Fluorescent ceramic as well as preparation method and application thereof

Abstract

The invention discloses fluorescent ceramic as well as a preparation method and application thereof and relates to the field of luminescent materials. The fluorescent ceramic raw material at least comprises components A, B and C; each of the component A and the component B comprises fluorescent powder and a barrier layer; the fluorescent powder in the component A is fluorescent powder capable of emitting yellow-green light after being excited by blue light or ultraviolet light; the fluorescent powder in the component B is fluorescent powder which emits red light after being excited by blue light or ultraviolet light; the component C is the same as the component of the barrier layer; uniformly mixing the fluorescent ceramic raw materials, forming, sintering to obtain a ceramic rough blank, and post-processing to obtain the fluorescent ceramic. Different fluorescent powder systems in the fluorescent ceramic are not in direct contact, the original interface reaction between the systems can be avoided to the maximum extent in the sintering process, and the quantum efficiency reduction degree caused by the interface reaction is reduced to the minimum. The preparation method is simple in process, easy to operate, wide in application range, theoretically suitable for preparation of all fluorescent powder system fluorescent ceramics, free of exhaust emission, environmentally friendly and suitable for industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of luminescent materials, and particularly to a fluorescent ceramic and a preparation method and application thereof. Background Art

[0002] At present, white light illumination achieved by encapsulating phosphors based on blue light LEDs (light emitting diodes) is the mainstream solid-state lighting technology. However, with the increase of the input current density, the "efficiency roll-off" problem appears in the LED chip, which limits the application of the LED white light source at high power and high power density. The "blue laser chip + light conversion material" emerges as the key technology for realizing laser lighting and display. The blue laser chip (LDs) has the technical advantages of high brightness, high power and small volume, and is expected to replace the LED lighting technology in the fields with high brightness and large size requirements. At present, the laser lighting technology based on remotely encapsulating YAG:Ce (yellow-green phosphor with a yttrium aluminum garnet structure doped with trivalent cerium ions) fluorescent ceramics with blue LDs chips has attracted extensive attention inside and outside the industry, and has performance advantages such as high brightness, high power density, high luminous efficiency, low light decay rate and low cost. It shows great application potential in both high-brightness lighting fields, such as outdoor lighting, automotive headlights and aircraft searchlights, and in ultra-large-size display fields, such as high-end projectors, IMAX movies and large-scale splicing display walls.

[0003] However, the yellow-green light conversion material represented by YAG:Ce fluorescent ceramics lacks the red part, resulting in two key problems in laser lighting: high correlated color temperature (CCT > 6000 K) and low color rendering index (CRI < 60), which seriously restricts the development and application promotion of this technology.

[0004] At present, there are two mainstream solutions. One is to replace matrix elements and adjust doped ions based on the YAG:Ce system. However, the redshift of the emission spectrum is very limited (the peak position redshifts from 535 nm to ~560 nm), and it is accompanied by a significant decrease in thermal stability and quantum efficiency. The other is to add orange or red fluorescence conversion materials to the YAG:Ce system fluorescent ceramics to supplement the red light band of the spectrum. This is one of the most effective solutions for supplementing the red light band at present. However, orange or red phosphors with high quantum efficiency and high thermal stability are concentrated in the oxynitride or nitride systems (such as Ca-α-Sialon:Eu, CaAlSiN3:Eu, Sr2Si5N8:Eu). During the sintering process of the fluorescent ceramics, there is a serious interfacial reaction between them and the YAG:Ce system phosphors, which leads to the destruction of the phosphor lattice structure and the decrease in the quantum efficiency of the fluorescent ceramics. Currently, there is a lack of a preparation method for fluorescent ceramics in the industry that can effectively avoid serious interfacial reactions between phosphors. The shortage of high-performance multi-system composite fluorescent ceramics is a major problem that urgently needs to be solved to limit the development of low-color-temperature, high-color-rendering-index, and high-brightness laser lighting sources. Summary of the Invention

[0005] The purpose of the present invention is to solve the above problems of the interfacial reaction that is difficult to avoid in the process of multi-system fluorescent ceramics in the prior art, and to provide a fluorescent ceramic, its preparation method and application. Applying the fluorescent ceramic prepared in the present invention to a laser lighting device to solve the problem of the lack of red light spectrum in the laser white light spectrum, so as to promote the realization of a laser lighting source with high optical quality (low color temperature, high color rendering index).

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A preparation method of a fluorescent ceramic, comprising the following steps:

[0008] 1) Weigh the raw materials of the fluorescent ceramic. The raw materials of the fluorescent ceramic at least include component A, component B, and component C. Both component A and component B include a phosphor and a barrier layer, and the barrier layer coats the phosphor. The phosphor in component A is a phosphor that emits yellow-green light after being excited by blue light or ultraviolet light. The phosphor in component B is a phosphor that emits red light after being excited by blue light or ultraviolet light. The barrier layer includes at least one of Al2O3, B2O3, SiO2, and BN, and component C has the same components as the barrier layer.

[0009] 2) Mix the raw materials of the fluorescent ceramic evenly, place them in a mold for forming, and then sinter to obtain a ceramic rough blank, and post-treat the ceramic rough blank to obtain the fluorescent ceramic.

[0010] The phosphor in component A is Ce that can effectively absorb blue light or ultraviolet light 3+Down-conversion phosphor doped with rare earth ions such as ions, specifically including at least one of YAG:Ce, LuAG:Ce, and YAGG:Ce.

[0011] The phosphor in component B is Eu doped with rare earth ions that can effectively absorb blue light or ultraviolet light 2+ Down-conversion phosphor doped with rare earth ions such as ions, specifically including at least one of Ca-α-SiAlON:Eu, CaAlSiN3:Eu, and Sr2Si5N8:Eu.

[0012] The total mass of component A and component B accounts for 30% - 90% of the total mass of the ceramic raw materials, and the mass of component C accounts for 10% - 70% of the total mass of the ceramic raw materials.

[0013] The mass ratio of component A to component B is 1:9 - 9:1.

[0014] In step 2), the sintering temperature is 1200 - 1600 °C, and the sintering pressure is 10 - 100 MPa.

[0015] The barrier layer is prepared by the sol-gel method.

[0016] In step 2), the post-treatment includes but is not limited to thinning, polishing, cutting, heat treatment, and pickling, etc.

[0017] The present invention can also add a flux to the fluorescent ceramic raw materials to promote sintering. Among them, the flux includes but is not limited to SiO2 and MgO.

[0018] In the present invention, the mixing method includes but is not limited to ball milling or magnetic stirring; the forming process includes but is not limited to dry pressing forming and cold isostatic pressing treatment; the sintering process includes but is not limited to SPS (spark plasma sintering), vacuum sintering, hot pressing sintering, atmosphere sintering, and annealing treatment.

[0019] A fluorescent ceramic prepared by the above preparation method.

[0020] The application of the fluorescent ceramic is used to prepare light-emitting, display, or lighting devices.

[0021] A light-emitting, display, or lighting device includes a light-emitting unit and a fluorescent ceramic. The light emitted by the light-emitting unit is blue light or ultraviolet light. The fluorescent ceramic is connected to a transparent substrate or a reflective substrate through thermal conductive silicone grease. The light emitted by the light-emitting unit is directed towards the fluorescent ceramic or the transparent substrate. The material of the reflective substrate is preferably but not limited to metal aluminum and metal silver; the material of the transparent substrate is preferably but not limited to sapphire. The device may also include an optical lens for collecting or reflecting the light emitted by the device.

[0022] Compared with the prior art, the beneficial effects achieved by the technical solution of the present invention are as follows:

[0023] In the fluorescent ceramic prepared by the method of the present invention, different phosphor systems inside are not in direct contact with each other, and during the sintering process, the original interfacial reaction between the systems can be avoided to the greatest extent, reducing the degree of quantum efficiency decline caused by the interfacial reaction to the lowest level. At the same time, the method for preparing the fluorescent ceramic provided by the present invention has a simple process, is easy to operate, has a wide application range, is theoretically applicable to the preparation of all multi-phosphor system fluorescent ceramics, and is more environmentally friendly without waste gas emissions, and is suitable for industrial production. Description of the Drawings

[0024] Figure 1 It is the surface morphology before and after the presence of the barrier layer of component A, where the upper figure is before the presence of the barrier layer and the lower figure is after the presence of the barrier layer;

[0025] Figure 2 It is the surface morphology before and after the presence of the barrier layer of component B, where the upper figure is before the presence of the barrier layer and the lower figure is after the presence of the barrier layer;

[0026] Figure 3 It is the photos of the fluorescent ceramics with different mass ratios obtained in Examples 1, 2, 5, 7, and 8. From left to right, the mass ratios of component A and component B of the ceramics are 1:0, 9:1, 4:1, 1:1, and 0:1 respectively;

[0027] Figure 4 It is the XRD patterns of the fluorescent ceramics in Examples 2, 5, and 7;

[0028] Figure 5 It is the emission spectra of the fluorescent ceramics in Examples 1 to 8 under 450 nm blue light excitation;

[0029] Figure 6 It is the chromaticity coordinate diagrams of the fluorescent ceramics in Examples 1 to 8 under 450 nm blue light excitation;

[0030] Figure 7 It is the physical diagrams of the fluorescent ceramics obtained in Example 2 and Comparative Example 1 under 365 nm excitation. Among them, the left figure is Comparative Example 1 and the right figure is Example 2;

[0031] Figure 8 It is the comparison diagram of the internal quantum efficiency of the fluorescent ceramics obtained in Example 2 and Comparative Example 1;

[0032] Figure 9 It is the schematic diagram of the fluorescent ceramic light source device provided by the present invention; among them, the left figure is the schematic structural diagram in the transmission mode and the right figure is the structural diagram in the reflection mode.

[0033] Reference numerals: 10 blue laser light source, 20 transparent substrate, 30 fluorescent ceramic, 41 white light, 50 convex lens, 61 horizontal white light, 70 reflective substrate. Detailed implementation manners

[0034] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the drawings and embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts belong to the scope of protection of the present invention.

[0035] The following raw materials are included in the following embodiments or comparative examples of the present invention: YAG:Ce phosphor, Ca-α-SiAlON:Eu phosphor, Al2O3; the specifications, chemical formulas and manufacturers of the above YAG:Ce phosphor and Ca-α-SiAlON:Eu phosphor are shown in Table 1.

[0036] Table 1

[0037]

[0038] The phosphor in Component A is YAG:Ce phosphor, the barrier layer is Al2O3, the thickness of the barrier layer is 1 - 3 μm, and the number of layers is 1 layer;

[0039] The phosphor in Component B is Ca-α-SiAlON:Eu phosphor, the barrier layer is Al2O3, the thickness of the barrier layer is 1 - 3 μm, and the number of layers is 1 layer;

[0040] Component C is Al2O3;

[0041] Among them, the barrier layer Al2O3 of the YAG:Ce phosphor and the Ca-α-SiAlON:Eu phosphor in Component A and Component B is prepared by the sol-gel method, and the preparation process is as follows:

[0042] Accurately weigh 1.0 g of YAG:Ce phosphor and Ca-α-SiAlON:Eu phosphor respectively, mix them with 0.55 g of Al(NO3)3·9H2O powder raw materials, dissolve them in 100 ml of deionized water, and stir magnetically at room temperature for 12 h. Then, add acetic acid-sodium acetate buffer solution to adjust the acidity and alkalinity of the solution, so that the pH value of the mixed solution is maintained at about 8.0 for 2 h. After filtration, the obtained precipitate is washed 5 times with deionized water and then dried in an 80°C environment for 24 h. After the dried product is sufficiently ground in a mortar, the product is placed in a corundum crucible and calcined in air at 550°C for 4 h. The calcined product is ground again and sieved through a 80-mesh sieve to finally obtain Component A and Component B.

[0043] To avoid affecting the absorption and emission of light by the phosphor, the thickness of the barrier layer is not greater than the median particle size of the phosphor raw materials used. Among them, the thickness of the barrier layer is controlled by adjusting the mass of the Al(NO3)3·9H2O powder raw material added in the barrier layer preparation process and the number of process steps.

[0044] The present invention prepares YAG:Ce, Ca-α-SiAlON:Eu, and Al2O3 fluorescent ceramics with different mass ratios, as shown in the following examples.

[0045] Example 1

[0046] Component A accounts for 40% of the total mass of the ceramic raw materials, and component C accounts for 60% of the total mass of the ceramic raw materials. After weighing components A and C in a certain proportion, they are placed in a beaker containing anhydrous ethanol solution and mixed evenly by magnetic stirring at a rotation speed of 800 rpm / min. The temperature of the anhydrous ethanol in the beaker is maintained at 80 °C until the anhydrous ethanol completely evaporates. Then, the remaining mixed powder in the beaker is placed in an oven at 80 °C and dried for 24 h. Then, 0.3 g of the dried powder is taken and placed in a graphite mold with an effective sintering diameter of 10 mm, and a layer of high-purity graphite paper (purity 99.99%) with a thickness of 0.2 mm is placed between the powder and the graphite mold.

[0047] The above mold containing the powder is sintered by a spark plasma sintering furnace to finally obtain a ceramic green body. Among them, the sintering temperature is 1480 °C, the sintering pressure is 40 MPa, and the heat preservation time is 5 min.

[0048] The ceramic green body obtained in the above step is first thinned to 0.4 mm, and then polished successively with 600-mesh, 800-mesh, 1000-mesh, 2000-mesh, and 3000-mesh sandpapers to obtain a fluorescent ceramic sample.

[0049] Example 2

[0050] The difference from Example 1 is that component B is added, where the mass ratio of component A to component B is 1:1, and the total mass of components A and B accounts for 40% of the total mass of the ceramic raw materials, and the mass of component C accounts for 60% of the total mass of the ceramic raw materials.

[0051] Example 3

[0052] The difference from Example 2 is that the mass ratio of component A to component B is 2:1.

[0053] Example 4

[0054] The difference from Example 2 is that the mass ratio of component A to component B is 3:1.

[0055] Example 5

[0056] Different from Example 2, the mass ratio of Component A to Component B is 4:1.

[0057] Example 6

[0058] Different from Example 2, the mass ratio of Component A to Component B is 5:1.

[0059] Example 7

[0060] Different from Example 2, the mass ratio of Component A to Component B is 9:1.

[0061] Example 8

[0062] Different from Example 1, Component A is replaced by Component B.

[0063] Comparative Example 1

[0064] Different from Example 2, there is no barrier layer in both Component A and Component B. Component A only contains YAG:Ce phosphor, and Component B only contains Ca-α-SiAlON:Eu phosphor.

[0065] The above examples will be described below in combination with the test results and the accompanying drawings, as follows.

[0066] As Figure 1 and Figure 2 shown, the barrier layers in Component A and Component B can very completely cover the surface of the phosphor layer. According to the microscopic morphology, the thickness of the barrier layer is about 1 - 2 μm. This shows that it can play the role of blocking the interfacial reaction between the two to the greatest extent.

[0067] As Figure 3 shown, the phosphor ceramics obtained through the examples have a certain transmittance and bright color, indicating that the phosphor ceramic sintering method provided by the present invention plays a role in both restricting the interfacial reaction and densification. At the same time, as Figure 4 shown, after the ultra-high temperature sintering condition, the phosphor ceramic sample can still well maintain the coexistence of the three phases of YAG:Ce, Ca-α-SiAlON:Eu, and Al2O3 without the generation of impurity phases, indicating that no obvious interfacial reaction is found between the three.

[0068] Table 2 shows the emission peak positions and full widths at half maximum of the phosphor ceramics with different mass ratios obtained in Examples 1, 2, 5, 7, and 8 under 450 nm blue light excitation.

[0069] Table 2

[0070]

[0071] As Figure 5As shown, with the change of the mass ratio of component A and component B, the peak position and full width at half maximum (FWHM) of the emission spectrum of the fluorescent ceramic under 450 nm blue light excitation also change. As can be seen from Table 2, when component A exists alone, the emission peak position is at 541 nm and the FWHM is 112 nm, significantly lacking the red light part. When component B exists alone, the emission peak position is at 601 nm and the FWHM is 83 nm, showing orange-red light emission. When component B increases compared to component A, the emission peak position significantly redshifts and reaches the maximum at 598 nm when the mass ratio is 1:1. When the mass ratio is 4:1, the FWHM increases from 112 nm when component A exists alone to 124 nm. The broadening of this part of the spectrum is due to the increase in the red light part, indicating that the color rendering index will also increase accordingly. From Figure 6 it can be seen that with the increase of the content of component B, the x value of the color coordinates of the fluorescent ceramic continuously increases and the y value continuously decreases. The overall color coordinates move from yellow-green to the red region. When combined with a certain proportion of 450 nm blue light, the correlated color temperature of the mixed white light can be significantly reduced from 6000 K to about 1700 K, realizing a super-large range of adjustable correlated color temperature.

[0072] In Comparative Example 1, since the Al2O3 barrier layer was not added, the color of the prepared fluorescent ceramic sample became darker. Under the excitation of a 365 nm light source, the sample only emitted weak light, as shown in the left figure of Figure 7 . After adding the Al2O3 barrier layer according to Example 2, the obtained fluorescent ceramic was brighter ( Figure 7 , the right figure).

[0073] As shown in Figure 8 , the internal quantum efficiency of the fluorescent ceramic prepared by the method of Comparative Example 1 was only 11.0%, indicating that obvious interfacial reactions occurred between the phosphor powders, leading to the deterioration of the luminescence performance of the fluorescent ceramic. The internal quantum efficiency of the fluorescent ceramic prepared by the method of Example 2 was 62.4%, which was 567% higher than that of the sample prepared in Comparative Example 1. This shows that the preparation method of the fluorescent ceramic of the present invention has obvious technical advantages compared with the preparation method of Comparative Example 1.

[0074] The present invention provides schematic structural diagrams of two laser illumination / display light source devices based on the fluorescent ceramics obtained by the above preparation method. As shown in Figure 9 , the left figure is a schematic diagram in the transmission mode. The structure includes a blue laser light source 10 and a transparent substrate 20, and the transparent substrate 20 and the fluorescent ceramic 30 are bonded through a heat-conducting connection layer. The material of the transparent substrate 20 includes but is not limited to sapphire, and the heat-conducting connection layer is preferably but not limited to heat-conducting silicone grease. Figure 9The right middle figure is a schematic structural diagram in the reflection mode. The structure includes a blue laser light source 10 and a reflection substrate 70. The reflection substrate 70 and the fluorescent ceramic 30 are bonded through a heat-conducting connection layer. The material of the reflection substrate 70 includes but is not limited to an aluminum sheet. After the blue laser excites the fluorescent ceramic, the remaining blue light and the emitted long-wavelength light are mixed to form white light 41 with a relatively large divergence angle. Finally, after the optical path of the white light 41 is adjusted by a convex lens 50, the horizontal white light 61 is emitted.

[0075] The present invention provides a method for preparing a novel fluorescent ceramic. Among them, through the design of a barrier layer, the interfacial contact of multi-system fluorescent powders during the ceramic sintering process is limited to the greatest extent, and the occurrence of interfacial reactions is theoretically avoided. The sintering method of the multi-system fluorescent ceramic provided by the present invention is simple and reliable, has strong applicability to the fluorescent powder system, and is applicable to the forming and sintering processes of various ceramics. The prepared multi-system fluorescent ceramic can be used in laser lighting or LED lighting devices. It can be expected that this high quantum efficiency small particle size red fluorescent powder and its preparation method can be widely applied, which will be conducive to promoting the development of higher quality solid-state lighting.

Claims

1. A method for preparing a fluorescent ceramic, characterized in that, Comprising the following steps: 1) Weigh the raw materials of the fluorescent ceramic, and the raw materials of the fluorescent ceramic at least include component A, component B and component C; both component A and component B include a phosphor and a barrier layer, and the barrier layer coats the phosphor; the phosphor in component A is a phosphor that emits yellow-green light after being excited by blue light or ultraviolet light; the phosphor in component B is a phosphor that emits red light after being excited by blue light or ultraviolet light; the barrier layer includes at least one of Al2O3, B2O3, SiO2, BN, and component C has the same components as the barrier layer; 2) Mix the raw materials of the fluorescent ceramic evenly, place them in a mold for forming, and then sinter to obtain a ceramic green body, and post-treat the ceramic green body to obtain the fluorescent ceramic.

2. The preparation method of a fluorescent ceramic according to claim 1, wherein: The phosphor in component A includes but is not limited to at least one of YAG:Ce, LuAG:Ce, YAGG:Ce.

3. The preparation method of a fluorescent ceramic according to claim 1, characterized in that: The phosphor in component B includes but is not limited to at least one of Ca-α-SiAlON:Eu, CaAlSiN3:Eu, Sr2Si5N8:Eu.

4. The preparation method of a fluorescent ceramic according to claim 1, characterized in that: The total mass of component A and component B accounts for 30% - 90% of the total mass of the ceramic raw materials, and the mass of component C accounts for 10% - 70% of the total mass of the ceramic raw materials.

5. The preparation method of a fluorescent ceramic according to claim 1, wherein: The mass ratio of component A to component B is 1:9 - 9:

1.

6. The preparation method of a fluorescent ceramic according to claim 1, characterized in that: In step 2), the sintering temperature is 1200 - 1600 °C, and the sintering pressure is 10 - 100 MPa.

7. The preparation method of a fluorescent ceramic according to claim 1, characterized in that: The barrier layer is prepared by the sol-gel method.

8. A fluorescent ceramic, characterized in that: Prepared by the preparation method according to any one of claims 1 - 7.

9. The application of a fluorescent ceramic according to claim 8, characterized in that: For preparing light-emitting, display or lighting devices.

10. A light-emitting, display or lighting device, characterized in that: Comprising a light-emitting unit and the fluorescent ceramic according to claim 8, the light emitted by the light-emitting unit is blue light or ultraviolet light, the fluorescent ceramic is connected to a transparent substrate or a reflective substrate, and the light emitted by the light-emitting unit is incident on the fluorescent ceramic or the transparent substrate.

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