Wavelength conversion element and light emitting device

Abstract

To improve the efficiency and quantity of light in a wavelength conversion element.SOLUTION: A wavelength conversion element comprises 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 to each other and includes glass. The thickness of the wavelength conversion unit is 30 μm or more and 100 μm or less. The volume concentration of the plurality of phosphor particles in the wavelength conversion unit is 20 vol% or more.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a wavelength conversion element and a light emitting device. [Background technology]

[0002] Wavelength conversion elements are known that irradiate a phosphor with excitation light and convert the excitation light into light of a different wavelength. For example, Patent Document 1 discloses a light emitting device that includes phosphor particle-dispersed glass having a configuration in which phosphor particles and a thermally conductive filler are dispersed in a glass matrix, and a semiconductor light emitting element that emits excitation light. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-26105 Summary of the Invention [Problem to be solved by the invention]

[0004] There is room for improvement in wavelength conversion elements in terms of increasing efficiency and light output. [Means for solving the problem]

[0005] A wavelength converting element is disclosed.

[0006] In one embodiment, the wavelength conversion element includes a wavelength conversion portion. The wavelength conversion portion includes a plurality of phosphor particles and a binder layer. The binder layer bonds the plurality of phosphor particles together and includes glass. The thickness of the wavelength conversion portion is 30 μm or more and 100 μm or less. The volume concentration of the plurality of phosphor particles in the wavelength conversion portion is 20 vol% or more. [Effects of the Invention]

[0007] The efficiency and amount of light in the wavelength conversion element can be improved. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing an example of the configuration of a lighting system according to a first embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing an example of the configuration of the wavelength conversion element according to the first embodiment. [Figure 3] FIG. 3 is a conceptual diagram showing an example of a cross-sectional configuration of the wavelength conversion element according to the first embodiment. [Figure 4] FIG. 4 is a graph showing the relationship between the thickness and the surface temperature of the wavelength converting portion. [Figure 5] FIG. 5 is a graph showing the relationship between the thickness of the wavelength converting portion and the amount of fluorescent light. [Figure 6] FIG. 6 is a graph showing the relationship between the thickness of the wavelength converting portion and the efficiency. [Figure 7] FIG. 7 is a graph obtained by removing the experimental results of the 31 vol % wavelength conversion section from the graph of FIG. [Figure 8] FIG. 8 is a graph obtained by removing the experimental results of the 31 vol % wavelength conversion section from the graph of FIG. [Figure 9] FIG. 9 is a graph showing the relationship between the density and the surface temperature in the wavelength converting portion. [Figure 10] FIG. 10 is a flowchart showing an example of a manufacturing flow of the wavelength conversion element according to the first embodiment. [Figure 11] FIG. 11 is a cross-sectional view showing an example of a wavelength conversion element in the middle of its manufacture. [Figure 12] FIG. 12 is a cross-sectional view showing an example of a wavelength conversion element in the middle of its manufacture. [Figure 13] FIG. 13 is a cross-sectional view showing an example of a wavelength conversion element in the middle of its manufacture. [Figure 14] FIG. 14 is a cross-sectional view showing an example of a state during the manufacturing of a wavelength conversion element. [Figure 15] FIG. 15 is a cross-sectional view showing an example of a wavelength conversion element in the middle of its manufacture. [Figure 16]FIG. 16 is a perspective view showing an example of the configuration of the base material according to the second embodiment. [Figure 17] FIG. 17 is a cross-sectional view showing an example of the configuration of the base material according to the second embodiment. [Figure 18] FIG. 18 is a flowchart showing an example of a manufacturing flow of the wavelength conversion element according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Wavelength conversion elements are known that irradiate a phosphor with excitation light such as laser light and convert it into light with a wavelength different from that of the excitation light. For example, such wavelength conversion elements may be configured to include a plurality of phosphor particles and a binder layer containing glass that connects adjacent phosphor particles.

[0010] This wavelength conversion element can be manufactured, for example, by mixing glass powder with a plurality of phosphor particles to obtain a mixture, and then sintering the glass powder.

[0011] In this wavelength conversion element, the binder layer formed by sintering the glass powder has low sinterability and contains many voids, resulting in low heat dissipation from the phosphor particles. Therefore, irradiation of the excitation light can raise the temperature of the phosphor particles, potentially reducing the luminous efficiency of the phosphor particles. In other words, the luminous efficiency of the wavelength conversion element can be reduced. The luminous efficiency here refers to the ratio of the energy of emitted light to the energy of the incident excitation light. In particular, when the energy of the excitation light increases, the phosphor particles are more likely to generate heat, further reducing the luminous efficiency of the wavelength conversion element and reducing the amount of fluorescent light emitted from the wavelength conversion element.

[0012] Therefore, the inventors of the present disclosure have created a wavelength conversion element that can emit a larger amount of light with higher efficiency.

[0013] In this regard, various embodiments and examples will be described below with reference to the drawings. In the drawings, parts having the same or similar configurations and functions are denoted by the same reference numerals. Duplicate explanations will be omitted in the following description. The drawings are schematic. A right-handed XYZ coordinate system is appropriately indicated in the drawings. In this XYZ coordinate system, the direction in which the first surface F1 of the wavelength conversion unit 30t (described later) faces is the +Z direction, one direction perpendicular to the +Z direction is the +X direction, and one direction perpendicular to the +Z direction and the +X direction is the +Y direction.

[0014] 1. First Embodiment <1-1. Lighting System> FIG. 1 is a schematic diagram showing an example of the configuration of a lighting system 1 according to a first embodiment. The lighting system 1 is capable of emitting fluorescence L1, which is generated when excitation light L0 is irradiated from a light source unit 2 onto a wavelength conversion element 30 containing a phosphor, as illumination light L2 into a predetermined space (also referred to as an illumination space). The lighting system 1 may emit the illumination light L2 into an indoor space or 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 the illumination light L2 into the same space, or multiple lighting systems 1 may each emit the illumination light L2 into multiple different spaces.

[0015] As shown in FIG. 1, the lighting system 1 includes, for example, a light source unit 2, a conversion unit 3, and a lighting unit 4.

[0016] The light source unit 2 can emit, for example, excitation light L0. The light source unit 2 has, for example, a light-emitting element. The light-emitting element includes, for example, a chip such as a laser diode (LD) or a light-emitting diode (LED). When the light-emitting element has a laser diode, the light source unit 2 can also be called a laser light source unit. When the light source unit 2 emits laser light, it can emit excitation light L0 with a large amount of light (or output).

[0017] The excitation light L0 emitted by the light-emitting element may be monochromatic light such as violet, blue-violet, or blue. More specifically, the light-emitting element may be a gallium nitride (GaN) semiconductor laser that emits one of a violet laser beam having a peak intensity at a wavelength of 405 nanometers (nm), a blue-violet laser beam having a peak intensity at a wavelength of 420 nm, and a blue laser beam having a peak intensity at a wavelength of 450 nm. In the example of FIG. 1 , the excitation light L0 emitted from the light source unit 2 is transmitted to the converter unit 3 via an optical transmission path (also referred to as a first optical transmission path) G1 such as an optical fiber. In this case, the light source unit 2 has a connection portion connected to an end portion (also referred to as a first incident end portion) of the first optical transmission path G1, into which the excitation light L0 is incident. In FIG. 1 , the transmission of the excitation light L0 through the first optical transmission path G1 is indicated by a thin, two-dot chain arrow.

[0018] The conversion unit 3 includes, for example, a wavelength conversion element 30. The wavelength conversion element 30 can convert, for example, the irradiated excitation light L0 into light of a different wavelength from the excitation light L0. The wavelength conversion element 30 includes, for example, a phosphor that emits fluorescence of a different wavelength from the excitation light L0 in response to irradiation with the excitation light L0. If the wavelength conversion element 30 includes, for example, phosphors that emit red (R), green (G), and blue (B) fluorescence in response to irradiation with purple excitation light L0, the purple excitation light L0 is converted into pseudo-white light in the wavelength conversion element 30. In the example of FIG. 1, the fluorescence L1 emitted from the wavelength conversion element 30 in response to irradiation with the excitation light L0 is transmitted to the illumination unit 4 via an optical transmission path (also referred to as a second optical transmission path) G2 such as an optical fiber. In FIG. 1, the transmission of the fluorescence L1 through the second optical transmission path G2 is indicated by a thin, two-dot chain arrow.

[0019] The conversion unit 3 also has, for example, a housing in which the wavelength conversion element 30 is fixed. In this case, the housing has, for example, a first opening connected to an end (also referred to as a first exit end) of the first optical transmission line G1 from which the excitation light L0 is emitted, and a second opening connected to an end (also referred to as a second entrance end) of the second optical transmission line G2 into which the fluorescence L1 is incident. An optical element such as a mirror may be arranged inside the housing to collect the fluorescence L1 emitted from the wavelength conversion element 30 in response to irradiation with the excitation light L0, onto the second entrance end of the second optical transmission line G2.

[0020] The device including the light source unit 2 and the conversion unit 3 is a light-emitting device that emits fluorescence L1. As described above, the light source unit 2 may emit laser light as excitation light L0, and the conversion unit 3 emits fluorescence L1 based on the excitation light L0, as described above. The output of the light source unit 2 may be, for example, 5 watts (W) to 8 W. For example, it may be 6 W or more, or 10 W or more. The light amount (e.g., illuminance) of the fluorescence L1 emitted by the conversion unit 3 may be 440 lumens (lm) or more, 460 lm or more, or 600 lm or more. The laser light may be irradiated onto the conversion unit 3 with a spot diameter in the range of 2.0 mm to 4.0 mm, for example. The surface of the wavelength conversion unit 30t described below is irradiated with 1.91 W / mm 2 When the wavelength conversion unit 30t is irradiated with excitation light L0 at a wavelength of 0.85 W / mm 2 , the fluorescence L1 emitted from the wavelength conversion unit 30t may have a light intensity of 440 lm or more. 2 When the wavelength conversion element 30 is irradiated with excitation light L0 at 1000 kJ / s, the fluorescence L1 emitted from the wavelength conversion unit 30t may have a light intensity of 460 lm or more. When the wavelength conversion element 30 absorbs such high-power excitation light L0, as will be described later, the heat generated in the wavelength conversion element 30 increases, and thermal degradation may become significant. As will be described later, the first embodiment can reduce the decrease in light intensity due to thermal degradation.

[0021] The illumination unit 4 can emit fluorescence L1 emitted from the wavelength conversion element 30 in response to irradiation with excitation light L0 emitted from the light source unit 2 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 connection portion to which an end portion (also referred to as a second emission end portion) of the second optical transmission line G2 that emits the fluorescence L1 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 the fluorescence L1 emitted from the second emission end portion of the second optical transmission line G2 as illumination light L2 toward the predetermined illumination space. In FIG. 1, the illumination light L2 emitted from the illumination unit 4 toward the predetermined illumination space is indicated by a thin, two-dot chain arrow.

[0022] The lighting system 1 may also include, for example, a control device 5 for controlling the operation of the light source unit 2. The control device 5 includes, 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 the other components of the control device 5. The control unit 51 includes, for example, a central processing unit (CPU) 511 and a storage unit 512. The storage unit 512 includes a non-transitory recording medium readable by the CPU 511, such as a read-only memory (ROM) and a random access memory (RAM). The storage unit 512 stores, for example, a program Pg1 for controlling the control device 5. Various functions of the control unit 51 are realized by the CPU 511 executing the program Pg1 stored in the storage unit 512. The drive unit 52 can drive the light source unit 2, for example, in response to an instruction from the control unit 51. The drive unit 52 can drive the light source unit 2 by, for example, supplying power from a power source to the light source unit 2 to cause the light source unit 2 to output excitation light L0. For example, the control unit 51 controls whether or not power is supplied from the power source to the light source unit 2 via the drive unit 52, thereby controlling the timing at which the light source unit 2 emits the excitation light L0.

[0023] <1-2. Configuration of wavelength conversion element> FIG. 2 is a cross-sectional view showing an example of the configuration of the wavelength conversion element 30 according to the first embodiment. In FIG. 2, the periphery of the first output end of the first optical transmission line G1 and the periphery of the second input end of the second optical transmission line G2 are schematically depicted. As shown in FIG. 2, the wavelength conversion element 30 includes a wavelength conversion section 30t and a substrate 30b. The cross-sectional structure of the wavelength conversion section 30t has a complex structure with intricate microstructures, but for convenience, a schematic illustration of the structure is omitted in FIG. 2.

[0024] The wavelength conversion unit 30t has, for example, a surface (also referred to as a first surface) F1 onto which the excitation light L0 is incident. In FIG. 2, the emission of the excitation light L0 from the first optical transmission path G1 toward the first surface F1 is indicated by a thin, two-dot chain line arrow. In FIG. 2, the emission of the fluorescence L1 from the first surface F1 toward the second optical transmission path G2 is indicated by a thin, two-dot chain line arrow. The wavelength conversion unit 30t also has, for example, a surface (also referred to as a 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 having a thickness along the direction from the second surface F2 toward the first surface F1.

[0025] The base material 30b is a member that supports the wavelength conversion unit 30t. From another perspective, the base material 30b is a member to which the wavelength conversion unit 30t is fixed. Here, for example, if the thermal conductivity of the base material 30b is higher than that of the wavelength conversion unit 30t, the base material 30b functions as a heat sink that dissipates heat from the wavelength conversion unit 30t. In other words, the presence of the base material 30b can increase the rate at which heat dissipates from the wavelength conversion unit 30t. This can increase the rate at which heat dissipates from the multiple phosphor particles 31 contained in the wavelength conversion unit 30t. As a result, the wavelength conversion element 30 can reduce a decrease in the amount of fluorescence L1 emitted in response to irradiation with excitation light L0. In other words, the wavelength conversion element 30 can increase the amount of fluorescence L1 emitted in response to irradiation with excitation light L0.

[0026] The material of the base material 30b may be, for example, a metal material. Examples of the metal material include copper (Cu), aluminum (Al), magnesium (Mg), gold (Au), silver (Ag), iron (Fe), chromium (Cr), cobalt (Co), beryllium (Be), molybdenum (Mo), tungsten (W), and alloys. Here, if Cu, Al, Mg, Fe, Cr, Co, or Be is used as the metal material, the base material 30b can be easily produced by a casting method such as die casting.

[0027] The reflectance of the substrate 30b for the excitation light L0 and the fluorescence L1 may be higher than the reflectance of the wavelength converting unit 30t. Such a substrate 30b may also be called a reflective substrate. Here, for example, if Al, Mg, Ag, Fe, Cr, or Co is used as the metal material, the reflectance of visible light on the surface of the substrate 30b can be increased. The reflectance of visible light may also be improved by processing the surface of the substrate 30b into a mirror finish by physical polishing, chemical polishing, or the like.

[0028] The base material 30b may be made of a non-metallic material such as aluminum nitride (AlN), gallium nitride (GaN), silicon carbide (SiC), silicon nitride (Si3N4), carbon (C), alumina (Al2O3), magnesia (MgO), or garnet. The non-metallic material may be, for example, a crystalline material or an amorphous material. Examples of crystalline non-metallic materials include SiC and Si3N4. If the material itself that is the main component of the base material 30b has low reflectivity, such as AlN, an optical reflection film may be formed on the surface of the base material 30b.

[0029] Alternatively, the base material 30b may be made of alumina (aluminum oxide: Al2O3). In this case, the base material 30b may have high reflectance for the excitation light L0 and the fluorescent light L1. The reflectance for the excitation light L0 and the fluorescent light L1 may be, for example, 80% or more, or 85% or more.

[0030] The shape and size of the base material 30b may be appropriately set depending on the size of the wavelength conversion element 30. For example, the thickness of the base material 30b may be set to 0.1 millimeters (mm) or more and 5 mm or less, or 0.5 mm or more and 1 mm or less. If the thickness of the base material 30b is 0.5 mm or more, the reflectance of the base material 30b can be ensured. In other words, if the base material 30b is too thin, the amount of excitation light L0 and fluorescence L1 transmitted through the base material 30b may increase. However, if the thickness of the base material 30b is 0.5 mm or more, the amount of transmitted excitation light L0 and fluorescence L1 can be sufficiently reduced. Furthermore, if the thickness of the base material 30b is 0.5 mm or more, the strength of the wavelength conversion element 30 can be sufficiently ensured even if the wavelength conversion section 30t is formed thin, as described below.

[0031] Furthermore, when the base material 30b has a rectangular shape in a plan view, the length and width of the base material 30b may be set to approximately 0.5 mm to 30 mm.

[0032] The base material 30b also has, for example, a surface (also referred to as a third surface) F3 on which the wavelength conversion unit 30t is arranged. The second surface F2 of the wavelength conversion unit 30t is fixed to the third surface F3. In the example of FIG. 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 disk-shaped member or a member having a rectangular shape in a plan view.

[0033] Fig. 3 is an image diagram schematically illustrating an example of a virtual cross-sectional configuration of the wavelength conversion element 30 according to the first embodiment. Fig. 3 shows an image of the cross section based on an image (also referred to as an SEM image) obtained by photographing a cross section of the wavelength conversion section 30t obtained by processes such as cutting, polishing, and cleaning using a scanning electron microscope (SEM). In Fig. 3, the base material 30b is hatched with multiple widely spaced diagonal lines slanting upward to the right.

[0034] As shown in FIG. 3, the wavelength converting section 30t includes a plurality of phosphor particles 31 and a binder layer 32. In FIG. 3, each of the plurality of phosphor particles 31 is hatched with a plurality of closely spaced oblique lines. In FIG. 3, the binder layer 32 is hatched with a matte pattern. Although not shown in FIG. 3, the wavelength converting section 30t may further include a substance other than the phosphor particles 31 and the binder layer 32. Furthermore, the wavelength converting section 30t may include appropriate voids inside.

[0035] <1-2-1. Phosphor particles> Each of the plurality of phosphor particles 31 is, for example, a phosphor particle that emits fluorescence in response to irradiation with the excitation light L0. The plurality of phosphor particles 31 includes, for example, one or more types of 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 the excitation light L0. The one or more types of 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 the 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 the excitation light L0. The green phosphor is a phosphor that emits green (G) fluorescence in response to irradiation with the excitation light L0. The blue phosphor is a phosphor that emits blue (B) fluorescence in response to irradiation with the excitation light L0.

[0036] The phosphor constituting the plurality of phosphor particles 31 may be, for example, a phosphor containing a rare earth such as europium (Eu), cerium (Ce) or yttrium (Y) in the form of a compound such as a phosphate, oxide, silicate, nitride, fluoride, aluminate or sulfide.

[0037] The red phosphor may be, for example, a phosphor whose peak wavelength of the fluorescent light intensity emitted in response to irradiation with excitation light L0 is in the range of about 620 nm to 750 nm. Examples of materials for the red phosphor include CaAlSiN3:Eu, Y3O3S:Eu, Y3O3:Eu, and SrCaClAlSiN3:Eu. 2+ Alternatively, CaAlSi(ON)3:Eu, etc. may be used. As the phosphor particles of the red phosphor, for example, phosphor particles that do not contain phosphorus (P) (also called non-phosphorus phosphor particles) or phosphor particles that contain nitride may be used.

[0038] The green phosphor may be, for example, a phosphor whose peak wavelength of the fluorescent light intensity emitted in response to irradiation with excitation light L0 is in the range of about 495 nm to 570 nm. Examples of materials for the green phosphor include β-sialon (β-SiAlON:Eu), SrSi2(O,Cl)2N2:Eu, and (Sr,Ba,Mg)2SiO4:Eu2. 2+ , ZnS:Cu,Al, or Zn2SiO4:Mn, etc. As the phosphor particles of the green phosphor, for example, phosphor particles that do not contain phosphorus (P) (non-phosphorus phosphor particles) or phosphor particles that contain nitride may be used.

[0039] As the blue phosphor, for example, a phosphor that emits fluorescent light in response to irradiation with excitation light L0 and has a peak intensity in the wavelength range of about 450 nm to 495 nm may be used. Examples of the material for the blue phosphor include (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 phosphor-based phosphor particles) or phosphor particles containing nitride may be used.

[0040] The particle size of the phosphor particles 31 may be, for example, about 5 micrometers (μm) to 50 μm.

[0041] <1-2-2. Binder layer> The binder layer 32 bonds the plurality of phosphor particles 31 together. In other words, the wavelength conversion element 30 has a configuration in which the plurality of 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 includes glass. The binder layer 32 may include glass as a main component. The main component refers to the component that is contained at the highest ratio (also referred to as the content) among the components constituting the substance. Glass has transparency for transmitting, for example, the excitation light L0 to the inside of the wavelength conversion unit 30t and for radiating, to the outside of the wavelength conversion unit 30t, the fluorescence L1 emitted by the phosphor particles 31 excited in response to irradiation with the excitation light L0. In other words, glass has transparency for transmitting, for example, the excitation light L0 and the fluorescence L1. The binder layer 32 may also be called a glass matrix. Typically, resin is used for the binder layer, but the heat generated by the phosphor particles can cause the resin to deteriorate, potentially resulting in a decrease in luminous efficiency or reliability. In contrast, if the binder layer 32 is a glass matrix, this can mitigate the decrease in luminous efficiency or reliability.

[0042] The glass constituting the binder layer 32 may be, for example, a low-melting-point glass. For example, an oxide glass having a melting point (Tm) of 200 degrees Celsius (200°C) to 700°C may be used as the low-melting-point glass. The oxide glass serving as the low-melting-point glass has, for example, a glass transition point (Tg) in the range of 100°C to 600°C and a crystallization temperature (Tc) in the range of 150°C to 650°C. For example, a glass containing, as a main component, two or more oxides selected from silicon dioxide (SiO), aluminum oxide (AlO), boron oxide (BO), sodium oxide (NaO), potassium oxide (KO), lithium oxide (LiO), calcium oxide (CaO), barium oxide (BaO), zinc oxide (ZnO), lead monoxide (PbO), and diphosphorus pentoxide (PO) may be used as the oxide glass. In other words, the oxide glass may contain an oxide of a metal element or an oxide of a metalloid element.

[0043] The binder layer 32 is located, for example, between the plurality of phosphor particles 31 and between the phosphor particles 31 and the substrate 30b. The binder layer 32 has the function of directly conducting heat from the phosphor particles 31 in the portions in direct contact with the phosphor particles 31. The surfaces of the phosphor particles 31 may be coated 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 that coats the phosphor particles 31 is in direct contact with the binder layer 32. 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 due to the irradiation of the excitation light L0. This heat is conducted to the substrate 30b via the binder layer 32 and the like and dissipated.

[0044] The binder layer 32 includes, for example, an amorphous phase of glass. This amorphous phase may be, for example, an amorphous portion of a low-melting-point glass. The amorphous phase made of glass has transparency that allows the excitation light L0 and the fluorescent light L1 to pass through.

[0045] The binder layer 32 may be bonded to, for example, the third surface F3 of the substrate 30b. That is, the binder layer 32 may be in direct contact with the third surface F3 of the substrate 30b. As shown in FIG. 3 , some of the phosphor particles 31 may be in contact with the third surface F3 of the substrate 30b, and the binder layer 32 may be in contact with most of the portion of the third surface F3 of the substrate 30b that is not in contact with the phosphor particles 31. The binder layer 32 is in a state of being directly bonded to the substrate 30b.

[0046] <1-3. Thickness of wavelength conversion section and phosphor particle content> Next, the thickness of the wavelength converting portion 30t (that is, the distance between the first face F1 and the second face F2) and the content of the phosphor particles 31 in the wavelength converting portion 30t will be described.

[0047] The thickness of the wavelength conversion portion 30t according to the first embodiment is 100 μm or less. The thickness of the wavelength conversion portion 30t can be measured, for example, as follows: First, a micrometer is used to measure the thickness of the substrate 30b before the wavelength conversion element 30 is fabricated. Next, the wavelength conversion element 30 is fabricated by forming the wavelength conversion portion 30t on the substrate 30b. Next, a micrometer is used to measure the thickness of the wavelength conversion element 30. Next, the thickness of the wavelength conversion element 30t is calculated by subtracting the thickness of the substrate 30b from the thickness of the wavelength conversion element 30. Alternatively, the thickness of the wavelength conversion portion 30t may be measured as follows: First, an image sensor captures the cut surface of the wavelength conversion element 30 (see FIG. 3 ) to generate an image (e.g., an SEM image). Then, for example, a computer may identify the first surface F1 and the second surface F2 of the wavelength conversion portion 30t in the image by edge extraction or other processing, and calculate the thickness of the wavelength conversion portion 30t based on the number of pixels in the pixel group in the thickness direction of the wavelength conversion portion 30t. For example, the average value of the thickness of the wavelength converting portion 30t may be used as the thickness of the wavelength converting portion 30t.

[0048] In the first embodiment, the thickness of the wavelength conversion portion 30t is as thin as 100 μm or less, and therefore heat generated in the wavelength conversion portion 30t can be dissipated more quickly from the first surface F1 or the second surface F2 of the wavelength conversion portion 30t. In other words, the heat dissipation properties of the wavelength conversion portion 30t can be improved. The thickness of the wavelength conversion portion 30t may be, for example, 70 μm or less. When the thickness of the wavelength conversion portion 30t is 70 μm or less, the heat dissipation properties of the wavelength conversion portion 30t can be further improved. The thickness of the wavelength conversion portion 30t may be, for example, 60 μm or less. When the thickness of the wavelength conversion portion 30t is 60 μm or less, the heat dissipation properties of the wavelength conversion portion 30t can be further improved.

[0049] By improving the heat dissipation properties of the wavelength conversion section 30t, thermal degradation of the phosphor particles 31 can be reduced. Thermal degradation here includes a phenomenon in which the internal quantum efficiency of the phosphor particles 31 decreases as the temperature of the phosphor particles 31 increases. The internal quantum efficiency is the ratio of the number of photons of the fluorescence L1 emitted by the phosphor particles 31 to the number of photons of the excitation light L0 absorbed by the phosphor particles 31. Therefore, as the temperature of the phosphor particles 31 increases, the internal quantum efficiency may decrease, resulting in a decrease in the amount of fluorescence L1 emitted by the phosphor particles 31. If the temperature of the phosphor particles 31 increases further, there is even a risk that the phosphor particles 31 may become quenched. In the first embodiment, by thinning the wavelength conversion section 30t, it is possible to reduce the decrease in the amount of fluorescence L1 emitted by the wavelength conversion section 30t due to temperature.

[0050] On the other hand, the light intensity of the wavelength conversion unit 30t naturally also depends on the amount of phosphor particles 31. Specifically, it is thought that the more phosphor particles 31 there are, the greater the light intensity of the fluorescence L1 from the wavelength conversion unit 30t. As the wavelength conversion unit 30t becomes thinner, the amount of phosphor particles 31 in the wavelength conversion unit 30t decreases, and from this perspective, the light intensity of the fluorescence L1 decreases. In other words, as the wavelength conversion unit 30t becomes thinner, the amount of excitation light L0 that transmits through the wavelength conversion unit 30t without being absorbed by the phosphor particles 31 increases, and as a result, the light intensity of the fluorescence L1 decreases.

[0051] Therefore, in the first embodiment, the volume concentration as the content of the phosphor particles 31 is set to 20 vol% or more. This can reduce the decrease in light intensity due to the insufficient amount of phosphor particles 31 that occurs with thinning. The thickness of the wavelength conversion section 30t and the content of the phosphor particles 31 will be further considered below.

[0052] FIG. 4 is a graph showing the relationship between the thickness of the wavelength conversion unit 30t and the surface temperature of the wavelength conversion unit 30t. FIG. 5 is a graph showing the relationship between the thickness of the wavelength conversion unit 30t and the light intensity of the fluorescence L1 emitted by the wavelength conversion unit 30t. FIG. 6 is a graph showing the relationship between the thickness of the wavelength conversion unit 30t and the efficiency of the wavelength conversion unit 30t. The efficiency is the ratio of the number of photons of the fluorescence L1 emitted from the wavelength conversion unit 30t to the number of photons of the excitation light L0 incident on the wavelength conversion unit 30t. This ratio may also be referred to as the external quantum efficiency. Here, if the ratio of the excitation light L0 absorbed by the phosphor particles 31 to the excitation light L0 incident on the wavelength conversion unit 30t is called the absorptance, the external quantum efficiency is expressed as the product of the internal quantum efficiency and the absorptance.

[0053] 4 to 6 show the experimental results. In this experiment, first, multiple types of wavelength conversion elements 30 were fabricated. Specifically, multiple wavelength conversion elements 30 were fabricated with different phosphor particle 31 content rates in the wavelength conversion sections 30t and different thicknesses of the wavelength conversion sections 30t. Here, multiple wavelength conversion elements 30 were fabricated with different thicknesses within a thickness range of 30 μm or more and 100 μm or less. Additionally, multiple wavelength conversion sections 30t were fabricated with different phosphor particle 31 content rates within a ratio range of 20 vol% or more and 70 vol%. More specifically, multiple wavelength conversion sections 30t were fabricated with phosphor particle 31 volume concentrations of 31 vol%, 48 vol%, and 61 vol%, respectively.

[0054] The volume concentration of the phosphor particles 31 can be measured, for example, as follows. That is, the mass of each material during fabrication of the wavelength conversion unit 30t is measured, and each mass is converted to a volume. The ratio of the total volume of the phosphor particles 31 to the total volume of the wavelength conversion unit 30t is calculated as the volume concentration. Alternatively, the volume concentration of the phosphor particles 31 may be measured as follows. First, an image sensor captures the cross section of the wavelength conversion element 30 (see FIG. 3) to generate an image (e.g., an SEM image). In this image, the phosphor particles 31, the binder layer 32, and the voids have different colors. Therefore, a computer identifies the first region of the phosphor particles 31 and the second region of the binder layer 32 from the image by, for example, binarization processing. The computer may calculate the volume concentration of the phosphor particles 31 based on the areas (i.e., the number of pixels) of the first and second regions. Specifically, the computer may calculate the volume concentration by dividing the area of the first region by the sum of the areas of the first region and the second region.

[0055] Then, the surface temperature of the wavelength conversion unit 30t was measured when the wavelength conversion unit 30t was spot-irradiated with excitation light L0 from the laser light source, and the light intensity of the fluorescence L1 emitted from the wavelength conversion unit 30t was measured. The surface temperature may be the temperature of the first surface F1 of the wavelength conversion unit 30t. The light intensity may be the illuminance. The output of the laser light source was 60 W, and the spot diameter of the excitation light L0 on the first surface F1 of the wavelength conversion unit 30t was 2 mm.

[0056] As can be seen from Figure 4, the thinner the wavelength converting portion 30t, the lower the surface temperature tends to be. For example, if the thickness of the wavelength converting portion 30t is 100 µm or less, the surface temperature of the wavelength converting portion 30t can be approximately 550°C or less. If the thickness is 90 µm or less, the surface temperature can be more reliably kept at 550°C or less. Furthermore, if the thickness is 70 µm or less, the surface temperature can be further reduced, and if the thickness is 60 µm or less, the surface temperature can be reduced even further. In other words, the thinner the wavelength converting portion 30t, the lower the surface temperature of the wavelength converting portion 30t.

[0057] 5 and 6, the amount of light and the efficiency tend to increase as the thickness of the wavelength converting section 30t decreases from 100 μm. This can be considered to be because the heat dissipation of the wavelength converting section 30t improves as the thickness is reduced, thereby reducing thermal degradation of the phosphor particles 31.

[0058] Here, we consider experimental results other than when the volume concentration of phosphor particles 31 is 31 vol%. In other words, we consider experimental results when the volume concentration of phosphor particles 31 is relatively high. FIG. 7 is a graph obtained by removing the experimental results for the 31 vol% wavelength conversion unit 30t from the graph of FIG. 5, and FIG. 8 is a graph obtained by removing the experimental results for the 31 vol% wavelength conversion unit 30t from the graph of FIG. 6. As shown in FIGS. 7 and 8, when the volume concentration of phosphor particles 31 in the wavelength conversion unit 30t is high, the graphs of light intensity and efficiency each have an upward convex shape (see the two-dot chain line), peaking when the thickness is approximately 50 μm. We believe this is due to the following reason.

[0059] That is, the thinner the wavelength converting section 30t, the fewer the number of phosphor particles 31. Therefore, the amount of excitation light L0 that is not absorbed by the phosphor particles 31 and that transmits through the binder layer 32 increases. That is, in the first range where the wavelength converting section 30t is thin, the thinner the wavelength converting section 30t, the more significantly the absorptance decreases. Therefore, in the first range, the external quantum efficiency is relatively significantly affected by the absorptance. For this reason, as shown in FIGS. 6 and 7, in the first range where the thickness of the wavelength converting section 30t is less than approximately 50 μm, the thinner the wavelength converting section 30t, the more the external quantum efficiency decreases.

[0060] On the other hand, the thicker the wavelength conversion section 30t, the greater the number of phosphor particles 31. Therefore, the excitation light L0 is absorbed by many phosphor particles 31, and the absorption rate remains high. Therefore, in the second range where the thickness of the wavelength conversion section 30t is large, the external quantum efficiency is relatively greatly affected by the internal quantum efficiency. The internal quantum efficiency tends to decrease as the temperature increases, and the temperature tends to increase as the wavelength conversion section 30t becomes thicker. Therefore, in the second range where the thickness of the wavelength conversion section 30t is approximately 50 μm or more and 100 μm or less, the light intensity and efficiency tend to decrease as the wavelength conversion section 30t becomes thicker.

[0061] When the volume concentration of the phosphor particles 31 is 31 vol% or less, the changes in light intensity and efficiency relative to the thickness of the wavelength conversion section 30t are relatively small (see the black diamonds in Figures 5 and 6). This is thought to be because when the volume concentration is 31 vol% or less, the amount of phosphor particles 31 is insufficient, and the changes in internal quantum efficiency and absorptance depending on the thickness of the wavelength conversion section 30t are offset. In other words, because the volume concentration of the phosphor particles 31 is relatively high, the relationships of light intensity and efficiency relative to thickness tend to be upwardly convex, as described above.

[0062] Therefore, in the wavelength converting section 30t, the volume concentration of the phosphor particles 31 may be greater than 31 vol% and the thickness of the wavelength converting section 30t may be 30 μm or more and 70 μm or less. This makes it possible to effectively improve the efficiency and light intensity of the wavelength converting section 30t when the volume concentration of the phosphor particles 31 is high. Furthermore, the volume concentration of the phosphor particles 31 may be 35 vol% or more, or 40 vol% or more. In other words, the volume concentration of the phosphor particles 31 may be 35 vol% or more and the thickness of the wavelength converting section 30t may be 30 μm or more and 70 μm or less. Furthermore, the volume concentration of the phosphor particles 31 may be 40 vol% or more and the thickness of the wavelength converting section 30t may be 30 μm or more and 70 μm or less.

[0063] Alternatively, the volume concentration of the phosphor particles 31 may be greater than 31 vol%, and the thickness of the wavelength converting section 30t may be 30 μm or more and 60 μm or less. Alternatively, the volume concentration of the phosphor particles 31 may be 35 vol% (or 40 vol%) or more, and the thickness of the wavelength converting section 30t may be 30 μm or more and 60 μm or less. Alternatively, the volume concentration may be within any of the above ranges, and the thickness of the wavelength converting section 30t may be 40 μm or more and 60 μm or less. This can further effectively improve the light intensity and efficiency of the wavelength converting section 30t.

[0064] The volume concentration of the phosphor particles 31 may be 70 vol% or less. This is because if the volume concentration of the phosphor particles 31 is too high, the amount of the binder layer 32 will be insufficient, which may cause problems in the wavelength conversion section 30t. One example of such a problem is an increase in voids that occur inside the wavelength conversion section 30t due to an insufficient binder layer 32. Because the thermal resistance of voids is higher than that of the binder layer 32, an increase in voids leads to a decrease in the heat dissipation performance of the wavelength conversion section 30t. If the volume concentration of the phosphor particles 31 is 70 vol% or less, the increase in voids can be more appropriately reduced. If the volume concentration of the phosphor particles 31 is 65 vol or less, the increase in voids can be further reduced.

[0065] <1-4. Alkali metal oxides> An alkali metal oxide may be used as one of the materials for the binder layer 32. For example, the alkali metal oxide may be at least one of lithium oxide and sodium oxide. The molar concentration of the alkali metal oxide in the binder layer 32 may be, for example, 10 mol% or more and 19 mol% or less. When the material for the binder layer 32 contains multiple types of alkali metal oxides, the molar concentration of the alkali metal oxide is the total molar concentration of the multiple types of alkali metal oxides. For example, when the material for the binder layer 32 contains both lithium oxide and sodium oxide, the sum of the molar concentration of the lithium oxide and the molar concentration of the sodium oxide is 10 mol% or more and 19 mol% or less.

[0066] The molar concentration of the alkali metal oxide can be measured, for example, as follows. That is, before fabricating the wavelength conversion element 30, the mass of each component of the binder layer 32 is determined by ICP (Inductively Coupled Plasma) mass spectrometry. Then, the mass is converted to moles, and the molar concentration of the alkali metal oxide is determined based on the moles of each component. Note that the binder layer 32 may be extracted after fabricating the wavelength conversion element 30. For example, the binder layer 32 may be fluidized by heating the wavelength conversion element 30, and the fluidized binder layer 32 may be separated from the wavelength conversion element 30 to obtain the binder layer 32. The mass of each component of the binder layer 32 may be determined by ICP mass spectrometry.

[0067] For example, zinc borosilicate glass may be used for the binder layer 32. In this case, the binder layer 32 may contain silicon dioxide, boron oxide, zinc oxide, and an alkali metal oxide. The binder layer 32 may further contain aluminum oxide. For example, the molar concentrations of the boron oxide and zinc oxide may each be higher than the molar concentration of silicon dioxide, which may be higher than the molar concentration of the alkali metal oxide, which may be higher than the molar concentration of the aluminum oxide.

[0068] In the above example, the binder layer 32 contains alkali metal oxide at a relatively high molar concentration of 10 mol % or more and 19 mol % or less. A molar concentration of alkali metal oxide of 10 mol % or more can lower the glass transition point of the binder layer 32. This improves the fluidity of the binder layer 32 during heating. Therefore, during fabrication of the wavelength conversion section 30t, the binder layer 32 has a relatively high fluidity, allowing it to penetrate between the plurality of phosphor particles 31 and also between the base material 30b and a pair of the plurality of phosphor particles 31. Therefore, the binder layer 32 can properly integrate the plurality of phosphor particles 31. As a result, the amount of voids generated inside the wavelength conversion section 30t can also be reduced. This improves the heat dissipation properties of the wavelength conversion section 30t.

[0069] As described above, because the molar concentration of the alkali metal oxide is 10 mol % or more, even if the volume concentration of the phosphor particles 31 is increased as in the first embodiment, the binder layer 32 can properly integrate the plurality of phosphor particles 31. Furthermore, the voids inside the wavelength conversion section 30t can be reduced. This improves the heat dissipation performance of the wavelength conversion section 30t. Therefore, the light intensity of the fluorescence L1 from the wavelength conversion section 30t can be improved in terms of both the amount of phosphor particles 31 and heat dissipation performance.

[0070] On the other hand, when the composition ratio of the alkali metal oxide is 19 mol % or less, the moisture resistance of the wavelength converting portion 30t can be improved.

[0071] <1-5. Density of wavelength conversion section> As described above, if the wavelength converting unit 30t contains many voids, the heat dissipation performance of the wavelength converting unit 30t may be reduced. FIG. 9 is a graph showing the relationship between the compactness of the wavelength converting unit 30t and the surface temperature of the wavelength converting unit 30t. The compactness is, for example, a value obtained by subtracting the porosity of the wavelength converting unit 30t from "1." The porosity is, for example, the ratio of the volume of the voids existing between the first surface F1 and the second surface F2 to the volume of the wavelength converting unit 30t between the first surface F1 and the second surface F2. In other words, the porosity is the ratio of the volume of the voids existing within the space surrounded by the first surface F1, the second surface F2, and the side surfaces of the wavelength converting unit 30t to the volume of the space.

[0072] The density of the wavelength conversion unit 30t can be measured, for example, as follows. First, an image sensor captures the cross section of the wavelength conversion element 30 (see FIG. 3) to generate an image (e.g., an SEM image). In this image, the phosphor particles 31, the binder layer 32, and the voids have different colors. Therefore, a computer identifies the third region of the voids and the fourth region of the wavelength conversion unit 30t other than the voids from the image by processing such as binarization. The computer may calculate the density based on the areas (i.e., the number of pixels) of the third and fourth regions. Specifically, the computer may calculate the density by dividing the area of the fourth region by the sum of the areas of the third and fourth regions.

[0073] The density may be 82% or more. This allows the surface temperature of the wavelength converting section 30t to be rapidly reduced, as shown in Fig. 9 (see also the two-dot chain line). The density may be 86% or more, or even 90% or more, allowing the surface temperature of the wavelength converting section 30t to be further reduced.

[0074] <1-6. Binder layer and substrate> As described above, the binder layer 32 may be made of zinc borosilicate glass. For example, the molar concentration of silicon oxide may be 5 mol% or more and 25 mol% or less, or 8 mol% or more and 18 mol% or less; the molar concentration of boron oxide may be 25 mol% or more and 50 mol% or less, or 30 mol% or more and 45 mol% or less; the molar concentration of zinc oxide may be 25 mol% or more and 50 mol% or less, or 30 mol% or more and 45 mol% or less; and the molar concentration of alkali metal oxide may be 10 mol% or more and 19 mol% or less. The material of the binder layer 32 may further contain aluminum oxide, and the molar concentration of aluminum oxide may be, for example, 10 mol% or less and 5 mol% or less.

[0075] In this case, the base material 30b may be made of aluminum oxide. This allows the difference between the linear expansion coefficient of the base material 30b and the linear expansion coefficient of the binder layer 32 to be sufficiently reduced. For example, the linear expansion coefficient of the binder layer 32 is approximately 7.5, and the linear expansion coefficient of the base material 30b is approximately 7.2. This allows the direct bond between the binder layer 32 and the base material 30b to be more reliably maintained, even in a high-temperature environment. In other words, partial peeling between the binder layer 32 and the base material 30b can be reduced or avoided. Because the direct bond between the binder layer 32 and the base material 30b is maintained, high heat dissipation properties can be maintained in the wavelength converting section 30t.

[0076] <1-7. Method for manufacturing wavelength conversion element> Fig. 10 is a flow chart showing an example of a manufacturing flow of the wavelength conversion element 30. Figs. 11 to 15 are cross-sectional views showing examples of states of the wavelength conversion element 30 during manufacturing. Hereinafter, a manufacturing method of the wavelength conversion element 30 will be described using Figs. 11 to 15 with reference to Fig. 10. Here, the wavelength conversion element 30 can be manufactured by performing the processes of step S1 to step S7 in the order described.

[0077] First, as shown in FIG. 11, a base material 30b is prepared (step S1). The base material 30b may be made of a metal material such as Cu, Al, Mg, Au, Ag, Fe, Cr, Co, Be, Mo, W, or an alloy. The base material 30b may be made of a non-metal material such as AlN, GaN, SiC, Si3N4, C, Al2O3, MgO, or garnet. Here, Al2O3 is used as the base material 30b. In other words, a base material 30b made of aluminum oxide is prepared.

[0078] Next, as shown in FIG. 12, a mask 30m having an opening 30o corresponding to the planar shape of the wavelength converting portion 30t is superimposed on the third surface F3 of the base material 30b, which is the main surface on which the wavelength converting portion 30t is formed (step S2). The mask 30m may be made of, for example, aluminum. In this case, the opening 30o having the desired planar shape can be formed by etching or other processing. The thickness of the mask 30m is set to be greater than the thickness of the wavelength converting portion 30t. For example, if the thickness of the wavelength converting portion 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 the opening 30o having the desired shape and is strong enough to withstand the subsequent powder filling process.

[0079] Next, as shown in Fig. 13, a powder (also referred to as mixed powder) obtained by thoroughly mixing powder of phosphor particles 31 (also referred to as phosphor powder) and glass powder (also referred to as glass powder) is filled into the opening 30o of the mask 30m to form a powder filler PW (step S4). The powder filler PW may contain powders other than phosphor powder and glass powder. The amounts of these powders added are set in advance so that the thickness of the wavelength conversion section 30t fabricated through steps S5 to S7 described below falls within the above-mentioned range.

[0080] Here, the plurality of phosphor particles 31o include, for example, red phosphor particles, green phosphor particles, and blue phosphor particles. The red phosphor may be, for example, a phosphor whose peak wavelength of fluorescence emitted in response to irradiation with excitation light L0 is in the range of approximately 620 nm to 750 nm. Examples of materials for the red phosphor include CaAlSiN3:Eu, Y3O3S:Eu, Y3O3:Eu, and SrCaClAlSiN3:Eu. 2+ For example, a phosphor having a peak wavelength of the fluorescent light intensity in response to irradiation with excitation light L0 in the range of about 495 nm to 570 nm is used as the green phosphor. Examples of materials for the green phosphor include β-sialon (β-SiAlON:Eu), SrSi2(O,Cl)2N2:Eu, and (Sr,Ba,Mg)2SiO4:Eu2 2+ , ZnS:Cu,Al, or Zn2SiO4:Mn, etc. are used as the blue phosphor. For example, a phosphor whose peak wavelength of the fluorescent light intensity emitted in response to irradiation with excitation light L0 is in the range of about 450 nm to 495 nm is used as the blue phosphor material. 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., are applied.

[0081] The phosphor particles 31o in the phosphor powder may have various particle size distributions, for example, the 50% particle diameter (D50) of the phosphor particles 31o in the phosphor powder may be in the range of 1 μm to 50 μm or in the range of 10 μm to 30 μm.

[0082] Here, in the mixed powder, for example, the content of the phosphor powder is 20 vol% or more and 70 vol% or less. When the content is expressed in terms of mass concentration, for example, the content of the phosphor powder is approximately 22.5 mass (wt)% or more and 67 wt% or less. Alternatively, the content of the phosphor powder may be greater than 31 vol% and 70 vol% or less, 35 vol% or more and 70 vol% or less, 35 vol% or more and 65 vol% or less, 40 vol% or more and 70 vol% or less, or 40 vol% or more and 65 vol% or less.

[0083] The glass powder may be, for example, a powder of low-melting-point glass that is transparent after sintering. The low-melting-point glass may be an oxide glass having a melting point of 200 degrees Celsius (200°C) to 700°C. In this case, the glass may be, for example, a zinc borosilicate glass. An example of the composition of the zinc borosilicate glass is as described above.

[0084] The particle size distribution of the glass powder may be various, similar to the particle size distribution of the phosphor powder. For example, the glass powder may contain glass particles with a 50% particle size (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.

[0085] The phosphor powder and the glass powder can be mixed using a vibration method or a rotary shaking method. A medium may also be used when mixing the phosphor powder and the glass powder. This medium can be used in various methods for mixing multiple types of powder, such as a dry method in which multiple types of powder are directly mixed in powder form, or a wet method in which multiple types of powder are mixed with a solvent or binder.

[0086] 14, the mask 30m is removed from the substrate 30b on which the powder filler PW has been formed (step S4), and the powder filler PW is heated to form a pre-sintered body PS (step S5). Here, the heating temperature is set to be equal to or higher than the melting point (Tm) of the glass constituting the glass powder, but lower than the temperature at which the phosphor particles 31 lose their fluorescent function. For example, the heating temperature may be in the range of about 260°C to 600°C, or may be in the range of 350°C to 450°C.

[0087] The heating of the powder filler PW and the pre-sintered body PS and the pressure processing described below are performed, for example, in a common chamber. This chamber may or may not be a vacuum container. For example, if the chamber is a vacuum container, the chamber can be evacuated during heating. For example, heating the chamber in a vacuum state reduces the generation of bubbles when the glass powder melts. The heating and pressure processing of the powder filler PW and the pre-sintered body PS may be performed, for example, in the atmosphere.

[0088] After the heating temperature reaches the set temperature, the pre-sintered body PS is pressurized on the substrate 30b while maintaining the set temperature, as shown in FIG. 15 (step S6). The heating and pressurization of the powder filler PW and pre-sintered body PS may be performed, for example, using a multipurpose high-temperature sintering furnace or a heater block and hand press. That is, the pre-sintered body PS may be hot-pressed. This pressurization reduces the porosity of the pre-sintered body PS. In other words, it improves its compactness. In hot pressing, a physical object called a press body (not shown) contacts the top surface of the pre-sintered body PS and presses it, thereby more effectively improving its compactness. For example, hot pressing can be performed to achieve a compactness of 82% or more. If the pressing surface of the press body that contacts the top surface of the pre-sintered body PS is flat, the top surface of the pre-sintered body PS will also be flat, as shown in FIG. 15.

[0089] The pressure during the pressurizing process can be set to a pressure that does not physically crush the phosphor particles 31o and cause them to lose their fluorescent function. For example, the pressure during the pressurizing process can be set to 20 kgf / cm. 2 to 300 kgf / cm 2 The pressure is set to about 2 MPa to about 30 MPa. Here, the pre-sintered body PS is maintained in a pressurized state at a pressure that satisfies this pressure condition for a period of about 30 seconds to 30 minutes, for example.

[0090] When hot pressing is performed, the press body presses the pre-sintered body PS so that the thickness of the pre-sintered body PS in the pressed state is 30 μm or more and 100 μm or less. The press body may press the pre-sintered body PS so that the thickness of the pre-sintered body PS in the pressed state is 30 μm or more and 70 μm or less, or may press the pre-sintered body PS so that the thickness of the pre-sintered body PS in the pressed state is 40 μm or more and 60 μm or less.

[0091] Next, the pre-sintered body PS is cooled while maintaining the pressure applied during pressurization (step S7). When the temperature of the pre-sintered body PS drops below the melting point of the glass that constituted the glass powder, the pressure is released. This converts the pre-sintered body PS into a wavelength converting section 30t. This cooling process causes the binder layer 32 to integrate the phosphor particles 31 and bond directly to the third surface F3 of the base material 30b. This converts the pre-sintered body PS into a wavelength converting section 30t having a shape such as that shown in FIG. 3, for example.

[0092] Through the above steps, the wavelength conversion element 30 can be manufactured.

[0093] In the above-described method for manufacturing the wavelength conversion element 30, the thickness of the wavelength conversion section 30t can be set within the range according to the first embodiment by appropriately setting various conditions, such as the amounts of phosphor powder and glass powder added and the pressure in the pressurizing step. Also, the content of the phosphor powder can be set within the range according to the first embodiment by appropriately setting the ratio of the amount of phosphor powder added to the amount of all powder added.

[0094] In the above-described method for manufacturing the wavelength conversion element 30, if the base material 30b is made of a material that is prone to forming an oxide film, such as aluminum, the base material 30b and the wavelength conversion portion 30t are bonded by an oxidation bond. In this case, the base material 30b and the wavelength conversion portion 30t are bonded by an oxidation bond formed between oxygen in the oxide film formed on the surface of the base material 30b by heating and oxygen in the oxide glass. This can increase the bonding strength between the base material 30b and the wavelength conversion portion 30t.

[0095] Furthermore, in the manufacturing method of the wavelength conversion element 30 described above, for example, when a material that is difficult to oxidize and bond is used as the material for the substrate 30b, minute irregularities of several micrometers may be formed on the surface of the substrate 30b, and glass may be entangled in these irregularities to enhance the bonding strength between the substrate 30b and the wavelength conversion section 30t through 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 may be such that the low-melting-point glass that is liquefied upon heating flows and penetrates these minute irregularities. In this case, the size of the minute irregularities may be set to, for example, 0.1 μm to 50 μm. Furthermore, the size of the minute irregularities may be set to a size that allows phosphor particles to penetrate these minute irregularities. In this case, the size of the minute irregularities may be set to, for example, 5 μm to 50 μm. The size of the minute irregularities (irregularities of the irregular shape) of the substrate 30b here refers to, for example, the dimension between the bottom (lowest point) of the concave portion of the minute irregularities and the top (highest point) of the convex portion in the thickness direction of the substrate 30b.

[0096] Furthermore, in the above-described manufacturing method of the wavelength conversion element 30, for example, when a material that cannot be expected to form an oxidative bond or an anchor effect is used as the material for the base material 30b, the wavelength conversion portion 30t and the base material 30b may be prepared separately. Here, for example, instead of forming the wavelength conversion portion 30t on the base material 30b, a powder filler PW may be formed separately from the base material 30b, the powder filler 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 portion 30t. In this case, a metal multilayer film may be formed on the surface of the wavelength conversion portion 30t facing the base material 30b, and the wavelength conversion portion 30t and the base material 30b may be joined by soldering.

[0097] An example of the multilayer film is a multilayer film (also referred to as a Ti / Pt / Au multilayer film) in which thin films of titanium (Ti), platinum (Pt), and gold (Au) are stacked in this order from the wavelength converting section 30t side. This multilayer film can be formed to a thickness of several to several hundred nanometers by, for example, sputtering or vapor deposition. Here, Ti has good bonding properties with oxide glass, and Au has good wettability with solder material. The Pt film functions as a barrier film that reduces peeling of the Ti film from the wavelength converting section 30t due to the molten solder material when the solder material melts. The multilayer film may be, for example, a multilayer film (also referred to as a Cr / Pt / Au multilayer film) in which thin films of chromium (Cr), Pt, and Au are stacked in this order from the wavelength converting section 30t side, or a multilayer film (also referred to as a Cr / Ni / Au multilayer film) in which thin films of Cr, nickel (Ni), and Au are stacked in this order from the wavelength converting section 30t side. 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.

[0098] <2. Other embodiments> The present disclosure is not limited to the first embodiment described above, and various modifications and improvements can be made without departing from the gist of the present disclosure.

[0099] <2-1. Second embodiment> Fig. 16 is a perspective view showing an example of the configuration of the wavelength conversion element 30 according to the second embodiment. Fig. 17 is a cross-sectional view showing an example of the configuration of the wavelength conversion element 30 according to the second embodiment.

[0100] 16 and 17, the wavelength conversion element 30 may be modified to a wavelength conversion element 30A in which a wavelength conversion portion 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 portion 30t is fixed to the third surface F3 of the recess 30r. The side surface of the wavelength conversion portion 30t contacts the fourth surface F4 of the recess 30r.

[0101] With this configuration, the excitation light L0 that is scattered inside the wavelength conversion unit 30t and is not converted into the fluorescence L1 is reflected by the fourth surface F4, which serves as the side surface of the recess 30r of the base material 30bA, and returns to the inside of the wavelength conversion unit 30t, where it can be converted into the fluorescence L1. Furthermore, because the side surface of the wavelength conversion unit 30t is in contact with the fourth surface F4 of the recess 30r, heat generated in the wavelength conversion unit 30t is dissipated from the fourth surface F4 to the outside via the base material 30b, and the temperature rise in the wavelength conversion unit 30t can be reduced.

[0102] With this configuration, excitation light L0 that is scattered inside the wavelength conversion unit 30t and is not converted into fluorescence L1 is reflected by the fourth surface F4, which serves as the side surface of the recess 30r of the base material 30bA, and returns to the inside of the wavelength conversion unit 30t, where it can be converted into fluorescence L1. Furthermore, because the side surface of the wavelength conversion unit 30t is in contact with the fourth surface F4 of the recess 30r, heat generated in the wavelength conversion unit 30t is dissipated from the fourth surface F4 to the outside via the base material 30b, and the temperature rise of the wavelength conversion unit 30t can be reduced.

[0103] 18 is a flowchart showing an example of a manufacturing flow of the wavelength conversion element 30A according to the second embodiment. Hereinafter, the manufacturing method of the wavelength conversion element 30A will be described with reference to FIG.

[0104] First, a substrate 30bA as shown in FIGS. 16 and 17 is prepared (step S11). The substrate 30bA has, for example, a disk-like shape overall, with a recess 30r on a first plate surface. For example, the depth of the recess 30r of the substrate 30bA is set to 0.03 mm to 1 mm, and the thickness of the substrate 30bA below the bottom surface of the recess 30r is set to 0.05 mm to 10 mm. The depth of the recess 30r is set to be greater than the thickness of the wavelength converting section 30t. For example, if the thickness of the wavelength converting section 30t is 0.03 mm, the depth of the recess 30r is set to 0.05 mm to 0.5 mm. Furthermore, for example, the diameter of the substrate 30bA is set to 0.5 mm to 30 mm, and the diameter of the recess 30r is set to 0.1 mm to 10 mm.

[0105] The material of the substrate 30bA is a material with a thermal expansion coefficient close to that of the wavelength converting section 30t. For example, a metal or inorganic material with a thermal expansion coefficient within ±50% of the thermal expansion coefficient of the low-melting-point glass that is the material of the binder layer 32 of the wavelength converting section 30t may be used. For example, when a metal material is used for the substrate 30bA, aluminum or an aluminum alloy may be used as the metal material. For example, when a material with high light reflectivity, such as aluminum, is used for the substrate 30bA, the surface of the substrate 30bA may be polished to a mirror finish by physical polishing or chemical polishing to improve the visible light reflectance of the surface of the substrate 30bA. Furthermore, when a metal material is used for the substrate 30bA, the substrate 30bA may be formed by, for example, cutting using a machining process or molding using a die-casting method.

[0106] Ceramics may also be used as the material for the substrate 30bA. In this case, the substrate 30bA may be formed using laminated ceramics, or by powder pressure molding. For example, the substrate 30bA may be formed from laminated ceramics by stacking a ring-shaped green sheet with a through-hole corresponding to the recess 30r and a disk-shaped green sheet without a through-hole, and sintering the stacked green sheets. Alternatively, the substrate 30bA may be formed by powder pressure molding, for example, by filling a first mold with ceramic powder having a cylindrical opening, and applying pressure to the ceramic powder filled in the first mold using a second mold for forming a recess corresponding to the recess 30r. For example, the substrate 30bA may be formed by mixing ceramic powder with wax, a binder, or the like, and applying pressure to form a molded body with a recess corresponding to the recess 30r, and then sintering the molded body. Ceramics that can be used as the material of the substrate 30bA include, for example, alumina (aluminum oxide), aluminum nitride, silicon nitride, mullite, and zirconia.

[0107] Alternatively, the base material 30bA may be formed of ceramic and metal. For example, the base material 30bA may be formed by bonding a ring-shaped member (also referred to as a metal member) made of metal such as 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 forms the recess 30r. Examples of the bonding material include brazing material primarily containing Ag or Cu. Alternatively, examples of the bonding material include brazing material primarily containing Al, solder primarily containing Sn, Ag, and Cu, or resin bonding materials such as epoxy, silicone, or acrylic. The thermal conductivity of the base material 30bA may be enhanced by adding a filler (also referred to as a high-thermal-conductivity filler) with high thermal conductivity, such as Ag, AlN, or boron nitride (BN).

[0108] The base material 30bA may be formed by bonding a ceramic substrate and a ceramic ring-shaped member with a bonding material, instead of forming the base material 30bA from laminated ceramics by co-firing. In this case, the bonding material described above can also be used.

[0109] Next, a powder (mixed powder) obtained by thoroughly mixing phosphor powder and glass powder is filled into the recess 30r to form a powder filler (step S12). The mixed powder may contain, for example, powders other than phosphor powder and glass powder. Here, the content of phosphor powder in the mixed powder, the materials, composition, and mixing method of the phosphor particles and glass powder are the same as those described in the first embodiment, and therefore will not be described again.

[0110] Next, the powder filler is heated together with the base material 30bA in which the powder filler is filled in the recesses 30r to form a pre-sintered body (step S13).

[0111] Next, after the heating temperature reaches the set temperature, the pre-sintered body is subjected to pressure processing on the base material 30bA while the set temperature is maintained (step S14).

[0112] The explanation of the heating and pressurizing of the powder packing body overlaps with the explanation in the first embodiment, and therefore will be omitted.

[0113] Next, the pre-sintered body is cooled while maintaining the pressure applied to the pre-sintered body during pressurization (step S15), and the pressure is released when the temperature of the pre-sintered body becomes lower than the melting point of the glass powder. As a result, the pre-sintered body becomes the wavelength converting unit 30t.

[0114] The wavelength conversion element 30A can be manufactured by the above steps. In addition, for example, since the powder filler is formed in the recess 30r of the base material 30bA, the step S2 of superposing the mask on the base material and the step S4 of removing the mask are not required in the manufacturing method of the wavelength conversion element 30 according to the first embodiment described using the manufacturing flow of Fig. 10, and therefore the manufacturing process can be simplified.

[0115] <3.Other> In each of the above embodiments, the wavelength converting unit 30t includes a plurality of phosphor particles 31 and a binder layer 32. The wavelength converting unit 30t may further include particles other than the plurality of phosphor particles 31 and the binder layer 32. The particles may be, for example, thermally conductive particles. The thermally conductive particles have a higher thermal conductivity than the binder layer 32. The thermally conductive particles may be made of a metal nitride such as boron nitride or aluminum nitride, or a metal oxide such as aluminum oxide, zinc oxide, titanium dioxide, beryllium oxide, magnesium oxide, nickel oxide, vanadium oxide, copper oxide, iron oxide, or silver oxide. The thermally conductive particles may be made of a silicon compound such as quartz powder, silicon carbide, or mica. The thermally conductive particles may be made of two or more types of particles made of different materials.

[0116] In each of the above embodiments, for example, each of the one or more types of phosphor particles corresponding to the plurality of phosphor particles 31 may be a single type of phosphor particle that emits fluorescence having one wavelength spectrum in response to irradiation with excitation light L0.

[0117] Furthermore, for example, the multiple types of phosphor particles 31 included in the multiple phosphor particles 31 may include at least a first type of phosphor particles 31 that emit a first fluorescence having a first wavelength spectrum in response to irradiation with excitation light L0, and a second type of phosphor particles 31 that emit 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 particles 31 and the second type of phosphor particles 31, for example, two types of phosphor particles selected from red phosphor particles, green phosphor particles, and blue phosphor particles may be used.

[0118] Furthermore, for example, the multiple types of phosphor particles 31 included in the multiple phosphor particles 31 may include a third type of phosphor particles 31 that emits third fluorescence having a third wavelength spectrum different from both the first wavelength spectrum and the second wavelength spectrum in response to irradiation with excitation light L0. As the first type of phosphor particles 31, the second type of phosphor particles 31, or the three types of phosphor particles 31, 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, may be used.

[0119] The blue-green phosphor is a phosphor that emits blue-green fluorescence in response to irradiation with excitation light L0. The yellow phosphor is a phosphor that emits yellow fluorescence in response to irradiation with excitation light L0. As the blue-green phosphor, for example, a phosphor that emits fluorescence in response to irradiation with excitation light L0 with a peak wavelength in the range of about 495 nm is used. As the material for the blue-green phosphor, for example, (Sr,Ba,Ca)5(PO4)3Cl:Eu or Sr4Al 14 O 25 :Eu, etc. is used. As the yellow phosphor, for example, a phosphor is used that emits fluorescence in response to irradiation with excitation light L0 with a peak wavelength in the range of approximately 570 nm to 590 nm. As the material for the yellow phosphor, for example, SrSi2(O,Cl)2N2:Eu, etc. is used. Here, the ratio of the elements in parentheses can be set arbitrarily as long as it is within the range of the molecular formula.

[0120] Furthermore, for example, the multiple types of phosphor particles 31 contained in the plurality of phosphor particles 31 may include four or more types of phosphor particles 31. The phosphor particles 31 may have five types of phosphors including red, green, and blue phosphors. As described above, the phosphor particles 31 may include at least a red phosphor, a green phosphor, and a blue phosphor. Furthermore, the general color rendering index (Ra) of the phosphor L1 may be 90 or more or 95 or more. This allows high color rendering properties to be achieved.

[0121] In each of the above embodiments, for example, the light source unit 2 and the conversion unit 3 may be positioned in close proximity to each other. 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 may be irradiated via an optical element such as a collimator lens.

[0122] In each of the above embodiments, for example, the binder layer 32 may contain a plurality of fine crystal particles (also referred to as "fine crystal particles") in addition to the amorphous phase of glass. The fine crystal particles are crystalline particles. Each of the plurality of fine crystal particles may contain at least some of the components contained in the amorphous phase of glass. Each of the plurality of fine crystal particles may be a crystal of one or more oxides from a group of oxides (also referred to as a first oxide group) including, for example, SiO2, Al2O3, BO3, Na2O3, KO, Li2O, CaO, BaO, ZnO, PbO, and PO5, or may be a crystal of an oxide (also referred to as a composite oxide) composed of two or more oxides from the first oxide group. For example, the fine crystal particles may be composed of ZnO. The fine crystal particles may be crystalline particles containing all of the components contained in the amorphous phase of glass. In other words, at least a portion of the components contained in the amorphous phase may be a portion of the components contained in the amorphous phase, or may be all of the components contained in the amorphous phase.

[0123] The size of the plurality of microcrystalline particles may be smaller than the size of the plurality of phosphor particles 31, for example. Here, the state in which the size of the plurality of microcrystalline particles is smaller than the size of the plurality of phosphor particles may mean, for example, that the average particle size of the plurality of microcrystalline particles is smaller than the average particle size of the plurality of phosphor particles 31, or that each particle size of the plurality of microcrystalline particles is smaller than the average particle size of the plurality of phosphor particles 31. The particle size of the particle may be, for example, the average (also referred to as the geometric mean diameter) of the diameter of the particle in the major axis direction (also referred to as the major axis diameter) and the diameter of the particle in the minor axis direction (also referred to as the minor axis diameter), or may be a value (also referred to as the equivalent diameter) converted into the diameter of a circular or spherical particle using the area or volume projected onto a plane and a predetermined geometric formula, or may be the length of the particle in the longitudinal direction (also referred to as the maximum diameter). The particle size of the microcrystalline particles may be, for example, approximately 0.1 μm to 3 μm.

[0124] The fine crystal particles have transparency that allows the excitation light L0 and the fluorescence L1 to pass through, for example. The fine crystal particles may also have a property of scattering a portion of the excitation light L0 and the fluorescence L1, for example.

[0125] The plurality of microcrystalline particles may include one or more microcrystalline particles in contact with one or more of the plurality of phosphor particles 31. For example, one microcrystalline particle may be in contact with one phosphor particle 31, or two or more microcrystalline particles may be in contact with one phosphor particle 31. Here, if the thermal conductivity of the microcrystalline particles is higher than that of the amorphous phase of the glass, the presence of the microcrystalline particles in contact with the phosphor particles 31 can improve the rate at which heat dissipates from the phosphor particles 31 due to heat transfer and conduction through the microcrystalline particles. This can reduce the decrease in the light intensity of the fluorescence L1 emitted in response to irradiation with the excitation light L0. In other words, the luminous efficiency of the wavelength conversion element 30 can be improved.

[0126] As mentioned above, the wavelength conversion element has been described in detail, but the above description is merely an example in all respects, and this disclosure is not limited thereto.In addition, the above-mentioned various examples can be applied in combination as long as they are not mutually contradictory.And, it is understood that countless examples that are not exemplified can be envisioned without departing from the scope of this disclosure.

[0127] This disclosure includes the following:

[0128] In one embodiment, (1) the wavelength conversion element has a wavelength conversion portion including a plurality of phosphor particles and a binder layer that bonds the plurality of phosphor particles together and contains glass, and the thickness of the wavelength conversion portion may be 30 μm or more and 100 μm or less, and the volume concentration of the plurality of phosphor particles in the wavelength conversion portion may be 20 vol% or more.

[0129] (2) In the wavelength conversion element of (1) above, the volume concentration may be 35 vol % or more, and the thickness may be 30 μm or more and 70 μm or less.

[0130] (3) In the wavelength conversion element of (2) above, the thickness may be 40 μm or more and 60 μm or less.

[0131] (4) In the wavelength conversion element of any one of (1) to (3), the volume concentration may be 70 vol % or less.

[0132] (5) A wavelength conversion element according to any one of (1) to (4), wherein the binder layer may contain an alkali metal oxide, and the molar concentration of the alkali metal oxide in the binder layer may be 10 mol% or more and 19 mol% or less.

[0133] (6) In the wavelength conversion element of any one of (1) to (5), the density of the wavelength conversion portion may be 82% or more.

[0134] (7) Any one of the wavelength conversion elements (1) to (6) above may further comprise a reflective substrate supporting the wavelength conversion portion and having a reflectivity higher than that of the wavelength conversion portion, and the binder layer may be directly bonded to the reflective substrate.

[0135] (8) In the wavelength conversion element of (7) above, the reflective substrate can be made of aluminum oxide.

[0136] (9) In the wavelength conversion element of (8), the binder layer can be made of borosilicate zinc glass.

[0137] (10) A light emitting device may include the wavelength conversion element according to any one of (1) to (9) above, and a laser light source unit that outputs excitation light to the wavelength conversion element.

[0138] (11) The light emitting device according to (10) above, wherein the laser light source unit emits 1.91 W / mm 2 When the excitation light is irradiated at 1000 nm, the fluorescence emitted from the wavelength conversion portion may have a light intensity of 440 lm or more.

[0139] (12) In the light-emitting device according to (10) or (11), the wavelength conversion unit may include at least a red phosphor, a green phosphor, and a blue phosphor, and the general color rendering index of the fluorescence emitted from the wavelength conversion unit may be 90 or more. [Explanation of symbols]

[0140] 2 Laser light source unit (light source unit) 30 Wavelength conversion element 30b,30bA base material 30t Wavelength conversion unit 31 Phosphor particles 32 binder layer L0 excitation light

Claims

1. a wavelength conversion unit including a plurality of phosphor particles and a binder layer that bonds the plurality of phosphor particles together and that contains glass; the thickness of the wavelength converting portion is 30 μm or more and 100 μm or less, A wavelength conversion element, wherein the volume concentration of the plurality of phosphor particles in the wavelength conversion portion is 20 vol % or more.

2. The wavelength conversion element according to claim 1, The volume concentration is 35 vol% or more, The wavelength conversion element has a thickness of 30 μm or more and 70 μm or less.

3. The wavelength conversion element according to claim 2, The wavelength conversion element has a thickness of 40 μm or more and 60 μm or less.

4. 4. The wavelength conversion element according to claim 1, The volume concentration of the wavelength conversion element is 70 vol % or less.

5. 4. The wavelength conversion element according to claim 1, the binder layer contains an alkali metal oxide; A wavelength conversion element, wherein the molar concentration of the alkali metal oxide in the binder layer is 10 mol % or more and 19 mol % or less.

6. 4. The wavelength conversion element according to claim 1, A wavelength conversion element, wherein the density of the wavelength conversion portion is 82% or more.

7. 4. The wavelength conversion element according to claim 1, a reflective substrate supporting the wavelength converting portion and having a reflectance higher than that of the wavelength converting portion; The wavelength converting element, wherein the binder layer is directly bonded to the reflective substrate.

8. The wavelength conversion element according to claim 7, The wavelength conversion element, wherein the reflective substrate is formed of aluminum oxide.

9. The wavelength conversion element according to claim 8, The wavelength conversion element, wherein the binder layer is formed of zinc borosilicate glass.

10. A wavelength conversion element according to any one of claims 1 to 3; a laser light source unit that outputs excitation light to the wavelength conversion element; A light emitting device comprising:

11. 11. The light emitting device according to claim 10, The laser light source unit emits 1.91 W / mm ２ When the excitation light is irradiated, the fluorescence emitted from the wavelength conversion unit has a light intensity of 440 lm or more.

12. 11. The light emitting device according to claim 10, the wavelength conversion unit includes at least a red phosphor, a green phosphor, and a blue phosphor; The light emitting device, wherein the fluorescence emitted from the wavelength converting portion has an average color rendering index of 90 or more.

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