Near-infrared light-emitting device and electronic apparatus

Abstract

A near-infrared light-emitting device (1) comprises: at least one solid-state light-emitting element (10) that emits primary light (11) having a maximum spectral intensity within a wavelength range of not less than 380 nm but less than 700 nm; a light diffuser (20) that diffuses the primary light (11) and emits diffused light (21); and a wavelength converter (30) including a near-infrared phosphor (31) that absorbs the diffused light (21) and converts the wavelength thereof into a near-infrared ray having a maximum fluorescence intensity within a wavelength range of not less than 700 nm but less than 2500 nm. The near-infrared light-emitting device emits output light (50) containing the near-infrared ray as a light component.

Description

Near-infrared light emitting device and electronic device

[0001] The present invention relates to a near-infrared light emitting device and an electronic device.

[0002] Conventionally, light-emitting devices that emit uniform white light by diffusing light emitted from solid-state light-emitting elements with a light diffuser have been known. Patent Document 1 discloses a lighting device that includes a substrate, a plurality of white LED elements mounted on the substrate, a plurality of near-infrared LED elements mounted on the substrate, and a diffused / transmitted case disposed opposite the plurality of white LED elements and the plurality of near-infrared LED elements. The blue LED elements emit blue light, and a diffuser containing a yellow phosphor is dispersed in the diffused / transmitted case. Therefore, the blue light emitted from the blue LED elements passes through the diffused / transmitted case and is diffused, resulting in the emission of white light.

[0003] JP 2015-076872 A

[0004] However, light emitted from solid-state light-emitting elements is highly directional, and near-infrared rays tend to penetrate materials more easily than visible light. It is believed that near-infrared rays emitted from the light output surface penetrate the transparent diffusion case of Patent Document 1 more easily than visible light, resulting in a weaker diffusion effect. Therefore, in the lighting device described in Patent Document 1, the in-plane distribution of the near-infrared intensity output from the light output surface becomes non-uniform, which may prevent the near-infrared rays from being uniformly irradiated onto the irradiated object.

[0005] The present invention has been made in view of the problems associated with the prior art, and an object of the present invention is to provide a near-infrared light-emitting device that emits near-infrared rays with a uniform intensity distribution within the light output surface, and an electronic device using the same.

[0006] In order to solve the above problems, a near-infrared light emitting device according to an embodiment of the present invention includes at least one solid-state light emitting element that emits primary light having a maximum spectral intensity within a wavelength range of 380 nm or more and less than 700 nm. The near-infrared light emitting device includes a light diffuser that diffuses the primary light to emit diffused light, and a wavelength converter that contains a near-infrared phosphor that absorbs the diffused light and converts it into near-infrared light having a maximum fluorescent intensity within a wavelength range of 700 nm or more and less than 2500 nm. The near-infrared light emitting device emits output light that contains near-infrared light as a light component.

[0007] An electronic device according to an aspect of the present invention includes a near-infrared light emitting device.

[0008] FIG. 1 is a schematic diagram showing an example of a near-infrared light emitting device according to an embodiment. FIG. 2 is a schematic diagram showing an example of the structure of a spectroscopy device according to an embodiment. FIG. 3 is a schematic diagram showing an example of the structure of a spectroscopy device according to another embodiment. FIG. 4 is a schematic diagram showing an evaluation device that captures output light from a near-infrared light emitting device according to an example. FIG. 5 is a fluorescence spectrum of a phosphor according to an example. FIG. 6 is a schematic diagram showing an evaluation device that captures output light from a near-infrared light emitting device according to Comparative Example 1. FIG. 7 is a schematic diagram showing an evaluation device that captures output light from a near-infrared light emitting device according to Comparative Example 2. FIG. 8 is a photograph capturing output light from a near-infrared light emitting device according to an example. FIG. 9 is a photograph capturing output light from a near-infrared light emitting device according to Comparative Example 1. FIG. 10 is a photograph capturing output light from a near-infrared light emitting device according to Comparative Example 2. FIG. 11 is a graph showing the relationship between blue LED power and fluorescent power. FIG. 12 is a graph showing the relationship between blue LED power and SWIR (short wave infrared) conversion efficiency.

[0009] The near-infrared light emitting device, electronic device, sensing system, and near-infrared spectroscopy according to the present embodiment will be described in detail below with reference to the drawings. Note that the dimensional proportions in the drawings are exaggerated for the sake of explanation and may differ from the actual proportions.

[0010] [Near-infrared Light-Emitting Device] As shown in FIG. 1 , the near-infrared light-emitting device 1 according to this embodiment includes at least one solid-state light-emitting element 10, a light diffuser 20, and a wavelength converter 30. The at least one solid-state light-emitting element 10 emits primary light 11 having a maximum spectral intensity within a wavelength range of 380 nm or more and less than 700 nm. The light diffuser 20 diffuses the primary light 11 to emit diffused light 21. The wavelength converter 30 includes a near-infrared phosphor 31 that absorbs the diffused light 21 and converts it into near-infrared light having a maximum fluorescence intensity within a wavelength range of 700 nm or more and less than 2500 nm. The near-infrared light-emitting device 1 emits output light 50 containing near-infrared light as a light component. The output light 50 may also contain the primary light 11.

[0011] With this configuration, the primary light 11, which includes highly directional visible light emitted by the solid-state light-emitting element 10, can be diffused by using a conventional light diffuser 20 that has the function of diffusing visible light. Furthermore, the diffused light 21, which is the result of diffusing the primary light 11, is absorbed by the near-infrared phosphor 31, which converts the wavelength of the diffused light 21 to near-infrared light. Therefore, near-infrared light with a homogenized intensity distribution within the light output surface due to the light scattering effect can be emitted from a relatively wide area. Therefore, the near-infrared light-emitting device 1 according to this embodiment can emit near-infrared light with a homogenized intensity distribution within the light output surface. The near-infrared light-emitting device 1 according to this embodiment can utilize conventional solid-state light-emitting elements 10 and a conventional light diffuser 20, and therefore has excellent industrial productivity.

[0012] Furthermore, according to the near-infrared light emitting device 1 of this embodiment, it is possible to emit output light 50 containing near-infrared light as a light component by using the solid-state light emitting elements 10 of visible light, without using expensive near-infrared solid-state light emitting elements. This makes it possible to reduce the manufacturing cost of the near-infrared light emitting device 1. Furthermore, in the near-infrared light emitting device 1 of this embodiment, the light is diffused using the light diffuser 20, so the number of solid-state light emitting elements 10 used can also be reduced. Each component will be described in detail below.

[0013] In this specification, light with a wavelength of 380 nm or more and less than 700 nm is defined as visible light, and light with a wavelength of 700 nm or more and less than 2500 nm is defined as near-infrared light. Also, in this specification, visible light is also referred to as visible light rays, and near-infrared light is also referred to as near-infrared light.

[0014] (Solid-state light-emitting element 10) The solid-state light-emitting element 10 is configured to emit primary light 11. The solid-state light-emitting element 10 is an element that converts electricity into light, and when power is supplied and driven, it converts the supplied electrical energy into light energy. The converted light energy is then emitted as primary light 11 (excitation light) from the light extraction surface. The solid-state light-emitting element 10 may include, for example, a light-emitting diode (LED) or a laser diode.

[0015] The at least one solid-state light-emitting element 10 may be a single solid-state light-emitting element 10, or may be a plurality of solid-state light-emitting elements 10 as shown in FIG. 1 . The plurality of solid-state light-emitting elements 10 may each emit primary light 11 in the same direction. Such a near-infrared light-emitting device 1 has a large light output surface area, making it suitable as a surface-emitting near-infrared light-emitting device 1. The number of solid-state light-emitting elements 10 may be 2 or more, 5 or more, 9 or more, 25 or more, 36 or more, 49 or more, 64 or more, 81 or more, or 100 or more. The number of solid-state light-emitting elements 10 may be 100 or less, 81 or less, 64 or less, 49 or less, 36 or less, 25 or less, 16 or less, or 9 or less.

[0016] The plurality of solid-state light-emitting elements 10 may be arranged at equal intervals. Such a near-infrared light-emitting device 1 can emit the primary light 11 at equal intervals. Therefore, the visible light diffused by the light diffuser 20 can also be emitted at equal intervals. Therefore, it is possible to provide a surface-emitting near-infrared light-emitting device 1 that emits uniform near-infrared light over a wide area.

[0017] The plurality of solid-state light-emitting elements 10 may be arranged at intervals of less than 100 cm on average. Arranging the plurality of solid-state light-emitting elements 10 closely in this manner can further reduce the intensity unevenness of the primary light 11 in any plane. Therefore, the diffused light 21 (visible light) diffused by the light diffuser 20 can be homogenized, thereby emitting uniform near-infrared light. The intervals between the plurality of solid-state light-emitting elements 10 may be less than 30 cm, less than 3 cm, or less than 1 cm on average. The intervals between the plurality of solid-state light-emitting elements 10 may be 1 cm or more on average. The solid-state light-emitting elements 10 may be arranged one-dimensionally to form a one-dimensional array, thereby forming a line-emitting near-infrared light-emitting device 1. The solid-state light-emitting elements 10 may also be arranged two-dimensionally to form a two-dimensional array, thereby forming a surface-emitting near-infrared light-emitting device 1. Note that an average interval of less than 100 cm means that the average interval between the most adjacent solid-state light-emitting elements 10 is less than 100 cm.

[0018] The primary light 11 has a maximum spectral intensity within a wavelength range of 380 nm or more and less than 700 nm. In this way, primary light 11 in the violet to red wavelength range can be utilized in an orthodox solid-state light-emitting device 10 including a light-emitting layer exhibiting a direct transition type luminescence transition, which is expected to achieve high efficiency or high output. Therefore, a near-infrared light-emitting device 1 can be provided that does not require advanced technology and has high industrial productivity.

[0019] The primary light 11 may be visible light having a maximum spectral intensity within a wavelength range of 440 nm or more and less than 660 nm. Specifically, the primary light 11 may be visible light having a maximum spectral intensity within either a blue wavelength range of 440 nm or more and less than 480 nm, or a red wavelength range of 620 nm or more and less than 660 nm. If the primary light 11 has a maximum spectral intensity within a wavelength range of 440 nm or more and less than 480 nm, a high-power, highly efficient, and easily available blue LED can be used. If the primary light 11 has a maximum spectral intensity within a wavelength range of 620 nm or more and less than 660 nm, a high-power, highly efficient, and easily available red LED can be used.

[0020] (Light diffuser 20) The light diffuser 20 diffuses the primary light 11 to emit diffused light 21. Near-infrared light has the property of easily passing through materials compared to visible light. Therefore, near-infrared light diffusion technology requires advanced technology. Implementing such technology is likely to increase manufacturing costs, which may hinder its industrial use. However, in the near-infrared light emitting device 1 according to this embodiment, the light diffuser 20 diffuses the primary light 11, which includes visible light. Therefore, it is possible to provide a near-infrared light emitting device 1 that emits near-infrared light with a uniform intensity distribution within the light output surface, without implementing such advanced technology.

[0021] The light diffuser 20 may transmit the primary light 11 and emit diffused light 21. For example, the light diffuser 20 may primarily contain a resin, particularly a translucent resin. Such a light diffuser 20 is easy to mold and process, and offers a wide range of technical options for materials and construction methods. Therefore, such a near-infrared light-emitting device 1 is highly industrially producible and can easily meet customer needs. Note that "the light diffuser 20 primarily contains a resin" means that the light diffuser 20 contains 50% or more by volume of resin. The light diffuser 20 may also contain 60% or more by volume, 70% or more by volume, 80% or more by volume, 90% or more by volume, or 99% or more by volume of resin. The light diffuser 20 may contain only a resin. The light diffuser 20 may be a diffusion plate or a light guide plate.

[0022] A light guide plate is a component processed to emit light from its light exit surface. The light guide plate may have at least one of concave and convex portions that reflect the primary light 11 on the processed surface, which is the surface opposite to the light exit surface. The primary light 11 may be guided from an end of the light guide plate perpendicular to the light exit surface, reflected by the concave or convex portions on the processed surface, and output from the light exit surface. This embodiment also makes it possible to irradiate a wide area with output light 50 containing near-infrared light components. This reduces the amount of solid-state light-emitting elements 10 used. Furthermore, since there is no need to use near-infrared LEDs, which are generally more expensive than blue LEDs, an inexpensive near-infrared light-emitting device 1 can be fabricated using only a small number of solid-state light-emitting elements 10 and a general light guide plate.

[0023] The light diffuser 20 may include, for example, a matrix and a plurality of diffusing particles dispersed in the matrix. The matrix may primarily contain a resin, particularly a translucent resin. The resin content of the matrix may be 50% by volume or more, 60% by volume or more, 70% by volume or more, 80% by volume or more, 90% by volume or more, or 99% by volume or more. The resin content of the matrix may be 90% by volume or less, 80% by volume or less, 70% by volume or less, or 60% by volume or less. The diffusing particles can diffuse light that has passed through the light diffuser 20 by causing diffuse reflection. The diffusing particles may include at least one of inorganic particles and organic particles.

[0024] The inorganic particles may contain at least one metal element selected from the group consisting of alkali metals, alkaline earth metals, transition metals, base metals, and metalloids. In this specification, alkali metals include lithium, sodium, potassium, rubidium, cesium, and francium. Alkaline earth metals include calcium, strontium, barium, and radium, as well as beryllium and magnesium. Base metals include aluminum, zinc, gallium, cadmium, indium, tin, mercury, thallium, lead, bismuth, and polonium. Metalloids include boron, silicon, germanium, arsenic, antimony, and tellurium. The inorganic particles may contain at least one element selected from the group consisting of metals, metal salts, oxides, hydroxides, nitrides, borides, carbonates, fluorides, carbides, and sulfides. The diffusing particles may contain, for example, silica.

[0025] The organic particles may contain resin particles, and the resin contained in the resin particles may contain at least one resin selected from the group consisting of polyethylene, polypropylene, polyester, acrylic resin, polycarbonate, polystyrene, epoxy resin, and polyurethane.

[0026] The average particle diameter of the diffusing particles is not particularly limited, and may be 0.5 μm or more, 1 μm or more, 3 μm or more, or 5 μm or more. The average particle diameter of the diffusing particles may be 50 μm or less, 30 μm or less, 20 μm or less, or 10 μm or less. The average particle diameter of the diffusing particles is calculated as the average value of particle diameters of particles observed in several to several tens of fields of view using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0027] The content of the matrix contained in the light diffuser 20 may be 10% by volume or more, 20% by volume or more, 30% by volume or more, 40% by volume or more, 50% by volume or more, 60% by volume or more, 70% by volume or more, 80% by volume or more, or 90% by volume or more. The content of the matrix contained in the light diffuser 20 may be 90% by volume or less, 80% by volume or less, 70% by volume or less, 60% by volume or less, 50% by volume or less, 40% by volume or less, 30% by volume or less, or 20% by volume or less.

[0028] The content of the diffusing particles contained in the light diffuser 20 may be 10% by volume or more, 20% by volume or more, 30% by volume or more, 40% by volume or more, 50% by volume or more, 60% by volume or more, 70% by volume or more, 80% by volume or more, or 90% by volume or more. The content of the diffusing particles contained in the light diffuser 20 may be 90% by volume or less, 80% by volume or less, 70% by volume or less, 60% by volume or less, 50% by volume or less, 40% by volume or less, 30% by volume or less, or 20% by volume or less.

[0029] The light diffuser 20 may have an uneven surface, and the uneven surface may diffuse light. The pitch, height, and density of the recesses or protrusions of the uneven surface are not particularly limited as long as they can diffuse light, and can be adjusted as appropriate. The light diffuser 20 may have unevenness on only one of the light incident surface and the light exit surface, or may have unevenness on both surfaces. The method for forming the unevenness is not particularly limited, and the surface of the substrate may be roughened, or a member having unevenness may be provided on the surface of the substrate.

[0030] The light diffuser 20 may not contain a phosphor. For example, the light diffuser 20 may not contain a phosphor that emits fluorescence with a fluorescence peak in the wavelength range of 700 nm or more and less than 2500 nm. For example, the diffused light 21 may include light with a maximum spectral intensity in the wavelength range of 380 nm or more and less than 700 nm, and may not include near-infrared light wavelength-converted by the near-infrared phosphor 31. In such a near-infrared light-emitting device 1, the light diffuser 20 does not emit near-infrared light derived from the phosphor. This makes it possible to simplify the spectral distribution of the output light 50 and suppress interference between fluorescence emitted by different phosphors. Furthermore, since the structure of the light diffuser 20 can be simplified, a near-infrared light-emitting device 1 with high industrial productivity can be provided without requiring advanced technology or a large number of steps. The light diffuser 20 may not contain a red phosphor that emits fluorescence with a fluorescence peak in the wavelength range of 600 nm or more and less than 660 nm. Furthermore, the diffused light 21 may have the same light components as the primary light 11.

[0031] The shape of the light diffuser 20 is not particularly limited and may be a plate or sheet. In this case, the light diffuser 20 has a shape that extends horizontally relative to the thickness direction. Therefore, the diffused light 21 emitted by the light diffuser 20 can be irradiated onto the wavelength converter 30 over a wide area.

[0032] The light diffuser 20 may have a flat light exit surface that emits the diffused light 21. In this case, the surface of the wavelength converter 30 that faces the light diffuser 20 becomes flat. Therefore, when the light diffuser 20 and the wavelength converter 30 are bonded together to form an integrated body, the near-infrared light emitting device 1 can be made thin. Note that a flat light exit surface means that the surface is curved and does not have irregularities.

[0033] (Wavelength Converter 30) The wavelength converter 30 includes a near-infrared phosphor 31. The near-infrared phosphor 31 absorbs the diffused light 21 and emits near-infrared light having a maximum fluorescence intensity within a wavelength range of 700 nm or more and less than 2500 nm.

[0034] The near-infrared phosphor 31 may emit near-infrared light having a maximum fluorescence intensity within a wavelength range of 700 nm or more and less than 1000 nm. Fluorescence having light components within such a wavelength range is suitable for detecting the characteristic absorption bands of the stretching vibrations of N-H, C-H, and O-H. The fluorescence emitted by the near-infrared phosphor 31 may have a maximum fluorescence intensity within a wavelength range of 700 nm or more and 900 nm or less, or within a wavelength range of 780 nm or more and 860 nm or less.

[0035] The near-infrared phosphor 31 may emit near-infrared light having a maximum fluorescence intensity within a wavelength range of 1000 nm or more but less than 2500 nm. Fluorescence having light components within such wavelength ranges is suitable for evaluating the quality of food products such as fresh fish and meat, and for analyzing resin components for the purpose of plastic sorting. The fluorescence emitted by the near-infrared phosphor 31 may have a maximum fluorescence intensity at 1050 nm or more, 1100 nm or more, 1150 nm or more, or 1200 nm or more. Furthermore, the fluorescence emitted by the near-infrared phosphor 31 may have a maximum fluorescence intensity at 1600 nm or less, 1500 nm or less, 1400 nm or less, 1300 nm or less, or 1250 nm or less.

[0036] In addition, when brightness saturation was investigated for near-infrared phosphors that emit near-infrared light with a maximum fluorescence intensity within a wavelength range of 1000 nm or more and less than 2500 nm, it was found that such near-infrared phosphors are prone to brightness saturation. For example, the brightness saturation constant, which represents the effect of brightness saturation, for such near-infrared phosphors was 0.1 or more and less than 0.8. However, the wavelength converter 30 according to this embodiment uses relatively low-output light transmitted through the light diffuser 20 as excitation light. Therefore, the effect of brightness saturation can be reduced.

[0037] The luminance saturation constant is expressed by the following formula: I=αI ｕｖ γ In the above formula, I is the luminance of light emitted, I ｕｖ is the excitation intensity, α is a constant, and γ is a brightness saturation constant. The brightness saturation constant γ is a positive number equal to or less than 1, and a brightness saturation constant γ of 1 means that there is no brightness saturation.

[0038] The near-infrared phosphor 31 preferably has an excitation spectrum with a wavelength of 400 nm to 700 nm, in which the ratio of the minimum intensity to the maximum intensity is 20% to 100%. This makes it less susceptible to the wavelength and spectrum of the primary light 11 and makes it easier to use with all kinds of LEDs, such as blue LEDs, red LEDs, and white LEDs. This makes it a highly versatile near-infrared phosphor.

[0039] The near-infrared phosphor 31 can be any of various inorganic phosphors known for use in near-infrared light sources. Specifically, the near-infrared phosphor 31 may contain at least one of transition metal ions and rare earth ions as fluorescent ions. Among these, it is preferable that the near-infrared phosphor 31 contains transition metal ions as fluorescent ions. In this way, it is possible to use a near-infrared phosphor 31 that is easy to procure or synthesize. Therefore, it is possible to provide a near-infrared light emitting device 1 that is highly practical. The transition metal ions are Ti, ３＋ , V ４＋ , Cr ４＋ , V ３＋ , Cr ３＋ , V ２＋ , Mn ４＋ , Fe ３＋ , Co ３＋ , Co ２＋ and Ni ２＋ Among these, the transition metal ion may be at least one selected from the group consisting of Cr ３＋ , Cr ４＋ and Ni ２＋ It is preferable that the ion is at least one selected from the group consisting of:

[0040] The near-infrared phosphor 31 may be an oxide, sulfide, nitride, halide, oxysulfide, oxynitride, or oxyhalide, or may be at least one selected from the group consisting of halophosphates, phosphates, halosilicates, silicates, aluminates, aluminosilicates, borates, germanates, nitridesilicates, nitride-aluminosilicates, oxynitride-silicates, and nitride-aluminosilicates.

[0041] Cr ３＋The activator phosphor may be a composite oxide phosphor having a garnet-type crystal structure, which has a proven track record in practical use. ３＋ The activated garnet phosphor is Y ３ Al ２ (AlO ４ ) ３ : Cr ３＋ , La ３ Al ２ (AlO ４ ) ３ : Cr ３＋ , Gd ３ Al ２ (AlO ４ ) ３ : Cr ３＋ , Y ３ Ga ２ (AlO ４ ) ３ : Cr ３＋ , La ３ Ga ２ (AlO ４ ) ３ : Cr ３＋ , Gd ３ Ga ２ (AlO ４ ) ３ : Cr ３＋ , Y ３ Sc ２ (AlO ４ ) ３ : Cr ３＋ , La ３ Sc ２ (AlO ４ ) ３ : Cr ３＋ , Gd ３ Sc ２ (AlO ４ ) ３ : Cr ３＋ , Y ３ Ga ２ (GaO ４ ) ３ : Cr ３＋ , La ３ Ga ２ (GaO ４ ) ３ : Cr ３＋ , (Gd, La) ３ Ga ２ (GaO ４ ) ３: Cr ３＋ , Gd ３ Ga ２ (GaO ４ ) ３ : Cr ３＋ , Y ３ Sc ２ (GaO ４ ) ３ : Cr ３＋ , La ３ Sc ２ (GaO ４ ) ３ : Cr ３＋ , Gd ３ Sc ２ (GaO ４ ) ３ : Cr ３＋ , and (Gd, La) ３ (Ga, Sc) ２ (GaO ４ ) ３ : Cr ３＋ It may be at least one selected from the group consisting of Cr ３＋ The activated garnet phosphor may be a solid solution containing these phosphors as end members.

[0042] The near-infrared phosphor 31 is a compound LiGa ５ O ８The near-infrared phosphor may include a near-infrared phosphor having at least chromium ions functioning as fluorescent ions added to a crystal of an inorganic compound having the same spinel-type crystal structure as the near-infrared phosphor described above. The near-infrared phosphor may emit fluorescence when irradiated with excitation light having a wavelength of 450 nm, and the spectral distribution of the fluorescence may have at least one fluorescence peak with a half-width of 120 nm or more within a wavelength range of 700 nm to 1600 nm. Such a near-infrared phosphor emits fluorescence having a wide spectrum anywhere in the near-infrared wavelength range of 700 nm to 1600 nm, and can be used alone as a near-infrared phosphor in a near-infrared light-emitting device 1. Therefore, the near-infrared phosphor is suitable for a near-infrared light-emitting device 1 for near-infrared spectroscopy. The half-width of the spectrum may be 140 nm or more, 160 nm or more, 180 nm or more, or 200 nm or more. The half-width of the spectrum may be 240 nm or less, or 220 nm or less. The number of the at least one fluorescence peak having the above-mentioned half-width may be one, two, or three or more.

[0043] Compound LiGa ５ O ８ Whether or not a near-infrared phosphor has the same spinel-type crystal structure as the compound LiGa registered in ICSD can be determined by measuring the X-ray diffraction pattern by X-ray diffraction. ５ O ８ (Registration No.: 33716). The near-infrared phosphor may contain nickel ions (described later) that function as fluorescent ions in the inorganic compound crystal. The near-infrared phosphor may contain only chromium as a fluorescent ion in the inorganic compound crystal.

[0044] The near-infrared phosphor is the compound LiGa ５ O ８At least nickel ions functioning as fluorescent ions may be added to the crystal of an inorganic compound having the same spinel-type crystal structure as the near-infrared phosphor. This configuration allows for the emission of fluorescence with a maximum fluorescence intensity within a wavelength range of 1000 nm to 1600 nm. Furthermore, such near-infrared phosphors may have a low proportion of emission line components and high fluorescence intensity. Furthermore, such near-infrared phosphors may have a high IQE (internal quantum efficiency) in the 1000-1600 nm wavelength range and a high ratio of the IQE in the 1000-1600 nm wavelength range to the total IQE. Therefore, such near-infrared phosphors can provide a near-infrared light-emitting device 1 advantageous for emitting light in the 1000-1600 nm wavelength range. The near-infrared phosphor does not necessarily need to have nickel ions functioning as fluorescent ions added to the inorganic compound crystal.

[0045] Compound LiGa ５ O ８ The same spinel type crystal as that of the phosphor of formula A may contain an alkali metal of group 1 element, at least one of a group 13 element and scandium, and oxygen. ｙ (D １－ｘ Cr ｘ ) ５ O ８ In the case where the composition is expressed as above, A may mainly contain an alkali metal, and D may mainly contain at least one of a Group 13 element and scandium. Note that D may mainly contain a Group 13 element. Such a composition has a chemical property similar to that of LiGa. ５ O ８ Therefore, LiGa, which has been found to exhibit a unique fluorescence spectrum shape and temperature quenching as a near-infrared phosphor, is used. ５ O ８ : Cr ３＋ It is expected that we can obtain near-infrared phosphors that exhibit fluorescence properties similar to those of

[0046] Here, "A containing an alkali metal as a main component" means that A contains 75 mol% or more of an alkali metal. A may contain 90 mol% or more, 95 mol% or more, or even 100 mol% of an alkali metal. Furthermore, "D containing at least one of a Group 13 element and scandium as a main component" means that D contains 75 mol% or more of at least one of a Group 13 element and scandium. D may contain 90 mol% or more, 95 mol% or more, or even 100 mol% of at least one of a Group 13 element and scandium.

[0047] The alkali metal is preferably at least one element selected from the group consisting of Li, Na, K, Rb, and Cs, and more preferably at least one element selected from the group consisting of Li, Na, and K. The Group 13 element is preferably at least one element selected from the group consisting of B, Al, Ga, and In, and more preferably Ga. In addition, LiGa ５ O ８ LiAl has the same spinel-type crystal structure as that of LiAl, and is doped with at least one of Cr and Ni. ５ O ８ The phosphor is LiGa ５ O ８ Compared to phosphors, it emits fluorescence with a shorter wavelength. ５ O ８ The phosphor can be sensed by a relatively inexpensive Si-based sensor, instead of a relatively expensive InGaAs-based sensor.

[0048] The above crystal is LiGa ５ O ８ It is preferable that the crystal contains LiGa as the main component, and that a part of Ga is substituted with Cr. ５ O ８ "Containing mainly LiGa" means that the crystal is ５ O ８ It means that the crystal contains 75 mol % or more of LiGa, and preferably 90 mol % or more of LiGa. ５ O ８It is also preferred that the alloy contains mainly Ga and that Ga is partially substituted with Cr and Ni.

[0049] The crystal preferably has a low alkali metal content relative to the stoichiometric composition. １－ｘ Cr ｘ ) ５ O ８ In this way, the chemical properties of the near-infrared phosphor are such that the element A is deficient. ５ O ８ Therefore, LiGa is a material that uses a crystal similar to that of ５ O ８ : Cr ３＋ It is expected to exhibit unique fluorescent properties similar to those of near-infrared phosphors, and when applied to spectroscopy, it is expected to enable highly accurate non-destructive measurements.

[0050] The near-infrared phosphor has the general formula A ｙ (D １－ｘ Cr ｘ ) ５ O ８ where A mainly contains an alkali metal, D mainly contains at least one of a Group 13 element and scandium, and y is preferably smaller than 1. When y is smaller than 1, a near-infrared phosphor with a low proportion of emission components of emission lines is obtained. y is more preferably 0.90 or less, even more preferably 0.85 or less, and particularly preferably 0.83 or less. y is preferably 0.70 or more. When y is 0.70 or more, the β-Ga ２ O ３ : Cr ３＋ This makes it difficult for phosphors to be mixed together, making it easier to obtain the desired unique fluorescent properties. y is more preferably 0.75 or more, and even more preferably 0.77 or more. Note that x is preferably greater than 0.005, more preferably greater than 0.01, even more preferably greater than 0.02, and particularly preferably greater than 0.03. Also, x is preferably less than 0.07, more preferably less than 0.06, even more preferably less than 0.05, and particularly preferably less than 0.04.

[0051] The near-infrared phosphor has the general formula Aｙ (D １－（ｘ＋ｚ） Cr ｘ Ni ｚ ) ５ O ８ It is preferable that the formula be represented by the formula: A and D, as well as x and y, are the same as above, and therefore their explanation will be omitted. z is preferably 0 or more, more preferably greater than 0.005, even more preferably greater than 0.01, particularly preferably greater than 0.02, and most preferably greater than 0.03. Furthermore, z is preferably less than 0.07, more preferably less than 0.06, even more preferably less than 0.05, and particularly preferably less than 0.04. (x + z) is preferably greater than 0.01, more preferably greater than 0.02, even more preferably greater than 0.025, and particularly preferably greater than 0.03. Furthermore, (x + z) is preferably less than 0.25, more preferably less than 0.10, and even more preferably less than 0.05. Furthermore, (x + z) may be less than 0.04. x may be greater than z, smaller than z, or the same as z. In the composition formula, A ｙ (D １－（ｘ＋ｚ） Cr ｘ Ni ｚ ) ５ O ８ However, the valence of Ni is not limited, and Ni can have any of the valences of 0, +1, +2, +3, and +4.

[0052] The wavelength converter 30 may contain only a near-infrared phosphor 31 as the phosphor. The near-infrared phosphor 31 may be a single type of near-infrared phosphor, or a combination of multiple types of near-infrared phosphors. When the wavelength converter 30 contains only a single type of near-infrared phosphor 31, not only is the configuration of the wavelength converter 30 simple, but only the light component of the primary light 11, which generally has a narrow spectral half-width, can be converted into near-infrared light. This makes it possible to provide a near-infrared light emitting device 1 that is suitable for industrial production and emits only near-infrared light. On the other hand, when the wavelength converter 30 contains multiple types of near-infrared phosphors 31, the spectral distribution of the near-infrared light component of the output light 50 can be easily controlled.

[0053] The wavelength converter 30 may further include a visible phosphor (not shown). The visible phosphor may be at least one phosphor selected from the group consisting of a green phosphor, a yellow phosphor, an orange phosphor, and a red phosphor. When the wavelength converter 30 includes a near-infrared phosphor 31 and a visible phosphor, the visibility of an object irradiated with the output light 50 can be ensured or improved. The green phosphor emits light having a maximum fluorescence intensity within a wavelength range of 490 nm or more and less than 570 nm. The yellow phosphor emits light having a maximum fluorescence intensity within a wavelength range of 570 nm or more and less than 585 nm. The orange phosphor emits light having a maximum fluorescence intensity within a wavelength range of 585 nm or more and less than 620 nm. The red phosphor emits light having a maximum fluorescence intensity within a wavelength range of 620 nm or more and less than 700 nm.

[0054] As shown in Fig. 1 , the wavelength converter 30 may further include a sealant 32 that seals the near-infrared phosphor 31. The sealant 32 may be at least one of an organic material and an inorganic material. Examples of organic materials include transparent or translucent organic materials such as silicone resin. Examples of inorganic sealants 32 include transparent or translucent inorganic materials such as low-melting-point glass. Note that although an example has been described in which the wavelength converter 30 includes the near-infrared phosphor 31 and the sealant 32, the wavelength converter 30 does not necessarily include the sealant 32.

[0055] In the wavelength converter 30, the light output surface that outputs near-infrared rays may be flat. In this case, the output light 50 containing near-infrared rays is output from a flat surface with a small surface area. This prevents the adhesion of dust to the light output surface and is convenient for cleaning work. Note that a flat light output surface means that the surface is curved and does not have any irregularities.

[0056] The wavelength converter 30 may be shaped like a plate or a sheet. In this way, the wavelength converter 30 has a shape that extends horizontally relative to the thickness direction. Therefore, the diffused light 21 of the primary light 11 emitted by the solid-state light-emitting element 10 can be incident on the wavelength converter 30 over a wide area. Therefore, the near-infrared light emitting device 1 can emit high-power output light 50 that is mainly composed of near-infrared light.

[0057] A gap may be provided between the light diffuser 20 and the wavelength converter 30. In such a near-infrared light-emitting device 1, the light diffuser 20 and the wavelength converter 30 are arranged at a distance from each other. Therefore, the diffused light 21 of the primary light 11 diffused by the light diffuser 20 can be further diffused in the gap and made incident on the wavelength converter 30. Therefore, the output light 50 can be made more homogenous.

[0058] The light diffuser 20 and the wavelength converter 30 may be in direct contact with each other without any gap therebetween. In such a near-infrared light-emitting device 1, the light diffuser 20 and the wavelength converter 30 are arranged without any distance between them. This allows the distance between the light diffuser 20 and the wavelength converter 30 to be reduced, thereby making it possible to reduce the thickness of the near-infrared light-emitting device 1.

[0059] 1 , when the near-infrared light emitting device 1 is viewed from the front of the light output surface that emits the output light 50, the light diffuser 20 may be arranged to cover the outer periphery of the main light extraction surface of the solid-state light emitting element 10, and the wavelength converter 30 may be arranged to cover the entire light diffuser 20. In this manner, most of the primary light 11 emitted by the solid-state light emitting element 10 is diffused by the light diffuser 20, and much of the diffused light 21 is easily wavelength-converted to near-infrared light by the wavelength converter 30. This improves the efficiency of converting input power to the solid-state light emitting element 10 or to an array of solid-state light emitting elements 10 into near-infrared light. The outer periphery of the main light extraction surface of the solid-state light emitting element 10 refers to the outer periphery of the array of main light extraction surfaces when the solid-state light emitting elements 10 are arranged in an array, for example.

[0060] The near-infrared light emitting device 1 according to this embodiment can output output light 50 containing near-infrared light components with a uniform in-plane distribution on the light output surface. It can also emit uniform near-infrared light components from a light output surface with a relatively large area. Since it can illuminate an irradiated object, such as a relatively large inspection target, with uniform near-infrared light, it is advantageous for high-precision near-infrared spectroscopic analysis. The near-infrared light emitting device 1 according to this embodiment can be used in electronic devices and near-infrared spectroscopy, as described below.

[0061] The near-infrared light emitting device 1 according to this embodiment can be used in methods such as an inspection method, a detection method, a monitoring method, a classification method, an analysis method, a measurement method, or an evaluation method.

[0062] [Electronic Device] Next, an electronic device according to this embodiment will be described. The electronic device according to this embodiment includes the near-infrared light emitting device 1 described above. In such an electronic device, the diffused light 21 is absorbed by the near-infrared phosphor 31, and the wavelength of the diffused light 21 is converted to near-infrared light. Therefore, the electronic device according to this embodiment can emit near-infrared light with a uniform intensity distribution within the light output surface.

[0063] The electronic devices can be used for any of the following purposes: medical care, veterinary care, biotechnology, agriculture, forestry and fisheries, livestock industry (meat, meat products, dairy products, etc.), or industrial use (for foreign matter inspection, content volume inspection, shape inspection, packaging condition inspection, etc.), and can be used for inspection of pharmaceuticals, animal experiments, food, beverages, agricultural, forestry and fishery products, livestock products, or industrial products.

[0064] The electronic device can be used for humans, animals, plants, or objects. The electronic device can also be used for gases, liquids, or solids.

[0065] The electronic device may be, for example, a medical device, a treatment device, a beauty device, a health device, a care-related device, an analytical device, a measuring device, or an evaluation device.

[0066] For example, for the purpose of medical or biotechnology development, the electronic device of this embodiment can be used for the inspection, detection, measurement, evaluation, analysis, interpretation, observation, monitoring, separation, diagnosis, treatment, purification, etc. of 1) blood and body fluids and their components, 2) excrement (urine and feces), 3) proteins and amino acids, 4) cells (including cancer cells), 5) genes, chromosomes, and nucleic acids, 6) biological samples, bacteria, specimens, and antibodies, 7) biological tissues, organs, and blood vessels, and 8) skin diseases and alopecia.

[0067] Furthermore, for example, for the purposes of beauty and healthcare, the electronic device of this embodiment can be used for the inspection, detection, measurement, evaluation, analysis, interpretation, observation, monitoring, beautification, hygiene, growth promotion, health enhancement, diagnosis, etc. of 1) skin, 2) hair and body hair, 3) inside the mouth, teeth, and periodontium, 4) ears and nose, and 5) vital signs.

[0068] Furthermore, for example, when used in agriculture, forestry, fisheries, livestock farming, or industry, the electronic device of the present embodiment can be used for inspecting, detecting, measuring, measuring, evaluating, analyzing, observing, monitoring, recognizing, sorting, and separating 1) industrial products (including electronic materials and electronic devices), 2) agricultural products (fruit and vegetables, etc.), 3) enzymes and bacteria, 4) marine products (fish, shellfish, crustaceans, and mollusks), 5) pharmaceuticals and biological samples, 6) food and beverages, 7) the presence and state of people, animals, and objects, 8) the state of gas (including water vapor), 9) liquids, fluids, water, moisture, and humidity, 10) the shape, color, internal structure, and physical state of objects, 11) space, position, and distance, 12) the contamination state of objects, 13) the state of molecules and particles, and 14) industrial waste.

[0069] Furthermore, for example, for the purpose of nursing care, the electronic device of this embodiment can be used for checking excretion, identifying, managing, and monitoring health conditions, etc.

[0070] In this way, the electronic device of this embodiment can be used for a wide variety of purposes, such as inspection, detection, measurement, gauging, evaluation, analysis, interpretation, observation, monitoring, beautification, hygiene, growth promotion, health promotion, separation, diagnosis, treatment, purification, recognition, sorting, classification, identification, and management.

[0071] [Sensing System and Near-Infrared Spectroscopy] Next, a sensing system and a near-infrared light emitting device 1 according to this embodiment will be described. The sensing system includes a near-infrared light emitting device 1. Near-infrared spectroscopy utilizes the near-infrared light emitting device 1. The near-infrared light emitting device 1 can emit near-infrared light with a uniform intensity distribution within the light output surface. This allows for high-precision near-infrared spectroscopy.

[0072] The sensing system may include a detector that detects near-infrared rays. The detector may be configured to irradiate an object with output light 50 emitted by the near-infrared light emitting device 1 and detect the reflected or transmitted near-infrared component. A quantum-type photodetector such as a photodiode, a phototransistor, a photo IC, a CCD image sensor, or a CMOS image sensor may be used as the detector. That is, the sensing system may include a near-infrared sensor or a near-infrared camera. The sensing system may include, for example, the near-infrared light emitting device 1, the near-infrared sensor or the near-infrared camera, and an output device that outputs data obtained by the near-infrared sensor or the camera. The output device may be a television monitor, a printer, or the like.

[0073] The sensing system may also be a transmission-type spectroscopic device as shown in FIG. 2. As shown in FIG. 2, the transmission-type spectroscopic device 100 includes a near-infrared light emitting device 1 and a spectrometer 120. The spectrometer 120 includes a detector. An inspection object 110 is disposed between the near-infrared light emitting device 1 and the spectrometer 120. The near-infrared light emitting device 1 is configured to emit output light 50. The inspection object 110 is disposed so as to be irradiated with the output light 50. The spectrometer 120 is disposed so as to receive transmitted light 111, particularly near-infrared transmitted light, that has passed through the interior of the inspection object 110, of the output light 50 irradiated onto the inspection object 110. The spectrometer 120 detects and separates the transmitted light 111. The spectrometer 120 may be, for example, a near-infrared spectrometer.

[0074] The sensing system may be a reflective spectroscopic device as shown in Fig. 3. As shown in Fig. 3, the reflective spectroscopic device 100 also includes a near-infrared light emitting device 1 and a spectroscope 120. However, in the reflective spectroscopic device 100, the spectroscope 120 is arranged to receive reflected light 112, particularly near-infrared reflected light, reflected by the inspection object 110 out of the output light 50 irradiated onto the inspection object 110. Other points are the same as those of the transmissive spectroscopic device 100, and therefore will not be described further.

[0075] The sensing system and near-infrared spectroscopy can be used in applications similar to those of the electronic devices described above. For example, the sensing system may be used as a quality control system for food or industrial products, or as a plastic discrimination system.

[0076] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0077] (Technology 1) A near-infrared light emitting device comprising: at least one solid-state light emitting element that emits primary light having a maximum spectral intensity within a wavelength range of 380 nm or more and less than 700 nm; a light diffuser that diffuses the primary light to emit diffused light; and a wavelength converter that includes a near-infrared phosphor that absorbs the diffused light and converts it into near-infrared light having a maximum fluorescent intensity within a wavelength range of 700 nm or more and less than 2500 nm, and that emits output light that includes the near-infrared light as a light component.

[0078] With this configuration, the primary light emitted by the solid-state light-emitting element, including highly directional visible light, can be diffused by using a conventional light diffuser that has the function of diffusing visible light. Furthermore, the diffused light resulting from the diffusion of the primary light is absorbed by the near-infrared phosphor, which converts the wavelength of the diffused light to near-infrared light. Therefore, near-infrared light with a homogenized intensity distribution within the light output surface due to the light scattering effect can be emitted from a relatively wide area. Therefore, the near-infrared light emitting device can emit near-infrared light with a homogenous intensity distribution within the light output surface.

[0079] (Technology 2) The near-infrared light emitting device according to Technology 1, wherein the at least one solid-state light emitting element is a plurality of solid-state light emitting elements, and the plurality of solid-state light emitting elements are arranged at intervals of less than 100 cm on average. With this configuration, the plurality of solid-state light emitting elements are arranged closely together. Therefore, it is possible to further reduce the intensity unevenness of the primary light in any plane. Therefore, it is possible to homogenize the diffused light, including visible light, diffused by the light diffuser, and emit homogeneous near-infrared light.

[0080] (Technology 3) The near-infrared light emitting device according to Technology 1 or 2, wherein the light diffuser mainly contains a resin. This configuration facilitates molding and processing, and provides a wide range of technical options for materials and construction methods. Therefore, such near-infrared light emitting devices are highly manufacturable and can easily meet customer needs.

[0081] (Technology 4) A near-infrared light-emitting device according to any one of Technologies 1 to 3, wherein the diffused light includes light having a maximum spectral intensity within a wavelength range of 380 nm or more and less than 700 nm, and does not include near-infrared light that has been wavelength-converted by the near-infrared phosphor. This configuration prevents the light diffuser from emitting near-infrared light derived from the phosphor. This makes it possible to simplify the spectral distribution of the output light and suppress interference between the fluorescence emitted by different phosphors. Furthermore, because the structure of the light diffuser can be simplified, it is possible to provide a near-infrared light-emitting device with high industrial productivity without requiring advanced technology or a large number of steps.

[0082] (Technology 5) The near-infrared light-emitting device according to any one of Technologies 1 to 4, wherein the light diffuser does not contain a phosphor. With this configuration, the light diffuser does not emit near-infrared light originating from the phosphor. This makes it possible to simplify the spectral distribution of the output light and suppress interference between the fluorescence emitted by different phosphors. Furthermore, because the structure of the light diffuser can be simplified, it is possible to provide a near-infrared light-emitting device with high industrial productivity without requiring advanced technology or a large number of steps.

[0083] (Technology 6) The near-infrared light emitting device according to any one of Technologies 1 to 5, wherein the light diffuser has a flat light exit surface that emits the diffused light. With this configuration, the surface of the wavelength converter facing the light diffuser is flat. Therefore, when the light diffuser and the wavelength converter are bonded together, the near-infrared light emitting device can be made thin.

[0084] (Technology 7) The near-infrared light emitting device according to any one of Technologies 1 to 6, wherein the wavelength converter has a flat surface that serves as a light output surface for outputting near-infrared light.

[0085] (Technology 8) The near-infrared light emitting device according to any one of Technologies 1 to 7, wherein the wavelength converter has a plate-like or sheet-like shape. This configuration allows the wavelength converter to have a shape that extends horizontally relative to the thickness direction. Therefore, diffused primary light emitted by the solid-state light emitting element can be incident on the wavelength converter over a wide area. Therefore, the near-infrared light emitting device can emit high-power output light that is mainly composed of near-infrared light.

[0086] (Technology 9) A near-infrared light emitting device according to any one of Technologies 1 to 8, wherein the wavelength converter contains only a near-infrared phosphor as a phosphor. This configuration not only simplifies the configuration of the wavelength converter 30, but also makes it possible to convert only the light component of primary light, which generally has a narrow spectral half-width, into near-infrared light. Therefore, it is possible to produce a near-infrared light emitting device that is suitable for industrial production and emits only near-infrared light.

[0087] (Technology 10) The near-infrared light emitting device according to any one of Technologies 1 to 9, wherein the near-infrared phosphor contains a transition metal ion as a fluorescent ion. This configuration makes it possible to use a near-infrared phosphor that is easy to procure or synthesize. Therefore, it is possible to provide a highly practical near-infrared light emitting device.

[0088] (Technology 11) An electronic device comprising the near-infrared light emitting device according to any one of Technologies 1 to 10. With this configuration, the diffused light is absorbed by the near-infrared phosphor, and the wavelength of the diffused light is converted to near-infrared light. As a result, the electronic device can emit near-infrared light with a uniform intensity distribution within the light output surface.

[0089] Hereinafter, the present embodiment will be described in more detail with reference to examples and comparative examples, but the present embodiment is not limited to these examples.

[0090] [Example] As shown in Figure 4, an evaluation device 200 was assembled, and the output light emitted from the near-infrared light emitting device 201 was photographed with a Vis-SWIR camera 250 (Omron Corporation's STC-LBS132U3V-SWIR: imaging bandwidth 400 nm to 1700 nm). A visible cut filter 260 (HOYA Corporation's sharp cut filter R70) was attached to the Vis-SWIR camera 250 to cut visible light emitted from the near-infrared light emitting device 201. As the visible cut filter 260, a filter was used that had a transmission limit wavelength λT of 700 ± 10 nm, which is the midpoint between the wavelength at which the transmittance is 5% and the wavelength at which the transmittance is 72%, and that cuts light with a wavelength of less than 700 nm.

[0091] The near-infrared light-emitting device 201 according to this example includes a solid-state light-emitting element 210, a light diffuser 220, and a wavelength converter 230, which are arranged in this order: solid-state light-emitting element 210, light diffuser 220, wavelength converter 230. Two blue LEDs (LC303PBL1-30Q, Kingbright Corporation, dominant wavelength 470 nm) were used as the solid-state light-emitting element 210. The two blue LEDs were attached to a substrate so that the distance between them was 2 cm. The light diffuser 220 was a diffuser plate SW-12 from Nikon Corporation. The wavelength converter 230 was manufactured as described below. The distance between the tip of the blue LED and the surface of the light diffuser 220 facing the solid-state light-emitting element 210 was 1 cm. The distance between the center of the light diffuser 220 and the center of the wavelength converter 230 was 1 cm. The distance between the center of the wavelength converter 230 and the center of the visible light cut filter 260 was 18 cm.

[0092] The wavelength converter 230 was fabricated as follows.

[0093] (Preparation of Raw Materials) First, the following compound powders were prepared as raw materials: Lithium carbonate (Li ２ CO ３ ): Purity 2N, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Gallium oxide (Ga ２ O ３ ): Purity 4N, manufactured by Asia Physical Materials Co., Ltd. Chromium oxide (Cr ２ O ３): Purity 3N, manufactured by Kojundo Chemical Laboratory Co., Ltd. Nickel oxide (NiO): Purity 3N, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0094] (Preparation of phosphor) Li(Ga ０．９４ Cr ０．０５ Ni ０．０１ ) ５ O ８ The compound powders were weighed so as to obtain a charge composition of the above, and the resulting raw materials were dry-mixed using a mortar and pestle to prepare a mixed raw material. The mixed raw material was transferred to an alumina crucible with a lid and fired in air at 1400°C for 4 hours using a box-type electric furnace. The fired product obtained by firing was lightly crushed to obtain Li(Ga ０．９４ Cr ０．０５ Ni ０．０１ ) ５ O ８ The fluorescent spectrum of the prepared phosphor is shown in Figure 5.

[0095] (Preparation of Wavelength Converter) Next, 0.40 g of the above phosphor and silicone resin (1 g of KER-2600A and 1 g of KER-2600B) were mixed using a stirring and degassing device, followed by degassing. The stirring and degassing device used was a Thinky Mixer (registered trademark) model ARE-310 manufactured by Shinki Corporation. The stirring and degassing device was set to a rotation speed of approximately 2000 rpm, and the process was carried out for 3 minutes. In this manner, a phosphor paste containing the above phosphor and silicone resin was prepared. The obtained phosphor paste was dropped into a frame approximately 320 μm high using a dispenser (model: ML-5000XII, manufactured by Musashi Engineering Co., Ltd.). The phosphor paste was then heated in air at 150°C for 2 hours to harden. In this manner, a wavelength converter 230 measuring 10 mm long, 10 mm wide, and approximately 300 μm thick was prepared.

[0096] Comparative Example 1 As shown in FIG. 6, an evaluation device 300 was assembled, and output light emitted from a near-infrared light emitting device 301 was photographed with a Vis-SWIR camera 250.

[0097] The near-infrared light emitting device 301 according to this example includes a solid-state light emitting element 210, a light diffuser 220, and a wavelength converter 230, which are arranged in this order: solid-state light emitting element 210, wavelength converter 230, light diffuser 220. The distance between the tip of the blue LED and the surface of the wavelength converter 230 facing the solid-state light emitting element 210 was approximately 0 cm. The distance between the center of the wavelength converter 230 and the center of the light diffuser 220 was 1 cm. The distance between the surface of the light diffuser 220 facing the visible light cut filter 260 and the center of the visible light cut filter 260 was 19 cm. Otherwise, the evaluation device 300 was assembled in the same manner as in the example.

[0098] Comparative Example 2 As shown in FIG. 7, an evaluation device 400 was assembled, and output light emitted from a near-infrared light emitting device 401 was photographed with a Vis-SWIR camera 250.

[0099] The near-infrared light-emitting device 401 according to this example includes a solid-state light-emitting element 410 and a light diffuser 220, which are arranged in this order: the solid-state light-emitting element 410, then the light diffuser 220. Two near-infrared LEDs (L13895-0145P, peak emission wavelength 1450 nm, manufactured by Hamamatsu Photonics K.K.) were used as the solid-state light-emitting element 410. The distance between the tip of the near-infrared LED and the surface of the light diffuser 220 facing the solid-state light-emitting element was 1 cm. The distance between the surface of the light diffuser 220 facing the visible light cut filter and the center of the visible light cut filter was 19 cm. Otherwise, the evaluation device 400 was assembled in the same manner as in the example.

[0100] 8 , in the near-infrared light emitting device 201 according to the example, the primary light including visible light emitted from the solid-state light emitting element 210 is diffused by the light diffuser 220 and then wavelength-converted to near-infrared light by the wavelength converter 230. Therefore, the output light of the example has a uniform intensity distribution within the light output surface.

[0101] On the other hand, as shown in Figure 9, in the near-infrared light-emitting device 301 according to Comparative Example 1, primary light containing visible light emitted from the solid-state light-emitting element 210 is wavelength-converted to near-infrared light by the wavelength converter 230 and then passes through the light diffuser 220. While a typical light diffuser 220 easily diffuses visible light, near-infrared light has a long wavelength and is therefore difficult to diffuse by the light diffuser 220, and tends to transmit with high directionality. Therefore, the output light containing near-infrared light output from the near-infrared light-emitting device 301 tends to have high intensity directly above the LED chips and low intensity between the LED chips. Therefore, the output light of Comparative Example 1 did not have a uniform intensity distribution within the light output surface compared to the output light of the Examples.

[0102] 10 , in the near-infrared light-emitting device 401 according to Comparative Example 2, the primary light including visible light emitted from the solid-state light-emitting element 410 passes through the light diffuser 220. Therefore, similar to Comparative Example 1, the output light of Comparative Example 2 did not have a uniform intensity distribution in the light output surface compared to the output light of the example.

[0103] Next, the brightness saturation of the near-infrared phosphor used in this example was investigated as follows.

[0104] (Fabrication of Near-Infrared Light Emitting Device) First, 0.8 g of the mixed raw material powder was filled into a mold, and the mixed raw material powder was compressed with a hand press at a pressure of about 3 MPa to fabricate a cylindrical molded body with a diameter of 13 mm.

[0105] (Firing of mixed raw materials) The produced molded body was placed in an alumina round sheath (material: SSA-S, manufactured by Nikkato Corporation, with a lid) and heated to 1400°C at a temperature increase / decrease rate of 300°C / hour. After firing for 4 hours in an air atmosphere, the mixture was cooled to room temperature at a rate of 300°C / hour to produce a ceramic sample.

[0106] (Polishing of fired sample) The prepared ceramic sample was processed using an automatic grinder (DAG810, Disco Corporation) to a film thickness of 140 μm.

[0107] (Fabrication of Near-Infrared Light-Emitting Device) The fabricated ceramic sample with a thickness of 140 μm was cut into an LED chip size of 3.2 mm × 2.6 mm using an automatic dicing saw (DAD3350, Disco Corporation). The cut ceramic sample was mounted on a blue LED chip to fabricate a near-infrared light-emitting device.

[0108] (Measurement of near-infrared emission intensity of near-infrared light-emitting device) In order to cut off the blue light, which is the excitation light, and measure the output of near-infrared fluorescence, a visible light-cutting sheet was placed on the fabricated near-infrared light-emitting device. Then, a current was applied to the blue LED starting from 0.4 A in steps of 0.1 A, and the light output was measured using a power meter (PM100D, Thorlabs). The results are shown in Figure 11.

[0109] (Measurement of the luminance saturation constant of near-infrared phosphor) From the relationship between the output of the blue LED and the output of the fluorescent light shown in FIG. 11, I=αI ｕｖ γ (I is the luminance of the light, I ｕｖ is the excitation intensity, α is a constant, and γ is the brightness saturation constant. As a result, the constant α=0.2 and the brightness saturation constant γ=0.4 were derived.

[0110] (Conversion Efficiency) Next, the conversion efficiency was calculated by dividing the output of near-infrared fluorescence by the output of the blue LED, and the result was plotted as a graph. The results are shown in FIG.

[0111] 11 and 12 show that the near-infrared phosphor used in this example has a brightness saturation constant of 0.4, making it a phosphor that is relatively prone to brightness saturation. However, the wavelength converter 230 according to the example uses relatively low-output light that has passed through the light diffuser 220 as excitation light. Therefore, even when a phosphor that is prone to brightness saturation, such as that used in this example, can relatively reduce the effect of brightness saturation.

[0112] The entire contents of Japanese Patent Application No. 2023-156367 (filing date: September 21, 2023) are incorporated herein by reference.

[0113] Although the present embodiment has been described above, the present embodiment is not limited to this, and various modifications are possible within the scope of the gist of the present embodiment.

[0114] According to the present disclosure, it is possible to provide a near-infrared light emitting device that emits near-infrared light with a uniform intensity distribution in the light output surface, and an electronic device using the same.

[0115] REFERENCE SIGNS LIST 1 Near-infrared light emitting device 10 Solid-state light emitting element 11 Primary light 20 Light diffuser 21 Diffused light 30 Wavelength converter 31 Near-infrared phosphor 50 Output light

Claims

1. A near-infrared light emitting device comprising: at least one solid-state light emitting element that emits primary light having a maximum spectral intensity within a wavelength range of 380 nm or more and less than 700 nm; a light diffuser that diffuses the primary light to emit diffused light; and a wavelength converter that includes a near-infrared phosphor that absorbs the diffused light and converts it to near-infrared light having a maximum fluorescent intensity within a wavelength range of 700 nm or more and less than 2500 nm, and which emits output light containing the near-infrared light as a light component.

2. The near infrared light emitting device according to claim 1, wherein the at least one solid-state light emitting element is a plurality of solid-state light emitting elements, and each of the plurality of solid-state light emitting elements is arranged at intervals of less than 100 cm on average.

3. The near-infrared light emitting device according to claim 1 or 2, wherein the light diffuser mainly contains a resin.

4. A near-infrared light emitting device according to any one of claims 1 to 3, wherein the diffused light includes light having a maximum spectral intensity within a wavelength range of 380 nm or more and less than 700 nm, and does not include near-infrared light that has been wavelength-converted by the near-infrared phosphor.

5. A near-infrared light emitting device according to any one of claims 1 to 4, wherein the light diffuser does not contain a phosphor.

6. A near-infrared light emitting device according to any one of claims 1 to 5, wherein the light diffuser has a flat light exit surface that emits the diffused light.

7. A near-infrared light emitting device according to any one of claims 1 to 6, wherein the wavelength converter has a flat light output surface that outputs near-infrared light.

8. A near-infrared light emitting device according to any one of claims 1 to 7, wherein the wavelength conversion body is in the form of a plate or sheet.

9. A near-infrared light emitting device according to any one of claims 1 to 8, wherein the wavelength conversion body contains only a near-infrared phosphor as a phosphor.

10. A near-infrared light emitting device according to any one of claims 1 to 9, wherein the near-infrared phosphor contains a transition metal ion as a fluorescent ion.

11. An electronic device comprising the near-infrared light emitting device according to any one of claims 1 to 10.

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