Wavelength conversion member and light-emitting device

Abstract

To provide a wavelength conversion member and a light-emitting device which can reduce the diameter of a light-emitting point.SOLUTION: A wavelength conversion member 10 is made of a ceramic sintered body 12 including: a fluorescence phase 14 which emits fluorescence by excitation light; a translucent phase 16 with translucency; and a plurality of gaps 18 surrounded by one of the fluorescence phase 14 and the translucent phase 16. The average circle corresponding diameter of the gaps 18 is in the range of 0.1 μm to 10 μm, both inclusive. The relative density of the ceramic sintered body 12 is in the range of 70% to 90%, both inclusive.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a wavelength conversion member and a light emitting device.

Background Art

[0002] There is known a light emitting device using a wavelength conversion member that emits light irradiated from a light source such as an LED (Light Emitting Diode) or an LD (Laser Diode), which is a light emitting element, as converted light having a wavelength different from that of the light source by a phosphor layer. In recent years, applications using an LD as a light source, which has high energy efficiency and is easy to miniaturize and increase in output, have been increasing.

[0003] As such a wavelength conversion member, a structure in which a phosphor is dispersed in a resin typified by epoxy or silicone is often used. In recent years, however, the output of light emitting elements has been increasing, and higher durability has been demanded. In response to such demands, a wavelength conversion member made of a ceramic sintered body and having excellent durability has been disclosed (Patent Document 1).

[0004] Also, for example, in applications of light emitting devices such as projectors, it is required to increase the luminance of fluorescence. From the viewpoint of increasing the luminance of fluorescence, it is disclosed that it is preferable to reduce the spot diameter of the fluorescence generated by the wavelength conversion member (Patent Document 2).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] As the ceramic sintered body of Patent Document 1, the component represented by YAG:Ce is 3 to 70 vol%, and the balance is Al 2 O 3 , and Ce has a composition of 10.0 mol% or less with respect to Y and has high thermal conductivity, so high durability can be obtained even in the case of increasing the output of the light source. On the other hand, since the ceramic sintered body of Patent Document 1 is a densified sintered body with a relative density of 99% or more, the converted light irradiated from the light source and wavelength-converted by the ceramic sintered body is likely to leak from the side surface of the ceramic sintered body, and the light-emitting point may be blurred.

[0007] In addition, in the fluorescent light-emitting element of Patent Document 2, in order to obtain high-intensity fluorescence by limiting the light-emitting area and reducing the spot diameter, the surface has a moth-eye structure having an uneven shape, but it is difficult to regularly process such a fine uneven shape.

[0008] The present invention has been made in view of such circumstances, and an object thereof is to provide a wavelength conversion member and a light-emitting device capable of reducing the diameter of a light-emitting point.

Means for Solving the Problems

[0009] (1) In order to achieve the above object, the wavelength conversion member of the present invention takes the following means. That is, the wavelength conversion member of the application example of the present invention is a wavelength conversion member made of a ceramic sintered body, and the ceramic sintered body includes a fluorescent phase that emits fluorescence by excitation light, a translucent phase having translucency, and a plurality of voids surrounded by the fluorescent phase or the translucent phase, the average circle equivalent diameter of the voids is 0.1 μm or more and 10 μm or less, and the relative density of the ceramic sintered body is 70% or more and 90% or less.

[0010] In this way, by setting the relative density of the wavelength conversion member made of the ceramic sintered body to 70% or more and 90% or less and the average circle equivalent diameter of the voids to 0.1 μm or more and 10 μm or less, it is possible to reduce the loss of light that escapes to the side surface of the ceramic sintered body and reduce the light-emitting point size.

[0011] (2) Further, in the wavelength conversion member of the application example of (1) above, in the direction perpendicular to the surface of the ceramic sintered body on which the excitation light is incident, the relative density of the ceramic sintered body in the region from the surface to 50% of the average thickness is 70% or more and 90% or less.

[0012] Thereby, it becomes possible to convert the light source light into fluorescence within a short range on the surface side, and the light loss to the side surface of the ceramic sintered body can be further reduced.

[0013] (3) Further, in the wavelength conversion member of the application example of (1) or (2) above, the content of the fluorescent phase of the ceramic sintered body is 80 vol% or less.

[0014] Thereby, since a light-transmitting phase having a higher thermal conductivity than the fluorescent phase can be sufficiently included in the ceramic sintered body, a heat dissipation path is ensured, and temperature quenching can be suppressed even for a high output of the light source.

[0015] (4) Further, in the wavelength conversion member of any one of the application examples of (1) to (3) above, the content of the fluorescent phase of the ceramic sintered body is 60 vol% or more.

[0016] Thereby, the color tone of the wavelength conversion member can be easily adjusted.

[0017] (5) Further, the light-emitting device of the application example is a light-emitting device including a light-emitting element that emits light of a specific wavelength range and a wavelength conversion member of any one of the application examples of (1) to (4) above.

[0018] The wavelength conversion member of the present invention can be used as a light-emitting device that can handle the high output of a light-emitting element such as an LD while reducing the light-emitting point.

Advantages of the Invention

[0019] The wavelength conversion member and the light-emitting device of the present invention can reduce the diameter of the light-emitting point.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0021] Next, embodiments of the present invention will be described with reference to the drawings. For ease of understanding the description, the same reference numerals are assigned to the same components in each drawing, and duplicate descriptions are omitted. In the configuration diagrams, the sizes of the respective components are conceptually represented and do not necessarily represent actual dimensional ratios.

[0022] [Configuration of Wavelength Conversion Member] FIG. 1 is a schematic cross-sectional view showing an example of the cross-sectional structure of a wavelength conversion member 10 according to the present embodiment. FIG. 1 shows a reflective wavelength conversion member 10. The wavelength conversion member 10 according to the present embodiment is made of a ceramic sintered body 12. The ceramic sintered body 12 includes a fluorescent phase 14 that emits fluorescence by excitation light, a translucent phase 16 having translucency, and a plurality of voids 18 surrounded by the fluorescent phase 14 or the translucent phase 16.

[0023] The wavelength conversion member 10 reflects or transmits the incident light irradiated from the light source, and excites the incident light to generate light with different wavelengths. For example, while reflecting or transmitting the incident light of blue light, it emits the converted light such as green, red, or yellow converted by the fluorescent phase 14, combines the converted light and the incident light, or uses only the converted light to convert it into light of various colors.

[0024] The fluorescent phase 14 is a phase mainly composed of crystalline particles having fluorescence. The crystalline particles of the fluorescent phase 14 have a composition represented by the chemical formula A 3 B 5 O 12 :Ce. The A element and the B element are each composed of at least one element selected from the following element groups.

[0025] A: Sc, Y, Lu, lanthanoids (excluding Ce) B: Al, Ga

[0026] Examples of lanthanoids other than Ce for the A element include La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0027] The Ce concentration of the compound of the above chemical formula is preferably in the range greater than 0 mol% and 5.0 mol% or less with respect to the A element of the compound. Thereby, sufficient fluorescence characteristics can be obtained. Specific examples of the above chemical formula are, for example, Y 3 Al 5 O 12 :Ce (yttrium aluminum garnet-based phosphor. Hereinafter, referred to as YAG), Lu 3 Al 5 O 12 :Ce (lutetium aluminum garnet-based phosphor. Hereinafter, referred to as LAG).

[0028] The light-transmitting phase 16 is a phase mainly composed of crystalline particles having light-transmitting properties. The crystalline particles of the light-transmitting phase 16 have a composition of, for example, Al 2 O 3 . The crystalline particles of the light-transmitting phase 16 have a higher thermal conductivity than the crystalline particles of the fluorescent phase 14.

[0029] The average circle equivalent diameter of the voids 18 is 0.1 μm or more and 10 μm or less. When the density of the ceramic sintered body 12 is the same, it is preferable that the average circle equivalent diameter of the voids 18 is smaller because more voids 18 can be dispersed in the ceramic sintered body 12. Therefore, the average circle equivalent diameter of the voids 18 is preferably 1.5 μm or less. The average circle equivalent diameter of the voids 18 can be generally controlled by changing the average particle diameter of the pore former added during manufacturing.

[0030] The circle equivalent diameter of the voids 18 can be measured by analyzing SEM (scanning electron microscope) images. The circle equivalent diameter of the voids 18 in the SEM image analysis can be measured, for example, as follows. First, a cross-section of the ceramic sintered body 12 is photographed with an SEM at a magnification of 1000 times. Next, using image analysis software, an appropriately sized image is cut out as a rectangle from the photographed photo data. The cut-out image is binarized with a certain threshold value so that the voids 18 in the ceramic sintered body 12 and other parts (such as the fluorescent phase 14 and the translucent phase 16) can be distinguished. Next, the areas of, for example, about 100 regions recognized as voids 18 are calculated from the image. Voids 18 that are cut off at the image edge are not included. Then, by converting the calculated areas into circle equivalent diameters and averaging them, the average value of the circle equivalent diameters of the voids 18 can be obtained.

[0031] Note that the images used at this time are preferably randomly obtained from a plurality of locations (for example, 5 or more) in the ceramic sintered body 12 so as to be the overall average value of the sizes of the voids 18 contained in the ceramic sintered body 12. As the image analysis software, for example, the free software "ImageJ" developed by the National Institutes of Health (NIH) in the United States can be used.

[0032] The relative density of the ceramic sintered body 12 is 70% or more and 90% or less. The relative density of the ceramic sintered body 12 is the relative density when the theoretical density of a dense ceramic sintered body with the same composition and no voids 18 is set to 100%.

[0033] The volume ratios of the fluorescent phase 14 and the translucent phase 16 in the ceramic sintered body 12 can be determined by analyzing the SEM image. The volume ratios of the fluorescent phase 14 and the translucent phase 16 in the SEM image analysis can be determined, for example, as follows. First, similar to obtaining the equivalent circle diameter of the void 18, a cross-section of the ceramic sintered body 12 is photographed with an SEM at a magnification of 1000 times. Next, using image analysis software, the area of the region recognized as the fluorescent phase 14 is calculated by cutting out and binarizing the image. Similarly, the area of the region recognized as the translucent phase 16 is calculated from the image. At this time, the binarization threshold values may be different. Then, the volume ratios of the fluorescent phase 14 and the translucent phase 16 are determined from the calculated areas. Since both the fluorescent phase 14 and the translucent phase 16 occur randomly in the ceramic sintered body 12, the area ratio in the cross-section can be regarded as the volume ratio as it is.

[0034] The composition of each crystal particle of the fluorescent phase 14 and the translucent phase 16 can be determined by XRD (X-ray diffraction). From the composition of each crystal particle of the fluorescent phase 14 and the translucent phase 16 and the volume ratios of the fluorescent phase 14 and the translucent phase 16 respectively, the relative density can be determined when the theoretical density of a dense ceramic sintered body with the same composition and no void 18 is taken as 100%.

[0035] In this way, by including voids 18 of a predetermined size in the ceramic sintered body 12 to lower the relative density, the loss of light exiting through the side surface of the ceramic sintered body 12 can be reduced due to light scattering at the voids 18, and it is possible to suppress the appearance of the light exiting from the side surface as blurred emission. Therefore, the emission point size can be reduced.

[0036] In addition, since the thermal conductivity of the light-transmitting phase 16 of the ceramic sintered body 12 is high compared to, for example, YAG polycrystals, the heat generated in the ceramic sintered body 12 by, for example, irradiation with laser light can be efficiently discharged to the outside. Therefore, temperature quenching in which the fluorescent phase 14 of the ceramic sintered body 12 stops emitting fluorescence can be suppressed. That is, a decrease in the luminous efficiency of the phosphor can be prevented, and high luminous efficiency can be achieved. Therefore, fluorescence can be suitably maintained even in a high output region of the laser.

[0037] The average thickness in the direction perpendicular to the surface on which the excitation light of the ceramic sintered body 12 is incident is preferably 100 μm or more and 300 μm or less, and more preferably 150 μm or more and 300 μm or less. If it is less than 100 μm, the processing difficulty increases, and the durability may decrease. If it exceeds 300 μm, the risk of a decrease in heat dissipation due to heat storage may increase.

[0038] In the direction perpendicular to the surface 20 on which the excitation light of the ceramic sintered body 12 is incident, the relative density of the ceramic sintered body 12 in the region from the surface to 50% of the average thickness is preferably 70% or more and 90% or less. Thereby, it becomes possible to convert the excitation light into fluorescence within a short range on the surface 20 side, and the light loss to the side surface of the ceramic sintered body 12 can be further reduced. The relative density of the ceramic sintered body 12 in the region from the surface to 50% of the average thickness can also be determined in the same manner as described above.

[0039] The content of the fluorescent phase 14 of the ceramic sintered body 12 is preferably 80 vol% or less. Thereby, since the light-transmitting phase 16 having a higher thermal conductivity than the fluorescent phase 14 can be sufficiently included in the ceramic sintered body 12, a heat dissipation path is ensured, and temperature quenching can be suppressed even for an increase in the output of the light source.

[0040] The content of the fluorescent phase 14 of the ceramic sintered body 12 is preferably 60 vol% or more. Thereby, the color tone of the wavelength conversion member 10 can be easily adjusted.

[0041] A reflective film 32 for reflecting light may be provided on the back surface 22 opposite to the surface 20 where the excitation light of the wavelength conversion member 10 is incident. Thereby, since the excitation light, the fluorescence emitted by the wavelength conversion member 10, etc. can be reflected, the wavelength conversion member 10 can be made into a reflective wavelength conversion member 10. Also, the light emission intensity of the wavelength conversion member 10 is improved.

[0042] As materials for the reflective film 32, for example, materials such as silver, aluminum, niobium oxide, titanium oxide, lanthanum oxide, tantalum oxide, yttrium oxide, gadolinium oxide, tungsten oxide, hafnium oxide, aluminum oxide, silicon nitride can be adopted. Note that the reflective film 32 may be a single layer or a multilayer structure.

[0043] An antireflection film 30 for suppressing light reflection may be provided on the surface 20 where the excitation light of the wavelength conversion member 10 is incident. Thereby, since the reflection of the incident light on the surface 20 of the wavelength conversion member 10 can be suppressed, the light incident on the wavelength conversion member 10 can be efficiently absorbed. Furthermore, the light generated inside the wavelength conversion member 10 can be efficiently taken out to the outside. Therefore, the light emission intensity of the wavelength conversion member 10 is improved.

[0044] As materials for the antireflection film 30, for example, materials such as niobium oxide, titanium oxide, tantalum oxide, aluminum oxide, zirconium oxide, silicon oxide, aluminum nitride, silicon nitride, magnesium fluoride can be adopted. Note that the antireflection film 30 may be a single layer or a multilayer structure.

[0045] FIG. 2 is a schematic cross-sectional view showing a modified example of the cross-sectional structure of the wavelength conversion member 10 according to the present embodiment. FIG. 2 shows a reflective wavelength conversion member 10. As shown in FIG. 2, the wavelength conversion member 10 may include a base material 40 that supports the ceramic sintered body 12. The shape of the base material 40 may be any shape applicable to the light-emitting device 100, and may be various shapes such as circular, rectangular, elliptical, polygonal shapes.

[0046] The material of the base material 40 is appropriately selected according to the intended use. When used for the purpose of reflecting the excitation light from the light source, metals such as aluminum, iron, and copper, or ceramics can be used. In particular, it is preferable to use aluminum which has high thermal conductivity and high reflectivity in the entire visible light region. Further, a reflective film 32 may be formed by providing a material that reflects light, such as silver, on the surface of the base material 40 on the side of the ceramic sintered body 12 by plating, vapor deposition, or the like. The reflective film 32 may be formed on the back surface 22 of the ceramic sintered body 12 as described above.

[0047] When forming the reflective film 32, since the light is reflected by the reflective film 32, even if there is a base material 40, the base material 40 does not necessarily require high optical properties such as high reflectivity. Also, for the bonding layer, light transmittance is not necessarily required. Therefore, the range of selection of the materials for the base material 40 and the bonding layer becomes wider.

[0048] When used for the purpose of transmitting the excitation light from the light source, inorganic materials such as sapphire and glass can be used. It is particularly preferable to use sapphire which has high thermal conductivity. For any of the reflective and transmissive wavelength conversion members 10, by using a material with high thermal conductivity for the base material 40, the heat storage of the ceramic sintered body 12 can be suppressed, and the deterioration of the characteristics of the fluorescent phase 14 due to temperature rise can be suppressed.

[0049] A bonding layer for bonding the ceramic sintered body 12 and the base material 40 may be provided between the ceramic sintered body 12 and the base material 40. Thereby, the ceramic sintered body 12 and the base material 40 can be easily bonded. In the case of the reflective wavelength conversion member 10, it is preferable to provide a bonding layer between the reflective film 32 and the base material 40. In the case of the reflective wavelength conversion member 10, solders, metal brazes, silver pastes, inorganic binders, etc. can be used as the bonding material for forming the bonding layer. In the case of the transmissive wavelength conversion member 10, it is preferable to provide a bonding layer between the antireflection film 30 or the ceramic sintered body 12 without the antireflection film 30 and the base material 40. In the case of the transmissive wavelength conversion member 10, an inorganic binder having light transmittance or the like can be used as the bonding material for forming the bonding layer.

[0050] In addition, in this specification, a substance having translucency refers to a substance having a property that when light is perpendicularly incident in the visible light wavelength region (λ = 380 to 780 nm) on a target substance of 0.5 mm, the radiant flux of the light passing through from the opposite side exceeds 80% of the incident light.

[0051] [Configuration of the light-emitting device] Figs. 3(a) and 3(b) are conceptual diagrams each showing a part of an example of a light-emitting device 100 according to an embodiment of the present invention. Fig. 3(a) represents a transmissive light-emitting device of the present invention, and Fig. 3(b) represents a reflective light-emitting device 100. The light-emitting device 100 includes a light source 50 and a wavelength conversion member 10. The light source 50 is a light-emitting element that generates light source light having a specific range of wavelengths, and for example, an LED, an LD, or the like can be used. Since the wavelength conversion member 10 can efficiently perform wavelength conversion even with high power, the light source 50 is preferably an LD. Note that, for the wavelength conversion member 10 of the transmissive light-emitting device 100 in Fig. 3(a), although the surface layers all show an antireflection film 30, the antireflection film 30 may not be provided. The same applies to the surface layer on the light source side of the wavelength conversion member 10 of the reflective light-emitting device 100 in Fig. 3(b).

[0052] [Manufacturing method of the wavelength conversion member] Next, an example of a manufacturing method of the wavelength conversion member will be described. As a manufacturing method of the wavelength conversion member, for example, it can be manufactured by the following method. First, A 3 B 5 O 12 :Ce (for example, YAG) in the ceramic sintered body constituting the wavelength conversion member is preferably adjusted so that the ratio is 1 vol% or more and 80 vol% or less. Y 2 O 3 , Al 2 O 3 , CeO 2 , Sc 2 O 3 , Lu 2 O 3 , Ga 2 O 3 and other raw material powders are weighed.

[0053] Next, in order to include voids so that the relative density of the ceramic sintered body is 70% or more and 90% or less, a pore former, an organic solvent or ion-exchanged water, and a dispersant are weighed. Next, the weighed raw material powder, pore former, organic solvent or ion-exchanged water, and dispersant are put into a ball mill and mixed for 16 hours or more to prepare a raw material slurry. As the pore former, an acrylic resin or the like can be used. As the organic solvent, high boiling point solvents such as α-terpineol, butanol, isophorone, and glycerin can be used.

[0054] Next, a sheet molded body is produced from the obtained raw material slurry by the doctor blade method. Next, the produced sheet molded body is degreased if necessary and then fired to obtain a ceramic sintered body. Note that the manufacturing method of the ceramic sintered body is not limited to the above, and a known method such as a method in which granulated powder obtained by drying and granulating the prepared raw material slurry is put into a predetermined mold, press-molded, and then fired may be used.

[0055] Next, the shape of the obtained ceramic sintered body is adjusted by grinding, polishing, etc. as necessary. Furthermore, if necessary, the wavelength conversion member of the present invention can be manufactured by forming a reflective film or an antireflection film, adhering to a substrate, joining, etc. Note that the manufacturing method of the wavelength conversion member is not limited to the above.

[0056] [Examples and Comparative Examples] (Production of Wavelength Conversion Member) (Sample 1) First, so that the ratio of YAG in the ceramic sintered body constituting the wavelength conversion member is 85 vol%, Y 2 O 3 、Al 2 O 3 、CeO 2The raw material powder was weighed. Ce was weighed so that the concentration was 0.3 mol% with respect to the Y element. Next, ion-exchanged water and a dispersant were weighed so that the relative density of the ceramic sintered body became 99%. Note that in Sample 1, no pore former was added. Next, the weighed raw material powder, ion-exchanged water, and dispersant were put into a ball mill and mixed for 16 hours or more to prepare a raw material slurry. Granulated powder was obtained by drying and granulating the obtained raw material slurry.

[0057] Next, the obtained granulated powder was put into a predetermined mold and press-molded to prepare a molded body, and the ceramic sintered body of Example 1 was obtained by firing in an air atmosphere at a firing temperature of 1685 °C and a holding time of 10 hours. The average thickness between the front surface of the obtained ceramic sintered body and the back surface opposite thereto was polished to be 150 μm, and the surface roughness Ra was polished to be 0.01 μm. Next, Ag was formed as a reflective film on the back surface by sputtering. Then, the wavelength conversion member of Sample 1 was manufactured by bonding it to an aluminum base material.

[0058] (Sample 2) A wavelength conversion member of Sample 2 was manufactured under the same conditions as Sample 1, except that the relative density was adjusted by adding a pore former. At this time, the relative density of the ceramic sintered body of Sample 2 was set to 82%. Note that the average particle diameter of the pore former was 1.5 μm. The same applies to Samples 3-4, 6-8, 10-12, and 14-16.

[0059] (Sample 3) A wavelength conversion member of Sample 3 was manufactured under the same conditions as Sample 1, except that the addition amount of the pore former was adjusted and the relative density of the ceramic sintered body was set to 75%.

[0060] (Sample 4) A wavelength conversion member of Sample 4 was manufactured under the same conditions as Sample 1, except that the addition amount of the pore former was adjusted and the relative density of the ceramic sintered body was set to 66%.

[0061] (Sample 5) The ratio of YAG in the ceramic sintered body was set to 80 vol% for Y 2 O3 , Al 2 O 3 , CeO 2 A wavelength conversion member of Sample 5 was fabricated under the same conditions as Sample 1, except that the raw material powders of 3 , Al, 2 , O, 3 , and CeO were weighed.

[0062] (Sample 6) A wavelength conversion member of Sample 6 was fabricated under the same conditions as Sample 5, except that the addition amount of the pore former was adjusted and the relative density of the ceramic sintered body was set to 88%.

[0063] (Sample 7) A wavelength conversion member of Sample 7 was fabricated under the same conditions as Sample 5, except that the addition amount of the pore former was adjusted and the relative density of the ceramic sintered body was set to 73%.

[0064] (Sample 8) A wavelength conversion member of Sample 8 was fabricated under the same conditions as Sample 5, except that the addition amount of the pore former was adjusted and the relative density of the ceramic sintered body was set to 64%.

[0065] (Sample 9) YAG in the ceramic sintered body was adjusted to 60 vol%, and a wavelength conversion member of Sample 9 was fabricated under the same conditions as Sample 1, except that the raw material powders of Y, 2 , O, 3 , Al, 2 , O, 3 , and CeO were weighed. 2 O 3 , Al 2 O 3 , CeO 2 A wavelength conversion member of Sample 9 was fabricated under the same conditions as Sample 1, except that the raw material powders of Y, 2 , O, 3 , Al, 2 , O, 3 , and CeO were weighed.

[0066] (Sample 10) A wavelength conversion member of Sample 10 was fabricated under the same conditions as Sample 9, except that the addition amount of the pore former was adjusted and the relative density of the ceramic sintered body was set to 90%.

[0067] (Sample 11) A wavelength conversion member of Sample 11 was fabricated under the same conditions as Sample 9, except that the addition amount of the pore former was adjusted and the relative density of the ceramic sintered body was set to 72%.

[0068] (Sample 12) A wavelength conversion member of Sample 12 was fabricated under the same conditions as Sample 9, except that the addition amount of the pore former was adjusted so that the relative density of the ceramic sintered body was 65%.

[0069] (Sample 13) A wavelength conversion member of Sample 13 was fabricated under the same conditions as Sample 1, except that the raw material powders of Y 2 O 3 , Al 2 O 3 , CeO 2 were weighed so that the proportion of YAG in the ceramic sintered body was 50 vol%.

[0070] (Sample 14) A wavelength conversion member of Sample 14 was fabricated under the same conditions as Sample 13, except that the addition amount of the pore former was adjusted so that the relative density of the ceramic sintered body was 86%.

[0071] (Sample 15) A wavelength conversion member of Sample 15 was fabricated under the same conditions as Sample 13, except that the addition amount of the pore former was adjusted so that the relative density of the ceramic sintered body was 71%.

[0072] (Sample 16) A wavelength conversion member of Sample 16 was fabricated under the same conditions as Sample 13, except that the addition amount of the pore former was adjusted so that the relative density of the ceramic sintered body was 60%.

[0073] (Sample 17) A wavelength conversion member of Sample 17 was fabricated under the same conditions as Sample 10, except that the pore former with an average particle diameter of 5 μm was used.

[0074] (Sample 18) A wavelength conversion member of Sample 18 was fabricated under the same conditions as Sample 10, except that the pore former with an average particle diameter of 7 μm was used.

[0075] (Sample 19) A wavelength conversion member of Sample 19 was fabricated under the same conditions as Sample 10, except that the pore former with an average particle diameter of 10 μm was used.

[0076] [Various evaluation methods] The following various evaluations were performed on the wavelength conversion members of the prepared samples.

[0077] (Measurement of relative density) Using the Archimedes method, the relative density of the ceramic sintered body of the sample was measured. The relative density was based on 100% of the theoretical value according to the composition of the ceramic sintered body.

[0078] (Measurement of emission point size) A laser beam (blue LD (wavelength 450 nm): output 0.5 W) was irradiated on the wavelength conversion member of the sample, and the luminance was measured with a color luminance meter (Konica Minolta: ProMetric IC-PM2 (ProMetric is a registered trademark)). The distance from the position with the highest luminance to the position where the luminance became 20% was defined as the emission point size. The increase or decrease in the distance of the emission point size was displayed as a percentage based on the emission point size of Sample 1.

[0079] (Measurement of luminance) The luminance at the position with the highest luminance was measured with a color luminance meter. The increase or decrease in luminance was displayed as a percentage based on the luminance of Sample 1.

[0080] (Measurement of void size) For the ceramic sintered bodies of Samples 10 and 17 to 19, the void size was confirmed by image analysis of a simple SEM measurement of the cross section. The void size was defined as the average value of the equivalent circle diameters obtained from the areas of the confirmed voids.

[0081] The table in Fig. 4 shows the composition and evaluation results of the wavelength conversion members of Samples 1 to 16. Also, the table in Fig. 5 shows the composition and evaluation results of the wavelength conversion members of Samples 10 and 17 to 19. In both Fig. 4 and Fig. 5, the columns for emission point size and luminance are described as the increase or decrease as a percentage based on Sample 1.

[0082] Samples 1, 5, 9, and 13 with a relative density exceeding 90% had the converted light wavelength-converted by the ceramic sintered body likely to leak from the side surface of the ceramic sintered body, the light-emitting points blurred, and the light-emitting point size could not be reduced. Also, in samples with the same composition, when taking sample 1 as a reference, it was found that the size of the light-emitting points became smaller as the relative density decreased.

[0083] On the other hand, samples 4, 8, 12, and 16 with a relative density below 70% could reduce the light-emitting point size when taking sample 1 as a reference, but a decrease in luminance due to quenching was observed. This is presumably due to a large proportion of voids and a decrease in thermal conductivity.

[0084] Also, in samples 2 and 3 with the same composition as sample 1, when taking sample 1 as a reference, the light-emitting point size could be reduced, but a decrease in luminance due to quenching was observed. This is presumably because the proportion of the light-transmitting phase, which has better thermal conductivity than the fluorescent phase, was small, resulting in temperature quenching due to a decrease in thermal conductivity.

[0085] For sample 1, samples 6, 7, 10, 11, 14, and 15, in which the composition ratio of the light-transmitting phase (Al 2 O 3 ) was increased to improve the thermal conductivity of the ceramic sintered body, not only could the light-emitting point size be reduced, but also high luminance was obtained. However, in samples 14 and 15, the proportion of the fluorescent phase was small, so the amount of light wavelength-converted was small, and there was a slight variation in chromaticity.

[0086] From these results, it was found that in order to achieve both a reduced light-emitting point size and high luminance, it is important to adjust the density by the voids contained in the ceramic sintered body and to adjust the content of the fluorescent phase in the ceramic sintered body.

[0087] Also, from the results of Samples 10, 17 to 19, it was found that by reducing the size of the voids (equivalent average circle diameter), the diameter of the light-emitting point was reduced and the luminance was improved. This is presumably because when the density is the same, a smaller void size allows more pores to be included in the ceramic sintered body, suppressing the leakage of excitation light and fluorescence from the side surface or the like of the ceramic sintered body. It was also found that the size of the voids can be adjusted by adjusting the average particle diameter of the pore-forming agent.

[0088] From the above results, it was confirmed that the wavelength conversion member or the light-emitting device of the present invention can reduce the diameter of the light-emitting point. It was also confirmed that the wavelength conversion member or the light-emitting device of the present invention can also increase the luminance.

[0089] The present invention is not limited to the above-described embodiments, and it goes without saying that the present invention extends to various modifications and equivalents included in the spirit and scope of the present invention. In addition, the structure, shape, number, position, size, etc. of the components shown in each drawing are for convenience of explanation and can be changed as appropriate.

Explanation of Reference Numerals

[0090] 10 Wavelength conversion member 12 Ceramic sintered body 14 Fluorescent phase 16 Translucent phase 18 Void 20 Surface 22 Back surface 30 Anti-reflection film 32 Reflective film 40 Substrate 50 Light source 100 Light-emitting device

Claims

1. A wavelength conversion member made of a ceramic sintered body, wherein the ceramic sintered body includes a fluorescent phase that emits fluorescence upon excitation light, a translucent phase having translucency, and a plurality of voids surrounded by the fluorescent phase or the translucent phase, wherein an average equivalent circle diameter of the voids is 0.1 μm or more and 10 μm or less, and a relative density of the ceramic sintered body is 70% or more and 90% or less. A wavelength conversion member characterized by the above.

2. In a direction perpendicular to a surface of the ceramic sintered body where the excitation light is incident, a relative density of the ceramic sintered body in a region from the surface to 50% of an average thickness is 70% or more and 90% or less. The wavelength conversion member according to claim 1, characterized by the above.

3. A content of the fluorescent phase of the ceramic sintered body is 80 vol% or less. The wavelength conversion member according to claim 1 or claim 2, characterized by the above.

4. A content of the fluorescent phase of the ceramic sintered body is 60 vol% or more. The wavelength conversion member according to claim 3, characterized by the above.

5. A light emitting device, comprising a light emitting element that emits light having a wavelength in a specific range, and the wavelength conversion member according to claim 1 or claim 2. A light emitting device characterized by the above.

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