A composite fluorescent ceramic for reflective laser illumination and a method for preparing the same

Abstract

This invention discloses a composite fluorescent ceramic for reflective laser illumination and its preparation method. The method includes: S1: preparing YAG powder, YAG:Ce powder, and YAG-Al2O3 powder respectively; S2: pressing the YAG / YAG:Ce / YAG-Al2O3 composite ceramic blank by dry pressing, followed by vacuum sintering and annealing; S3: forming a conical structure array on the YAG portion of the composite ceramic surface using laser engraving, resulting in a final composite fluorescent ceramic thickness of 4–5 mm. The composite fluorescent ceramic for reflective laser illumination prepared by this invention has advantages as a luminescent material, including high thermal conductivity, high luminous efficiency, and low incident light surface temperature.

Description

Technical Field

[0001] This invention relates to the field of fluorescent ceramics technology, specifically to a composite fluorescent ceramic for reflective laser illumination and its preparation method. Background Technology

[0002] Fluorescent ceramics are light-to-light conversion functional materials with high conversion efficiency, high temperature resistance, excellent thermal shock resistance, and long service life under high-power blue diode excitation. They can be widely used in high-power lighting and high-lumen displays. Laser-excited fluorescent ceramics have many advantages, including high brightness, long range, long lifespan, and small size, making them widely applicable in outdoor plaza lighting, sports stadiums, automotive headlights, and aerospace and marine lighting. However, fluorescent ceramics are limited by high-power-density lasers (>10W / mm²). 2 Under the excitation of light, a large amount of heat accumulates in the laser-irradiated region of the fluorescent ceramic (mainly due to energy loss during the light conversion process). This is because the thermal conductivity of the fluorescent ceramic is approximately 12 W / m². -1 K -1 The heat is not dissipated quickly enough, causing the ceramic temperature at the laser point to rise sharply, resulting in reduced luminescence intensity and luminescence saturation.

[0003] Currently, researchers have implemented special structural designs for fluorescent materials to achieve higher luminous efficiency and quality. The paper *Heat-conducting LSN:Ce-in-glass film on AlN substrate for high-brightness laser-driven white lighting* (CERAM INT, 48(24) 2022) reports coating a LuAG:Ce PiG glass film onto a high thermal conductivity AlN ceramic substrate to reduce the temperature of the laser spot and increase the saturation threshold of the fluorescent material. However, due to the poor heat transfer capacity of the glass phosphor, the final luminous efficiency was only 158 lm / W under high-power excitation of 4.82 W. Furthermore, as the laser power increases, the temperature at the laser spot on the fluorescent ceramic gradually rises. However, due to the insufficient heat dissipation capacity of the fluorescent ceramic, thermal quenching may occur, and the ceramic may even break due to excessively high temperature at the spot. Chinese patent application CN108527960A uses fluorescent ceramics and sapphire as a composite. Although it also uses sapphire with high thermal conductivity as the base material, it uses glass powder and epoxy resin as the intermediate connecting layer. The low thermal conductivity of the connecting colloid affects the heat dissipation performance of the ceramic, and the connection between the ceramic and sapphire is not very tight, which will further affect the luminescence performance of the composite ceramic.

[0004] To address the issue of low thermal conductivity in fluorescent ceramics used in laser illumination, a second phase can be introduced to improve the overall thermal conductivity of the ceramic. However, in multiphase ceramics, the high thermal conductivity second phase exists as a dispersed phase within the matrix, which greatly reduces its heat dissipation capacity. Furthermore, laser illumination also suffers from the effect of heat accumulation at the laser spot. Although adding a second phase can improve the overall heat dissipation capacity, this method cannot improve the heat dissipation at the laser spot. Summary of the Invention

[0005] One of the objectives of this invention is to provide a method for preparing composite fluorescent ceramics for reflective laser illumination, which is easy to industrialize.

[0006] The second objective of this invention is to provide a composite fluorescent ceramic for reflective laser illumination prepared by the above-mentioned method. This ceramic, as a luminescent material, has the advantages of high thermal conductivity, high luminous efficiency, and low incident light surface temperature.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] In a first aspect, the present invention provides a method for preparing composite fluorescent ceramics for reflective laser illumination, comprising the following steps:

[0009] S1: Prepare YAG powder, YAG:Ce powder and YAG-Al2O3 powder respectively;

[0010] S2: YAG / YAG:Ce / YAG-Al2O3 composite ceramic blanks are pressed using dry pressing technology, followed by vacuum sintering and annealing;

[0011] S3: A conical array of structures is formed on the YAG layer of the composite ceramic surface by laser engraving, and the final thickness of the composite fluorescent ceramic is 4-5 mm.

[0012] Preferably, in step S1, the Ce doping concentration of YAG:Ce is 0.05–0.3 at%.

[0013] Preferably, in step S1, the mass percentage of the second phase Al2O3 in YAG-Al2O3 is 50% to 80%.

[0014] Preferably, in step S2, YAG-Al2O3 powder is pressed first, then YAG:Ce powder is pressed, and finally YAG powder is pressed; wherein the mass ratio of YAG-Al2O3 powder, YAG:Ce powder, and YAG powder is 2:2:1.

[0015] Preferably, in step S2, the sintering temperature is 1750℃~1770℃ and the holding time is 10h; the annealing temperature is 1350~1450℃ and the holding time is 10h.

[0016] Preferably, in step S3, the bottom diameter of the conical structure is 0.5-0.7 mm, the height is 0.3-0.5 mm, and the cone angle is 30°-60°.

[0017] Secondly, the present invention provides a composite fluorescent ceramic for reflective laser illumination prepared by the above-mentioned preparation method, which is composed of a three-layer structure from top to bottom: microstructured YAG transparent ceramic, YAG:Ce fluorescent ceramic and YAG-Al2O3 ceramic; the microstructured YAG transparent ceramic is used to increase the average propagation path of photons and obtain a larger extraction area; the YAG:Ce fluorescent ceramic is used to absorb blue light from the excitation source and convert it into yellow light; the YAG-Al2O3 ceramic is used to reflect blue light and yellow light.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] 1. The composite fluorescent ceramic prepared by this invention achieves high-brightness white light emission when excited by a 455nm blue LD chip, and can withstand an excitation power density of 60W / mm². 2 ~75W / mm 2 Its luminous efficacy is 230–280 lm / W. Its thermal conductivity at room temperature is 20–27 Wm. -1 k -1 .

[0020] 2. The composite fluorescent ceramic prepared by this invention is composed of microstructured YAG transparent ceramic, YAG:Ce fluorescent ceramic and YAG-Al2O3 ceramic. The surface is microstructured YAG transparent ceramic, which can disperse the size of the laser spot, increase the average propagation path of photons, obtain a larger extraction area and improve the luminescence performance. In addition, the heat generated by the YAG:Ce fluorescent ceramic layer can be transferred bidirectionally to the microstructured YAG transparent ceramic layer and the YAG-Al2O3 ceramic layer, further improving the heat dissipation performance of the composite fluorescent ceramic.

[0021] 3. The present invention uses dry pressing to prepare composite fluorescent ceramic blanks, which can effectively control the fine structure of the blanks without defects such as cracks and deformation, and at the same time realize mass production, which is conducive to the industrialization of the preparation of composite fluorescent ceramics.

[0022] 4. This invention uses a co-firing method to tightly bond microstructured YAG transparent ceramic, YAG:Ce fluorescent ceramic and YAG-Al2O3 ceramic together. Since all three belong to the YAG system and have similar coefficients of thermal expansion, they can be sintered in one step without cracking. The high thermal conductivity of YAG-Al2O3 ceramic provides better heat dissipation, thereby improving the overall thermal conductivity of the composite ceramic, making it applicable to high-power lighting devices. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of 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 some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the composite fluorescent ceramic blank in this invention;

[0025] Figure 2 This is a schematic diagram of the optical path of the composite fluorescent ceramic in this invention.

[0026] Figure 3 The graph shows the luminescence efficiency of the composite fluorescent ceramics prepared in Examples 1-3 of this invention.

[0027] Figure 4 The surface temperature diagrams are of the composite fluorescent ceramics prepared in Examples 1-3 of this invention.

[0028] Figure 5 This is a reflectance diagram of the YAG-80%Al2O3 ceramic prepared in Example 3 of this invention;

[0029] In the figure: 1. Microstructured YAG transparent ceramic; 2. YAG:Ce fluorescent ceramic; 3. YAG-Al2O3 ceramic. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] The raw material powders used in the following examples are all commercially available products with a purity greater than 99.9%.

[0032] Example 1

[0033] This embodiment provides a composite fluorescent ceramic for reflective laser illumination, such as... Figure 2As shown, the composite fluorescent ceramic comprises, in sequence: a microstructured YAG transparent ceramic 1, a YAG:Ce fluorescent ceramic 2, and a YAG-Al2O3 ceramic 3. The microstructured YAG transparent ceramic 1 is used to increase the average propagation path of photons, resulting in a larger extraction area. The YAG:Ce fluorescent ceramic 2 absorbs blue light from the excitation source and converts it into yellow light. The YAG-Al2O3 ceramic 3 reflects both blue and yellow light. Due to its special conical structure, it can disperse the size of the laser spot, increase the average propagation path of photons, obtain a larger extraction area, and improve luminescence performance. The specific preparation steps are as follows:

[0034] S1: YAG powder, YAG:Ce powder and YAG-Al2O3 powder were prepared respectively; the Ce doping concentration of YAG:Ce was 0.1 at%; the mass percentage of Al2O3 in the second phase of YAG-Al2O3 was 50%;

[0035] S2: YAG / YAG:Ce / YAG-Al2O3 composite ceramic preforms are pressed using dry pressing technology. First, YAG-Al2O3 powder is pressed, then YAG:Ce powder is pressed, and finally YAG powder is pressed. The mass ratio of YAG-Al2O3 powder, YAG:Ce powder, and YAG powder is 2:2:1. Vacuum sintering and annealing are then performed. The sintering temperature is 1770℃, and the holding time is 10 hours. The annealing temperature is 1450℃, and the holding time is 10 hours. The composite fluorescent ceramic preform is shown below. Figure 1 As shown;

[0036] S3: A conical structure array is formed on the YAG surface of the composite ceramic by laser engraving. The bottom diameter of the conical structure is 0.5mm, the height is 0.35mm, the cone angle is 30°, and the final thickness of the composite fluorescent ceramic is 5mm.

[0037] By using blue laser to excite composite fluorescent ceramics, a power density of 70.71 W / mm² is achieved when the blue light output power is 5 W. 2 Fluorescent ceramic devices exhibit stable luminescence, such as Figure 4 As shown, the operating temperature is 76.6℃; its thermal conductivity is 23.8 W / m². -1 k -1 ,like Figure 3 As shown, at the highest power density of 70.71 W / mm² 2 Under excitation, the luminous efficiency of the composite fluorescent ceramic is 235.9 lm / W, and the luminous flux is as high as 1179.5 lm.

[0038] Example 2

[0039] This embodiment provides a composite fluorescent ceramic for reflective laser illumination, such as... Figure 2As shown, the composite fluorescent ceramic comprises, in sequence: a microstructured YAG transparent ceramic 1, a YAG:Ce fluorescent ceramic 2, and a YAG-Al2O3 ceramic 3. The microstructured YAG transparent ceramic 1 is used to increase the average propagation path of photons, resulting in a larger extraction area. The YAG:Ce fluorescent ceramic 2 absorbs blue light from the excitation source and converts it into yellow light. The YAG-Al2O3 ceramic 3 reflects both blue and yellow light. The specific preparation steps are as follows:

[0040] S1: YAG powder, YAG:Ce powder and YAG-Al2O3 powder were prepared respectively; the Ce doping concentration of YAG:Ce was 0.2 at%; the mass percentage of Al2O3 in the second phase of YAG-Al2O3 was 70%;

[0041] S2: YAG / YAG:Ce / YAG-Al2O3 composite ceramic preforms are pressed using dry pressing technology. First, YAG-Al2O3 powder is pressed, then YAG:Ce powder is pressed, and finally YAG powder is pressed. The mass ratio of YAG-Al2O3 powder, YAG:Ce powder, and YAG powder is 2:2:1. Vacuum sintering and annealing are then performed. The sintering temperature is 1760℃, and the holding time is 10 hours. The annealing temperature is 1350℃, and the holding time is 10 hours. The composite fluorescent ceramic preform is shown below. Figure 1 As shown;

[0042] S3: A conical structure array is formed on the YAG surface of the composite ceramic by laser engraving. The bottom diameter of the conical structure is 0.6 mm, the height is 0.4 mm, the cone angle is 45°, and the final thickness of the composite fluorescent ceramic is 5 mm.

[0043] By using blue laser to excite composite fluorescent ceramics, a power density of 70.71 W / mm² is achieved when the blue light output power is 5 W. 2 Fluorescent ceramic devices exhibit stable luminescence, such as Figure 4 As shown, the operating temperature is 68.8℃; its thermal conductivity is 25.8 W / m². -1 k -1 ,like Figure 3 As shown, at the highest power density of 70.71 W / mm² 2 Under excitation, the luminous efficiency of the composite fluorescent ceramic is 245.3 lm / W, and the luminous flux is as high as 1226.5 lm.

[0044] Example 3

[0045] This embodiment provides a composite fluorescent ceramic for reflective laser illumination, such as... Figure 2As shown, the composite fluorescent ceramic comprises, in sequence: a microstructured YAG transparent ceramic 1, a YAG:Ce fluorescent ceramic 2, and a YAG-Al2O3 ceramic 3. The microstructured YAG transparent ceramic 1 is used to increase the average propagation path of photons, resulting in a larger extraction area. The YAG:Ce fluorescent ceramic 2 absorbs blue light from the excitation source and converts it into yellow light. The YAG-Al2O3 ceramic 3 reflects both blue and yellow light. The specific preparation steps are as follows:

[0046] S1: YAG powder, YAG:Ce powder and YAG-Al2O3 powder were prepared respectively; the Ce doping concentration of YAG:Ce was 0.3 at%; the mass ratio of Al2O3 in the second phase of YAG-Al2O3 was 80%;

[0047] S2: A YAG / YAG:Ce / YAG-Al2O3 composite ceramic preform is pressed using dry pressing technology. First, YAG-Al2O3 powder is pressed, then YAG:Ce powder is pressed, and finally YAG powder is pressed. The mass ratio of YAG-Al2O3 powder, YAG:Ce powder, and YAG powder is 2:2:1. Vacuum sintering and annealing are then performed. The sintering temperature is 1750℃, and the holding time is 10 hours. The annealing temperature is 1400℃, and the holding time is 10 hours. The composite fluorescent ceramic preform is shown below. Figure 1 As shown;

[0048] S3: A conical structure array is formed on the YAG surface of the composite ceramic by laser engraving. The bottom diameter of the conical structure is 0.7mm, the height is 0.5mm, the cone angle is 60°, and the final thickness of the composite fluorescent ceramic is 5mm.

[0049] Using blue laser to excite composite fluorescent ceramics, such as Figure 5 As shown, the third layer is YAG-Al2O3 ceramic. When the second phase Al2O3 accounts for 80%, the final reflectivity is approximately 72%. When the blue light output power is 5W, its power density reaches 70.71W / mm². 2 Fluorescent ceramic devices exhibit stable luminescence, such as Figure 4 As shown, the operating temperature is 56.7℃; its thermal conductivity is 26.1 W / m². -1 k -1 ,like Figure 3 As shown, at the highest power density of 70.71 W / mm² 2 Under excitation, the luminous efficiency of the composite fluorescent ceramic is 251.3 lm / W; the luminous flux is as high as 1256.5 lm.

Claims

1. A method for preparing a composite fluorescent ceramic for a reflective laser illumination, characterized by, Includes the following steps: S1: YAG powder, YAG:Ce powder, and YAG-Al2O3 powder were prepared respectively; the Ce doping concentration of YAG:Ce was 0.05~0.3 at%; the mass percentage of Al2O3 in the second phase of YAG-Al2O3 was 50%~80%. S2: A YAG / YAG:Ce / YAG-Al2O3 composite ceramic green body is pressed by dry pressing, followed by vacuum sintering and annealing. YAG-Al2O3 powder is pressed first, then YAG:Ce powder, and finally YAG powder. The mass ratio of YAG-Al2O3 powder, YAG:Ce powder, and YAG powder is 2:2:

1. The sintering temperature is 1750℃~1770℃, with a holding time of 10h. The annealing temperature is 1350~1450℃, with a holding time of 10h. The bottom diameter of the conical structure is 0.5~0.7mm, the height is 0.3~0.5mm, and the cone angle is 30°~60°. S3: A conical array of structures is formed on the YAG layer of the composite ceramic surface by laser engraving, and the final thickness of the composite fluorescent ceramic is 4~5mm.

2. A composite fluorescent ceramic for reflective laser illumination prepared by the method of claim 1, characterized in that: The composite fluorescent ceramic is composed of a three-layer structure from top to bottom: microstructured YAG transparent ceramic (1), YAG:Ce fluorescent ceramic (2), and YAG-Al2O3 ceramic (3). The microstructured YAG transparent ceramic (1) is used to increase the average propagation path of photons and obtain a larger extraction area. The YAG:Ce fluorescent ceramic (2) is used to absorb blue light from the excitation source and convert it into yellow light. The YAG-Al2O3 ceramic (3) is used to reflect blue light and yellow light.

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