Ceramic phosphor plate

Abstract

To provide a ceramic phosphor plate with improved extraction efficiency.SOLUTION: A ceramic phosphor plate is composed of a ceramic substrate having a light incident surface and a light emission surface facing the light incident surface, and an antireflection film formed at least on the light emission surface. The light emission surface of the ceramic substrate has an uneven shape consisting of concave parts and convex parts, an arithmetic mean roughness (Ra) is 0.1 μm or more and 0.7 μm or less, and a kurtosis (Rku) obtained from a surface roughness curve is 5 or more and 10 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a ceramic phosphor plate that converts the wavelength of light emitted from a light-emitting diode (LED) or a laser diode (LD) to obtain white light. [Background technology]

[0002] LEDs are used in mobile phones and various display devices due to their power saving, long life, small size, etc. Furthermore, with the recent improvement in luminous efficiency, they have also attracted attention for lighting applications and are rapidly becoming more widespread.

[0003] Currently, the mainstream method for white LED lighting is to obtain white light by mixing the light emitted by a blue LED with the light emitted by a phosphor that receives the incident blue light and emits yellow light, which is the complementary color of blue. Wavelength conversion materials using such phosphors have traditionally been made by dispersing phosphor powder in resin, but in recent years, composites with ceramics have become more widely used due to their heat resistance.

[0004] Patent Document 1 discloses an invention of an optical wavelength conversion device having a structure including an optical wavelength conversion member, a heat dissipation member having better heat dissipation properties than the optical wavelength conversion member, and a joint for joining the optical wavelength conversion member and the heat dissipation member, wherein the optical wavelength conversion member has an anti-reflection film on a first surface onto which light is incident, a reflective film on a second surface opposite to the first surface, and an intermediate film between the reflective film and the joint, and the optical wavelength conversion member emits light reflected by the reflective film from the first surface. The optical wavelength conversion member in Patent Document 1 is made of a ceramic sintered body having a fluorescent phase mainly composed of fluorescent crystal particles and a translucent phase mainly composed of translucent crystal particles, and the ceramic sintered body is made of A3B5O 12 :Ce (A is Sc, Y, or a lanthanide (excluding Ce), and B is Al. Both A and B may further contain Gd).

[0005] The surface roughness (arithmetic mean roughness Ra) of the first surface of the light wavelength conversion member is preferably 0.001 μm < Ra < 0.4 μm, and an antireflection film is formed on such a first surface. Here, in the case of the ceramic sintered body, if the surface roughness is large, irregular reflection occurs on the first surface, making it difficult to efficiently extract the emitted light. On the other hand, if the surface roughness is small, specular reflection occurs on the first surface, making it difficult to efficiently take in the incident light. In the light wavelength conversion member of Patent Document 1, an antireflection film is formed on the surface as fired. As shown in Fig. 2(a), since the surface has an uneven shape that is concave and convex up and down with the center line as the boundary, when the first surface is used as the emission surface, light is reflected within the convex portion, resulting in low light extraction efficiency and also prone to color unevenness.

[0006] In LED lighting where a uniform emission color is required, for the wavelength conversion member made of a ceramic sintered body, in order to suppress the occurrence of color unevenness caused by the surface roughness and improve the light extraction efficiency, improvements such as adjusting the surface roughness of the ceramic sintered body were necessary.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] An object of the present invention is to provide a ceramic phosphor plate that suppresses the occurrence of color unevenness and improves the light extraction efficiency.

Means for Solving the Problems

[0009] The ceramic phosphor plate of the present invention comprises a ceramic substrate having a light incident surface and a light exit surface opposite the light incident surface, and an anti-reflection film formed on at least the light exit surface, wherein the light exit surface of the ceramic substrate has an uneven shape consisting of concave and convex portions, the arithmetic mean roughness (Ra) of the light exit surface is 0.1 μm or more and 0.7 μm or less, and the kurtosis (Rku) calculated from the surface roughness curve is 5 or more and 10 or less.

[0010] It is preferable that the upper surface of the convex portion of the light emitting surface is a surface obtained by grinding or polishing the fired surface of the ceramic substrate approximately parallel to the light incident surface, and that the concave portion of the light emitting surface is the fired surface of the ceramic substrate. The anti-reflection film is preferably made of two or more materials having different refractive indices, and the total thickness thereof is preferably 500 nm or more and 700 nm or less. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a ceramic phosphor plate that suppresses the occurrence of color unevenness and improves light extraction efficiency. [Brief explanation of the drawings]

[0012] [Figure 1] Figure 1 is a graph showing the linear transmittance (%) versus the angle of incidence (°) of obliquely incident light, assuming that the linear transmittance is 100% when an anti-reflection film (seven layers of 75 nm thick SiO2 and 100 nm thick Ta2O5 films are laminated in sequence, for a total thickness of 600 nm) is formed on one side of a sapphire plate with a refractive index similar to that of the ceramic phosphor, and light with a wavelength of 550 nm, which is close to the conversion wavelength of the ceramic phosphor, is incident from the opposite side at an angle of incidence of 0°. [Figure 2]Fig. 2(a) is a local cross-sectional view showing that the first surface (the light-emitting surface) of a conventional optical wavelength conversion member (conventional example) on which an anti-reflection film is formed on the fired surface has gently undulating surfaces above and below the center line. Fig. 2(b) is a local cross-sectional view of the light-emitting surface of the ceramic phosphor plate of the present invention, showing a configuration consisting of smooth convex surfaces and concave valleys. [Figure 3] FIG. 3 is a graph showing the roughness curve of the surface (light emitting surface) of a conventional unprocessed sintered body.

[0013] [Figure 4] FIG. 4 is a graph showing the roughness curve of the surface (light-emitting surface) of the sintered body after processing in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0014] The ceramic phosphor plate of the present invention is described in detail below. The ceramic phosphor plate of the present invention comprises a ceramic substrate having a light incident surface and a light exit surface opposite to the light incident surface, and an antireflection film formed on at least the light exit surface, the light exit surface of the ceramic substrate having an uneven shape consisting of recesses and protrusions, the arithmetic mean roughness (Ra) of the light exit surface being 0.1 μm or more and 0.7 μm or less, and the kurtosis (Rku) calculated from the surface roughness curve being 5 or more and 10 or less.

[0015] Fig. 2(b) is a schematic cross-sectional view of a ceramic phosphor plate of the present invention. The ceramic phosphor plate is a plate-like body made of a ceramic substrate on which an anti-reflection coating is formed. As shown in Fig. 2(b), the anti-reflection coating side of the plate is the light exit surface, and the main surface opposite the exit surface is the light entrance surface.

[0016] The ceramic phosphor plate of the present invention is based on a ceramic substrate. Specifically, it is made of a ceramic sintered body and is made of yttrium aluminum garnet (YAlO 12 ) to Ce 3+It is preferable that the ceramic substrate is made of a YAG:Ce phosphor doped with Cr and a sintered body of alumina (Al2O3) transparent body. This allows the surface condition (Ra, Rku) of the ceramic substrate, which will be described later, to be more appropriately controlled during formation.

[0017] The thickness of the ceramic substrate is preferably 0.05 mm or more and 1 mm or less.

[0018] The anti-reflection film is provided on at least the light-emitting surface of the ceramic substrate. The anti-reflection coating may be a single layer or multiple layers, but is usually a multilayer coating made of two or more materials with different refractive indices on the light-emitting surface, such as niobium (V) oxide (Nb2O5), titanium (IV) oxide (TiO2), tantalum (IV) oxide (TaO2), tantalum (V) oxide (Ta2O5), aluminum oxide (Al2O3), zirconium oxide (ZrO2), silicon dioxide (SiO2), magnesium fluoride (MgF2), aluminum nitride (AlN), and silicon nitride (Si3N4).

[0019] The thickness of the anti-reflection film is preferably 500 nm to 700 nm, which provides a more excellent anti-reflection effect, particularly in a blue LED phosphor plate used in a white LED lamp. The anti-reflection film is preferably formed not only on the light exit surface but also on the light incident surface, thereby reducing the reflection of blue LED light incident on the ceramic substrate.

[0020] The antireflection film is, for example, a dielectric multilayer film, and a preferred form thereof is a laminated film in which SiO2 films and Ta2O5 films, each having a thickness of 10 nm to 100 nm, are alternately stacked in 3 to 10 layers, with a total thickness of 800 nm or less. When the antireflection film is a dielectric multilayer film, the wavelength range in which the antireflection function is exhibited can be adjusted by changing the thickness of each film or the number of layers.

[0021] The light-emitting surface of the ceramic substrate has an irregular shape and an arithmetic mean roughness (Ra) of 0.1 μm to 0.7 μm, preferably 0.4 μm to 0.7 μm. The arithmetic mean roughness (Ra) is determined in accordance with JIS B 0601:2013 by observing the surface from above with a confocal microscope to obtain a roughness curve, and averaging the height of the area enclosed by the roughness curve and its average value when smoothed into a rectangle.

[0022] The ceramic phosphor plate consists of a ceramic substrate and an anti-reflection coating formed on the light-emitting surface of the ceramic substrate. Since the arithmetic mean roughness (Ra) and kurtosis (Rku) of the ceramic substrate are substantially equivalent to the arithmetic mean roughness (Ra) and kurtosis (Rku) of the ceramic phosphor plate after the anti-reflection coating is formed, the arithmetic mean roughness (Ra) and kurtosis (Rku) of the ceramic substrate can be measured from the top surface of the anti-reflection coating using the above-mentioned method.

[0023] If Ra is less than 0.1 μm, specular reflection reduces the light extraction efficiency. On the other hand, if Ra is greater than 0.7 μm, the proportion of light that is obliquely incident on the anti-reflection coating increases, reducing the extraction efficiency. The graph in Figure 1 shows that the linear transmittance of light with a wavelength of 550 nm decreases as the angle of oblique incidence of light on the anti-reflection coating increases. If the linear transmittance is 100% when the angle of incidence is 0°, the decrease in linear transmittance becomes significant when the angle of incidence is greater than 40°, reaching approximately 95% at 60°.

[0024] At least the light-emitting surface of the ceramic substrate has a kurtosis (Rku) of 5 or more and 10 or less, preferably 6 or more and 9 or less, determined from a surface roughness curve. Kurtosis (Rku) is defined in JIS B 0601:2013 and is an index that indicates the degree of sharpness of the tips of uneven portions. If kurtosis (Rku) is 3, the height distribution is normal, and the concave and convex portions have the same shape. If kurtosis (Rku) is less than 3, the shape of the convex and / or concave portions will be gentle and close to flat. On the other hand, if kurtosis (Rku) is greater than 3, the shape of the convex and / or concave portions will be sharp.

[0025] The ceramic substrate of the present invention has, for example, as shown in Figure 2(b), a light exit surface consisting of the upper surface of a convex portion formed by grinding the fired surface of the ceramic substrate approximately parallel to the light entrance surface, and an acute-angled concave portion where the fired surface remains intact, and the kurtosis Rku of this light exit surface is 5 or more. In the embodiment shown in Figure 2(b), the distance between the bottom of the concave portion and the top of the convex portion is not as long as in the optical wavelength conversion member of Figure 2(a), but as indicated by the arrows in the figure, blue light undergoes multiple reflections and propagates a relatively long distance, thereby improving the light conversion efficiency. Furthermore, in the embodiment shown in Figure 2(b), the upper surface of the convex portion is flat, so diffuse reflection does not occur and the extraction efficiency does not decrease.

[0026] The ceramic substrate may have an uneven shape consisting of flat convex apexes and sharp-angled concaves as shown in Fig. 2(b), or the convex portions on the light emitting surface may have a structure resembling a fine pin-holder with a spacing of several µm. However, to obtain an uneven shape with a kurtosis Rku of 5 or more, it is common to grind the convex portions of the uneven shape on the fired surface by a specific height, and a flat convex surface is easier to handle than a pin-holder-shaped surface, so the uneven shape shown in Fig. 2(b) is preferred.

[0027] However, when the kurtosis (Rku) exceeds 10, there are many recesses and the kurtosis of the recesses increases, which increases diffuse reflection and reduces the extraction efficiency. In the ceramic substrate of the present invention, the upper surfaces of the convex portions of the light emitting surface are formed by grinding or polishing the fired surface of the ceramic substrate substantially parallel to the light incident surface, thereby achieving a more sufficient light extraction efficiency. Furthermore, since the concave portions of the light emitting surface are formed by the fired surface of the ceramic substrate, light that is obliquely incident on the concave portions (in other words, the side surfaces of the convex portions with flat upper surfaces) is easily scattered, causing multiple reflections and further improving the conversion efficiency.

[0028] A method for manufacturing a ceramic phosphor plate will be described using an example in which a sintered body of YAG:Ce phosphor and alumina translucent body is used. Yttrium (III) oxide (Y2O3), cerium (IV) oxide (CeO2), gadolinium (III) oxide (Gd2O3), and aluminum oxide (Al2O3) are mixed and formed into a sheet, which is then degreased and pressed to create a green molded product of the desired shape. Next, the green molded product is cut into 1.0 x 10 -2 A ceramic substrate is obtained by firing in a vacuum atmosphere of medium to low vacuum of not more than Pa. The ceramic substrate is a sintered body of a YAG:Ce phosphor and an alumina translucent body.

[0029] In the sintered body, the concentration of YAG particles is preferably 20 vol% or more and 30 vol% or less, based on a total of 100 vol% of YAG particles and Al2O3 particles. On the other hand, the concentration of Al2O3 particles is preferably 70 vol% or more and 80 vol% or less, based on a total of 100 vol% of YAG particles and Al2O3 particles. The average particle size of the YAG particles is usually 4 μm or more and 6 μm or less, and the ratio of the average particle size of the Al2O3 particles to the average particle size of the YAG particles (average particle size of Al2O3 / average particle size of YAG) is preferably 1 or more and 2 or less. This allows for a ceramic substrate with improved luminous efficiency.

[0030] The surface of the ceramic substrate is processed into an uneven shape consisting of concave and convex portions by, for example, using an abrasive grain blasting polishing device to blast a large amount of abrasive grains using compressed air or the like. Specifically, by using compressed air at 0.4 MPa to 0.6 MPa and blasting abrasive grains such as synthetic diamonds with an average grain size of 30 μm to 70 μm onto the surface of the ceramic substrate for a predetermined time (for example, about 10 minutes), the kurtosis (Rku) of the surface of the ceramic substrate can be set to 5 or more and 10 or less. This grinding process using abrasive grain blasting can be performed only on the side that will become the light emitting surface, or it can be performed on both the light emitting surface and the light incident surface. The method for forming the uneven shape is not limited to the above-mentioned method, and for example, grinding using a grindstone surface plate may be used, and etching or lapping may be performed after grinding.

[0031] Next, an anti-reflection film is formed on the surface-treated ceramic substrate. When the above-mentioned dielectric multilayer film is formed as the anti-reflection film, SiO2 films and Ta2O5 films are alternately laminated using a film formation method such as vacuum deposition or sputtering. [Example]

[0032] The present invention will be specifically described below based on examples, but the present invention is not limited to the examples shown below.

[0033] [Example 1] Cerium (IV) oxide powder (average particle size: 0.7 μm), yttrium (III) oxide powder (average particle size: 0.6 μm), and aluminum oxide powder (average particle size: 1 μm) were mixed in a predetermined ratio to obtain a raw powder. Alcohol as a dispersion medium, polyvinyl butyral as a binder, and dibutyl succinate as a plasticizer were added to this raw powder, and the mixture was ground and mixed in a ball mill to prepare a slurry. This slurry is used to form a green sheet of a specified thickness by the doctor blade method, and is degreased and fired in the air to form Al2O3 + Y3Al5O 12 A sintered body of Ce was obtained.

[0034] Al2O3+Y3Al5O 12 A mirror shot blast machine (product name SMAP, manufactured by Toyo Abrasives Co., Ltd.) was used to spray an elastic abrasive with an abrasive grain size of 1 μm or less onto one surface of the Ce sintered compact for approximately 10 minutes to create an irregular shape. That is, a ceramic substrate was produced in which the upper surfaces of the convex portions of the light emitting surface were formed by grinding or polishing the fired surface of the ceramic base material approximately parallel to the light incident surface, and the concave portions of the light emitting surface were formed by the fired surface of the ceramic base material.

[0035] Al2O3+Y3Al5O after processing 12 The arithmetic mean roughness (Ra) and kurtosis (Rku) of the light-emitting surface of the Ce sintered body were measured using a laser microscope HD-100D manufactured by Lasertec Corporation with a measurement length of 0.032 mm and a cutoff value of 0.8 mm. The Ra was 0.47 μm and the Rku was 6.5. The kurtosis (Rku) was calculated based on the formula Al2O3 + Y3Al5O 12 : The surface roughness curve was obtained from the surface roughness curve of the light-emitting surface of the Ce sintered body. Figure 4 is a graph plotting the reference length on the horizontal axis and the height from the average surface on the vertical axis, and shows the surface roughness curve.

[0036] Next, the processed Al2O3+Y3Al5O 12 Seven layers of SiO2 films with a thickness of 75 nm and Ta2O5 films with a thickness of 100 nm were laminated on the Ce sintered body in this order to form an anti-reflection film with a total thickness of 600 nm, thereby obtaining a ceramic phosphor plate. After forming the anti-reflection film, the arithmetic mean roughness (Ra) and kurtosis (Rku) of the light-emitting surface of the ceramic phosphor plate were measured in the same manner. Both were found to be Al2O3 + Y3Al5O 12 The measured value was the same as that of the light emitting surface of the Ce sintered body.

[0037] Using a spectrophotometer with an integrating sphere (UH4150, manufactured by Hitachi High-Tech Science Corporation), the total transmittance over the entire visible light range was measured without the ceramic phosphor plate set, i.e., the transmittance at an incident angle of 0°. Then, the ceramic phosphor plate prepared in Example 1 was set, and the total transmittance over the entire visible light range was measured. The ratio of the latter transmittance to the former transmittance at a wavelength of 550 nm was measured and calculated as the light extraction efficiency. The light extraction efficiency measured by this method was 65%.

[0038] [Example 2] A ceramic phosphor plate was produced in the same manner as in Example 1, except that the surface processing was carried out using a mirror shot machine (product name SMAP; manufactured by Toyo Abrasives Industries Co., Ltd.) by spraying an elastic abrasive with an abrasive grain size of 1 μm or less for approximately 20 minutes. The arithmetic mean roughness (Ra) and kurtosis (Rku) of the light-emitting surface of the ceramic phosphor plate were measured in the same manner as in Example 1, and the Ra of the ceramic phosphor plate was 0.10 μm and the Rku was 6.7. Furthermore, the light extraction efficiency of the ceramic phosphor plate was measured in the same manner as in Example 1 and was found to be 63%.

[0039] [Example 3] A ceramic phosphor plate was produced in the same manner as in Example 1, except that the surface was processed using a mirror shot machine (product name SMAP; manufactured by Toyo Abrasives Co., Ltd.) by spraying an elastic abrasive with an abrasive grain size of 1 μm or less for approximately 5 minutes. The arithmetic mean roughness (Ra) and kurtosis (Rku) of the light-emitting surface of the ceramic phosphor plate were measured in the same manner as in Example 1, and the Ra of the ceramic phosphor plate was 0.70 μm and the Rku was 6.5. Furthermore, the light extraction efficiency of the ceramic phosphor plate was measured in the same manner as in Example 1 and was found to be 61%.

[0040] [Example 4] A ceramic phosphor plate was produced in the same manner as in Example 1, except that the average particle size of the yttrium (III) oxide powder was 0.4 μm and the average particle size of the aluminum oxide powder was 0.1 μm. The arithmetic mean roughness (Ra) and kurtosis (Rku) of the light-emitting surface of the ceramic phosphor plate were measured in the same manner as in Example 1, and the Ra of the ceramic phosphor plate was 0.45 μm and the Rku was 5.0. Furthermore, the light extraction efficiency of the ceramic phosphor plate was measured in the same manner as in Example 1 and was found to be 61%.

[0041] [Example 5] A ceramic phosphor plate was produced in the same manner as in Example 1, except that the average particle size of the yttrium (III) oxide powder was 0.8 μm and the average particle size of the aluminum oxide powder was 2.0 μm. The arithmetic mean roughness (Ra) and kurtosis (Rku) of the light-emitting surface of the ceramic phosphor plate were measured in the same manner as in Example 1, and the Ra of the ceramic phosphor plate was 0.49 μm and the Rku was 10.0. Furthermore, the light extraction efficiency of the ceramic phosphor plate was measured in the same manner as in Example 1 and was found to be 63%.

[0042] [Conventional example] Same as Example 1: Al2O3 + Y3Al5O 12 An anti-reflection film was formed in the same manner as in Example 1 using the Ce sintered body without surface treatment. The arithmetic mean roughness (Ra) and kurtosis (Rku) of the light-emitting surface of the ceramic phosphor plate were measured in the same manner as in Example 1. The Ra of the ceramic phosphor plate was 0.56 μm, and the Rku was 2.9. The graph in Figure 3 shows a surface roughness curve, with the horizontal axis representing the reference length and the vertical axis representing the height from the average surface. Furthermore, the light extraction efficiency of the ceramic phosphor plate was measured in the same manner as in Example 1 and was found to be 59%.

[0043] [Comparative Example 1] In Example 1, a ceramic phosphor plate was produced in the same manner as in Example 1, except that after surface grinding was performed for approximately 10 minutes using a 600-800 grit grinding stone, surface processing was performed using a mirror shot machine (product name SMAP; manufactured by Toyo Abrasives Industries Co., Ltd.) (by spraying an elastic abrasive with an abrasive grain size of 1 μm or less for approximately 10 minutes). The arithmetic mean roughness (Ra) and kurtosis (Rku) of the light-emitting surface of the ceramic phosphor plate were measured in the same manner as in Example 1, and the results were Ra of 0.05 μm and Rku of 6.4. Furthermore, the light extraction efficiency of the ceramic phosphor plate was measured in the same manner as in Example 1 and was found to be 58%.

[0044] Comparative Example 2 In Example 1, a ceramic phosphor plate was produced in the same manner as in Example 1, except that after surface grinding was performed for about 10 minutes with a 320 to 400 grit grinding stone, surface processing was performed using a mirror shot machine (product name SMAP; manufactured by Toyo Abrasives Industries Co., Ltd.) (spraying an elastic abrasive with an abrasive grain size of 1 μm or less for about 10 minutes). The arithmetic mean roughness (Ra) and kurtosis (Rku) of the light-emitting surface of the ceramic phosphor plate were measured in the same manner as in Example 1, and the Ra of the ceramic phosphor plate was 0.90 μm and the Rku was 6.6. Furthermore, the light extraction efficiency of the ceramic phosphor plate was measured in the same manner as in Example 1 and was found to be 50%.

[0045] Comparative Example 3 A ceramic phosphor plate was produced in the same manner as in Example 1, except that the average particle size of the yttrium (III) oxide powder was 0.3 μm and the average particle size of the aluminum oxide powder was 0.1 μm. The arithmetic mean roughness (Ra) and kurtosis (Rku) of the light-emitting surface of the ceramic phosphor plate were measured in the same manner as in Example 1, and the Ra of the ceramic phosphor plate was 0.44 μm and the Rku was 3.2. Furthermore, when the light extraction efficiency was measured in the same manner as in Example 1, the light extraction efficiency of the ceramic phosphor plate was found to be 52%.

[0046] Comparative Example 4 A ceramic phosphor plate was produced in the same manner as in Example 1, except that the average particle size of the yttrium (III) oxide powder was 1.0 μm and the average particle size of the aluminum oxide powder was 2.5 μm. The arithmetic mean roughness (Ra) and kurtosis (Rku) of the light-emitting surface of the ceramic phosphor plate were measured in the same manner as in Example 1, and the Ra of the ceramic phosphor plate was 0.50 μm and the Rku was 11.9. Furthermore, when the light extraction efficiency was measured in the same manner as in Example 1, the light extraction efficiency of the ceramic phosphor plate was found to be 58%.

[0047] The results of Examples 1 to 5 and Comparative Examples 1 to 4 are shown in Table 1.

[0048] [Table 1] From the above, it has been confirmed that in a ceramic phosphor plate consisting of a ceramic substrate having a light incident surface and a light exit surface opposite the light incident surface, and an anti-reflection film formed on the light exit surface, the light exit surface of the ceramic substrate has an uneven shape consisting of concave and convex portions, the arithmetic mean roughness (Ra) of the light exit surface is 0.1 μm or more and 0.7 μm or less, and the kurtosis (Rku) calculated from the surface roughness curve is 5 or more and 10 or less, thereby improving the light extraction efficiency.

Claims

1. a ceramic substrate having a light incident surface and a light emitting surface facing the light incident surface, and an anti-reflection film formed on at least the light emitting surface; the light-emitting surface of the ceramic substrate has an uneven shape consisting of recesses and protrusions, The arithmetic mean roughness (Ra) is 0.1 μm or more and 0.7 μm or less, The kurtosis (Rku) calculated from the surface roughness curve is 5 or more and 10 or less. A ceramic phosphor plate characterized by:

2. an upper surface of a convex portion of the light exit surface is a surface obtained by grinding or polishing the fired surface of the ceramic base substantially parallel to the light incident surface, 2. The ceramic phosphor plate according to claim 1, wherein the recessed portion of the light-emitting surface is a fired surface of the ceramic substrate.

3. 3. The ceramic phosphor plate according to claim 1, wherein the anti-reflection film is made of two or more materials having different refractive indices, and the total thickness of the anti-reflection film is 500 nm or more and 700 nm or less.

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