Near-infrared fluorescent ceramic and near-infrared light-emitting device provided with same

Abstract

The near-infrared fluorescent ceramic (1) is a fluorescent ceramic which contains at least a first inorganic compound and a second inorganic compound different from the first inorganic compound and emits fluorescence. 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 (inclusive). The near-infrared fluorescent ceramic (1) has a sea-island structure provided with a continuous phase (2) comprising a first inorganic compound and a dispersed phase (3) comprising a second inorganic compound and dispersed within the continuous phase. A near-infrared light-emitting device (10) is provided with a near-infrared fluorescent ceramic.

Description

Technical Field

[0001] This invention relates to near-infrared fluorescent ceramics and near-infrared emitting devices incorporating such near-infrared fluorescent ceramics. Background Technology

[0002] Near-infrared light has the characteristic of easily penetrating living organisms, making it suitable for acquiring information about the interior of organisms and treating lesions within them. Furthermore, near-infrared light has the property of penetrating organic matter, thus it is advantageous when inspecting the contents of containers made of organic materials or foreign objects in an unopened state. Therefore, near-infrared emitting devices are expected to be used in medical lighting and lighting for inspection devices.

[0003] Patent Document 1 discloses a red / near-infrared luminescent 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 luminescent material characterized by comprising a compound with the molecular formula aSc2O3·Ga2O3·bR2O3, wherein the R element comprises one or two of the elements Cr, Ni, Fe, Yb, Nd, or Er, wherein 0.001 ≤ a ≤ 0.6 and 0.001 ≤ b ≤ 0.1. Additionally, Patent Document 1 discloses a red / near-infrared luminescent material represented by the general formula aSc2O3·Ga2O3·bCr2O3.

[0004] Furthermore, there has always been a demand for near-infrared fluorescent ceramics that can be used in near-infrared light-emitting devices and contain near-infrared phosphors with excellent luminescence properties.

[0005] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2021-529240 Summary of the Invention

[0006] However, previously known near-infrared fluorescent ceramics have numerous internal voids and grain boundaries. Therefore, conventional near-infrared fluorescent ceramics suffer from poor ceramic quality. Furthermore, due to the aforementioned potential problems, conventional near-infrared emitting devices incorporating such ceramics have shortcomings in performance and reliability.

[0007] This invention was made in view of the problems inherent in the prior art. Furthermore, the object of this invention is to provide a near-infrared fluorescent ceramic with high luminescence properties and excellent quality as a ceramic, and a near-infrared luminescent device incorporating this near-infrared fluorescent ceramic.

[0008] To address the aforementioned issues, the near-infrared fluorescent ceramic according to the first aspect of the present invention is a near-infrared fluorescent ceramic that contains at least a first inorganic compound and a second inorganic compound different from the first inorganic compound and emits fluorescence. The first inorganic compound is a phosphor that emits near-infrared light with a fluorescence peak in a wavelength range of 730 nm or higher and 2500 nm or lower. The near-infrared fluorescent ceramic has an island structure, which comprises 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] The near-infrared emitting device according to the second aspect of the present invention comprises near-infrared fluorescent ceramic. Attached Figure Description

[0010] Figure 1 This is a schematic diagram illustrating an example of the island structure of the near-infrared fluorescent ceramic according to this embodiment.

[0011] Figure 2 This is a schematic diagram illustrating an example of the near-infrared emitting device according to this embodiment.

[0012] Figure 3 This is a schematic diagram illustrating an example of an electronic device according to this embodiment.

[0013] Figure 4 The image shows a scanning electron microscope image (2000x) of the part of the fluorescent ceramic in Example 1 that has undergone elemental analysis, as well as a graph of the semi-quantitative analysis results corrected by the ZAF method.

[0014] Figure 5 The image shows a scanning electron microscope image (2000x) of the part of the fluorescent ceramic in Example 2 that has undergone elemental analysis, as well as a graph of the semi-quantitative analysis results corrected by the ZAF method.

[0015] Figure 6 The image shows a scanning electron microscope image (2000x) of the part of the fluorescent ceramic in Example 3 that underwent elemental analysis, as well as a graph of the semi-quantitative analysis results corrected by the ZAF method.

[0016] Figure 7 This is a diagram showing the X-ray diffraction patterns of the fluorescent ceramics of Examples 1-3 and Comparative Example 1.

[0017] Figure 8 These are photographs showing the results of the fluorescent ceramics of Examples 1-3 and Comparative Example 1 observed using a scanning electron microscope at 1000x magnification.

[0018] Figure 9These are photographs showing the results of the fluorescent ceramics of Examples 1-3 and Comparative Example 1 observed using a scanning electron microscope at 3000x magnification.

[0019] Figure 10 This is a graph showing the emission spectra of the fluorescent ceramics of Examples 1-3 and Comparative Example 1 when excited with excitation light of wavelength 450 nm.

[0020] Figure 11 This is a diagram showing the X-ray diffraction pattern of the fluorescent ceramic of Example 4.

[0021] Figure 12 These are photographs showing the results of observing the fluorescent ceramics of Example 4 using a scanning electron microscope at 1000x and 3000x magnification.

[0022] Figure 13 This is a graph showing the reflected electron image of the fluorescent ceramic of Example 4, and the elemental spectra of gallium, scandium, phosphorus and boron based on energy-dispersive X-ray analysis. Detailed Implementation

[0023] Hereinafter, the near-infrared fluorescent ceramic according to this embodiment and the near-infrared emitting device using the near-infrared fluorescent ceramic will be described in detail with the help of the accompanying drawings. It should be noted that, for ease of explanation, the scale of the drawings has been exaggerated and may sometimes differ from the actual scale.

[0024] Near-infrared fluorescent ceramics

[0025] Previously known near-infrared fluorescent ceramics were primarily composed of near-infrared phosphors. Furthermore, these ceramics were formed with the following objectives: to increase the light absorption rate of light-absorbing ions (fluorescent ions) with generally low light absorption rates contained in the near-infrared phosphor, and to improve the thermal conductivity as a wavelength converter, thereby achieving high near-infrared light output. It should be noted that, in order to improve the light absorption rate of near-infrared fluorescent ceramics, increasing the concentration of light-absorbing ions, achieving high density, achieving high purity of the near-infrared phosphor bulk, and maximally eliminating substances other than the desired phosphor components are conventional methods in this technical field.

[0026] However, as mentioned above, the development history of near-infrared fluorescent ceramics, especially those emitting fluorescence with emission peaks in the long wavelength region exceeding 800 nm, is sometimes short, and they often have many internal voids and grain boundaries. Therefore, these near-infrared fluorescent ceramics suffer from poor ceramic quality as a single unit.

[0027] Furthermore, when using solid solutions with two different end-component crystal phases, such as β-Ga2O3 (monoclinic) and Sc2O3 (cubic), as the parent compound of a phosphor, the following problems arise: (1) Internal stress is easily generated in the solid solution crystal, making it difficult to obtain high-quality ceramics. (2) The crystal system changes from monoclinic to cubic or vice versa around a certain solid solution ratio, making it impossible to adjust the solid solution ratio to obtain the desired fluorescence properties. (3) Multiple phases are easily formed in the solid solution ratio that exhibits the desired fluorescence properties, resulting in a ceramic with a mixture of heterogeneous phases. Therefore, it is not only difficult to achieve high quality, but also easy to generate characteristic deviations between manufacturing batches, thus reducing the yield.

[0028] Therefore, conventional near-infrared emitting devices and near-infrared utilizing devices that utilize near-infrared fluorescent ceramics have such potential problems, posing risks not only in terms of performance and reliability but also in terms of manufacturing yield. The purpose of this embodiment is to provide high-quality near-infrared fluorescent ceramics, particularly long-wavelength near-infrared fluorescent ceramics, which are beneficial for industrial production.

[0029] The near-infrared fluorescent ceramic of this embodiment comprises at least a first inorganic compound that serves as a phosphor emitting near-infrared light and a second inorganic compound different from the first inorganic compound. Furthermore, the near-infrared fluorescent ceramic has an inorganic phase composed of the first inorganic compound and an inorganic phase composed of the second inorganic compound, and also has a structure in which these inorganic phases are mixed and phase-separated.

[0030] Specifically, such as Figure 1 As shown, in the near-infrared fluorescent ceramic 1, an inorganic phase composed of a first inorganic compound forms a continuous phase 2, and an inorganic phase composed of a second inorganic compound forms a dispersed phase 3. Furthermore, multiple small dispersed phases 3 are dispersed within the continuous phase 2, and each dispersed phase 3 is entirely covered by the continuous phase 2. Therefore, the near-infrared fluorescent ceramic 1 has an island structure, which includes the continuous phase 2 composed of the first inorganic compound and the dispersed phase 3 composed of the second inorganic compound dispersed within the continuous phase 2.

[0031] In near-infrared fluorescent ceramic 1, such as Figure 1As shown, the first and second inorganic compounds form a sea-island structure, in which the first inorganic compound, which acts as a continuous structure resembling an ocean, surrounds the second inorganic compound, which acts as a discontinuous structure resembling an island. Through this sea-island structure, the second inorganic compound functions by binding 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, thus improving the quality of the obtained near-infrared fluorescent ceramic 1. That is, a dense near-infrared fluorescent ceramic with high mechanical strength, suitable as a wavelength converter emitting near-infrared light, can be obtained. Furthermore, due to the reduction in grain boundaries and voids between the first inorganic compounds, excitation light irradiating the near-infrared fluorescent ceramic 1 easily reaches the first inorganic compounds. As a result, the first inorganic compounds effectively absorb a portion of the excitation light and emit near-infrared light, thus increasing the luminescence intensity of the near-infrared light.

[0032] It should be noted that in the 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. 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 composed of the first inorganic compound is 50% or more by volume, and the dispersed phase 3 composed of the second inorganic compound is less than 50% by volume. It should be noted that in the near-infrared fluorescent ceramic 1, the continuous phase 2 can be 60% or more by volume, and the dispersed phase 3 can be 40% or less by volume, or the continuous phase 2 can be 70% or more by volume, and the dispersed phase 3 can be 30% or less by volume. Alternatively, in the near-infrared fluorescent ceramic 1, the continuous phase 2 can be 80% or more by volume, and the dispersed phase 3 can be 20% or less by volume.

[0033] 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, more preferably 70 mol% or more. The continuous phase 2 can 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, more preferably 70 mol% or more. Alternatively, the dispersed phase 3 can also be composed of the second inorganic compound.

[0034] 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 each contain the same constitutive elements. In this case, the constitutive elements function to mitigate the sharp compositional difference at the interface between the first and second inorganic compounds and to bind the first and second inorganic compounds together via the constitutive elements. Therefore, a near-infrared fluorescent ceramic can be produced that achieves homogenization of internal stress distribution and is suitable for forming a robust morphology that is not easily broken.

[0035] In the near-infrared fluorescent ceramic 1, the constituent elements contained in the first and second inorganic compounds are preferably metallic 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. Furthermore, the second inorganic compound may or may not be a phosphor. Additionally, if the second inorganic compound is a phosphor, it may also be a phosphor that emits near-infrared light. Furthermore, if the constituent elements contained in the first and second inorganic compounds are metallic elements that form trivalent metal ions, Cr, a known phosphor ion that emits near-infrared fluorescence, can be used. 3+ Both the first and second inorganic compounds are ion-activated. Therefore, the resulting near-infrared fluorescent ceramic 1 becomes a high-performance fluorescent ceramic in which both the first and second inorganic compounds function as near-infrared phosphors. It should be noted that the constituent elements are preferably at least one of scandium and gallium.

[0036] 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. As such a near-infrared phosphor, it is preferable to be a phosphor that emits near-infrared light with 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 with a fluorescence peak in a wavelength range of 780 nm or more and less than 2500 nm. Furthermore, as a near-infrared phosphor, it is preferable to be a phosphor that emits near-infrared light with 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 with a maximum intensity in a wavelength range of 780 nm or more and less than 900 nm. In this way, the wavelength of primary light emitted by the solid-state light-emitting element can be easily converted into near-infrared light components, and therefore, for example, it is suitable to obtain the near-infrared light components required for inspection light.

[0037] As a near-infrared phosphor, various inorganic phosphors known as near-infrared light sources can be used, for example. Specifically, as a near-infrared phosphor, a phosphor that emits fluorescence containing a near-infrared light component upon activation by at least one of rare-earth ions and transition metal ions can be used. The rare-earth ions are preferably selected from Nd... 3+ Eu 2+ Ho 3+ Er 3+ Tm 3 + and Yb 3+At least one of the group consisting of. The transition metal ion is preferably selected from Ti. 3+ V 4+ Cr 4+ V 3+ Cr 3+ V 2+ Mn 4 + Fe 3+ Co 3+ Co 2+ and Ni 2+ At least one of the groups. Furthermore, the near-infrared phosphor is preferably an oxide, sulfide, nitride, halide, oxysulfide, oxynitride, or acyl halide containing the fluorescent ion.

[0038] Furthermore, in the near-infrared fluorescent ceramic 1, the first inorganic compound preferably contains Cr. 3+ Ions act as activators. Cr 3+ These ions are conventional fluorescent ions capable of absorbing visible light, particularly blue or red light, and converting it into near-infrared light components. Therefore, by including Cr in the first inorganic compound... 3+ Ions can be appropriately combined with near-infrared fluorescent ceramics 1 to form solid-state light-emitting elements that emit visible light. It should be noted that the first inorganic compound, besides Cr... 3+ In addition to ions, it can also contain Ni. 2+ As an activator.

[0039] As described above, in the near-infrared fluorescent ceramic 1, the first inorganic compound preferably contains Cr. 3+ Ions act as activators. Furthermore, in this structural case, the near-infrared light emitted from the near-infrared fluorescent ceramic 1 contains at least those originating from Cr. 3+ Fluorescence of ions, i.e., based on 4 T2→ 4 Fluorescence of A2 electron energy transitions. Such fluorescence containing Cr. 3+ The near-infrared fluorescent ceramic 1 exhibits a fluorescence peak in the wavelength range above 780 nm and below 1000 nm, and can emit fluorescence with a wide half-width of fluorescence spectrum, thus making it suitable for use in near-infrared spectroscopy analysis applications.

[0040] Furthermore, in the near-infrared fluorescent ceramic 1, the first inorganic compound is preferably a compound having the same crystal structure as β-Ga₂O₃. For example, (Ga,Sc)₂O₃:Cr, which has the same crystal structure as β-Ga₂O₃, is known. 3+A phosphor is a near-infrared phosphor that emits near-infrared light with a wide half-width of fluorescence and low temperature quenching. Therefore, by using a phosphor whose parent inorganic compound is a compound with the same crystal structure as β-Ga2O3, it is possible to obtain near-infrared fluorescent ceramics that emit near-infrared light with a wide half-width of fluorescence and low temperature quenching.

[0041] 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, which is composed of a phosphor that emits at least near-infrared light. However, if the second inorganic compound forms the dispersed phase 3, it may or may not be a phosphor. Furthermore, the second inorganic compound is preferably a compound of the same type as the first inorganic compound. That is, if the first inorganic compound is an oxide, the second inorganic compound is also preferably an oxide. Similarly, if the first inorganic compound is a nitride, the second inorganic compound is also preferably a nitride.

[0042] 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 and second inorganic compounds can be manufactured using conventional ceramic technology, thus making it a near-infrared fluorescent ceramic suitable for industrial production.

[0043] In the near-infrared fluorescent ceramic 1, the second inorganic compound is preferably a compound containing boron (B). Furthermore, the second inorganic compound is more preferably a compound mainly composed of MBO3 (where M is a metallic element). When the second inorganic compound is a boron-containing compound, for example, by using boric acid (H3BO3) or boron oxide (B2O3), known as low-melting-point materials, as part of the ceramic raw material, the near-infrared fluorescent ceramic 1 can be manufactured. That is, as described later, by adding boric acid or boron oxide to the raw material of the first inorganic compound and calcining it, a second inorganic compound composed of a boron-containing compound can be manufactured in addition to the first inorganic compound. Furthermore, at this time, a sea-island structure can be formed, comprising a continuous phase 2 composed of the first inorganic compound and a dispersed phase 3 composed of the second inorganic compound.

[0044] Thus, when boric acid (H3BO3) or boron oxide (B2O3) is used as part of the raw materials, intermediate compounds are readily formed in the low-temperature region during the calcination process. As a result, near-infrared fluorescent ceramics with the aforementioned island-like 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 other ceramic raw materials, shifting the reaction temperature region where multiple phases are easily formed towards a lower temperature. Therefore, it is suitable to achieve high crystallinity by making the first inorganic compound constituting continuous phase 2 a single crystalline phase.

[0045] In the near-infrared fluorescent ceramic 1, the first inorganic compound may contain (Ga 1-（x+y） Sc x Cr y )₂O₃ as a main component. It should be noted that x and y satisfy 0 < x < 1, 0 < y < 0.1, and 0 < x + y < 1. That is, the first inorganic compound may contain a phosphor having the same crystal structure as β-Ga₂O₃, with a composite oxide of gallium and scandium ((Ga, Sc)₂O₃) as a matrix and containing Cr 3+ ions as an activator as a main component. In addition, the second inorganic compound preferably contains (Sc 1-z Cr z )BO₃ as a main component. It should be noted that z satisfies 0 ≤ z < 0.1. That is, the second inorganic compound may contain an inorganic oxide represented by ScBO₃ as a main component. In addition, the second inorganic compound may also contain a phosphor having ScBO₃ as a matrix and containing Cr 3+ ions as an activator as a main component. By the first inorganic compound and the second inorganic compound containing the above oxides as main components, it is easy to form an island structure having 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 functions to bond the first inorganic compounds, reducing the grain boundaries and voids between the first inorganic compounds, and thus the near-infrared fluorescent ceramic 1 can be made of high quality.

[0046] It should be noted that in the near-infrared fluorescent ceramic 1, the first inorganic compound preferably contains 50 mol% or more of (Ga 1-（x+y） Sc x Cr y )₂O₃, and preferably contains 70 mol% or more. The first inorganic compound may be composed of (Ga 1-（x+y） Sc x Cr y )₂O₃. In addition, the second inorganic compound preferably contains 50 mol% or more of (Sc 1-z Cr z )BO₃, and preferably contains 70 mol% or more. The second inorganic compound may be composed of (Sc 1-z Cr z )BO₃.

[0047] As described above, when the first inorganic compound is a compound containing (Ga 1-（x+y） Sc x Cr y )₂O₃ as a main component, the second inorganic compound may be a compound containing (Sc 1-z Cr zA compound with BO3 as the main component. However, this embodiment is not limited to such a manner. For example, when the first inorganic compound is a compound containing (Ga 1-（x+y） Sc x Cr y )2O3 (where x and y satisfy 0 < x < 1, 0 < y < 0.1, 0 < x + y < 1) as the main component, the second inorganic compound can be a compound containing (Sc 1-z Cr z )PO4 (where z satisfies 0 ≤ z < 0.1) as the main component.

[0048] In addition, when the first inorganic compound is a compound containing (Ga 1-（x+y） Sc x Cr y )2O3 (where x and y satisfy 0 < x < 1, 0 < y < 0.1, 0 < x + y < 1) as the main component, the second inorganic compound can be a compound containing (Sc 1-z Cr z )BO3 and (Sc 1- z Cr z )PO4 (where z satisfies 0 ≤ z < 0.1) as the main component.

[0049] Furthermore, when the first inorganic compound is a compound containing (Ga 1-（x+y） Sc x Cr y )2O3 (where x and y satisfy 0 < x < 1, 0 < y < 0.1, 0 < x + y < 1) as the main component, the second inorganic compound can be a compound containing at least one selected from the group consisting of LiScO2, LiGaO2, LiGa5O8, ScAlO3, and BaSc2O4 as the main component.

[0050] Here, the phosphor represented by (GaSc)2O3:Cr 3+ has the property that the higher the concentration of scandium, the more it emits light toward the long wavelength side. Therefore, when it is desired to shift the emission peak of the near-infrared fluorescent ceramic 1 toward the long wavelength side, it is preferable to increase the concentration of scandium contained in the first inorganic compound.

[0051] In addition, (GaSc)2O3:Cr 3+It exhibits the characteristic that the temperature at which the phase change occurs when the scandium concentration is high, i.e., the temperature at which it transforms into crystals other than β-Ga₂O₃ crystals decreases. Furthermore, by adding a low-melting-point material such as boric acid, crystal growth is promoted, resulting in a densified fluorescent ceramic. Therefore, by adjusting the scandium concentration and the type and amount of low-melting-point material added, it is possible to obtain a composite of (Ga,Sc)₂O₃ crystals and ScBO₃ crystals, i.e., an island structure composed of these compounds.

[0052] Thus, the near-infrared fluorescent ceramic 1 of this embodiment is a fluorescent ceramic that contains at least a first inorganic compound and a second inorganic compound different from the first inorganic compound and emits fluorescence. The first inorganic compound is a phosphor that emits near-infrared light with a fluorescence peak in the wavelength range of 730 nm to 2500 nm. Furthermore, the near-infrared fluorescent ceramic 1 has a sea-island structure, which includes a continuous phase 2 composed of the first inorganic compound and a dispersed phase 3 composed of the second inorganic compound dispersed within the continuous phase 2.

[0053] The near-infrared fluorescent ceramic 1 has a structure in which a first inorganic compound, as a continuous structure, surrounds a second inorganic compound, which is a discontinuous structure. Therefore, the second inorganic compound acts as a binder for the first inorganic compound. As a result, the grain boundaries and voids between the first inorganic compounds are reduced, thus improving the mechanical strength of the near-infrared fluorescent ceramic 1. Furthermore, due to the reduced grain boundaries and voids between the first inorganic compounds, excitation light irradiating the near-infrared fluorescent ceramic 1 easily reaches the first inorganic compounds. Therefore, the first inorganic compounds effectively absorb the excitation light and emit near-infrared light, thus improving the luminescence intensity of the near-infrared light. In addition, the near-infrared fluorescent ceramic 1 is entirely formed of inorganic compounds with high thermal conductivity, resulting in high heat dissipation and suppressing the temperature quenching of the phosphor composed of the first inorganic compounds.

[0054] Next, the method for manufacturing the near-infrared fluorescent ceramic of this embodiment will be described. The near-infrared fluorescent ceramic of this embodiment can be manufactured by adding a low-melting-point material that can react with the raw material to the raw material used to prepare the first inorganic compound and allowing it to react.

[0055] Specifically, in the first inorganic compound composed of (Ga 1-（x+y） Sc x Cr yIn the case of a composition of 2O3, gallium oxide (Ga2O3), scandium oxide (Sc2O3), and chromium oxide (Cr2O3) are used as raw materials for preparing the first inorganic compound. Additionally, low-melting-point materials capable of reacting with these raw materials include, for example, boric acid (H3BO3), boron oxide (B2O3), diammonium hydrogen phosphate ((NH4)2HPO4), lithium carbonate (Li2CO3), lithium fluoride (LiF), aluminum chloride (AlCl3), aluminum fluoride (AlF3), and barium chloride (BaCl2).

[0056] Then, the raw materials for the first inorganic compound are weighed in a manner that constitutes the stoichiometric composition of the first inorganic compound or a composition similar to it, and then thoroughly mixed using a mortar and pestle, a ball mill, or similar method to obtain a mixed raw material. Further, a low-melting-point material is added to this mixed raw material and thoroughly mixed. Then, the resulting mixed raw material is filled into a mold and pressurized to produce a molded body composed of the mixed raw material. It should be noted that the molding of the mixed raw material can be carried out in the atmosphere at room temperature.

[0057] Then, the obtained molded body is calcined using an electric furnace or similar means. It should be noted that during calcination, it is preferable to heat the molded body for several hours in an atmosphere and / or a weakly reducing atmosphere at a calcination temperature of 900°C to 1700°C, particularly 1300°C to 1600°C. Through this calcination, the low-melting-point material reacts with other ceramic raw materials, i.e., a portion of the raw material for the first inorganic compound, to form multiple phases. As a result, an 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.

[0058] Then, by grinding and processing the obtained sintered body as needed, the near-infrared fluorescent ceramic of this embodiment can be obtained.

[0059] [Near-infrared emitting device]

[0060] Next, the near-infrared emitting device according to this embodiment will be described. It should be noted that in this specification, "near-infrared emitting device" will be simply referred to as "emitting device".

[0061] like Figure 2As shown, the near-infrared light-emitting device 10 of this embodiment includes the aforementioned near-infrared fluorescent ceramic 1 and a solid-state light-emitting element 11 that emits light (primary light) irradiating the near-infrared fluorescent ceramic 1. As such a solid-state light-emitting element, an element that emits primary light with a maximum intensity in the 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. Alternatively, an element that emits primary light with a maximum intensity in the 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, an element that emits primary light with a maximum intensity in the 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.

[0062] Solid-state light-emitting elements can be, for example, light-emitting diodes (LEDs) or laser diodes. Furthermore, by utilizing LED modules or laser diodes that emit high-energy light of 1W or more, light-emitting devices capable of producing light output in the hundreds of mW range can be achieved. Additionally, by utilizing LED modules that emit high-energy light of 3W or more, or 10W or more, light-emitting devices capable of producing light output in the several W range can be achieved. Further, by utilizing LED modules that emit high-energy light of 30W or more, light-emitting devices capable of producing light output exceeding 10W can be achieved. Moreover, by utilizing LED modules that emit high-energy light of 100W or more, light-emitting devices capable of producing light output exceeding 30W can be achieved.

[0063] If a laser diode is used as a solid-state light-emitting element, and the primary light is laser light, it can be used to irradiate near-infrared fluorescent ceramic 1 with high-density point light. Therefore, the resulting light-emitting device can become a high-output point light source, thus expanding the industrial applications of solid-state lighting. Examples of such laser diodes include edge-emitting lasers (EELs) and vertical-cavity surface-emitting lasers (VCSELs).

[0064] Alternatively, a light-guiding component such as an optical fiber can be sandwiched between the solid-state light-emitting element and the near-infrared fluorescent ceramic. This allows for a structure in which the solid-state light-emitting element and the near-infrared fluorescent ceramic are spatially separated. Consequently, the light-emitting part can be moved easily and freely, resulting in a light-emitting device whose illumination location can be easily and freely changed.

[0065] As described above, in the near-infrared light-emitting device 10, the solid-state light-emitting element 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 this; any light-emitting element that can emit high-output primary light can be used.

[0066] It should be noted that there is no particular limitation on the number of solid-state light-emitting elements in a near-infrared light-emitting device; it can be a single element or multiple elements. By using multiple solid-state light-emitting elements, the output of primary light can be easily increased, thus making it a light-emitting device conducive to high output. It should also be noted that there is no particular limitation on the number of solid-state light-emitting elements; for example, it can be appropriately selected from 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. Furthermore, there is no particular upper limit on the number; for example, it can be appropriately selected from 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.

[0067] In near-infrared light-emitting devices, the solid-state light-emitting element is preferably a surface-emitting light source. This suppresses deviations in the intensity distribution and unevenness in the color tone of the primary light irradiating the near-infrared fluorescent ceramic 1, thus making it a light-emitting device that effectively suppresses uneven intensity distribution of the output light.

[0068] In this near-infrared light-emitting device 10, firstly, primary light 12 emitted from the solid-state light-emitting element 11 illuminates the front surface 1a of the near-infrared fluorescent ceramic 1. The illuminated primary light 12 is transmitted through the near-infrared fluorescent ceramic 1. Furthermore, when the primary light 12 is transmitted through the near-infrared fluorescent ceramic 1, a near-infrared phosphor composed of a first inorganic compound contained within the near-infrared fluorescent ceramic 1 absorbs a portion of the primary light 12 and emits near-infrared light. Thus, light containing both primary light 12 and near-infrared light 13 is emitted from the back surface 1b of the near-infrared fluorescent ceramic 1 as output light.

[0069] As described above, the near-infrared fluorescent ceramic 1 is formed from an inorganic compound with high thermal conductivity, thus exhibiting 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 setting the solid-state light-emitting element 11 to a high-output type or increasing the number of solid-state light-emitting elements 11. As a result, the light energy of the output light emitted from the light-emitting device can exceed 3W, preferably 10W, and more preferably exceed 30W. By setting the light-emitting device to such a high-output type, it is possible to irradiate with a stronger output light (e.g., near-infrared light), so that even at a large distance from the irradiated object, a relatively strong near-infrared irradiation can be achieved. In addition, it can also be a light-emitting device that can easily obtain information related to the object even if the irradiated object is a small object or an object with thickness.

[0070] Furthermore, the near-infrared light-emitting device 10 can also increase the photon density supplied to the phosphor by setting the solid-state light-emitting element 11 as a light-emitting element that emits high-density primary light such as a laser diode, or by using an optical lens to focus the light emitted by the solid-state light-emitting element 11. For example, the light energy density of the primary light emitted by the solid-state light-emitting element 11 can be set to 0.3 W / mm². 2 Preferably 1.0W / mm 2 More preferably, it exceeds 3.0W / mm 2 In this case, due to the high light energy density of the primary light, even if the primary light diffused before being irradiated onto the near-infrared fluorescent ceramic 1 is configured to emit diffused primary light, it can still become a light-emitting device that emits relatively strong output light. Furthermore, if the primary light that does not diffuse is irradiated onto the near-infrared fluorescent ceramic 1, it can become a light-emitting device that emits output light with a high light energy density. Therefore, it is possible to provide a light-emitting device that can utilize a light-emitting element with a small light-emitting surface and irradiate output light over a large area, and a light-emitting device that irradiates output light with a high light energy density. Furthermore, it can also be a light-emitting device capable of point-outputting near-infrared light with a high light energy density. It should be noted that there is no particular upper limit to the light energy density of the primary light emitted by the solid-state light-emitting element; for example, it can be set to 30 W / mm². 2 .

[0071] Furthermore, by using a solid-state light-emitting element 11 that emits such high light density primary light, the near-infrared fluorescent ceramic 1 can achieve an energy density of emitted light exceeding 0.3 W / mm². 2 Preferably exceeding 1.0W / mm 2 More preferably, exceeding 3.0W / mm 2 .

[0072] [Electronic Devices]

[0073] Next, the electronic device according to this embodiment will be described. The electronic device according to this embodiment includes the near-infrared emitting device 10 described above. Figure 3 The image shows a schematic example of an 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 comprising 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.

[0074] As described above, the near-infrared emitting device 10 converts electrical energy into light energy. The near-infrared emitting device 10 converts at least a portion of the electrical energy supplied from the power supply circuit 21 into light energy, which becomes the output light 23, and outputs it. It should be noted that... Figure 3 The near-infrared emitting device 10 is configured to emit output light 23 containing near-infrared light.

[0075] Figure 3 The electronic device 20 also includes a first detector 27A and a second detector 27B. The first detector 27A detects the transmitted light component 25 of the output light 23 emitted from the near-infrared emitting device 10 and illuminating the irradiated object 24. Specifically, the first detector 27A detects the near-infrared light in the transmitted light component 25 that has been transmitted to the irradiated object 24. The second detector 27B detects the reflected light component 26 in the output light 23 emitted from the near-infrared emitting device 10 and illuminating the irradiated object 24. Specifically, the second detector 27B detects the near-infrared light in the reflected light component 26 reflected by the irradiated object 24.

[0076] In the electronic device 20 with such a structure, output light 23 containing near-infrared light components is irradiated onto the object 24. The transmitted light component 25 that passes through the object 24 and the reflected light component 26 that is reflected by the 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 object 24 related to the near-infrared light components.

[0077] Here, the near-infrared emitting device 10 of this embodiment contains at least near-infrared light and is capable of emitting suitable output light 23 to the detector. Therefore, by combining this emitting device with a near-infrared detector, it can become an electronic device suitable for industrial applications.

[0078] Furthermore, the near-infrared emitting device 10 of this embodiment can be configured to have high energy output light 23 and a wide illumination range. Therefore, even when the output light 23 is irradiated onto the irradiated object 24 from a distance, a signal with a good S / N ratio (signal-to-noise ratio) can be detected. Thus, it can be an electronic device suitable for inspecting large irradiated objects 24, inspecting objects distributed over a wide area, detecting objects existing in a portion of a wide inspection area, and detecting people or objects from a distance.

[0079] The first detector 27A and the second detector 27B can be various photodetectors. Specifically, depending on the method of use of the electronic device, quantum-type photodetectors (photodiodes, phototransistors, photoelectric ICs, CCD image sensors, CMOS image sensors, etc.) that detect the charge generated when light is incident on the PN junction of a semiconductor can be used. In addition, thermal photodetectors (thermoelectric piles utilizing the thermoelectric effect, thermoelectric elements utilizing the thermoelectric effect, etc.) that detect the change in electrical properties caused by the temperature rise due to the heat generated when receiving light, or photosensitive infrared films, can also be used as photodetectors.

[0080] The first detector 27A and the second detector 27B can be individual elements using photoelectric conversion elements alone, or they can be imaging elements that integrate photoelectric conversion elements. The imaging element can be a one-dimensional linear configuration or a two-dimensional planar configuration. A camera can also be used as the first detector 27A and the second detector 27B.

[0081] It should be noted that, Figure 12 The electronic device 20 has both a first detector 27A and a second detector 27B, but the electronic device only needs to have at least one of the first detector 27A and the second detector 27B.

[0082] Furthermore, the electronic device of this embodiment can be used as an inspection device, detection device, monitoring device, or sorting device for the irradiated object using the output light. The near-infrared component of the output light has the property of transmitting through most substances. Therefore, by using near-infrared light to irradiate the material from the outside to detect its transmitted or reflected light structure, it is possible to inspect the internal state, the presence or absence of foreign objects, etc., without damaging the material.

[0083] Furthermore, the near-infrared component of light is invisible to the human eye, and its reflectivity depends on the material. Therefore, by illuminating an object with near-infrared light and detecting the structure of its reflected light, it is possible to detect people, animals, plants, and objects even in darkness without being noticed.

[0084] Furthermore, the electronic device of this embodiment can inspect the internal state and presence of foreign objects of a substance without damaging it, determine the quality of the substance, and sort qualified and unqualified products. Therefore, the electronic device also has a mechanism for classifying irradiated objects in a normal state and irradiated objects in an abnormal state, enabling the differentiation of objects.

[0085] In the electronic device of this embodiment, the near-infrared emitting device 10 may be fixed rather than movable. This eliminates the need for a complex mechanism to mechanically move the emitting device, thus making it a less prone-to-malfunction electronic device. Furthermore, by fixing the emitting device indoors or outdoors, it is possible to perform point-to-point observation of the state of people and objects in a predetermined location, or to count the number of people and objects. Therefore, it can become an electronic device that facilitates the collection of useful big data for research findings, business applications, and other purposes.

[0086] The electronic device of this embodiment can also be made movable by illuminating the near-infrared light-emitting device 10 and changing the irradiated location. For example, the near-infrared light-emitting device 10 can be mounted on a mobile platform or mobile body (vehicle, aircraft, etc.) to make it movable. In this way, the near-infrared light-emitting device 10 can illuminate the desired location and a wide range, thus making it an electronic device that is advantageous for inspecting the condition of large objects and outdoor objects.

[0087] In addition to the light-emitting device, the electronic device of this embodiment can also be configured as a hyperspectral camera, which serves as the imaging camera. Therefore, this electronic device can perform hyperspectral imaging. An electronic device equipped with a hyperspectral camera can distinguish differences that are indistinguishable to the naked eye or by a conventional camera, thus becoming a useful inspection device in a wide range of fields related to product inspection, sorting, etc.

[0088] The electronic device of this embodiment can be used for medical purposes, animal medical purposes, biotechnology purposes, agricultural, forestry and fishery purposes, animal husbandry purposes (meat, meat products, dairy products, etc.), and industrial purposes (foreign object inspection, content volume inspection, shape inspection, packaging condition inspection, etc.). Furthermore, the electronic device can also be used for the inspection of 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 on any human body, animal or plant, or any object, and can also be used on any gas, liquid, or solid.

[0089] The electronic device in this embodiment is preferably used as a medical device, treatment device, beauty device, health device, nursing-related device, analysis device, measurement device, or evaluation device.

[0090] For example, in the context of medical and biotechnology development, the electronic device of this embodiment can be used for the examination, detection, measurement, evaluation, analysis, interpretation, observation, monitoring, separation, diagnosis, treatment, and purification of 1) blood, body fluids and their components, 2) excretions (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.

[0091] In addition, for example, for the purposes of beauty and health care, the electronic device of this embodiment can be used for 1) examination, detection, measurement, evaluation, analysis, interpretation, observation, monitoring, beautification, hygiene, development promotion, health enhancement, diagnosis, etc. of skin, 2) hair and body hair, 3) oral cavity, dental cavity and periodontal tissue, 4) ear and nose, and 5) vital signs.

[0092] For example, in agricultural, forestry, fishery, animal husbandry, and industrial applications, the electronic device of this embodiment can be used for: 1) industrial products (including electronic components and devices), 2) agricultural products (fruits and vegetables, etc.), 3) enzymes and bacteria, 4) seafood (fish, shellfish, crustaceans, and mollusks), 5) pharmaceuticals and biological samples, 6) food and beverages, 7) the existence and state of humans, animals, and objects, 8) the state of gases (including water vapor), 9) liquids, fluids, water, moisture, and humidity, 10) the shape, color, internal structure, and physical state of objects, 11) space, location, and distance, 12) the contamination state of objects, 13) the state of molecules and particles, and 14) the inspection, detection, determination, measurement, evaluation, analysis, interpretation, observation, monitoring, identification, sorting, and classification of industrial waste.

[0093] For example, in nursing purposes, the electronic device of this embodiment can be used for excretion confirmation, health status identification, management, monitoring, etc.

[0094] Thus, the electronic device of this embodiment can handle all uses such as inspection, detection, measurement, evaluation, analysis, interpretation, observation, monitoring, identification, sorting, and classification.

[0095] (appendix)

[0096] The following technology has been disclosed through the above description of the embodiments.

[0097] (Technology 1) A near-infrared fluorescent ceramic, comprising at least a first inorganic compound and a second inorganic compound different from the first inorganic compound, and emitting fluorescence. The first inorganic compound is a phosphor that emits near-infrared light with a fluorescence peak in the wavelength range of above 730 nm and below 2500 nm. The near-infrared fluorescent ceramic has an island structure, wherein the island structure comprises 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.

[0098] This structure reduces grain boundaries and voids between the first inorganic compounds, thus improving the quality of the resulting near-infrared fluorescent ceramic. Furthermore, excitation light irradiating the near-infrared fluorescent ceramic readily reaches the first inorganic compounds, allowing them to effectively absorb the excitation light and increase the luminescence intensity of the near-infrared light. Additionally, the near-infrared fluorescent ceramic is entirely formed of inorganic compounds with high thermal conductivity, resulting in excellent heat dissipation and suppressing temperature quenching of the near-infrared phosphor, which is the first inorganic compound.

[0099] (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.

[0100] According to this structure, the constituent elements function by mitigating the abrupt compositional difference at the interface between the first and second inorganic compounds and by bonding the first and second inorganic compounds together. Therefore, a robust near-infrared fluorescent ceramic that achieves homogenized internal stress distribution and is resistant to breakage can be obtained.

[0101] (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.

[0102] Based on this structure, Cr that emits near-infrared fluorescence can be used. 3+ Both the first and second inorganic compounds are ion-activated. Therefore, the first and second inorganic compounds become fluorescent ceramics that function as near-infrared phosphors.

[0103] (Technology 4) A near-infrared fluorescent ceramic according to any one of Technologies 1 to 3, wherein the first inorganic compound comprises Cr 3+ Ions act as activators.

[0104] Through this structure, near-infrared fluorescent ceramics can absorb visible light, especially blue or red light, and effectively convert the wavelength into near-infrared light components.

[0105] (Technology 5) The near-infrared fluorescent ceramic according to any one of Technology 1 to Technology 4, wherein the first inorganic compound is a compound having the same crystal structure as β-Ga2O3.

[0106] Based on this structure, near-infrared fluorescent ceramics with a wide half-width and low temperature quenching of near-infrared emission spectrum can be obtained.

[0107] (Technology 6) The near-infrared fluorescent ceramic according to any one of Technologies 1 to 5, wherein the second inorganic compound is a boron-containing compound.

[0108] With this structure, boric acid (H3BO3) or boron oxide (B2O3), which is known as a low-melting-point material, can be used as a part of the ceramic raw material, so that the near-infrared fluorescent ceramic can be easily manufactured.

[0109] (Technology 7) The near-infrared fluorescent ceramic according to any one of Technologies 1 to 6, wherein the first inorganic compound contains (Ga 1-（x+y） Sc x Cr y )2O3 as a main component, and the second inorganic compound contains at least one of (Sc 1-z Cr z )BO3 and (Sc 1-z Cr z )PO4 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).

[0110] With this structure, it is easy to form an island structure having 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 bond the first inorganic compounds, and the grain boundaries and voids between the first inorganic compounds are reduced, so that the near-infrared fluorescent ceramic can be made of high quality.

[0111] (Technology 8) A near-infrared light-emitting device comprising the near-infrared fluorescent ceramic according to any one of Technologies 1 to 7.

[0112] According to this structure, since a near-infrared fluorescent ceramic made of all-inorganic materials having excellent thermal conductivity, being dense and having high mechanical strength and emitting near-infrared rays is used, a near-infrared light-emitting device with high output and high reliability is obtained.

[0113] Examples

[0114] 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.

[0115] [Examples 1 to 3 and Comparative Example 1]

[0116] (Synthesis of fluorescent ceramic)

[0117] Using a preparation method based on solid-phase reaction, the fluorescent ceramics of Examples 1 to 3 and Comparative Example 1 were synthesized. Specifically, in Examples 1 to 3, a synthesis was carried out of a composition composed of (Ga 1-（x+y） , Scx , Cr y ) 2O3 and an inorganic compound represented by the compositional formula of (Sc 1-z , Cr z ) BO3. Additionally, in Comparative Example 1, a fluorescent ceramic composed of an inorganic compound represented by the compositional formula of (Ga 1-（x+y） , Sc x , Cr y ) 2O3 was synthesized. It should be noted that x, y, and z are values that satisfy 0 < x < 1, 0 < y < 0.1, 0 < x + y < 1, and 0 ≤ z < 0.1.

[0118] Moreover, when synthesizing the fluorescent ceramics of each example, the following compound powders were used as the main raw materials. Gallium oxide (Ga2O3): purity 4N, manufactured by Asian Materials Co., Ltd. Scandium oxide (Sc2O3): purity 3N, manufactured by High-Purity Chemical Research Institute Co., Ltd. Chromium oxide (Cr2O3): purity 3N, manufactured by High-Purity Chemical Research Institute Co., Ltd. Boric acid (H3BO3): purity 2N, manufactured by FUJIFILM Wako Pure Chemical Corporation

[0119] First, the raw materials for the fluorescent ceramics of each example were weighed under the blending conditions shown in Table 1. Next, the weighed raw materials were placed in the pot of a planetary ball mill, and water and alumina balls with a diameter of φ3 mm were further added. Then, the raw materials were wet-mixed using the planetary ball mill. Then, the obtained mixed slurry was sufficiently dried in a constant-temperature bath at 125°C, and then gently pulverized using a mortar and pestle to obtain a raw material mixed powder.

[0120] Next, 1 g of the obtained raw material mixed powder of each example was filled into a mold (Φ13 mm), and then pressed with a hand press at a pressure of 10 MPa to produce a green body. Then, the green bodies of each example were calcined in the atmosphere at 1400°C to obtain a sintered body. Finally, the produced sintered bodies of each example were polished using an automatic polishing machine (model: DAG810, manufactured by DISCO Corporation) to make the film thickness 300 μm, thereby obtaining the fluorescent ceramics of each example.

[0121] [Table 1]

[0122] (Evaluation)

[0123] For the fluorescent ceramics of each example obtained as described above, the following evaluations were carried out for the composition analysis, crystal structure analysis, scanning electron microscope observation, luminescence characteristics, and sintering density.

[0124] Compositional Analysis

[0125] The elemental composition of the fluorescent ceramics in Examples 1-3 was analyzed using an electron probe microanalyzer (EPMA, product name JXA-8530F plus, manufactured by NEC Corporation) via wavelength dispersive X-ray spectrometry (WDS, accelerating voltage 10kV). Figures 4-6 Scanning electron microscope images (2000x) of the parts of the fluorescent ceramics in Examples 1-3 that underwent elemental analysis, and semi-quantitative analysis results corrected by the ZAF method.

[0126] Depend on Figure 4 Scanning electron microscope (SEM) images show that the fluorescent ceramic of Example 1 forms an island structure. Furthermore, from... Figure 4 The semi-quantitative analysis results show that the main constituent elements of dispersed phase A are scandium, boron, and oxygen. In contrast, the main constituent elements of continuous phase B are gallium, scandium, and oxygen. Similarly, from... Figure 5 and Figure 6 SEM images show that the fluorescent ceramics in Examples 2 and 3 also form island structures. Furthermore, from... Figure 5 and Figure 6 The semi-quantitative analysis results show that the main constituent elements of dispersed phase A are scandium, boron, and oxygen. In contrast, the main constituent elements of continuous phase B are gallium, scandium, and oxygen.

[0127] Therefore, it can be seen that in the fluorescent ceramics of Examples 1 to 3, the first inorganic compound as the continuous phase is a compound mainly composed of gallium, scandium, and oxygen, and the second inorganic compound as the dispersed phase is a compound mainly composed of scandium, boron, and oxygen.

[0128] <Crystal Structure Analysis>

[0129] X-ray diffraction patterns of the fluorescent ceramics in each example were determined using an X-ray diffraction apparatus (trade name Miniflex (registered trademark), manufactured by Rigaku Corporation). The crystal structure of each fluorescent ceramic was then determined by comparing the determined X-ray diffraction patterns with patterns registered in the Inorganic Crystal Structure Database (ICSD). Furthermore, considering the crystal structure of the fluorescent ceramics and the aforementioned compositional analysis results, the crystal composition of each fluorescent ceramic was estimated.

[0130] exist Figure 7 The X-ray diffraction patterns of the fluorescent ceramics of Examples 1-3 and Comparative Example 1 are shown in the figure. Further, in Figure 7 In the middle, Ga is also shown. 1.17 Sc 0.83Patterns from the inorganic crystal structure database of O3. (Example) Figure 7 As shown, the fluorescent ceramics of Examples 1-3 were strongly observed to correlate with Ga. 1.17 Sc 0.83 The peak pattern of O3 is the same, indicating that it mainly contains compounds with the same crystal structure as (Ga,Sc)2O3. In addition, the fluorescent ceramics of Examples 1-3 showed peaks of ScBO3, indicating that they contain compounds with the same crystal structure as ScBO3.

[0131] Furthermore, it can be seen that the peak intensity of ScBO3 in Examples 1-3 increases with the increase of boric acid content. Therefore, it can be concluded that as the amount of boric acid, a low-melting-point material, increases, the proportion of the second inorganic compound as the dispersed phase also increases.

[0132] <Observation using scanning electron microscopy>

[0133] SEM images (reflectance electron images) of the fluorescent ceramics in each case were observed using a scanning electron microscope (Miniscope TM4000II desktop microscope, manufactured by Hitachi High Technology Co., Ltd.). The results observed at 1000x magnification are shown below. Figure 8 The results will be shown at a 3000x magnification. Figure 9 .

[0134] like Figure 8 and Figure 9 As shown, the fluorescent ceramics of Examples 1-3 formed a sea-island structure. Furthermore, based on the above compositional analysis, in the fluorescent ceramics of Examples 1-3, the constituent elements of the dispersed phase are mainly scandium, boron, and oxygen, while the constituent elements of the continuous phase are mainly gallium, scandium, and oxygen. Additionally, based on the above crystal structure analysis, the fluorescent ceramics of Examples 1-3 mainly contain compounds with the same crystal structure as (Ga,Sc)₂O₃, and also contain compounds with the same crystal structure as ScBO₃. Therefore, it can be seen that in the fluorescent ceramics of Examples 1-3, the continuous phase is mainly composed of (Ga,Sc)₂O₃, and the dispersed phase is mainly composed of ScBO₃.

[0135] In addition, by Figure 8 and Figure 9 It can be seen that in the fluorescent ceramics of Examples 1-3, there are few voids at the interface between the continuous phase and the dispersed phase in the island structure. In contrast, it can be seen that the fluorescent ceramic of Comparative Example 1 has many grain boundaries, and thus has multiple voids. Therefore, it can be seen that by having an island structure composed of a first inorganic compound and a second inorganic compound, it is possible to obtain fluorescent ceramics with reduced voids and grain boundaries and excellent ceramic quality.

[0136] <Luminous Properties>

[0137] Using an absolute PL quantum yield measuring device (product number C13534-24, manufactured by Hamamatsu Photonics Co., Ltd.), the emission spectrum, internal quantum efficiency (IQE), light absorption rate (Abs.), and external quantum efficiency (EQE) of each fluorescent ceramic were measured at an excitation wavelength of 450 nm.

[0138] The emission spectra of the fluorescent ceramics in each example are shown in... Figure 10 The internal quantum efficiency, light absorption rate, and external quantum efficiency are shown in Table 2. Figure 10 It can be seen that the fluorescent ceramics of Examples 1-3 and Comparative Example 1 emit broad fluorescence with emission peaks in the range exceeding 800 nm. Furthermore, it can be seen that the maximum luminescence intensity of the fluorescent ceramics of Examples 1-3 is nearly double that of the fluorescent ceramic of Comparative Example 1. In addition, as shown in Table 2, the fluorescent ceramics of Examples 1-3 exhibit significantly improved light absorption rate and external quantum efficiency compared to the fluorescent ceramic of Comparative Example 1. Specifically, the internal quantum efficiency exceeds 85%, and in a preferred embodiment, it is at a high level exceeding 90%. On the other hand, the light absorption rate exceeds 70%, and in a preferred embodiment, it is at a high level exceeding 75%. Therefore, the external quantum efficiency exceeds 60%, and in a preferred embodiment, it is at a high level exceeding 65%.

[0139] Therefore, reducing voids and grain boundaries improves the quality of ceramics, resulting in fluorescent ceramics with significantly enhanced luminescent properties.

[0140] [Table 2]

[0141] <Sintering Density>

[0142] The sintering density (bulk density) of the fluorescent ceramics in each example was determined. The sintering density was obtained by measuring the dimensions of the fluorescent ceramics in each example, calculating the volume, and then dividing the dry weight of the fluorescent ceramics in each example by the volume. The measurement results are shown in Table 2.

[0143] As shown in Table 2, it can be seen that the fluorescent ceramics of Examples 1 to 3 are denser ceramics with higher density and reduced porosity compared to the fluorescent ceramic of Comparative Example 1.

[0144] Example 4

[0145] (Synthesis of fluorescent ceramics)

[0146] The fluorescent ceramic of Example 4 was synthesized using a solid-state reaction-based preparation method. Specifically, in Example 4, a fluorescent ceramic composed of Ga (Ga 1-（x+y） ,Sc x Cr y Inorganic compounds represented by the compositional formula of 2O3, and those expressed in terms of (Sc1-z , Cr z ), an inorganic compound represented by the compositional formula of BO3, and a fluorescent ceramic composite composed of an inorganic compound represented by the compositional formula of (Sc 1-z , Cr z ), PO4. It should be noted that x, y, and z are values that satisfy 0 < x < 1, 0 < y < 0.1, 0 < x + y < 1, and 0 ≤ z < 0.1.

[0147] Moreover, when synthesizing the fluorescent ceramics of each example, the following compound powders are used as the main raw materials. Gallium oxide (Ga2O3): purity 4N, manufactured by Asian Materials Co., Ltd. Scandium oxide (Sc2O3): purity 3N, manufactured by High-Purity Chemical Research Institute Co., Ltd. Chromium oxide (Cr2O3): purity 3N, manufactured by High-Purity Chemical Research Institute Co., Ltd. Boric acid (H3BO3): purity 2N, manufactured by Fujifilm Wako Pure Chemical Corporation Diammonium hydrogen phosphate ((NH4)2HPO4): purity 2N, manufactured by Fujifilm Wako Pure Chemical Corporation

[0148] First, after weighing the raw materials of the fluorescent ceramics of each example under the blending conditions shown in Table 3, raw material mixed powders are obtained in the same manner as in Example 1.

[0149] Next, 1 g of the obtained raw material mixed powder of each example is filled into a mold (Φ13 mm), and then pressed with a hand press at a pressure of 10 MPa to produce a molded body. Then, the molded body is calcined in the atmosphere at 1350 °C to obtain a sintered body. Finally, the produced sintered body is polished using an automatic polishing machine to make the film thickness 300 μm, and the fluorescent ceramic of this example is obtained.

[0150] [Table 3]

[0151] (Evaluation)

[0152] For the fluorescent ceramic of Example 4 obtained as described above, crystal structure analysis, scanning electron microscope observation, luminescence characteristics, and sintering density evaluation are performed in the same manner as in Example 1. Further, energy-dispersive X-ray analysis is performed on the fluorescent ceramic of Example 4 to evaluate the elemental distribution.

[0153] <Crystal Structure Analysis>

[0154] In Figure 11 , the X-ray diffraction pattern of the fluorescent ceramic of Example 4 is shown. As Figure 11 shown, the fluorescent ceramic of Example 4 strongly observes Ga 1.17Sc 0.83 The peak pattern of O3 is the same, indicating that it mainly contains compounds with the same crystal structure as (Ga,Sc)2O3. Furthermore, the fluorescent ceramic of Example 4 showed peaks of ScBO3 and ScPO4, indicating that it contains compounds with the same crystal structure as ScBO3 and compounds with the same crystal structure as ScPO4.

[0155] <Observation using scanning electron microscopy>

[0156] exist Figure 12 The image shows SEM (electron reflectance) images of the fluorescent ceramic of Example 4, observed at 1000x and 3000x magnification. Figure 12 As shown, the fluorescent ceramic of Example 4 formed a sea-island structure. Furthermore, from Figure 12 It is evident that in the fluorescent ceramic of Example 4, there are few voids at the interface between the continuous phase and the dispersed phase in the island structure. Therefore, it is clear that by having an island structure composed of a first inorganic compound and a second inorganic compound, it is possible to obtain a fluorescent ceramic with reduced voids and grain boundaries, resulting in excellent ceramic quality.

[0157] <Luminous Properties>

[0158] Table 4 shows the internal quantum efficiency, light absorption rate, and external quantum efficiency of the fluorescent ceramic of Example 4. As can be seen from Table 4, the light absorption rate and external quantum efficiency of the fluorescent ceramic of Example 4 are significantly improved compared to the fluorescent ceramic of Comparative Example 1. Therefore, Example 4 demonstrates that by reducing porosity and grain boundaries, the quality of the ceramic is improved, resulting in a fluorescent ceramic with significantly enhanced luminescence properties.

[0159] [Table 4]

[0160] <Sintering Density>

[0161] As shown in Table 4, it can be seen that the fluorescent ceramic of Example 4 is a dense ceramic with high density and reduced porosity compared to the fluorescent ceramic of Comparative Example 1.

[0162] <Energy Dispersion X-ray Analysis>

[0163] The SEM images (reflected electron images) of the fluorescent ceramic of Example 4 were observed using a scanning electron microscope (Miniscope TM4000II desktop microscope, manufactured by Hitachi High Technology Co., Ltd.). Further, energy-dispersive X-ray diffraction (EDX) analysis was performed to prepare elemental spectra for gallium, scandium, phosphorus, and boron.

[0164] like Figure 13As shown, in the electron reflectance image of the fluorescent ceramic of Example 4, the phosphorus concentration is high in the region with high contrast. Furthermore, although scandium is included in both the high-contrast and low-contrast regions of the electron reflectance image, the concentration in the high-contrast region is relatively high. Therefore, it can be seen that the gallium concentration is high in the low-contrast regions of the electron reflectance image. Based on these results and the above crystal structure analysis, it can be concluded that in the fluorescent ceramic of Example 4, the continuous phase consists of (Ga,Sc)₂O₃, and the dispersed phase consists of at least ScPO₄.

[0165] The above describes this embodiment, but this embodiment is not limited thereto, and changes can be made without departing from the spirit of this embodiment.

[0166] This document quotes the full contents of Japanese Special Appeal No. 2023-115837 (application date: July 14, 2023).

[0167] Industrial availability According to this disclosure, it is possible to provide near-infrared fluorescent ceramics with high luminescence properties and excellent quality as ceramics, as well as near-infrared luminescent devices incorporating the near-infrared fluorescent ceramics.

[0168] Explanation of reference numerals in the attached figures 1: Near-infrared fluorescent ceramic; 2: Continuous phase; 3: Dispersed phase; 10: Near-infrared light-emitting device

Claims

1. A near-infrared fluorescent ceramic comprising at least a first inorganic compound and a second inorganic compound different from the first inorganic compound and emitting fluorescence, the first inorganic compound being a fluorescent substance emitting near-infrared light having a fluorescent peak in a wavelength range of 730 nm or more and 2500 nm or less, the near-infrared fluorescent ceramic having an island-in-sea structure having a continuous phase composed of the first inorganic compound and a dispersed phase composed of the second inorganic compound and dispersed in the inside of the continuous phase.

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

3. The near-infrared fluorescent ceramic according to claim 2, wherein, the constituent element being a metal element forming a metal ion having a valence number of three.

4. The near-infrared fluorescent ceramic according to any one of claims 1 to 3, wherein, The first inorganic compound comprises Cr 3+ ions as activators.

5. The near-infrared fluorescent ceramic according to any one of claims 1 to 4, wherein, the first inorganic compound being a compound having the same crystal structure as β-Ga2O3.

6. The near-infrared fluorescent ceramic according to any one of claims 1 to 5, wherein, the second inorganic compound being a compound containing boron.

7. The near-infrared fluorescent ceramic according to any one of claims 1 to 6, wherein, The first inorganic compound contains (Ga 1-（x+y） Sc x Cr y )2O3 as a main component, and the second inorganic compound contains at least one of (Sc 1-z Cr z )BO3 and (Sc 1-z Cr z )PO4 as a main component (the x, y, and z satisfy 0 < x < 1, 0 < y < 0.1, 0 < x + y < 1, and 0 ≤ z < 0.1).

8. A near-infrared light emitting device provided with the near-infrared fluorescent ceramic according to any one of claims 1 to 7.

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