Oxide crystals, methods for producing the same, and their uses

Abstract

The present invention provides an oxide crystal that does not contain harmful substances such as cadmium and has scintillation properties comparable to or better than those of cadmium tungstate (CdWO4), as well as a method for producing the same. [Solution] An oxide crystal according to one embodiment of the present invention has the general formula ((Y 1-p RE p ) 1-x Tb x )(Ta 1-y Nb y )O 4-z (In the formula, p, x, y, and z each independently satisfy 0 ≤ p ≤ 1, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, and -0.5 ≤ z ≤ 0.5, and RE is represented as (at least one selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu), and is characterized by containing a hydrogen atom (H).

Description

[Technical Field]

[0001] This invention relates to oxide crystals, methods for producing the same, and applications thereof. [Background technology]

[0002] Radiation inspection equipment is used in a variety of fields and applications, including non-destructive testing equipment and medical diagnostic equipment. Examples of applications include irradiating a subject with radiation (X-rays, neutrons, etc.) and detecting the transmitted radiation with a radiation detector, and placing a radiation source (radioactive material) inside a subject beforehand and detecting the radiation (gamma rays, etc.) emitted from the radiation source and transmitted through the subject with a radiation detector.

[0003] A radiation detector generally comprises a scintillator (also called a scintillator material) that converts radiation into light, and a photoelectric converter that detects the light emitted from the scintillator and converts it into an electrical signal.

[0004] Conventionally, scintillators used in X-ray detectors have included single crystals such as cadmium tungstate (CdWO4) and thallium-doped cesium iodide (Tl:CsI), as well as polycrystalline ceramics such as terbium-doped gadolinium oxysulfide (Tb:Gd2O2S) and praseodymium-doped gadolinium oxysulfide (Pr:Gd2O2S).

[0005] In particular, CdWO4 is widely used as a scintillator in X-ray detectors for inspecting checked baggage and cargo at airports and other locations. Single crystals of CdWO4 have practical scintillation characteristics, such as high luminescence and low afterglow. However, since cadmium is a hazardous substance, single crystals of CdWO4 may degrade the environment.

[0006] In recent years, there have been research reports on yttrium tantalate (YTaO4) and niobium (Nb)-containing YTaO4 as scintillators that do not contain harmful substances (harmful elements) such as cadmium (Non-Patent Documents 1-5). Non-Patent Document 1 describes the scintillation characteristics of a single crystal of YTaO4 produced in a vacuum by vertically directed crystallization, but the measured scintillation efficiency (%) using NaI(Tl) as a standard sample is only half (20%) of that of CdWO4 (40%). Non-Patent Documents 2-5 describe ceramics of YTaO4 and Nb-containing YTaO4 produced by solid-phase methods, and some are said to have obtained higher luminescence than CdWO4. However, since the ceramic materials described in Non-Patent Documents 2-5 are opaque, their use is limited to thin plate forms and they can only be used as scintillators in X-ray detectors that use low-energy X-rays. Furthermore, because ceramics are polycrystalline, there are concerns that their scintillation properties may deteriorate due to grain boundaries and crystal defects that inevitably occur during manufacturing.

[0007] On the other hand, Non-Patent Document 6 describes that terbium (Tb)-doped YTaO4 crystals have potential usefulness as sensor materials for fluorescent thermometers. According to Non-Patent Document 6, YTaO4 crystals prepared by doping with 0.25 mol% Tb4O7 are long-lasting fluorescent materials that exhibit phosphorescence for 120 minutes. However, Non-Patent Document 6 does not describe the scintillation properties of the crystal, and its potential as a scintillator remains completely unknown. [Prior art documents] [Non-patent literature]

[0008] [Non-Patent Document 1] LI Kazakova, et al., Radiation Measurements, 1995, 24, 359-360. [Non-Patent Document 2] C. W. E. Eijk, et al., Physics in Medicine and Biology, 2002, 47, R85-R106. [Non-Patent Document 3] OV Voloshyna, et al., Materials Science and Engineering B, 2013, 178, 1491-1496. [Non-Patent Document 4] E. Bourret, et al., Journal of Luminescence, 2018, 202, 332-338. [Non-Patent Document 5] OV Voloshyna, et al., Nuclear Instruments and Methods in Physics Research A, 2014, 764, 227-231. [Non-Patent Document 6] T. Takayama, et al., Journal of Crystal Growth, 2005, 275, e2013-e2017. [Overview of the project] [Problems that the invention aims to solve]

[0009] This invention has been made in view of these circumstances, and aims to provide an oxide crystal that does not contain harmful substances such as cadmium and has scintillation properties comparable to or better than those of CdWO4. Furthermore, the present invention aims to provide a method for producing the above-mentioned oxide crystals. Furthermore, the present invention aims to provide applications for the oxide crystals described above. [Means for solving the problem]

[0010] The oxide crystal according to the present invention has the general formula ((Y 1-p RE p ) 1-x Tb x )(Ta 1-yNb y )O 4-z (wherein p, x, y, and z are each independently 0 ≦ p ≦ 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, -0.5 ≦ z ≦ 0.5, and RE is at least one selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu)).) It is represented by and contains a hydrogen atom (H), thereby solving the above problems. In the oxide crystal of the present invention, the concentration of hydrogen atoms is 1×10 16 atoms / cm 3 or more and 1×10 23 atoms / cm 3 or less may be in the range. The oxide crystal of the present invention has a crystal structure belonging to the P 1 2 / a 1 space group, P 1 2 / c 1 space group, P 1 21 / c 1 space group, or I 1 2 / a 1 space group, and the crystal phase may be a single phase of monoclinic crystal. The oxide crystal of the present invention may further contain an alkali metal and / or an alkaline earth metal. The concentration of the above alkali metal and / or alkaline earth metal is 1×10 12 atoms / cm 3 or more and 1×10 20 atoms / cm 3 or less may be in the range.

[0011] In one embodiment, the method for producing the above-described oxide crystal according to the present invention includes crystal growth by a hydrothermal synthesis method in the presence of a mineralizer containing an alkali metal and / or an alkaline earth metal, or an acid mineralizer, or a mixed mineralizer of both, thereby solving the above problems. In another embodiment, the method for producing the above-described oxide crystal according to the present invention is the general formula ((Y 1-p RE p ) 1-x Tbx )(Ta 1-y Nb y )O 4-z The present invention relates to growing crystals of one or more raw material compounds having a composition represented by the formula (wherein p, x, y, and z are each independently satisfying 0≦p≦1, 0≦x≦1, 0≦y≦1, and -0.5≦z≦0.5, and RE is selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) by hydrothermal synthesis in the presence of a mineralizing agent containing an alkali metal and / or an alkaline earth metal, or an acid mineralizing agent, or a mixed mineralizing agent of both, thereby solving the above problem. The concentration of the mineralizing agent may be in the range of 1 M to 50 M. In growing crystals using the hydrothermal synthesis method described above, the temperature may be in the range of 400°C to 800°C, and the maximum achievable pressure may be in the range of 25 MPa to 250 MPa.

[0012] The optical material according to the present invention consists of the above-mentioned oxide crystal, thereby solving the above-mentioned problems. The optical material mentioned above may also be a laser material. The optical material mentioned above may be a scintillator. The radiation detector according to the present invention comprises the scintillator described above and a photoelectric converter that detects light from the scintillator and converts it into an electrical signal, thereby solving the above problem. The radiation inspection apparatus according to the present invention comprises a radiation source that irradiates a subject with radiation and the above-mentioned radiation detector that detects radiation that penetrates the subject, thereby solving the above-mentioned problems. The magnetic material according to the present invention consists of the above-mentioned oxide crystal, thereby solving the above-mentioned problems. The magnetic material mentioned above may also be a magnetic refrigeration material. [Effects of the Invention]

[0013] The present invention provides an oxide crystal that does not contain harmful substances such as cadmium and has scintillation properties comparable to or better than those of CdWO4. The oxide crystal of the present invention is useful as an optical material, a magnetic material, and the like. Typically, the oxide crystal of the present invention is suitable for use as a laser material or a scintillator. The scintillator of the present invention is suitable for use as a scintillator for radiation detectors, and in particular for use as a scintillator for X-ray radiation detectors. Furthermore, a radiation detector equipped with the scintillator of the present invention can be suitably used in a radiation inspection device. Alternatively, the oxide crystal of the present invention may be suitable for use as a magnetic refrigeration material.

[0014] Since the oxide crystals of the present invention are produced by hydrothermal synthesis, they can be grown at significantly lower temperatures compared to conventional methods, and bulk single crystals can be grown under high oxygen partial pressure conditions (an atmosphere rich in oxygen). As a result, the resulting crystals have suppressed oxygen defects and are defect-controlled crystals. Furthermore, in the present invention, there is no need to use iridium (Ir) or rhodium (Rh) components such as crucibles and dies used in conventional methods, thus reducing the production cost of the target crystals. In addition, by using hydrothermal synthesis, it is relatively easy to increase the size and mass-produce crystals compared to conventional methods. Moreover, since no harmful substances such as cadmium are used, it is an environmentally friendly material, and the manufacturing process is also environmentally friendly. [Brief explanation of the drawing]

[0015] [Figure 1] This is a schematic diagram showing the configuration of a radiation detector relating to one embodiment of the present invention. [Figure 2] This is a schematic diagram showing the configuration of a radiation inspection device according to one embodiment of the present invention. [Figure 3-1] This figure shows a microscopic image of the crystal obtained in Example 1 in the example. [Figure 3-2] This figure shows a microscopic image of the crystal obtained in Example 5 in the examples. [Figure 3-3]This figure shows a microscopic image of the crystal of Example 6 obtained in the examples. [Figure 3-4] This figure shows a microscopic image of the crystal obtained in Example 7 in the examples. [Figure 3-5] This figure shows a microscopic image of the crystal of Example 8 obtained in the example. [Figure 3-6] This figure shows a microscopic image of the crystal of Example 9a obtained in the examples. [Figure 3-7] This figure shows a microscopic image of the crystal of Example 10 obtained in the example. [Figure 3-8] This figure shows a microscopic image of the crystal of Example 11 obtained in the examples. [Figure 3-9] This figure shows a microscopic image of the crystal of Example 12 obtained in the example. [Figure 3-10] This figure shows a microscopic image of the crystal of Example 13 obtained in the example. [Figure 3-11] This figure shows a microscopic image of the crystal of Example 14 obtained in the example. [Figure 3-12] This figure shows a microscopic image of the crystal of Example 15 obtained in the examples. [Figure 3-13] This figure shows a microscopic image of the crystal of Example 16 obtained in the example. [Figure 3-14] This figure shows a microscopic image of the crystal of Example 17 obtained in the example. [Figure 3-15] This figure shows a microscopic image of the crystal of Example 18 obtained in the example. [Figure 3-16] This figure shows a microscopic image of the crystal of Example 19 obtained in the example. [Figure 3-17] This figure shows a microscopic image of the crystal of Example 20 obtained in the examples. [Figure 3-18] This figure shows a microscopic image of the crystal of Example 21 obtained in the example. [Figure 3-19] This figure shows a microscopic image of the crystal of Example 22 obtained in the example. [Figure 3-20] This figure shows a microscopic image of the crystal of Example 23 obtained in the example. [Figure 3-21] This figure shows a microscopic image of the crystal of Example 24 obtained in the example. [Figure 3-22] This figure shows a microscopic image of the crystal of Example 25 obtained in the examples. [Figure 3-23] This figure shows a microscopic image of the crystal of Example 26 obtained in the example. [Figure 3-24] This figure shows a microscopic image of the crystal of Example 27 obtained in the example. [Figure 3-25] This figure shows a microscopic image of the crystal of Example 28 obtained in the example. [Figure 4-1] This figure shows the results of powder X-ray diffraction measurements of the crystal in Example 1, and the simulation results of the diffraction chart of YTaO4 (monoclinic P12 / a1). [Figure 4-2] This figure shows the results of powder X-ray diffraction measurements of the crystal in Example 5, and the simulation results of the diffraction chart of YNbO4 (monoclinic system I 1 2 / a 1). [Figure 4-3] This figure shows the results of powder X-ray diffraction measurements of the crystal in Example 9a, and the simulation results of the diffraction chart of TbTaO4 (monoclinic P12 / a1). [Figure 4-4] This figure shows the results of powder X-ray diffraction measurements of the crystal in Example 9b, and the simulation results of the diffraction chart of TbTaO4 (monoclinic P12 / a1). [Figure 4-5] This figure shows the results of powder X-ray diffraction measurements of the crystal in Example 10, and the simulation results of the diffraction chart of TbNbO4 (monoclinic system I 1 2 / a 1). [Figure 4-6] This figure shows the results of powder X-ray diffraction measurements of the crystal in Example 11, and the simulation results of the diffraction chart of PrTaO4 (monoclinic P121 / c1). [Figure 4-7] This figure shows the results of powder X-ray diffraction measurements of the crystal in Example 12, and the simulation results of the diffraction chart of PrNbO4 (monoclinic system I 1 2 / a 1). [Figure 4-8] This figure shows the results of powder X-ray diffraction measurements of the crystal in Example 13, and the simulation results of the diffraction chart of GdTaO4 (monoclinic P12 / c1). [Figure 4-9]This figure shows the results of powder X-ray diffraction measurements of the crystal in Example 14, and the simulation results of the diffraction chart of GdNbO4 (monoclinic system I 1 2 / a 1). [Figure 4-10] This figure shows the results of powder X-ray diffraction measurements of the crystal in Example 15, and the simulation results of the diffraction chart of DyTaO4 (monoclinic P12 / c1). [Figure 4-11] This figure shows the results of powder X-ray diffraction measurements of the crystal in Example 16, and the simulation results of the diffraction chart of DyNbO4 (monoclinic system I 1 2 / a 1). [Figure 4-12] This figure shows the results of powder X-ray diffraction measurements of the crystal in Example 17, and the simulation results of the diffraction chart of HoTaO4 (monoclinic P12 / c1). [Figure 4-13] This figure shows the results of powder X-ray diffraction measurements of the crystal in Example 18, and the simulation results of the diffraction chart of HoNbO4 (monoclinic system I 1 2 / a 1). [Figure 4-14] This figure shows the results of powder X-ray diffraction measurements of the crystal in Example 19, and the simulation results of the diffraction chart of ErTaO4 (monoclinic P12 / c1). [Figure 4-15] This figure shows the results of powder X-ray diffraction measurements of the crystal in Example 20, and the simulation results of the diffraction chart of ErNbO4 (monoclinic system I 1 2 / a 1). [Figure 4-16] This figure shows the results of powder X-ray diffraction measurements of the crystal in Example 21, and the simulation results of the diffraction chart of YbTaO4 (monoclinic P12 / c1). [Figure 4-17] This figure shows the results of powder X-ray diffraction measurements of the crystal in Example 22, and the simulation results of the diffraction chart of YbNbO4 (monoclinic system I 1 2 / a 1). [Figure 4-18] This figure shows the results of powder X-ray diffraction measurements of the crystal in Example 23, and the simulation results of the diffraction chart of LuTaO4 (monoclinic P12 / c1). [Figure 4-19]This figure shows the results of powder X-ray diffraction measurements of the crystal in Example 24, and the simulation results of the diffraction chart of LuNbO4 (monoclinic system I 1 2 / a 1). [Figure 5] This figure shows the results of secondary ion mass spectrometry of the crystal in Example 1, specifically the concentrations of hydrogen and potassium. [Figure 6] This figure shows the PL spectra of sample 1, sample 3, and sample 4. [Figure 7] This figure shows the XRL spectra of sample 1, sample 2, and sample 4. [Figure 8] This figure shows the PL spectra of sample 6 and sample 9a. [Figure 9] This figure shows the XRL spectra of sample 6 and sample 9a. [Figure 10] This figure shows the PL spectra and excitation spectra of sample 9a and sample 9b. [Figure 11] This is a diagram showing the energy levels of Tb3+. [Figure 12] This figure shows the XRL spectra of sample 9a and sample 9b. [Figure 13] This figure shows the PL spectrum and excitation spectrum of sample 7. [Figure 14] This figure shows the PL spectrum and excitation spectrum of sample 8. [Figure 15] This figure shows the XRL spectra of sample 1, sample 7, and sample 8. [Figure 16] This figure shows the PL spectrum and excitation spectrum of sample 25. [Figure 17] This figure shows the PL spectrum and excitation spectrum of sample 26. [Figure 18] This figure shows the PL spectrum and excitation spectrum of sample 27. [Figure 19] This figure shows the XRL spectra of sample 23 and sample 25. [Figure 20] This figure shows the XRL spectra of sample 23, sample 26, and sample 27. [Figure 21]This figure shows the PL spectra of sample 23, sample 24, and sample 28. [Figure 22] This figure shows the XRL spectra of sample 23, sample 24, and sample 28. [Modes for carrying out the invention]

[0016] Embodiments of the present invention will be described below.

[0017] [Oxide crystals] <Composition> The oxide crystal of the present invention is of the general formula ((Y 1-p RE p ) 1-x Tb x )(Ta 1-y Nb y )O 4-z (In the formula, p, x, y, and z each independently satisfy 0≦p≦1, 0≦x≦1, 0≦y≦1, and -0.5≦z≦0.5, and RE is represented as RE, and contains a hydrogen atom (H). In the following, unless otherwise specified, the term "hydrogen" refers to a hydrogen atom.

[0018] In one embodiment, p, y, and z in the above general formula are zero, in which case the oxide crystal may be called a terbium-substituted yttrium tantalate crystal and can be written as Tb:YTaO4. When x is 1, the oxide crystal has a composition represented as TbTaO4, as all of the constituent elements yttrium (Y) are replaced with terbium (Tb).

[0019] In another embodiment, p, x, and z in the above general formula are zero, in which case the oxide crystal may be called a niobium-substituted yttrium tantalate crystal and can be written as Y(Ta,Nb)O4. When y is 1, the oxide crystal has a composition represented as YNbO4, as all of the constituent elements tantalum (Ta) are replaced with niobium (Nb).

[0020] In yet another aspect, p in the above general formula is zero, x satisfies the condition 0 < x ≤ 1, y satisfies the condition 0 < y ≤ 1, and z is zero. In this case, the oxide crystal can be referred to as a terbium-niobium-substituted yttrium tantalate crystal and can be represented as Tb:Y(Ta,Nb)O4. When x is 1, as a result of all of the Y in the oxide crystal being substituted by Tb, a composition in which a part of Ta in the composition represented by TbTaO4 is substituted by Nb (that is, Tb(Ta 1-y Nb y )O4 (where 0 < y ≤ 1)) can be obtained. Further, when y is 1, as a result of all of the Ta in the composition being substituted by Nb, it has a composition represented by TbNbO4.

[0021] Due to defects in the oxide crystal of the present invention, the number of oxygen atoms may be less than 4 or may be greater. However, by satisfying the condition -0.5 ≤ z ≤ 0.5 for z in the above general formula, a decrease in the transmittance of the crystal is sufficiently suppressed. In other words, in the above general formula, the value of z is preferably close to zero. Most preferably, z in the above general formula is zero. In this case, the oxide crystal has a composition represented by the general formula ((Y 1-p RE p ) 1-x Tb x )(Ta 1-y Nb y )O4 (where 0 ≤ p ≤ 1, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1).

[0022] In the oxide crystal of the present invention, p may satisfy the condition 0 < p ≤ 1. In this case, the oxide crystal may be expressed as Tb:(Y,RE)TaO4, Tb:(RE)TaO4, (Y,RE)(Ta,Nb)O4, (RE)(Ta,Nb)O4, (Y,RE)NbO4, (RE)NbO4, Tb:(Y,RE)(Ta,Nb)O4, Tb:(RE)(Ta,Nb)O4, etc. Here, RE is at least one element selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). In a preferred embodiment, p in the above general formula satisfies 0.01 ≤ p ≤ 1. Thereby, the oxide crystal of the present invention has a density comparable to CdWO4 and ρ·(Z eff ) 4 and may have. Here, ρ·(Z eff ) 4 is the value of the product of the density (ρ) and the fourth power of the effective atomic number (Z eff ) and is known to be in a proportional relationship with the radiation stopping power (stopping power). Thereby, the oxide crystal has the stopping power required for a scintillator and may have an X-ray stopping power comparable to CdWO4.

[0023] It should be noted that the above general formula represents the stoichiometric composition of the oxide crystals of the present invention. As will be described later, the oxide crystals of the present invention are grown by hydrothermal synthesis, and the resulting crystals are obtained with the most stable composition. Therefore, even if there is a deviation from the target composition, the difference is expected to be very small. On the other hand, when measuring the composition of the crystals actually obtained, there may be cases where the sum of Y and RE elements does not equal 1 mole, or where the molar ratio of (Y+RE+Tb) to (Ta+Nb) is not exactly 1:1. These are due to, for example, a deviation between the stoichiometric composition and the harmonious melt composition (congluent melt composition), which is the most stable composition, the inclusion of H and / or other arbitrary constituent elements described later, or the influence of measurement errors.

[0024] In one embodiment, the concentration of hydrogen contained in the oxide crystal of the present invention is 1 × 10⁻⁶ 16 atoms / cm 3 The above 1 x 10 23 atoms / cm 3 The range is as follows, preferably 1 × 10 17 atoms / cm 3 The above 1 x 10 22 atoms / cm 3 The range is as follows, more preferably 1 × 10 18 atoms / cm 3 The above 1 x 10 22 atoms / cm 3 The range is as follows:

[0025] The method for measuring the hydrogen concentration in the oxide crystal of the present invention is not particularly limited and can be confirmed by conventional methods, for example, secondary ion mass spectrometry (SIMS) can be used. The same applies to the concentrations of elements other than hydrogen (for example, the concentrations of arbitrary constituent elements (alkali metals and / or alkaline earth metals) described later). Here, when using SIMS, the hydrogen concentration is taken as the value at a depth of 3 μm, and the concentrations of alkali metals and alkaline earth metals are taken as the values ​​at a depth of 6 μm. An example of SIMS measurement will be described in the Examples section.

[0026] <Optional constituent elements> The oxide crystals of the present invention may further contain any constituent elements other than the above-mentioned Y, RE elements (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and / or Lu), Tb, Ta, Nb, O, and H.

[0027] In one embodiment, the oxide crystal of the present invention further contains an alkali metal and / or an alkaline earth metal as an optional constituent element. In one exemplary embodiment, the alkali metal is selected from the group consisting of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr), and is preferably selected from the group consisting of K, Rb, and Cs. The alkaline earth metal is selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra), and is preferably selected from the group consisting of Ca, Sr, and Ba. The alkali metal and alkaline earth metal may be present individually or in combination of two or more. It is expected that the presence of an alkali metal and / or alkaline earth metal in the oxide crystal will deactivate defects within the crystal.

[0028] In an embodiment of the present invention in which the oxide crystal contains alkali metals and / or alkaline earth metals, the concentration of the alkali metals and / or alkaline earth metals is 1 × 10⁻⁶ 12 atoms / cm 3 The above 1 x 10 20 atoms / cm 3 The range is as follows, preferably 1 × 10 13 atoms / cm 3 The above 1 x 10 19 atoms / cm 3 The range is as follows, more preferably 1 × 10 14 atoms / cm 3 The above 1 x 10 19 atoms / cm 3 The range is as follows:

[0029] <Crystal structure> In one embodiment, the oxide crystal of the present invention belongs to the monoclinic crystal system and is located in one of the following space groups: P12 / a1, P12 / c1 (space group 13 of the International Tables for Crystallography (also simply called the International Table(s))), P121 / c1 (space group 14), or I12 / a1 (space group 15). Tables 1 to 18 below list representative examples of iodine bodies: YTaO4 (P 1 2 / a 1), YNbO4 (I 1 2 / a 1), TbTaO4 (P 1 2 / a 1), TbNbO4 (I 1 2 / a 1), PrTaO4 (P 1 21 / c 1), PrNbO4 (I 1 2 / a 1), GdTaO4 (P 1 2 / c 1), GdNbO4 (I 1 2 / a 1), DyTaO4 (P 1 2 / c 1), DyNbO4 (I 1 2 / a 1), HoTaO4 (P 1 2 / c 1), HoNbO4 (I 1 2 / a 1), ErTaO4 (P 1 2 / c 1), ErNbO4 (I 1 1 The crystal parameters and atomic coordinate positions of 2 / a 1), YbTaO4(P 1 2 / c 1), YbNbO4(I 1 2 / a 1), LuTaO4(P 1 2 / c 1), and LuNbO4(I 1 2 / a 1) are shown. Note that there are reports in which P 1 2 / c 1 is treated as having the same structure as P 1 2 / a 1. Furthermore, it is preferable that the oxide crystals of the present invention have a single-phase crystal structure as determined by powder X-ray diffraction.

[0030] The method for measuring the space group is not particularly limited, but for example, if the composition (design composition or result of compositional analysis) and structure of the target crystal are specified (or estimated or assumed), the space group can be estimated by obtaining a powder X-ray diffraction chart (also referred to as a simulation result in this specification) of a crystal having that composition and structure (or something similar) using information obtained from generally available databases, and comparing the simulation result with the powder X-ray diffraction measurement result of the target crystal. Specific examples of this method will be described in the Examples section.

[0031] Table 1

[0032] Table 2

[0033] Table 3

[0034] Table 4

[0035] Table 5

[0036] Table 6

[0037] Table 7

[0038] Table 8

[0039] Table 9

[0040] Table 10

[0041] Table 11

[0042] Table 12

[0043] Table 13

[0044] Table 14

[0045] Table 15

[0046] Table 16

[0047] Table 17

[0048] Table 18

[0049] In the oxide crystal of the present invention, the lattice constant may change due to the solid solution of RE and / or Tb, which are Y substitution elements, relative to the composition of YTaO4. However, 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, and the structure maintains that belongs to the P12 / a1 space group, P12 / c1 space group, or P121 / c1 space group. On the other hand, when the amount of solid solution of Nb, which is a Ta substitution element relative to the composition of (Y,RE)TaO4, exceeds a certain amount, the oxide crystal takes on a structure belonging to I12 / a1.

[0050] <Main Features> The oxide crystal of the present invention can have transparency comparable to that of conventional CdWO4. When the oxide crystal of the present invention is used as a scintillator, light generated within the scintillator crystal can be efficiently transmitted, thus preventing a decrease in the amount of light emitted.

[0051] The oxide crystal of the present invention has a density and ρ·(Z) comparable to that of CdWO4. eff ) 4 It may have the above ρ·(Z eff ) 4 The value of is 0.8 or greater as a ratio to the value in CdWO4. Here, the value of the ratio is preferably 0.85 or greater, more preferably 0.9 or greater, even more preferably 0.95 or greater, even more preferably 1 or greater, and most preferably greater than 1.

[0052] Indicators representing the scintillation characteristics of the oxide crystal of the present invention include, for example, the amount of light emitted, decay time (decay characteristics), and afterglow (afterglow characteristics). In one preferred embodiment, the oxide crystal of the present invention may exhibit a luminescence amount comparable to or exceeding that of conventional CdWO4. In another preferred embodiment, the oxide crystal of the present invention may exhibit a practically acceptable scintillation decay time. In yet another preferred embodiment, the oxide crystal of the present invention may exhibit afterglow comparable to that of CdWO4.

[0053] In the context described above, it should be noted that the oxide crystal of the present invention does not necessarily require all properties to surpass those of CdWO4. That is, depending on the various applications as a scintillator, as exemplified below, the oxide crystal of the present invention can be considered a practically useful scintillator if it satisfies the scintillation properties required for that application. In other words, the oxide crystal of the present invention can be said to be environmentally friendly, both as a scintillator itself and in its manufacturing method, because it does not contain harmful substances such as cadmium. Even if it has properties that are slightly inferior to (not comparable to) those of CdWO4, it can still serve as a scintillator that can replace CdWO4.

[0054] Furthermore, in one embodiment, the oxide crystal of the present invention can function as a magnetic refrigeration material for ultra-low temperatures because its Néel temperature is at extremely low temperatures, for example, below a few K.

[0055] [Method for manufacturing oxide crystals] Next, the method for producing the oxide crystals described above will be explained.

[0056] <First Embodiment> A method for producing oxide crystals according to one embodiment of the present invention includes growing crystals from raw materials containing each element to be included in the crystal by hydrothermal synthesis in the presence of a mineralizing agent containing alkali metals and / or alkaline earth metals, or an acid mineralizing agent, or a mixed mineralizing agent of both. Here, the term "hydrothermal synthesis" as used herein refers to a method in which water is used as the solvent in a "solvothermal method". An example of this production method is described below.

[0057] <Step S110: Step to prepare raw materials> In step S110, the raw materials necessary to obtain a compound that satisfies the composition of the target crystal are prepared.

[0058] Specifically, raw materials containing yttrium (Y) and / or RE (RE is selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu) are prepared and / or raw materials containing terbium (Tb), and raw materials containing tantalum (Ta) and / or raw materials containing niobium (Nb), and one or more compounds from these are made into oxides. For convenience, in this specification, the raw materials containing each constituent element prepared in step S110 will also be referred to as raw materials of each constituent element. For example, "raw material containing Y" and "raw material of Y" are synonymous.

[0059] The raw materials can include elemental elements, oxides, hydroxides, halides, inorganic salts (sulfates, nitrates, carbonates, etc.), and organic salts (acetates, etc.). Compounds other than elemental elements may be anhydrous or hydrated. The following are non-limiting examples of raw materials that can be used in the manufacturing method of this embodiment.

[0060] For example, Y2O3 can be used as the raw material for Y. For example, an oxide of RE (such as RE2O3) can be used as a raw material for RE. For example, Ta2O5 can be used as a raw material for Ta. For example, Tb4O7 and Tb2O3 can be used as raw materials for Tb. For example, Nb2O5 can be used as a raw material for Nb.

[0061] Each raw material is prepared such that Y, RE, Ta, Tb, and Nb are present in atomic ratios that satisfy the relation (Y+RE):Ta:Tb:Nb=1-x:1-y:x:y (where (Y+RE)=1, 0≦x≦1, 0≦y≦1). Here, a raw material mixture containing each raw material may be prepared as needed.

[0062] For example, if the composition of the target oxide crystal is YTaO4, you can use Y2O3 and Ta2O5 and weigh them so that the molar ratio of Y2O3:Ta2O5 = 1:1, in which case RE, Tb and Nb raw materials are not needed. Also, if the composition of the target oxide crystal is (Y 0.9 Tb 0.1 If the composition is TaO4, then Y2O3, Ta2O5, and Tb4O7 should be used and weighed so that the molar ratio Y2O3:Ta2O5:Tb4O7 = 0.9:1:0.05 is satisfied, and in this case, RE and Nb raw materials are not required. Here, if Tb2O3 is used as the raw material for Tb, then weighing should be satisfied so that the molar ratio Y2O3:Ta2O5:Tb2O3 = 0.9:1:0.1 is satisfied. Also, if the composition of the target oxide crystal is Y(Ta 0.9 Nb 0.1 If the target oxide crystal composition is O4, Y2O3, Ta2O5, and Nb2O5 should be used and weighed to satisfy a molar ratio of Y2O3:Ta2O5:Nb2O5=1:0.9:0.1. In this case, RE and Tb raw materials are not required. If the target oxide crystal composition is YNbO4, Y2O3 and Nb2O5 should be used and weighed to satisfy a molar ratio of Y2O3:Nb2O5=1:1. In this case, RE, Tb, and Ta raw materials are not required. If the target oxide crystal composition is TbTaO4, Ta2O5 and Tb4O7 should be used and weighed to satisfy a molar ratio of Ta2O5:Tb4O7=1:0.5. In this case, Y, RE, and Nb raw materials are not required. Here, if Tb2O3 is used as the raw material for Tb, it should be weighed to satisfy a molar ratio of Ta2O5:Tb2O3=1:1. Furthermore, if the composition of the target oxide crystal is RETaO4, RE2O3 and Ta2O5 can be used and weighed to satisfy a molar ratio of RE2O3:Ta2O5=1:1, in which case Y, Tb, and Nb raw materials are not required. Similarly, if the composition of the target oxide crystal is RENbO4, RE2O3 and Nb2O5 can be used and weighed to satisfy a molar ratio of RE2O3:Nb2O5=1:1, in which case Y, Tb, and Ta raw materials are not required.

[0063] <Step S120: Step of growing crystals from raw materials by hydrothermal synthesis in the presence of a mineralizing agent> In step S120, the raw materials prepared in step S110 (or a mixture of raw materials prepared by mixing each raw material) are grown as crystals by hydrothermal synthesis in the presence of a mineralizing agent.

[0064] As mineralizing agents, mineralizing agents containing alkali metals and / or alkaline earth metals, acidic mineralizing agents, or mixed mineralizing agents of both can be used. Mineralizing agents containing alkali metals and / or alkaline earth metals are compounds containing alkali metals and / or alkaline earth metals, and for example, hydroxides and inorganic salts (carbonates, etc.) of alkali metals and / or alkaline earth metals can be used. Non-limiting examples of mineralizing agents include, for example, KOH, K2CO3, RbOH, Rb2CO3, CsOH, Cs2CO3, Ca(OH)2, CaCO3, Sr(OH)2, SrCO3, Ba(OH)2, BaCO3, etc., and it is preferable to select at least one from the group consisting of these compounds. Examples of acid mineralizers include, but are not limited to, hydrochloric acid, nitric acid, sulfuric acid, formic acid, and phosphoric acid. Furthermore, alkali metals and / or alkaline earth metals contained in the mineralizing agent, or elements contained in the acid mineralizing agent, may be present in the final oxide crystal.

[0065] The method for preparing the solution (reaction solution) used for crystal growth by hydrothermal synthesis is not particularly limited. For example, if a raw material mixture is prepared in step S110 described above, a solution of the mineralizing agent may be added to the raw material mixture, and may be further mixed as needed. Alternatively, a mineralizing agent (preferably in powder or tablet form) may be added to the raw material mixture, and may be further mixed as needed. Alternatively, each of the above raw materials may be added to an aqueous solution of the mineralizing agent and mixed as appropriate. Here, the concentration of the mineralizing agent in the final solution is preferably in the range of 1 M to 50 M, more preferably in the range of 3 M to 45 M, even more preferably in the range of 5 M to 40 M, and particularly preferably in the range of 7 M to 30 M. Within the above concentration range, the upper limit may be less than 30 M. In exemplary embodiments, the concentration of the mineralizing agent may be in the range of 1 M or more and less than 30 M, in the range of 1 M or more and 25 M or less, in the range of 1 M or more and 20 M or less, in the range of 3 M or more and 20 M or less, in the range of 5 M or more and 20 M or less, or in the range of 7 M or more and 20 M or less.

[0066] Here, the crystal growth conditions (specifically temperature conditions) by hydrothermal synthesis can be adjusted by the type of alkali metal and / or alkaline earth metal contained in the mineralizing agent used, and the concentration of the mineralizing agent. Although certain care is required when handling highly alkaline solutions, the desired solution can be prepared by appropriately adjusting the concentration of the mineralizing agent. It is also preferable to select the type of mineralizing agent depending on the raw materials used and / or the type of constituent elements of the target crystal.

[0067] The crystal growth conditions for hydrothermal synthesis are not particularly limited and can be set according to the size of the hydrothermal synthesis vessel (reaction vessel) used. In one exemplary embodiment, the temperature is preferably in the range of 400°C to 800°C. This ensures that the desired crystals are reliably obtained. If the temperature is below 400°C, the desired crystals may not be formed, and if the temperature exceeds 800°C, it may exceed the heat resistance temperature of the reaction vessel. Furthermore, from the viewpoint of increasing the size of the crystals, the temperature is preferably between 400°C and 750°C. The pressure is preferably in the range of 25 MPa to 250 MPa. In this context, the pressure is intended to be such that the maximum pressure achieved during crystal growth is within the above range. This pressure varies depending on the amount of water contained in the reaction vessel, the size of the ampoule (sealed container) holding the reaction solution, the temperature conditions, etc. In an exemplary embodiment, the maximum pressure achieved may be in the range of 30 MPa to 250 MPa, 50 MPa to 225 MPa, or 75 MPa to 200 MPa.

[0068] The time required for hydrothermal synthesis can be adjusted as appropriate to ensure the crystal growth is completed, depending on the type and amount of raw materials used. Here, two or more temperature conditions may be set within the aforementioned temperature range to establish a predetermined temperature profile. Such a temperature profile can be designed considering factors such as improving the homogeneity and stability of the solution, and more efficiently generating the desired crystals. An example of a specific temperature profile is shown in the embodiments described later.

[0069] In the manufacturing method according to this embodiment, crystals are grown by hydrothermal synthesis of raw materials (or a mixture of raw materials) under significantly lower temperature conditions compared to conventional methods. For example, in the CZ method, due to the melting point of the target crystal, a phenomenon in which certain components evaporate from the melt (or its interface) during the crystal growth process is likely to occur, and such decomposition and evaporation phenomena may also occur in the grown crystal, potentially causing defects in the grown crystal. However, in the manufacturing method of the present invention, such decomposition and evaporation phenomena are less likely to occur, thus suppressing defects that may occur in the grown crystal. Furthermore, in general, with hydrothermal synthesis, the resulting crystal is obtained with the most stable composition, and although there may be a slight deviation from the target composition, even if such a deviation occurs, the difference from the target composition is considered to be very small and is adjustable.

[0070] <Second Embodiment> Another embodiment of the present invention provides a method for producing oxide crystals of the general formula ((Y 1-p RE p ) 1-x Tb x )(Ta 1-y Nb y )O 4-z The process involves growing one or more raw material compounds having a composition represented by the formula (wherein p, x, y, and z are each independently satisfying 0≦p≦1, 0≦x≦1, 0≦y≦1, and -0.5≦z≦0.5, and RE is selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) into crystals by hydrothermal synthesis in the presence of a mineralizing agent containing alkali metals and / or alkaline earth metals, or an acid mineralizing agent, or a mixed mineralizing agent of both. An example of this production method is described below.

[0071] <Step S210: Step to prepare the starting compound> In step S210, the starting compounds necessary to obtain a compound that satisfies the composition of the target crystal are prepared.

[0072] Specifically, one or more compounds having compositions such as YTaO4, Tb:YTaO4, TbTaO4, Y(Ta,Nb)O4, YNbO4, Tb:Y(Ta,Nb)O4, Tb(Ta,Nb)O4, TbNbO4, Tb:(Y,RE)TaO4, Tb:(RE)TaO4, (Y,RE)(Ta,Nb)O4, (RE)(Ta,Nb)O4, (Y,RE)NbO4, (RE)NbO4, Tb:(Y,RE)(Ta,Nb)O4, and Tb:(RE)(Ta,Nb)O4 are prepared as raw material compounds. Here, the raw material compounds may have fewer than 4 oxygen atoms. In the hydrothermal synthesis method described later, the raw material compounds are treated in an atmosphere rich in oxygen, so oxygen vacancies in the final oxide crystal can be suppressed. Furthermore, the raw material compound may be a product (powder) obtained by calcining a mixture (mixed powder) of the raw materials (powder) exemplified in step S110 of the first embodiment described above.

[0073] <Step S220: Step of growing crystals of the raw material compound by hydrothermal synthesis in the presence of a mineralizing agent> In step S220, the raw material compound prepared in step S210 is grown as a crystal by hydrothermal synthesis in the presence of a mineralizing agent.

[0074] The type of mineralizing agent used in step S220, the method for preparing the solution used for crystal growth by hydrothermal synthesis, the concentration of the mineralizing agent in the solution, and the crystal growth conditions by hydrothermal synthesis are the same as those in step S120 of the first embodiment described above, so a detailed explanation is omitted here.

[0075] In the manufacturing method according to this embodiment, the raw material compound is grown as a crystal by hydrothermal synthesis under significantly lower temperature conditions compared to conventional crystal growth methods. The raw material compound may contain defects resulting from its manufacturing method, but even if the raw material compound contains such defects, the crystal grown by hydrothermal synthesis results in the most stable composition, and defects in the crystal are significantly reduced and suppressed.

[0076] [Uses of oxide crystals] The oxide crystals of the present invention, which can be manufactured as described above, are not particularly limited in their applications, but are useful as optical materials, magnetic materials, and the like. In a typical embodiment, the oxide crystals of the present invention are suitable for use as scintillators. In particular, because the oxide crystals of the present invention have very few defects, scintillators made from these crystals may have properties such as density, fluorescence decay time, and fluorescence output comparable to existing materials, and may even exhibit scintillation properties comparable to or better than those of CdWO4. Alternatively, in another embodiment, the oxide crystals of the present invention may be suitable for use as magnetic refrigeration materials because their Néel temperature is extremely low, for example, below a few K. Alternatively, in yet another embodiment, the oxide crystals of the present invention may be suitable for use as laser materials capable of oscillating at various wavelengths.

[0077] [Uses of scintillators] The use of the above-mentioned scintillator, which is in crystalline form, is not particularly limited, but it is preferably used in a radiation detector. The configuration of the radiation detector is not particularly limited, and a configuration similar to that of conventional radiation detectors can be adopted. Specifically, as schematically shown in Figure 1, a radiation detector 10 according to one embodiment of the present invention comprises a scintillator 11 made of the above-mentioned oxide crystal and a photoelectric converter 12 (for example, a photomultiplier tube (PMT), silicon photomultiplier (SiPM), solid-state image sensor (CCD), avalanche photodiode (APD), multipixel photon counter (MPPC), etc.) that detects light L emitted from the scintillator 11 and converts it into an electrical signal. By using the above-mentioned scintillator made of oxide crystal instead of the scintillator used in conventional radiation detectors, an improvement in the accuracy of radiation detection can be expected.

[0078] Furthermore, it is possible to configure a radiation inspection device by using the above-mentioned radiation detector and combining it with a radiation source that irradiates a subject with radiation. For example, as schematically shown in Figure 2, a radiation inspection device 20 according to one embodiment of the present invention comprises a radiation detector 10 (see Figure 1) and a radiation source 23, wherein the radiation source 23 irradiates the subject Sbj with radiation R, and the radiation detector 10 is configured to detect radiation E that penetrates the subject Sbj. In this case, the radiation detector 10 emits light L when excited by radiation E, and the photoelectric converter 12 detects the light L emitted from the scintillator 11 and converts it into an electrical signal. Such a radiation inspection device 20 can be used, for example, as an inspection device for non-destructive testing such as a non-destructive testing detector, a resource exploration detector, or a high-energy physics detector, or as a medical diagnostic device such as a medical image processing device (X-ray CT, etc.).

[0079] Alternatively, the aforementioned radiation detectors may also be applied to the detection of radiation (such as gamma rays) emitted from a subject. Specifically, examples include medical image processing equipment such as SPECT (Single Photon Emission Computed Tomography) devices, exploration equipment for underground resource exploration, hazardous material detection equipment, and equipment used in research and development fields related to space, such as cosmic ray and astrophysics.

[0080] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples. [Examples]

[0081] [Crystal Manufacturing] <Example 1: YTaO4> As raw materials for Y and Ta, Y2O3 and Ta2O5 (powder form, manufactured by Furuchi Chemical Co., Ltd.) were prepared. Each raw material was weighed and mixed so as to satisfy the ratio of YTaO4, and a powdery raw material mixture was obtained. The obtained raw material mixture, KOH as a mineralizer (tablets in a quantity corresponding to a 20M aqueous solution), and pure water (0.7 mL) were put into a silver ampoule (diameter 5 mm × length 10 cm) and sealed. After that, this sealed ampoule was put into a reaction vessel containing pure water, and hydrothermal synthesis was carried out. As the conditions for hydrothermal synthesis, a temperature profile was used in which the temperature was raised to 700 °C over 12 hours and held for 100 hours to complete crystal growth. The maximum pressure reached at this time was 188 MPa. In addition, as the temperature reduction program from 700 °C to room temperature at the end of crystal growth, 12 hours was set, and then natural cooling was performed. Thereby, the crystal of Example 1 was obtained.

[0082] <Example 2: YTa 0.99 Nb 0.01 O4> As raw materials for Y, Ta and Nb, Y2O3, Ta2O5 and Nb2O5 (powder form, manufactured by Furuchi Chemical Co., Ltd.) were prepared. Each raw material was weighed and mixed so as to satisfy the ratio of YTa 0.99 Nb 0.01 O4, and a powdery raw material mixture was obtained. The subsequent procedures and the conditions for crystal growth were the same as those in Example 1, and the crystal of Example 2 was obtained. In addition, the maximum pressure reached during crystal growth was 135 MPa.

[0083] <Example 3: YTa 0.98 Nb 0.02 O4> Y2O3, Ta2O5 and Nb2O5 were weighed and mixed so as to satisfy the ratio of YTa 0.98 Nb 0.02 O4, and a powdery raw material mixture was obtained. The subsequent procedures and the conditions for crystal growth were the same as those in Example 1, and the crystal of Example 3 was obtained. In addition, the maximum pressure reached during crystal growth was 169 MPa.

[0084] <Example 4: YTa 0.9 Nb 0.1 O4> Y2O3, Ta2O5 and Nb2O5 were weighed and mixed so as to satisfy the ratio of YTa 0.9Nb 0.1 Weighed and mixed them so as to satisfy the ratio of O4 to obtain a powdery raw material mixture. The subsequent procedures and crystal growth conditions were the same as those in Example 1 to obtain the crystals of Example 4. Note that the maximum pressure reached during crystal growth was 131 MPa.

[0085] <Example 5: YNbO4> As raw materials for Y and Nb, Y2O3 and Nb2O5 (powdery, manufactured by Furuchi Chemical Co., Ltd.) were prepared. Each raw material was weighed and mixed so as to satisfy the ratio of YNbO4 to obtain a powdery raw material mixture. The subsequent procedures and crystal growth conditions were the same as those in Example 1 except that the holding time at 700 °C was 150 hours to obtain the crystals of Example 5. Note that the maximum pressure reached during crystal growth was 168 MPa.

[0086] <Example 6: Y 0.99 Tb 0.01 TaO4> As raw materials for Y, Tb and Ta, Y2O3, Tb4O7 and Ta2O5 (powdery, manufactured by Furuchi Chemical Co., Ltd.) were prepared. Each raw material was weighed and mixed so as to satisfy the ratio of Y 0.99 Tb 0.01 TaO4 to obtain a powdery raw material mixture. The subsequent procedures and crystal growth conditions were the same as those in Example 1 to obtain the crystals of Example 6. Note that the maximum pressure reached during crystal growth was 187 MPa.

[0087] <Example 7: Y 0.99 Eu 0.01 TaO4> As raw materials for Y, Eu and Ta, Y2O3, Eu2O3 and Ta2O5 (powdery, manufactured by Furuchi Chemical Co., Ltd.) were prepared. Each raw material was weighed and mixed so as to satisfy the ratio of Y 0.99 Eu 0.01The raw materials were weighed to meet the required ratio for TaO4 and mixed to obtain a powdered mixture. The obtained raw material mixture, KOH as a mineralizing agent (in the form of tablets equivalent to a 20M aqueous solution), and pure water (0.65 mL) were placed in a silver ampoule (5 mm in diameter × 10 cm in length) and sealed. This sealed ampoule was then placed in a reaction vessel containing pure water, and hydrothermal synthesis was carried out. The hydrothermal synthesis conditions involved raising the temperature to 700°C over 12 hours and holding it for 60 hours to complete crystal growth. The maximum pressure reached during this process was 139 MPa. After crystal growth was complete, natural cooling was performed. This yielded the crystals of Example 7.

[0088] <Example 8: Y 0.99 Pr 0.01 TaO4> Y, Pr, and Ta are used as raw materials, Y2O3, Pr6O 11 And Ta2O5 (powder, manufactured by Furuuchi Chemical Co., Ltd.) was prepared. Each raw material was Y 0.99 Pr 0.01 The raw materials were weighed and mixed to meet the required ratio of TaO4, and a powdered raw material mixture was obtained. The subsequent procedures and crystal growth conditions were the same as in Example 7 to obtain the crystals of Example 8. The maximum pressure achieved during crystal growth was 148 MPa.

[0089] <Example 9a: TbTaO4> Tb4O7 and Ta2O5 (in powder form, manufactured by Furuuchi Chemical Co., Ltd.) were prepared as raw materials for Tb and Ta. Each raw material was weighed to satisfy the ratio of TbTaO4 and mixed to obtain a powdered raw material mixture. The obtained raw material mixture, KOH as a mineralizing agent (in the form of tablets equivalent to a 20M aqueous solution), and pure water (0.7 mL) were placed in a silver ampoule (5 mm in diameter × 10 cm in length) and sealed. This sealed ampoule was then placed in a reaction vessel containing pure water, and hydrothermal synthesis was carried out. The conditions for hydrothermal synthesis were a temperature profile in which the temperature was raised to 700°C over 12 hours, held for 24 hours, and then cooled to 600°C over 100 hours to complete crystal growth. The maximum pressure reached during this process was 150 MPa. The cooling program from 600°C to room temperature at the end of crystal growth was set to 12 hours, after which natural cooling was allowed. This yielded the crystal of Example 9a.

[0090] <Example 9b: TbTaO4> As a starting compound, a compound powder having the composition represented by TbTaO4 (a powder obtained by calcining a mixed powder of Tb4O7 and Ta2O5) was prepared. This compound powder, KOH as a mineralizing agent (a tablet equivalent to a 20M aqueous solution), and pure water (0.7 mL) were placed in a silver ampoule (5 mm in diameter × 10 cm in length) and sealed. This sealed ampoule was then placed in a reaction vessel containing pure water, and hydrothermal synthesis was carried out. The hydrothermal synthesis conditions were the same as in Example 9a, and the crystals of Example 9b were obtained. The maximum pressure reached during crystal growth was 150 MPa.

[0091] <Example 10: TbNbO4> Tb4O7 and Nb2O5 (in powder form, manufactured by Furuuchi Chemical Co., Ltd.) were prepared as raw materials for Tb and Nb. Each raw material was weighed to satisfy the ratio of TbNbO4 and mixed to obtain a powdered raw material mixture. The obtained raw material mixture, KOH as a mineralizing agent (in the form of tablets equivalent to a 20M aqueous solution), and pure water (0.7 mL) were placed in a silver ampoule (5 mm in diameter x 10 cm in length) and sealed. This sealed ampoule was then placed in a reaction vessel containing pure water, and hydrothermal synthesis was carried out. The hydrothermal synthesis conditions involved raising the temperature to 670°C over 12 hours and holding it for 100 hours to complete crystal growth. The maximum pressure reached during this process was 146 MPa. After crystal growth, natural cooling was performed. This yielded the crystals of Example 10.

[0092] <Example 11: PrTaO4> As raw materials for Pr and Ta, Pr6O 11 PrTaO4 and Ta2O5 (powdered, manufactured by Furuuchi Chemical Co., Ltd.) were prepared. Each raw material was weighed to satisfy the ratio of PrTaO4 and mixed to obtain a powdered raw material mixture. The obtained raw material mixture, KOH as a mineralizing agent (a tablet equivalent to a 20M aqueous solution), and pure water (0.65 mL) were placed in a silver ampoule (5 mm in diameter × 10 cm in length) and sealed. This sealed ampoule was then placed in a reaction vessel containing pure water, and hydrothermal synthesis was carried out. The conditions for hydrothermal synthesis were a temperature profile in which the temperature was raised to 700°C over 12 hours and held for 40 hours to complete crystal growth. The maximum pressure reached during this process was 162 MPa. After crystal growth, natural cooling was performed. This yielded the crystals of Example 11.

[0093] <Example 12: PrNbO4> As raw materials for Pr and Nb, Pr6O 11 And Nb2O5 (in powder form, manufactured by Furuuchi Chemical Co., Ltd.) was prepared. Each raw material was weighed to satisfy the ratio of PrNbO4 and mixed to obtain a powdered raw material mixture. The subsequent procedures and crystal growth conditions were the same as in Example 11 to obtain the crystal of Example 12. The maximum pressure achieved during crystal growth was 155 MPa.

[0094] <Example 13: GdTaO4> As raw materials for Gd and Ta, Gd2O3 and Ta2O5 (in powder form, manufactured by Furuuchi Chemical Co., Ltd.) were prepared. Each raw material was weighed to satisfy the ratio of GdTaO4 and mixed to obtain a powdered raw material mixture. The subsequent procedure and crystal growth conditions were the same as in Example 11, except that the holding time at 700°C was 60 hours, to obtain the crystal of Example 13. The maximum pressure reached during crystal growth was 156 MPa.

[0095] <Example 14: GdNbO4> As raw materials for Gd and Nb, Gd2O3 and Nb2O5 (in powder form, manufactured by Furuuchi Chemical Co., Ltd.) were prepared. Each raw material was weighed to satisfy the ratio of GdNbO4 and mixed to obtain a powdered raw material mixture. The subsequent procedures and crystal growth conditions were the same as in Example 13 to obtain the crystals of Example 14. The maximum pressure achieved during crystal growth was 160 MPa.

[0096] <Example 15: DyTaO4> Dy2O3 and Ta2O5 (in powder form, manufactured by Furuuchi Chemical Co., Ltd.) were prepared as raw materials for Dy and Ta. Each raw material was weighed to satisfy the ratio of DyTaO4 and mixed to obtain a powdered raw material mixture. The subsequent procedures and crystal growth conditions were the same as in Example 13 to obtain the crystals of Example 15. The maximum pressure achieved during crystal growth was 172 MPa.

[0097] <Example 16: DyNbO4> Dy2O3 and Nb2O5 (in powder form, manufactured by Furuuchi Chemical Co., Ltd.) were prepared as raw materials for Dy and Nb. Each raw material was weighed to satisfy the ratio of DyNbO4 and mixed to obtain a powdered raw material mixture. The subsequent procedures and crystal growth conditions were the same as in Example 11 to obtain the crystal of Example 16. The maximum pressure achieved during crystal growth was 173 MPa.

[0098] <Example 17:HoTaO4> Ho2O3 and Ta2O5 (in powder form, manufactured by Furuuchi Chemical Co., Ltd.) were prepared as raw materials for Ho and Ta. Each raw material was weighed to satisfy the ratio of HoTaO4 and mixed to obtain a powdered raw material mixture. The subsequent procedures and crystal growth conditions were the same as in Example 11 to obtain the crystals of Example 17. The maximum pressure achieved during crystal growth was 172 MPa.

[0099] <Example 18: HoNbO4> As raw materials for Ho and Nb, Ho2O3 and Nb2O5 (in powder form, manufactured by Furuuchi Chemical Co., Ltd.) were prepared. Each raw material was weighed to satisfy the ratio of HoNbO4 and mixed to obtain a powdered raw material mixture. The subsequent procedures and crystal growth conditions were the same as in Example 13 to obtain the crystals of Example 18. The maximum pressure achieved during crystal growth was 193 MPa.

[0100] <Example 19: ErTaO4> As raw materials for Er and Ta, Er2O3 and Ta2O5 (in powder form, manufactured by Furuuchi Chemical Co., Ltd.) were prepared. Each raw material was weighed to satisfy the ratio of ErTaO4 and mixed to obtain a powdered raw material mixture. The subsequent procedures and crystal growth conditions were the same as in Example 11 to obtain the crystals of Example 19. The maximum pressure achieved during crystal growth was 148 MPa.

[0101] <Example 20: ErNbO4> As raw materials for Er and Nb, Er2O3 and Nb2O5 (in powder form, manufactured by Furuuchi Chemical Co., Ltd.) were prepared. Each raw material was weighed to satisfy the ratio of ErNbO4 and mixed to obtain a powdered raw material mixture. The subsequent procedures and crystal growth conditions were the same as in Example 13 to obtain the crystals of Example 20. The maximum pressure achieved during crystal growth was 153 MPa.

[0102] <Example 21: YbTaO4> Yb2O3 and Ta2O5 (in powder form, manufactured by Furuuchi Chemical Co., Ltd.) were prepared as raw materials for Yb and Ta. Each raw material was weighed to satisfy the ratio of YbTaO4 and mixed to obtain a powdered raw material mixture. The subsequent procedures and crystal growth conditions were the same as in Example 11 to obtain the crystals of Example 21. The maximum pressure achieved during crystal growth was 167 MPa.

[0103] <Example 22: YbNbO4> Yb2O3 and Nb2O5 (in powder form, manufactured by Furuuchi Chemical Co., Ltd.) were prepared as raw materials for Yb and Nb. Each raw material was weighed to satisfy the ratio of YbNbO4 and mixed to obtain a powdered raw material mixture. The subsequent procedures and crystal growth conditions were the same as in Example 13 to obtain the crystals of Example 22. The maximum pressure achieved during crystal growth was 149 MPa.

[0104] <Example 23: LuTaO4> Lu2O3 and Ta2O5 (in powder form, manufactured by Furuuchi Chemical Co., Ltd.) were prepared as raw materials for Lu and Ta. Each raw material was weighed to satisfy the ratio of LuTaO4 and mixed to obtain a powdered raw material mixture. The subsequent procedure and crystal growth conditions were the same as in Example 11, except that the holding time at 700°C was 72 hours, to obtain the crystal of Example 23. The maximum pressure reached during crystal growth was 144 MPa.

[0105] <Example 24: LuNbO4> Lub2O3 and Nb2O5 (in powder form, manufactured by Furuuchi Chemical Co., Ltd.) were prepared as raw materials for Lu and Nb. Each raw material was weighed to satisfy the ratio of LuNbO4 and mixed to obtain a powdered raw material mixture. The subsequent procedures and crystal growth conditions were the same as in Example 11 to obtain the crystal of Example 24. The maximum pressure achieved during crystal growth was 187 MPa.

[0106] <Example 25: Lu 0.99 Tb 0.01 TaO4> Lu2O3, Tb4O7, and Ta2O5 (in powder form, manufactured by Furuuchi Chemical Co., Ltd.) were prepared as raw materials for Lu, Tb, and Ta. 0.99 Tb 0.01 The raw materials were weighed to meet the required ratio of TaO4 and mixed to obtain a powdered mixture. The subsequent procedures and crystal growth conditions were the same as in Example 11, except that the holding time at 700°C was 58 hours, to obtain the crystals of Example 25. The maximum pressure reached during crystal growth was 160 MPa.

[0107] <Example 26: Lu 0.99 EU 0.01 TaO4> Lu2O3, Eu2O3, and Ta2O5 (in powder form, manufactured by Furuuchi Chemical Co., Ltd.) were prepared as raw materials for Lu, Eu, and Ta. 0.99 EU 0.01 The raw materials were weighed and mixed to meet the required ratio of TaO4, and a powdered raw material mixture was obtained. The subsequent procedures and crystal growth conditions were the same as in Example 25 to obtain the crystals of Example 26. The maximum pressure reached during crystal growth was 151 MPa.

[0108] <Example 27: Lu 0.99 Pr 0.01 TaO4> Lu, Pr, and Ta are used as raw materials, Lu2O3, Pr6O 11 And Ta2O5 (powdered, manufactured by Furuuchi Chemical Co., Ltd.) was prepared. Each raw material was Lu 0.99 Pr 0.01 The raw materials were weighed to meet the required ratio of TaO4 and mixed to obtain a powdered mixture. The subsequent procedures and crystal growth conditions were the same as in Example 11, except that the holding time at 700°C was 50 hours, to obtain the crystals of Example 27. The maximum pressure reached during crystal growth was 169 MPa.

[0109] <Example 28: LuTa 0.97 Nb 0.03 O4> Lu2O3, Ta2O5, and Nb2O5 (in powder form, manufactured by Furuuchi Chemical Co., Ltd.) were prepared as raw materials for Lu, Ta, and Nb. 0.97 Nb0.03 Weighed and mixed so as to satisfy the ratio of O4 to obtain a powdery raw material mixture. The subsequent procedures and crystal growth conditions were the same as those in Example 11 except that the holding time at 700 °C was 60 hours, and crystals of Example 28 were obtained. The maximum pressure reached during crystal growth was 179 MPa.

[0110] Table 19-1 and Table 19-2 respectively show the crystal production conditions of Examples 1 to 10 and Examples 11 to 28 described above.

[0111]

Table 19-1

[0112]

Table 19-2

[0113] [[ID=2Q]] [Measurement and Evaluation] <Microscopic Observation> The crystals obtained in Examples 1 to 28 above were observed with an optical microscope. Figures 3-1 to 3-25 respectively show the microscopic images of the crystals of Example 1, Examples 5 to 9a, and Examples 10 to 28. The scale bars in each image are 1 mm for Figures 3-2, 3-8, 3-9 and 3-21, 2 mm for Figure 3-11, and 0.5 mm for the others.

[0114] According to Figures 3-1 to 3-25, it was confirmed that the obtained crystals were highly transparent in the as-grown state under microscopic observation. Also, although not shown, the crystals of Examples 2 to 4 and Example 9b were also highly transparent crystals in the as-grown state.

[0115] <X-ray Diffraction Measurement> Powder samples were prepared from the crystals obtained in each example, and powder X-ray diffraction measurements were performed. Figures 4-1 to 4-19 respectively show the measurement results of the crystals of Example 1, Example 5, Example 9a, Example 9b, and Examples 10 to 24.

[0116] The upper part of Figure 4-1 shows the results of powder X-ray diffraction measurement of the crystal of Example 1, and the lower part of Figure 4-1 shows the simulation results of the diffraction chart of YTaO4 (monoclinic P12 / a1). By comparing the diffraction charts of the two, the space group of the obtained crystal (crystal of Example 1) can be easily estimated. It is preferable to use about 3 to 10 peaks with high peak intensity as the main peaks. The crystal parameters and atomic coordinate positions shown in Tables 1 to 18 above are important as they serve as a basis for estimating or determining the space group of the oxide crystal of the present invention. Furthermore, the crystal structure of the oxide crystal of the present invention can be approximated using other monoclinic crystal systems, in which case it will be expressed using different space groups, lattice constants, and plane indices, but the X-ray diffraction measurement results (e.g., the upper part of Figure 4-1) and the crystal structure will not change, and the identification method and identification results using them will also be the same. For this reason, in this embodiment, powder X-ray diffraction measurement was performed as monoclinic.

[0117] In the measurement results for the crystal in Example 1, the fact that all the peaks shown in the simulation diffraction chart were confirmed indicates that the obtained single crystal has the structure used in the simulation. On the other hand, in the diffraction chart obtained by powder X-ray diffraction measurement, very weak peaks may be seen in addition to the peak positions shown in the simulation diffraction chart. These indicate the presence of phases other than the target crystal, but this does not mean that an impurity phase is present in the obtained single crystal. Rather, it means that the impurity phase is attached to the surface of the obtained single crystal and was inevitably mixed in when the powder sample was prepared, resulting in it appearing as a peak in the diffraction chart. In this example, due to the reaction scale and other factors, the obtained single crystal is relatively small, making it difficult to isolate only the target single crystal, and the above phenomenon is observed in such cases. The same applies to crystals other than Example 1, which will be described later.

[0118] Although not shown in the figures, it was confirmed that the crystals in Examples 2-4 and 6-8 also possess a monoclinic YTaO4(P12 / a1) crystalline phase, similar to the crystal in Example 1.

[0119] The upper part of Figure 4-2 shows the powder X-ray diffraction measurement results for the crystal of Example 5, and the lower part of Figure 4-2 shows the simulation results of the diffraction chart for YNbO4 (monoclinic I 1 2 / a 1).

[0120] The upper part of Figure 4-3 shows the results of powder X-ray diffraction measurements of the crystal of Example 9a, and the lower part of Figure 4-3 shows the simulation results of the diffraction chart of TbTaO4 (monoclinic P12 / a1).

[0121] The upper part of Figure 4-4 shows the results of powder X-ray diffraction measurements of the crystal of Example 9b, and the lower part of Figure 4-4 shows the simulation results of the diffraction chart of TbTaO4 (monoclinic P12 / a1).

[0122] Comparing the diffraction charts of the crystals in Example 9a (Figure 4-3) and Example 9b (Figure 4-4), it is suggested that the crystals in Example 9a contain a small amount of crystalline phases other than monoclinic, which is thought to be due to unreacted raw materials. On the other hand, no such crystalline phases were observed in the crystals in Example 9b. From this, it can be concluded that the Tb4O7 used in the production of the crystals in Example 9a contains Tb 4+ and Tb 3+ Tb is present during crystal growth. 4+ All are Tb 3+ The valence should change, but even after crystal growth, Tb 4+ The presence of other crystalline phases was suggested due to the persistence of Tb. Furthermore, the TbTaO4 (starting compound) used in the production of the crystal in Example 9b contains Tb 3+ The presence of only one phase suggests that the presence of other crystalline phases is significantly reduced.

[0123] The upper part of Figure 4-5 shows the results of powder X-ray diffraction measurements of the crystal in Example 10, and the lower part of Figure 4-5 shows the simulation results of the diffraction chart of TbNbO4 (monoclinic system I 1 2 / a 1).

[0124] The upper panel of Figure 4-6 shows the results of powder X-ray diffraction measurements of the crystal in Example 11, and the lower panel of Figure 4-6 shows the simulation results of the diffraction chart of PrTaO4 (monoclinic P121 / c1).

[0125] The upper part of Figure 4-7 shows the results of powder X-ray diffraction measurements of the crystal of Example 12, and the lower part of Figure 4-7 shows the simulation results of the diffraction chart of PrNbO4 (monoclinic system I 1 2 / a 1).

[0126] The upper part of Figure 4-8 shows the results of powder X-ray diffraction measurements of the crystal in Example 13, and the lower part of Figure 4-8 shows the simulation results of the diffraction chart of GdTaO4 (monoclinic P12 / c1).

[0127] The upper part of Figure 4-9 shows the results of powder X-ray diffraction measurements of the crystal of Example 14, and the lower part of Figure 4-9 shows the simulation results of the diffraction chart of GdNbO4 (monoclinic system I 1 2 / a 1).

[0128] The upper part of Figure 4-10 shows the results of powder X-ray diffraction measurements of the crystal of Example 15, and the lower part of Figure 4-10 shows the simulation results of the diffraction chart of DyTaO4 (monoclinic P12 / c1).

[0129] The upper part of Figure 4-11 shows the results of powder X-ray diffraction measurements of the crystal of Example 16, and the lower part of Figure 4-11 shows the simulation results of the diffraction chart of DyNbO4 (monoclinic system I 1 2 / a 1).

[0130] The upper part of Figure 4-12 shows the results of powder X-ray diffraction measurements of the crystal of Example 17, and the lower part of Figure 4-12 shows the simulation results of the diffraction chart of HoTaO4 (monoclinic P12 / c1).

[0131] In the upper part of Fig. 4-13, the powder X-ray diffraction measurement results of the crystal of Example 18 are shown, and in the lower part of Fig. 4-13, the simulation results of the diffraction chart of HoNbO4 (monoclinic system I 1 2 / a 1) are shown.

[0132] In the upper part of Fig. 4-14, the powder X-ray diffraction measurement results of the crystal of Example 19 are shown, and in the lower part of Fig. 4-14, the simulation results of the diffraction chart of ErTaO4 (monoclinic system P 1 2 / c 1) are shown.

[0133] In the upper part of Fig. 4-15, the powder X-ray diffraction measurement results of the crystal of Example 20 are shown, and in the lower part of Fig. 4-15, the simulation results of the diffraction chart of ErNbO4 (monoclinic system I 1 2 / a 1) are shown.

[0134] In the upper part of Fig. 4-16, the powder X-ray diffraction measurement results of the crystal of Example 21 are shown, and in the lower part of Fig. 4-16, the simulation results of the diffraction chart of YbTaO4 (monoclinic system P 1 2 / c 1) are shown.

[0135] In the upper part of Fig. 4-17, the powder X-ray diffraction measurement results of the crystal of Example 22 are shown, and in the lower part of Fig. 4-17, the simulation results of the diffraction chart of YbNbO4 (monoclinic system I 1 2 / a 1) are shown.

[0136] In the upper part of Fig. 4-18, the powder X-ray diffraction measurement results of the crystal of Example 23 are shown, and in the lower part of Fig. 4-18, the simulation results of the diffraction chart of LuTaO4 (monoclinic system P 1 2 / c 1) are shown.

[0137] In the upper part of Fig. 4-19, the powder X-ray diffraction measurement results of the crystal of Example 24 are shown, and in the lower part of Fig. 4-19, the simulation results of the diffraction chart of LuNbO4 (monoclinic system I 1 2 / a 1) are shown.

[0138] <Secondary Ion Mass Spectrometry> For the crystal in Example 1, the hydrogen and potassium concentrations were measured using a secondary ion mass spectrometer (Cameca IMS-6F) and a time-of-flight secondary ion mass spectrometer (TOF-SIMS, IonTOF), respectively. The results are shown in Figure 5. The horizontal axis in Figure 5 represents the measurement depth (μm).

[0139] According to Figure 5, in the obtained crystal, the hydrogen concentration at a depth of 3 μm is approximately 2 × 10⁻⁶. 20 atom / cm 3 And, 1 × 10 21 atoms / cm 3 The following conditions must be met, and the potassium concentration at a depth of 6 μm should be approximately 2 × 10⁻⁶ 17 atom / cm 3 And, 1 × 10 19 atoms / cm 3 The following conditions were found to be met. Furthermore, it was confirmed that the concentration ratios of yttrium, tantalum, and oxygen were in close agreement with the theoretical composition. Although not shown in the figures, similar component analysis was performed on the crystals of Examples 2 to 28, and the hydrogen concentration was found to be 1 × 10⁻⁶. 16 atoms / cm 3 The above 1 x 10 23 atoms / cm 3 The following range applies, and the potassium concentration is 1 × 10⁻⁶ 12 atoms / cm 3 The above 1 x 10 20 atoms / cm 3 We confirmed that it falls within the following range.

[0140] <Luminous properties> Powder samples were prepared by grinding the crystals obtained in each example, and the luminescence properties of each sample were measured. Hereafter, the sample prepared from the crystal in Example 1 will be referred to as Sample 1, and the same will apply to Examples 2 to 28.

[0141] For photoluminescence (PL) measurements, a spectrofluorometer (Hitachi High-Tech Corporation, F-7100) is used, and a predetermined excitation wavelength (λ) is measured. exWhen excited by (λ), the emission wavelength (λ em The emission wavelength (λ) and emission intensity were measured. em ) is fixed at a predetermined wavelength, and each excitation wavelength (λ ex The emission intensity was measured when excited by ) and the excitation spectrum was obtained. For X-ray radioluminescence (XRL) measurements, a fiber multi-channel compact spectrometer (Stellarnet Inc., Blue Wave UVN-50) is used, and the emission wavelength (λ) when excited with X-rays (Rigaku Corporation, 18kW X-ray generator RA-HF 18RB) is measured. em ) and luminescence intensity were measured.

[0142] Figure 6 shows the PL spectra of sample 1, sample 3, and sample 4. Here, the excitation wavelength (λ) ex The peak wavelengths were 213 nm for sample 1, 218 nm for sample 3, and 227 nm for sample 4. In Figure 6, the emission intensity on the vertical axis has been normalized so that the peak values ​​of each PL spectrum match.

[0143] As shown in Figure 6, it was found that by substituting Ta with Nb, based on the composition of the crystal in Example 1 (YTaO4), emission in the blue wavelength region is produced. Crystals with emission wavelengths in the blue region are useful as scintillators used in combination with, for example, Si photodiodes. The presence of blue emission wavelengths in the scintillator is expected to improve sensitivity to Si photodiodes. This may allow Si photodiodes to be used as photoelectric converters. Note that, as shown in Figure 6, YTa 0.98 Nb 0.02 Since sample 3, which has an O4 composition, showed almost no emission in the ultraviolet region as observed in sample 1, it was suggested that, in order to obtain crystals with the aforementioned blue emission wavelength, it is preferable that the substitution ratio of Nb to Ta be about 2%, based on the composition of YTaO4.

[0144] Figure 7 shows the XRL spectra of sample 1, sample 2, and sample 4. In Figure 7, the emission intensity on the vertical axis has been normalized so that the peak values ​​of each XRL spectrum match.

[0145] As shown in Figure 7, and referring to the PL spectrum in Figure 6 as described above, it was found that the substitution of Ta with Nb, based on the crystal composition of Example 1 (YTaO4), results in emission in the blue wavelength region. Also, similar to the PL spectrum in Figure 6, YTa 0.99 Nb 0.01 Since sample 2, which has an O4 composition, showed almost no emission in the ultraviolet region as observed in sample 1, it was suggested that in order to obtain crystals with the aforementioned blue emission wavelength, the substitution ratio of Nb to Ta may be approximately 1% or more, based on the composition of YTaO4.

[0146] Figure 8 shows the PL spectra of sample 6 and sample 9a. Here, the excitation wavelength (λ) ex The peak wavelength was 261 nm for sample 6 and 272 nm for sample 9a. In Figure 8, the emission intensity on the vertical axis is normalized so that the largest peak values ​​of each PL spectrum match. As a result, the PL spectra of the two samples match very well, and in particular, the PL spectra in the wavelength range of approximately 460 nm to 700 nm on the horizontal axis almost completely overlap.

[0147] As shown in Figure 8, it was found that by substituting Y with Tb, based on the composition of the crystal in Example 1 (YTaO4), emission in the green wavelength region is produced. Crystals with emission wavelengths in the green region are useful as scintillators used in combination with photodetectors, for example, using photodiodes. Note that although outside the wavelength range of the horizontal axis in Figure 8, Y 0.99 Tb 0.01 In sample 6, which has a TaO4 composition, the ultraviolet emission observed in sample 1 (see Figure 6) was almost completely absent.

[0148] Figure 9 shows the XRL spectra of sample 6 and sample 9a. In Figure 9, the emission intensity on the vertical axis has been normalized so that the largest peak values ​​of each XRL spectrum match. Therefore, the degree of agreement between the two XRL spectra in the wavelength range of approximately 530 nm to 570 nm on the horizontal axis is very high.

[0149] As shown in Figure 9, and referring to the PL spectrum in Figure 8 as described above, it was found that the substitution of Y with Tb, based on the crystal composition of Example 1 (YTaO4), results in emission of wavelengths in the green region. Although outside the wavelength range on the horizontal axis of Figure 9, similar to the PL spectrum, Y 0.99 Tb 0.01 In sample 6, which has a TaO4 composition, the ultraviolet emission observed in sample 1 (see Figure 7) was almost completely absent.

[0150] Figure 10 shows the PL spectra of sample 9a and sample 9b. Here, the excitation wavelength (λ) ex The peak wavelength (λ) was 272 nm for sample 9a and 286 nm for sample 9b. In Figure 10, the emission intensity on the vertical axis is normalized so that the largest peak value of each PL spectrum matches. Figure 10 also shows the main emission wavelengths (λ) which will be discussed later. em The excitation spectra (normalized spectra) of samples 9a and 9b, obtained using the detection wavelength ), are also shown.

[0151] As described above, the crystal composition of both Example 9a and Example 9b is TbTaO4, but the raw materials (raw material compounds) used to produce the crystals are different. As shown in Figure 10, in sample 9a, the main emission wavelength (λ em The peak was 549 nm, and the largest peak was obtained in the green region wavelength. In contrast, sample 9b, like sample 9a, had a peak at 549 nm, and in addition, the main emission wavelength (λ) was in the orange region at 614 nm. em ) was observed. Based on these results, as described above with reference to the X-ray diffraction measurement results shown in Figures 4-3 and 4-4, the Tb4O7 used in the production of the crystal in Example 9a contains Tb 4+ and Tb 3+In the production of the crystal in Example 9b, TbTaO4 (the raw material compound) is present, and Tb 3+ It was suggested that only this exists. In other words, it was found that the oxide crystal of the present invention has an absorption cross-section suitable for optical pumping at a wavelength of approximately 378 nm and an emission cross-section effective at a wavelength of approximately 614 nm and other specific wavelengths.

[0152] That is, Tb shown in Figure 11 3+ As can be understood from the energy level diagram, Tb 3+ The material inherently possesses the property of emitting light in the green wavelength range, and according to the oxide crystal of the present invention, it is possible to resolve the problem of lack of green emission, which has been referred to as the "green gap" in the field of LEDs and other technologies. Furthermore, it is possible that it can be applied to applications as a visible light solid-state laser. Regarding sample 9b, it was confirmed that in the emission wavelength range measured in this embodiment, there was almost no change in the PL spectrum even when excited at a wavelength different from the above-mentioned wavelength (286 nm).

[0153] Figure 12 shows the XRL spectra of sample 9a and sample 9b. In Figure 12, the emission intensity on the vertical axis has been normalized so that the largest peak values ​​of each XRL spectrum match. Therefore, the degree of agreement between the two XRL spectra in the wavelength range of approximately 530 nm to 570 nm on the horizontal axis is very high.

[0154] As described above, the crystal composition of both Example 9a and Example 9b is TbTaO4, but the raw materials (raw material compounds) used to produce the crystals are different. As shown in Figure 12, in sample 9a, the main emission wavelength (λ em The peak was 549 nm, and the largest peak was obtained in the green region wavelength. In contrast, sample 9b, like sample 9a, had a peak at 549 nm, but also a prominent emission wavelength (λ) in the orange region at 614 nm. em) were observed. These results are consistent with the results described above with reference to the PL spectra in Fig. 10, whether for the crystals of Example 9a or for the crystals of Example 9b. This suggests that the oxide crystals of the present invention are useful as scintillators used in combination with, for example, photodetectors using photodiodes.

[0155] Figs. 13 and 14 show the PL spectra and excitation spectra of Sample 7 and Sample 8, respectively. Here, the excitation wavelength (λ ex ) for the PL spectrum is 244 nm for Sample 7 and 268 nm for Sample 8, and the emission wavelength (λ em ) for the excitation spectrum is 614 nm for Sample 7 and 615 nm for Sample 8. In Figs. 13 and 14, the emission intensity on the vertical axis is normalized so that the maximum peak values of the PL spectrum and the excitation spectrum coincide.

[0156] According to Figs. 13 and 14, it was found that the emission wavelength changes to the longer wavelength side by substituting Y with Eu and Pr based on the composition (YTaO4) of the crystal of Example 1 (see the PL spectrum of Sample 1 shown in Fig. 6). In any of the samples, almost no emission in the ultraviolet region observed in Sample 1 was seen.

[0157] Fig. 15 shows the XRL spectra of Sample 1, Sample 7, and Sample 8. In Fig. 15, the emission intensity on the vertical axis is normalized so that the peak values of each XRL spectrum coincide. At a wavelength of about 615 nm on the horizontal axis, peaks of the spectra of Sample 7 and Sample 8 exist.

[0158] According to Fig. 15, as described above with reference to the PL spectra in Figs. 13 and 14, it was found that the emission wavelength changes to the longer wavelength side by substituting Y with Eu and Pr based on the composition (YTaO4) of the crystal of Example 1. In any of the samples, almost no emission in the ultraviolet region observed in Sample 1 was seen.

[0159] Figures 16, 17, and 18 show the PL spectra and excitation spectra of sample 25, sample 26, and sample 27, respectively. Here, the excitation wavelength (λ) for the PL spectrum is shown. ex The emission wavelength (λ) for the excitation spectrum is 264 nm for sample 25, 210 nm for sample 26, and 271 nm for sample 27. em The peak wavelengths were 548 nm for sample 25, 614 nm for sample 26, and 616 nm for sample 27. In Figures 16, 17, and 18, the emission intensity on the vertical axis is normalized so that the largest peak values ​​of the PL spectrum and excitation spectrum coincide.

[0160] As shown in Figures 16, 17, and 18, it was found that the emission wavelength shifts to longer wavelengths when Lu is substituted with Tb, Eu, and Pr, relative to the composition of the crystal in Example 23 (LuTaO4) (see the PL spectrum of sample 23 shown in Figure 21 later). In the PL spectrum of sample 25, the largest peak was obtained at wavelengths in the green region, indicating that the crystal of sample 25 is useful as a scintillator used in combination with a photodetector, for example, using a photodiode. Notably, in all samples, almost no emission in the ultraviolet region was observed, unlike in sample 23.

[0161] Figure 19 shows the XRL spectra of samples 23 and 25. Figure 20 shows the XRL spectra of samples 23, 26, and 27. In Figures 19 and 20, the emission intensity on the vertical axis has been normalized so that the peak values ​​of each XRL spectrum match. In Figure 20, peaks of the spectra for samples 26 and 27 are present at a wavelength of approximately 615 nm on the horizontal axis.

[0162] As shown in Figures 19 and 20, and as described above with reference to the PL spectra in Figures 16, 17, and 18, it was found that the emission wavelength shifts to the longer wavelength side when Lu is substituted with Tb, Eu, and Pr relative to the crystal composition of Example 23 (LuTaO4). In all samples, the emission in the ultraviolet region observed in Sample 23 was hardly observed.

[0163] Figure 21 shows the PL spectra of sample 23, sample 24, and sample 28. Here, the excitation wavelength (λ) ex The peak wavelengths were 210 nm for sample 23, 240 nm for sample 24, and 210 nm for sample 28. In Figure 21, the emission intensity on the vertical axis has been normalized so that the peak values ​​of each PL spectrum match.

[0164] As shown in Figure 21, it was found that by substituting Ta with Nb, based on the composition of the crystal in Example 23 (LuTaO4), emission in the blue wavelength region is produced. Crystals with emission wavelengths in the blue region are useful as scintillators used in combination with, for example, Si photodiodes. The presence of blue emission wavelengths in the scintillator is expected to improve sensitivity to Si photodiodes. This may allow Si photodiodes to be used as photoelectric converters. Note that, as shown in Figure 21, LuTa 0.97 Nb 0.03 In sample 28, which has an O4 composition, almost no ultraviolet emission was observed, as seen in sample 23. This suggests that, in order to obtain crystals having the blue emission wavelengths described above, it is preferable that the substitution ratio of Nb to Ta is approximately 3% or more, based on the composition of LuTaO4. Furthermore, considering the above in relation to Figures 6 and 7, it is considered that even if the substitution ratio of Nb to Ta is approximately 1% or more, based on the composition of LuTaO4, crystals having the blue emission wavelengths described above can be obtained.

[0165] Figure 22 shows the XRL spectra of samples 23, 24, and 28. In Figure 22, the emission intensity on the vertical axis has been normalized so that the peak values ​​of each XRL spectrum match.

[0166] As shown in Figure 22, and referring to the PL spectrum in Figure 21 as described above, it was found that the substitution of Ta with Nb, based on the crystal composition of Example 23 (LuTaO4), results in emission in the blue wavelength region. Also, similar to the PL spectrum in Figure 21, LuTa0.97 Nb 0.03 In sample 28, which had an O4 composition, almost no ultraviolet emission was observed, unlike in sample 23.

[0167] <Density etc.> Table 20 below shows the crystal density for each example, and the ρ·(Z) calculated based on the reference (HP Schatzler., Int. J. Appl. Radiat. Isot., 1979, 30, 115-121.). eff ) 4 The values ​​were shown. Here, the comparative crystal Z1 is a commercially available CdWO4 crystal (manufactured by Nippon Crystal Optics Co., Ltd.).

[0168] [Table 20]

[0169] Here, the densities of the crystals in Example 9a (TbTaO4), Example 13 (GdTaO4), and Example 23 (LuTaO4) shown in Table 20 are greater than the densities of the crystals of Example 1 (YTaO4) and the comparative crystal CdWO4, and ρ·(Z eff ) 4 The same applies to the values ​​of . These results suggest that, when using the composition of YTaO4 as a reference, substituting not only some or all of Y with Tb, but also with Gd, Lu, etc., can produce crystals with a density exceeding that of conventional YTaO4 crystals, and crystals that can have X-ray stopping power comparable to or exceeding that of CdWO4.

[0170] As described above, the present invention can provide an oxide crystal that does not contain harmful substances such as cadmium and has scintillation properties comparable to or better than those of CdWO4. Furthermore, the present invention can provide a method for producing the above-mentioned oxide crystals under milder conditions than conventional methods, particularly at lower temperatures. According to the manufacturing method of the present invention, chemically stable bulk single crystal growth and production are possible, making it suitable for large-scale and mass production, and reducing manufacturing costs. In addition, since no harmful substances such as cadmium are used, it is an environmentally friendly material, and the manufacturing process is also environmentally friendly. The oxide crystal and its manufacturing method of the present invention, possessing these characteristics, are expected to be applied to a variety of uses, such as a scintillator that replaces conventional CdWO4 and its manufacturing method, or as a magnetic material such as a magnetic refrigeration material and its manufacturing method, in addition to the scintillator y being limited to optical materials such as laser materials. [Explanation of symbols]

[0171] 10. Radiation detectors 11 Scintillator 12 Photoelectric Converter 20. Radiation Inspection Equipment 23 Radiation Source L light R radiation E. Radiation that penetrates the subject Sbj subject

Claims

1. General formula ((Y １－ｐ RE ｐ ) １－ｘ Tb ｘ ) (Ta １－ｙ Nb ｙ ) O ４－ｚ An oxide crystal containing hydrogen atoms (H), represented by the formula (wherein p, x, y, and z are each independently satisfying 0 ≤ p ≤ 1, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, and -0.5 ≤ z ≤ 0.5, and RE is selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu)).

2. The concentration of hydrogen atoms is 1 × 10 １６ atoms / cm ３ or more and 1 × 10 ２３ atoms / cm ３ or less, and the oxide crystal according to claim 1.

3. The oxide crystal according to claim 1 or 2, having a crystal structure belonging to the P12 / a 1 space group, P12 / c 1 space group, P121 / c 1 space group, or I12 / a 1 space group, and having a monoclinic single phase.

4. The oxide crystal according to any one of claims 1 to 3, further comprising an alkali metal and / or an alkaline earth metal.

5. The concentration of the alkali metal and / or alkaline earth metal is 1 × 10 １２ atoms / cm ３ The above 1 x 10 ２０ atoms / cm ３ The oxide crystal according to claim 4, wherein the range is as follows.

6. A method for producing an oxide crystal according to any one of claims 1 to 5, comprising growing a crystal from a raw material containing each element contained in the crystal by hydrothermal synthesis in the presence of a mineralizing agent containing an alkali metal and / or an alkaline earth metal, or an acid mineralizing agent, or a mixed mineralizing agent of both.

7. General formula ((Y １－ｐ RE ｐ ) １－ｘ Tb ｘ ) (Ta １－ｙ Nb ｙ ) O ４－ｚ A method for producing oxide crystals according to any one of claims 1 to 5, comprising treating one or more raw material compounds having a composition represented by the formula (wherein p, x, y, and z are each independently satisfying 0 ≤ p ≤ 1, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, and -0.5 ≤ z ≤ 0.5, and RE is selected from the group consisting of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu)) by a hydrothermal synthesis method in the presence of a mineralizing agent containing an alkali metal and / or an alkaline earth metal, or an acid mineralizing agent, or a mixed mineralizing agent of both.

8. The method according to claim 6 or 7, wherein the concentration of the mineralizing agent is in the range of 1 M or more and 50 M or less.

9. The method according to any one of claims 7 to 8, wherein, in growing crystals by the hydrothermal synthesis method, the temperature is in the range of 400°C to 800°C, and the maximum achievable pressure is in the range of 25 MPa to 250 MPa.

10. An optical material comprising an oxide crystal according to any one of claims 1 to 5.

11. The optical material according to claim 10, which is a laser material.

12. The optical material according to claim 10, which is a scintillator.

13. The optical material according to claim 12, A photoelectric converter that detects light from the optical material and converts it into an electrical signal, A radiation detector equipped with the following features.

14. A radiation source that irradiates the subject with radiation, A radiation detector according to claim 13, which detects radiation passing through the subject, A radiation inspection device equipped with the following features.

15. A magnetic material comprising an oxide crystal according to any one of claims 1 to 5.

16. The magnetic material according to claim 15, which is a magnetic refrigeration material.

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