Near-infrared fluorescent ceramic and near-infrared fluorescent device comprising same

Abstract

A near-infrared fluorescent ceramic (1) is a fluorescent ceramic which contains at least a first inorganic compound and a second inorganic compound that is different from the first inorganic compound and which emits fluorescence. The first inorganic compound is a fluorescent material which emits near-infrared light having a fluorescent peak within the wavelength range 730-2500 nm. The near-infrared fluorescent ceramic (1) has a sea-island structure comprising: a continuous phase (2) constituted from the first inorganic compound; and a dispersed phase (3) which is constituted from the second inorganic compound and is dispersed inside the continuous phase. A near-infrared fluorescent device (10) comprises the near-infrared fluorescent ceramic.

Description

Near-infrared fluorescent ceramics and near-infrared light-emitting device including the same

[0001] The present invention relates to a near-infrared fluorescent ceramic and a near-infrared light emitting device including the near-infrared fluorescent ceramic.

[0002] Near-infrared light has the property of easily penetrating living organisms, making it convenient for obtaining information about the inside of a living organism and for treating lesions inside the organism. Furthermore, because near-infrared light has the property of penetrating organic matter, it is also advantageous for inspecting the contents of unopened organic containers or foreign objects. Therefore, near-infrared light-emitting devices that emit near-infrared light are expected to be used for medical lighting and lighting for inspection equipment.

[0003] Patent Document 1 discloses a red / near-infrared light emitting material that emits red / near-infrared light in the range of 650 nm to 1700 nm. Specifically, Patent Document 1 discloses a red / near-infrared light emitting material having the molecular formula aSc ２ O ３ ・Ga ２ O ３ ・bR ２ O ３ In Patent Document 1, a red / near-infrared emitting material is disclosed, which is characterized in that the R element includes one or two of Cr, Ni, Fe, Yb, Nd, and Er, and 0.001≦a≦0.6 and 0.001≦b≦0.1. ２ O ３ ・Ga ２ O ３ bCr ２ O ３ The present invention discloses a red / near infrared emitting material represented by the formula:

[0004] There has been a demand for near-infrared fluorescent ceramics containing near-infrared phosphors that can be used in near-infrared light emitting devices and have excellent light emitting properties.

[0005] Special Publication No. 2021-529240

[0006] However, conventionally known near-infrared fluorescent ceramics have many voids and grain boundaries inside them. As a result, conventional near-infrared fluorescent ceramics have the problem of inferior quality as ceramics. Furthermore, conventional near-infrared light-emitting devices equipped with such near-infrared fluorescent ceramics have the problem of insufficient performance and reliability due to the potential issues of the near-infrared fluorescent ceramics described above.

[0007] The present invention has been made in view of the problems inherent in the conventional techniques, and an object of the present invention is to provide a near-infrared fluorescent ceramic that has high light-emitting properties and excellent ceramic quality, and a near-infrared light-emitting device including the near-infrared fluorescent ceramic.

[0008] In order to solve the above-mentioned problems, a near-infrared fluorescent ceramic according to a first aspect of the present invention is a near-infrared fluorescent ceramic that emits fluorescence and contains at least a first inorganic compound and a second inorganic compound different from the first inorganic compound, wherein the first inorganic compound is a phosphor that emits near-infrared light having a fluorescence peak in a wavelength range of 730 nm or more and 2500 nm or less, and has a sea-island structure including a continuous phase composed of the first inorganic compound and a dispersed phase composed of the second inorganic compound and dispersed within the continuous phase.

[0009] A near-infrared light emitting device according to a second aspect of the present invention includes a near-infrared fluorescent ceramic.

[0010] FIG. 1 is a schematic diagram showing an example of a sea-island structure of a near-infrared fluorescent ceramic according to this embodiment. FIG. 2 is a schematic diagram showing an example of a near-infrared light-emitting device according to this embodiment. FIG. 3 is a schematic diagram showing an example of an electronic device according to this embodiment. FIG. 4 is a scanning electron microscope photograph (2000x magnification) showing a portion of the fluorescent ceramic of Example 1 where elemental analysis was performed, and a diagram showing the results of semi-quantitative analysis corrected by the ZAF method. FIG. 5 is a scanning electron microscope photograph (2000x magnification) showing a portion of the fluorescent ceramic of Example 2 where elemental analysis was performed, and a diagram showing the results of semi-quantitative analysis corrected by the ZAF method. FIG. 6 is a scanning electron microscope photograph (2000x magnification) showing a portion of the fluorescent ceramic of Example 3 where elemental analysis was performed, and a diagram showing the results of semi-quantitative analysis corrected by the ZAF method. FIG. 7 is a diagram showing the X-ray diffraction patterns of the fluorescent ceramics of Examples 1 to 3 and Comparative Example 1. FIG. 8 is a photograph showing the results of observation of the fluorescent ceramics of Examples 1 to 3 and Comparative Example 1 using a scanning electron microscope at 1000x magnification. Fig. 9 is a photograph showing the results of observing the fluorescent ceramics of Examples 1 to 3 and Comparative Example 1 at 3000x magnification using a scanning electron microscope. Fig. 10 is a diagram showing the emission spectra of the fluorescent ceramics of Examples 1 to 3 and Comparative Example 1 when excited with excitation light having a wavelength of 450 nm. Fig. 11 is a diagram showing the X-ray diffraction pattern of the fluorescent ceramic of Example 4. Fig. 12 is a photograph showing the results of observing the fluorescent ceramic of Example 4 at 1000x and 3000x magnification using a scanning electron microscope. Fig. 13 is a diagram showing a backscattered electron image of the fluorescent ceramic of Example 4 and elemental maps of gallium, scandium, phosphorus, and boron obtained by energy dispersive X-ray analysis.

[0011] The near-infrared fluorescent ceramic according to the present embodiment and the near-infrared light emitting device using the near-infrared fluorescent ceramic 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 convenience and may differ from the actual proportions.

[0012] [Near-infrared fluorescent ceramics] Conventionally known near-infrared fluorescent ceramics are primarily composed of near-infrared phosphors. Near-infrared fluorescent ceramics are ceramicized to increase the light absorption rate of light-absorbing ions (fluorescent ions) contained in near-infrared phosphors, which generally have low light absorption rates, and to enhance the thermal conductivity of wavelength converters, thereby achieving high near-infrared light output. To improve the light absorption rate of near-infrared fluorescent ceramics, conventional methods in this technical field include increasing the concentration of light-absorbing ions, increasing density, and increasing the purity of the near-infrared phosphor bulk, while eliminating substances other than the desired phosphor components as much as possible.

[0013] However, as described above, conventional near-infrared fluorescent ceramics, particularly those that emit fluorescence with an emission peak in the long wavelength region exceeding 800 nm, have a short history of material development and therefore have many voids and grain boundaries inside them, which has led to the problem that these near-infrared fluorescent ceramics are inferior in quality to ceramics as monolithic bodies.

[0014] Also, for example, β-Ga ２ O ３ (monoclinic) and Sc ２ O ３ When a solid solution in which the two end-members have different crystalline phases, such as a cubic solid solution, is used as the base compound for a phosphor, the following problems arise: (1) Internal stress is likely to occur in the solid solution crystals, making it difficult to obtain high-quality ceramics. (2) At a certain solid solution ratio, the crystal system changes from monoclinic to cubic or from cubic to monoclinic, making it difficult to obtain the desired fluorescent properties by adjusting the solid solution ratio. (3) At a solid solution ratio that exhibits the desired fluorescent properties, multiple types of phases are likely to form, resulting in a ceramic with a mixture of different phases. As a result, not only is it difficult to achieve high quality, but variations in properties between production lots are likely to occur, resulting in low yields.

[0015] For this reason, conventional near-infrared light-emitting devices and near-infrared utilization devices that use near-infrared fluorescent ceramics have risks not only in terms of performance and reliability but also in terms of manufacturing yield, because they include near-infrared fluorescent ceramics that have these potential issues. The object of this embodiment is to provide high-quality near-infrared fluorescent ceramics, particularly long-wavelength type near-infrared fluorescent ceramics, that are advantageous for industrial production.

[0016] The near-infrared fluorescent ceramic of this embodiment contains at least a first inorganic compound that is a phosphor that emits near-infrared light and a second inorganic compound that is different from the first inorganic compound. The near-infrared fluorescent ceramic has an inorganic phase constituted by the first inorganic compound and an inorganic phase constituted by the second inorganic compound, and further has a phase-separated structure in which these inorganic phases are mixed together.

[0017] Specifically, as shown in Fig. 1, in near-infrared fluorescent ceramic 1, an inorganic phase composed of a first inorganic compound forms continuous phase 2, and an inorganic phase composed of a second inorganic compound forms dispersed phase 3. A plurality of dispersed phases 3 each having a small volume are dispersed within continuous phase 2, and each dispersed phase 3 is entirely surrounded by continuous phase 2. Therefore, near-infrared fluorescent ceramic 1 has a sea-island structure including continuous phase 2 composed of the first inorganic compound and dispersed phase 3 composed of the second inorganic compound that is dispersed within continuous phase 2.

[0018] In the near-infrared fluorescent ceramic 1, the first inorganic compound and the second inorganic compound form a sea-island structure, as shown in FIG. 1 , in which the first inorganic compound, which appears as a continuous sea, surrounds the second inorganic compound, which appears as discontinuous islands. This sea-island structure allows the second inorganic compound to bind the first inorganic compound, which functions as a near-infrared phosphor. As a result, the grain boundaries and voids between the first inorganic compounds are reduced, thereby improving the quality of the resulting near-infrared fluorescent ceramic 1. In other words, a near-infrared fluorescent ceramic can be obtained that is dense, has high mechanical strength, and is suitable for use as a wavelength converter that emits near-infrared light. Furthermore, the reduced grain boundaries and voids between the first inorganic compounds allow excitation light irradiated onto the near-infrared fluorescent ceramic 1 to more easily reach the first inorganic compound. As a result, the first inorganic compound efficiently absorbs a portion of the excitation light and emits near-infrared light, thereby increasing the emission intensity of the near-infrared light.

[0019] In the sea-island structure of the near-infrared fluorescent ceramic 1, the first inorganic compound constitutes the continuous phase 2 and the second inorganic compound constitutes the dispersed phase 3, and therefore the volume of the first inorganic compound is larger than the volume of the second inorganic compound. Specifically, in the near-infrared fluorescent ceramic 1, the continuous phase 2 constituted by the first inorganic compound is 50 vol% or more, and the dispersed phase 3 constituted by the second inorganic compound is less than 50 vol%. In the near-infrared fluorescent ceramic 1, the continuous phase 2 may be 60 vol% or more and the dispersed phase 3 may be 40 vol% or less, or the continuous phase 2 may be 70 vol% or more and the dispersed phase 3 may be 30 vol% or less. In addition, in the near-infrared fluorescent ceramic 1, the continuous phase 2 may be 80 vol% or more and the dispersed phase 3 may be 20 vol% or less.

[0020] In the near-infrared fluorescent ceramic 1, the continuous phase 2 is mainly composed of a first inorganic compound. Specifically, the continuous phase 2 preferably contains 50 mol % of the first inorganic compound, and preferably contains 70 mol % or more of the first inorganic compound. The continuous phase 2 may be composed of the first inorganic compound. Furthermore, the dispersed phase 3 is mainly composed of a second inorganic compound. Specifically, the dispersed phase 3 preferably contains 50 mol % of the second inorganic compound, and preferably contains 70 mol % or more of the second inorganic compound. Furthermore, the dispersed phase 3 may be composed of the second inorganic compound.

[0021] In the near-infrared fluorescent ceramic 1, the first inorganic compound of the continuous phase 2 and the second inorganic compound of the dispersed phase 3 preferably contain the same constituent elements. In this case, the constituent elements act to alleviate the abrupt composition difference at the interface between the first inorganic compound and the second inorganic compound, and also to bond the first inorganic compound and the second inorganic compound together via the constituent elements. This results in a near-infrared fluorescent ceramic that is advantageous for homogenizing the internal stress distribution and achieving a strong, fracture-resistant structure.

[0022] In the near-infrared fluorescent ceramic 1, the constituent elements contained in the first inorganic compound and the second inorganic compound are preferably metal elements that form trivalent metal ions. As described above, in the near-infrared fluorescent ceramic 1, at least the first inorganic compound is a phosphor that emits near-infrared light. The second inorganic compound may or may not be a phosphor. Furthermore, when the second inorganic compound is a phosphor, it may be a phosphor that emits near-infrared light. When the constituent elements contained in the first inorganic compound and the second inorganic compound are metal elements that form trivalent metal ions, both the first inorganic compound and the second inorganic compound may be Cr, which is known as a fluorescent ion that emits near-infrared fluorescence. ３＋ The resulting near-infrared fluorescent ceramic 1 is a high-performance fluorescent ceramic in which both the first inorganic compound and the second inorganic compound function as near-infrared phosphors. Preferably, the constituent element is at least one of scandium and gallium.

[0023] The first inorganic compound in the near-infrared fluorescent ceramic 1 will be described in more detail. As described above, the first inorganic compound is composed of a near-infrared phosphor that emits at least near-infrared light. Specifically, the near-infrared phosphor constituting the first inorganic compound is a phosphor that absorbs primary light emitted by a solid-state light-emitting element and converts it into wavelength-converted light containing near-infrared light. Such a near-infrared phosphor is preferably a phosphor that emits near-infrared light having a fluorescence peak in a wavelength range of 730 nm or more and less than 2500 nm, and more preferably a phosphor that emits near-infrared light having a fluorescence peak in a wavelength range of 780 nm or more and less than 2500 nm. Furthermore, the near-infrared phosphor is preferably a phosphor that emits near-infrared light having a fluorescence peak in a wavelength range of 730 nm or more and less than 1000 nm, and more preferably a phosphor that emits near-infrared light having a maximum intensity in a wavelength range of 780 nm or more and less than 900 nm. In this way, the wavelength of the primary light emitted by the solid-state light emitting element can be easily converted into a near-infrared light component, which is advantageous for obtaining the near-infrared light component required for inspection light, for example.

[0024] As the near-infrared phosphor, for example, various inorganic phosphors known for use as near-infrared light sources can be used. Specifically, as the near-infrared phosphor, a phosphor activated with at least one of rare earth ions and transition metal ions, which emits fluorescence containing a near-infrared light component, can be used. The rare earth ions include Nd ３＋ , Eu ２＋ , Ho ３＋ , Er ３＋ , Tm ３＋ and Yb ３＋ The transition metal ion is preferably at least one selected from the group consisting of Ti, ３＋ , V ４＋ , Cr ４＋ , V ３＋ , Cr ３＋ , V ２＋ , Mn ４＋ , Fe ３＋ , Co ３＋ , Co ２＋ and Ni ２＋It is preferable that the near-infrared phosphor is at least one selected from the group consisting of: and it is preferable that the near-infrared phosphor is an oxide, sulfide, nitride, halide, oxysulfide, oxynitride, or oxyhalide containing the fluorescent ion.

[0025] In the near-infrared fluorescent ceramic 1, the first inorganic compound contains Cr as an activator. ３＋ It is preferable that the ions include Cr. ３＋ The ion is an orthodox fluorescent ion that can absorb visible light, particularly blue light or red light, and convert it into a near-infrared light component. ３＋ By including ions, it becomes possible to suitably combine the near-infrared fluorescent ceramic 1 with a solid-state light-emitting device that emits visible light. ３＋ In addition to ions, Ni ２＋ It may further include:

[0026] As described above, in the near-infrared fluorescent ceramic 1, the first inorganic compound is Cr as an activator. ３＋ In this configuration, the near-infrared light emitted from the near-infrared fluorescent ceramic 1 contains at least Cr ions. ３＋ Fluorescence due to ions, i.e. ４ T ２ → ４ A ２ This type of Cr contains fluorescence based on the electron energy transition. ３＋ The near-infrared fluorescent ceramic 1 containing ions has a fluorescence peak in the wavelength range of 780 nm or more and 1000 nm or less, and can emit fluorescence with a wide half-width of the fluorescence spectrum, making it suitable for use in applied technologies of near-infrared spectroscopic analysis.

[0027] In the near-infrared fluorescent ceramic 1, the first inorganic compound is β-Ga ２ O ３ It is preferable that the compound has the same crystal structure as that of β-Ga. ２ O ３ (Ga, Sc) with the same crystal structure ２ O ３ : Cr ３＋The phosphor is known to be a near-infrared phosphor that emits near-infrared light with a wide half-width of the fluorescence spectrum and relatively small temperature quenching. ２ O ３ By using a phosphor composed of a compound having the same crystal structure as that of the compound as a base, it is possible to obtain a near-infrared fluorescent ceramic that has a wide half-width of the fluorescence spectrum and is advantageous in emitting near-infrared light with little thermal quenching.

[0028] The second inorganic compound in the near-infrared fluorescent ceramic 1 will be described in more detail. In this embodiment, the first inorganic compound forms the continuous phase 2 and is composed of a phosphor that emits at least near-infrared light, but the second inorganic compound may or may not be a phosphor as long as it forms the dispersed phase 3. The second inorganic compound is preferably the same type of compound as the first inorganic compound. In other words, if the first inorganic compound is an oxide, it is preferable that the second inorganic compound is also an oxide. Similarly, if the first inorganic compound is a nitride, it is preferable that the second inorganic compound is also a nitride.

[0029] In the near-infrared fluorescent ceramic 1, both the first inorganic compound and the second inorganic compound are preferably oxides. In this case, the first inorganic compound and the second inorganic compound can be produced using conventional ceramic techniques, making the near-infrared fluorescent ceramic convenient for industrial production.

[0030] In the near-infrared fluorescent ceramic 1, the second inorganic compound is preferably a compound containing boron (B). ３ (M is a metal element) is more preferable. When the second inorganic compound is a compound containing boron, for example, boric acid (H ３ BO ３ ) or boron oxide (B ２ O ３) as part of the ceramic raw materials, near-infrared fluorescent ceramic 1 can be produced. That is, as will be described later, by adding boric acid or boron oxide to the raw material of the first inorganic compound and firing the resulting mixture, a second inorganic compound consisting of a boron-containing compound can be produced in addition to the first inorganic compound. In this process, a sea-island structure is formed, which includes a continuous phase 2 consisting of the first inorganic compound and a dispersed phase 3 consisting of the second inorganic compound.

[0031] In this way, boric acid (H ３ BO ３ ) or boron oxide (B ２ O ３ When a low-melting-point material is used as part of the raw materials, the reaction to form intermediate compounds is likely to occur in a low-temperature region during the firing process. As a result, a near-infrared fluorescent ceramic having the above-mentioned sea-island structure can be obtained. Furthermore, when a low-melting-point material is used as part of the raw materials, the low-melting-point material acts on the other ceramic raw materials to shift the reaction temperature region in which multiple phases are likely to form to a lower temperature. This is therefore advantageous for converting the first inorganic compound constituting the continuous phase 2 into a single crystalline phase and achieving high crystal quality.

[0032] In the near-infrared fluorescent ceramic 1, the first inorganic compound is (Ga １－（ｘ＋ｙ） Sc ｘ Cr ｙ ) ２ O ３ The first inorganic compound may contain β-Ga as a main component. Note that x and y satisfy the following conditions: 0<x<1, 0<y<0.1, 0<x+y<1. That is, the first inorganic compound may contain β-Ga ２ O ３ A composite oxide of gallium and scandium ((Ga,Sc) ２ O ３ ) as the base material, and Cr as the activator. ３＋ The second inorganic compound may contain a phosphor containing ions as a main component. １－ｚ Cr ｚ ) BO ３ It is preferable that the second inorganic compound contains ScBO as a main component. Note that z satisfies 0≦z<0.1. That is, the second inorganic compound is ScBO ３The second inorganic compound may contain, as a main component, an inorganic oxide represented by the formula: ３ The base material is Cr as an activator. ３＋ The near-infrared fluorescent ceramic 1 may contain, as a main component, a phosphor containing ions. When the first inorganic compound and the second inorganic compound contain the oxide as a main component, a sea-island structure having a continuous phase 2 composed of the first inorganic compound and a dispersed phase 3 composed of the second inorganic compound is easily formed. As a result, the second inorganic compound acts to bind the first inorganic compounds, reducing the grain boundaries and voids between the first inorganic compounds, thereby improving the quality of the near-infrared fluorescent ceramic 1.

[0033] In the near-infrared fluorescent ceramic 1, the first inorganic compound is (Ga １－（ｘ＋ｙ） Sc ｘ Cr ｙ ) ２ O ３ The first inorganic compound preferably contains 50 mol % or more, and more preferably 70 mol % or more. １－（ｘ＋ｙ） Sc ｘ Cr ｙ ) ２ O ３ The second inorganic compound may be composed of (Sc １－ｚ Cr ｚ ) BO ３ The second inorganic compound preferably contains 50 mol % or more, more preferably 70 mol % or more. １－ｚ Cr ｚ ) BO ３ It may consist of:

[0034] As described above, the first inorganic compound is (Ga １－（ｘ＋ｙ） Sc ｘ Cr ｙ ) ２ O ３ When the second inorganic compound is a compound containing as a main component (Sc １－ｚ Cr ｚ ) BO ３ However, the present embodiment is not limited to this. For example, the first inorganic compound may be a compound containing (Ga １－（ｘ＋ｙ） Scｘ Cr ｙ ) ２ O ３ (x and y satisfy 0<x<1, 0<y<0.1, 0<x+y<1) as a main component, the second inorganic compound is (Sc １－ｚ Cr ｚ ) P.O. ４ (z satisfies 0≦z<0.1) as a main component.

[0035] In addition, the first inorganic compound is (Ga １－（ｘ＋ｙ） Sc ｘ Cr ｙ ) ２ O ３ (x and y satisfy 0<x<1, 0<y<0.1, 0<x+y<1) as a main component, the second inorganic compound is (Sc １－ｚ Cr ｚ ) BO ３ and (Sc １－ｚ Cr ｚ ) P.O. ４ (z satisfies 0≦z<0.1) as a main component.

[0036] Furthermore, the first inorganic compound is (Ga １－（ｘ＋ｙ） Sc ｘ Cr ｙ ) ２ O ３ (x and y satisfy 0<x<1, 0<y<0.1, 0<x+y<1) as a main component, the second inorganic compound is LiScO ２ , LiGaO ２ , LiGa ５ O ８ , ScAlO ３ and BaSc ２ O ４ The compound may contain, as a main component, at least one selected from the group consisting of:

[0037] Here, the first inorganic compound is (GaSc) ２ O ３ : Cr ３＋has the property that the higher the concentration of scandium, the longer the wavelength of light it emits. Therefore, if it is desired to shift the emission peak of near-infrared fluorescent ceramic 1 to the longer wavelength side, it is preferable to increase the concentration of scandium contained in the first inorganic compound.

[0038] Also, (GaSc) ２ O ３ : Cr ３＋ is the temperature at which the phase changes when the concentration of scandium is high, i.e., β-Ga ２ O ３ It has the property of lowering the temperature at which it changes into non-crystalline forms. Furthermore, by adding a low-melting-point material such as boric acid to promote crystal growth, the resulting fluorescent ceramic becomes dense. Therefore, by adjusting the concentration of scandium and the type and amount of the low-melting-point material, it is possible to achieve a (Ga, Sc) ２ O ３ Crystal and ScBO ３ It is possible to obtain a complex with the crystal, that is, an island-in-a-sea structure made up of these compounds.

[0039] As described above, the near-infrared fluorescent ceramic 1 of this embodiment is a fluorescent ceramic that emits fluorescence and contains at least a first inorganic compound and a second inorganic compound different from the first inorganic compound. The first inorganic compound is a phosphor that emits near-infrared light having a fluorescence peak in the wavelength range of 730 nm to 2500 nm. The near-infrared fluorescent ceramic 1 has a sea-island structure including a continuous phase 2 composed of the first inorganic compound and a dispersed phase 3 composed of the second inorganic compound and dispersed within the continuous phase 2.

[0040] The near-infrared fluorescent ceramic 1 has a structure in which the first inorganic compound, which is a continuous substance, envelops the second inorganic compound, which is a discontinuous substance, and the second inorganic compound acts to bind the first inorganic compound. As a result, the grain boundaries and voids between the first inorganic compounds are reduced, thereby increasing the mechanical strength of the near-infrared fluorescent ceramic 1. Furthermore, the reduced grain boundaries and voids between the first inorganic compounds make it easier for excitation light irradiated onto the near-infrared fluorescent ceramic 1 to reach the first inorganic compound. Therefore, the first inorganic compound efficiently absorbs the excitation light and emits near-infrared light, thereby increasing the emission intensity of the near-infrared light. Furthermore, the near-infrared fluorescent ceramic 1 is formed entirely of inorganic compounds with high thermal conductivity, which provides high heat dissipation and suppresses temperature quenching of the phosphor made of the first inorganic compound.

[0041] Next, a method for producing the near-infrared fluorescent ceramic of this embodiment will be described. The near-infrared fluorescent ceramic of this embodiment can be produced by adding a low-melting-point material that can react with the raw material for preparing the first inorganic compound to the raw material, and then reacting the raw material.

[0042] Specifically, the first inorganic compound is (Ga １－（ｘ＋ｙ） Sc ｘ Cr ｙ ) ２ O ３ In the case where the first inorganic compound is composed of, for example, gallium oxide (Ga ２ O ３ ), scandium oxide (Sc ２ O ３ ), chromium oxide (Cr ２ O ３ ) is used. In addition, as a low melting point material that can react with the raw material, for example, boric acid (H ３ BO ３ ), boron oxide (B ２ O ３ ), diammonium hydrogen phosphate ((NH ４ ) ２ HPO ４ ), lithium carbonate (Li ２ CO ３), lithium fluoride (LiF), aluminum chloride (AlCl ３ ), aluminum fluoride (AlF ３ ), barium chloride (BaCl ２ ) is used.

[0043] The raw materials of the first inorganic compound are then weighed to have a stoichiometric composition of the first inorganic compound or a composition close to it, and then thoroughly mixed using a mortar, ball mill, or the like to obtain a mixed raw material. A low-melting-point material is then added to the mixed raw material and thoroughly mixed. The resulting mixed raw material is then filled into a mold and pressurized to produce a molded body made from the mixed raw material. The mixed raw material can be molded in the atmosphere at room temperature.

[0044] The resulting molded body is then fired using an electric furnace or the like. It is preferable to fire the molded body in air and / or a weakly reducing atmosphere at a firing temperature of 900 to 1700°C, particularly 1300 to 1600°C, for several hours. By firing the molded body in this manner, the low-melting-point material reacts with the other ceramic raw materials, i.e., part of the raw material of the first inorganic compound, to form multiple phases. As a result, a sea-island structure is formed, consisting of a continuous phase composed of the first inorganic compound and a dispersed phase composed of the second inorganic compound.

[0045] The sintered body thus obtained can be polished or otherwise processed as necessary to obtain the near-infrared fluorescent ceramic of this embodiment.

[0046] [Near-infrared light emitting device] Next, a near-infrared light emitting device according to this embodiment will be described. In this specification, the "near-infrared light emitting device" may also be simply referred to as a "light emitting device."

[0047] As shown in FIG. 2 , the near-infrared light-emitting device 10 of this embodiment includes the near-infrared fluorescent ceramic 1 described above and a solid-state light-emitting element 11 that emits light (primary light) that is irradiated onto the near-infrared fluorescent ceramic 1. As such a solid-state light-emitting element, an element that emits primary light having a maximum intensity within a wavelength range of 435 nm or more and less than 560 nm, preferably 440 nm or more and less than 480 nm, can be used. Furthermore, as the solid-state light-emitting element, an element that emits primary light having a maximum intensity within a wavelength range of 580 nm or more and less than 680 nm, preferably 600 nm or more and less than 660 nm, can be used. Furthermore, as the solid-state light-emitting element, an element that emits primary light having a maximum intensity within a wavelength range of 700 nm or more and less than 780 nm, preferably 700 nm or more and less than 750 nm, can be used.

[0048] The solid-state light-emitting element may be, for example, a light-emitting diode (LED) or a laser diode. For example, by using an LED module or laser diode that emits high-energy light of 1 W or more, a light-emitting device can be obtained that can be expected to have an optical output of several hundred mW. Furthermore, by using an LED module that emits high-energy light of 3 W or more or 10 W or more, a light-emitting device can be obtained that can be expected to have an optical output of several W. Furthermore, by using an LED module that emits high-energy light of 30 W or more, a light-emitting device can be obtained that can be expected to have an optical output of more than 10 W. Furthermore, by using an LED module that emits high-energy light of 100 W or more, a light-emitting device can be obtained that can be expected to have an optical output of more than 30 W.

[0049] When a laser diode is used as the solid-state light-emitting element and the primary light is converted into laser light, a high-density spot light is irradiated onto the near-infrared fluorescent ceramic 1. Therefore, the resulting light-emitting device can be used as a high-output point light source, thereby expanding the range of industrial applications of solid-state lighting. Examples of such laser diodes that can be used include edge-emitting lasers (EELs) and vertical-cavity surface-emitting lasers (VCSELs).

[0050] A light-guiding member such as an optical fiber may be interposed between the solid-state light-emitting element and the near-infrared fluorescent ceramic. This allows the solid-state light-emitting element and the near-infrared fluorescent ceramic to be spatially separated. This makes the light-emitting unit light-weight and easily movable, resulting in a light-emitting device that can easily change the irradiation location.

[0051] As described above, the solid-state light-emitting element in the near-infrared light-emitting device 10 is preferably at least one of a light-emitting diode and a laser diode. However, the solid-state light-emitting element is not limited to these, and any light-emitting element can be used as long as it is capable of emitting high-power primary light.

[0052] The number of solid-state light-emitting elements included in the near-infrared light-emitting device is not particularly limited and may be either a single element or multiple elements. Having multiple solid-state light-emitting elements makes it easy to increase the output of primary light, resulting in a light-emitting device advantageous for achieving high output. The number of solid-state light-emitting elements is not particularly limited, but may be appropriately selected from, for example, 9 or more, 16 or more, 25 or more, 36 or more, 49 or more, 64 or more, 81 or more, or 100 or more. The upper limit of the number is also not particularly limited, but may be appropriately selected from, for example, 9 or less, 16 or less, 25 or less, 36 or less, 49 or less, 64 or less, 81 or less, or 100 or less.

[0053] In the near-infrared light-emitting device, the solid-state light-emitting element is preferably a surface-emitting light source, which suppresses variations in the intensity distribution and color tone of the primary light irradiating the near-infrared fluorescent ceramic 1, making the light-emitting device advantageous in suppressing variations in the intensity distribution of the output light.

[0054] In such a near-infrared light-emitting device 10, first, primary light 12 emitted from the solid-state light-emitting element 11 is irradiated onto the front surface 1a of the near-infrared fluorescent ceramic 1. The irradiated primary light 12 passes through the near-infrared fluorescent ceramic 1. Then, as the primary light 12 passes through the near-infrared fluorescent ceramic 1, the near-infrared phosphor made of the first inorganic compound contained in the near-infrared fluorescent ceramic 1 absorbs a portion of the primary light 12 and emits near-infrared light. In this way, light containing the primary light 12 and near-infrared light 13 is emitted as output light from the back surface 1b of the near-infrared fluorescent ceramic 1.

[0055] As described above, the near-infrared fluorescent ceramic 1 is formed from an inorganic compound with high thermal conductivity, resulting in high heat dissipation and suppressing temperature quenching of the near-infrared phosphor composed of the first inorganic compound. Therefore, the near-infrared light-emitting device 10 of this embodiment can increase the absolute number of photons constituting the output light by using high-output solid-state light-emitting elements 11 or by increasing the number of solid-state light-emitting elements 11. This allows the light energy of the output light emitted from the light-emitting device to exceed 3 W, preferably 10 W, and more preferably 30 W. Such a high-output light-emitting device can emit strong output light (e.g., near-infrared light), allowing it to irradiate a relatively strong near-infrared light even when the object is far from it. Furthermore, this light-emitting device can easily obtain information about the object, even if the object is small or thick.

[0056] Furthermore, the near-infrared light emitting device 10 can increase the photon density supplied to the phosphor by using a light emitting element that emits primary light with a high optical density, such as a laser diode, as the solid-state light emitting element 11, or by concentrating the light emitted by the solid-state light emitting element 11 with an optical lens. For example, the optical energy density of the primary light emitted by the solid-state light emitting element 11 can be increased to 0.3 W / mm ２ , preferably 1.0 W / mm ２ , more preferably 3.0 W / mm ２In this case, since the optical energy density of the primary light is high, even if the near-infrared fluorescent ceramic 1 is irradiated with diffused primary light, the light emitting device will emit relatively strong output light. Furthermore, if the near-infrared fluorescent ceramic 1 is irradiated with non-diffused primary light, the light emitting device will emit output light with a high optical energy density. Therefore, it is possible to provide a light emitting device that can irradiate output light over a large area while utilizing a light emitting element with a small light emitting surface, or a light emitting device that irradiates output light with a high optical energy density. Furthermore, for example, it can also be a light emitting device that can output near-infrared light with a high optical energy density at a point. Note that there is no particular upper limit on the optical energy density of the primary light emitted by the solid-state light emitting element, but it may be, for example, 30 W / mm ２ It can be said that:

[0057] By using the solid-state light emitting element 11 that emits such high-density primary light, the near-infrared fluorescent ceramic 1 can emit light with an energy density of 0.3 W / mm ２ , preferably 1.0 W / mm ２ , more preferably 3.0 W / mm ２ It can be made to exceed that.

[0058] [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 10 described above. Fig. 3 shows a schematic diagram of an example of the electronic device according to this embodiment. The electronic device 20 includes at least a power supply circuit 21, a conductor 22, and a near-infrared light emitting device 10 including a near-infrared fluorescent ceramic 1 and a solid-state light emitting element 11. The power supply circuit 21 supplies power to the solid-state light emitting element 11 in the near-infrared light emitting device 10 through the conductor 22.

[0059] As described above, the near-infrared light emitting device 10 converts electrical energy into light energy. The near-infrared light emitting device 10 converts at least a portion of the electrical energy supplied from the power supply circuit 21 into light energy that becomes output light 23 and outputs the converted light. The near-infrared light emitting device 10 in Fig. 3 is configured to emit output light 23 that includes near-infrared light.

[0060] 3 further includes a first detector 27A and a second detector 27B. The first detector 27A detects a transmitted light component 25 of output light 23 emitted from the near-infrared light emitting device 10 and irradiated onto the irradiated object 24. Specifically, the first detector 27A detects near-infrared light in the transmitted light component 25 that has passed through the irradiated object 24. The second detector 27B detects a reflected light component 26 of the output light 23 emitted from the near-infrared light emitting device 10 and irradiated onto the irradiated object 24. Specifically, the second detector 27B detects near-infrared light in the reflected light component 26 that has reflected from the irradiated object 24.

[0061] In the electronic device 20 configured as described above, the irradiated object 24 is irradiated with output light 23 containing a near-infrared light component, and a transmitted light component 25 that has passed through the irradiated object 24 and a reflected light component 26 that has been reflected by the irradiated object 24 are detected by the first detector 27A and the second detector 27B, respectively. Therefore, the electronic device 20 can detect characteristic information of the irradiated object 24 that involves the near-infrared light component.

[0062] The near-infrared light emitting device 10 of this embodiment can emit output light 23 that includes at least near-infrared light and is suitable for a detector. Therefore, by combining the light emitting device with a near-infrared detector, an electronic device suitable for industrial applications can be obtained.

[0063] Furthermore, the near-infrared light emitting device 10 of this embodiment can be configured to emit high energy output light 23, illuminating a wide area. Therefore, even if the output light 23 is irradiated onto the object 24 from a long distance, a signal with a good S / N ratio (signal / noise ratio) can be detected. Therefore, the near-infrared light emitting device 10 is suitable for inspecting a large object 24, inspecting objects distributed over a wide area, detecting objects present in a portion of a wide inspection area, and detecting people or objects from a long distance.

[0064] Various types of photodetectors can be used for the first detector 27A and the second detector 27B. Specifically, depending on the usage mode of the electronic device, quantum-type photodetectors (such as photodiodes, phototransistors, photo ICs, CCD image sensors, and CMOS image sensors) that detect electric charges generated when light is incident on a PN junction of a semiconductor can be used. Furthermore, thermal-type photodetectors (such as thermopiles that utilize the thermoelectric effect and pyroelectric elements that utilize the pyroelectric effect) that detect changes in electrical properties caused by a temperature rise due to heat generated when light is received, or infrared films that are sensitive to light can also be used as photodetectors.

[0065] The first detector 27A and the second detector 27B may be a single element using a single photoelectric conversion element, or an imaging element in which photoelectric conversion elements are integrated. The imaging element may be a linear type arranged one-dimensionally, or a surface type arranged two-dimensionally. Imaging cameras may also be used as the first detector 27A and the second detector 27B.

[0066] Although the electronic device 20 in FIG. 12 is equipped with both the first detector 27A and the second detector 27B, it is sufficient for the electronic device to be equipped with at least one of the first detector 27A and the second detector 27B.

[0067] Furthermore, the electronic device of this embodiment can be used as an inspection device, detection device, monitoring device, or sorting device for an irradiated object using the output light. The near-infrared light component of the output light has the property of passing through most materials. Therefore, by irradiating a material with near-infrared light from the outside and detecting the transmitted or reflected light, it is possible to inspect the internal condition and the presence or absence of foreign matter without destroying the material.

[0068] Furthermore, since near-infrared light components are invisible to the human eye and their reflection characteristics depend on the material, by irradiating an object with near-infrared light and detecting the reflected light, it is possible to detect people, animals, plants, objects, etc., even in the dark, without being noticed by humans.

[0069] Furthermore, the electronic device of this embodiment can inspect the internal state and the presence or absence of foreign matter without destroying the material, determine the quality of the material, and sort out good and bad products. Therefore, by further providing the electronic device with a mechanism for distinguishing between irradiated objects in a normal state and irradiated objects in an abnormal state, it becomes possible to sort the objects.

[0070] In the electronic device of this embodiment, the near-infrared light-emitting device 10 can be fixed rather than movable. This eliminates the need for a complex mechanism for mechanically moving the light-emitting device, making the electronic device less susceptible to breakdowns. Furthermore, by fixing the light-emitting device indoors or outdoors, it is possible to perform fixed-point observation of the status of people and objects in a predetermined location, or to count the number of people and objects. This makes the electronic device advantageous for collecting big data that can be used to identify issues and for business applications.

[0071] In the electronic device of this embodiment, the near-infrared light emitting device 10 is movable, so that the location of irradiation can be changed. For example, the near-infrared light emitting device 10 can be attached to a moving stage or a moving body (such as a vehicle or an aircraft) to make it movable. In this way, the near-infrared light emitting device 10 can irradiate a desired location or a wide area, making the electronic device advantageous for inspecting large objects or inspecting the condition of objects outdoors.

[0072] The electronic device of this embodiment can be configured to further include a hyperspectral camera as an imaging camera in addition to the light-emitting device. This allows the electronic device to perform hyperspectral imaging. An electronic device equipped with a hyperspectral camera can distinguish, as an image, differences that cannot be distinguished by the naked eye or a normal camera, making it a useful inspection device in a wide range of fields related to product inspection and sorting.

[0073] The electronic device of this embodiment can be used for medical purposes, animal medical purposes, biotechnology, agriculture, forestry, and fisheries, livestock farming (meat, meat products, dairy products, etc.), and industrial purposes (foreign object inspection, content volume inspection, shape inspection, packaging condition inspection, etc.). The electronic device can also be used for inspecting pharmaceuticals, animal experiments, food, beverages, agricultural, forestry, and fishery products, livestock products, and industrial products. In other words, the electronic device of this embodiment can be used for inspecting any of the human body, animals, plants, and objects, and further for inspecting any of gases, liquids, and solids.

[0074] The electronic device of the present embodiment is preferably used as 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.

[0075] 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, observation, monitoring, separation, diagnosis, treatment, purification, etc. of 1) blood, 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.

[0076] 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 / body hair, 3) inside the mouth / dental / periodontia, 4) ears / nose, and 5) vital signs.

[0077] For example, for purposes in agriculture, forestry, fisheries, livestock farming, and industry, the electronic device of the present embodiment can be used for inspecting, detecting, measuring, counting, evaluating, analyzing, interpreting, observing, monitoring, recognizing, sorting, and separating 1) industrial products (including electronic materials and electronic devices), 2) agricultural products (such as fruits and vegetables), 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.

[0078] For example, for the purpose of nursing care, the electronic device of this embodiment can be used to check excretion, identify, manage, and monitor health conditions, and the like.

[0079] In this way, the electronic device of this embodiment can be used for a variety of purposes, such as inspection, detection, measurement, evaluation, analysis, observation, monitoring, recognition, sorting, and separation.

[0080] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0081] (Technology 1) A near-infrared fluorescent ceramic that emits fluorescence and contains at least a first inorganic compound and a second inorganic compound different from the first inorganic compound, wherein the first inorganic compound is a phosphor that emits near-infrared light having a fluorescence peak in a wavelength range of 730 nm or more and 2500 nm or less, and the near-infrared fluorescent ceramic has a sea-island structure including a continuous phase composed of the first inorganic compound and a dispersed phase composed of the second inorganic compound and dispersed within the continuous phase.

[0082] This configuration reduces grain boundaries and voids between the first inorganic compounds, thereby improving the quality of the resulting near-infrared fluorescent ceramic. Furthermore, the excitation light irradiated onto the near-infrared fluorescent ceramic can more easily reach the first inorganic compound, allowing the first inorganic compound to efficiently absorb the excitation light and increase the emission intensity of the near-infrared light. Furthermore, since the near-infrared fluorescent ceramic is made entirely of inorganic compounds with high thermal conductivity, it has high heat dissipation properties, which can suppress temperature quenching of the near-infrared phosphor, which is the first inorganic compound.

[0083] (Technology 2) The near-infrared fluorescent ceramic according to Technology 1, wherein the first inorganic compound and the second inorganic compound each contain the same constituent elements.

[0084] This configuration allows the constituent elements to mitigate the abrupt compositional difference at the interface between the first inorganic compound and the second inorganic compound, and also acts to bond the first inorganic compound and the second inorganic compound together via the constituent elements, thereby homogenizing the internal stress distribution and producing a strong, break-resistant near-infrared fluorescent ceramic.

[0085] (Technology 3) The near-infrared fluorescent ceramic according to Technology 2, wherein the constituent element is a metal element that forms a trivalent metal ion.

[0086] With this configuration, both the first inorganic compound and the second inorganic compound are Cr, which emits near-infrared fluorescence. ３＋ The first inorganic compound and the second inorganic compound can be activated with ions, and therefore the fluorescent ceramic functions as a near-infrared phosphor.

[0087] (Technology 4) The first inorganic compound contains Cr as an activator. ３＋ The near-infrared fluorescent ceramic according to any one of techniques 1 to 3, containing ions.

[0088] With this configuration, the near-infrared fluorescent ceramic can absorb visible light, particularly blue or red light, and efficiently convert the wavelength into a near-infrared light component.

[0089] (Technology 5) The first inorganic compound is β-Ga ２ O ３The near-infrared fluorescent ceramic according to any one of techniques 1 to 4, wherein the compound has the same crystal structure as that of the compound.

[0090] This configuration makes it possible to obtain a near-infrared fluorescent ceramic that has a wide half-width of the fluorescent spectrum and is suitable for emitting near-infrared light with little thermal quenching.

[0091] (Technology 6) The near-infrared fluorescent ceramic according to any one of Technology 1 to Technology 5, wherein the second inorganic compound is a compound containing boron.

[0092] This configuration allows the use of boric acid (H ３ BO ３ ) or boron oxide (B ２ O ３ ) can be used as part of the ceramic raw material, making it easy to produce near-infrared fluorescent ceramics.

[0093] (Technology 7) The first inorganic compound is (Ga １－（ｘ＋ｙ） Sc ｘ Cr ｙ ) ２ O ３ as a main component, and the second inorganic compound is (Sc １－ｚ Cr ｚ ) BO ３ and (Sc １－ｚ Cr ｚ ) P.O. ４ As a main component, at least one of the following is contained (wherein x, y, and z satisfy 0<x<1, 0<y<0.1, 0<x+y<1, and 0≦z<0.1).

[0094] This configuration facilitates the formation of a sea-island structure comprising a continuous phase 2 composed of the first inorganic compound and a dispersed phase 3 composed of the second inorganic compound. As a result, the second inorganic compound acts to bind the first inorganic compounds, reducing the grain boundaries and voids between the first inorganic compounds, thereby improving the quality of the near-infrared fluorescent ceramic.

[0095] (Technology 8) A near-infrared light emitting device comprising the near-infrared fluorescent ceramic according to any one of Technology 1 to Technology 7.

[0096] This configuration utilizes an all-inorganic near-infrared fluorescent ceramic that has excellent thermal conductivity, is dense, has high mechanical strength, and emits near-infrared rays, resulting in a near-infrared light-emitting device that ensures high output and high reliability.

[0097] 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.

[0098] [Examples 1 to 3 and Comparative Example 1] (Synthesis of fluorescent ceramics) The fluorescent ceramics of Examples 1 to 3 and Comparative Example 1 were synthesized using a preparation method based on a solid-state reaction. Specifically, in Examples 1 to 3, (Ga １－（ｘ＋ｙ） , Sc ｘ , Cr ｙ ) ２ O ３ and an inorganic compound represented by the composition formula (Sc １－ｚ , Cr ｚ ) BO ３ In Comparative Example 1, a composite fluorescent ceramic was synthesized, which was composed of an inorganic compound represented by the following composition formula: １－（ｘ＋ｙ） , Sc ｘ , Cr ｙ ) ２ O ３ A fluorescent ceramic was synthesized from an inorganic compound represented by the following composition formula: where x, y, and z are values ​​that satisfy the following relationships: 0<x<1, 0<y<0.1, 0<x+y<1, and 0≦z<0.1.

[0099] The fluorescent ceramics of each example were synthesized using the following compound powders as the main raw materials: gallium oxide (Ga ２ O ３ ): Purity 4N, manufactured by Asia Materials Co., Ltd. Scandium oxide (Sc ２ O ３ Chromium oxide (Cr): Purity 3N, manufactured by High Purity Chemical Laboratory Co., Ltd. ２ O ３ ): Purity 3N, manufactured by Kojundo Kagaku Kenkyusho Co., Ltd. Boric acid (H ３ BO ３ ): Purity 2N, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0100] First, the raw materials for each example of fluorescent ceramic were weighed out under the formulation conditions shown in Table 1. Next, the weighed raw materials were placed in the pot of a planetary ball mill, and water and φ3 mm alumina balls were added. The raw materials were then wet-mixed using the planetary ball mill. The resulting mixed slurry was then thoroughly dried in a thermostatic chamber at 125°C and lightly crushed using a mortar and pestle to obtain a raw material mixed powder.

[0101] Next, 1 g of the resulting raw material mixed powder for each example was filled into a mold (Φ13 mm) and pressed at 10 MPa using a hand press to produce a molded body. The molded body for each example was then fired in air at 1400°C to obtain a sintered body. Finally, the sintered body for each example was polished using an automatic grinder (product number: DAG810, manufactured by Disco Corporation) to a film thickness of 300 μm, thereby obtaining a fluorescent ceramic for each example.

[0102]

[0103] (Evaluation) The fluorescent ceramics of each example obtained as described above were subjected to composition analysis, crystal structure analysis, observation with a scanning electron microscope, and evaluation of luminescence characteristics and sintered density as follows.

[0104] <Composition Analysis> Using an electron probe microanalyzer (EPMA, product name JXA-8530F plus, manufactured by JEOL Ltd.), wavelength dispersive X-ray spectroscopy (WDS, accelerating voltage 10 kV) was used to analyze the elements contained in the fluorescent ceramics of Examples 1 to 3. Figures 4 to 6 show scanning electron micrographs (2000x magnification) showing the locations where elemental analysis was performed in the fluorescent ceramics of Examples 1 to 3, and the results of semi-quantitative analysis corrected by the ZAF method.

[0105] The scanning electron microscope (SEM) photograph in FIG. 4 shows that the fluorescent ceramic of Example 1 forms a sea-island structure. The semi-quantitative analysis results in FIG. 4 show that the dispersed phase A is primarily composed of scandium, boron, and oxygen. In contrast, the continuous phase B is primarily composed of gallium, scandium, and oxygen. Similarly, the SEM photographs in FIGS. 5 and 6 show that the fluorescent ceramics of Examples 2 and 3 also form a sea-island structure. The semi-quantitative analysis results in FIGS. 5 and 6 show that the dispersed phase A is primarily composed of scandium, boron, and oxygen. In contrast, the continuous phase B is primarily composed of gallium, scandium, and oxygen.

[0106] Therefore, it can be seen that in the fluorescent ceramics of Examples 1 to 3, the first inorganic compound, which is the continuous phase, is a compound mainly consisting of gallium, scandium, and oxygen, and the second inorganic compound, which is the dispersed phase, is a compound mainly consisting of scandium, boron, and oxygen.

[0107] <Crystal structure analysis> The X-ray diffraction pattern of each fluorescent ceramic was measured using an X-ray diffractometer (trade name: Miniflex (registered trademark), manufactured by Rigaku Corporation). The measured X-ray diffraction pattern was then compared with patterns in the Inorganic Crystal Structure Database (ICSD) to identify the crystal structure of each fluorescent ceramic. Furthermore, the crystal composition of each fluorescent ceramic was estimated taking into account the crystal structure of the fluorescent ceramic and the above-mentioned composition analysis results.

[0108] FIG. 7 shows the X-ray diffraction patterns of the fluorescent ceramics of Examples 1 to 3 and Comparative Example 1. Furthermore, FIG. １．１７ Sc ０．８３ O ３ As shown in FIG. 7, the fluorescent ceramics of Examples 1 to 3 have Ga １．１７ Sc ０．８３ O ３ Since a peak similar to the peak pattern of (Ga, Sc) is strongly observed, ２ O３ It can be seen that the fluorescent ceramics of Examples 1 to 3 mainly contain compounds having the same crystal structure as ScBO. ３ Since a peak of ScBO is observed, ３ It can be seen that the compound contains a compound having the same crystal structure as

[0109] And, ScBO in Examples 1 to 3 ３ It can also be seen that the intensity of the peak increases as the amount of boric acid added increases. Therefore, it can be seen that the proportion of the second inorganic compound, which is the dispersed phase, increases as the amount of boric acid, which is the low-melting point material, increases.

[0110] <Scanning Electron Microscope Observation> SEM images (backscattered electron images) of the fluorescent ceramics of each example were observed using a scanning electron microscope (tabletop microscope, Miniscope (registered trademark) TM4000II, manufactured by Hitachi High-Technologies Corporation). The results of observation at 1000x magnification are shown in Fig. 8, and the results of observation at 3000x magnification are shown in Fig. 9.

[0111] 8 and 9, the fluorescent ceramics of Examples 1 to 3 are found to have a sea-island structure. The composition analysis above reveals that the fluorescent ceramics of Examples 1 to 3 have dispersed phases that are primarily composed of scandium, boron, and oxygen, and continuous phases that are primarily composed of gallium, scandium, and oxygen. The crystal structure analysis also reveals that the fluorescent ceramics of Examples 1 to 3 have a (Ga, Sc) ２ O ３ and further comprising a compound having the same crystal structure as ScBO ３ Therefore, in the fluorescent ceramics of Examples 1 to 3, the continuous phase is mainly composed of (Ga, Sc) ２ O ３ The dispersed phase is mainly ScBO ３ It can be seen that it is composed of

[0112] 8 and 9 show that the fluorescent ceramics of Examples 1 to 3 have few voids at the interface between the continuous phase and the dispersed phase in the sea-island structure. In contrast, the fluorescent ceramic of Comparative Example 1 has many grain boundaries and many voids. Therefore, it can be seen that the presence of a sea-island structure made up of the first inorganic compound and the second inorganic compound reduces the number of voids and grain boundaries, resulting in a fluorescent ceramic with excellent ceramic quality.

[0113] <Emission characteristics> Using an absolute PL quantum yield measurement device (product number C13534-24, manufactured by Hamamatsu Photonics K.K.), the emission spectrum, internal quantum efficiency (IQE), light absorptance (Abs.), and external quantum efficiency (EQE) of each example of the fluorescent ceramic were measured at an excitation wavelength of 450 nm.

[0114] The emission spectra of the fluorescent ceramics of each example are shown in Figure 10, and the internal quantum efficiency, light absorptance, and external quantum efficiency are shown in Table 2. Figure 10 shows that the fluorescent ceramics of Examples 1 to 3 and Comparative Example 1 emit broad fluorescence with an emission peak in the range exceeding 800 nm. Furthermore, the maximum emission intensity of the fluorescent ceramics of Examples 1 to 3 is nearly twice as high as that of the fluorescent ceramic of Comparative Example 1. Table 2 also shows that the fluorescent ceramics of Examples 1 to 3 have significantly improved light absorptance and external quantum efficiency compared to the fluorescent ceramic of Comparative Example 1. Specifically, the internal quantum efficiency exceeded 85%, exceeding 90% in the preferred embodiment, while the light absorptance exceeded 70%, exceeding 75% in the preferred embodiment. Therefore, the external quantum efficiency exceeded 60%, exceeding 65% in the preferred embodiment.

[0115] Thus, it can be seen that the reduction of voids and grain boundaries and the improvement of ceramic quality result in a fluorescent ceramic with greatly improved luminescence properties.

[0116]

[0117] <Sintered Density> The sintered density (bulk density) of each fluorescent ceramic was measured. The sintered density was determined by measuring the dimensions of each fluorescent ceramic to calculate the volume, and then dividing the dry weight of each fluorescent ceramic by the volume. The measurement results are also shown in Table 2.

[0118] As shown in Table 2, it can be seen that the fluorescent ceramics of Examples 1 to 3 are denser ceramics with a higher density and reduced voids than the fluorescent ceramic of Comparative Example 1.

[0119] [Example 4] (Synthesis of fluorescent ceramics) The fluorescent ceramics of Example 4 were synthesized using a preparation method based on a solid-state reaction. Specifically, in Example 4, １－（ｘ＋ｙ） , Sc ｘ , Cr ｙ ) ２ O ３ and an inorganic compound represented by the composition formula (Sc １－ｚ , Cr ｚ ) BO ３ and an inorganic compound represented by the composition formula (Sc １－ｚ , Cr ｚ ) P.O. ４ Here, x, y, and z are values ​​that satisfy the following relationships: 0<x<1, 0<y<0.1, 0<x+y<1, and 0≦z<0.1.

[0120] The fluorescent ceramics of each example were synthesized using the following compound powders as the main raw materials: gallium oxide (Ga ２ O ３ ): Purity 4N, manufactured by Asia Materials Co., Ltd. Scandium oxide (Sc ２ O ３ Chromium oxide (Cr): Purity 3N, manufactured by High Purity Chemical Laboratory Co., Ltd. ２ O ３ ): Purity 3N, manufactured by Kojundo Kagaku Kenkyusho Co., Ltd. Boric acid (H ３ BO ３ ): Purity 2N, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Diammonium hydrogen phosphate ((NH ４ ) ２ HPO ４ ): Purity 2N, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0121] First, the raw materials for the fluorescent ceramics of each example were weighed under the blending conditions shown in Table 3, and then a raw material powder mixture was obtained in the same manner as in Example 1.

[0122] Next, 1 g of the obtained raw material mixed powder of each example was filled into a mold (Φ13 mm), and then pressed at a pressure of 10 MPa using a hand press to produce a molded body. The molded body was then fired in air at 1350°C to obtain a sintered body. Finally, the produced sintered body was polished using an automatic grinder to a film thickness of 300 μm, thereby obtaining the fluorescent ceramic of this example.

[0123]

[0124] (Evaluation) The fluorescent ceramic of Example 4 obtained as described above was subjected to crystal structure analysis, scanning electron microscope observation, and evaluation of luminescence characteristics and sintered density in the same manner as in Example 1. Furthermore, the fluorescent ceramic of Example 4 was subjected to energy dispersive X-ray analysis to evaluate element distribution.

[0125] <Crystal Structure Analysis> Fig. 11 shows the X-ray diffraction pattern of the fluorescent ceramic of Example 4. As shown in Fig. 11, the fluorescent ceramic of Example 4 has Ga １．１７ Sc ０．８３ O ３ Since a peak similar to the peak pattern of (Ga, Sc) is strongly observed, ２ O ３ It can be seen that the fluorescent ceramic of Example 4 mainly contains a compound having the same crystal structure as ScBO. ３ and ScPO ４ Since a peak of ScBO is observed, ３ and a compound having the same crystal structure as ScPO ４ It can be seen that the compound contains a compound having the same crystal structure as

[0126] <Scanning Electron Microscope Observation> Fig. 12 shows SEM images (backscattered electron images) of the fluorescent ceramic of Example 4 observed at 1000x and 3000x magnifications. As shown in Fig. 12, it can be seen that the fluorescent ceramic of Example 4 forms a sea-island structure. Furthermore, Fig. 12 also shows that the fluorescent ceramic of Example 4 has few voids at the interface between the continuous phase and the dispersed phase of the sea-island structure. Therefore, it can be seen that the sea-island structure composed of the first inorganic compound and the second inorganic compound reduces voids and grain boundaries, resulting in a fluorescent ceramic with excellent ceramic quality.

[0127] <Luminescence properties> Table 4 shows the internal quantum efficiency, light absorption rate, and external quantum efficiency of the fluorescent ceramic of Example 4. Table 4 shows that the fluorescent ceramic of Example 4 has significantly improved light absorption rate and external quantum efficiency compared to the fluorescent ceramic of Comparative Example 1. Therefore, it is clear from Example 4 that the reduction in voids and grain boundaries and the improvement in ceramic quality result in a fluorescent ceramic with significantly improved luminescence properties.

[0128]

[0129] <Sintered Density> As shown in Table 4, the fluorescent ceramic of Example 4 is denser than the fluorescent ceramic of Comparative Example 1, and has reduced voids.

[0130] <Energy Dispersive X-ray Analysis> Using a scanning electron microscope (tabletop microscope, Miniscope (registered trademark) TM4000II, manufactured by Hitachi High-Technologies Corporation), SEM images (backscattered electron images) of the fluorescent ceramic of Example 4 were observed. Furthermore, energy dispersive X-ray analysis (EDX analysis) was performed to create element maps of gallium, scandium, phosphorus, and boron.

[0131] As shown in Figure 13, in the backscattered electron image of the fluorescent ceramic of Example 4, it can be seen that the areas with dark contrast have a high concentration of phosphorus. Also, although scandium is contained in both the areas with dark contrast and the areas with light contrast in the backscattered electron image, it can be seen that the dark areas have a relatively higher concentration. Furthermore, it can be seen that the areas with light contrast in the backscattered electron image have a high concentration of gallium. From this result and the above crystal structure analysis, it can be seen that in the fluorescent ceramic of Example 4, the continuous phase is (Ga, Sc) ２ O ３ The dispersed phase is composed of at least ScPO ４ It can be seen that it is composed of

[0132] 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.

[0133] The entire contents of Japanese Patent Application No. 2023-115837 (filing date: July 14, 2023) are incorporated herein by reference.

[0134] According to the present disclosure, it is possible to provide a near-infrared fluorescent ceramic that has high light-emitting properties and excellent ceramic quality, and a near-infrared light-emitting device that includes the near-infrared fluorescent ceramic.

[0135] 1 Near-infrared fluorescent ceramic 2 Continuous phase 3 Dispersed phase 10 Near-infrared light-emitting device

Claims

1. A near-infrared fluorescent ceramic that emits fluorescence, comprising at least a first inorganic compound and a second inorganic compound different from the first inorganic compound, The first inorganic compound is a phosphor that emits near-infrared light having a fluorescence peak in the wavelength range of 730 nm to 2500 nm. A near-infrared fluorescent ceramic having a sea-island structure comprising a continuous phase composed of the first inorganic compound and a dispersed phase composed of the second inorganic compound and dispersed within the continuous phase.

2. The near-infrared fluorescent ceramic according to claim 1, wherein the first inorganic compound and the second inorganic compound each contain the same constituent elements.

3. The near-infrared fluorescent ceramic according to claim 2, wherein the constituent element is a metallic element that forms a trivalent metal ion.

4. The first inorganic compound further includes Cr as an activator. ３＋ A near-infrared fluorescent ceramic according to any one of claims 1 to 3, comprising ions.

5. The first inorganic compound is β-Ga ２ O ３ A near-infrared fluorescent ceramic according to any one of claims 1 to 3, which is a compound having the same crystal structure as the one described above.

6. The near-infrared fluorescent ceramic according to any one of claims 1 to 3, wherein the second inorganic compound is a boron-containing compound.

7. The first inorganic compound contains (Ga １－（ｘ＋ｙ） Sc ｘ Cr ｙ ) ２ O ３ as a main component, and the second inorganic compound contains at least one of (Sc １－ｚ Cr ｚ )BO ３ and (Sc １－ｚ Cr ｚ )PO ４ as a main component (where x, y, and z satisfy 0 < x < 1, 0 < y < 0.1, 0 < x + y < 1, and 0 ≤ z < 0.1). The near-infrared fluorescent ceramics according to any one of claims 1 to 3.

8. A near-infrared light-emitting device comprising a near-infrared fluorescent ceramic according to any one of claims 1 to 3.