Rare earth oxide crystal, method for producing same, and use thereof

Abstract

The present invention provides a rare earth oxide crystal useful as an optical material, a magnetic material, or the like, and a method for producing the same. The rare earth oxide crystal according to one embodiment of the present invention is characterized by containing a rare earth element (RE) and oxygen (O), wherein an inorganic crystal represented by general formula REOx (1.45≤x≤2.05) contains at least a hydrogen atom (H), and the RE is at least one element selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

Description

Rare earth oxide crystal, method for producing the same, and use thereof

[0001] The present invention relates to a rare earth oxide crystal, a method for producing the same, and a use thereof.

[0002] Conventionally, research has been conducted on the growth of rare earth sesquioxide crystals and their applications as optical materials (e.g., laser materials, phosphors, scintillators, Faraday rotators, etc.) and magnetic materials.

[0003] Patent Document 1 describes that scandium oxide (Sc ２ O ３ ) crystals and ytterbium (Yb)-added Sc ２ O ３ crystals were grown by a hydrothermal synthesis method (see Examples 1 to 6). According to Patent Document 1, yttrium oxide (Y ２ O ３ ) crystals and lanthanoid sesquioxide (Ln ２ O ３ ) crystals were also supposed to be grown by the same hydrothermal synthesis method, but there is only a simple description that small crystals were obtained (see Example 7).

[0004] Non-Patent Document 1 describes that lutetium oxide (Lu ２ O ３ ) crystals, erbium (Er)-added Lu ２ O ３ crystals, and Yb-added Lu ２ O ３ crystals were grown by a hydrothermal synthesis method. However, it is described that LuO(OH) is obtained when the temperature is 640°C or lower, and 650°C to 700°C is required to obtain Lu ２ O ３ . This means that Lu ２ O ３The necessary condition for obtaining it is temperature, and it is suggested that high temperatures are required. Furthermore, Non-Patent Literature 1 states that it took one week to test to confirm the phase and three weeks to obtain a 6 mm square crystal, which suggests that the crystal growth rate is slow. In addition, Non-Patent Literature 1 states that the obtained crystal contains LuO(OH), and the target Lu ２ O ３ It cannot be said that manufacturing conditions for stably obtaining crystals have been found. Those skilled in the art will understand that these technical implications mean that developing technologies for large-scale production and mass production will be difficult.

[0005] Regarding terbium (Tb), one of the lanthanides, Patent Document 2 states that terbium (oxy) hydroxide (TbO ２ A Faraday rotator using H) (which can also be written as TbO(OH)) crystals is described. However, TbO ２ Since H is a biaxial crystal, it is considered unsuitable for use as a Faraday rotator.

[0006] Terbium oxide (Tb ２ O ３ The crystal has a cubic structure and is theoretically considered an ideal material for a Faraday rotator. However, as is common with rare earth oxide crystals in general, Tb ２ O ３ Growing single crystals of Tb has been extremely difficult with conventional crystal growth techniques due to its extremely high melting point and the presence of phase transitions. In this context, the aforementioned Patent Document 2 describes a hydrothermal synthesis method for Tb ２ O ３ Although we attempted to grow a single crystal of Tb, ２ O ３ TbO could not be obtained. ２ Only H is obtained, and in conventional hydrothermal synthesis methods, Tb ２ O ３ It is thought that the production of crystals, especially bulk single crystals, was difficult. On the other hand, Non-Patent Document 2 states that Tb can be produced by the flux method. ２ O ３The document describes the growth of crystals. However, the obtained crystals cannot be called bulk single crystals, and although they were described as transparent crystals without defects upon visual observation, it is difficult to say that they possess sufficient transparency for practical use (see Figure 2). Furthermore, in the manufacturing method described in Non-Patent Document 2, Li is used as the flux. ６ Tb(BO) ３ ) ３ Although elemental analysis of the sample has ruled out solvent-induced inclusions, the extent of the impact when attempting mass production (such as the inclusion of impurity elements into the growing crystals or a decrease in the properties required for the crystals) is uncertain due to the principle of the manufacturing method, and it is also thought to be difficult to increase the crystal growth rate.

[0007] U.S. Patent No. 7,563,320 and U.S. Patent No. 10,942,381

[0008] Colin MacMillen, et al., Cryst. Growth Des., 2011, 11, 4386-4391. Philippe Veber, et al., CrystEngComm, 2015, 17, 492-497.

[0009] This invention has been made in view of these circumstances, and aims to provide rare earth oxide crystals useful as optical materials, magnetic materials, etc. Furthermore, this invention aims to provide a method for producing the above-mentioned rare earth oxide crystals. Finally, this invention aims to provide applications for the above-mentioned rare earth oxide crystals.

[0010] The rare earth oxide crystal according to the present invention contains a rare earth element (RE) and oxygen (O), and has the general formula REO ｘThe inorganic crystal represented by (1.45 ≤ x ≤ 2.05) contains at least one hydrogen atom (H), and the above RE is at least one element selected from the group consisting of scandium (Sc), yttrium (Y), 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), thereby solving the above problem. The above inorganic crystal has the general formula REO ｘ It may also be expressed as (1.95 ≤ x ≤ 2.05). The above inorganic crystal has the general formula REO ｘ It may also be expressed as (1.45 ≤ x ≤ 1.55). The concentration of hydrogen atoms contained in the above inorganic crystal is 1 × 10⁻⁶ １５ atoms / cm ３ The above 1 x 10 ２３ atoms / cm ３ The following ranges are also possible. The inorganic crystal may have a crystal structure belonging to the I a-3 space group or the F m-3 m space group, and the crystal phase may be a single cubic phase, or it may have a crystal structure belonging to the P-3 m-1 space group, and the crystal phase may be a single hexagonal phase. The inorganic crystal may further contain at least one element selected from the group consisting of cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), and ytterbium (Yb), which is different from the RE. The inorganic crystal may further contain 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 following range is also acceptable. The inorganic crystal may further contain at least one element selected from the group consisting of aluminum (Al), gallium (Ga), and germanium (Ge).

[0011] The method for producing the above-mentioned rare earth oxide crystals according to the present invention includes growing crystals by hydrothermal synthesis using raw materials containing each element included in an inorganic crystal in the presence of a first mineralizer which is an alkali metal and / or alkaline earth metal mineralizer, or an acid mineralizer, or a mixed mineralizer of both, and a second mineralizer which is at least one selected from the group consisting of aluminum oxide, gallium oxide, and germanium oxide, thereby solving the above-mentioned problems. The concentration of the first mineralizer may be in the range of 1 M to 50 M. The concentration of the second mineralizer may be in the range of 0.01 M to 20 M. In growing crystals by hydrothermal synthesis, the temperature may be in the range of 400°C to less than 750°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 rare earth oxide crystal, thereby solving the above problem. The optical material may be a laser material or a laser host material. The optical material may be a phosphor material. The optical material may be a Faraday rotator. The optical isolator according to the present invention comprises the above-mentioned Faraday rotator, thereby solving the above problem. The optical isolator may be polarization-independent. The optical communication device, optical communication line, or laser processing machine according to the present invention comprises the above-mentioned optical isolator, thereby solving the above problem. The optical material may be a scintillator. The radiation detector according to the present invention comprises the above-mentioned scintillator 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 device according to the present invention comprises a radiation source that irradiates a subject with radiation and the above-mentioned radiation detector that detects radiation passing through the subject, thereby solving the above problem. The magnetic material according to the present invention consists of the above-mentioned rare earth oxide crystal, thereby solving the above problem. The magnetic material may be a magnetic refrigeration material.

[0013] The present invention provides rare earth oxide crystals suitable for application in the various uses described above. The rare earth oxide crystals of the present invention can be provided as large, high-quality single crystals and are suitable for use as various optical materials, magnetic materials, and the like.

[0014] The rare earth oxide crystals of the present invention are produced by hydrothermal synthesis, which allows for growth under significantly lower temperature conditions and gentler temperature gradients compared to conventional methods. In addition, 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. Furthermore, the present invention eliminates the 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 crystal. Moreover, by using hydrothermal synthesis, it is relatively easy to increase the crystal growth rate and to produce larger crystals and mass-produce them compared to conventional methods. 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.

[0015] This is a schematic diagram showing one embodiment of a photoisolator using rare earth oxide crystals according to the present invention. This is a schematic diagram showing another embodiment of a photoisolator using rare earth oxide crystals according to the present invention. This is a schematic diagram showing one embodiment of a laser processing machine using rare earth oxide crystals according to the present invention. This is a schematic diagram showing the configuration of a radiation detector according to one embodiment of the present invention. This is a schematic diagram showing the configuration of a radiation inspection device according to one embodiment of the present invention. This is a diagram showing a microscopic image of the crystal of Example 1 obtained in the examples. This is a diagram showing a microscopic image of the crystal of Example 2 obtained in the examples. This is a diagram showing a microscopic image of the crystal of Example 3 obtained in the examples. This is a diagram showing a microscopic image of the crystal of Example 4 obtained in the examples. This is a diagram showing a microscopic image of the crystal of Example 4a obtained in the examples. This is a diagram showing a microscopic image of the crystal of Example 4b obtained in the examples. This is a diagram showing a microscopic image of the crystal of Example 4c obtained in the examples. This is a diagram showing a microscopic image of the crystal of Example 4d obtained in the examples. This is a diagram showing a microscopic image of the crystal of Example 5d obtained in the examples. This is a diagram showing a microscopic image of the crystal of Example 5a obtained in the examples. This is a diagram showing a microscopic image of the crystal of Example 5b obtained in the examples. This is a diagram showing a microscopic image of the crystal of Example 5c obtained in the examples. This figure shows a microscopic image of the crystal of Example 5d obtained in the examples. This figure shows a microscopic image of the crystal of Example 6 obtained in the examples. This figure shows a microscopic image of the crystal of Example 7 obtained in the examples. This figure shows a microscopic image of the crystal of Example 8 obtained in the examples. This figure shows a microscopic image of the crystal of Example 9 obtained in the examples. This figure shows a microscopic image of the crystal of Example 10 obtained in the examples. Powder X-ray diffraction measurement results of the crystal of Example 1, and CeO ２ This figure shows the simulation results of the diffraction chart for a cubic crystal system (F m -3 m). It also shows the powder X-ray diffraction measurement results of the crystal in Example 2, and Tb ２ O ３ This figure shows the simulation results of the diffraction chart for (cubic crystal system I a-3). It also shows the powder X-ray diffraction measurement results of the crystal in Example 17, and TbO ２ H (monoclinic system) and Tb (OH) ３ This figure shows the simulation results of the diffraction chart (hexagonal crystal system). It also shows the powder X-ray diffraction measurement results of the crystal in Example 3, and Gd ２ O ３This figure shows the simulation results of the diffraction chart for (cubic crystal system I a-3). It also shows the powder X-ray diffraction measurement results of the crystal of Example 18, and GdO ２ H (monoclinic system) and Gd(OH) ３ This figure shows the simulation results of the diffraction chart (hexagonal crystal system). It also shows the powder X-ray diffraction measurement results of the crystal in Example 4, and Y ２ O ３ This figure shows the simulation results of the diffraction chart for (cubic crystal system I a-3). It also shows the powder X-ray diffraction measurement results of the crystal in Example 19, and YO ２ H (monoclinic system) and Y (OH) ３ This figure shows the simulation results of the diffraction chart (hexagonal crystal system). It also shows the powder X-ray diffraction measurement results of the crystal in Example 5, and Lu ２ O ３ This figure shows the simulation results of the diffraction chart for (cubic crystal system I a-3). It also shows the powder X-ray diffraction measurement results of the crystal in Example 6, and Dy ２ O ３ This figure shows the simulation results of the diffraction chart for (cubic crystal system I a-3). It also shows the powder X-ray diffraction measurement results of the crystal in Example 7, and Ho ２ O ３ This figure shows the simulation results of the diffraction chart for (cubic crystal system I a-3). It also shows the powder X-ray diffraction measurement results of the crystal in Example 8, and Er ２ O ３ This figure shows the simulation results of the diffraction chart for (cubic crystal system I a -3). It also shows the powder X-ray diffraction measurement results of the crystal in Example 9, and Tm ２ O ３ This figure shows the simulation results of the diffraction chart for (cubic crystal system I a -3). It also shows the powder X-ray diffraction measurement results of the crystal in Example 10, and Yb ２ O ３ This figure shows the simulation results of the diffraction chart for (cubic crystal system I a -3). It also shows the powder X-ray diffraction measurement results of the crystal in Example 31, and Tb ２ O ３ This figure shows the simulation results of the diffraction chart for (cubic crystal system I a -3). It also shows the powder X-ray diffraction measurement results of the crystal in Example 32, and Tb ２ O ３This figure shows the simulation results of the diffraction chart for (cubic crystal system I a -3). It also shows the powder X-ray diffraction measurement results of the crystal in Example 33, and Tb ２ O ３ This figure shows the simulation results of the diffraction chart for (cubic crystal system I a -3). It also shows the powder X-ray diffraction measurement results of the crystal of Example 34, and Tb ２ O ３ This figure shows the simulation results of the diffraction chart (cubic crystal system I a -3). This figure shows the concentrations of hydrogen and potassium in the secondary ion mass spectrometry results of the crystal of Example 2. This figure shows the PL spectrum and excitation spectrum of sample 4a. This figure shows the PL spectrum and excitation spectrum of sample 4b. This figure shows the PL spectrum and excitation spectrum of sample 4c. This figure shows the PL spectrum and excitation spectrum of sample 5a. This figure shows the PL spectrum and excitation spectrum of sample 5b. This figure shows the PL spectrum and excitation spectrum of sample 5c.

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

[0017] [Rare Earth Oxide Crystals] <Composition> The rare earth oxide crystals of the present invention contain rare earth elements (RE) and oxygen (O), and the general formula is REO ｘ An inorganic crystal represented by (1.45 ≤ x ≤ 2.05) contains at least one hydrogen atom (H). In the following, unless otherwise specified, "hydrogen" refers to a hydrogen atom.

[0018] In the above general formula, RE is at least one element selected from the group consisting of scandium (Sc), yttrium (Y), 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). RE may be a single element or a combination of two or more elements.

[0019] In one embodiment, the inorganic crystal is of the general formula REO ｘIt may be represented by (1.95 ≤ x ≤ 2.05). Here, x is preferably 2. In this aspect, RE may be an element selected from at least one of the group consisting of, for example, Ce, Tb, and Pr. Specifically, the inorganic crystal of this aspect is, for example, CeO ｘ , TbO ｘ , PrO ｘ (all of which may be represented by 1.95 ≤ x ≤ 2.05), and preferably, CeO ２ , TbO ２ , PrO ２ .

[0020] In another aspect, the inorganic crystal may be represented by the general formula REO ｘ (1.45 ≤ x ≤ 1.55). That is, the inorganic crystal of this aspect may be expressed as RE ２ O ｘ (2.9 ≤ x ≤ 3.1). Here, x preferably satisfies the condition 2.95 ≤ x ≤ 3.05, and more preferably, x is 3. In this aspect, RE may be an element selected from at least one of the group consisting of, for example, Sc, Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Specifically, the inorganic crystal of this aspect is, for example, Sc ２ O ｘ , Y ２ O ｘ , La ２ O ｘ , Pr ２ O ｘ , Nd ２ O ｘ , Sm ２ O ｘ , Eu ２ O ｘ , Gd ２ O ｘ , Tb ２ O ｘ , Dy ２ O ｘ , Ho ２ O ｘ , Er ２ O ｘ , Tm ２ O ｘ , Yb ２ O ｘ , Lu ２ Oｘ (In both cases, this can be expressed as 2.9 ≤ x ≤ 3.1), preferably Sc ２ O ３ , Y ２ O ３ La ２ O ３ , Pr ２ O ３ , Nd ２ O ３ Sm ２ O ３ , Eu ２ O ３ , Gd ２ O ３ , Tb ２ O ３ , Dy ２ O ３ Ho ２ O ３ Er ２ O ３ , Tm ２ O ３ Yb ２ O ３ Lu ２ O ３ It is possible.

[0021] It should be noted that the above general formula for the composition of the rare earth oxide crystals of the present invention is a theoretical formula representing the stoichiometric composition. As will be described later, the rare earth 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 within a controllable range.

[0022] Furthermore, although the number of oxygen atoms in the rare earth oxide crystal of the present invention may be smaller or larger than that of the stoichiometric composition due to defects in the crystal, the decrease in the transmittance of the crystal is sufficiently suppressed by satisfying the condition of x in the above general formula.

[0023] In one embodiment, the concentration of hydrogen contained in the rare earth oxide crystal of the present invention is 1 × 10⁻⁶ １５ atoms / cm ３ The above 1 x 10 ２３ atoms / cm ３ The range is as follows, preferably 1 × 10 １６ atoms / cm３ The above 1 x 10 ２２ atoms / cm ３ The range is as follows, more preferably 1 × 10 １７ atoms / cm ３ The above 1 x 10 ２２ atoms / cm ３ The range is as follows:

[0024] The method for measuring the hydrogen concentration in the rare earth 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 described later (alkali metals and / or alkaline earth metals, or Al, Ga and / or Ge)). 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 value at a depth of 6 μm. An example of SIMS measurement will be described in the Examples section.

[0025] <Additive Element Q> The rare earth oxide crystal of the present invention may also contain elements other than RE in the inorganic crystal described above. In this specification, such elements will also be referred to as additive element Q, and hereafter, unless otherwise specified, the description of "additive element Q" or "Q" will mean an element different from RE.

[0026] The additive element Q is not particularly limited, but for example, it may be at least one element selected from the group consisting of cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), and ytterbium (Yb). Q may be a single element or a combination of two or more elements. Here, in the embodiment in which the inorganic crystal contains the additive element Q, in order to distinguish RE, which is the main constituent element of the inorganic crystal, from the additive element Q, the composition of the crystal is defined as "Q:REO ｘ It may be written as " or similar.

[0027] In the embodiment of the present invention in which the rare earth oxide crystal contains the above-mentioned additive element Q, the concentration of the additive element Q is not particularly limited. By containing an appropriate additive element Q at an appropriate concentration in the inorganic crystal, a material with desired properties suitable for the intended application can be obtained.

[0028] <Optional constituent elements> The rare earth oxide crystals of the present invention may further contain optional constituent elements other than RE, O, H, and the additive element Q mentioned above.

[0029] In one embodiment, the inorganic crystal further contains alkali metals and / or alkaline earth metals as optional constituent elements. 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 alkali metals and / or alkaline earth metals in the inorganic crystal will deactivate defects within the crystal.

[0030] In an embodiment of the present invention in which the rare earth 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 ２１ 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, and more preferably, 1 × 10 １４ atoms / cm ３ The above 1 x 10 １９atoms / cm ３ The range is as follows. Here, if the inorganic crystal contains two or more alkali metals and alkaline earth metals in total, it is intended that the sum of their concentrations be within the above range.

[0031] In one embodiment, the inorganic crystal further contains, as an optional constituent element, at least one element selected from the group consisting of aluminum (Al), gallium (Ga), and germanium (Ge). It is expected that the presence of these elements in the inorganic crystal will deactivate defects within the crystal.

[0032] <Crystal Structure> In one embodiment, the rare earth oxide crystal of the present invention belongs to the cubic crystal system and is located in I a -3 (space group 206 of the International Tables for Crystallography (also simply called the International Table(s))) or F m -3 m (space group 225). In another embodiment, the rare earth oxide crystal of the present invention belongs to the hexagonal crystal system and is located in P -3 m 1 (space group 164). Tables 1 to 15 below show representative examples of Y ２ O ３ (I a -3), La ２ O ３ (P -3 m 1), CeO ２ (F m -3 m), Pr ２ O ３ (P -3 m 1), Nd ２ O ３ (P -3 m 1), Sm ２ O ３ (I a -3), Eu ２ O ３ (I a -3), Gd ２ O ３ (I a -3), Tb ２ O ３ (I a -3), Dy ２ O ３ (I a -3), Ho ２ O ３ (I a -3), Er ２O ３ (I a -3), Tm ２ O ３ (I a -3), Yb ２ O ３ (I a -3), and Lu ２ O ３ The crystal parameters and atomic coordinate positions of (I a -3) are shown. Furthermore, it is preferable that the rare earth oxide crystal of the present invention has a single phase as determined by powder X-ray diffraction measurement.

[0033] 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.

[0034]

[0035]

[0036]

[0037]

[0038]

[0039]

[0040]

[0041]

[0042]

[0043]

[0044]

[0045]

[0046]

[0047]

[0048]

[0049] In the present invention, at least in the embodiment where RE in the general formula is a single element, the lattice constant of the rare earth oxide crystal changes as its constituent elements are replaced by other elements or as activating elements are dissolved in solid solution. 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 it is considered that the structure maintains that belongs to the I a-3 space group, the F m-3 m space group, or the P 1 21 / c 1 space group.

[0050] <Main Properties> The rare earth oxide crystals of the present invention can exhibit properties suitable for their respective applications as optical materials, magnetic materials, etc.

[0051] In one embodiment, the rare earth oxide crystal of the present invention exhibits superior characteristics such as transmittance, thermal conductivity, laser resistance, Faraday rotation angle, and Verde constant compared to materials used in conventional Faraday rotors. Therefore, by using the rare earth oxide crystal of the present invention in a Faraday rotor to construct an optical isolator, it becomes possible to miniaturize, reduce the cost, and extend the lifespan of the optical isolator. Furthermore, in a laser processing machine equipped with such an optical isolator, not only is it possible to reduce the frequency of optical isolator replacement, but it also becomes possible to increase the power output of the laser (laser light source) used in the laser processing machine.

[0052] In one embodiment, the rare earth oxide crystal of the present invention is a conventional scintillator material (e.g., CdWO ４ It can have a level of transparency comparable to that of (etc.). When the rare earth oxide crystal of the present invention is used as a scintillator, the light generated within the scintillator crystal can be efficiently transmitted, thus preventing a decrease in the amount of light emitted.

[0053] In one embodiment, the rare earth oxide crystal of the present invention is CdWO ４ Densities comparable to or exceeding those of ρ・(Z ｅｆｆ ) ４It may have the above ρ·(Z ｅｆｆ ) ４ The value of is CdWO ４ The ratio to the value in is 0.8 or greater. 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. Here, ρ・(Z ｅｆｆ ) ４ This is the density (ρ) and the effective atomic number (Z). ｅｆｆ It is the product of () to the fourth power and is known to be proportional to the radiation stopping power. As a result, the rare earth oxide crystal of the present invention has the stopping power required for a scintillator, and CdWO ４ It may have X-ray stopping power comparable to that of ρ・(Z). ｅｆｆ ) ４ The value can be calculated, for example, based on the reference (HP Schatzler., Int. J. Appl. Radiat. Isot., 1979, 30, 115-121.).

[0054] In embodiments of the present invention in which the rare earth oxide crystal is used as a scintillator, indicators representing the scintillation characteristics include, for example, the amount of light emitted, decay time (decay characteristics), and afterglow (afterglow characteristics). The rare earth oxide crystal of the present invention is a conventional CdWO ４ It can exhibit a luminescence amount comparable to or exceeding that of CdWO under the same measurement conditions. In one preferred embodiment, the rare earth oxide crystal of the present invention exhibits a luminescence amount obtained under predetermined measurement conditions that is comparable to or exceeds that of CdWO under the same measurement conditions. ４ The ratio to the amount of light emitted is 0.8 or more. Here, the value of the ratio is preferably 0.85 or more, more preferably 0.9 or more, even more preferably 0.95 or more, even more preferably 1 or more, and most preferably greater than 1.

[0055] In the above context, the rare earth oxide crystal of the present invention has all properties of CdWO ４Please note that exceeding the specified value is not a mandatory requirement. In other words, depending on the various applications as a scintillator as exemplified below, if the rare earth oxide crystal of the present invention satisfies the scintillation characteristics required for that application, it can be said to be a practically useful scintillator. To put it another way, the rare earth oxide crystal of the present invention does not contain harmful substances such as cadmium, and can be said to be environmentally friendly both as a scintillator material itself and in its manufacturing method, and CdWO ４ Even if it has slightly inferior characteristics (not comparable) compared to CdWO ４ It can serve as a substitute scintillator.

[0056] [Method for producing rare earth oxide crystals] Next, the method for producing the rare earth oxide crystals described above will be explained.

[0057] A method for producing rare earth oxide crystals according to one embodiment of the present invention includes growing crystals from raw materials containing each element included in an inorganic crystal by hydrothermal synthesis in the presence of a first mineralizing agent which is an alkali metal and / or alkaline earth metal mineralizing agent, or an acid mineralizing agent, or a mixture of both mineralizing agents, and a second mineralizing agent which is at least one selected from the group consisting of aluminum oxide, gallium oxide, and germanium dioxide. Here, the term "hydrothermal synthesis" in this specification refers to an embodiment in which water is used as the solvent in the "solvothermal method". An example of the production method is described below.

[0058] <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.

[0059] Specifically, raw materials containing rare earth elements (RE) and, if necessary, additive elements Q are prepared, and one or more compounds from these are made into oxides. Here, RE is an element selected from the group consisting of scandium (Sc), yttrium (Y), 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). Q is an element selected from the group consisting of cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), and ytterbium (Yb), which are different from RE mentioned above. For convenience, in this specification, the raw materials containing each constituent element prepared in step S110 will also be referred to as the raw materials for each constituent element. For example, "raw material containing Y" and "raw material for Y" are synonymous.

[0060] 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.

[0061] For example, RE is an oxide of RE (REO ２ RE ２ O ３ (etc.) can be used. As raw materials for the additive element Q, for example, oxides, fluorides, etc. of Q can be used.

[0062] Here, if there are two or more raw materials for RE, a raw material mixture containing each raw material may be prepared as needed. Furthermore, in embodiments in which the target rare earth oxide crystal contains additive element Q, it is preferable that the additive element Q is prepared in a desired proportion (for example, 0.1% to 15%) relative to RE in terms of atomic ratio.

[0063] <Step S120: Step of growing crystals from raw materials by hydrothermal synthesis in the presence of a first mineralizing agent and a second 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 first mineralizing agent and a second mineralizing agent.

[0064] As the first mineralizing agent, a mineralizing agent containing alkali metals and / or alkaline earth metals, an acidic mineralizing agent, or a mixture of both can be used. The mineralizing agent containing alkali metals and / or alkaline earth metals is a compound containing alkali metals and / or alkaline earth metals, and for example, hydroxides, inorganic salts (carbonates, etc.) of alkali metals and / or alkaline earth metals can be used. Non-limiting examples of the first mineralizing agent include, for example, NaOH, Na ２ CO ３ KOH, K ２ CO ３ , RbOH, Rb ２ CO ３ , CsOH, Cs ２ CO ３ Mg(OH) ２ , MgCO ３ Ca(OH) ２ CaCO ３ , Sr(OH) ２ SrCO ３ , Ba(OH) ２ BaCO ３ Examples include these, 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. The alkali metals and / or alkaline earth metals contained in the first mineralizer, or the elements contained in the acid mineralizer, may be contained in the rare earth oxide crystals finally obtained.

[0065] The second mineralizing agent is aluminum oxide (Al ２ O ３ ), gallium oxide (Ga ２ O ３ ) and germanium dioxide (GeO ２At least one is selected from the group consisting of ). In one preferred embodiment, the second mineralizer contains aluminum oxide, and in a more preferred embodiment, the second mineralizer is aluminum oxide. By using the above-described first mineralizer and second mineralizer, it is possible to grow crystals at significantly lower temperatures compared to conventional methods other than hydrothermal synthesis, and it is also possible to grow crystals at a faster growth rate than conventional hydrothermal synthesis methods such as those described in Non-Patent Document 1. Furthermore, by using the first mineralizer and second mineralizer, it is possible to increase the size of the grown crystals. Moreover, the inorganic crystal of the target rare earth oxide crystal is of the above general formula REO ｘ In the embodiment represented by (1.45 ≤ x ≤ 1.55), one of the additive / synergistic effects of using the second mineralizer together with the first mineralizer is that the cubic REO in the crystal growth process ｘ The growth of single-phase crystals becomes dominant, and the generation of REO(OH) is suppressed. This has been specifically confirmed for various REs in the examples described later. The elements contained in the second mineralizing agent may be contained in the rare earth oxide crystals that are ultimately obtained.

[0066] 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 first mineralizer and a solution of the second mineralizer, adjusted to any concentration, may be added to the raw material mixture and further mixed as necessary. Alternatively, the first mineralizer and the second mineralizer (preferably in powder or tablet form) may be added to the raw material mixture and further mixed as necessary. Alternatively, the above-mentioned raw materials may be added to an aqueous solution obtained by mixing a solution of the first mineralizer and a solution of the second mineralizer, adjusted to any concentration, and mixed as appropriate.

[0067] Here, the concentration of the first mineralizer 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 first mineralizer may be in the range of 1 M to less than 30 M, in the range of 1 M to 25 M, in the range of 1 M to 20 M, in the range of 3 M to 20 M, in the range of 5 M to 20 M, or in the range of 7 M to 20 M.

[0068] 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 first mineralizing agent used, and the concentration of the first 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 first mineralizing agent. It is also preferable to select the type of first mineralizing agent depending on the raw materials used and / or the type of constituent elements of the target crystal.

[0069] Furthermore, the concentration of the second mineralizer in the final solution is preferably in the range of 0.01 M to 20 M, more preferably in the range of 0.02 M to 15 M, even more preferably in the range of 0.03 M to 12 M, even more preferably in the range of 0.05 M to 10 M, and particularly preferably in the range of 0.1 M to 7 M. By having the concentration of the second mineralizer within the above range, the growth temperature of the target crystal is lowered, making it possible to grow larger crystals. On the other hand, if the concentration of the second mineralizer is less than 0.01 M, the above-mentioned effects may not be sufficiently obtained, and if the concentration of the second mineralizer exceeds 20 M, the contamination of elements derived from the second mineralizer may exceed the acceptable range, making it difficult to apply the solution to the intended use of the grown crystal.

[0070] 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 less than 750°C. This ensures that the desired crystals can be reliably obtained. If the temperature is below 400°C, the desired crystals may not be formed, if the temperature is above 750°C, it becomes difficult to increase the size of the crystals, and if the temperature exceeds 800°C, it may exceed the heat resistance temperature of the reaction vessel. 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. The pressure is affected by the amount of water contained in the reaction vessel, the size of the ampoule (sealed container) containing the reaction solution, the temperature, 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.

[0071] 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 target crystal. An example of a specific temperature profile is shown in the embodiments described later.

[0072] In the manufacturing method according to this embodiment, crystals are grown by hydrothermal synthesis at significantly lower temperature conditions compared to conventional methods. For example, with the floating zone (FZ) method, it is difficult to grow large crystals. In contrast, with the skull melt method, it is possible to grow large crystals, but due to the principle of crystal growth, residual stress and dislocations caused by the steep temperature gradient in the crystal growth field may occur, raising concerns that various defects may remain in the grown crystal. The manufacturing method of the present invention makes it possible to grow large crystals and suppress the various defects mentioned above. Furthermore, in other melt growth methods, including the FZ method, the phenomenon of evaporation of specific components during the crystal growth process is likely to occur due to the melting point of the target crystal, and such decomposition and evaporation phenomena may also occur in the grown crystal, potentially causing defects in the grown crystal. However, with 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 the case of hydrothermal synthesis, the resulting crystals are obtained with the most stable composition. While this composition may deviate slightly from the target composition, any such deviation can be adjusted.

[0073] [Uses of Rare Earth Oxide Crystals] The uses of the rare earth oxide crystals of the present invention, which can be manufactured as described above, are not particularly limited. However, in one exemplary embodiment, they are suitable for use as a Faraday rotator, and a photoisolator can be constructed using a Faraday rotator made of the rare earth oxide crystals of the present invention.

[0074] <Optical Isolator> Figure 1 is a schematic diagram showing one embodiment of the optical isolator according to the present invention. As shown in Figure 1, the optical isolator 100 comprises a polarizer 110, a Faraday rotator 120, and an analyzer 130. Here, the Faraday rotator 120 is made of the rare earth oxide crystal of the present invention. The polarizer 110 and the analyzer 130 are arranged so that their transmission axes are non-parallel to each other, for example, at an angle of 45°.

[0075] A magnetic flux density B is applied to the Faraday rotator 120, for example, in the direction from the polarizer 110 toward the analyzer 130, that is, along the incident direction of light L1. By applying the magnetic flux density B, the Faraday rotator 120 rotates the polarization plane of the light L1 that has passed through the polarizer 110, causing it to pass through the transmission axis of the analyzer 130.

[0076] Here, the optical isolator 100 is not limited to the above configuration, and any configuration having at least one polarizer or analyzer is acceptable. That is, an analyzer 130 may be used instead of a polarizer 110, so that both are analyzers, or a polarizer 110 may be used instead of an analyzer 130, so that both are polarizers. This configuration is called a polarization-dependent type, but the configuration of the optical isolator is not limited to this, and for example, a polarization-independent type may also be used.

[0077] Figure 2 is a schematic diagram showing another embodiment of the optical isolator according to the present invention. As shown in Figure 2, the optical isolator 200 comprises polarizers 210 (210a, 210b), a Faraday rotator 220, and a half-wave plate 230. The optical isolator 200 according to this embodiment has a configuration called polarization-independent, and is characterized by being usable regardless of the polarization state of the incident light. Here, the Faraday rotator 220 is made of the rare-earth oxide crystal of the present invention. The polarizers 210a and 210b are made of, for example, birefringent crystals. Note that the configuration of the optical isolator is not limited to the embodiment shown in Figure 2, and various design changes are possible, such as a configuration without a wave plate.

[0078] In the optical isolator 200 shown in Figure 2, when light L2, indicated by the rightward arrow, is incident on the polarizer 210a, the incident light is separated into ordinary light and extraordinary light, whose polarization planes are 90° apart (birefringence). These polarizations are rotated by 45° by the Faraday rotator 220 and another 45° by the half-wave plate 230 (i.e., rotated by a total of 90°), so that the ordinary light becomes the extraordinary light and the extraordinary light becomes the ordinary light, and so on, before being incident on the polarizer 210b. As a result, the light is combined at the polarizer 210b and emitted as a single beam of light. On the other hand, light in the opposite direction is separated into ordinary light and extraordinary light at the polarizer 210b, as in the case described above, and passes through the half-wave plate 230 and the Faraday rotator 220, but unlike the case described above, the polarization planes remain in their original state, so it is emitted without being combined at the polarizer 210a. The combination of rotation angle and waveplate generated by the Faraday rotor is illustrative and not limited to the above-described embodiment.

[0079] Optical isolators 100 and 200 having the above-described configuration can be suitably used, for example, in optical communication equipment or optical communication lines. Examples of optical communication equipment include, but are not limited to, optical amplifiers (optical amps) that constitute repeaters. Examples of optical communication lines include, but are not limited to, optical submarine cables and optical cables for terrestrial communication. Furthermore, the applications of the optical isolators of the present invention are not limited to the optical communication equipment and optical communication lines described above, but can also be used in fields such as laser processing machines (also called optical processing machines) and other laser technology fields.

[0080] <Laser Processing Machine> Here, the laser processing machine according to the present invention will be described with reference to Figure 3. In Figure 3, components that are the same as or equivalent to those in Figure 1 or Figure 2 are denoted by the same reference numerals, and redundant explanations are omitted.

[0081] Figure 3 is a schematic diagram showing one embodiment of a laser processing machine according to the present invention. As shown in Figure 3, the laser processing machine 300 includes a laser light source 310 and an optical isolator 100 (or optical isolator 200) arranged on the optical path P of the laser light L3 emitted from the laser light source 310. With this laser processing machine 300, the laser light L3 emitted from the laser light source 310 passes through the optical isolator 100 (or optical isolator 200) and is emitted, and the workpiece Q can be processed by the emitted light. The laser light source 310 is not particularly limited, and a laser light source having a predetermined oscillation wavelength can be used.

[0082] Here, the rare earth oxide crystal of the present invention used in the Faraday rotor of the optical isolator 100 (reference numeral 120 in Figure 1) or the Faraday rotor of the optical isolator 200 (reference numeral 220 in Figure 1) is transparent, so the absorption of light by the crystal is reduced. For this reason, in the laser processing machine 300 according to this embodiment, the damage resistance of the laser light source 310 due to light from the Faraday rotor can be increased.

[0083] Furthermore, the rare-earth oxide crystal of the present invention used as a Faraday rotor has extremely few defects within the crystal, thus suppressing crack formation and exhibiting a larger Faraday rotation angle than conventional Faraday rotors. Therefore, in the laser processing machine 300 according to this embodiment, it is possible to miniaturize, reduce the cost of, and extend the lifespan of the optical isolator 100 (or optical isolator 200). As a result, not only is it possible to reduce the frequency of replacement of the optical isolator 100 (or optical isolator 200) in the laser processing machine 300, but it is also possible to increase the output of the laser light source 310 used in the laser processing machine 300.

[0084] In the above embodiment, the optical isolator composed of the rare earth oxide crystal of the present invention is used as an optical isolator for a laser processing machine. However, the rare earth oxide crystal of the present invention is not limited to optical isolators and can also be applied to optical magnetic field sensors that observe changes in the magnetic field by measuring changes in the Faraday rotation angle using a Faraday rotor. Furthermore, the rare earth oxide crystal of the present invention can be used for applications other than Faraday rotors.

[0085] In another exemplary embodiment, the rare earth oxide crystals of the present invention are suitable for use as scintillators. In particular, because the rare earth oxide crystals of the present invention have very few defects, scintillators made from the rare earth oxide crystals of the present invention 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 existing materials.

[0086] <Radiation Detector> The use of the above-mentioned scintillator, which is in the form of a crystal, 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 4, a radiation detector 400 according to one embodiment of the present invention comprises a scintillator 410 made of the rare earth oxide crystal of the present invention, and a photoelectric converter 420 (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 L4 emitted from the scintillator 410 and converts it into an electrical signal. By using the above-mentioned scintillator made of rare earth oxide crystal instead of the scintillator used in conventional radiation detectors, an improvement in the accuracy of radiation detection can be expected.

[0087] 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 5, a radiation inspection device 500 according to one embodiment of the present invention comprises a radiation detector 400 (see Figure 4) and a radiation source 530, wherein the radiation source 530 irradiates the subject Sbj with radiation R, and the radiation detector 400 is configured to detect radiation E that penetrates the subject Sbj. In the radiation detector 400, the scintillator 410 emits (luminesces) light L5 when excited by radiation E, and the photoelectric converter 420 detects the light L5 emitted from the scintillator 410 and converts it into an electrical signal. Such a radiation inspection device 500 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.).

[0088] 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 rays and astrophysics.

[0089] In yet another exemplary embodiment, the rare earth oxide crystal of the present invention may be suitable for use as a magnetic refrigeration material. Alternatively, in yet another embodiment, the rare earth oxide crystal of the present invention may be suitable for use as a laser material capable of oscillating at various wavelengths. Alternatively, in yet another embodiment, the rare earth oxide crystal of the present invention may be suitable for use as a laser host material. Alternatively, in yet another embodiment, the rare earth oxide crystal of the present invention may also be suitable as a phosphor material.

[0090] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0091] [Crystal Production] <Example 1: RE = Ce> CeO ２ (In powder form, manufactured by Furuuchi Chemical Co., Ltd.) was prepared. The CEO ２ , KOH as the first mineralizing agent (a tablet equivalent to a 20M aqueous solution), and Al as the second mineralizing agent ２ O ３ A silver ampoule (5 mm in diameter x 10 cm in length) containing a quantity of powder equivalent to a 0.2 M aqueous solution and 0.65 mL of pure water was 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 40 hours to complete crystal growth. The maximum pressure reached during this process was 160 MPa. After crystal growth, the mixture was allowed to cool naturally. This yielded the crystals of Example 1.

[0092] <Example 2: RE = Tb> As a raw material for Tb, Tb ２ O ３ (In powder form) was prepared. Tb ２ O ３ , KOH as the first mineralizing agent (a tablet equivalent to a 20M aqueous solution), and Al as the second mineralizing agent ２ O ３ A corresponding amount of powder (to make a 0.2 M aqueous solution) and pure water (0.65 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 were the same as in Example 1, and the crystals of Example 2 were obtained. The maximum pressure reached during crystal growth was 150 MPa.

[0093] <Example 3: RE = Gd> As a raw material for Gd, Gd ２ O ３ (In powder form, manufactured by Furuuchi Chemical Co., Ltd.) was prepared. ２ O ３ , KOH as the first mineralizing agent (a tablet equivalent to a 20M aqueous solution), and Al as the second mineralizing agent ２ O ３A corresponding amount of powder (to make a 0.2 M aqueous solution) and pure water (0.65 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 were the same as in Example 1, and the crystals of Example 3 were obtained. The maximum pressure reached during crystal growth was 180 MPa.

[0094] <Example 4: RE = Y> Y is used as a raw material for Y. ２ O ３ (In powder form, manufactured by Furuuchi Chemical Co., Ltd.) was prepared. ２ O ３ , KOH as the first mineralizing agent (a tablet equivalent to a 20M aqueous solution), and Al as the second mineralizing agent ２ O ３ A corresponding amount of powder (to make a 0.2 M aqueous solution) and pure water (0.65 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 conditions for hydrothermal synthesis were the same as in Example 1, except that the holding time at 700°C was 50 hours, and the crystals of Example 4 were obtained. The maximum pressure reached during crystal growth was 158 MPa.

[0095] <Example 4a: RE=Y (with Tb added)> Tb as a raw material for Tb ２ O ３ Prepare (powdered), Y ２ O ３ The amount added to Y should be 1 mol% (i.e., Y ２ O ３ and Tb ２ O ３ The materials were weighed and mixed (so that the molar ratio of Y:Tb = 0.99:0.01) to obtain a powdered raw material mixture. The subsequent procedures and crystal growth conditions were the same as in Example 4 to obtain the crystal of Example 4a.

[0096] <Example 4b: RE=Y (Eu added)> Eu is used as a raw material for Eu ２ O ３ Prepare (powdered, manufactured by Furuuchi Chemical Co., Ltd.), Y ２ O ３ The amount added to Y should be 1 mol% (i.e., Y ２ O ３and EU ２ O ３ The materials were weighed and mixed (so that the molar ratio of Y:Eu = 0.99:0.01) to obtain a powdered raw material mixture. The subsequent procedures and crystal growth conditions were the same as in Example 4 to obtain the crystal of Example 4b.

[0097] <Example 4c: RE=Y (Pr added)> Pr as a raw material for Pr ６ O １１ Prepare (powdered, manufactured by Furuuchi Chemical Co., Ltd.), Y ２ O ３ The amount added to Y should be 1 mol% (i.e., Y ２ O ３ and Pr ６ O １１ The materials were weighed and mixed (so that the molar ratio of Y:Pr = 0.99:0.01) to obtain a powdered raw material mixture. The subsequent procedures and crystal growth conditions were the same as in Example 4 to obtain the crystal of Example 4c.

[0098] <Example 4d: RE=Y (Nd added)> Nd as a raw material ２ O ３ Prepare (powdered, manufactured by Furuuchi Chemical Co., Ltd.), Y ２ O ３ The amount added to Y should be 1 mol% (i.e., Y ２ O ３ and Nd ２ O ３ The materials were weighed and mixed (so that the molar ratio of Y:Nd = 0.99:0.01) to obtain a powdered raw material mixture. The subsequent procedures and crystal growth conditions were the same as in Example 4 to obtain the crystal of Example 4d.

[0099] <Example 5: RE = Lu> Lu is used as a raw material for Lu ２ O ３ (In powder form, manufactured by Furuuchi Chemical Co., Ltd.) was prepared. ２ O ３ , KOH as the first mineralizing agent (a tablet equivalent to a 20M aqueous solution), and Al as the second mineralizing agent ２ O ３A corresponding amount of powder (to make a 0.2 M aqueous solution) and pure water (0.65 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 were the same as in Example 4, and the crystals of Example 5 were obtained. The maximum pressure reached during crystal growth was 153 MPa.

[0100] <Example 5a: RE = Lu (with Tb added)> Tb as a raw material for Tb ２ O ３ Prepare (powdered) Lu ２ O ３ The amount added to the ratio should be 1 mol% (i.e., Lu ２ O ３ and Tb ２ O ３ The materials were weighed and mixed (in such a molar ratio that Lu:Tb = 0.99:0.01) to obtain a powdered raw material mixture. The subsequent procedures and crystal growth conditions were the same as in Example 5 to obtain the crystal of Example 5a.

[0101] <Example 5b: RE = Lu (Eu added)> Eu is used as a raw material for Eu ２ O ３ Prepare (powdered, manufactured by Furuchi Chemical Co., Ltd.) and Lu ２ O ３ The amount added to the ratio should be 1 mol% (i.e., Lu ２ O ３ and EU ２ O ３ The materials were weighed and mixed (in such a molar ratio that Lu:Eu = 0.99:0.01) to obtain a powdered raw material mixture. The subsequent procedures and crystal growth conditions were the same as in Example 5 to obtain the crystal of Example 5b.

[0102] <Example 5c: RE = Lu (Pr added)> Pr as a raw material for Pr ６ O １１ Prepare (powdered, manufactured by Furuchi Chemical Co., Ltd.) and Lu ２ O ３ The amount added to the ratio should be 1 mol% (i.e., Lu ２ O ３ and Pr ６ O １１The materials were weighed (in a molar ratio of Lu:Pr = 0.99:0.01) and mixed to obtain a powdered raw material mixture. The subsequent procedures and crystal growth conditions were the same as in Example 5 to obtain the crystal of Example 5c.

[0103] <Example 5d: RE=Y (Nd added)> Nd as a raw material ２ O ３ Prepare (powdered, manufactured by Furuchi Chemical Co., Ltd.) and Lu ２ O ３ The amount added to the ratio should be 1 mol% (i.e., Lu ２ O ３ and Nd ２ O ３ The materials were weighed and mixed (so that the molar ratio of Lu:Nd = 0.99:0.01) to obtain a powdered raw material mixture. The subsequent procedures and crystal growth conditions were the same as in Example 5 to obtain the crystal of Example 5d.

[0104] <Example 6: RE = Dy> Dy is used as a raw material. ２ O ３ (In powder form, manufactured by Furuuchi Chemical Co., Ltd.) was prepared. ２ O ３ , KOH as the first mineralizing agent (a tablet equivalent to a 20M aqueous solution), and Al as the second mineralizing agent ２ O ３ A corresponding amount of powder (to make a 0.2 M aqueous solution) and pure water (0.65 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 were the same as in Example 1, and the crystals of Example 6 were obtained. The maximum pressure reached during crystal growth was 152 MPa.

[0105] <Example 7: RE = Ho> As a raw material for Ho, Ho ２ O ３ (In powder form, manufactured by Furuuchi Chemical Co., Ltd.) was prepared. ２ O ３ , KOH as the first mineralizing agent (a tablet equivalent to a 20M aqueous solution), and Al as the second mineralizing agent ２ O ３A corresponding amount of powder (to make a 0.2 M aqueous solution) and pure water (0.65 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 were the same as in Example 1, and the crystals of Example 7 were obtained. The maximum pressure reached during crystal growth was 169 MPa.

[0106] <Example 8: RE = Er> Er is used as a raw material for Er ２ O ３ (In powder form, manufactured by Furuuchi Chemical Co., Ltd.) was prepared. ２ O ３ , KOH as the first mineralizing agent (a tablet equivalent to a 20M aqueous solution), and Al as the second mineralizing agent ２ O ３ A corresponding amount of powder (to make a 0.2 M aqueous solution) and pure water (0.65 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 were the same as in Example 1, and the crystals of Example 8 were obtained. The maximum pressure reached during crystal growth was 158 MPa.

[0107] <Example 9: RE = Tm> As a raw material for Tm, Tm ２ O ３ (In powder form, manufactured by Furuuchi Chemical Co., Ltd.) was prepared. ２ O ３ , KOH as the first mineralizing agent (a tablet equivalent to a 20M aqueous solution), and Al as the second mineralizing agent ２ O ３ A corresponding amount of powder (to make a 0.2 M aqueous solution) and pure water (0.65 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 were the same as in Example 1, and the crystals of Example 9 were obtained. The maximum pressure reached during crystal growth was 157 MPa.

[0108] <Example 10: RE = Yb> Yb is used as a raw material for Yb. ２ O ３ (In powder form, manufactured by Furuuchi Chemical Co., Ltd.) was prepared. Yb ２ O ３, KOH as the first mineralizing agent (a tablet equivalent to a 20M aqueous solution), and Al as the second mineralizing agent ２ O ３ A corresponding amount of powder (to make a 0.2 M aqueous solution) and pure water (0.65 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 were the same as in Example 1, and the crystals of Example 10 were obtained. The maximum pressure reached during crystal growth was 173 MPa.

[0109] <Example 11: RE = La> As a raw material for La, La ２ O ３ (In powder form, manufactured by Furuuchi Chemical Co., Ltd.) was prepared. ２ O ３ , KOH as the first mineralizing agent (a tablet equivalent to a 20M aqueous solution), and Al as the second mineralizing agent ２ O ３ A corresponding amount of powder (to make a 0.2 M aqueous solution) and pure water (0.65 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 were the same as in Example 1, and the crystals of Example 11 were obtained. The maximum pressure reached during crystal growth was 169 MPa.

[0110] <Example 12: RE = Pr> As a raw material for Pr, Pr ２ O ３ (In powder form, manufactured by Furuuchi Chemical Co., Ltd.) was prepared. ２ O ３ , KOH as the first mineralizing agent (a tablet equivalent to a 20M aqueous solution), and Al as the second mineralizing agent ２ O ３ A corresponding amount of powder (to make a 0.2 M aqueous solution) and pure water (0.65 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 were the same as in Example 1, and the crystals of Example 12 were obtained. The maximum pressure reached during crystal growth was 171 MPa.

[0111] <Example 13: RE = Nd> As a raw material for Nd, ２O ３ (In powder form, manufactured by Furuuchi Chemical Co., Ltd.) was prepared. ２ O ３ , KOH as the first mineralizing agent (a tablet equivalent to a 20M aqueous solution), and Al as the second mineralizing agent ２ O ３ A corresponding amount of powder (to make a 0.2 M aqueous solution) and pure water (0.65 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 were the same as in Example 1, and the crystals of Example 13 were obtained. The maximum pressure reached during crystal growth was 177 MPa.

[0112] <Example 14: RE = Sm> Sm is used as a raw material for Sm. ２ O ３ (In powder form, manufactured by Furuuchi Chemical Co., Ltd.) was prepared. ２ O ３ , KOH as the first mineralizing agent (a tablet equivalent to a 20M aqueous solution), and Al as the second mineralizing agent ２ O ３ A corresponding amount of powder (to make a 0.2 M aqueous solution) and pure water (0.65 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 were the same as in Example 1, and the crystals of Example 14 were obtained. The maximum pressure reached during crystal growth was 178 MPa.

[0113] <Example 15: RE = Eu> Eu is used as a raw material for Eu. ２ O ３ (In powder form, manufactured by Furuuchi Chemical Co., Ltd.) was prepared. ２ O ３ , KOH as the first mineralizing agent (a tablet equivalent to a 20M aqueous solution), and Al as the second mineralizing agent ２ O ３A corresponding amount of powder (to make a 0.2 M aqueous solution) and pure water (0.65 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 were the same as in Example 1, and the crystals of Example 15 were obtained. The maximum pressure reached during crystal growth was 168 MPa.

[0114] <Example 16: RE=Ce> The crystals of Example 16 were prepared using the same procedure as in Example 1. However, in this example, the second mineralizing agent was not used. The maximum pressure reached during crystal growth was 150 MPa.

[0115] <Example 17: RE = Tb> The crystals of Example 17 were prepared using the same procedure as in Example 2. However, in this example, the second mineralizing agent was not used. The maximum pressure reached during crystal growth was 170 MPa.

[0116] <Example 18: RE = Gd> The crystals of Example 18 were prepared using the same procedure as in Example 3. However, in this example, the second mineralizing agent was not used. The maximum pressure reached during crystal growth was 160 MPa.

[0117] <Example 19: RE=Y> The crystal of Example 19 was prepared using the same procedure as in Example 4. However, in this example, the second mineralizing agent was not used, and the holding time at 700°C was set to 40 hours. The maximum pressure reached during crystal growth was 165 MPa.

[0118] <Example 20: RE=Lu> The crystals of Example 20 were prepared using the same procedure as in Example 5. However, in this example, the second mineralizing agent was not used, and the holding time at 700°C was set to 40 hours. The maximum pressure reached during crystal growth was 175 MPa.

[0119] <Example 21: RE=Dy> The crystals of Example 21 were prepared using the same procedure as in Example 6. However, in this example, the second mineralizing agent was not used. The maximum pressure reached during crystal growth was 154 MPa.

[0120] <Example 22: RE = Ho> The crystals of Example 22 were prepared using the same procedure as in Example 7. However, in this example, the second mineralizing agent was not used. The maximum pressure reached during crystal growth was 166 MPa.

[0121] <Example 23: RE = Er> The crystals of Example 23 were prepared using the same procedure as in Example 8. However, in this example, the second mineralizing agent was not used. The maximum pressure reached during crystal growth was 157 MPa.

[0122] <Example 24: RE = Tm> The crystals of Example 24 were prepared using the same procedure as in Example 9. However, in this example, the second mineralizing agent was not used. The maximum pressure reached during crystal growth was 156 MPa.

[0123] <Example 25: RE=Yb> The crystals of Example 25 were prepared using the same procedure as in Example 10. However, in this example, the second mineralizing agent was not used. The maximum pressure reached during crystal growth was 162 MPa.

[0124] <Example 26: RE=La> The crystals of Example 26 were prepared using the same procedure as in Example 11. However, in this example, the second mineralizing agent was not used. The maximum pressure reached during crystal growth was 171 MPa.

[0125] <Example 27: RE=Pr> The crystals of Example 27 were prepared using the same procedure as in Example 12. However, in this example, the second mineralizing agent was not used. The maximum pressure reached during crystal growth was 182 MPa.

[0126] <Example 28: RE=Nd> The crystals of Example 28 were prepared using the same procedure as in Example 13. However, in this example, the second mineralizing agent was not used. The maximum pressure reached during crystal growth was 148 MPa.

[0127] <Example 29: RE = Sm> The crystals of Example 29 were prepared using the same procedure as in Example 14. However, in this example, the second mineralizing agent was not used. The maximum pressure reached during crystal growth was 167 MPa.

[0128] <Example 30: RE = Eu> The crystals of Example 30 were prepared using the same procedure as in Example 15. However, in this example, the second mineralizing agent was not used. The maximum pressure reached during crystal growth was 157 MPa.

[0129] <Example 31: RE = Tb> As a raw material for Tb, Tb ２ O ３ (In powder form) was prepared. Tb ２ O ３, NaOH as the first mineralizing agent (a tablet equivalent to a 20M aqueous solution), Al as the second mineralizing agent ２ O ３ A silver ampoule (5 mm in diameter x 10 cm in length) containing a quantity of powder equivalent to a 0.2 M aqueous solution and 0.65 mL of pure water was 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 730°C over 12 hours and holding it for 100 hours to complete crystal growth. The maximum pressure reached during this process was 151.4 MPa. After crystal growth, the mixture was allowed to cool naturally. This yielded the crystals of Example 31.

[0130] <Example 32: RE = Tb> As a raw material for Tb, Tb ２ O ３ (In powder form) was prepared. Tb ２ O ３ , KOH as the first mineralizing agent (a tablet equivalent to a 20M aqueous solution), and Al as the second mineralizing agent ２ O ３ A silver ampoule (5 mm in diameter x 10 cm in length) containing a quantity of powder equivalent to a 0.2 M aqueous solution and 0.65 mL of pure water was 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 590°C over 12 hours and holding it for 100 hours to complete crystal growth. The maximum pressure reached during this process was 136.3 MPa. After crystal growth, the mixture was allowed to cool naturally. This yielded the crystals of Example 32.

[0131] <Example 33: RE = Tb> As a raw material for Tb, Tb ２ O ３ (In powder form) was prepared. Tb ２ O ３ , RbOH (10 M aqueous solution, 0.85 mL) as the first mineralizing agent, and Al as the second mineralizing agent ２ O ３A quantity of powder equivalent to a 0.2 M aqueous solution was 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 were the same as in Example 31, and the crystals of Example 33 were obtained. The maximum pressure reached during crystal growth was 133.7 MPa.

[0132] <Example 34: RE = Tb> As a raw material for Tb, Tb ２ O ３ (In powder form) was prepared. Tb ２ O ３ , CsOH (6.7 M aqueous solution, 0.85 mL) as the first mineralizing agent, and Al as the second mineralizing agent ２ O ３ A quantity of powder equivalent to a 0.2 M aqueous solution was 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 were the same as in Example 31, and the crystals of Example 34 were obtained. The maximum pressure reached during crystal growth was 166.6 MPa.

[0133] Tables 16-1, 16-2, and 16-3 show the crystal manufacturing conditions for Examples 1 to 15, 16 to 30, and 31 to 34, respectively.

[0134]

[0135]

[0136]

[0137] [Measurement and Evaluation] <Microscopic Observation> The crystals obtained in each of the above examples were observed with an optical microscope. Figures 6-1 to 6-18 show microscopic images of the crystals from Examples 1 to 4, Examples 4a to 4d, Example 5, Examples 5a to 5d, and Examples 6 to 10 as representative examples. The scale bar in each image is 1 mm in Figures 6-1, 6-2, 6-11, and 6-12, 2 mm in Figures 6-13 and 6-18, 3 mm in Figure 6-10, and 0.5 mm (500 μm) for all others.

[0138] As shown in Figures 6-1 to 6-18, the obtained crystals were confirmed to have high transparency under microscopic observation. Although not shown, the crystals of Examples 11 to 15 were also highly transparent. On the other hand, the crystals of Examples 16 to 30 had a certain degree of transparency, but their shapes differed from those of Examples 1 to 15, being needle-shaped and plate-shaped. When comparing crystals with common RE (for example, the crystal of Example 1 and the crystal of Example 16), the difference in crystal shape was clear. From these results, the effectiveness of using the above-mentioned first and second mineralizing agents in combination as mineralizing agents in hydrothermal synthesis was confirmed. Although not shown, the crystals of Examples 31 to 34, which were prepared using different materials as the first mineralizing agent, were also highly transparent.

[0139] <X-ray Diffraction Measurement> Powder samples were prepared from the crystals of each example, and powder X-ray diffraction measurements were performed. Figures 7-1 to 7-17 show the measurement results for the crystals of Examples 1 to 10, Examples 17 to 19, and Examples 31 to 34 as representative examples.

[0140] The upper part of Figure 7-1 shows the powder X-ray diffraction measurement results of the crystal in Example 1, and the lower part of Figure 7-1 shows the results of CeO ２ The simulation results of the diffraction chart for the cubic crystal system F m -3 m are shown. 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 15 above are important as they serve as a basis for estimating or determining the space group of the rare earth oxide crystal of the present invention. Furthermore, the crystal structure of the rare earth oxide crystal of the present invention can be approximately defined using other crystal systems such as cubic or hexagonal. In that case, the expression will use a different space group, lattice constant, and plane indices, but the X-ray diffraction measurement results (e.g., upper panel of Figure 4-1) and the crystal structure will remain the same, and the identification method and identification results will also be the same. For this reason, in this embodiment, powder X-ray diffraction measurements were performed as either cubic or hexagonal.

[0141] As shown in Figure 7-1, the diffraction chart of the crystal in Example 1 showed a high degree of agreement in peak position (angle 2θ) with the diffraction chart obtained from the above simulation. Therefore, the obtained crystal is a cubic CeO ２ It was confirmed that the crystalline phase (F m - 3 m) exists.

[0142] The upper part of Figure 7-2 shows the powder X-ray diffraction measurement results of the crystal in Example 2, and the lower part of Figure 7-2 shows Tb ２ O ３ The simulation results of the diffraction chart for (cubic crystal system I a -3) are shown.

[0143] As shown in Figure 7-2, the diffraction chart of the crystal in Example 2 showed a high degree of agreement in peak position (angle 2θ) with the diffraction chart obtained from the above simulation. Therefore, the obtained crystal is a cubic Tb crystal. ２ O ３ It was confirmed that it possesses a crystalline phase of (I a -3).

[0144] Here, comparing the diffraction chart of the crystal in Example 2 and the crystal in Example 17, which share the same RE, with the diffraction chart shown in the lower part of Figure 7-2, it was found that, unlike the crystal in Example 2, the peak positions (angle 2θ) do not match. Therefore, a comparison was made with the simulation results of the diffraction charts of terbium (oxy) hydroxide (monoclinic) and terbium trihydroxyl (hexagonal).

[0145] The upper part of Figure 7-3 shows the powder X-ray diffraction measurement results of the crystal of Example 17, and the middle and lower parts of Figure 7-3 show, respectively, TbO ２ H and Tb(OH) ３ The simulation results of the diffraction chart are shown.

[0146] As shown in Figure 7-3, the diffraction chart of the crystal in Example 17 was found to have characteristics that combine the two types of diffraction charts obtained from the above simulation. As a result, the obtained crystal is monoclinic TbO ２ H and hexagonal Tb(OH) ３ It is a mixture of cubic Tb ２ O ３ It was confirmed that it does not have a crystalline phase.

[0147] The upper part of Figure 7-4 shows the powder X-ray diffraction measurement results of the crystal in Example 3, and the lower part of Figure 7-4 shows Gd ２ O ３ The simulation results of the diffraction chart for (cubic crystal system I a -3) are shown.

[0148] As shown in Figure 7-4, the diffraction chart of the crystal in Example 3 showed a high degree of agreement in peak position (angle 2θ) with the diffraction chart obtained from the above simulation. Therefore, the obtained crystal is a cubic Gd crystal. ２ O ３ It was confirmed that it possesses a crystalline phase of (I a -3).

[0149] Here, comparing the diffraction chart of the crystal in Example 3 and the crystal in Example 18, which share the same RE, with the diffraction chart shown in the lower part of Figure 7-4, it was found that, unlike the crystal in Example 3, the peak positions (angle 2θ) do not match. Therefore, a comparison was made with the simulation results of the diffraction charts of gadolinium (oxy) hydroxide (monoclinic) and gadolinium trihydroxyl (hexagonal).

[0150] The upper part of Figure 7-5 shows the powder X-ray diffraction measurement results of the crystal of Example 18, and the middle and lower parts of Figure 7-5 show, respectively, GdO ２ H and Gd(OH) ３ The simulation results of the diffraction chart are shown.

[0151] As shown in Figure 7-5, the diffraction chart of the crystal in Example 18 was found to have characteristics that combine the two types of diffraction charts obtained from the above simulation. As a result, the obtained crystal is monoclinic GdO ２ H and hexagonal Gd(OH) ３ It is a mixture of cubic Gd ２ O ３ It was confirmed that it does not have a crystalline phase.

[0152] The upper part of Figure 7-6 shows the powder X-ray diffraction measurement results of the crystal in Example 4, and the lower part of Figure 7-6 shows Y ２ O ３ The simulation results of the diffraction chart for (cubic crystal system I a -3) are shown.

[0153] As shown in Figure 7-6, the diffraction chart of the crystal in Example 4 showed a high degree of agreement in peak position (angle 2θ) with the diffraction chart obtained from the above simulation. Therefore, the obtained crystal is a cubic Y crystal. ２ O ３ It was confirmed that it possesses a crystalline phase of (I a -3).

[0154] Here, comparing the diffraction chart of the crystal in Example 4 and the crystal in Example 19, which share the same RE, with the diffraction chart shown in the lower part of Figure 7-6, it was found that, unlike the crystal in Example 4, the peak positions (angle 2θ) do not match. Therefore, a comparison was made with the simulation results of the diffraction charts of yttrium (oxy) hydroxide (monoclinic) and yttrium trihydroxyl (hexagonal).

[0155] The upper part of Figure 7-7 shows the powder X-ray diffraction measurement results of the crystal of Example 19, and the middle and lower parts of Figure 7-7 show, respectively, YO ２ H and Y (OH) ３ The simulation results of the diffraction chart are shown.

[0156] As shown in Figure 7-7, the diffraction chart of the crystal in Example 19 was found to have characteristics that combine the two types of diffraction charts obtained from the above simulation. As a result, the obtained crystal is monoclinic YO ２ H and hexagonal Y (OH) ３ It is a mixture of cubic Y ２ O ３ It was confirmed that it does not have a crystalline phase.

[0157] The upper part of Figure 7-8 shows the powder X-ray diffraction measurement results of the crystal in Example 5, and the lower part of Figure 7-8 shows Lu ２ O ３ The simulation results of the diffraction chart for (cubic crystal system I a -3) are shown.

[0158] As shown in Figure 7-8, the diffraction chart of the crystal in Example 5 showed a high degree of agreement in peak position (angle 2θ) with the diffraction chart obtained from the above simulation. Therefore, the obtained crystal is a cubic Lu crystal. ２ O３ It was confirmed that it possesses a crystalline phase of (I a -3).

[0159] The upper part of Figure 7-9 shows the powder X-ray diffraction measurement results of the crystal in Example 6, and the lower part of Figure 7-9 shows Dy ２ O ３ The simulation results of the diffraction chart for (cubic crystal system I a -3) are shown.

[0160] As shown in Figure 7-9, the diffraction chart of the crystal in Example 6 showed a high degree of agreement in peak position (angle 2θ) with the diffraction chart obtained from the above simulation. Therefore, the obtained crystal is a cubic Dy ２ O ３ It was confirmed that it possesses a crystalline phase of (I a -3).

[0161] The upper part of Figure 7-10 shows the powder X-ray diffraction measurement results of the crystal in Example 7, and the lower part of Figure 7-10 shows Ho ２ O ３ The simulation results of the diffraction chart for (cubic crystal system I a -3) are shown.

[0162] As shown in Figure 7-10, the diffraction chart of the crystal in Example 7 showed a high degree of agreement in peak position (angle 2θ) with the diffraction chart obtained from the above simulation. Therefore, the obtained crystal is a cubic Ho crystal. ２ O ３ It was confirmed that it possesses a crystalline phase of (I a -3).

[0163] The upper part of Figure 7-11 shows the powder X-ray diffraction measurement results of the crystal in Example 8, and the lower part of Figure 7-11 shows Er ２ O ３ The simulation results of the diffraction chart for (cubic crystal system I a -3) are shown.

[0164] As shown in Figure 7-11, the diffraction chart of the crystal in Example 8 showed a high degree of agreement in peak position (angle 2θ) with the diffraction chart obtained from the above simulation. Therefore, the obtained crystal is a cubic Er crystal. ２ O ３ It was confirmed that it possesses a crystalline phase of (I a -3).

[0165] The upper part of Figure 7-12 shows the powder X-ray diffraction measurement results of the crystal in Example 9, and the lower part of Figure 7-12 shows Tm ２ O ３ The simulation results of the diffraction chart for (cubic crystal system I a -3) are shown.

[0166] As shown in Figure 7-12, the diffraction chart of the crystal in Example 9 showed a high degree of agreement in peak position (angle 2θ) with the diffraction chart obtained from the above simulation. Therefore, the obtained crystal has a cubic Tm ２ O ３ It was confirmed that it possesses a crystalline phase of (I a -3).

[0167] The upper part of Figure 7-13 shows the powder X-ray diffraction measurement results of the crystal of Example 10, and the lower part of Figure 7-13 shows Yb ２ O ３ The simulation results of the diffraction chart for (cubic crystal system I a -3) are shown.

[0168] As shown in Figure 7-13, the diffraction chart of the crystal in Example 10 showed a high degree of agreement in peak position (angle 2θ) with the diffraction chart obtained from the above simulation. Therefore, the obtained crystal is a cubic Yb crystal. ２ O ３ It was confirmed that it possesses a crystalline phase of (I a -3).

[0169] Although not shown in the diagram, the diffraction charts of the crystals in Examples 14 and 15 showed a number of peaks attributable to crystalline phases other than cubic. However, by raising the temperature reached during crystal growth in Examples 14 and 15 to 740°C, it was possible to obtain a crystal that was almost entirely cubic Sm ２ O ３ , Eu ２ O ３ It was found that a single phase could be obtained. Sm ２ O ３ and EU ２ O ３ Regarding this, it was confirmed that raising the temperature also has an effect.

[0170] The upper panels of Figures 7-14 to 7-17 show the powder X-ray diffraction measurement results for the crystals of Examples 31 to 34, respectively, and the lower panels of Figures 7-14 to 7-17 show Tb ２ O３ The simulation results of the diffraction chart of (cubic system Ia-3) are shown.

[0171] According to FIGS. 7-14 to FIGS. 7-17, it was found that the diffraction charts of the crystals of Examples 31 to 34 had a high degree of coincidence in peak positions (angle 2θ) with respect to the diffraction chart by the above simulation. Thus, the obtained crystal was confirmed to have a crystal phase of cubic Tb ２ O ３ (Ia-3).

[0172] <Secondary ion mass spectrometry> For the crystal of Example 2, the concentration of hydrogen and the concentration of potassium were measured using a secondary ion mass spectrometer (manufactured by Cameca, IMS-6F) and a time-of-flight secondary ion mass spectrometer (Time-of-flight Secondary Ion Mass Spectrometry: TOF-SIMS, manufactured by IonTOF), respectively. The results are shown in FIG. 8. The horizontal axis of FIG. 8 indicates the measurement depth (μm).

[0173] According to FIG. 8, in the obtained crystal, the concentration of hydrogen was about 1×10 １９ atoms / cm ３ at a depth of 3 μm, and satisfied 1×10 ２０ atoms / cm ３ or less. The concentration of potassium was about 3×10 １８ atom / cm ３ at a depth of 6 μm, and satisfied 1×10 １９ atoms / cm ３ or less. Also, it was confirmed that terbium and oxygen had concentration ratios that almost agreed with the theoretical composition. Also, although not shown, as a result of performing component analysis on the crystals of Example 1 and Examples 3 to 15 in the same manner, the concentration of hydrogen was in the range of 1×10 １６ atoms / cm ３ or more and 1×10 ２３ atoms / cm ３ or less, and the concentration of potassium was in the range of 1×10 １２ atoms / cm ３ or more and 1×10 ２０ atoms / cm ３It was confirmed that it was within the following range.

[0174] <Emission characteristics> Powder samples obtained by pulverizing the crystals of Examples 4a to 4c and Examples 5a to 5c were prepared, and the emission characteristics of each sample were measured. Hereinafter, the sample prepared from the crystal of Example 4a will be referred to as Sample 4a, and the same applies to samples prepared from other crystals.

[0175] For the measurement of photoluminescence (PL), a spectrofluorometer (F-7100, manufactured by Hitachi High-Tech Corporation) was used, and the emission wavelength (λ ｅｘ ) and the emission intensity when excited at a predetermined excitation wavelength (λ ｅｍ ) were measured. Further, the emission wavelength to be detected (λ ｅｍ ) was fixed at a predetermined wavelength, and the emission intensity when excited at each excitation wavelength (λ ｅｘ ) was measured to obtain an excitation spectrum.

[0176] FIGS. 9 to 11 show the PL spectra of Sample 4a, Sample 4b, and Sample 4c, respectively. Here, the excitation wavelength (λ ｅｘ ) was 302 nm for Sample 4a, 238 nm for Sample 4b, and 288 nm for Sample 4c. In each figure, the emission intensity on the vertical axis is normalized based on the peak value. Also, in each figure, based on the main emission wavelength, the excitation spectra (normalized spectra) of each sample obtained with 544 nm, 613 nm, and 632 nm as the detection wavelength (λ ｅｍ ) are also shown together.

[0177] According to FIGS. 9 to 11, it was suggested that the crystals of Examples 4a, 4b, and 4c have emission wavelengths in the range of approximately 480 nm to 750 nm. Here, for example, in the crystal of Example 4a, it was found that by substituting a part of Y with Tb based on the composition (Y ２ O ３ ) of the crystal of Example 4, emission of wavelengths in the green region was brought about. Crystals having emission wavelengths in the green region are useful as scintillators used in combination with, for example, a photodetector using a photodiode.

[0178] FIGS. 12 to 14 show the PL spectra of Sample 5a, Sample 5b, and Sample 5c, respectively. Here, the excitation wavelength (λｅｘ The emission wavelengths were 303 nm for sample 5a, 241 nm for sample 5b, and 271 nm for sample 5c. In each figure, the emission intensity on the vertical axis is normalized to the peak value. In addition, each figure shows the detection wavelengths (λ) at 544 nm, 613 nm, and 634 nm, based on the main emission wavelengths. ｅｍ The excitation spectra (normalized spectra) of each sample obtained are also shown.

[0179] Figures 12 to 14 suggest that the crystals of Examples 5a, 5b, and 5c have emission wavelengths in the range of approximately 480 nm to 750 nm. Here, for example, the crystal of Example 5a has the same composition as the crystal of Example 5 (Lu ２ O ３ It was found that by substituting a portion of Lu with Tb, based on ), emission in the green wavelength range is produced. Crystals with emission wavelengths in the green region are useful as scintillators used in combination with photodetectors, for example, using photodiodes.

[0180] As described above, the present invention can provide rare earth oxide crystals that are useful as optical materials, magnetic materials, etc. One notable example is Tb ２ O ３ It has been specifically demonstrated that it is possible to grow bulk single crystals of Sc (see Example 2 of the above examples). Considering from the viewpoint of ionic radius, there are previously reported examples of Sc ２ O ３ In crystals, the ionic radius of Sc is smaller than that of Lu, and since Lu has the smallest ionic radius among lanthanides, even in conventional hydrothermal synthesis methods, Sc ２ O ３ It is presumed that crystal growth was relatively easy. In fact, according to preliminary experiments by the inventors, not only when using the first and second mineralizing agents described above with the same procedure and crystal growth conditions as in Examples 1 to 15, but also when applying the same procedure and crystal growth conditions as in Examples 16 to 30 without using the second mineralizing agent, Sc ２ O ３ We confirmed that single crystals of Sc (and Lu) were obtained. However, for Tb (and other lanthanides) with a larger ionic radius than Sc (and Lu), Lu２ O ３ (and RE for other lanthanides) ２ O ３ It has been considered extremely difficult to stably obtain bulk single crystals of ). The manufacturing method of the present invention represents a breakthrough that overcomes these technical barriers of conventional methods.

[0181] Furthermore, according to the manufacturing method of the present invention, the type of RE is not limited, and all of the above-mentioned rare earth elements can be used comprehensively. There is a wide range of RE options, and the desired RE can be obtained. ２ or RE ２ O ３ The manufacturing method of the present invention, which can grow bulk single crystals, can be said to be extremely practical.

[0182] Furthermore, the manufacturing method of the present invention is a method for producing the above-mentioned rare earth element oxide crystals under milder conditions than conventional methods, particularly at lower temperatures. According to the manufacturing method of the present invention, it is possible to grow and produce chemically stable bulk single crystals, making it suitable for mass production and reducing manufacturing costs. In addition, since it does not use harmful substances such as cadmium, it is an environmentally friendly material, and the manufacturing process is also environmentally friendly.

[0183] The rare earth element oxide crystals and their manufacturing methods of the present invention, possessing these characteristics, are expected to be highly applicable to a wide range of uses.

[0184] 100 Optical isolator 110 Polarizer 120 Faraday rotator 130 Analyzer L1 Light B Magnetic flux density 200 Optical isolator 210 (210a, 210b) Polarizer (birefringent crystal) 220 Faraday rotator 230 Half-wave plate L2 Light 300 Laser processing machine (optical processing machine) 310 Laser light source L3 Light (laser light) P Optical path Q Workpiece 400 Radiation detector 410 Scintillator 420 Photoelectric converter L4 Light 500 Radiation inspection device 530 Radiation source L5 Light R Radiation E Radiation penetrating the subject Sbj Subject

Claims

1. Contains rare earth elements (RE) and oxygen (O), with the general formula REO ｘ A rare earth oxide crystal in which an inorganic crystal represented by (1.45 ≤ x ≤ 2.05) contains at least one hydrogen atom (H), and RE is at least one element selected from the group consisting of scandium (Sc), yttrium (Y), 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 inorganic crystal is of the general formula REO ｘ A rare earth oxide crystal according to claim 1, represented by (1.95 ≤ x ≤ 2.05).

3. The inorganic crystal is of the general formula REO ｘ A rare earth oxide crystal according to claim 1, represented by (1.45 ≤ x ≤ 1.55).

4. The concentration of hydrogen atoms contained in the inorganic crystal is 1 × 10⁻⁶ １５ atoms / cm ３ The above 1 x 10 ２３ atoms / cm ３ A rare earth oxide crystal according to any one of claims 1 to 3, wherein the crystal is within the following range.

5. The rare earth oxide crystal according to any one of claims 1 to 4, wherein the inorganic crystal has a crystal structure belonging to the I a-3 space group or the F m-3 m space group and the crystal phase is a single cubic phase, or has a crystal structure belonging to the P-3 m-1 space group and the crystal phase is a single hexagonal phase.

6. The rare earth oxide crystal according to any one of claims 1 to 5, wherein the inorganic crystal further contains at least one element selected from the group consisting of cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), and ytterbium (Yb), which is different from RE.

7. The rare earth oxide crystal according to any one of claims 1 to 6, wherein the inorganic crystal further contains an alkali metal and / or an alkaline earth metal.

8. The concentration of the 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, and the rare earth oxide crystal according to claim 7.

9. The rare earth oxide crystal according to any one of claims 1 to 8, wherein the inorganic crystal further contains at least one element selected from the group consisting of aluminum (Al), gallium (Ga), and germanium (Ge).

10. A method for producing rare earth oxide crystals according to any one of claims 1 to 9, comprising growing crystals by hydrothermal synthesis using raw materials containing each element contained in an inorganic crystal in the presence of a first mineralizing agent which is an alkali metal and / or alkaline earth metal mineralizing agent, or an acid mineralizing agent, or a mixed mineralizing agent of both, and a second mineralizing agent which is at least one selected from the group consisting of aluminum oxide, gallium oxide, and germanium oxide.

11. The method according to claim 10, wherein the concentration of the first mineralizing agent is in the range of 1 M or more and 50 M or less.

12. The method according to claim 10 or 11, wherein the concentration of the second mineralizing agent is in the range of 0.01 M or more and 20 M or less.

13. The method according to any one of claims 11 to 12, wherein, in growing crystals by the hydrothermal synthesis method, the temperature is in the range of 400°C or more and less than 750°C, and the maximum achievable pressure is in the range of 25 MPa or more and 250 MPa or less.

14. An optical material comprising a rare earth oxide crystal according to any one of claims 1 to 9.

15. The optical material according to claim 14, which is a laser material or a laser host material.

16. The optical material according to claim 14, wherein the material is a phosphor material.

17. The optical material according to claim 14, which is a Faraday rotor.

18. An optical isolator comprising the optical material described in claim 17.

19. The optical isolator according to claim 18, wherein it is polarization-independent.

20. An optical communication device, an optical communication line, or a laser processing machine comprising the optical isolator according to claim 18 or 19.

21. The optical material according to claim 14, which is a scintillator.

22. A radiation detector comprising an optical material according to claim 21, and a photoelectric converter that detects light from the optical material and converts it into an electrical signal.

23. A radiation inspection apparatus comprising a radiation source for irradiating a subject with radiation, and a radiation detector according to claim 22 for detecting radiation that penetrates the subject.

24. A magnetic material comprising rare earth oxide crystals according to any one of claims 1 to 9.

25. The magnetic material according to claim 24, which is a magnetic refrigeration material.

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