Wavelength conversion element

Abstract

To increase the luminous energy of fluorescence emitted in response to irradiation with excitation light in a wavelength conversion element.SOLUTION: The wavelength conversion element is provided with a wavelength conversion unit. The wavelength conversion unit includes a plurality of phosphor particles and a binder layer. The binder layer joins the plurality of phosphor particles together and includes glass. The binder layer includes a plurality of fine crystal particles and an amorphous phase. The plurality of fine crystal particles include one or more fine crystal particles that are in contact with one or more phosphor particles among the plurality of phosphor particles. Each of the plurality of fine crystal particles includes at least some of the components included in the amorphous phase. When the binder layer is divided into a first region that is in contact with each of the plurality of phosphor particles and a second region that is spaced from the plurality of phosphor particles, the abundance of the fine crystal particles in the first region is larger than the abundance of the fine crystal particles in the second region.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] This disclosure relates to a wavelength conversion element. [Background technology]

[0002] Wavelength conversion elements are known that irradiate a phosphor with excitation light and convert this excitation light into light of a different wavelength. For example, there is a wavelength conversion member comprising a plurality of phosphor particles and a binder layer connecting adjacent phosphor particles, wherein the binder layer comprises a plurality of fine crystalline inorganic particles and an amorphous phase containing an amorphous inorganic compound present between the plurality of fine inorganic particles (see, for example, the description in Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 6945133 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Regarding wavelength conversion elements, there is room for improvement in increasing the amount of fluorescence emitted in response to excitation light irradiation. [Means for solving the problem]

[0005] A wavelength conversion element is disclosed.

[0006] One embodiment of a wavelength conversion element comprises a wavelength conversion section. The wavelength conversion section includes a plurality of phosphor particles and a binder layer. The binder layer bonds the plurality of phosphor particles together and also includes glass. The binder layer includes a plurality of fine crystalline particles and an amorphous phase. The plurality of fine crystalline particles include one or more fine crystalline particles in contact with one or more of the plurality of phosphor particles. Each of the plurality of fine crystalline particles includes at least a portion of the components contained in the amorphous phase. When the binder layer is divided into a first region in contact with each of the plurality of phosphor particles and a second region away from the plurality of phosphor particles, the abundance of the plurality of fine crystalline particles in the first region is greater than the abundance of the plurality of fine crystalline particles in the second region. The plurality of phosphor particles include one or more first phosphor particles containing phosphorus and one or more second phosphor particles not containing phosphorus. The first region includes a first A region in contact with the one or more first phosphor particles and a first B region in contact with the one or more second phosphor particles. The abundance of the plurality of fine crystalline particles in the first A region is less than the abundance of the plurality of fine crystalline particles in the first B region. [Effects of the Invention]

[0007] In a wavelength conversion element, the amount of fluorescence emitted in response to the irradiation of excitation light can be increased. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic diagram showing an example of the configuration of a lighting system according to the first embodiment. [Figure 2] Figure 2 is a cross-sectional view showing an example of the configuration of a wavelength conversion element according to the first embodiment. [Figure 3] Figure 3 is a schematic diagram illustrating an example of a hypothetical cross-sectional configuration of the wavelength conversion element according to the first embodiment. [Figure 4] Figure 4 is a schematic diagram illustrating an example of the configuration of a hypothetical cross-section of section IV, enclosed by the dashed line in Figure 3. [Figure 5] Figure 5 is a simplified diagram illustrating an example of the distribution of multiple fine crystal particles in a hypothetical cross-sectional configuration of a wavelength conversion element according to the first embodiment. [Figure 6]FIG. 6 is an image diagram showing an example of the distribution of a plurality of fine crystal particles and one or more voids in a partial configuration of a virtual cross section of the wavelength conversion element according to the first embodiment. [Figure 7] FIG. 7 is a flowchart showing an example of the manufacturing process of the wavelength conversion element according to the first embodiment. [Figure 8] FIG. 8 is a cross-sectional view showing an example of the state during the manufacturing of the wavelength conversion element. [Figure 9] FIG. 9 is a cross-sectional view showing an example of the state during the manufacturing of the wavelength conversion element. [Figure 10] FIG. 10 is a cross-sectional view showing an example of the state during the manufacturing of the wavelength conversion element. [Figure 11] FIG. 11 is a cross-sectional view showing an example of the state during the manufacturing of the wavelength conversion element. [Figure 12] FIG. 12 is a cross-sectional view showing an example of the state during the manufacturing of the wavelength conversion element. [Figure 13] FIG. 13 is a cross-sectional view schematically showing an image of the state immediately before the appearance of fine crystal particles during the manufacturing of the wavelength conversion element. [Figure 14] FIG. 14 is a cross-sectional view schematically showing an image of the state immediately after the appearance of fine crystal particles during the manufacturing of the wavelength conversion element. [Figure 15] FIG. 15 is a perspective view showing an example of the configuration of the wavelength conversion element according to the second embodiment. [Figure 16] FIG. 16 is a cross-sectional view showing an example of the configuration of the wavelength conversion element according to the second embodiment. [Figure 17] FIG. 17 is a flowchart showing an example of the manufacturing process of the wavelength conversion element according to the second embodiment. [Figure 18] FIG. 18 is a perspective view showing an example of the configuration of the base material according to the second embodiment. [Figure 19] FIG. 19 is a cross-sectional view showing an example of the configuration of the base material according to the second embodiment. [Figure 20] FIG. 20 is an image diagram schematically showing an example of the configuration of a virtual cross section of a portion corresponding to part IV surrounded by the dashed-dotted line in FIG. 3 of the virtual cross section of the wavelength conversion element according to the third embodiment. [Modes for carrying out the invention]

[0009] Wavelength conversion elements are known that convert excitation light, such as laser light, into light of a different wavelength from the excitation light by irradiating a phosphor with it. One possible configuration for such a wavelength conversion element is one that comprises multiple phosphor particles and a binder layer that connects adjacent phosphor particles.

[0010] Incidentally, in the binder layer of this wavelength conversion element, it is conceivable to disperse multiple fine inorganic particles that are crystalline, and to have amorphous inorganic compounds present between these multiple fine inorganic particles. In this configuration, for example, the excitation light irradiated onto the wavelength conversion element is scattered by the multiple fine inorganic particles, making it difficult for the excitation light to pass through between the multiple phosphor particles. In other words, the probability of the excitation light irradiating multiple phosphor particles may increase.

[0011] However, for example, if the number of fine inorganic particles in the binder layer increases, the number of interfaces between the fine inorganic particles and the amorphous inorganic compound increases, and Fresnel reflection at these interfaces may reduce the amount of excitation light incident on the multiple phosphor particles. Also, for example, if the number of fine inorganic particles in the binder layer increases, the amount of excitation light absorbed by the multiple fine inorganic particles increases, which may reduce the amount of excitation light incident on the multiple phosphor particles. And when the amount of excitation light incident on the multiple phosphor particles decreases, the amount of fluorescence emitted in response to the irradiation of excitation light decreases.

[0012] Therefore, there is room for improvement in wavelength conversion elements in terms of increasing the amount of fluorescence emitted in response to excitation light irradiation.

[0013] Therefore, the inventors of this disclosure have created a technique that can increase the amount of fluorescence emitted from a wavelength conversion element in response to the irradiation of excitation light.

[0014] This will be explained below with reference to the drawings, describing various embodiments and examples. In the drawings, parts having the same or similar configuration and function are denoted by the same reference numerals, and redundant explanations will be omitted in the following description. The drawings schematically show various configurations, etc. Figures 2 to 6, 13, 14, 16, 19, and 20 are each shown with a right-handed XYZ coordinate system. More specifically, the direction in which the first surface F1 of the wavelength conversion unit 30t faces is defined as the +Z direction, one direction perpendicular to the +Z direction is defined as the +X direction, and one direction perpendicular to both the +Z direction and the +X direction is defined as the +Y direction.

[0015] <1. First Embodiment> <1-1. Lighting System> Figure 1 is a schematic diagram showing an example of the configuration of a lighting system 1 according to the first embodiment. The lighting system 1 can emit fluorescence L1, which is generated when excitation light L0 is irradiated from the light source unit 2 onto a wavelength conversion element 30 containing a phosphor, as illumination light L2 into a predetermined space (also called an illuminated space). The lighting system 1 may emit illumination light L2 into an indoor space or into an outdoor space. In other words, the illumination light L2 emitted by the lighting system 1 may be used indoors or outdoors. Furthermore, multiple lighting systems 1 may each emit illumination light L2 into the same space, or multiple lighting systems 1 may each emit illumination light L2 into multiple different spaces.

[0016] As shown in Figure 1, the lighting system 1 includes, for example, a light source unit 2, a conversion unit 3, and an illumination unit 4.

[0017] The light source unit 2 can, for example, emit excitation light L0. The light source unit 2 has, for example, a light-emitting element. The light-emitting element includes, for example, a laser diode (LD) or a light-emitting diode (LED) chip. The excitation light L0 emitted by the light-emitting element may be monochromatic light such as purple, blue-violet, or blue. More specifically, the light-emitting element may be, for example, a gallium nitride (GaN) semiconductor laser that emits purple laser light at 405 nanometers (nm). In the example in Figure 1, the excitation light L0 emitted by the light source unit 2 is transmitted to the conversion unit 3 via an optical transmission path (also called the first optical transmission path) G1, such as an optical fiber. In this case, the light source unit 2 has a connection part to which the end of the first optical transmission path G1 into which the excitation light L0 is incident (also called the first incident end) is connected. In Figure 1, the transmission of the excitation light L0 by the first optical transmission path G1 is shown by arrows drawn with thin dotted lines.

[0018] The conversion unit 3 includes, for example, a wavelength conversion element 30. The wavelength conversion element 30 can convert, for example, irradiated excitation light L0 into light of a different wavelength than the excitation light L0. The wavelength conversion element 30 includes, for example, a phosphor that emits fluorescence of a different wavelength than the excitation light L0 in response to irradiation with the excitation light L0. If the wavelength conversion element 30 includes, for example, a phosphor that emits red (R), green (G), and blue (B) fluorescence in response to irradiation with purple excitation light L0, then the purple excitation light L0 is converted into pseudo-white light in the wavelength conversion element 30. In the example in Figure 1, the fluorescence L1 emitted from the wavelength conversion element 30 in response to irradiation with excitation light L0 is transmitted to the illumination unit 4 via an optical transmission path (also called a second optical transmission path) G2 such as an optical fiber. In Figure 1, the transmission of fluorescence L1 by the second optical transmission path G2 is shown by arrows drawn with thin dotted lines.

[0019] Furthermore, the conversion unit 3 has a housing in which, for example, a wavelength conversion element 30 is fixed inside. In this case, the housing has, for example, a first opening to which the end of the first optical transmission path G1 that emits excitation light L0 (also called the first emission end) is connected, and a second opening to which the end of the second optical transmission path G2 to which the fluorescence L1 is incident (also called the second incidence end) is connected. Inside the housing, optical elements such as mirrors may be arranged to collect the fluorescence L1 emitted from the wavelength conversion element 30 in response to the irradiation of excitation light L0 at the second incidence end of the second optical transmission path G2.

[0020] The illumination unit 4 can, for example, emit fluorescence L1 from the wavelength conversion element 30 in response to irradiation with excitation light L0 emitted from the light source unit 2, and direct it toward a predetermined illumination space. The illumination unit 4 includes, for example, a main body and an optical element. In this case, the main body has, for example, a connecting portion to which the end of the second optical transmission path G2 that emits fluorescence L1 (also called the second output end) is connected. The main body may be, for example, a cylindrical member. The optical element is, for example, attached to the main body and emits fluorescence L1 emitted from the second output end of the second optical transmission path G2 as illumination light L2 toward a predetermined illumination space. In Figure 1, the emission of illumination light L2 from the illumination unit 4 toward a predetermined illumination space is shown by arrows drawn with thin dotted lines.

[0021] Furthermore, the lighting system 1 may include, for example, a control device 5 for controlling the operation of the light source unit 2. The control device 5 may include, for example, a control unit 51 and a drive unit 52. The control unit 51 can comprehensively manage the operation of the control device 5 by controlling other components of the control device 5. The control unit 51 may include, for example, a CPU (Central Processing Unit) 511 and a storage unit 512. The storage unit 512 includes a non-temporary recording medium that can be read by the CPU 511, such as ROM (Read Only Memory) and RAM (Random Access Memory). The storage unit 512 stores, for example, a program Pg1 for controlling the control device 5. Various functions in the control unit 51 are realized by the CPU 511 executing the program Pg1 in the storage unit 512. The drive unit 52 may, for example, drive the light source unit 2 in response to instructions from the control unit 51. The drive unit 52 may, for example, drive the light source unit 2 by supplying power from a power source to the light source unit 2, thereby causing the light source unit 2 to output excitation light L0. For example, the control unit 51 can control the timing at which the light source unit 2 emits excitation light L0 by controlling whether or not power is supplied from the power source to the light source unit 2 via the drive unit 52.

[0022] <1-2. Wavelength conversion elements> Figure 2 is a cross-sectional view showing an example of the configuration of the wavelength conversion element 30 according to the first embodiment. In Figure 2, the area around the first output end of the first optical transmission path G1 and the area around the second input end of the second optical transmission path G2 are schematically depicted. As shown in Figure 2, the wavelength conversion element 30 comprises a wavelength conversion section 30t and a substrate 30b. The cross-sectional structure of the wavelength conversion section 30t has a complex structure with many minute structures interwoven, but for convenience, a schematic illustration of the structure is omitted in Figure 2.

[0023] The wavelength conversion unit 30t has, for example, a surface (also called the first surface) F1 to which the excitation light L0 is incident. In Figure 2, the emission of the excitation light L0 from the first optical transmission path G1 toward the first surface F1 is shown by a thin dashed-dotted arrow. In Figure 2, the emission of fluorescence L1 from the first surface F1 toward the second optical transmission path G2 is shown by a thin dashed-dotted arrow. The wavelength conversion unit 30t also has, for example, a surface (also called the second surface) F2 located on the opposite side from the first surface F1. The wavelength conversion unit 30t has, for example, a plate-like or film-like shape with a thickness along the direction from the second surface F2 toward the first surface F1.

[0024] The substrate 30b is a component that supports the wavelength conversion section 30t. From another perspective, the substrate 30b is a component to which the wavelength conversion section 30t is fixed. Here, for example, if the thermal conductivity of the substrate 30b is higher than that of the wavelength conversion section 30t, the substrate 30b functions as a heat sink that releases heat from the wavelength conversion section 30t. In other words, the presence of the substrate 30b can improve the rate at which heat is dissipated from the wavelength conversion section 30t. This can reduce the degradation of the multiple phosphor particles 31 contained in the wavelength conversion section 30t. As a result, the decrease in the amount of fluorescence L1 emitted in the wavelength conversion element 30 in response to the irradiation of excitation light L0 can be reduced. In other words, the amount of fluorescence L1 emitted in the wavelength conversion element 30 in response to the irradiation of excitation light L0 can be increased.

[0025] The material of the base material 30b may be, for example, a metallic material. Examples of metallic materials include copper (Cu), aluminum (Al), magnesium (Mg), gold (Au), silver (Ag), iron (Fe), chromium (Cr), cobalt (Co), beryllium (Be), molybdenum (Mo), tungsten (W), or alloys. If, for example, Cu, Al, Mg, Fe, Cr, Co, or Be is used as the metallic material, the base material 30b can be easily manufactured by a casting method such as die casting. If, for example, Al, Mg, Ag, Fe, Cr, or Co is used as the metallic material, the reflectivity of visible light on the surface of the base material 30b can be increased. The reflectivity of visible light may also be improved by processing the surface of the base material 30b to a mirror finish by physical polishing or chemical polishing.

[0026] Furthermore, nonmetallic materials such as aluminum nitride (AlN), gallium nitride (GaN), silicon carbide (SiC), silicon nitride (Si3N4), carbon (C), sapphire (Al2O3), magnesia (MgO), or garnet may be used as the material for the substrate 30b. The nonmetallic material may be, for example, a crystalline material or an amorphous material. As a crystalline nonmetallic material, for example, SiC or Si3N4 may be used. Since these nonmetallic materials have low reflectivity to visible light, an optical reflective film may be formed on the surface when, for example, AlN is used. The shape and size of the substrate 30b may be appropriately set according to the size of the wavelength conversion element 30. For example, in the case of a rectangular substrate 30b in plan view, the thickness of the substrate 30b may be set to about 0.1 millimeters (mm) to 5 mm, and the length and width of the substrate 30b may be set to about 0.5 mm to 30 mm, respectively.

[0027] Furthermore, the base material 30b has, for example, a surface (also called the third surface) F3 on which the wavelength conversion unit 30t is arranged. More specifically, the second surface F2 of the wavelength conversion unit 30t is fixed to the third surface F3. In the example in Figure 2, the first surface F1 faces the +Z direction, the second surface F2 faces the -Z direction, and the third surface F3 faces the +Z direction. The base material 30b may be, for example, a plate-shaped member. The plate-shaped member may be, for example, a disc-shaped member, or a member having a rectangular shape in plan view.

[0028] Figure 3 is a schematic diagram illustrating an example of the configuration of a hypothetical cross-section of the wavelength conversion element 30 according to the first embodiment. Figure 4 is a schematic diagram illustrating an example of the configuration of a hypothetical cross-section of section IV enclosed by the dashed line in Figure 3. Figures 3 and 4 each show cross-sectional images drawn based on images (also called SEM images) obtained by imaging with a scanning electron microscope (SEM) targeting the cross-section of the wavelength conversion section 30t. In Figure 3, the substrate 30b is hatched using multiple widely spaced upward-sloping diagonal lines.

[0029] As shown in Figures 3 and 4, the wavelength conversion unit 30t includes a plurality of phosphor particles 31 and a binder layer 32. In Figures 3 and 4, each of the plurality of phosphor particles 31 is hatched using multiple closely spaced diagonal lines.

[0030] Each of the plurality of phosphor particles 31 is, for example, a phosphor particle that emits fluorescence in response to irradiation with excitation light L0. The plurality of phosphor particles 31 includes, for example, one or more phosphor particles 31 that emit fluorescence of one or more wavelength spectra different from the wavelength spectrum of the excitation light L0 in response to irradiation with excitation light L0. The one or more phosphor particles 31 may include, for example, multiple types of phosphor particles 31 that emit fluorescence having mutually different wavelength spectra in response to irradiation with excitation light L0. The multiple types of phosphor particles 31 include, for example, red phosphor particles, green phosphor particles, and blue phosphor particles. The red phosphor is a phosphor that emits red (R) fluorescence in response to irradiation with excitation light L0. The green phosphor is a phosphor that emits green (G) fluorescence in response to irradiation with excitation light L0. The blue phosphor is a phosphor that emits blue (B) fluorescence in response to irradiation with excitation light L0.

[0031] As the phosphors constituting the multiple phosphor particles 31, for example, phosphors containing rare earth elements such as europium (Eu), cerium (Ce), or yttrium (Y) in the form of compounds such as phosphates, oxides, silicates, nitrides, fluorides, aluminates, or sulfides may be used.

[0032] As the red phosphor, for example, a phosphor whose fluorescence wavelength peak in response to irradiation with excitation light L0 is in the range of approximately 620 nm to 750 nm may be used. Examples of red phosphor materials include CaAlSiN3:Eu, Y3O3S:Eu, Y3O3:Eu, and SrCaClAlSiN3:Eu. 2+ Alternatively, CaAlSi(ON)3:Eu may be used. As the phosphor particles of the red phosphor, for example, phosphor particles that do not contain phosphorus (also called non-phosphorus phosphor particles) may be used, or phosphor particles containing nitrides may be used.

[0033] As the green phosphor, for example, a phosphor whose fluorescence wavelength peak in response to irradiation with excitation light L0 is in the range of approximately 495 nm to 570 nm may be used. Examples of green phosphor materials include β-sialon (β-SiAlON:Eu), SrSi2(O,Cl)2N2:Eu, and (Sr,Ba,Mg)2SiO4:Eu2. 2+ ZnS:Cu,Al or Zn2SiO4:Mn may be used. As the phosphor particles of the green phosphor, for example, phosphor particles that do not contain phosphorus (non-phosphorus phosphor particles) may be used, or phosphor particles containing nitrides may be used.

[0034] As the blue phosphor, for example, a phosphor whose fluorescence wavelength peak in response to irradiation with excitation light L0 is in the range of approximately 450 nm to 495 nm may be used. As the material for the blue phosphor, for example, (Ba,Sr)MgAl 10 O 17 :Eu,BaMgAl 10 O 17 :Eu, (Sr,Ca,Ba) 10 (PO4)6Cl2:Eu, (Sr,Ba) 10 (PO4)6Cl2:Eu or α-sialon may be used. As the phosphor particles of the blue phosphor, for example, phosphor particles containing phosphorus (P) (also called phosphorus-based phosphor particles) or phosphor particles containing nitride may be used.

[0035] The particle size of the phosphor particles 31 may be, for example, 5 micrometers (μm) to about 50 μm.

[0036] The binder layer 32 bonds multiple phosphor particles 31 together. In other words, the wavelength conversion element 30 has a form in which multiple phosphor particles 31 are dispersed in the binder layer 32. Glass is used as the material for the binder layer 32. In other words, the binder layer 32 contains glass. The binder layer 32 may contain glass as its main component. The main component refers to the component that makes up the substance in the largest proportion (also called the content) of the components. The glass has transparency to, for example, transmit excitation light L0 into the interior of the wavelength conversion section 30t and to radiate fluorescence L1 emitted by the phosphor particles 31 excited in response to the irradiation of excitation light L0 to the outside of the wavelength conversion section 30t. In other words, the glass has transparency to transmit excitation light L0 and fluorescence L1.

[0037] As the glass constituting the binder layer 32, for example, a low-melting-point glass may be used. As the low-melting-point glass, for example, an oxide glass with a melting point (Tm) of 200 degrees Celsius (200°C) to 700°C may be used. This oxide glass as the low-melting-point glass has, for example, a glass transition temperature (Tg) in the range of 100°C to 600°C and a crystallization temperature (Tc) in the range of 150°C to 650°C. As the oxide glass, for example, a glass containing two or more oxides from among silicon dioxide (SiO2), aluminum oxide (Al2O3), boron oxide (B2O3), sodium oxide (Na2O3), potassium oxide (K2O), lithium oxide (Li2O), calcium oxide (CaO), barium oxide (BaO), zinc oxide (ZnO), lead monoxide (PbO), and phosphorus pentoxide (P2O5) as the main component may be used. In other words, oxide glass may contain oxides of metallic elements or oxides of metalloid elements.

[0038] The binder layer 32 is located, for example, between a plurality of phosphor particles 31 and between the phosphor particles 31 and the substrate 30b. In the portion of the binder layer 32 that is in direct contact with the phosphor particles 31, it has the function of directly conducting the heat of the phosphor particles 31. Here, the surface of the phosphor particles 31 may be covered with a coating layer. In this case, the state in which "the binder layer 32 is in direct contact with the phosphor particles 31" includes the state in which the coating layer covering the phosphor particles 31 and the binder layer 32 are in direct contact. When the first surface F1 of the wavelength conversion unit 30t is irradiated with excitation light L0, heat is generated in the plurality of phosphor particles 31 by the irradiation of excitation light L0. This heat is conducted to the substrate 30b via the binder layer 32 and the like and dissipated.

[0039] As shown in Figures 3 and 4, the binder layer 32 comprises an amorphous phase 321 and a plurality of fine crystalline particles (also called microcrystalline particles) 322. The microcrystalline particles 322 are crystalline particles. In Figures 3 and 4, the amorphous phase 321 is hatched using a textured surface pattern. In Figures 3 and 4, the plurality of microcrystalline particles 322 are not hatched for the sake of simplicity in the figures.

[0040] The amorphous phase 321 may be, for example, a portion of the amorphous phase of glass. More specifically, the amorphous phase 321 may be, for example, a portion of the amorphous phase of low-melting-point glass. The amorphous phase 321 composed of glass has transparency that allows excitation light L0 and fluorescence L1 to pass through, for example.

[0041] Each of the multiple fine crystalline particles 322 contains at least some of the components contained in the amorphous phase 321. The fine crystalline particles 322 are crystalline particles containing at least some of the components contained in the amorphous phase 321. Each of the multiple fine crystalline particles 322 may be a crystal of one or more oxides from the group of oxides (also called the first oxide group) including SiO2, Al2O3, B2O3, Na2O3, K2O, Li2O, CaO, BaO, ZnO, PbO, and P2O5, or it may be a crystal of an oxide (also called a composite oxide) which is a composite of two or more oxides from the first oxide group. For example, an example in which the fine crystalline particles 322 are composed of ZnO can be considered. The fine crystalline particles 322 may also be crystalline particles containing all of the components contained in the amorphous phase 321. In other words, at least some of the components contained in the amorphous phase 321 may be some of the components contained in the amorphous phase 321, or they may be all of the components contained in the amorphous phase 321.

[0042] The size of the multiple fine crystalline particles 322 may be smaller than, for example, the size of the multiple phosphor particles 31. Here, the state in which the size of the multiple fine crystalline particles 322 is smaller than the size of the multiple phosphor particles 31 may be, for example, a state in which the average value of the particle diameters of the multiple fine crystalline particles 322 is smaller than the average value of the particle diameters of the multiple phosphor particles 31, or a state in which the particle diameter of each of the multiple fine crystalline particles 322 is smaller than the average value of the particle diameters of the multiple phosphor particles 31. The particle diameter of the particles may be, for example, the average value of the diameter in the long axis direction of the particle (also called the long axis diameter) and the diameter in the short axis direction of the particle (also called the short axis diameter) (also called the geometric average diameter), or a value converted to the diameter of a circular or spherical particle using the area or volume projected onto a plane and a predetermined geometric formula (also called the equivalent diameter), or the length in the longitudinal direction of the particle (also called the maximum diameter). The particle diameter of the fine crystalline particles 322 may be, for example, about 0.1 μm to 3 μm.

[0043] The fine crystalline particles 322, for example, have transparency that allows excitation light L0 and fluorescence L1 to pass through, and also have the property of scattering a portion of the excitation light L0 and fluorescence L1. Therefore, the excitation light L0 irradiated onto the wavelength conversion element 30 is scattered by the multiple fine crystalline particles 322, making it difficult for the excitation light L0 to pass through the multiple phosphor particles 31. In other words, the presence of multiple fine crystalline particles 322 can increase the probability that the excitation light L0 irradiates multiple phosphor particles 31.

[0044] The plurality of fine crystalline particles 322 include one or more fine crystalline particles 322 that are in contact with one or more of the plurality of phosphor particles 31. As shown in Figures 3 and 4, for example, one fine crystalline particle 322 may be in contact with one phosphor particle 31, or two or more fine crystalline particles 322 may be in contact with one phosphor particle 31. Here, since the thermal conductivity of the fine crystalline particles 322 is higher than that of the amorphous phase 321, the presence of fine crystalline particles 322 in contact with the phosphor particles 31 can improve the rate at which heat is dissipated from the phosphor particles 31 by heat transfer and heat conduction through the fine crystalline particles 322. This can reduce the degradation of the plurality of phosphor particles 31. As a result, the decrease in the amount of fluorescence L1 emitted in response to the irradiation of excitation light L0 in the wavelength conversion element 30 can be reduced. In other words, the amount of fluorescence L1 emitted in response to the irradiation of excitation light L0 in the wavelength conversion element 30 can be increased.

[0045] Figure 5 is a simplified diagram illustrating an example of the distribution of multiple fine crystal particles 322 in a hypothetical cross-sectional configuration of the wavelength conversion element 30 according to the first embodiment. In Figure 5, the shape of the multiple phosphor particles 31 is conveniently represented as circular.

[0046] Here, we assume that the binder layer 32 is divided into a region A1 that is in contact with each of the multiple phosphor particles 31 (also called the first region or contact region) and a region A2 that is away from the multiple phosphor particles 31 (also called the second region or peripheral region). In Figure 5, the boundary between the first region A1 and the second region A2 is shown by a circle drawn with a thin dashed line. In the example in Figure 5, the region inside the multiple circles drawn with thin dashed lines is the first region A1, and the region outside the multiple circles drawn with thin dashed lines is the second region A2. In the first embodiment, the abundance of multiple fine crystalline particles 322 in the first region A1 (also called the first abundance) is greater than the abundance of multiple fine crystalline particles 322 in the second region A2 (also called the second abundance).

[0047] If this configuration is adopted, in the binder layer 32, the first region A1, which is close to the multiple phosphor particles 31, contains relatively more fine crystalline particles 322 than the second region A2, which is further away from the multiple phosphor particles 31. Therefore, in the second region A2, the decrease in the multiple fine crystalline particles 322 can reduce the interface between the multiple fine crystalline particles 322 and the amorphous phase 321. This can reduce Fresnel reflection at the interface between the multiple fine crystalline particles 322 and the amorphous phase 321, and can also reduce the amount of excitation light L0 absorbed by the multiple fine crystalline particles 322. As a result, the amount of excitation light L0 incident on the multiple phosphor particles 31 can increase. Thus, the wavelength conversion element 30 can increase the amount of fluorescence L1 emitted in response to the irradiation of excitation light L0.

[0048] The first region A1 may be, for example, a region within the binder layer 32 that is within a predetermined distance (also called the first distance) from the surface of each of the multiple phosphor particles 31. The first distance may be set, for example, according to the degree of dispersion of the multiple phosphor particles 31. When the multiple phosphor particles 31 are densely distributed, the first distance may be smaller than when the multiple phosphor particles 31 are sparsely distributed. The first distance may be set, for example, according to the particle size of the multiple fine crystalline particles 322. The first distance may be, for example, 2 μm, 3 μm, or any length of 4 μm or more.

[0049] The relative abundance of multiple fine crystalline particles 322 in the first region A1 (first abundance) and the relative abundance of multiple fine crystalline particles 322 in the second region A2 (second abundance) can be compared using various comparison methods. One such comparison method is to compare, for example, the area ratio of multiple fine crystalline particles 322 in the first region A1 (also called the first area occupancy) with the area ratio of multiple fine crystalline particles 322 in the second region A2 (also called the second area occupancy) using an SEM image of the cross-section of the wavelength conversion section 30t. In this case, for example, the first abundance may be the area ratio of multiple fine crystalline particles 322 in a virtual cross-section of the first region A1 (also called a virtual cross-section), and the second abundance may be the area ratio of multiple fine crystalline particles 322 in a virtual cross-section of the second region A2. Here, the virtual cross-section of the first region A1 and the virtual cross-section of the second region A2 may be located on the same virtual cross-section of the wavelength conversion unit 30t, or they may be located on different virtual cross-sections of the wavelength conversion unit 30t.

[0050] For example, a scanning electron microscope (SEM) that acquires an SEM image of the cross-section of the wavelength conversion unit 30t may be equipped with an energy-dispersive X-ray analyzer (also called an EDS device). In this case, for example, the phosphor particles 31, amorphous phase 321, and fine crystalline particles 322 may be distinguished by elemental analysis using the EDS device in the region of the cross-section of the wavelength conversion unit 30t that is the target of the SEM image. Furthermore, the first abundance may be, for example, the volume ratio of multiple fine crystalline particles 322 in the first region A1 (also called the first volume occupancy), and the second abundance may be the volume ratio of multiple fine crystalline particles 322 in the second region A2 (also called the second volume occupancy).

[0051] Here, the abundance of multiple fine crystalline particles 322 in the first region A1 (first abundance) may be, for example, 40 percent or more and 80% or less. The abundance of multiple fine crystalline particles 322 in the second region A2 (second abundance) may be, for example, 10% or more and 20% or less. For example, the first abundance may be 40% and the second abundance may be 10%. Alternatively, for example, the first abundance may be 80% and the second abundance may be 20%.

[0052] In the first embodiment, for example, if one or more phosphor particles 31 that are in contact with one or more fine crystalline particles 322 are phosphor particles 31 containing nitride, then the surface of these nitride-containing phosphor particles 31 is protected by the one or more fine crystalline particles 322 that are in contact with this surface. This reduces the degree of oxidation of the nitride in the phosphor particles 31, and thus reduces the degradation of the nitride-containing phosphor particles 31. As a result, the decrease in the amount of fluorescence L1 emitted in the wavelength conversion element 30 in response to the irradiation of excitation light L0 can be reduced. In other words, the amount of fluorescence L1 emitted in the wavelength conversion element 30 in response to the irradiation of excitation light L0 can be increased.

[0053] Here, the larger the proportion of the surface area of ​​a single phosphor particle 31 that is in contact with one or more fine crystalline particles 322, the greater the degree to which this single phosphor particle 31 is protected by one or more fine crystalline particles 322. Furthermore, for example, it is conceivable that multiple phosphor particles 31 include phosphor particles 31 composed of a material with a relatively low oxygen content and phosphor particles 31 composed of a material with a relatively high oxygen content. In this case, for example, one possible configuration is in which the material with a relatively low oxygen content is the aforementioned red phosphor material containing nitride, and the material with a relatively high oxygen content is the aforementioned blue phosphor material that does not contain nitride. In this example configuration, if the surface of the phosphor particle 31 of the nitride-containing red phosphor is protected by one or more fine crystalline particles 322 in contact with this surface, the degree of oxidation of the red phosphor can be reduced, and the degradation of the red phosphor can be reduced. As a result, the decrease in the amount of fluorescence L1 emitted in response to the irradiation of excitation light L0 in the wavelength conversion element 30 can be reduced. In other words, the wavelength conversion element 30 can increase the amount of fluorescence L1 emitted in response to the irradiation of excitation light L0.

[0054] Furthermore, in the first embodiment, for example, as shown in Figures 3 to 5, the plurality of phosphor particles 31 may include one or more phosphorus-based phosphor particles (also called first phosphor particles) 31a and one or more non-phosphorus-based phosphor particles (also called second phosphor particles) 31b. In this case, the first region A1 includes a region A1a that is in contact with each of the one or more first phosphor particles 31a (also called the first A region) and a region A1b that is in contact with each of the one or more second phosphor particles 31b (also called the first B region). In Figures 3 to 5, the first phosphor particles 31a are hatched using multiple closely spaced diagonal lines rising to the right, and the second phosphor particles 31b are hatched using multiple closely spaced diagonal lines rising to the left.

[0055] Furthermore, as shown in Figure 5, for example, the abundance of multiple fine crystalline particles 322 in the first A region A1a (also called the first A abundance) may be smaller than the abundance of multiple fine crystalline particles 322 in the first B region A1b (also called the first B abundance). If this configuration is adopted, the presence of many fine crystalline particles 322 in the first B region A1b, which is close to the non-phosphorus second phosphor particles 31b, can improve the rate at which heat is dissipated from the non-phosphorus second phosphor particles 31b by heat transfer and conduction via the fine crystalline particles 322. Here, for example, we assume a case where the rate of thermal degradation of the non-phosphorus second phosphor particles 31b is greater than that of the phosphorus first phosphor particles 31a. In this case, if the rate at which heat is dissipated from the non-phosphorus second phosphor particles 31b by heat transfer and conduction via the fine crystalline particles 322 is improved, the degradation of the non-phosphorus second phosphor particles 31b can be reduced. This reduces the degradation of multiple second phosphor particles 31b in the wavelength conversion element 30. As a result, the decrease in the amount of fluorescence L1 emitted in response to the irradiation of excitation light L0 in the wavelength conversion element 30 can be reduced. In other words, the amount of fluorescence L1 emitted in response to the irradiation of excitation light L0 in the wavelength conversion element 30 can be increased.

[0056] For example, if an EDS device is installed in a scanning electron microscope (SEM), the phosphorus-based phosphor particles (first phosphor particles) 31a and non-phosphorus-based phosphor particles (second phosphor particles) 31b may be distinguished by elemental analysis using the EDS device in the region of the cross-section of the wavelength conversion unit 30t that is the target of the SEM image.

[0057] The first A region A1a may be, for example, a region within a predetermined distance (also called the first A distance) from the surface of one or more phosphorus-based phosphor particles (first phosphor particles) 31a in the binder layer 32. The first B region A1b may be, for example, a region within a predetermined distance (also called the first B distance) from the surface of one or more non-phosphorus-based phosphor particles (second phosphor particles) 31b in the binder layer 32. The first A distance and the first B distance may be the same or different, for example. The first A distance and the first B distance may be set, for example, according to the degree of dispersion of the multiple phosphor particles 31. If one or more first phosphor particles 31a are densely distributed, the first A distance may be smaller than when the multiple first phosphor particles 31a are sparsely distributed. If one or more second phosphor particles 31b are densely distributed, the first B distance may be smaller than when the multiple second phosphor particles 31b are sparsely distributed. The first A distance and the first B distance may each be set according to, for example, the particle size of the multiple fine crystalline particles 322. The first A distance and the first B distance may each be, for example, 2 μm, 3 μm, or any length of 4 μm or more.

[0058] The abundance of multiple fine crystalline particles 322 in the first A region A1a (first A abundance) and the abundance of multiple fine crystalline particles 322 in the first B region A1b (first B abundance) can be compared using various comparison methods. One such comparison method is to compare, for example, the area ratio of multiple fine crystalline particles 322 in the first A region A1a (also called the first A area occupancy rate) and the area ratio of multiple fine crystalline particles 322 in the first B region A1b (also called the first B area occupancy rate) using an SEM image of the cross-section of the wavelength conversion section 30t. In this case, for example, the first A abundance may be the area ratio of multiple fine crystalline particles 322 in a virtual cross-section of the first A region A1a, and the first B abundance may be the area ratio of multiple fine crystalline particles 322 in a virtual cross-section of the first B region A1b. Here, the virtual cross-section of the first A region A1a and the virtual cross-section of the first B region A1b may, for example, be located on the same virtual cross-section of the wavelength conversion unit 30t, or they may be located on different virtual cross-sections of the wavelength conversion unit 30t. Furthermore, the abundance of the first A region may be, for example, the ratio of the volume of the multiple fine crystalline particles 322 in the first A region A1a (also called the first A volume occupancy rate), and the abundance of the first B region may be the ratio of the volume of the multiple fine crystalline particles 322 in the first B region A1b (also called the first B volume occupancy rate).

[0059] Here, the abundance of multiple fine crystalline particles 322 in the first A region A1a (first A abundance) may be, for example, 20% or more and 60% or less. The abundance of multiple fine crystalline particles 322 in the first B region A1b (first B abundance) may be, for example, 40% or more and 80% or less. For example, the first A abundance may be 20% and the first B abundance may be 40%. Alternatively, for example, the first A abundance may be 60% and the first B abundance may be 80%.

[0060] Furthermore, in the first embodiment, the wavelength conversion unit 30t may include a plurality of thermally conductive particles 33, as shown in Figures 3 to 5. In Figures 3 to 5, the plurality of thermally conductive particles 33 are depicted by thick straight lines. Each of the plurality of thermally conductive particles 33 may be located in one or more of the following locations: within the binder layer 32, at the boundary between the plurality of phosphor particles 31 and the binder layer 32, and between two phosphor particles 31. Each of the plurality of thermally conductive particles 33 may be a particle having better thermal conductivity than glass. Each of the plurality of thermally conductive particles 33 may be boron nitride (also called hexagonal boron nitride or h-BN) having a hexagonal crystal structure. For example, if an EDS device is mounted on the scanning electron microscope (SEM), hexagonal boron nitride particles may be detected by elemental analysis using the EDS device in the region of the cross-section of the wavelength conversion unit 30t that is the target of the SEM image.

[0061] Hexagonal boron nitride particles are known to have a plate-like shape and exhibit high thermal conductivity in the direction along the plate surface (also referred to as the direction along the ab plane or the direction along the (002) plane) (see, for example, Natsumi Torase, Junichi Tatami, Shiyuki Iijima, and Takumi Takahashi, "Fabrication of Nitride Phosphor Particle Dispersed h-BN / Glass Composite," Journal of the Japan Society of Powder Technology, Vol. 57, No. 3, 2020, pp. 137-143, etc.). In other words, the thermally conductive particles 33 have high thermal conductivity in the direction along the plate surface. The length of each of the multiple thermally conductive particles 33 along the plate surface may be, for example, about 1 μm to 10 μm, or about 5 μm to 6 μm. In the portion of the thermally conductive particles 33 that is in direct contact with the phosphor particles 31, they have the function of directly conducting the heat of the phosphor particles 31. In the portion of the thermally conductive particle 33 that is in contact with the binder layer 32, it has the function of indirectly conducting heat from the phosphor particle 31 through the binder layer 32.

[0062] Furthermore, as shown in Figures 3 to 5, for example, the plurality of thermally conductive particles 33 may include one or more thermally conductive particles 33 located along the surface of one or more fine crystalline particles 322 that are in contact with the surface of one or more phosphor particles 31. If this configuration is adopted, the fact that the plurality of hexagonal boron nitride (h-BN) particles with excellent thermal conductivity are located along the surface of the fine crystalline particles 322 can improve the rate at which heat is dissipated from the plurality of phosphor particles 31 through heat transfer and conduction via the fine crystalline particles 322 and thermally conductive particles 33. This can reduce the degradation of the plurality of phosphor particles 31. As a result, the decrease in the amount of fluorescence L1 emitted in the wavelength conversion element 30 in response to the irradiation of excitation light L0 can be reduced. In other words, the amount of fluorescence L1 emitted in the wavelength conversion element 30 in response to the irradiation of excitation light L0 can be increased. Here, one thermally conductive particle 33 may be located along the surface of one fine crystalline particle 322 in contact with the surface of one phosphor particle 31, or along the surfaces of two or more fine crystalline particles 322 each in contact with the surface of one phosphor particle 31, or along the surfaces of two or more fine crystalline particles 322 each in contact with the surfaces of two or more phosphor particles 31.

[0063] Furthermore, as shown in Figures 3 to 5, for example, one or more thermally conductive particles 33 located along the surface of one or more fine crystalline particles 322 that are in contact with the surface of one or more phosphor particles 31 may also be in contact with the surface of one or more fine crystalline particles 322 that are in contact with the surface of one or more phosphor particles 31. If this configuration is adopted, the thermally conductive particles 33, which have excellent thermal conductivity, are in contact with the surface of the fine crystalline particles 322 that are in contact with the phosphor particles 31. This can improve the rate at which heat is dissipated from the phosphor particles 31 through heat transfer and conduction via the fine crystalline particles 322 and the thermally conductive particles 33. This can reduce the degradation of multiple phosphor particles 31. As a result, the decrease in the amount of fluorescence L1 emitted in the wavelength conversion element 30 in response to the irradiation of excitation light L0 can be reduced. In other words, the amount of fluorescence L1 emitted in the wavelength conversion element 30 in response to the irradiation of excitation light L0 can be increased.

[0064] Furthermore, in the first embodiment, the binder layer 32 may contain one or more voids 323, for example, as shown in Figure 6. Figure 6 is an image diagram showing an example of the distribution of multiple fine crystalline particles 322 and one or more voids 323 in a part of the configuration of a hypothetical cross-section of the wavelength conversion element 30 according to the first embodiment. The image diagram in Figure 6 is a diagram in which multiple voids 323, each drawn as a white circle, are added to the image diagram shown in Figure 5. In Figure 6, the binder layer 32 contains nine voids 323, but is not limited to this. The binder layer 32 may contain, for example, one void 323, or any number of voids 323, two or more. Here, for example, as shown in Figure 6, the abundance of one or more voids 323 in the first region A1 (also called the third abundance) may be smaller than the abundance of one or more voids 323 in the second region A2 (also called the fourth abundance). If this configuration is adopted, even if voids 323 exist in the binder layer 32, if the abundance of one or more voids 323 in the first region A1 (third abundance) is relatively smaller than the abundance of one or more voids 323 in the second region A2 (fourth abundance), the degree to which the rate of heat radiated from the phosphor particles 31 decreases due to the presence of voids 323 can be reduced. This can reduce the degradation of multiple phosphor particles 31. As a result, the decrease in the amount of fluorescence L1 emitted in the wavelength conversion element 30 in response to the irradiation of excitation light L0 can be reduced. In other words, the amount of fluorescence L1 emitted in the wavelength conversion element 30 in response to the irradiation of excitation light L0 can be increased.

[0065] For example, if an EDS device is mounted on a scanning electron microscope (SEM), elemental analysis using the EDS device may be performed on the region of the cross-section of the wavelength conversion unit 30t that is the target of the SEM image to distinguish between the amorphous phase 321, the fine crystalline grains 322, and the voids 323 in the binder layer 32.

[0066] The comparison between the prevalence of one or more voids 323 in the first region A1 (third prevalence) and the prevalence of one or more voids 323 in the second region A2 (fourth prevalence) can be performed by various comparison methods. One such comparison method is to compare, for example, the area ratio of one or more voids 323 in the first region A1 (also called the third area occupancy) and the area ratio of one or more voids 323 in the second region A2 (also called the fourth area occupancy) in an SEM image targeting the cross-section of the wavelength conversion section 30t. In this case, for example, the third prevalence may be the area ratio of one or more voids 323 in a virtual cross-section of the first region A1, and the fourth prevalence may be the area ratio of one or more voids 323 in a virtual cross-section of the second region A2. Here, the virtual cross-section of the first region A1 and the virtual cross-section of the second region A2 may be located on the same virtual cross-section of the wavelength conversion unit 30t, or they may be located on different virtual cross-sections of the wavelength conversion unit 30t. Furthermore, the third abundance may be, for example, the ratio of the volume of one or more voids 323 in the first region A1 (also called the third volume occupancy), and the fourth abundance may be the ratio of the volume of one or more voids 323 in the second region A2 (also called the fourth volume occupancy).

[0067] <1-3. Method for manufacturing wavelength conversion elements> Figure 7 is a flowchart showing an example of the manufacturing flow of the wavelength conversion element 30 according to the first embodiment. Figures 8 to 12 are cross-sectional views showing examples of states during the manufacturing of the wavelength conversion element 30. Figure 13 is a schematic cross-sectional view showing an image of the state immediately before the appearance of fine crystalline particles 322 during the manufacturing of the wavelength conversion element 30. Figure 14 is a schematic cross-sectional view showing an image of the state immediately after the appearance of fine crystalline particles 322 during the manufacturing of the wavelength conversion element. The manufacturing method of the wavelength conversion element 30 will be described below with reference to Figure 7 and using Figures 8 to 14.

[0068] First, prepare the substrate 30b as shown in Figure 8 (Step S1). For the substrate 30b, metallic materials such as Cu, Al, Mg, Au, Ag, Fe, Cr, Co, Be, Mo, W, or alloys may be used. Alternatively, non-metallic materials such as AlN, GaN, SiC, Si3N4, C, Al2O3, MgO, or garnet may be used.

[0069] Next, as shown in Figure 9, a mask 30m having an opening 30o corresponding to the planar shape of the wavelength conversion section 30t is superimposed on the third surface F3, which is the main surface of the substrate 30b on the side where the wavelength conversion section 30t is formed (step S2). For example, aluminum may be used as the material for the mask 30m. In this case, the opening 30o with the desired planar shape can be formed by etching or the like. The thickness of the mask 30m is set to be greater than the thickness of the wavelength conversion section 30t. For example, if the thickness of the wavelength conversion section 30t is 0.1 mm, the thickness of the mask 30m may be set to 0.15 mm to 0.2 mm. Here, for example, the material of the mask 30m may be resin. There are no limitations on the material of the mask as long as it is possible to form an opening 30o of the desired shape and has sufficient strength to withstand the next powder filling process.

[0070] Next, as shown in Figure 10, a powder (also called mixed powder) obtained by thoroughly mixing one or more types of phosphor particle powder 31 (also called phosphor powder), glass powder (also called glass powder), and thermal conductive particle powder 33 (also called thermal conductive powder) is filled into the opening 30o of the mask 30m to form a powder packing body PW (step S3).

[0071] In this mixed powder, for example, the content of the phosphor powder is approximately 10 wt% to 80 wt%, the content of the glass powder is approximately 20 wt% to 90 wt%, and the content of the thermally conductive powder is approximately 0 wt% to 30 wt%.

[0072] The phosphor powder contains, for example, particles of a red phosphor, particles of a green phosphor, and particles of a blue phosphor. As the material of the red phosphor, as described above, for example, CaAlSiN3:Eu, Y3O3S:Eu, Y3O3:Eu, SrCaClAlSiN3:Eu 2+ or CaAlSi(ON)3:Eu etc. may be adopted. As the material of the green phosphor, as described above, for example, β-sialon (β-SiAlON:Eu), SrSi2(O,Cl)2N2:Eu, (Sr,Ba,Mg)2SiO4:Eu2 2+ , ZnS:Cu,Al or Zn2SiO4:Mn etc. may be adopted. As the material of the blue phosphor, for example, (Ba,Sr)MgAl 10 O 17 :Eu, BaMgAl 10 O 17 :Eu, (Sr,Ca,Ba) 10 (PO4)6Cl2:Eu, (Sr,Ba) 10 (PO4)6Cl2:Eu or α-sialon etc. may be adopted. The particle size distribution of the phosphor powder may have various particle diameter distributions. For example, the phosphor powder may contain phosphor particles 31 with a 50% particle diameter (D50) in the range of 0.1 μm to 100 μm, or may contain phosphor particles 31 with a D50 in the range of 10 μm to 30 μm.

[0073] The glass powder may be, for example, a powder of a low melting point glass that has transparency after sintering. As the low melting point glass, an oxide glass with a melting point (Tm) of 200°C to 700°C may be adopted. As this oxide glass, as described above, for example, a glass containing two or more of the oxides of SiO2, Al2O3, B2O3, Na2O3, K2O, Li2O, CaO, BaO, ZnO, PbO and P2O5 as the main components may be adopted. The particle size distribution of the glass powder may, like the particle size distribution of the phosphor powder, have various particle diameter distributions. For example, the glass powder may contain glass particles with a D50 in the range of 0.1 μm to 100 μm, or may contain glass particles with a D50 in the range of 10 μm to 20 μm.

[0074] The thermally conductive powder may be, for example, a powder of hexagonal boron nitride (h-BN) particles as thermally conductive particles 33. The hexagonal boron nitride particles have a plate-like shape. The particle size distribution of the thermally conductive powder may have a distribution of various particle sizes. For example, the thermally conductive powder may contain thermally conductive particles 33 with a 50% particle size (D50) in the range of 1 μm to 10 μm, or it may contain thermally conductive particles 33 with a D50 in the range of 5 μm to 6 μm.

[0075] Vibration or rotational oscillation methods can be used to mix the phosphor powder, glass powder, and thermal conductive powder. A media may also be used when mixing the phosphor powder, glass powder, and thermal conductive powder. This media can be used in various methods for mixing multiple types of powders, such as a dry method where multiple types of powders are mixed directly in powder form, and a wet method where multiple types of powders are mixed with a solvent or binder.

[0076] Next, as shown in Figure 11, the mask 30m is removed from the substrate 30b on which the powder-filled body PW is formed (step S4), and the powder-filled body PW is heated to form a pre-sintered body PS (step S5). Here, the heating temperature is set to be above the melting point (Tm) of the glass constituting the glass powder, and lower than the temperature at which the phosphor particles 31 lose their fluorescence function. For example, the heating temperature may be in the temperature range of 260°C to 600°C, or in the temperature range of 350°C to 450°C.

[0077] The heating and pressurizing processes of the powder-filled body PW and the pre-sintered body PS, as described below, are carried out, for example, in a common chamber. This chamber may or may not be a vacuum chamber. For example, if the chamber is a vacuum chamber, the chamber can be kept under vacuum during heating. For example, heating under vacuum reduces the generation of bubbles when the glass powder melts. The heating and pressurizing processes of the powder-filled body PW and the pre-sintered body PS may be carried out, for example, in the atmosphere. The heating and pressurizing processes of the powder-filled body PW and the pre-sintered body PS may be carried out, for example, using a multi-purpose high-temperature sintering furnace, or using a heater block and a hand press.

[0078] Next, as shown in Figure 12, after the heating temperature reaches the set temperature, the pre-sintered body PS is subjected to pressure processing on the substrate 30b while maintaining the set temperature (step S6). The pressure during the pressure processing can be set to a pressure that does not physically crush the phosphor particles 31 and cause them to lose their fluorescent function. For example, the pressure during the pressure processing may be 20 kgf / cm². 2 From 300 kgf / cm² 2 The pressure is set to approximately 2 MPa to 30 MPa. Here, the temporary sintered body PS is subjected to pressure processing at a pressure that satisfies this condition for a period of, for example, 30 seconds to 30 minutes.

[0079] Next, the pre-sintered body PS is held at a predetermined temperature (also called the first predetermined temperature) while maintaining the pressure applied to the pre-sintered body PS during the pressurizing process (step S7). During this time, the pre-sintered body PS is held at the first predetermined temperature for a period of, for example, 30 seconds to 30 minutes. The first predetermined temperature is set to a temperature between the crystallization temperature (Tc) and the melting point (Tm) of the glass that constituted the glass powder. Here, for example, the glass is in an energetically unstable state in the part of the glass that is in contact with the phosphor particles 31, so at least some of the components constituting the glass can crystallize, mainly starting from the surface of the multiple phosphor particles 31. For example, as shown in Figures 13 and 14, at least some of the components constituting the glass 32p can crystallize, mainly starting from the surface of the multiple phosphor particles 31, thereby generating multiple fine crystalline particles 322. In Figures 13 and 14, hatching using a low-density matte pattern is applied to the glass 32p portion. Furthermore, in Figures 13 and 14, as in Figures 3 and 4, multiple phosphor particles 31 are each hatched with multiple closely spaced diagonal lines, multiple thermal conductive particles 33 are depicted with straight, thick lines, and multiple fine crystalline particles 322 are not hatched for convenience.

[0080] Next, while maintaining the pressure applied to the pre-sintered body PS during pressurization, the pre-sintered body PS is cooled to a temperature lower than the glass transition temperature (Tg) (step S8). When the temperature of the pre-sintered body PS falls below the glass transition temperature (Tg) of the glass that constituted the glass powder, the pressure is released. As a result, the pre-sintered body PS becomes a wavelength conversion section 30t having a configuration such as that shown in Figures 3 to 5. That is, as described above, a wavelength conversion section 30t can be obtained in which the abundance of multiple fine crystalline particles 322 in the first region A1 (first abundance) is greater than the abundance of multiple fine crystalline particles 322 in the second region A2 (second abundance).

[0081] By following the steps described above, the wavelength conversion element 30 can be manufactured.

[0082] In the above manufacturing method, for example, by controlling the first predetermined temperature and the length of the period during which the pre-sintered body PS is held at the first predetermined temperature, the distribution, number, and size of the multiple fine crystalline particles 322 can be adjusted. For example, a wavelength conversion unit 30t can be obtained having a configuration in which the abundance of multiple fine crystalline particles 322 in the first region A1 (first abundance) is 40% or more and 80% or less, and the abundance of multiple fine crystalline particles 322 in the second region A2 (second abundance) is 10% or more and 20% or less.

[0083] Furthermore, in the above manufacturing method, for example, one or more phosphor particles 31 constituting the phosphor powder may include phosphor particles 31 containing nitride. In this case, for example, a wavelength conversion unit 30t can be obtained in which one or more phosphor particles 31 in contact with one or more fine crystalline particles 322, as described above, include phosphor particles 31 containing nitride.

[0084] Furthermore, in the above manufacturing method, for example, one or more phosphorus particles 31 constituting the phosphor powder may include phosphorus-based phosphorus particles (first phosphorus particles) 31a and non-phosphorus-based phosphorus particles (second phosphorus particles) 31b. In this case, for example, the surface of the phosphorus-based first phosphorus particles 31a may have fewer irregularities than the surface of the non-phosphorus-based second phosphorus particles 31b. In this case, for example, during the period in which the pre-sintered body PS is held at a first predetermined temperature, the area of ​​the interface between the glass and the phosphorus-based first phosphorus particles 31a becomes smaller than the area of ​​the interface between the glass and the non-phosphorus-based second phosphorus particles 31b. As a result, the degree to which at least some of the components constituting the glass crystallize starting from the surface of the phosphorus-based first phosphorus particles 31a may be smaller than the degree to which at least some of the components constituting the glass crystallize starting from the surface of the non-phosphorus-based second phosphorus particles 31b. As a result, for example, a wavelength conversion unit 30t can be obtained having a configuration in which the abundance of multiple fine crystalline particles 322 in the first A region A1a (first A abundance) is smaller than the abundance of multiple fine crystalline particles 322 in the first B region A1b (first B abundance). Here, the state in which the surface of the phosphor particles 31 has relatively few irregularities may be, for example, a state in which the density of irregularities on the surface of the phosphor particles 31 is relatively small, or a state in which the density of irregularities on the surface of the phosphor particles 31 is equal to or greater than and the size of the irregularities is relatively large.

[0085] Furthermore, in the above manufacturing method, for example, when applying pressure processing to the pre-sintered body PS in step S6 described above, if the content of multiple phosphor particles 31 in the pre-sintered body PS is sufficiently high, the number of areas where the spacing between the multiple phosphor particles 31 is narrow can increase. As a result, for example, molten glass can flow between the multiple phosphor particles 31 by capillary action. At that time, a portion may be formed in which multiple thermal conductive particles 33 are located along the surface of the multiple phosphor particles 31. In the subsequent step S7 described above, when multiple fine crystalline particles 322 are generated starting from the surface of the multiple phosphor particles 31, some of the multiple thermal conductive particles 33 may be located along the multiple fine crystalline particles 322 that were generated starting from the surface of the multiple phosphor particles 31. Therefore, for example, a wavelength conversion unit 30t can be obtained having a configuration in which the multiple thermal conductive particles 33 described above include one or more thermal conductive particles 33 located along the surface of one or more fine crystalline particles 322. Here, for example, by controlling the first predetermined temperature and the length of time the pre-sintered body PS is held at the first predetermined temperature, the size of the multiple fine crystalline particles 322 can be adjusted, so that some of the multiple thermal conductive particles 33 can come into contact with the surface of the multiple fine crystalline particles 322 that originated from the surface of the multiple phosphor particles 31. Therefore, for example, a wavelength conversion unit 30t can be obtained having a configuration in which one or more thermal conductive particles 33 located along the surface of one or more fine crystalline particles 322, as described above, are in contact with the surface of one or more fine crystalline particles 322 that are in contact with the surface of one or more phosphor particles 31.

[0086] Furthermore, in the above manufacturing method, if, for example, a material that easily forms an oxide film, such as aluminum, is used for the base material 30b, the base material 30b and the wavelength conversion unit 30t are bonded by oxidative bonding. In this case, the base material 30b and the wavelength conversion unit 30t are bonded by oxidative bonding, where the oxygen of the oxide film formed on the surface of the base material 30b by heating combines with the oxygen of the oxide glass. This can increase the bonding strength between the base material 30b and the wavelength conversion unit 30t.

[0087] Furthermore, in the above manufacturing method, if, for example, a material that is not easily oxidized is used for the substrate 30b, minute irregularities of several μm may be provided on the surface of the substrate 30b, and the glass may be entangled in these irregularities to increase the bonding force between the substrate 30b and the wavelength conversion unit 30t by an anchoring effect. In other words, the surface of the substrate 30b may have an irregular shape (minute irregularities). For example, the size of the minute irregularities referred to here should be such that the low-melting-point glass that has liquefied during heating flows and enters these minute irregularities. In this case, the size of the minute irregularities can be set to, for example, 0.1 μm to 50 μm. Alternatively, the size of the minute irregularities may be set to such that the phosphor particles 31 enter these minute irregularities. In this case, the size of the minute irregularities can be set to, for example, 5 μm to 50 μm. The size of the minute irregularities (irregularities in the irregular shape) of the base material 30b referred to here means, for example, the dimension between the bottom (lowest point) of the recess and the top (highest point) of the convex part of the minute irregularities in the thickness direction of the base material 30b.

[0088] Furthermore, in the above manufacturing method, if, for example, a material is used for the base material 30b that cannot be expected to exhibit oxidative bonding or anchoring effects, the wavelength conversion section 30t and the base material 30b may be prepared separately. In this case, for example, instead of forming the wavelength conversion section 30t on the base material 30b, a powder packing body PW may be formed separately from the base material 30b, the powder packing body PW may be heated to form a pre-sintered body PS, and the wavelength conversion section 30t may be obtained by performing pressure processing on the pre-sintered body PS. In this case, a multilayer metal film may be formed on the surface of the wavelength conversion section 30t facing the base material 30b, and the wavelength conversion section 30t and the base material 30b may be joined by soldering.

[0089] Here, an example of a multilayer film is a multilayer film in which thin films of titanium (Ti), platinum (Pt), and gold (Au) are stacked in that order from the wavelength conversion section 30t side (also called a Ti / Pt / Au multilayer film). This multilayer film can be formed to a thickness of several nanometers to several hundred nanometers by, for example, sputtering or vapor deposition. Here, Ti is a material that has good bonding properties with oxide glass, and Au is a material that has good wettability with solder material. The Pt film functions as a barrier film that reduces the peeling of the Ti film from the wavelength conversion section 30t by the molten solder material when the solder material melts. As for the multilayer film, for example, a multilayer film in which thin films of chromium (Cr), Pt, and Au are stacked in that order from the wavelength conversion section 30t side (also called a Cr / Pt / Au multilayer film) or a multilayer film in which thin films of Cr, nickel (Ni), and Au are stacked in that order from the wavelength conversion section 30t side (also called a Cr / Ni / Au multilayer film) may be used. Here, for example, the thickness of the Ti thin film may be about 0.1 μm, the thickness of the Pt thin film may be about 0.2 μm, and the thickness of the Au thin film may be about 0.2 μm. Also, as the solder material, for example, tin (Sn)-phosphorus (P)-copper (Cu) solder or Au-Sn solder may be used.

[0090] <1-4. Summary of the First Embodiment> In the wavelength conversion element 30 according to the first embodiment, for example, one or more fine crystalline particles 322 are in contact with one or more of the phosphor particles 31. Here, the thermal conductivity of the fine crystalline particles 322 is higher than that of the amorphous phase 321, and the presence of the fine crystalline particles 322 in contact with the phosphor particles 31 can improve the rate at which heat is dissipated from the phosphor particles 31 by heat transfer and conduction through the fine crystalline particles 322. This can reduce the degradation of the multiple phosphor particles 31. As a result, the decrease in the amount of fluorescence L1 emitted in response to the irradiation of excitation light L0 in the wavelength conversion element 30 can be reduced. In other words, the amount of fluorescence L1 emitted in response to the irradiation of excitation light L0 in the wavelength conversion element 30 can be increased.

[0091] Furthermore, in the wavelength conversion element 30 according to the first embodiment, for example, when the binder layer 32 is divided into a first region A1 that is in contact with each of the plurality of phosphor particles 31 and a second region A2 that is away from the plurality of phosphor particles 31, the abundance of the plurality of fine crystalline particles 322 in the first region A1 (first abundance) is greater than the abundance of the plurality of fine crystalline particles 322 in the second region A2 (second abundance). Here, in the binder layer 32, there are relatively more fine crystalline particles 322 in the first region A1 that is close to the plurality of phosphor particles 31 than in the second region A2 that is away from the plurality of phosphor particles 31. As a result, in the second region A2, the interface between the plurality of fine crystalline particles 322 and the amorphous phase 321 may decrease due to the decrease in the plurality of fine crystalline particles 322. This may reduce Fresnel reflection at the interface between the plurality of fine crystalline particles 322 and the amorphous phase 321, and may also reduce the amount of excitation light L0 absorbed by the plurality of fine crystalline particles 322. As a result, the amount of excitation light L0 incident on multiple phosphor particles 31 can increase. Therefore, the amount of fluorescence L1 emitted in the wavelength conversion element 30 in response to the irradiation of excitation light L0 can be increased.

[0092] <2. Other Embodiments> This disclosure is not limited to the first embodiment described above, and various modifications and improvements are possible without departing from the gist of this disclosure.

[0093] <2-1. Second Embodiment> In the first embodiment described above, for example, the substrate 30b may be a substrate having various structures on which the wavelength conversion unit 30t is arranged.

[0094] Figure 15 is a perspective view showing an example of the configuration of the wavelength conversion element 30A according to the second embodiment. Figure 16 is a cross-sectional view showing an example of the configuration of the wavelength conversion element 30A according to the second embodiment.

[0095] As shown in Figures 15 and 16, the wavelength conversion element 30 according to the first embodiment may be changed to a wavelength conversion element 30A in which, for example, the wavelength conversion part 30t is located in a recess 30r of a substrate 30bA. The recess 30r has a third surface F3 as a bottom surface and a fourth surface F4 as a side surface. The second surface F2 of the wavelength conversion part 30t is fixed to the third surface F3 of the recess 30r. The side surface of the wavelength conversion part 30t is in contact with the fourth surface F4 of the recess 30r.

[0096] If this configuration is adopted, excitation light L0 that is scattered inside the wavelength conversion unit 30t and not converted to fluorescence L1 can be reflected by the fourth surface F4, which is the side surface of the recess 30r of the substrate 30bA, and return to the inside of the wavelength conversion unit 30t, where it can be converted to fluorescence L1. In addition, since the side surface of the wavelength conversion unit 30t is in contact with the fourth surface F4 of the recess 30r, the heat generated in the wavelength conversion unit 30t can be dissipated to the outside from the fourth surface F4 through the substrate 30b, thereby reducing the temperature rise of the wavelength conversion unit 30t.

[0097] Figure 17 is a flowchart showing an example of the manufacturing flow of the wavelength conversion element 30A according to the second embodiment. The manufacturing method of the wavelength conversion element 30A will be described below with reference to Figure 17.

[0098] First, a substrate 30bA is prepared as shown in Figures 18 and 19 (Step S11). Figure 18 is a perspective view showing an example of the configuration of the substrate 30bA according to the second embodiment. Figure 19 is a cross-sectional view showing an example of the configuration of the substrate 30bA according to the second embodiment. The substrate 30bA has an overall disc shape and has a recess 30r on the first plate surface. The depth of the recess 30r of the substrate 30bA is set to, for example, 0.01 mm to 1 mm. The thickness of the portion of the substrate 30bA located on the -Z side of the bottom surface of the recess 30r is set to, for example, 0.05 mm to 10 mm. The depth of the recess 30r is set to be greater than the thickness of the wavelength conversion section 30t. For example, if the thickness of the wavelength conversion section 30t is 0.1 mm, the depth of the recess 30r is set to 0.15 mm to 0.2 mm. Furthermore, for example, the diameter of the base material 30bA is set from 0.5 mm to 30 mm, and the diameter of the recess 30r is set from 0.1 mm to 10 mm.

[0099] The material used for the base material 30bA is one that has a thermal expansion coefficient close to that of the wavelength conversion section 30t. For example, a metallic or inorganic material with a thermal expansion coefficient of ±50% of the thermal expansion coefficient of the glass constituting the binder layer 32 of the wavelength conversion section 30t may be used. For example, if a metallic material is used for the base material 30bA, aluminum or an aluminum alloy may be used as the metallic material. For example, if a material with high light reflectivity such as aluminum is used for the base material 30bA, the reflectivity of visible light on the surface of the base material 30bA may be improved by processing the surface of the base material 30bA to a mirror finish by physical polishing or chemical polishing. Also, if a metallic material is used for the base material 30bA, the base material 30bA may be formed by cutting by machining or molding by die casting, for example.

[0100] Furthermore, ceramics may be used as the material for the base material 30bA. In this case, the base material 30bA may be formed using multilayer ceramics, or it may be formed by pressure molding of powder. For example, the base material 30bA can be formed by multilayer ceramics by laminating a ring-shaped green sheet with a through hole corresponding to the recess 30r and a disc-shaped green sheet without a through hole, and then sintering them. Alternatively, for example, the base material 30bA can be formed by pressure molding of powder by filling a first mold having a cylindrical opening with ceramic powder and applying pressure to the ceramic powder filled in the first mold using a second mold for creating a recess (corresponding to the recess 30r). For example, the base material 30bA can be formed by mixing ceramic powder with wax and a binder, applying pressure to form a molded body with a recess corresponding to the recess 30r, and then sintering this molded body. Ceramics applicable to the material of the base material 30bA include, for example, alumina, aluminum nitride, silicon nitride, mullite, and zirconia.

[0101] Furthermore, the base material 30bA may be formed from ceramics and metal. For example, the base material 30bA can be formed by joining a ring-shaped metal member (also called a metal member) made of aluminum or an aluminum alloy to a disc-shaped ceramic substrate using a bonding material. In this case, the through-hole of the ring-shaped member becomes the recess 30r. As the bonding material, for example, a brazing material mainly composed of Ag or Cu may be used. Alternatively, the bonding material may be a brazing material mainly composed of Al, solder mainly composed of Sn, Ag and Cu, or a resin bonding material such as epoxy, silicone or acrylic. In the resin bonding material, for example, the thermal conductivity of the base material 30bA may be increased by adding a filler with high thermal conductivity (also called a high thermal conductivity filler) such as Ag, AlN or boron nitride (BN).

[0102] Furthermore, the base material 30bA may not be formed by integral firing of laminated ceramics, but rather by joining a ceramic substrate and a ceramic ring-shaped member with a bonding material. In this case as well, the bonding material described above can be used.

[0103] Now, returning to the explanation of Figure 17, next, a powder (mixed powder) obtained by thoroughly mixing one or more types of phosphor particle 31 powder (phosphor powder), glass powder, and thermal conductive particle 33 powder (thermal conductive powder) is filled into the recess 30r to form a powder filler (step S12). Here, the explanation of the respective contents of phosphor powder, glass powder, and thermal conductive powder in the mixed powder, the materials, composition, and mixing method of the phosphor particle 31, glass powder, and thermal conductive particle 33 will be omitted as it will be redundant with the explanation in the first embodiment above.

[0104] Next, the powder filler, along with the substrate 30bA in which the powder filler is filled in the recess 30r, is heated to form a pre-sintered body (step S13). The explanation of heating the powder filler will be omitted as it will be redundant with the explanation in the first embodiment described above.

[0105] Next, after the heating temperature reaches the set temperature, the pre-sintered body is subjected to pressure processing on the substrate 30bA while maintaining the set temperature (step S14). The explanation of heating and pressure processing of the pre-sintered body will be omitted as it will overlap with the explanation in the first embodiment above.

[0106] Next, the pre-sintered body is held at a predetermined temperature (first predetermined temperature) while maintaining the pressure applied to the pre-sintered body during the pressurizing process (step S15). The explanation of the process of holding the pre-sintered body at the first predetermined temperature is omitted as it overlaps with the explanation in the first embodiment described above.

[0107] Next, while maintaining the pressure applied to the pre-sintered body during the pressurizing process, the pre-sintered body is cooled to a temperature lower than the glass transition temperature (Tg) (step S16). Once the temperature of the pre-sintered body falls below the glass transition temperature (Tg) of the glass that constituted the glass powder, the pressure is released.

[0108] The wavelength conversion element 30A can be manufactured by the above steps. Furthermore, for example, since the powder filling is formed in the recess 30r of the substrate 30bA, the steps of superimposing the mask 30m onto the substrate in step S2 and removing the mask 30m in step S4 become unnecessary compared to the manufacturing method of the wavelength conversion element 30 according to the first embodiment described using the manufacturing flow in Figure 7, thus simplifying the manufacturing process.

[0109] Here, the wavelength conversion element 30A shown in Figure 15 had a configuration in which a recess 30r with a circular shape in plan view was provided on the upper surface of a disc-shaped substrate 30bA. However, the substrate 30bA is not limited to a disc shape, and the shape of the recess 30r in plan view is not limited to a circle.

[0110] Here, for example, the shape of the internal space of the recess 30r of the base material 30bA is not limited to a plate-like or columnar shape. The shape of the internal space of the recess 30r of the base material 30bA may be a cone-like shape such as a cone or pyramidal shape, or it may be a hemispherical or semi-ellipsoidal shape. In these cases, the base material 30bA may have a third surface F3 as the bottom surface of the recess 30r, but may not have a fourth surface F4 as the side surface of the recess 30r.

[0111] Here, the first surface F1 of the wavelength conversion section 30t may be a flat surface along the XY plane, or it may not be a flat surface along the XY plane, as long as it is a surface parallel to the third surface F3 which is the bottom surface of the recess 30r.

[0112] For example, if the shape of the internal space of the recess 30r of the base material 30bA is conical, such as a cone or pyramidal shape, the first surface F1 of the wavelength conversion section 30t may be, for example, a flat surface along the XY plane, or a surface parallel to the third surface F3. The wavelength conversion section 30t may have a conical shape, such as a cone or pyramidal shape, corresponding to the shape of the recess 30r, or it may have a plate-like shape curved along the third surface F3.

[0113] For example, if the shape of the internal space of the recess 30r of the base material 30bA is hemispherical or semi-ellipsoidal, the first surface F1 of the wavelength conversion section 30t may be, for example, a flat surface along the XY plane or a surface parallel to the third surface F3. The wavelength conversion section 30t may have a hemispherical or semi-ellipsoidal shape corresponding to the shape of the recess 30r, or it may have a plate-like shape curved along the third surface F3.

[0114] The wavelength conversion section 30t having a recessed first surface F1 can be realized, for example, by pressing the pre-sintered body with a pressing body having a convex portion corresponding to the shape of the third surface F3 during pressurization processing.

[0115] <2-2. Third Embodiment> In each of the above-described first and second embodiments, for example, the wavelength conversion section 30t does not need to include a plurality of thermally conductive particles 33. Figure 20 is a schematic diagram illustrating an example of the configuration of a hypothetical cross-section of the wavelength conversion elements 30, 30A according to the third embodiment, specifically the portion corresponding to section IV enclosed by the dashed line in Figure 3. The diagram in Figure 20 is obtained by removing the plurality of thermally conductive particles 33 from the diagram in Figure 4.

[0116] In this case, for example, when manufacturing the wavelength conversion elements 30 and 30A, the mixed powder may be a powder obtained by thoroughly mixing one or more types of phosphor particle powders 31 (phosphor powder) and glass powder.

[0117] <3. Others> In each of the above embodiments, for example, each of the one or more types of phosphor particles 31 corresponding to the plurality of phosphor particles 31 may be a single type of phosphor particle 31 that emits fluorescence having a single wavelength spectrum in response to irradiation with excitation light L0.

[0118] Furthermore, for example, the multiple types of phosphor particles 31 contained in the multiple phosphor particles 31 may include at least a first type of phosphor particle 31 that emits a first fluorescence having a first wavelength spectrum in response to irradiation with excitation light L0, and a second type of phosphor particle 31 that emits a second fluorescence having a second wavelength spectrum different from the first wavelength spectrum in response to irradiation with excitation light L0. As the first type of phosphor particle 31 and the second type of phosphor particle 31, for example, two types of phosphor particles selected from red phosphor particles, green phosphor particles, and blue phosphor particles may be used.

[0119] Furthermore, for example, the multiple types of phosphor particles 31 contained in the multiple phosphor particles 31 may include a third type of phosphor particle 31 that emits a third fluorescence having a third wavelength spectrum different from both the first and second wavelength spectra in response to irradiation with excitation light L0. The first type of phosphor particle 31, the second type of phosphor particle 31, or the third type of phosphor particle 31 may be phosphor particles that emit fluorescence of various colors in response to irradiation with excitation light L0, such as blue-green phosphor particles or yellow phosphor particles.

[0120] A blue-green phosphor is a phosphor that emits blue-green fluorescence in response to irradiation with excitation light L0. A yellow phosphor is a phosphor that emits yellow fluorescence in response to irradiation with excitation light L0. For example, a blue-green phosphor is used in which the wavelength peak of the fluorescence emitted in response to irradiation with excitation light L0 is in the range of approximately 495 nm. Examples of materials for blue-green phosphors include (Sr,Ba,Ca)5(PO4)3Cl:Eu or Sr4Al 14 O 25 Elements such as :Eu are used. As a yellow phosphor, for example, a phosphor whose fluorescence wavelength peak in response to irradiation with excitation light L0 is in the range of approximately 570 nm to 590 nm is used. As a material for the yellow phosphor, for example, SrSi2(O,Cl)2N2:Eu is used. Here, the proportion of the elements in parentheses can be arbitrarily set as long as it is within the range of the molecular formula.

[0121] Furthermore, for example, the multiple types of phosphor particles 31 contained in the multiple phosphor particles 31 may include four or more types of phosphor particles 31.

[0122] In each of the above embodiments, for example, the light source unit 2 and the conversion unit 3 may be located in close proximity. In this case, the excitation light L0 emitted from the light source unit 2 may be directly irradiated onto the wavelength conversion elements 30, 30A of the conversion unit 3, or it may be irradiated via an optical element such as a collimator lens.

[0123] In each of the above embodiments, for example, the wavelength conversion element 30 may not have a base material 30b, but may have a wavelength conversion section 30t. In this case, the binder layer 32 included in the wavelength conversion section 30t may be located, for example, between at least a plurality of phosphor particles 31. Here, for example, a powder packing body PW may be formed separately from the base material 30b using a mold or the like, the powder packing body PW may be heated to form a pre-sintered body PS, and the pre-sintered body PS may be subjected to pressure processing or the like to obtain the wavelength conversion section 30t as a wavelength conversion element.

[0124] As described above, wavelength conversion elements have been explained in detail, but the above explanation is illustrative in all respects, and this disclosure is not limited thereto. Furthermore, the various examples described above can be combined and applied insofar as they do not contradict each other. And it is understood that countless examples not illustrated can be conceived without falling outside the scope of this disclosure.

[0125] This disclosure includes the following:

[0126] In one embodiment, (1) the wavelength conversion element comprises a wavelength conversion section including a plurality of phosphor particles and a binder layer that bonds the plurality of phosphor particles together and includes glass, wherein the binder layer includes a plurality of fine crystalline particles and an amorphous phase, the plurality of fine crystalline particles include one or more fine crystalline particles in contact with one or more of the plurality of phosphor particles, each of the plurality of fine crystalline particles includes at least a portion of the components contained in the amorphous phase, and when the binder layer is divided into a first region in contact with each of the plurality of phosphor particles and a second region away from the plurality of phosphor particles, the abundance of the plurality of fine crystalline particles in the first region is greater than the abundance of the plurality of fine crystalline particles in the second region.

[0127] (2) In the wavelength conversion element described in (1) above, the abundance of the plurality of fine crystal particles in the first region may be 40% or more and 80% or less, and the abundance of the plurality of fine crystal particles in the second region may be 10% or more and 20% or less.

[0128] (3) In the wavelength conversion element of (1) or (2) above, the one or more phosphor particles may include nitrides.

[0129] (4) In any one of the wavelength conversion elements described in (1) to (3) above, the plurality of phosphor particles include one or more first phosphor particles containing phosphorus and one or more second phosphor particles not containing phosphorus, and the first region includes a first A region in contact with the one or more first phosphor particles and a first B region in contact with the one or more second phosphor particles, and the abundance of the plurality of fine crystalline particles in the first A region may be less than the abundance of the plurality of fine crystalline particles in the first B region.

[0130] (5) In any one of the wavelength conversion elements described in (1) to (4) above, the binder layer includes one or more voids, and the abundance of the one or more voids in the first region may be less than the abundance of the one or more voids in the second region.

[0131] (6) In any one of the wavelength conversion elements described in (1) to (5) above, the wavelength conversion portion includes a plurality of thermally conductive particles, each containing hexagonal boron nitride, and the plurality of thermally conductive particles may include one or more thermally conductive particles located along the surface of one or more fine crystal particles.

[0132] (7) In the wavelength conversion element described in (6) above, the one or more thermally conductive particles may be in contact with the surface of the one or more fine crystalline particles.

[0133] (8) Any one of the wavelength conversion elements described in (1) to (7) above further comprises a substrate supporting the wavelength conversion unit, wherein the thermal conductivity of the substrate may be higher than the thermal conductivity of the wavelength conversion unit. [Explanation of Symbols]

[0134] 30,30A Wavelength Conversion Element 30b,30bA base material 30t Wavelength Conversion Unit 31 Phosphorescent particles 31a First phosphor particle 31b Second phosphor particle 32 Binder Layers 321 Amorphous phase 322 Fine crystalline grains 323 void 33 Thermally conductive particles A1 1st area A1a Area 1A A1b Area 1B A2 2nd area L0 excitation light L1 fluorescence

Claims

1. A wavelength conversion section comprises a plurality of phosphor particles and a binder layer containing glass that bonds the plurality of phosphor particles together, The binder layer comprises a plurality of fine crystalline particles and an amorphous phase. The plurality of fine crystalline particles include one or more fine crystalline particles that are in contact with one or more of the plurality of phosphor particles. Each of the plurality of fine crystalline particles contains at least some of the components contained in the amorphous phase, When the binder layer is divided into a first region in contact with each of the plurality of phosphor particles and a second region away from the plurality of phosphor particles, the abundance of the plurality of fine crystalline particles in the first region is greater than the abundance of the plurality of fine crystalline particles in the second region. The plurality of phosphor particles include one or more first phosphor particles containing phosphorus and one or more second phosphor particles that do not contain phosphorus. The first region includes a first A region in contact with one or more first phosphor particles and a first B region in contact with one or more second phosphor particles. A wavelength conversion element wherein the abundance of the plurality of fine crystal particles in the first A region is smaller than the abundance of the plurality of fine crystal particles in the first B region.

2. A wavelength conversion element according to claim 1, The abundance of the plurality of fine crystalline particles in the first region is 40% or more and 80% or less. A wavelength conversion element in which the abundance of the plurality of fine crystal particles in the second region is 10% or more and 20% or less.

3. A wavelength conversion element according to claim 1 or claim 2, The one or more phosphor particles mentioned above are wavelength conversion elements containing nitrides.

4. A wavelength conversion element according to claim 1 or claim 2, The binder layer includes one or more voids, A wavelength conversion element wherein the abundance of one or more voids in the first region is less than the abundance of one or more voids in the second region.

5. A wavelength conversion element according to claim 1 or claim 2, The wavelength conversion unit includes a plurality of thermally conductive particles, each containing hexagonal boron nitride, A wavelength conversion element comprising one or more thermally conductive particles located along the surface of one or more fine crystalline particles.

6. A wavelength conversion element according to claim 5, A wavelength conversion element in which the one or more thermally conductive particles are in contact with the surface of the one or more fine crystalline particles.

7. A wavelength conversion element according to claim 1 or claim 2, The substrate supporting the wavelength conversion section further comprises, A wavelength conversion element wherein the thermal conductivity of the substrate is higher than that of the wavelength conversion section.

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