Corundum-type scandium oxide phosphor activated by europium and terbium, method for producing the same, light-emitting device, and light-emitting apparatus.

Abstract

This invention provides a phosphor with desired luminescence properties using an inorganic compound having a crystalline structure previously unknown as a phosphor. [Solution] A phosphor is provided which comprises an inorganic compound containing scandium oxide having a corundum-type structure and containing at least one or more activating elements A (A is one or more elements selected from Mn, Ce, Pr, Nd, Sm, Eu, Tb, Dy, and Yb). This corundum-type structure is obtained by relaxation after creating a high-pressure crystal structure. Since the luminescence properties of a phosphor containing activating elements depend on its crystal structure, different crystal structures will result in different luminescence properties.

Description

[Technical Field]

[0001] The present invention relates to a corundum-type scandium oxide phosphor containing activating elements such as europium and terbium, and to a method for producing the same. It also relates to a light-emitting device and a light-emitting apparatus using such a corundum-type scandium oxide phosphor. [Background technology]

[0002] Phosphors are used in applications such as vacuum fluorescent displays (VFDs), field emission displays (FEDs or SEDs), plasma display panels (PDPs), cathode ray tubes (CRTs), liquid crystal display backlights, and light-emitting diodes (LEDs). In all of these applications, energy must be supplied to the phosphor to excite it in order to make it emit light. Phosphors are excited by high-energy excitation sources such as vacuum ultraviolet light, ultraviolet light, electron beams, and blue light, and emit visible light such as blue, green, yellow, orange, and red light.

[0003] Many phosphors have been reported to date. An orange-emitting sialon phosphor containing alkaline earth elements has been disclosed (for example, Patent Document 1). β-type sialon with Eu 2+ A green phosphor with activated oxynitride has been disclosed (for example, Patent Document 2). An example of an oxynitride phosphor is JEM phase (LaAl(Si 6-z Al z )N 10-z O zA blue phosphor was disclosed in which Ce was activated using a matrix crystal (for example, Patent Document 3). In this phosphor, it was found that by substituting a portion of La with Ca while maintaining the crystal structure, the excitation wavelength and emission wavelength were lengthened. Furthermore, as another example of an oxynitride phosphor, La-N crystal La3Si8N 11 A blue phosphor obtained by activating Ce with O4 as the host crystal has been disclosed (for example, Patent Document 4).

[0004] Thus, the emission color of a phosphor is determined by the combination of the parent crystal and the metal ions (activating ions) dissolved in it. Furthermore, the combination of the parent crystal and the activating ions determines the emission characteristics such as the emission spectrum and excitation spectrum, as well as the chemical stability and thermal stability. Therefore, if the parent crystal or the activating ions are different, they are considered different phosphors. Also, even if the chemical composition is the same, materials with different crystal structures are considered different phosphors because the emission characteristics and stability differ due to the difference in the parent crystal.

[0005] It is well known that the structure of a potential crystal is influenced by environmental factors such as the types of elements that make up the crystal, as well as temperature, atmosphere, and pressure. For example, α-Al2O3, α-Ga2O3, α-In2O3, α-Fe2O3, α-Cr2O3, α-V2O3, α-Ti2O3, and α-Rh2O3 are known as corundum-type oxides, but α-Al2O3, α-Fe2O3, α-Cr2O3, and α-Rh2O3 are said to be the most thermally stable phases under standard conditions, while the others are considered unstable or metastable phases. The corundum-type structure is a typical structure of A2B3 type ionic crystals, based on a hexagonal close-packed structure of oxygen atoms, with metal atoms occupying 2 / 3 of the octahedral coordination pores between oxygen atoms, leaving 1 / 3 as vacancies. Since the corundum-type structure belongs to the 167th space group, R-3c, the crystal is rhombosymmetric. In most cases, it is more convenient to consider the crystal structure in hexagonal form, so it is often depicted in hexagonal form.

[0006] Here, general scandium(III) oxide or scandia is an oxide of a rare earth element represented by the composition formula Sc2O3. The crystal structure of this scandium oxide has a cubic structure in which oxygen is six-coordinated to the metal center of the scandium element, and the point group is T in the Schoenflies symbol h , and the space group is represented by the Hermann-Mauguin symbol Ia3. The Sc-O bond distance is shown to be 2.159 - 2.071 angstroms from powder diffraction. Such scandium oxide doped with Eu 3+ , Tb 3+ by a wet method has a luminescence spectrum of 20 - 30 nm microcrystals of scandium oxide having a C-type rare earth oxide structure disclosed (for example, Non-Patent Document 2. Fig. 4). Also, a method of doping Eu 3+ , or Tb 3+ into the scandium oxide of the C-type rare earth oxide structure at normal pressure by the floating zone method has also been disclosed (for example, Non-Patent Document 3). However, only the spectrum peculiar to the C-type rare earth oxide structure can be obtained. Phosphors having different luminescence characteristics can be utilized as a combination with other phosphors or as a phosphor having different luminescence characteristics. If different luminescence characteristics are obtained with different compositions and crystal structures, the range of choices for combinations will expand. Also, in accordance with the environment in which it is used, it can be used in view of its physical and chemical properties, so it is preferable that the range of choices expands. Also, if the particle size is very small, the luminescence intensity will inevitably decrease.

[0007] Furthermore, scandium oxide crystals having a corundum-type structure, produced by synthesizing a high-density scandium oxide phase (gadolinium sulfide type structure) in a laser-heated diamond anvil cell and then reducing the pressure, have also been disclosed (for example, Patent Document 5). This corundum-type structure was considered to be a modification of the gadolinium sulfide type structure. The structure under high pressure is a gadolinium sulfide (Gd2S3) type structure, but the corundum-type structure was stabilized during the reduced pressure process at room temperature (see Figure 2). Here, scandium oxide (Sc2O3) with a C-type rare earth structure was sealed in a diamond anvil cell high-pressure apparatus, pressurized to a pressure of 23 GPa or higher, irradiated with an infrared laser, heated, and heated for a predetermined time. This synthesized scandium oxide with a gadolinium sulfide (Gd2S3) type structure in the high-pressure phase. Subsequently, the laser was cut off, and when the temperature fell below 30°C, the pressure was reduced to atmospheric pressure, thereby synthesizing scandium oxide with a corundum-type structure. As shown in Figure 2, it was reported that under high temperature and high pressure conditions of 1300°C or higher and 18 GPa or higher, the corundum type is generated via the gadolinium sulfide type, and then during the depressurization process. Furthermore, scandium oxide having a corundum type structure, which is generated by synthesizing a high-density scandium oxide phase (gadolinium sulfide type structure) in a laser-heated diamond anvil cell and then reducing the pressure, has also been disclosed (for example, Non-Patent Document 1). [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2002-363554 [Patent Document 2] Japanese Patent Publication No. 2005-255895 [Patent Document 3] International Publication No. 2005 / 019376 [Patent Document 4] Japanese Patent Publication No. 2005-112922 [Patent Document 5] Patent No. 5419073 [Non-patent literature]

[0009] [Non-Patent Document 1] H.Yusa, T.Tsuchiya, N.Sata, and Y.Ohishi, “High-presure phase transition to the Gd2S3 structure in Sc2O3:A new trend in dense structures in sesquioxides”, Inorg.Chem.48, 7537-7543 (2009) [Non-Patent Document 2] D. Li, W. Qin, S. Liu, W. Pei, Z. Wang, P. Zhang, L. Wang, and L. Huang, “Synthesis and luminescence properties of RE3+(RE=Yb,Er,Tm,Eu,Tb)-doped Sc2O3 microcrystals”, J.Alloys Compd.653, 304-309(2015) [Non-Patent Document 3] L. Zhuang, H. Feng, S. Huang, Z. Zhang, W. Yong, R. Mao, and J. Zhao, “The luminescent properties comparison of RE2O3:Eu(RE=Lu,Y,Sc) with high and low Eu doping concentrations”, J. Alloys Compd.781, 302-307 (2019) [Overview of the project] [Problems that the invention aims to solve]

[0010] Generally, when the parent crystal structure differs, new luminescence properties can be expected, but there is no way to know what these properties will be except by actually confirming them through experimentation. And, to the best of the inventors' knowledge, no emission spectra of phosphors with relaxed crystal structures existed. [Means for solving the problem]

[0011] Therefore, in the present application, an object is to produce a phosphor having favorable light emission characteristics by making the matrix crystal structure different from the conventional ones. Further, a phosphor composed of crystals of a sufficient size is desired. And a phosphor that is as homogeneous as possible is preferred.

[0012] More specifically, the following can be provided. (1) A phosphor comprising an inorganic compound containing at least one or two or more activating elements A (A is one or two or more elements selected from Mn, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Yb) and containing scandium oxide having a corundum-type structure. (2) The corundum-type structure is hexagonal, the space group is R-3c, The lattice constants are a = 5.34416 angstroms ± 0.26721 angstroms, b = 5.34416 angstroms ± 0.26721 angstroms, c = 14.20773 angstroms ± 0.71039 angstroms, α = 90 degrees ± 1 degree, β = 90 degrees ± 1 degree, and γ = 120 degrees ± 1 degree, The phosphor according to (1) above, characterized in that it is so. (3) The inorganic compound is constituted by the activating element A substituting Sc of scandium oxide, and the molar amount m of the activating element A in the inorganic compound is 0 < m ≦ 0.2, the phosphor according to (1) or (2) above. (4) The phosphor according to any one of (1) to (3) above, characterized in that the activating element A is Eu and / or Tb. (5) The phosphor according to any one of (1) to (4) above, characterized in that the corundum-type structure is modified from a gadolinium sulfide-type structure. (6) A bulk phosphor comprising the phosphor according to any one of (1) to (5) above and consisting only of a light-transmissive substance. (7) A method for producing a phosphor according to any one of (1) to (6) above, characterized by weighing a compound of activating element A (where A is one or more elements selected from Mn, Ce, Pr, Nd, Sm, Eu, Tb, Dy, and Yb) and a compound of scandium (Sc) in a molar ratio of element A to Sc of any of the following ratios: 0.0001:0.9999 to 0.100:0.900, mixing and grinding the mixture, filling it into a designated sample chamber, applying a pressure of 19 GPa or higher and a temperature of 1000°C or higher to the raw material mixture in the sample chamber, holding it for a predetermined time, then lowering the temperature to 300°C or lower, and then applying a pressure of 1 MPa. (8) The method according to (7) above, characterized in that a multi-anvil device, a belt device, or a piston-cylinder device is used for pressurizing and heating the raw material mixture in the sample chamber. (9) The method according to (7) or (8) above, characterized in that a diamond anvil apparatus is used for pressurizing and heating the raw material mixture in the sample chamber. (10) The method according to any one of (7) to (9) above, characterized in that a KAWAI type anvil apparatus is used for pressurizing and heating the raw material mixture in the sample chamber. (11) A light-emitting element comprising an excitation source and a phosphor, wherein the excitation source emits light with a wavelength in the range of 200 nm to 500 nm, and the phosphor contains at least one of the phosphors described in (1) to (6) above. (12) The light-emitting element according to (11) above, wherein the excitation source is a light-emitting diode (LED) or a laser diode (LD). (13) A light-emitting device which is a lighting fixture, a backlight for a liquid phase panel, a lamp for a projector, an infrared illumination, or an infrared measurement light source, including the light-emitting element described in (11) or (12) above.

[0013] Here, in scandium oxide crystals having a corundum-type structure, the lattice constant changes when its constituent elements are replaced by other elements or when activating elements such as Eu and Tb are dissolved in solid solution. However, it is considered that the atomic positions given by the crystal structure, the sites occupied by atoms, and their coordinates do not change to such an extent that the chemical bonds between skeletal atoms are broken. In this invention, if the length of the chemical bonds (nearest interatomic distance) calculated from the lattice constant and atomic coordinates obtained by Rietveld analysis of X-ray diffraction and neutron diffraction results in the R-3c space group is within ±5% of the length of the chemical bonds calculated from the lattice constant and atomic coordinates of the crystals shown in Table 1, then it can be defined as the same crystal structure, and a determination can be made as to whether it is a crystal with a corundum-type structure. This is because if the length of the chemical bonds changes by more than ±5%, it is considered that the chemical bonds are broken and a different crystal is formed. For crystal structure identification, the interplanar spacing of major peaks in X-ray diffraction patterns, neutron diffraction patterns, etc., can be used.

[0014] The molar amount m of the activating element A can be determined from its ratio to the amount s of the scandium element. That is, the ratio R = m / (m + s) may be used. For it to be a phosphor, m > 0, but this minimum value can be defined as the smallest amount technically possible. It may also be m > 0.000001. The upper limit does not need to be particularly limited, but it may be the maximum value as long as the phosphor functions as a scandium oxide crystal having a corundum-type structure. It may be m ≤ 0.2, m ≤ 0.1, or m ≤ 0.05.

[0015] A bulky phosphor can be defined as an inorganic compound consisting of scandium oxide crystals having a corundum-type structure contained within the phosphor, with an average particle size of 10 μm or more. Since larger particle sizes are thought to result in superior luminescence characteristics, a larger average particle size is preferable. For example, it may be 12 μm or more, 15 μm or more, or 18 μm or more. The average particle size may be determined by binarizing images of the tissue taken with an optical microscope or scanning electron microscope and performing image analysis. For example, the area measurement method can be applied in a field of view where approximately 200 particles are visible. The average may be calculated using either a count-based or volume-based method. In this specification, the count-based method using ImageJ was used.

[0016] A light-transmitting material can refer to a material that does not easily absorb light energy and generate heat when exposed to laser light. Examples of light-transmitting materials may include scandium oxide, yttrium oxide, lanthanum oxide, silicon oxide, and aluminum oxide. For example, metals like gold do not easily transmit light because they contain free electrons.

[0017] Scandium oxide containing activating element A is, for example, (Sc 1-x A x )2O 3+αIt can be expressed as such, where x>0 and x≦0.2. α represents the amount of oxygen that can be adjusted to maintain charge neutrality when A is not trivalent. For example, α may take values ​​such as -0.5, 0, +0.7, etc. When x>0, the value of x may be the smallest positive value for which the inorganic compound can become a phosphor, as far as is technically possible. It may also be x≦0.2, x≦0.15, or x≦0.1. The pressure when converting scandium oxide to gadolinium sulfide type is preferably 18 GPa or higher, 19 GPa or higher, 20 GPa or higher, 21 GPa or higher, 22 GPa or higher, or 24 Pa or higher. The temperature at this time is preferably 1000°C or higher, 1300°C or higher, 1400°C or higher, or 1500°C or higher, respectively. These pressures and temperatures can be combined independently, for example: 18 GPa or more and 1000°C or higher, 18 GPa or more and 1300°C or higher, 18 GPa or more and 1400°C or higher, 18 GPa or more and 1500°C or higher, 19 GPa or more and 1000°C or higher, 19 GPa or more and 1300°C or higher, 19 GPa or more and 1400°C or higher, 19 GPa or more and 1500°C or higher, 20 GPa or more and 1000°C or higher, 20 GPa or more and 1300°C or higher, 20 GPa or more and 1400°C or higher, 20 GPa The temperature can be set to a or above 1500°C, 21 GPa or above 1000°C, 21 GPa or above 1300°C, 21 GPa or above 1400°C, 21 GPa or above 1500°C, 22 GPa or above 1000°C, 22 GPa or above 1300°C, 22 GPa or above 1400°C, 22 GPa or above 1500°C, 24 GPa or above 1000°C, 24 GPa or above 1300°C, 24 GPa or above 1400°C, or 24 GPa or above 1500°C. The holding time can also be 1 second or more, 2 seconds or more, 1 minute or more, 5 minutes or more, 10 minutes or more, 20 minutes or more, 30 minutes or more, or 60 minutes or more. Then, while maintaining the held pressure, the temperature may be reduced to 500°C or below, 400°C or below, 300°C or below, 200°C or below, 100°C or below, or 30°C or below. Such heating or cooling rates may be, for example, 50°C / min or more, 100°C / min or more, 200°C / min or more, 400°C / min or more, 700°C / min or more, or 1000°C / min or more.There is no particular upper limit required for the heating or cooling rate, but it may be as high as technically possible for the apparatus. For example, it may be 1100°C / min or less. After that, the pressure may be reduced to 1 MPa or less or 0.1 MPa or less (atmospheric pressure). It is preferable to avoid setting the temperature and pressure to change to the gadolinium sulfide type and then, after the predetermined holding time has elapsed, raising the temperature above 500°C and reducing the pressure to less than 18 GPa (e.g., 10 GPa). There is a risk that it will revert back to the C-type rare earth crystal structure.

[0018] Multiple anvil devices are widely used in research institutions and come in many types, but the two most common are the Kawai-type multiple anvil device (also known as the 6-8 type or MA8 type) and the cubic anvil device. Belt devices are ultra-high pressure generators commonly used in industrial production, and can stably generate ultra-high pressures of around 80,000 atmospheres. In this device, a pressurized space is formed by upper and lower pistons with opposing convex curved surfaces and left and right cylinders, which also have convex curved surfaces, and is sealed with a gasket. The pressurized space is pressurized by pressing the pistons from above and below. Piston-cylinder devices are a type that pressurizes by inserting a piston into a cylinder, and can stably generate pressures of around 30,000 atmospheres. They have the advantage of a simple structure and the ability to stably generate ultra-high pressures.

[0019] The sample chamber of the KAWAI-type anvil apparatus may be made of platinum. It has low reactivity and can withstand the temperatures that can be raised. A larger sample chamber is preferable to obtain scandium oxide with a large particle size. However, if it is too large, it may be difficult to achieve sufficient pressure and temperature, as well as a uniform pressure and temperature distribution within the sample chamber, so it is preferable to adjust it appropriately. For example, a sample chamber of a size or volume that allows for obtaining an average particle size of scandium oxide of 10 μm or more is preferable. Assuming a cylindrical shape, for example, if the inner diameter is 1.6 mm and the inner height is 1.9 mm, the volume would be approximately 3.82 mm³. 3 3mm 3 Above, 3.5mm 3 or more, 4mm 3 or more, or 4.5mm 3The above is preferable. The size may be such that the desired pressure and temperature can be obtained. It is also preferable that the heater be installed so as to enclose the entire sample chamber. A spacer that can act as a pressure medium may be included between the heater and the sample chamber. The spacer may contain magnesium oxide. In a light-emitting element comprising an excitation source and a phosphor, the excitation source may be light (including UV) having a wavelength of 200 nm or more, 250 nm or more, 300 nm or more, 350 nm or more, or 400 nm or more. Alternatively, it may be light in a range of wavelengths below the excitation range, for example, 600 nm or less, 550 nm or less, 500 nm or less, or 450 nm or less. Alternatively, it may be between 200 nm and 400 nm. [Effects of the Invention]

[0020] As described above, since we can provide phosphors made from inorganic compounds containing scandium oxide having a corundum-type crystal structure achievable through relaxation, we can obtain unprecedented luminescence properties. Furthermore, we can provide new types of inorganic compounds that can obtain such luminescence properties. [Brief explanation of the drawing]

[0021] [Figure 1] This is a schematic diagram showing the crystal structure of corundum-type scandium oxide containing an activating element, relating to an embodiment of the present invention. [Figure 2] This is a schematic diagram showing the formation pathway of corundum-type scandium oxide and a comparison of various crystal structures. [Figure 3] This is a conceptual diagram illustrating the principle of a diamond anvil cell high-pressure device. [Figure 4] This is a schematic diagram showing the diamond anvil cell and the sample section. [Figure 5] This is a diagram showing the measurement system for X-ray structural analysis. [Figure 6] This is a photograph showing the inside of a Sc2O3:Eu sample. The sample contains dispersed, light-impermeable gold particles. There is a mixture of areas that emit red fluorescence and areas that do not. [Figure 7]This is a photograph showing the inside of a Sc2O3:Tb sample. The sample contains dispersed, light-impermeable gold particles. There is a mixture of areas that emit green fluorescence and areas that do not. [Figure 8] This is a schematic diagram of the KAWAI type anvil device (two-stage multi-anvil device). [Figure 9] This is a schematic diagram showing the configuration of the second-stage anvil of a KAWAI-type anvil device (two-stage multi-anvil device). [Figure 10] This is a schematic diagram showing the sample chamber of the second anvil in a KAWAI-type anvil apparatus (two-stage multi-anvil apparatus). [Figure 11] This is a schematic diagram showing the configuration of the sample chamber in the second anvil of a KAWAI-type anvil apparatus (two-stage multi-anvil apparatus). [Figure 12] This is a photograph showing Sc2O3:Eu inside the sample chamber (under LED illumination) produced using a KAWAI-type anvil apparatus (two-stage multi-anvil apparatus). [Figure 13] This is a photograph showing Sc2O3:Eu (under UV illumination) inside the sample chamber, prepared using a KAWAI-type anvil apparatus (two-stage multi-anvil apparatus). [Figure 14] This is a photograph showing Sc2O3:Tb inside the sample chamber (under LED illumination) produced using a KAWAI-type anvil apparatus (two-stage multi-anvil apparatus). [Figure 15] This is a photograph showing Sc2O3:Tb (under UV illumination) inside the sample chamber, prepared using a KAWAI-type anvil apparatus (two-stage multi-anvil apparatus). [Figure 16] This graph shows the luminescence characteristics of the sample used in Experimental Example 1. [Figure 17] This graph shows the luminescence characteristics of the sample in Experimental Example 3. [Figure 18] This graph shows the luminescence characteristics of the sample in Experimental Example 8. [Figure 19] This graph shows the luminescence characteristics of the sample in Experimental Example 9. [Figure 20] This graph shows the excitation and emission spectra of the sample from Experimental Example 1. [Figure 21]This graph shows the excitation and emission spectra of the sample from Experimental Example 3. [Figure 22] This graph shows the X-ray diffraction pattern of the sample from Experimental Example 1. [Figure 23] This graph shows the X-ray diffraction pattern of the sample from Experimental Example 3. [Figure 24] This graph shows the X-ray diffraction pattern of the sample from Experimental Example 8. [Figure 25] This graph shows the X-ray diffraction pattern of the sample from Experimental Example 9. [Modes for carrying out the invention]

[0022] The embodiments of the present invention will be described below with reference to the drawings. Similar elements will be given the same numbers, and their descriptions will be omitted.

[0023] Figure 1 is a schematic diagram showing the crystal structure of a corundum-type scandium oxide containing an activating element, relating to an embodiment of the present invention. To the best of the inventors' knowledge, this structure is formed by relaxation from a high-pressure crystal structure. By replacing a portion of Sc with Eu or Tb, a phosphor with specific luminescence properties can be obtained. Table 1 summarizes the crystal parameters of this corundum-type scandium oxide.

[0024] [Table 1]

[0025] Corundum-type scandium oxide crystals are hexagonal, with a space group of R-3c and a space group number of 167. Such corundum-type scandium oxide crystals (Sc2O3), inorganic crystals with the same crystal structure, or inorganic crystals that are solid solutions of these are hexagonal, and phosphors that use these as matrix crystals are thought to have high emission intensity. Corundum-type scandium oxide crystals (Sc2O3), inorganic crystals with the same crystal structure, or inorganic crystals that are solid solutions of these are hexagonal crystals, possess the symmetry of space group R-3c, and have lattice constants a, b, and c. a = 5.34416 angstroms ± 0.26721 angstroms b = 5.34416 angstroms ± 0.26721 angstroms. c = 14.20773 angstroms ± 0.71039 angstroms. Values ​​within this range are considered particularly stable, and phosphors based on these matrix crystals are thought to have high luminescence intensity.

[0026] Figure 2 is a schematic diagram showing the formation pathway of corundum-type scandium oxide and a comparison of various crystal structures. The formation process of corundum-type scandium oxide is illustrated. Generally, scandium oxide with a C-type rare-earth structure (see Table 2) changes to a gadolinium sulfide-type crystal structure at temperatures above 1000°C or 1300°C and 19 GPa, or at temperatures above 1500°C and 19 GPa. Table 3 summarizes the crystal parameters of gadolinium sulfide (Gd2S3)-type scandium oxide under high pressure (30 GPa).

[0027] [Table 2] [Table 3]

[0028] The gadolinium sulfide (Gd2S3) type scandium oxide crystal is orthorhombic, has Pnma symmetry in its space group, and has a space group number of 62. The lattice constants a, b, and c under high pressure (30 GPa) are as follows: a = 5.3565 angstroms, b = 2.9282 angstroms, c = 11.2681 angstroms.

[0029] When scandium oxide crystals (Sc2O3) with a gadolinium sulfide structure are cooled to below 30°C under high pressure and then reduced to 0.1 MPa, they change to a corundum-type crystal structure (see Table 1). As shown in Figure 2, if scandium oxide crystals (Sc2O3) with a gadolinium sulfide structure are reduced to 0.1 MPa while at a high temperature and then cooled, they revert back to a C-type rare-earth structure. Furthermore, when the C-type rare-earth structure is heated to below 18 GPa, it changes to a B-type rare-earth structure at around 1300°C.

[0030] Figure 3 is a conceptual diagram illustrating the principle of the diamond anvil cell (DAC) high-pressure device used in the specification of this application. Figure 4 is a schematic diagram showing the details of the sample section. Diamond anvils 10, polished to have flat bottoms, are installed with their bottoms facing each other, and pressure is applied to these bottoms to pressurize the sample section 14 surrounded by gaskets 12. As shown in Figure 4, the sample section 14 is filled with a mixture of scandium oxide and europium oxide / terbium oxide, which have a C-type rare-earth structure, mixed with gold particles 16. Since the raw material mixture is colorless, the energy from the laser beam 20 is directed primarily at heating the gold particles. As shown in the figure, the laser 20 is scanned, so the gold particles that receive its light become hot, and the heat is transferred to the surrounding area, thereby heating the raw material mixture. In other words, it is necessary to disperse and mix opaque gold and platinum powder in the raw materials, and the heating becomes heterogeneous, centered on the absorber, making it difficult to uniformly diffuse the fluorescence-activating element and synthesize a uniform phosphor throughout. Because heating proceeds for a short time only in the area where the surface absorber (gold and platinum powder) is present, it is easy for only a very small part of the whole to become activated and emit light. Moreover, since the generation is limited to the surface, the intensity tends to be significantly weak. As a result, temperature inhomogeneity is likely to occur within the sample part 14, and this temperature inhomogeneity tends to result in a non-uniform crystal structure of the generated scandium oxide. That is, since laser heating heats only the area of ​​the absorber (gold powder), the temperature field is also non-uniform, making it difficult to obtain a uniform phosphor. Also, naturally, opaque gold particles are present as impurities. And the luminescent area is limited to about 20%, and its intensity tends to be weak.

[0031] Figure 5 shows a measurement system for X-ray structural analysis. Synchrotron X-rays pass through a diamond anvil and are irradiated onto a diamond anvil cell (DAC). This allows the measurement system cell to be used directly without depressurization, enabling X-ray structural analysis. For example, X-rays from synchrotron radiation (KEK Photon Factory) can be monochromatized with silicon (λ=0.418140Å) to obtain an X-ray diffraction pattern. X-ray structural analysis can be performed from the obtained X-ray diffraction pattern to determine crystal structure parameters such as lattice constants. Alternatively, after depressurizing to 0.1 MPa, the sample can be removed from the cell, and X-ray structural analysis can be performed to determine crystal structure parameters such as lattice constants.

[0032] Figure 6 shows, as an example, a grayscale photograph of a sample of the generated Sc2O3:Eu taken with an optical microscope. In the center (circular area) of the figure, a phosphor containing an inorganic compound made of corundum-type scandium oxide crystals containing Eu was observed, glowing pink. Dark spots, presumably due to gold particles, were also seen.

[0033] Figure 7 shows, as an example, a grayscale photograph of a sample of the generated Sc2O3:Tb taken with an optical microscope. In the center (circular area) of the figure, a phosphor containing an inorganic compound made of Tb-containing corundum-type scandium oxide crystals was observed to glow green, but the fluorescence was not uniform, with a mixture of fluorescent and non-fluorescent areas. Dark spots, presumably due to gold particles, were also observed.

[0034] Figure 8 shows a schematic diagram of the KAWAI-type anvil device (two-stage multi-anvil device) 50. This is a two-stage multi-anvil device 50 that uses a single-stage multi-anvil device to pressurize the second-stage anvil in order to generate higher pressure. Figure 9 shows the configuration of the second-stage anvil 52. Anvil 54 refers to a high-hardness component that applies pressure directly to the pressure medium. Instead of the cubic pressure medium of the single-stage multi-anvil device, eight cubic cemented carbide anvils are incorporated as the second-stage anvil. The cubic cemented carbide anvils are often made of tungsten carbide sintered bodies (sintered with a few percent of Co added to WC powder) (for example, manufactured by Fuji Die Co., Ltd., a cube with sides of 32 mm). Each of the second-stage anvils has an equilateral triangle 58 cut out at its vertex. These eight anvils pressurize the octahedral pressure medium 56, which is made of a regular octahedron of magnesia (MgO) placed in the center, and pressurizes the six faces of the cube composed of the eight anvils 54. The solid pressure medium used is a relatively soft, unreactive, electrically insulating, and low-thermal-conducting solid material that generates quasi-hydrostatic pressure. Pyrophyllite (Al2Si4O) is a material that satisfies these conditions. 10 (OH)2), talc (Mg3Si4O 10 (OH)2) and semi-sintered magnesia (MgO) bodies are widely used. A pyrophyllite gasket is placed between the anvils 54 to seal the high pressure generated in the center. This two-stage multi-anvil apparatus 50 can generate ultra-high pressures of over 200,000 atmospheres, but on the other hand, the octahedral pressure medium 56 made of magnesia octahedra and the gasket must be manufactured with high precision. A spacer 60 is placed on the top surface of the anvil 54. In terms of simplicity of handling, the cubic anvil apparatus is superior. In this apparatus, the solid pressure medium can be a pyrophyllite cube, which is easy to manufacture, and a gasket is not required.

[0035] Figures 10 and 11 show schematic diagrams illustrating the details of the octahedral pressure medium 56. The octahedral pressure medium 56, made of solid pressure medium 68 (for example, one with sides of approximately 10 mm may be used), is equipped with a cylindrical LaCrO3 heater 72 inside (for example, one with an outer diameter of approximately 3.2 mm and an outer height of approximately 8.16 mm, and an internal volume with a diameter of approximately 2.3 mm and an inner height of approximately 5.16 mm may be used), and an electrode 64 is provided at one end of the heater with insulating material 66 arranged around it. A thermocouple 70 is provided in this octahedral pressure medium 56. Figure 11 is a cross-sectional view showing an example of the sample heating section inside the octahedral pressure medium 56. Inside the LaCrO3 heater 72, which is covered by the MgO pressure medium 74 constituting the octahedral pressure medium 56, is a cylindrical Pt capsule 78 (for example, one with a diameter of approximately 1.6 mm and a height of approximately 1.9 mm may be used) surrounded by an MgO spacer 76. This capsule is filled with a mixture of scandium oxide and europium oxide / terbium oxide, which have a C-type rare-earth structure and serve as the raw materials. A thermocouple 82 is placed at the bottom of the Pt capsule 78 and extends outside the MgO pressure medium 74 (70). Here, a LaCrO3 heater 72 is used, which is generally considered suitable for heating from room temperature to 2300°C. This LaCrO3 heater 72 is thought to exhibit semiconducting behavior. Other general-purpose heaters can be used. For example, a graphite heater is considered suitable for heating from room temperature to 3000°C, but a pressure of 8 GPa or less is desirable. This heater is also thought to exhibit semiconducting behavior. Additionally, rhenium heaters can be used, and are considered suitable for heating from room temperature to 2500°C. These heaters are thought to exhibit metallic behavior. These heaters can be appropriately selected and used depending on the manufacturing method.

[0036] The phosphor described above is excited by ultraviolet to visible light and emits visible to near-infrared light depending on the selection of activating element A. Therefore, by combining it with an excitation source that emits light with a wavelength in the range of 200 nm to 500 nm, a light-emitting element can be provided. Light-emitting diodes (LEDs) or laser diodes (LDs) can be used as the excitation source. Furthermore, such light-emitting elements can be used to provide light-emitting devices such as lighting fixtures, backlights for liquid phase panels, lamps for projectors, infrared illumination, and light sources for infrared measurement.

[0037] [Example of experiment] As raw materials, the samples used were scandium oxide (Sc2O3:PN:294020:99.999%) and europium oxide (Eu2O3:PN:323543:99.999%) manufactured by Sigma-Aldrich, or terbium oxide (Tb2O3:PN:590509:99.99%) manufactured by Aldrich.

[0038] [Laser DAC (Diamond Anvil Cell)] The scandium oxide and europium oxide / terbium oxide, both possessing the C-type rare earth structure described above, were weighed in a molar ratio of 0.99:0.01. Furthermore, 0.1-0.5 wt% of gold powder was added to the total mixed raw materials and mixed and ground in an agate mortar. After drying the sample in a vacuum dryer at 120°C for 3 hours, it was packed into a sample chamber with a diameter of 120 μm and a height of 50 μm, opened in the center of a rhenium gasket. A diamond anvil with a tip diameter of 400 μm was used to apply pressure from above and below, and once the desired pressure (25-30 GPa) was reached, heating was performed by scanning the sample with a fiber laser (wavelength: approximately 1 μm) focused to a diameter of 20 μm. During this process, the laser was absorbed by the gold particles dispersed in the sample, heating the oxide mixture adjacent to the gold particles. Since the heating was not uniform, the temperature range was estimated to be between 1000°C and 2000°C. The heating time was approximately 2-3 seconds, which corresponds to 0.0006 to 0.0008 hours. After heating, the pressure was released to atmospheric pressure (0.1 MPa), allowing the sample to be recovered while still held in place by the rhenium gasket.

[0039] [KAWAI-type high-pressure device (large press)] The scandium oxide and europium oxide / terbium oxide mentioned above were weighed in molar ratios of 0.99:0.01 or 0.995:0.005, respectively, and mixed and ground in an agate mortar. The mixed powder was dried in a vacuum dryer at 120°C for 3 hours, and then filled into a platinum tube with an inner diameter of 1.6 mm and a height of 1.9 mm, with both ends closed by platinum discs with a diameter of 1.8 mm and a wall thickness of 0.02 mm. The platinum tube containing the sample was set inside a LaCrO3 heater via an MgO spacer and inserted into an octahedral-shaped MgO pressure medium. This pressure medium was pressurized using a hydraulic press with a cubic tungsten carbide anvil with rounded corners. After pressurizing to the desired pressure, heating was performed by passing current through electrodes to the LaCrO3 heater and held for 1 hour. The heating rate at this time was approximately 100 K / min. A holding time of 10 minutes or more is considered preferable. The sample was then cooled to below 100°C (cooling rate: approximately 1000°C / sec), reduced to 0.1 MPa, and recovered.

[0040] Table 4 summarizes Experimental Examples 1 to 9, which were generated using the two methods described above. [Table 4]

[0041] Experimental Examples 8 and 9 were produced by laser DAC, with scandium oxide and europium oxide / terbium oxide in a molar ratio of 0.99:0.01. The laser was scanned under a pressure of 25-30 GPa to raise the temperature to 1000-2000°C, but it is thought that the temperature was not uniform due to the heating method. The particle sizes of the corundum-type inorganic compounds Sc2O3:Eu (Experimental Example 8) and Sc2O3:Tb (Experimental Example 9) were 3 μm or less. When the average particle size was measured using the ImageJ software on images captured with a CMOS camera microscope, the number-based average particle size was approximately 2 μm or less for Experimental Example 8 and approximately 2 μm or less for Experimental Example 9. Furthermore, not all of these examples possessed a corundum-type crystalline structure; they were mixed with inorganic compounds having a C-type rare-earth crystalline structure. Photographs of these samples under UV irradiation in the sample area are shown in Figures 6 and 7.

[0042] Experimental Examples 1 and 2 used scandium oxide and europium oxide in molar ratios of 0.99:0.01 and 0.995:0.005, respectively. The samples were pressurized at 25 GPa, heated to 1600°C using a heater, and held for 1 hour. Although the temperature within the samples was considered to be uniform, only corundum-type inorganic compounds were detected. The particle size of the corundum-type Sc2O3:Eu (Experimental Examples 1 and 2) inorganic compounds ranged from 5 to 30 μm. Experimental Examples 3 and 4 used scandium oxide and terbium oxide in molar ratios of 0.99:0.01 and 0.995:0.005, respectively. The samples were pressurized at 24 GPa, heated to 1500°C using a heater, and held for 1 hour. Although the temperature within the samples was considered to be uniform, only corundum-type inorganic compounds were detected. The particle sizes of the corundum-type Sc2O3:Tb inorganic compounds (Experimental Examples 3 and 4) ranged from 5 to 30 μm. When the average particle size was measured using ImageJ software, based on the number of particles, it was approximately 15 μm for Experimental Example 1, 15 μm for Experimental Example 2, 10 μm for Experimental Example 3, 10 μm for Experimental Example 4, 15 μm for Experimental Example 5, 15 μm for Experimental Example 6, and 15 μm for Experimental Example 7. Photographs of the phosphors from Experimental Examples 1 and 3 with the platinum discs removed from the top and bottom of the platinum tubes are shown in Figures 12, 13, 14, and 15. Figures 12 and 14 show the samples illuminated with a white LED, while Figures 13 and 15 show the samples irradiated with 280 nm UV light. No clear luminescence was observed when illuminated with a white LED, but the samples irradiated with UV light emitted red and green fluorescence, respectively.

[0043] Experimental Examples 5 to 7 in Table 4 attempt to generate corundum-type inorganic compounds using scandium oxide without activating elements, employing a KAWAI-type high-pressure apparatus. In Experimental Example 5, the pressure was somewhat low at 23 GPa, but the temperature was 1600°C, similar to Experimental Examples 1 and 2. From this sample, not only corundum-type structures but also C-type rare-earth-type inorganic compounds were detected. This is likely due to experimental errors such as a slightly low pressure value and an insufficiently uniform temperature distribution. On the other hand, in Experimental Examples 6 and 7, the pressures were 24 GPa and 25 GPa, and the temperature was sufficiently high at 1600°C, and only corundum-type inorganic compounds were detected. The particle sizes of the inorganic compounds in Experimental Examples 5 to 7 were all large, ranging from 5 to 30 μm.

[0044] Figure 16 is a graph showing the emission spectrum of the sample (Sc2O3:Eu) from Experimental Example 1. A 472.8 nm laser beam was used as the excitation light. As can be seen from this graph, a spectrum with a peak around 610-620 nm (approximately 615 nm) is observed, and it extends to around 630 nm. In addition, a somewhat weaker spectrum with a peak near 590 nm and a spectrum whose intensity increases upward from 650 nm to 700 nm are also recognized. Generally, these are perceived as violet (380-430 nm), blue (430-490 nm), green (490-550 nm), yellow (550-590 nm), orange (590-640 nm), and red (640-770 nm), so this emission is perceived as orange to red light. Figure 18 is a graph showing the emission spectrum of the sample (Sc2O3:Eu) from Experimental Example 8. Compared to Figure 16, the peak intensity of the spectrum is lower, based on the noise level. It is 2 to 3 orders of magnitude weaker than synthesis using a large press as in Experimental Examples 1 and 2. This is likely because the heating was heterogeneous, making it impossible to synthesize a uniform phosphor throughout. Since heating proceeded for a short time only in the areas where the surface absorber was present, and the formation remained on the surface, it is thought that unreacted phase, specifically scandium oxide in the C-type rare-earth structure, remained in the unheated areas. Similar to Figure 16, a spectrum with a peak around 610-620 nm (approximately 615 nm) was observed, and further, a spectrum with a peak around 620-630 nm (approximately 625 nm) was observed. Therefore, although weak, this emission is perceived as orange to red light. Both are light emitted by the luminescent element Eu.

[0045] Figure 17 is a graph showing the emission spectrum of the sample (Sc2O3:Tb) from Experimental Example 3. A 472.8 nm laser beam was used as the excitation light. As can be seen from this graph, a spectrum with a peak around 540-550 nm (approximately 543 nm), a spectrum of moderate intensity with peaks around 548 nm and approximately 551 nm, and the strongest spectrum with a peak around 550-560 nm (approximately 554 nm) were observed. Furthermore, low-intensity spectra with peaks around 480-490 nm (approximately 485 nm) and approximately 500 nm, as well as low-intensity spectra with peaks around 587 nm, approximately 590 nm, and approximately 625 nm were observed. Therefore, this emission is perceived as a slightly bluish-green light. Figure 19 is a graph showing the emission spectrum of the sample (Sc2O3:Tb) from Experimental Example 9. A 472.8 nm laser beam was used as the excitation light. Compared to the case in Figure 18, the intensity evaluation relative to noise was slightly higher, but compared to Figure 17, a spectrum of significantly lower intensity was observed. Similar to Figure 17, a spectrum with a peak around 540-550 nm (approximately 543 nm), a spectrum of moderate intensity with peaks around 548 nm and 551 nm, and the strongest spectrum with a peak around 550-560 nm (approximately 554 nm) were observed. Furthermore, low-intensity spectra with peaks around 480-490 nm (approximately 485 nm) and 500 nm, as well as low-intensity spectra with peaks around 587 nm, 590 nm, and 625 nm were observed. Therefore, this emission is perceived as a slightly bluish-green light. All of these are light emitted from the light-emitting element Tb.

[0046] Figure 20 is a graph showing the excitation light spectrum and the fluorescence spectrum emitted from the sample when the luminescence characteristics of the sample in Experimental Example 1 were evaluated. The graph captioned "Excitation Spectrum" shows the wavelength λ of the fluorescence spectrum. em The excitation spectrum when λ = 615 nm was obtained is shown. On the other hand, the graph with the caption "Fluorescence Spectrum" shows the excitation spectrum wavelength λex The fluorescence spectrum obtained when excited at 250 nm is shown. The excitation light spectrum has a peak at approximately 250 nm, and the fluorescence spectrum is almost the same as that in Figure 16. However, since it was measured at a longer wavelength, a spectrum with a peak at approximately 710 nm is observed. That is, in Figure 16, the spectrum in which the intensity increases sharply from 650 nm to 700 nm is this spectrum. In other words, the emission was considered to be quite close to red.

[0047] Figure 21 is a graph showing the excitation light spectrum and the fluorescence spectrum emitted from the sample when the luminescence characteristics of the sample in Experimental Example 3 were evaluated. Graphs captioned "Excitation Spectrum" show the fluorescence spectrum wavelength λ. em The excitation spectrum when λ = 501 nm was obtained is shown. On the other hand, the graph with the caption "Fluorescence Spectrum" shows the excitation spectrum wavelength λ ex The fluorescence spectrum obtained when excited at 278 nm is shown. The excitation light spectrum has a peak at approximately 278 nm, and the fluorescence spectrum is almost the same as that in Figure 17. However, since the measurement was performed at a shorter wavelength, lower intensity spectra with peaks around 420 nm and 445 nm were also observed.

[0048] Figures 22, 23, 24, and 25 are graphs showing the X-ray diffraction patterns of samples from experimental examples 1, 3, 8, and 9, respectively, with Miller indices assigned to each peak. Identification by these X-ray diffractions reveals that all samples possessed a corundum-type structure. However, in Figures 24 and 25, peaks attributable to unreacted C-type rare earth elements and gold were also observed. Thus, it is evident that obtaining a desirable, uniform phosphor is difficult using diamond anvil cell manufacturing due to factors inherent in the method.

[0049] As described above, with a large-scale press method, if C-type rare-earth scandium oxide is heated to a temperature of, for example, 1500°C or higher, the temperature distribution tends to become uniform. When placed under a pressure of 22 GPa or higher, it is thought to transform into a scandium oxide compound with a gadolinium sulfide (Gd2S3) type structure. Then, under that pressure, the temperature is cooled to 300°C or lower, 100°C or lower, or around 30°C, and the pressure is reduced to around 0.1 MPa (atmospheric pressure) to form corundum-type scandium oxide (for example, Patent Document 5). Due to the characteristics of the manufacturing equipment, the large-scale press method makes it easy to obtain phosphors with relatively large particle sizes. For example, it is thought that particles of approximately 2 μm or larger, approximately 5 μm or larger, approximately 10 μm or larger, approximately 20 μm or larger, or approximately 30 μm or larger are possible with a spherical approximation. Depending on the size of the sample chamber and the magnitude of the achievable pressure, particles of 100 μm or less are realistic, but there is no particular upper limit. It is considered preferable to obtain particles as large as technically possible. [Industrial applicability]

[0050] In the embodiments of the present invention, it was found that a corundum-type scandium oxide phosphor can be provided. This increases the variety of phosphors available, allowing for greater selection based on environmental conditions and thus enhancing usefulness. Furthermore, obtaining phosphors with larger particle sizes enables desirable luminescence characteristics. [Explanation of Symbols]

[0051] 50 Two-stage multi-anvil device 52 Second Anvil 54 Anvil 56. Regular Octahedral Pressure Medium 58 equilateral triangle 60 Spacer 64 electrodes 66 Insulation 68 Solid pressure medium 70 Thermocouples

Claims

1. A phosphor comprising an inorganic compound containing scandium oxide having a corundum-type structure, which contains at least one or more activating elements A (where A is one or more elements selected from Mn, Ce, Pr, Nd, Sm, Eu, Tb, Dy, and Yb).

2. The aforementioned corundum-type structure is hexagonal, with a space group of R-3c. The lattice constant is, a = 5.34416 angstroms ± 0.26721 angstroms b = 5.34416 angstroms ± 0.26721 angstroms c = 14.20773 angstroms ± 0.71039 angstroms α = 90 degrees ± 1 degree, β = 90 degrees ± 1 degree, and γ = 120 degrees ± 1 degree, The phosphor according to claim 1, characterized in that it is the same as the one described in claim 1.

3. The inorganic compound is composed of the activating element A substituting for the Sc atom of scandium oxide. The phosphor according to claim 1 or 2, characterized in that the molar amount m of the activating element A in the inorganic compound is 0 < m ≤ 0.

2.

4. The phosphor according to claim 1 or 2, characterized in that the activating element A is Eu and / or Tb.

5. The phosphor according to claim 1 or 2, characterized in that the corundum-type structure is modified from a gadolinium sulfide-type structure.

6. A bulk phosphor comprising the phosphor described in claim 1 or 2, and consisting solely of light-transmitting materials.

7. A method for producing a phosphor according to claim 1 or 2, characterized by weighing a compound of activating element A (where A is one or more elements selected from Mn, Ce, Pr, Nd, Sm, Eu, Tb, Dy, and Yb) and a compound of scandium (Sc) in a molar ratio of elements M and Sc of any of 0.0001:0.9999 to 0.100:0.900, mixing and grinding the mixture, filling it into a predetermined sample chamber, applying a pressure of 19 GPa or higher and a temperature of 1000°C or higher to the raw material mixture in the sample chamber, holding it for a predetermined time, then lowering the temperature to 300°C or lower, and then reducing the pressure to 1 MPa or lower.

8. The method according to 7, characterized in that a multi-anvil device, a belt device, or a piston-cylinder device is used for pressurizing and heating the raw material mixture in the sample chamber.

9. The method according to 7, characterized in that a diamond anvil apparatus is used for pressurizing and heating the raw material mixture in the sample chamber.

10. The method according to claim 7, characterized in that a Kawai-type anvil apparatus is used for pressurizing and heating the raw material mixture in the sample chamber.

11. A light-emitting element comprising an excitation source and a phosphor, The excitation source emits light with a wavelength in the range of 200 nm to 500 nm. The light-emitting element contains at least the phosphor described in claim 1.

12. The light-emitting element according to claim 11, wherein the excitation source is a light-emitting diode (LED) or a laser diode (LD).

13. A light-emitting device that includes a light-emitting element according to claim 11 or 12, which is a lighting fixture, a backlight for a liquid phase panel, a lamp for a projector, an infrared illuminator, or an infrared measurement light source.

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