A thermal gradient inorganic phosphor and its preparation method

Abstract

The present invention relates to a thermal gradient inorganic phosphor and a preparation method thereof, belonging to the field of lighting and display technology. It comprises: a thermally conductive substrate, a thermal gradient layer, a fluorescent glass film and a thermally conductive cover plate. Preferably, the thermally conductive substrate is made of aluminum nitride or aluminum sheet; the thermal gradient layer is a low-melting-point glass containing thermally conductive particles of different concentrations, which is coated on the thermally conductive substrate; the fluorescent glass film is prepared on the thermal gradient layer; the thermally conductive cover plate is covered on the fluorescent glass film, and the material is sapphire or diamond. The present invention utilizes a double-sided thermal conductive structure and a thermal gradient layer to improve the heat dissipation performance of the fluorescent glass film, avoid the problem of luminous saturation, and improve the conversion efficiency and thermal stability of the inorganic phosphor. The thermal gradient inorganic phosphor can be excited by a high-power laser light source to achieve a high-power, high-brightness laser white light source.

Description

Technical Field

[0001] The present invention belongs to the field of lighting and display technology, and more specifically, relates to a thermal gradient inorganic phosphor and a preparation method thereof. Background Art

[0002] In the current context of global energy shortage, semiconductor solid-state lighting, with its advantages of high light efficiency, low energy consumption, long life, and environmental friendliness, has led to the continuous improvement of the country's energy conservation and environmental protection capabilities. With the increasing demand for high-brightness lighting equipment, semiconductor lighting technology is developing in the direction of high current, high power density, lightweight and small size. Laser lighting, as a new generation of lighting technology, has emerged. Compared with existing LED technology, laser light source technology not only avoids the problem of sudden drop in efficiency, but also has the characteristics of ultra-high power, ultra-high brightness, high collimation, and long irradiation distance. It can be applied to automotive headlights, projection displays, medical equipment, visible light communications and other fields, and has huge market potential.

[0003] Laser white light sources (white light LD) often use laser fluorescence technology, that is, the blue light LD chip excites the remote yellow phosphor (or fluorescence conversion material). Due to the high light power density and small radiation spot of the blue light LD, the phosphor must withstand high laser radiation energy and fluorescence conversion heat, which places higher requirements on the heat resistance of the phosphor. At present, researchers use highly thermally stable inorganic phosphors to replace traditional organic phosphors and develop corresponding "laser + inorganic phosphor" laser white light sources. Among them, fluorescent glass is an inorganic composite phosphor composed of phosphor and glass, which has the advantages of adjustable luminescence characteristics, rich material system, simple process and low cost. Although fluorescent glass achieves white light irradiation effect under blue light LD excitation, as the laser power density increases, the photoheat increases sharply, and high-temperature quenching and luminescence thermal saturation occur in the micro-area of ​​fluorescent glass, causing the fluorescent glass to melt and break.

[0004] To solve this problem, researchers have proposed a method for preparing fluorescent glass films on thermally conductive substrates. Compared with fluorescent glass sheets, fluorescent glass films have higher heat dissipation performance, and a thermally conductive substrate can be used to provide a heat transfer channel for the film layer. However, the difference in thermal expansion coefficients of heterogeneous materials will cause excessive interface stress, resulting in problems such as cracks and shedding in the film layer; since the commonly used low-melting-point glass has a low thermal conductivity, it limits the thermal conductivity of the film layer itself, resulting in the film layer. The heat far away from the substrate, especially near the top surface, is difficult to conduct effectively, and the local temperature of the film layer is high; the film layer-substrate heterogeneous interface quality is poor, which affects the laser fluorescence photothermal effect and limits the improvement of the heat dissipation performance of the fluorescent glass. Therefore, it is necessary to propose a new type of inorganic phosphor to meet the needs of high-power density laser excitation. Summary of the invention

[0005] In view of the defects of the prior art and the need for improvement, the present invention provides a thermal gradient inorganic phosphor and a method for preparing the same, with the aim of solving the problem of thermal mutation interface between heterogeneous materials caused by differences in thermal conductivity, and cracks and shedding between film layers caused by differences in thermal expansion coefficients. A thermal gradient inorganic phosphor is used to achieve a smooth transition of thermal conductivity and thermal expansion coefficient from the fluorescent glass film to the thermally conductive substrate, thereby improving heat conduction efficiency and reducing interface stress. At the same time, a double-sided thermal conductive structure is adopted to increase the heat conduction path and efficiency, and improve the heat dissipation performance of the fluorescent glass, thereby meeting the packaging requirements of the laser white light source.

[0006] According to a first aspect of the present invention, a thermal gradient inorganic phosphor is provided, which comprises, from bottom to top, a thermal conductive substrate, a thermal gradient layer, a fluorescent glass film and a thermal conductive cover plate; the thermal gradient layer is a layer of low-melting-point glass containing thermal conductive particles;

[0007] Alternatively, the thermal gradient layer is a structure of at least two layers, each layer is a low-melting-point glass containing thermally conductive particles of different concentrations, wherein the concentration of the thermally conductive particles decreases from the thermally conductive substrate to the fluorescent glass film;

[0008] The glass transition temperature of the low melting point glass is lower than 800°C.

[0009] Preferably, the thermal conductivity of the thermally conductive particles is greater than 100 W·m -1 ·K -1 .

[0010] Preferably, the thermally conductive particles are aluminum nitride, boron nitride or diamond.

[0011] Preferably, the thermal expansion coefficient of the thermal gradient layer is between the thermal expansion coefficients of the thermal conductive substrate and the fluorescent glass film.

[0012] Preferably, the thermal conductivity of the thermally conductive substrate is greater than 150 W·m -1 ·K -1 , reflectivity greater than 90%;

[0013] Preferably, the thermally conductive substrate is aluminum nitride or aluminum sheet.

[0014] Preferably, the thermal conductivity of the heat-conducting cover plate is greater than 30 W·m -1 ·K -1 , transmittance greater than 85%;

[0015] Preferably, the heat-conducting cover plate is sapphire or diamond.

[0016] Preferably, the fluorescent glass film is solidified by fluorescent glass slurry, which includes fluorescent powder, low-melting point glass powder, organic solvent and adhesive; wherein the glass transition temperature of the low-melting point glass powder is lower than 800°C, the fluorescent powder is monochrome fluorescent powder or multi-color fluorescent powder, and the concentration of the fluorescent powder is 20% to 200% of the weight of the low-melting point glass powder.

[0017] According to another aspect of the present invention, there is provided a method for preparing any of the thermal gradient inorganic phosphors, comprising the following steps:

[0018] S1: coating a layer of low-melting-point glass powder containing thermally conductive particles on the thermally conductive substrate to form a thermal gradient layer;

[0019] Alternatively, low melting point glass powders containing heat conductive particles of different concentrations are coated on the heat conductive substrates, and the concentration of the heat conductive particles decreases from bottom to top to form a thermal gradient layer;

[0020] S2: coating fluorescent glass slurry on the thermal gradient layer obtained in step S1, the fluorescent glass slurry comprising fluorescent powder, low melting point glass powder, organic solvent and adhesive, and then covering the thermal conductive cover plate on the glass slurry;

[0021] S3: sintering the structure obtained in step S2 to obtain the thermal gradient inorganic phosphor;

[0022] The glass transition temperature of the low melting point glass powder in step S1 and step S2 is lower than 800°C.

[0023] Preferably, the sintering temperature is 600-800°C.

[0024] Preferably, the thermally conductive particles are aluminum nitride, boron nitride or diamond;

[0025] The thermally conductive substrate is aluminum nitride or aluminum sheet;

[0026] The heat-conducting cover plate is made of sapphire or diamond.

[0027] In general, the above technical solution conceived by the present invention has the following technical advantages compared with the prior art:

[0028] (1) The present invention improves the heat dissipation performance of the fluorescent glass film by using a double-sided heat-conducting structure and a thermal gradient layer, avoids the problem of luminescence saturation, and improves the conversion efficiency and thermal stability of the inorganic phosphor. The thermal gradient inorganic phosphor can be excited by a high-power laser light source to achieve a high-power, high-brightness laser white light source.

[0029] (2) The present invention utilizes a double-layer heat-conducting structure to increase the heat dissipation path, enhance the heat dissipation performance, increase the luminescence saturation threshold, and improve the conversion efficiency and thermal stability of the inorganic phosphor.

[0030] (3) The present invention utilizes a thermal gradient layer to achieve a smooth transition of thermal conductivity and thermal expansion coefficient between the thermally conductive substrate and the fluorescent glass film, thereby improving heat conduction efficiency, reducing interface stress, and enhancing heat dissipation performance.

[0031] (4) The thermal gradient inorganic phosphor of the present invention can be excited by a high-power laser light source due to its excellent heat dissipation performance, thereby realizing a high-power and high-brightness laser white light source. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a schematic structural diagram of the thermal gradient inorganic phosphor in Example 1 of the present invention;

[0033] Figure 2 is a schematic structural diagram of a thermal gradient inorganic phosphor in Example 2 of the present invention;

[0034] Figure 3 The present invention provides a thermal gradient inorganic phosphor preparation process flow chart.

[0035] In all drawings, the same reference numerals are used to denote the same elements or structures, wherein: 1 - thermally conductive substrate, 2 - thermal gradient layer, 3 - fluorescent glass film, 4 - thermally conductive cover plate. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0037] The thermal gradient inorganic phosphor of the present invention comprises, from bottom to top, a thermal conductive substrate 1, a thermal gradient layer 2, a fluorescent glass film 3 and a thermal conductive cover plate 4; the thermal gradient layer 2 is a layer of low melting point glass containing thermal conductive particles;

[0038] Alternatively, the thermal gradient layer 2 is a structure of at least two layers, each layer is a low-melting-point glass containing thermally conductive particles of different concentrations, wherein the concentration of the thermally conductive particles decreases from the thermally conductive substrate to the fluorescent glass film;

[0039] The glass transition temperature of the low melting point glass is lower than 800°C.

[0040] In some embodiments, the thermal gradient layer 2 is a two-layer or three-layer structure, each layer is a low-melting point glass containing thermal conductive particles of different concentrations, and the concentration of the thermal conductive particles decreases from the thermal conductive substrate 1 to the fluorescent glass film 3 to achieve a smooth transition of the thermal conductivity coefficient between the two structures.

[0041] The method for preparing the thermal gradient inorganic phosphor of the present invention comprises the following steps:

[0042] S1: coating a layer of low-melting-point glass powder containing thermally conductive particles on the thermally conductive substrate to form a thermal gradient layer;

[0043] Alternatively, low melting point glass powders containing heat conductive particles of different concentrations are coated on the heat conductive substrates, and the concentration of the heat conductive particles decreases from bottom to top to form a thermal gradient layer;

[0044] S2: coating fluorescent glass slurry on the thermal gradient layer obtained in step S1, the fluorescent glass slurry comprising fluorescent powder, low melting point glass powder, organic solvent and adhesive, and then covering the thermal conductive cover plate on the glass slurry;

[0045] S3: sintering the structure obtained in step S2 under high temperature conditions to obtain the thermal gradient inorganic phosphor;

[0046] The glass transition temperature of the low melting point glass powder in step S1 and step S2 is lower than 800°C.

[0047] In some embodiments, the sintering temperature is 600-800° C.; when the sintering is performed using a muffle furnace, the sintering time is 30-60 min; when the sintering is performed using a spark plasma sintering (SPS) process, the sintering time is 5-10 min.

[0048] Example 1

[0049] like Figure 1 As shown, the thermal gradient inorganic phosphor comprises: a thermal conductive substrate 1, a thermal gradient layer 2, a fluorescent glass film 3 and a thermal conductive cover plate 4; wherein the thermal conductive substrate 1 is made of aluminum nitride, on which is coated a thermal gradient layer 2 with a two-layer structure, the material of which is a low-melting-point glass doped with aluminum nitride particles, each layer has the same thickness of 50 μm, and is coated in sequence with a low-temperature glass powder slurry having a boron nitride particle concentration of 30 wt% and 10 wt%; the fluorescent glass film 2 is made of fluorescent glass containing YAG fluorescent powder, and is prepared on the thermal gradient layer 2; the thermal conductive cover plate 4 is made of sapphire, and covers the fluorescent glass film 3.

[0050] like Figure 3 As shown, the steps of preparing the thermal gradient inorganic phosphor include:

[0051] Step 1: Select a thermally conductive substrate 1 made of aluminum nitride, prepare low-melting-point glass powder doped with aluminum nitride thermally conductive particles into glass pastes of different concentrations, and apply them on the thermally conductive substrate 1 in descending order of concentration to form a two-layer structure of the thermal gradient layer 2;

[0052] Step 2: 2g of pineol and 0.1g of ethyl cellulose are mixed, and ultrasonic stirring is performed at 80°C until the ethyl cellulose is completely dissolved, so as to serve as an organic solvent for the glass slurry, and then 3g of YAG yellow phosphor and 2g of low-temperature borosilicate glass powder are added, and finally the fluorescent glass slurry is obtained by magnetic stirring for 15 minutes; the fluorescent glass slurry is coated on the thermal gradient layer 2 obtained in step 1, and sapphire is selected as the thermal conductive cover plate 4, which is placed on the thermal conductive substrate 1 and aligned;

[0053] Step three, placing the above structure in a muffle furnace and sintering at 600° C. for 30 minutes to form the fluorescent glass layer 3; fixing the thermal conductive cover plate 4 and the thermal conductive substrate 1 through the thermal gradient layer 2 and the fluorescent glass layer 3 to obtain a thermal gradient inorganic phosphor.

[0054] Example 2

[0055] like Figure 2 As shown, the thermal gradient inorganic phosphor comprises: a thermal conductive substrate 1, a thermal gradient layer 2, a fluorescent glass film 3 and a thermal conductive cover plate 4; wherein the thermal conductive substrate 1 is made of an aluminum sheet, on which a three-layer thermal gradient layer 2 is coated, the material of which is a low-melting-point glass doped with boron nitride particles, each layer has the same thickness of 50 μm, and low-temperature glass powder slurry with boron nitride particle concentrations of 50wt%, 30wt% and 10wt% is coated in sequence; the fluorescent glass film 3 is made of a YAG (yttrium aluminum garnet crystal (Y3Al5O 12 )) The fluorescent glass of the fluorescent powder is prepared on the thermal gradient layer 2; the thermal conductive cover plate 4 is made of sapphire and covers the fluorescent glass film 3.

[0056] like Figure 3 As shown, the steps of preparing the thermal gradient inorganic phosphor include:

[0057] Step 1: select aluminum sheet as thermal conductive substrate 1, prepare low melting point glass powder doped with boron nitride thermal conductive particles into glass pastes of different concentrations, and apply them on thermal conductive substrate 1 in descending order of concentration to form a thermal gradient layer 2 structure;

[0058] Step 2: 3 g of pineol and 0.15 g of ethyl cellulose are mixed, and ultrasonic stirring is performed at 80° C. until the ethyl cellulose is completely dissolved, so as to serve as an organic solvent for the glass slurry. Then, 4.5 g of YAG yellow phosphor and 3 g of low-temperature borosilicate glass powder are added, and finally, the fluorescent glass slurry is obtained by magnetic stirring for 15 minutes. The fluorescent glass slurry is coated on the thermal gradient layer 2 obtained in step 1, and sapphire is selected as the thermal conductive cover plate 4, which is placed on the thermal conductive substrate 1 and aligned.

[0059] Step three, sinter the above structure by spark plasma sintering process at 600°C for 10 minutes to form a fluorescent glass layer 3; fix the thermal conductive cover plate 4 and the thermal conductive substrate 1 through the thermal gradient layer 2 and the fluorescent glass layer 3 to obtain a thermal gradient inorganic phosphor.

[0060] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A thermal gradient inorganic phosphor, characterized in that: From bottom to top, there are a heat-conducting substrate, a thermal gradient layer, a fluorescent glass film and a heat-conducting cover plate; the thermal gradient layer is a layer of low-melting-point glass containing thermally conductive particles; Alternatively, the thermal gradient layer is a structure of at least two layers, each layer is a low-melting-point glass containing thermally conductive particles of different concentrations, wherein the concentration of the thermally conductive particles decreases from the thermally conductive substrate to the fluorescent glass film; The glass transition temperature of the low melting point glass is lower than 800°C.

2. The thermal gradient inorganic phosphor according to claim 1, characterized in that: The thermal conductivity of the thermally conductive particles is greater than 100 W·m -1 ·K -1 .

3. The thermal gradient inorganic phosphor according to claim 1 or 2, characterized in that: The thermally conductive particles are aluminum nitride, boron nitride or diamond.

4. The thermal gradient inorganic phosphor according to claim 1, characterized in that: The thermal expansion coefficient of the thermal gradient layer is between the thermal expansion coefficients of the thermal conductive substrate and the fluorescent glass film.

5. The thermal gradient inorganic phosphor according to claim 1, characterized in that: The thermal conductivity of the thermally conductive substrate is greater than 150 W·m -1 ·K -1 , reflectivity is greater than 90%.

6. The thermal gradient inorganic phosphor according to claim 5, characterized in that: The heat conductive substrate is aluminum nitride or aluminum sheet.

7. The thermal gradient inorganic phosphor according to claim 1, characterized in that: The thermal conductivity of the heat-conducting cover plate is greater than 30 W·m -1 ·K -1 , transmittance is greater than 85%.

8. The thermal gradient inorganic phosphor according to claim 7, characterized in that: The heat-conducting cover plate is made of sapphire or diamond.

9. The thermal gradient inorganic phosphor according to claim 1, characterized in that: The fluorescent glass film is solidified by fluorescent glass slurry, which includes fluorescent powder, low-melting point glass powder, organic solvent and adhesive; the glass transition temperature of the low-melting point glass powder is lower than 800°C, the fluorescent powder is monochrome fluorescent powder or multi-color fluorescent powder, and the concentration of the fluorescent powder is 20% to 200% of the weight of the low-melting point glass powder.

10. The method for preparing a thermal gradient inorganic phosphor according to any one of claims 1 to 9, characterized in that: The following steps are involved: S1: coating a layer of low-melting-point glass powder containing thermally conductive particles on the thermally conductive substrate to form a thermal gradient layer; Alternatively, low melting point glass powders containing heat conductive particles of different concentrations are coated on the heat conductive substrates, and the concentration of the heat conductive particles decreases from bottom to top to form a thermal gradient layer; S2: coating fluorescent glass slurry on the thermal gradient layer obtained in step S1, the fluorescent glass slurry comprising fluorescent powder, low melting point glass powder, organic solvent and adhesive, and then covering the thermal conductive cover plate on the glass slurry; S3: sintering the structure obtained in step S2 to obtain the thermal gradient inorganic phosphor; The glass transition temperature of the low melting point glass powder in step S1 and step S2 is lower than 800°C.

11. The method for preparing a thermal gradient inorganic phosphor according to claim 10, characterized in that: The sintering temperature is 600-800°C.

12. The method for preparing a thermal gradient inorganic phosphor according to claim 10, characterized in that: The thermally conductive particles are aluminum nitride, boron nitride or diamond; The thermally conductive substrate is aluminum nitride or aluminum sheet; The heat-conducting cover plate is made of sapphire or diamond.

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