = 1 mol%, 3 mol%, 5 mol%, 7mol%, Y2O3, Sc2O3, Al2O3 and Cr2O3 are used as raw materials, H3BO3 accounting for 5 wt% of the raw materials is added as a co-solvent, each component is accurately weighed according to the molar ratio, and then ground in an agate mortar for 60 minutes to ensure uniform mixing, and then the mixture is transferred to an alumina crucible, and sintered into a block at 1500°C in a muffle furnace for 15 hours, and then ground again to obtain a fluorescent ceramic powder; ② Preparation of slurry: First, YSAO: x Cr3+ The ceramic powder was mixed with a dispersant BYK-111 accounting for 2.5% of the powder weight for 15 minutes; 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 a photoinitiator 2,4,6-trimethylbenzoyldiphenylphosphine oxide (TPO) were added. In order to break up possible powder agglomerates, 2 mm zirconium oxide grinding balls were added to the slurry with a ball-to-material mass ratio of 4:1, and mixed at a speed of 2550 r / min for 15 minutes under a vacuum environment of 200 mbar to obtain a fluorescent ceramic layer slurry with a volume fraction of 61 vol%. Among them, dispersant BYK-111 accounts for YSAO: x Cr 3+ The mass fraction of ceramic powder is 2.5 wt%, and 1,6-hexanediol diacrylate accounts for YSAO: x Cr 3+ The mass fraction of ceramic powder is 4.50 wt%, polyethylene glycol diacrylate accounts for YSAO: x Cr 3+ The mass fraction of ceramic powder is 5.0 wt%, and the photoinitiator 2,4,6-trimethylbenzoyldiphenylphosphine oxide accounts for 1.3% of YSAO: x Cr 3+ The mass fraction of ceramic powder is 0.055 wt%, and the non-reactive diluent PPEG-400 accounts for YSAO: x Cr 3+ The mass fraction of ceramic powder is 4.50 wt%. (1) Preparation of silicon carbide composite ceramic layer slurry: ① Preparation of powder: Silicon carbide particles (SiCp) and graphene nanosheets (GNPs) were mixed and ball-milled for 6 and 2 h at 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 220 rpm to obtain a dispersion; the two were mixed by pulse ultrasonication for 1.5 h at an ultrasonic power of 200 W and isopropanol was removed by evaporation, and then ground 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; ② Preparation of slurry: Polycarbosilane (PCS) solution, graphene / silicon carbide composite powder, and tetramethylammonium hydroxide (TMAH) were ball-milled in a weight ratio of 1:1:34, where 1g PCS powder corresponded to 2mL n-hexane to prepare PCS solution, the ball-milling speed was 450r / min and the time was 2.5h, and finally magnetic stirring was performed for 4h at a magnetic stirring speed of 350rpm to obtain silicon carbide composite ceramic layer slurry, where polycarbosilane (PCS) had a softening point of 180-220℃ and a molecular weight of 1500-1550g / mol -1 .

[0071] (3) Printing the fluorescent ceramic layer. 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 nozzle 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+ 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 to achieve a concentration gradient distribution in which the concentration of rare earth Cr³⁺ gradually decreases from the center of the fluorescent ceramic layer cylinder to the surrounding area with equal spacing. The radii of the four nozzles for spraying are 1.5mm, 3mm, 4.5mm and 6mm from the inside to the outside.

[0072] Before printing, the slurry needs to be centrifuged at 5500rpm for 3min. The printing process is carried out at room temperature using a direct ink writing (DIW) 3D printer, using "yellow light" lighting in the laboratory.

[0073] The air pressure in the syringe was set to 0.30 mbar, combined with a feed speed of 15 mm / s. After each layer was printed, the extruded slurry was scanned at a scanning speed of 2 mm / s and 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. The curing time was 35 seconds, and a fluorescent ceramic layer with a radius of 6 mm and a height of 3 cm was finally obtained.

[0074] (4) Printing of silicon carbide composite ceramic layer: The printing path of its main structure is generated by the RegenHU Slicing Software code generator. The structure is drawn using SolidWorks software. Then, Cura software is used for slicing, path planning and generation of G-code files, which are then imported for printing. This is done with a line spacing of 0.5 mm and a layer height of 0.5 mm. A 0.6 mm tungsten steel nozzle is selected and preheated before printing. The nozzle temperature is controlled at 70 ° C, and the printing speed is set to 15 mm / s in a nitrogen atmosphere. A hollow cylindrical silicon carbide composite ceramic with a thickness of 3 mm and a height of 2 cm is printed and then placed in a UV light curing box with a wavelength of 405 nm.

[0075] (5) Water degreasing and thermal degreasing of the fluorescent ceramic layer. The sample was soaked in distilled water for 24 hours and then dried in air in an oven at 35°C for 24 hours. Next, the sample was heated to 200°C at room temperature and heated to 510°C at a low heating rate of 1.0°C / min and maintained for 60 minutes. Subsequently, it was heated to 1200°C at a heating rate of 5°C / min and pre-sintered for 2 hours. Finally, the sample was heated to 1550°C at a heating rate of 10°C / min and sintered for 24 hours. The fired fluorescent ceramic was wiped with alcohol and polished.

[0076] (6) Sintering the silicon carbide composite ceramic layer: After printing, the printed part is placed in a sintering furnace and sintered in a nitrogen atmosphere. The temperature is set to 2000°C with a heating rate of 15°C / min. Then, it is kept 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 continued to be reduced at 10°C / min until it reaches room temperature. The fired silicon carbide composite ceramic is wiped with alcohol and polished.

[0077] (7) Preparation of thermal conductive silicone layer: ① Composition of slurry Silica gel SG and graphite powder GP were dried in a furnace at 100°C for 6 hours, and the dried SG and GP were mixed with polyvinyl alcohol PVA and titanium dioxide and stirred. Subsequently, the mixture was compressed by a punch at a pressure of 15MPa and dried again at 150°C for 8 hours to obtain a thermally conductive silica gel slurry, in which the mass fractions of the components were as follows: SG 59%, PVA 9%, GP 18%, and titanium dioxide 14%.

[0078] ②Coating process: After completing the above steps, clean the prepared ceramic and then apply the thermal 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 to avoid bubbles or gaps. Multiple coatings can be performed, and after each coating, let it completely cure or dry before applying the next layer.

[0079] (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, thereby obtaining a concentration gradient fluorescent ceramic with high light extraction efficiency.

[0080] The silicon carbide ceramic layer prepared in this embodiment has a power of 700 W·m - ¹·K - ¹Thermal conductivity, 2.5Gpa tensile strength, 675 S·m - Conductivity of ¹, 1.49 g·cm -3 After packaging with blue LEDs, the internal quantum efficiency (IQE) reaches 80%, the external quantum efficiency (EQE) reaches 35%, and it can maintain 99% of the luminous efficiency at room temperature under 473K conditions.

[0081] Comparative Example 1 The fluorescent ceramic layer in this comparative example 1 is pure Y3Sc3Al2O 12 :Cr 3+ Phosphor, Cr 3+ The doping amount is 7 mol%, and one nozzle is used in the printing process. The remaining steps are the same as in Example 1. The thermal conductivity of the ceramic shell is 400 W·m - ¹·K - ¹, tensile strength 2GPa, 675 S·m - Conductivity of ¹, 1.49 g·cm -3 After packaging with blue LEDs, the internal quantum efficiency (IQE) reaches 60%, the external quantum efficiency (EQE) reaches 25%, and the luminous efficiency can be maintained at 71% at room temperature under 473K conditions.

[0082] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A concentration gradient fluorescent ceramic with high light extraction efficiency, characterized in that: The fluorescent ceramic adopts a cylindrical structure with a three-layer composite structure design, which includes a fluorescent ceramic layer, a thermal conductive silicone layer and a silicon carbide composite ceramic layer from the inside to the outside. The fluorescent ceramic layer is a cylindrical structure with a radius of 3-6 mm and a height of 1-2 cm. The fluorescent ceramic layer adopts Y3Sc3Al2O 12 : x Cr 3+ Phosphor, including x = 1-7 mol%, Cr in 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 direction 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 by using 3D printing technology, a thermal conductive silicone layer slurry prepared by a hot pressing process is applied on 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 concentration gradient fluorescent ceramic with high light extraction efficiency in which the fluorescent ceramic layer, the thermal conductive silicone layer and the silicon carbide composite ceramic layer are firmly combined is obtained, wherein the thickness of the thermal conductive silicone layer is 2-6 mm.

2. The method for preparing a concentration gradient fluorescent ceramic with high light extraction efficiency according to claim 1, characterized in that: The fluorescent ceramic layer and the silicon carbide composite ceramic layer were prepared by 3D printing technology, and the thermal conductive silicone layer slurry was prepared by 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 the fluorescent ceramic layer and the silicon carbide composite ceramic layer; (4) Sintering the fluorescent ceramic layer and the silicon carbide composite ceramic layer; (5) A thermally conductive silicone layer slurry is prepared by a hot pressing process, and the thermally conductive silicone layer slurry is coated on the outer surface of the fluorescent ceramic layer and the inner surface of the silicon carbide composite ceramic layer after being treated in step (4). After curing, a concentration gradient ceramic with high light extraction efficiency is obtained.

3. The method for preparing a concentration gradient fluorescent ceramic with high light extraction efficiency according to claim 2, characterized in that The steps for preparing the fluorescent ceramic layer slurry in (1) are as follows: ① Preparation of fluorescent ceramic powder: A series of Y3Sc3Al2O 12 : x Cr 3+ Phosphor, including x =1-7 mol%, indicating Cr 3+ In phosphor Y3Sc3Al2O 12 : x Cr 3+ The molar percentage of Y2O3, Sc2O3, Al2O3 and Cr2O3 is taken as raw materials, and 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, and then the mixture is transferred to an alumina crucible, and sintered into a block at 1500°C in a muffle furnace for 15 hours, and then ground again to obtain a fluorescent ceramic powder; ② Preparation of fluorescent ceramic layer slurry: First, under atmospheric pressure, use a dual asymmetric centrifugal vacuum mixer at a speed of 2500-2550r / min to mix the fluorescent ceramic powder with a dispersant BYK-111 accounting for 2.3-2.5% of the powder weight for 10-15min; then, under the same speed conditions, add monomers 1,6-hexanediol diacrylate (HDDA) and polyethylene glycol diacrylate (PEGDA) with an average molecular weight of 700, and a non-reactive diluent PPEG-400 mixed with a photoinitiator 2,4,6-trimethylbenzoyldiphenylphosphine oxide (TPO), and mix at a speed of 2500-2550r / min for 10-15min under a vacuum environment of 150-200mbar to prepare a fluorescent ceramic layer slurry with a volume fraction of 51-61 vol%; wherein the mass fraction of the dispersant BYK-111 in the fluorescent ceramic powder is 2.3-2.5 wt%, the mass fraction of 1,6-hexanediol diacrylate in the fluorescent ceramic powder is 4.43-4.50wt%, the mass fraction of polyethylene glycol diacrylate in the fluorescent ceramic powder is 4.91-5.0 wt%, the mass fraction of the photoinitiator 2,4,6-trimethylbenzoyldiphenylphosphine oxide in the fluorescent ceramic powder is 0.037-0.055 wt%, and the mass fraction of the non-reactive diluent PPEG-400 in the fluorescent ceramic powder is 4.43-4.50 wt%.

4. The method for preparing a concentration gradient fluorescent ceramic with high light extraction efficiency according to claim 2, characterized in that The steps for preparing 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 h and 2 h at 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 pulse-ultrasound mixed for 1-1.5 h at a mass ratio of graphene to silicon carbide of 1:4, at an ultrasonic power of 150-200 W, and isopropanol was removed by evaporation, followed by grinding 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: ball mill polycarbosilane (PCS) solution, graphene / silicon carbide composite powder, and tetramethylammonium hydroxide (TMAH) at a weight ratio of 1:1:34, at a ball milling speed of 400-450r / min, for 2-2.5h, and finally magnetically stir for 3-4h at a magnetic stirring speed of 300-350rpm to obtain silicon carbide composite ceramic layer slurry, wherein 2mL of n-hexane is added to every 1g of PCS powder to obtain PCS solution, the softening point of polycarbosilane (PCS) is 180-220℃, and the molecular weight is 1500-1550g / mol -1 .

5. The method for preparing a concentration gradient fluorescent ceramic with high light extraction efficiency according to claim 2, characterized in that The fluorescent ceramic layer is printed using UV-assisted 3D printing technology. 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 nozzle was planned using the RegenHU Slicing Software. Nozzle 1 was loaded with Y3Sc3Al2O 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; Calculate the Cr at each position of the layer according to the preset distribution function 3+ concentration, adjust the motion trajectory of the four nozzles 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 to the surrounding areas and is distributed in an equidistant concentration gradient, that is, the radii of the four nozzles for spraying are R / 4, R / 2, 3R / 4 and R from the inside to the outside.

6. The method for preparing the concentration gradient fluorescent ceramic with high light extraction efficiency according to claim 2, characterized in that The steps of printing silicon carbide composite ceramic layers using UV-assisted 3D printing technology are as follows: select a 0.6mm tungsten steel nozzle and preheat it before printing. The nozzle temperature is controlled at 50°C-70°C, the printing speed is set to 10-15mm / s, and the printing is carried out in a nitrogen atmosphere. Printing is performed 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. The obtained sample is placed in a UV light curing box with a wavelength of 405 nanometers.

7. The method for preparing the concentration gradient fluorescent ceramic with high light extraction efficiency according to claim 2, characterized in that The step (4) of sintering the fluorescent ceramic layer is as follows: first, removing non-reactive diluents and organic polymers by water degreasing and thermal degreasing, soaking the printed fluorescent ceramic layer sample in distilled water for 12-24 hours, and then drying it in an oven at 30-35°C in air for 12-24 hours, then heating the sample to 180-200°C at room temperature, and heating it to 505-510°C at a heating rate of 0.5-1.0°C / min, and keeping it for 30-60 minutes, then heating it to 1100-1200°C at a heating rate of 5°C / min, and pre-sintering it, and keeping it for 1-2 hours, finally, heating the sample to 1500-1550°C at a heating rate of 5-10°C / min, and sintering it for 23-24 hours, and then wiping and polishing the sintered fluorescent ceramic; The step (4) of sintering the silicon carbide composite ceramic layer is as follows: placing the silicon carbide composite ceramic layer printout into a sintering furnace, sintering in a nitrogen atmosphere, setting the temperature to 1800°C-2000°C, with a heating rate of 10-15°C / min, and then keeping the temperature at 1950°C-2000°C for 2-4h; in the cooling stage, first reducing the temperature to 1000°C at a rate of 50-100°C / min, and then continuing to reduce the temperature to room temperature at a rate of 5-10°C / min; and wiping and polishing the sintered silicon carbide composite ceramic with alcohol.

8. The method for preparing the concentration gradient fluorescent ceramic with high light extraction efficiency according to claim 2, characterized in that The preparation steps of thermal conductive silicone layer slurry are as follows: Silica gel SG and graphite powder GP are dried in a furnace at 100°C for 5-6h to remove residual moisture, the dried SG and GP are mixed with polyvinyl alcohol PVA and titanium dioxide, and stirred to ensure uniform mixing to obtain a mixture, then the mixture is compressed by a punch at a pressure of 10-15MPa to make the mixture more dense and smooth, and then dried again at 100-150°C for 6-8h to obtain a thermally conductive silica gel slurry, wherein the mass fraction composition of each component is as follows: silica gel SG 58-60%, polyvinyl alcohol PVA 8-10%, graphite powder GP 18-20%, and titanium dioxide 13-15%.

9. The method for preparing the concentration gradient fluorescent ceramic with high light extraction efficiency 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 scraping tool to evenly coat the prepared thermal conductive silicone layer slurry on 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 to the outside of the fluorescent ceramic, the two ends are aligned, and placed in a drying oven and dried at 60-100°C. The coated thermal conductive silicone layer is then cured at a temperature of 150-200°C for 2-6h. After curing, the thickness of the thermal conductive silicone is 2-6mm, thereby obtaining a concentration gradient fluorescent ceramic with high light extraction efficiency.

10. Application of the concentration gradient fluorescent ceramic with high light extraction efficiency as claimed in claim 1 in the field of laser lighting and near-infrared detection, characterized in that: When concentration gradient fluorescent ceramics are used in 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 the luminous efficiency can be maintained at 96-99% at room temperature under 473K conditions.

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