Oxide crystals, methods for producing the same, scintillator materials using the same, and their applications.

Abstract

The present invention provides an oxide crystal that does not contain harmful substances such as cadmium and has scintillation properties comparable to or better than those of cadmium tungstate (CdWO4), as well as a method for producing the same. [Solution] The oxide crystal according to one embodiment of the present invention is of general formula M x Hf y O 3-z (In the formula, x, y, and z each independently satisfy 0.5 ≤ x ≤ 1.5, 0.5 ≤ y ≤ 1.5, and -0.5 ≤ z ≤ 0.5, and M is selected from the group consisting of Be, Mg, Ca, Sr, and Ba.) It is characterized by being expressed as and containing a hydrogen atom (H).

Description

Technical Field

[0001] The present invention relates to an oxide crystal, a method for producing the same, a scintillator material using the same, and uses thereof.

Background Art

[0002] Radiation inspection devices are used in various fields and modes, such as inspection devices for non-destructive inspection and diagnostic devices for medical use. Exemplary modes include a mode in which a subject is irradiated with radiation (X-rays, neutron rays, etc.) and the transmitted radiation is detected by a radiation detector, and a mode in which a radiation source (radioactive substance) is previously placed inside the subject and the radiation (γ-rays, etc.) generated from the radiation source and transmitted through the subject is detected by a radiation detector.

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

[0004] Conventionally, as scintillator materials used in X-ray detectors, single crystals such as cadmium tungstate (CdWO4) and cesium iodide with thallium addition (Tl:CsI), and polycrystalline ceramics such as gadolinium oxysulfide with terbium addition (Tb:Gd2O2S) and gadolinium oxysulfide with praseodymium addition (Pr:Gd2O2S) are known.

[0005] Among them, CdWO4 is widely used as a scintillator material for X-ray detectors for checking deposited luggage and cargo at airports and the like. The single crystal of CdWO4 has practical scintillation characteristics such as high light emission amount and low afterglow. However, since cadmium is a harmful substance, the single crystal of CdWO4 may deteriorate the environment.

[0006] As scintillator materials that do not contain harmful substances (harmful elements) such as cadmium, hafnium-based materials such as SrHfO3 and BaHfO3 are known. For example, Non-Patent Document 1 describes the scintillation characteristics of Ce-doped BaHfO3 crystals prepared by the floating zone (FZ) method. However, the materials described in Non-Patent Document 1 exhibit a brown color, and the samples with 0.3% Ce doping and 1% Ce doping are said to be black due to the inclusion of graphite powder, so their transparency is impaired. When used as a scintillator material, there is concern that the light generated within the crystal will not be efficiently transmitted and the emission amount will decrease.

[0007] Since the hydrothermal synthesis method can grow high-quality single crystals at relatively low temperatures and is also capable of scaling up and mass production, attempts have been made to grow crystals by the hydrothermal synthesis method in the past. For example, Non-Patent Document 2 describes the crystal growth of BaHfO3, etc. (see page 320, etc.). According to Non-Patent Document 2, it was possible to grow single crystals of zirconia by the hydrothermal synthesis method under high-temperature conditions (specifically, 750 °C) (see pages 295-302, etc.). Therefore, as the crystal growth conditions for BaHfO3, etc., the temperature was set to 750 °C, and 5M, 10M, or 20M KOH was used (see pages 320-321, Figure 8.10, Table 8.3). That is, Non-Patent Document 2 suggests that setting the temperature condition to a high temperature is the key point for growing the target crystal. However, a person skilled in the art who has read the description of Non-Patent Document 2 should understand that a temperature condition of 750 °C in the hydrothermal synthesis method indicates that it is extremely difficult to scale up the crystal considering the configuration of the apparatus used for crystal growth.

Prior Art Documents

Non-Patent Documents

[0008]

Non-Patent Document 1

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

[0010] The oxide crystal according to the present invention has the general formula M x Hf y O 3-z (In the formula, x, y, and z each independently satisfy 0.5 ≤ x ≤ 1.5, 0.5 ≤ y ≤ 1.5, and -0.5 ≤ z ≤ 0.5, and M is selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba).) This is expressed as a compound containing a hydrogen atom (H), thereby solving the above problem. In the oxide crystal of the present invention, the concentration of hydrogen atoms is 1 × 10⁻⁶ 16 atoms / cm 3 The above 1 x 10 23 atoms / cm 3 The following range is also acceptable. The oxide crystal of the present invention has a crystal structure belonging to the P m -3 m space group, and the crystal phase may be a single cubic phase. The oxide crystal of the present invention may be activated with an activating element Q selected from at least one of the group consisting of cerium (Ce), praseodymium (Pr), europium (Eu), terbium (Tb), erbium (Er), and ytterbium (Yb). The activating element Q may be Ce. The above Ce may be Ce 3+ as well. The oxide crystal of the present invention may further contain an alkali metal and / or an alkaline earth metal other than the above M. The concentration of the above alkali metal and / or alkaline earth metal other than M is 1×10 12 atoms / cm 3 or more and 1×10 23 atoms / cm 3 or less. The oxide crystal of the present invention may further contain an element selected from at least one of the group consisting of aluminum (Al), gallium (Ga), and germanium (Ge).

[0011] The method for producing the above-described oxide crystal according to the present invention includes crystal growth by a hydrothermal synthesis method in the presence of a first mineralizer that is a raw material containing each element contained in the crystal, a mineralizer containing an alkali metal and / or an alkaline earth metal other than the above M, or a mineralizer of an acid, or a mixed mineralizer of both, and a second mineralizer selected from at least one of the group consisting of aluminum oxide, gallium oxide, and germanium dioxide, thereby solving the above problems. The concentration of the above first mineralizer may be in the range of 1M or more and 50M or less. The concentration of the above second mineralizer may be in the range of 0.01M or more and 20M or less. In the crystal growth by the above hydrothermal synthesis method, the temperature may be in the range of 400°C or more and less than 750°C, and the maximum pressure reached may be in the range of 25MPa or more and 250MPa or less.

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

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

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

[0015] [Figure 1] This is a schematic diagram showing the configuration of a radiation detector relating to one embodiment of the present invention. [Figure 2] This is a schematic diagram showing the configuration of a radiation inspection device according to one embodiment of the present invention. [Figure 3-1] This figure shows a microscopic image of the crystal obtained in Example 1 in the example. [Figure 3-2] This figure shows a microscopic image of the crystal obtained in Example 2 in the example. [Figure 3-3] This figure shows a microscopic image of the crystal obtained in Example 3 in the examples. [Figure 4] This figure shows the results of powder X-ray diffraction measurements of the crystal in Example 1, and the simulation results of the diffraction chart of BaHfO3 (cubic crystal system P m - 3 m). [Figure 5] This figure shows the results of secondary ion mass spectrometry of the crystal in Example 1, specifically the concentrations of hydrogen and potassium. [Figure 6] This figure shows the PL spectra of sample 1 and sample 2. [Figure 7] This figure shows the XRL spectra of sample 1 and sample 2. [Modes for carrying out the invention]

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

[0017] [Oxide crystals] <Composition> The oxide crystal of the present invention has the general formula M x Hf y O 3-z (In the formula, x, y, and z each independently satisfy 0.5 ≤ x ≤ 1.5, 0.5 ≤ y ≤ 1.5, and -0.5 ≤ z ≤ 0.5, and M is selected from the group consisting of Be, Mg, Ca, Sr, and Ba.) It is represented as and contains a hydrogen atom (H). In the following, unless otherwise specified, the term "hydrogen" refers to a hydrogen atom.

[0018] In the above general formula, M is an element selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). Here, M may be partially substituted with an alkaline earth metal element other than Be, Mg, Ca, Sr, and Ba. Such a substituted element may be radium (Ra).

[0019] In one embodiment, x in the above general formula is 1 and y is 1, and in this case, the oxide crystal is MHfO 3-z (where -0.5 ≤ z ≤ 0.5) it has a composition represented by the above-mentioned MHfO 3-z It is preferable that the composition be represented by the formula. Here, as will be described later, the oxide crystal of the present invention is grown by a hydrothermal synthesis method, and the resulting crystal is obtained with the most stable composition, so even if there is a deviation from the target composition, the difference is considered to be very small. On the other hand, when the composition of the crystal actually obtained is measured, there may be cases where the molar ratio of M to Hf is not exactly 1:1. This is due to, for example, a deviation between the harmonious melt composition (congluent melt composition), which is the most stable composition, and the stoichiometric composition, the inclusion of H and / or arbitrary constituent elements described later, or the influence of measurement errors, etc. However, even in such cases, the conditions for x 0.5≦x≦1.5 and for y 0.5≦y≦1.5 in the above general formula can be satisfied.

[0020] The oxide crystal of the present invention may have fewer or more oxygen atoms than 3 due to defects in the crystal, but by satisfying the condition for z in the above general formula -0.5 ≤ z ≤ 0.5, the decrease in the transmittance of the crystal is sufficiently suppressed. In other words, it is preferable that the value of z in the above general formula is close to zero. Most preferably, z in the above general formula is zero, in which case the oxide crystal is in the general formula M x Hf y It has a composition represented by O3 (where 0.5 ≤ x ≤ 1.5 and 0.5 ≤ y ≤ 1.5).

[0021] In one embodiment, the concentration of hydrogen contained in the oxide crystal of the present invention is 1 × 10⁻⁶ 16 atoms / cm 3 The above 1 x 10 23 atoms / cm 3 The range is as follows, preferably 1 × 10 17 atoms / cm 3 The above 1 x 10 22 atoms / cm 3 The range is as follows, more preferably 1 × 10 18 atoms / cm 3 The above 1 x 10 22 atoms / cm 3 The range is as follows:

[0022] The method for measuring the hydrogen concentration in the oxide crystal of the present invention is not particularly limited and can be confirmed by conventional methods, for example, secondary ion mass spectrometry (SIMS) can be used. The same applies to the concentrations of elements other than hydrogen (for example, the concentrations of the arbitrary constituent elements described later (Al, Ga and / or Ge, or alkali metals and / or alkaline earth metals other than M)). 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 other than M are taken as the value at a depth of 6 μm. An example of SIMS measurement will be described in the Examples section.

[0023] <Activating element Q> The oxide crystal of the present invention may further contain another element Q as an activator (also called a dopant). In this specification, such an element included as an activator will also be referred to as activating element Q. By containing activating element Q in the oxide crystal of the present invention, activating element Q functions as a luminescence center, and a scintillator material with excellent luminescence properties can be obtained. When the oxide crystal of the present invention contains activating element Q, the manner in which the activating element Q is present is not limited, and for example, it may be contained in either M or Hf, or in both M and Hf.

[0024] In one embodiment, the activating element Q is a rare earth element, preferably at least one element selected from the group consisting of cerium (Ce), praseodymium (Pr), europium (Eu), terbium (Tb), erbium (Er), and ytterbium (Yb). From the viewpoint of obtaining better scintillation performance as a scintillator material, it is preferable that the activating element Q contains Ce, and Ce is Ce 3+ It is more preferable that the activating element Q is Ce, in an embodiment where Ce is 3+ It is preferable that Ce exists in the crystal in this state. This allows Ce to effectively exhibit its function as a luminescence center, and a scintillator material with superior luminescence properties can be obtained. On the other hand, if part or most of the Ce is Ce 4+ When present in a crystal in this state, it may not be possible to obtain the desired scintillation performance as a scintillator material.

[0025] Conventionally, it has been reported that adding trace amounts of Ca or Sr to Ce-doped Lu2SiO5 (Ce:LSO) increases the amount of luminescence or shortens the fluorescence lifetime, and in these reports, these doping elements are found to be present in the Ce crystal. 3+ It is sometimes explained that this leads to an increase in Ce. However, considering the relationship between the valence of Ce and the valence of the additive element, Ce 3+ The causal relationship with the increase remains speculative; rather, it is possible that the presence of the added element slightly deactivates defects in the crystal, thereby improving scintillation performance. In contrast, in the oxide crystal of the present invention, the presence of hydrogen is thought to contribute to the deactivation of defects in the crystal.

[0026] In embodiments of the present invention in which the oxide crystal contains the above-mentioned activating element Q, the concentration of the activating element Q is not particularly limited. By containing an appropriate activating element Q in an appropriate concentration in the oxide crystal, a scintillator material having the desired scintillation performance can be obtained.

[0027] <Optional constituent elements> The oxide crystals of the present invention may further contain any constituent elements other than the above-mentioned M (Be, Mg, Ca, Sr and / or Ba), Hf, O, H, and the activating element Q.

[0028] In one embodiment, the oxide crystal of the present invention further contains an alkali metal and / or an alkaline earth metal other than M as an optional constituent element. Hereafter, when referring to an alkaline earth metal as an optional constituent element, it shall mean an alkaline earth metal other than M unless otherwise specified. 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 may also be radium (Ra). The alkali metal and alkaline earth metal may be one type alone or two or more types in combination. It is expected that the presence of an alkali metal and / or alkaline earth metal in the oxide crystal will deactivate defects within the crystal.

[0029] In an embodiment of the present invention in which the oxide crystal contains alkali metals and / or alkaline earth metals, the concentration of the alkali metals and / or alkaline earth metals is 1 × 10⁻⁶ 12 atoms / cm 3 The above 1 x 10 23 atoms / cm 3 The range is as follows, preferably 1 × 10 13 atoms / cm 3 The above 1 x 10 22 atoms / cm 3 The range is as follows, more preferably 1 × 10 14 atoms / cm 3 The above 1 x 10 21 atoms / cm 3 The range is as follows:

[0030] In one embodiment, the oxide crystal of the present invention 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 oxide crystal will deactivate defects within the crystal.

[0031] In another embodiment, the oxide crystal of the present invention may further contain zirconium (Zr) as an optional constituent element. When the oxide crystal of the present invention contains Zr, the manner in which Zr is present is not limited, and for example, it may be present in either M or Hf, or in both M and Hf. In other words, Zr may be present in the crystal in a manner that substitutes for either one or both sites of M and Hf.

[0032] <Crystal structure> In one embodiment, the oxide crystal of the present invention belongs to the cubic crystal system and to the space group P m - 3 m (space group 221 of the International Tables for Crystallography (also simply called the International Table(s))). Table 1 below shows the crystal parameters and atomic coordinate positions of BaHfO3 as a typical example. Furthermore, it is preferable that the 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] [Table 1]

[0035] In the oxide crystal of the present invention, the lattice constant 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.

[0036] <Main Features> The oxide crystal of the present invention can have transparency comparable to that of conventional CdWO4. When the oxide crystal of the present invention is used as a scintillator material, light generated within the scintillator crystal can be efficiently transmitted, thus preventing a decrease in the amount of light emitted.

[0037] The oxide crystal of the present invention has a density and ρ·(Z) comparable to that of CdWO4. eff ) 4 It may have the above ρ·(Z eff ) 4 The value of is 0.8 or greater as a ratio to the value in CdWO4. Here, the value of the ratio is preferably 0.85 or greater, more preferably 0.9 or greater, even more preferably 0.95 or greater, even more preferably 1 or greater, and most preferably greater than 1.

[0038] Indicators representing the scintillation characteristics of the oxide crystal of the present invention include, for example, the amount of light emitted, the decay time (decay characteristics), and the afterglow (afterglow characteristics). In one preferred embodiment, the oxide crystal of the present invention may exhibit an amount of light emitted comparable to or exceeding that of conventional CdWO4. In another preferred embodiment, the oxide crystal of the present invention may exhibit a practically acceptable scintillation decay time. In yet another preferred embodiment, the oxide crystal of the present invention may exhibit an afterglow comparable to or lower than that of CdWO4.

[0039] In the context described above, it should be noted that the oxide crystal of the present invention does not necessarily require all properties to surpass those of CdWO4. That is, depending on the various applications as a scintillator material, as exemplified below, the oxide crystal of the present invention can be considered a practically useful scintillator material if it satisfies the scintillation properties required for that application. In other words, the oxide crystal of the present invention can be said to be environmentally friendly, both as a scintillator material itself and in its manufacturing method, because it does not contain harmful substances such as cadmium. Even if it has properties that are slightly inferior to (not comparable to) those of CdWO4, it can still serve as a scintillator material that can replace CdWO4.

[0040] [Method for manufacturing oxide crystals] Next, the method for producing the oxide crystals described above will be explained.

[0041] A method for producing oxide crystals according to one embodiment of the present invention includes growing crystals from raw materials containing each element to be included in the crystal by hydrothermal synthesis in the presence of a first mineralizing agent which is an alkali metal and / or an alkaline earth metal other than M mentioned above, or an acid mineralizing agent, or a mixture of both, 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.

[0042] <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.

[0043] Specifically, a raw material containing M (where M is selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba)) is prepared, a raw material containing hafnium (Hf) is prepared, a raw material containing an activating element Q (where Q is selected from the group consisting of cerium (Ce), praseodymium (Pr), europium (Eu), terbium (Tb), erbium (Er), and ytterbium (Yb)) is prepared as needed, and a raw material containing zirconium (Zr) is prepared as needed, and one or more compounds from these are made into oxides. For convenience, in this specification, the raw materials containing each constituent element prepared in step S110 will also be referred to as raw materials for each constituent element. For example, "raw material containing Hf" and "raw material for Hf" are synonymous.

[0044] 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.

[0045] As a raw material for M, for example, an inorganic salt of M can be used. For example, if M is Be, BeCO3 can be used; if M is Mg, MgCO3 can be used; if M is Ca, CaCO3 can be used; if M is Sr, SrCO3 can be used; and if M is Ba, BaCO3 can be used. For example, HfO2 can be used as a raw material for Hf. As raw materials for the activating element Q, for example, oxides and fluorides of Q can be used. For example, if Q is Ce, then CeO2, Ce2O3, and CeF3 can be used. For example, ZrO2 can be used as a raw material for Zr.

[0046] In one embodiment, the above-mentioned raw materials are prepared to satisfy the composition of the general formula MHfO3. Here, a raw material mixture containing each raw material may be prepared as needed. Also, when an inorganic salt is used as the raw material for M as exemplified above, a raw material mixture (mixed powder) having the MHfO3 phase may be prepared by calcining it under arbitrary temperature and time conditions to remove the CO2 contained in the raw material (powder).

[0047] <Step S120: A step in which the raw material is grown as a crystal 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.

[0048] As the first mineralizing agent, a mineralizing agent containing an alkali metal and / or an alkaline earth metal other than M, an acid mineralizing agent, or a mixed mineralizing agent of both can be used. Hereafter, when alkaline earth metals are referred to in the context of the first mineralizing agent, it is assumed that alkaline earth metals other than M are intended unless otherwise specified. The mineralizing agent containing an alkali metal and / or an alkaline earth metal is a compound containing an alkali metal and / or an alkaline earth metal, and for example, hydroxides or 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, KOH, K2CO3, RbOH, Rb2CO3, CsOH, Cs2CO3, Ra(OH)2, RaCO3, etc., and it is preferable to select at least one from the group consisting of these compounds. Examples of acid mineralizers include, but are not limited to, hydrochloric acid, nitric acid, sulfuric acid, formic acid, and phosphoric acid. Furthermore, alkali metals and / or alkaline earth metals contained in the first mineralizing agent, or elements contained in the acid mineralizing agent, may be present in the final oxide crystal.

[0049] The second mineralizing agent is selected from the group consisting of aluminum oxide (Al2O3), gallium oxide (Ga2O3), and germanium dioxide (GeO2), with at least one selected from this group. In one preferred embodiment, the second mineralizing agent includes aluminum oxide, and in a more preferred embodiment, the second mineralizing agent is aluminum oxide. By using the first and second mineralizing agents described above, it becomes possible to grow crystals at significantly lower temperatures compared to conventional methods other than hydrothermal synthesis, and even at lower temperatures than the conventional hydrothermal synthesis method described in Non-Patent Document 1. Furthermore, by using the first and second mineralizing agents, it becomes possible to grow larger crystals. Furthermore, the elements contained in the second mineralizing agent may be present in the final oxide crystal.

[0050] 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.

[0051] 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 an exemplary embodiment, 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.

[0052] 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.

[0053] Furthermore, the concentration of the second mineralizer in the final prepared 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 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 growing crystals.

[0054] 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. This pressure condition varies depending on the amount of water contained in the reaction vessel, the size of the ampoule (sealed container) containing the reaction solution, the temperature conditions, etc. In an exemplary embodiment, the maximum pressure achieved may be in the range of 30 MPa to 250 MPa, 50 MPa to 225 MPa, or 75 MPa to 200 MPa.

[0055] The time required for hydrothermal synthesis can be adjusted as appropriate to ensure the crystal growth is completed, depending on the type and amount of raw materials used. Here, two or more temperature conditions may be set within the aforementioned temperature range to establish a predetermined temperature profile. Such a temperature profile can be designed considering factors such as improving the homogeneity and stability of the solution, and more efficiently generating the desired crystals. An example of a specific temperature profile is shown in the embodiments described later.

[0056] In the manufacturing method according to this embodiment, crystals are grown by hydrothermal synthesis at significantly lower temperature conditions compared to conventional methods. In the above-mentioned FZ method, it is difficult to grow large crystals. In addition, in other melt growth methods, including the FZ method, the phenomenon of evaporation of certain 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, in the manufacturing method of the present invention, such decomposition and evaporation phenomena are less likely to occur, thus suppressing defects that may occur in the grown crystal. Furthermore, in general, in the case of hydrothermal synthesis, the obtained crystal is obtained with the most stable composition, and although there is a possibility that this composition may deviate slightly from the target composition, even if such a deviation occurs, it can be adjusted.

[0057] [Uses of oxide crystals] The oxide crystals of the present invention, which can be manufactured as described above, are not particularly limited in their applications, but are suitable for use as scintillator materials. In particular, because the oxide crystals of the present invention have very few defects, scintillator materials made from these oxide crystals can have properties such as density, fluorescence decay time, and fluorescence output comparable to existing materials, and can even exhibit scintillation properties comparable to or better than those of CdWO4.

[0058] [Applications of scintillator materials] The use of the above-mentioned scintillator material, which is in crystalline form, is not particularly limited, but it is preferably used in radiation detectors. The configuration of the radiation detector is not particularly limited, and a configuration similar to that of conventional radiation detectors can be adopted. Specifically, as schematically shown in Figure 1, a radiation detector 10 according to one embodiment of the present invention comprises a scintillator material (scintillator) 11 made of the above-mentioned oxide crystal, and a photoelectric converter 12 (for example, a photomultiplier tube (PMT), silicon photomultiplier (SiPM), solid-state image sensor (CCD), avalanche photodiode (APD), multipixel photon counter (MPPC), etc.) that detects light L emitted from the scintillator material 11 and converts it into an electrical signal. By using the above-mentioned scintillator material made of oxide crystal instead of the scintillator used in conventional radiation detectors, an improvement in the accuracy of radiation detection can be expected.

[0059] Furthermore, it is possible to construct a radiation inspection device by using the above-mentioned radiation detector and combining it with a radiation source that irradiates a subject with radiation. For example, as schematically shown in Figure 2, a radiation inspection device 20 according to one embodiment of the present invention comprises a radiation detector 10 (see Figure 1) and a radiation source 23, wherein the radiation source 23 irradiates the subject Sbj with radiation R, and the radiation detector 10 is configured to detect radiation E that penetrates the subject Sbj. In this case, the radiation detector 10 emits light L when excited by radiation E, and the photoelectric converter 12 detects the light L emitted from the scintillator material 11 and converts it into an electrical signal. Such a radiation inspection device 20 can be used, for example, as an inspection device for non-destructive testing such as a non-destructive testing detector, a resource exploration detector, or a high-energy physics detector, or as a medical diagnostic device such as a medical image processing device (X-ray CT, etc.).

[0060] Alternatively, the aforementioned radiation detectors may also be applied to the detection of radiation (such as gamma rays) emitted from a subject. Specifically, examples include medical image processing equipment such as SPECT (Single Photon Emission Computed Tomography) devices, exploration equipment for underground resource exploration, hazardous material detection equipment, and equipment used in research and development fields related to space, such as cosmic ray and astrophysics.

[0061] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples. [Examples]

[0062] [Crystal Manufacturing] <Example 1: BaHfO3> BaCO3 and HfO2 (in powder form, manufactured by Furuuchi Chemical Co., Ltd.) were prepared as raw materials for Ba and Hf. Each raw material was weighed to satisfy the ratio of BaHfO3 and mixed to obtain a powdered raw material mixture. This raw material mixture was then calcined (held at 1300°C for 10 hours) to remove the CO2 contained in the raw material powder, thereby obtaining a mixed powder having a BaHfO3 phase. This mixed powder, KOH (a tablet equivalent to a 20M aqueous solution) as the first mineralizing agent, Al2O3 (a powder equivalent to a 0.2M aqueous solution) as the second mineralizing agent, and pure water (0.7 mL) were placed in a silver ampoule (5 mm in diameter x 10 cm in length) and sealed. This sealed ampoule was then placed in a reaction vessel containing pure water, and hydrothermal synthesis was carried out. For the hydrothermal synthesis, a temperature profile was used in which the temperature was raised to 700°C over 12 hours, held for 24 hours, and then cooled to 600°C over 100 hours to complete crystal growth. The highest pressure reached during this process was 158 MPa. The cooling program from 600°C to room temperature at the end of crystal growth was set to 1 hour, after which natural cooling was allowed. This resulted in the crystals of Example 1.

[0063] <Example 2: Ce-added BaHfO3> BaCO3 and HfO2 (in powder form, manufactured by Furuuchi Chemical Co., Ltd.) were prepared as raw materials for Ba and Hf, and a mixed powder having a BaHfO3 phase was obtained in the same manner as in Example 1. Next, CeO2 (in powder form, manufactured by Furuuchi Chemical Co., Ltd.) was prepared as a raw material for Ce, and weighed so that the amount added to BaHfO3 was 1 mol% (i.e., the molar ratio of HfO2 to CeO2 was Hf:Ce = 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 1 to obtain the crystal of Example 2. The maximum pressure achieved during crystal growth was 167 MPa.

[0064] <Example 3: BaHfO3> Crystals for Example 3 were prepared using the same procedure as in Example 1. However, in this example, the second mineralizing agent was not used, and the hydrothermal synthesis conditions involved raising the temperature to 700°C over 12 hours and holding it for 24 hours to complete crystal growth. After crystal growth, natural cooling was performed. The maximum pressure reached during crystal growth was 55 MPa.

[0065] <Example 4: Ce-added BaHfO3> The crystals of Example 4 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 167 MPa.

[0066] Table 2 shows the crystal manufacturing conditions for Examples 1 to 4 described above.

[0067] [Table 2]

[0068] [Measurement and Evaluation] <Microscopic observation> The crystals obtained in each of the above examples were observed using an optical microscope. Figures 3-1 to 3-3 show microscopic images of the crystals from Examples 1 to 3, respectively. The scale bar in each image is 0.5 mm in Figures 3-1 and 3-3, and 1.0 mm in Figure 3-2.

[0069] According to FIGS. 3-1 and 3-2, the crystals of Example 1 and Example 2 were confirmed to have a certain size in the as-grown state and to be highly transparent under microscopic observation. On the other hand, according to FIG. 3-3, the crystals of Example 3 were in the form of particles ranging from submicrons to several microns. When comparing crystals of the same type (the crystals of Example 1 and the crystals of Example 3), the difference in crystal size is obvious. From this result, the effectiveness of using the above-mentioned first mineralizer and second mineralizer in combination as mineralizers in the hydrothermal synthesis method was confirmed. Although not shown, the crystals of Example 4 were also in the form of particles ranging from submicrons to several microns.

[0070] <X-ray diffraction measurement> A powder sample was prepared from the crystals of Example 1, and powder X-ray diffraction measurement was performed. FIG. 4 shows the measurement results of the crystals of Example 1.

[0071] In the upper part of FIG. 4, the powder X-ray diffraction measurement results of the crystals of Example 1 are shown, and in the lower part of FIG. 4, the simulation results of the diffraction chart of BaHfO3 (cubic system P m -3 m) are shown. Here, by comparing the diffraction charts of both, the space group of the obtained crystal (the crystal of Example 1) can be simply estimated. It is advisable to use about 3 to 10 peaks with large peak intensities as the main peaks. The crystal parameters and atomic coordinate positions shown in Table 1 above are important as reference for estimating or determining the space group of the oxide crystal of the present invention in that sense. In addition, the crystal structure of the oxide crystal of the present invention can be defined as an approximate structure even using other crystal systems of cubic crystals. In that case, it will be expressed using different space groups, lattice constants, and plane indices, but there is no change in the X-ray diffraction measurement results (for example, the upper part of FIG. 4) and the crystal structure, and the identification method and identification results using them are also the same. Therefore, in this example, powder X-ray diffraction measurement was performed assuming a cubic crystal.

[0072] As shown in Figure 4, 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. This confirmed that the obtained crystal has a cubic BaHfO3(P m - 3 m) crystalline phase.

[0073] <Secondary Ion Mass Spectrometry> For the crystal in Example 1, the hydrogen and potassium concentrations were measured using a secondary ion mass spectrometer (Cameca IMS-6F) and a time-of-flight secondary ion mass spectrometer (TOF-SIMS, IonTOF), respectively. The results are shown in Figure 5. The horizontal axis in Figure 5 represents the measurement depth (μm).

[0074] According to Figure 5, in the obtained crystal, the hydrogen concentration at a depth of 3 μm is approximately 8 × 10⁻¹⁴. 19 atoms / cm 3 And, 1 × 10 21 atoms / cm 3 The following conditions must be met, and the potassium concentration at a depth of 6 μm should be approximately 8 × 10⁻⁶ 19 atom / cm 3 And, 1 × 10 21 atoms / cm 3 The following conditions were found to be met. Furthermore, it was confirmed that the concentration ratios of barium, hafnium, and oxygen were in close agreement with the theoretical composition.

[0075] <Luminous properties> Powder samples were prepared by grinding the crystals from Example 1 and Example 2, and the luminescence properties of each sample were measured. Hereafter, the sample prepared from the crystals of Example 1 will be referred to as Sample 1, and the same will apply to Example 2.

[0076] For photoluminescence (PL) measurements, a spectrofluorometer (Hitachi High-Tech Corporation, F-7100) is used, and a predetermined excitation wavelength (λ) is measured. ex When excited by (λ), the emission wavelength (λ em ) and luminescence intensity were measured. For X-ray radioluminescence (XRL) measurements, a fiber multi-channel compact spectrometer (Stellarnet Inc., Blue Wave UVN-50) is used, and the emission wavelength (λ) when excited with X-rays (Rigaku Corporation, 18kW X-ray generator RA-HF 18RB) is measured. em ) and luminescence intensity were measured.

[0077] Figure 6 shows the PL spectra of sample 1 and sample 2. Here, the excitation wavelength (λ) ex The peak wavelengths for sample 1 were 219 nm and 237 nm, while for sample 2 it was 305 nm. In Figure 6, the emission intensity on the vertical axis has been normalized so that the peak values ​​of each PL spectrum match.

[0078] Figure 6 suggests that the crystal in Example 1 emits light primarily in the ultraviolet to blue wavelength range. Crystals with blue emission wavelengths are useful as scintillator materials, for example, when used in combination with Si photodiodes. The presence of blue emission wavelengths in the scintillator is expected to improve sensitivity to Si photodiodes. This may allow Si photodiodes to be used as photoelectric converters.

[0079] On the other hand, the crystal in Example 2 showed a narrower peak width compared to the crystal in Example 1, suggesting that the luminescence mainly consisted of wavelengths in the ultraviolet to violet region, due to the influence of Ce contained in the crystal.

[0080] Figure 7 shows the XRL spectra of sample 1 and the sample. In Figure 7, the emission intensity on the vertical axis has been normalized so that the peak values ​​of each XRL spectrum match.

[0081] As shown in Figure 7, and referring to the PL spectrum in Figure 6 as described above, it was suggested that the crystal in Example 1 produces emission mainly in the ultraviolet to blue wavelength range, and the crystal in Example 2 produces emission mainly in the ultraviolet to violet wavelength range.

[0082] Here, the density of the crystal (BaHfO3) in Example 3 is 8.3 g / cm³. 3 (Reported value) and ρ·(Z eff ) 4 The value is 140 × 10 6 On the other hand, the density of the CdWO4 crystal (manufactured by Nippon Crystal Optics Co., Ltd.) prepared as a comparative sample was 7.9 g / cm³. 3 (Reported value) and ρ·(Z eff ) 4 The value is 134 × 10 6 These results suggest that the oxide crystal of the present invention may have X-ray stopping power comparable to or exceeding that of CdWO4. eff ) 4 The value was calculated based on the reference (HP Schatzler., Int. J. Appl. Radiat. Isot., 1979, 30, 115-121.).

[0083] As described above, the present invention can provide an oxide crystal that does not contain harmful substances such as cadmium and has scintillation properties comparable to or better than those of CdWO4. Furthermore, the present invention can provide a method for producing the above-mentioned oxide crystals under milder conditions than conventional methods, particularly at lower temperatures. According to the manufacturing method of the present invention, chemically stable bulk single crystal growth and production are possible, making it suitable for large-scale and mass production, and reducing manufacturing costs. In addition, since no harmful substances such as cadmium are used, it is an environmentally friendly material, and the manufacturing process is also environmentally friendly. The oxide crystals and their manufacturing methods of the present invention, possessing these characteristics, are expected to be applied to a variety of applications as scintillator materials and their manufacturing methods that can replace conventional CdWO4. [Explanation of Symbols]

[0084] 10. Radiation detectors 11. Scintillator materials (scintillators) 12 Photoelectric Converter 20. Radiation Inspection Equipment 23 Radiation Source L light R radiation E. Radiation that penetrates the subject Sbj subject

Claims

1. General formula M ｘ HF ｙ O ３－ｚ An oxide crystal containing hydrogen atoms (H), represented by the formula (wherein x, y, and z are each independently satisfying 0.5 ≤ x ≤ 1.5, 0.5 ≤ y ≤ 1.5, and -0.5 ≤ z ≤ 0.5, and M is selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba)).

2. The concentration of hydrogen atoms is 1 × 10⁻⁶ １６ atoms / cm ３ The above 1 x 10 ２３ atoms / cm ３ The oxide crystal according to claim 1, wherein the range is as follows.

3. The oxide crystal according to claim 1 or 2, having a crystal structure belonging to the Pm-3m space group and having a cubic single phase.

4. An oxide crystal according to any one of claims 1 to 3, which is activated with an activating element Q selected from the group consisting of cerium (Ce), praseodymium (Pr), europium (Eu), terbium (Tb), erbium (Er), and ytterbium (Yb).

5. The oxide crystal according to claim 4, wherein the activating element Q is Ce.

6. The aforementioned Ce is Ce ３＋ The oxide crystal according to claim 5.

7. The oxide crystal according to any one of claims 1 to 6, further containing an alkali metal and / or an alkaline earth metal other than M.

8. The concentration of the alkali metal and / or alkaline earth metal other than M is 1×10 １２ atoms / cm ３ or more and 1×10 ２３ atoms / cm ３ or less, and the oxide crystal according to claim 7.

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

10. A method for producing an oxide crystal according to any one of claims 1 to 9, comprising growing a crystal from a raw material containing each element contained in the crystal by hydrothermal synthesis in the presence of a first mineralizing agent which is an alkali metal and / or an alkaline earth metal other than M, 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 dioxide.

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

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 10 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. A scintillator material comprising an oxide crystal according to any one of claims 1 to 9.

15. The scintillator material according to claim 14, A photoelectric converter that detects light from the scintillator material and converts it into an electrical signal. A radiation detector equipped with the following features.

16. A radiation source that irradiates the subject with radiation, A radiation detector according to claim 15, which detects radiation passing through the subject, A radiation inspection device equipped with the following features.

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