JP4851810B2 - Single crystal material for scintillator and manufacturing method - Google Patents

Abstract

The present invention aims to obtain a novel single crystal material for scintillators by suppressing phase transition during the cooling and solidification process from the melting point in the production of a rare earth borate mainly containing Lu. Specifically, in a method for producing a single crystal material for scintillators wherein a mixture containing an Lu raw material and a boron oxygen raw material is melted and then cooled and solidified, the single crystal material for scintillators is obtained, while suppressing phase transition of a crystal material by adding an element raw material selected from the group consisting of Sc, Ga and In. By adding Sc or the like into a rare earth borate mainly containing Lu, phase transition can be suppressed while maintaining the radiation absorbing ability and the density at high levels.

Description

  The present invention relates to a scintillator single crystal material that can be used as a scintillator in a radiation detector or the like, and more particularly to a scintillator single crystal material comprising a rare earth borate mainly composed of Lu (lutetium) belonging to a rare earth element, and a method for producing the same .

  A radiation detector generally includes a scintillator unit that receives radiation such as X-rays and γ rays and converts it into visible light, and a photomultiplier that detects visible light converted and transmitted by the scintillator unit and converts it into an electrical signal. It consists of a light detection unit such as a tube (hereinafter referred to as “photomal”) and a photodiode. In addition to the function of absorbing radiation and converting it into visible light, the scintillator part is required to have transparency that allows the converted visible light to pass through to the light detection part without being attenuated. In addition to a function as a scintillator that absorbs radiation and emits light, it is required to be a transparent and large crystal body, preferably a single crystal material.

Conventionally, as this type of single crystal material, in addition to materials that emit light only from a base material single crystal such as CdWO ₄ , Bi ₄ Ge ₃ O ₁₂ , Nd (NaI: Tl) added with Tl, Gd added with Ce There are known materials in which a small amount of a light emitting element is added to a single crystal of a base material such as ₂ SiO ₅ (Gd ₂ SiO ₅ : Ce), Lu ₂ SiO ₅ (Lu ₂ SiO ₅ : Ce) to which Ce is added. .
For example, cerium-doped gadolinium silicate (Ce: Gd ₂ SiO ₅ (Ce: GSO)) single crystal (patent document 1), cerium-doped Ce: Lu ₂ SiO ₅ : (Ce: LSO)) or Ce _α (Lu _gamma Gd _2-gamma) single crystal scintillator is expressed by the _2-alpha SiO ₅ has been proposed (Patent documents 2 and 3).

Patent Document 4, in _{Ce α (Lu γ Gd 2-} γ) single crystal scintillator is expressed by the _2-α SiO _5, Ta (tantalum), W (tungsten), Ca (calcium), F (fluorine) Patent Document 5 discloses a scintillator using a PbWO ₄ single crystal as a scintillator for radiation detection.
Patent Document 6 discloses an inorganic scintillator having a chemical composition represented by Ln _2x Si _y O _{(3x + 2y)} (Ln: an element belonging to a rare earth element). Patent Document 7 discloses a light rare earth fluoride. A fluoride single crystal material for radiation detection represented by REF ₃ (RE is at least one selected from Nd and Pr) is disclosed.

  These single crystal materials can be obtained by melting the raw material composition and lowering the temperature from the melt to solidify and precipitate the crystals, such as the rotational pulling method (Czochralski method), the Bridgeman growth method, or the slow cooling method. It is manufactured by the method to get it.

Japanese Examined Patent Publication No. 62-8472 Japanese Examined Patent Publication No. 7-78215 JP-A-9-118593 JP-T-2001-524163 JP 2003-41244 A JP 2005-206640 A Japanese Patent Application Laid-Open No. 2005-119952

By the way, rare earth borate (XBO ₃ , X: rare earth element) has been conventionally used as a phosphor. For example, it has been proposed that a phosphor powder is applied to a paper or plastic substrate to form a radiation detection plate or an intensifying screen for an X-ray film, but it has been difficult to grow a single crystal. It could not be used as a scintillator material used for the radiation detector as described above.
However, if such a rare earth borate can be used as a scintillator material used in radiation detectors, etc., it can be expected to further increase the amount of light emitted, and it is manufactured because the melting point is lower than that of conventional scintillator materials. It can also be expected that it can be provided at low cost with low costs.

Furthermore, for example, in a scintillator material used in a γ-ray detector, since γ-rays are absorbed by interaction with electrons in the scintillator material, the scintillator material has a high electron density, in other words, a large atomic number. A material made of an element is desirable. Therefore, it would be extremely useful if a single crystal material for scintillators could be developed from rare earth borates mainly composed of Lu (lutetium) having a large atomic number among rare earth elements. For example, LuBO ₃ has a large light emission amount and a high density. Therefore, if a single crystal can be produced, it can be expected as an excellent scintillator material for a radiation detector.

However, since rare-earth borates such as LuBO ₃ change in phase between the melting point and room temperature, it is difficult to produce a single crystal because, for example, phase changes occur in the process of cooling from the melting point to room temperature, and cracks occur. I had a serious problem.

  Therefore, the present invention provides a new single scintillator single crystal by suppressing the phase transition in the process of cooling and solidifying from the melting point in the production of rare earth borates mainly composed of Lu. It is intended to provide crystalline material.

The present invention provides a new method for producing a scintillator material, a Lu raw material, an elemental raw material of at least one of Sc, Ga and In, and a raw material containing boron and oxygen (hereinafter referred to as “boron oxygen raw material”). A scintillator material manufacturing method comprising a melting step of mixing and heating and melting a light emitting element raw material, and a cooling and solidifying step of cooling and solidifying the melt to obtain a single crystal is proposed.
That is, as a result of the present inventors' research, the ability to absorb radiation and the amount of emitted light are practically achieved by adding at least one element of Sc, Ga and In to a rare earth borate containing Lu as a main component. It was found that the phase transition of the additive material (rare earth borate containing Lu as a main component) can be suppressed while maintaining a high level.

The present invention also provides a new single crystal material for a scintillator having the composition formula: (Lu _1-x M ¹ _x ) _1-y M ² _y BO ₃ (where 0.02 ≦ x <1, 0.0001 ≦ y A single crystal material for a scintillator represented by ≦ 0.1, M ¹ : an element composed of one or a combination of two or more selected from the group consisting of Sc, Ga and In, and M ² : a light-emitting element) is proposed.

Composition formula: (Lu _1-x M ¹ _x ) BO ₃ (where 0.02 ≦ x <1, M ¹ : element composed of one or a combination of two or more selected from the group consisting of Sc, Ga and In) ) Is chemically and mechanically stable. When this is used as a base crystal and a light-emitting element (M ² ) such as Ce is added to form a single-crystal material, the amount of light emitted is reduced. Large, short emission lifetime, composition formula: (Lu _1-x M ¹ _x ) _1-y M ² _y BO ₃ (where 0.02 ≦ x < ¹ , 0.0001 ≦ y ≦ 0.1, M ¹ : Single element selected from the group consisting of Sc, Ga and In) or a combination of two or more of them can be obtained.
Therefore, the new scintillator material of the present invention includes medical PET (Positron Emission Tomography), TOF-PET (Time of Flight Positron Emission Tomography), CT (Computer Tomography), It can be suitably used as a material for scintillators of various radiation detectors such as personal belongings inspection devices used at airports and the like, and various radiation detectors can be configured using these as scintillators.
Moreover, the new scintillator material of the present invention has a feature that the heating energy required for the production is small because the melting point is 500 ° C. or more lower than Lu ₂ SiO ₅ (melting point 2150 ° C.) or the like. Moreover, since the consumption of the refractory and the crucible used in the synthesis furnace can be reduced, it can be manufactured more economically.

  In the present invention, the “scintillator” means that it absorbs radiation such as γ-rays and X-rays, and has a wavelength close to visible light or visible light (the wavelength range of light may extend from near ultraviolet to near infrared. ) And a component of a radiation detector having such a function.

BEST MODE FOR CARRYING OUT THE INVENTION

  Embodiments of the present invention will be described in detail below, but the scope of the present invention is not limited to the embodiments described below.

In this specification, “X to Y” (X and Y are arbitrary numbers) means “X or more and Y or less” unless otherwise specified, and “preferably larger than X and smaller than Y”. Is included.
Further, in the present specification, the “main component” or “main phase” is a component contained in a proportion that the function of the component or phase affects, and other components or It is intended to allow the inclusion of other phases. The content ratio of “main component” or “main phase” is not particularly limited, and depends on the function of “main component” or “main phase”, but it is 20% by mass or more, particularly 30% by mass or more, and especially 50%. It is preferable that it is at least 80% by mass.
In this specification, “elements belonging to rare earth elements” are Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er among group 3 elements. , Tm, Yb and Lu are shown.

(Single crystal material for scintillators)
The scintillator single crystal material of the present embodiment has a composition formula: (Lu _1-x M ¹ _x ) _1-y M ² _y BO ₃ (where M ^{1 is} a metal element such as Sc, M ^{2 is a} light emitting element). The material represented.

  This single crystal material is composed of a single phase single crystal of calcite phase, a single phase single crystal of Vaterite phase, and a mixture thereof, for example, calcite phase as a main phase. Including those containing a Vaterite phase and those containing a calcite phase with the Vaterite phase as the main phase. However, since the Vaterite phase is unstable with a high-temperature phase and a low-temperature phase, the single phase single crystal of the calcite phase or the calcite phase is the main phase. In particular, those containing a Vaterite phase are preferable, and among them, a single-phase single crystal of a calcite phase is particularly preferable in terms of stabilizing the structure (to stably eliminate the phase transition).

In the above composition formula, examples of the metal element that can function as M ¹ include an element composed of one or a combination of two or more selected from the group consisting of Sc, Ga, and In. Among these, Sc and In are particularly preferable in that a single-phase single crystal of a calcite phase can be obtained.
There is a possibility that elements other than Sc, Ga, and In may have the same effect. However, as a result of testing by adding Gd instead of Sc, the phase transition cannot be suppressed. Has been confirmed. Therefore, what works effectively is unknown without experimentation.
However, the addition of other elements is not prevented as long as the function as M ¹ is not hindered, and the present embodiment can include materials containing such additional elements.

It is important that the content ratio of M ¹ , that is, the range of x in the composition formula is 0.02 ≦ x <1. At this time, phase transfer occurs particularly when the ratio is less than 0.02. Considering that a practical density as a scintillator can be easily obtained, it is more preferable that 0.02 ≦ x ≦ 0.5, and 0.02 ≦ x in consideration of other crystal densities in practical use. ≦ 0.2 is more preferable, and among them, 0.02 ≦ x ≦ 0.05 is particularly preferable from the viewpoint that the amount of addition of Sc or the like can be suppressed.

M ² (light emitting element) in the above composition formula is one or more selected from the group consisting of Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, Cr, Bi and Tl. Any element consisting of a combination of these may be used. Among these, Ce is preferable when it is particularly required to have a short emission lifetime (time from light absorption to light emission) as in PET.

The content ratio of M ² , that is, the range of y in the above composition formula depends on the type of the light emitting element and the concentration of Sc, but is important to be, for example, 0.0001 ≦ y ≦ 0.1. In this case, 0.001 ≦ y ≦ 0.01 is preferable from a practical viewpoint, and among them, 0.003 ≦ y ≦ 0.007 is particularly preferable from the viewpoint of light emission intensity.

(Use)
The single crystal material for scintillator as described above is a single crystal material mainly composed of Lu having a large atomic number, and has a high density, so it has excellent radiation absorption capability, and even a thinner scintillator material has sufficient radiation. Can be absorbed. Therefore, when viewed from the whole radiation detector, it is possible to reduce the size (thinner thickness) while maintaining the function.

  From such a point of view, the scintillator single crystal material of this embodiment can be processed into a scintillator and combined with a light detection unit such as a photomultiplier or a photodiode, so that a radiation detector can be suitably configured. Therefore, in addition to medical PET (positron emission tomography), TOF-PET (time-of-flight positron emission tomography), CT (computer tomography), personal belongings inspection equipment used in airports, etc. It can use suitably as a material for scintillators of various radiation detectors, and various radiation detectors can be constituted using this.

(Production method)
Next, an embodiment as a method for manufacturing the scintillator single crystal material as described above will be described. However, the manufacturing method of the scintillator single crystal material of the present invention is not limited to the method described below.

The manufacturing method of this embodiment includes a melting process in which a Lu raw material, an M ¹ element raw material, a boron oxygen raw material, and an M ² element (light emitting element) raw material are mixed and heated and melted, and cooling that solidifies the molten liquid to obtain a single crystal. A scintillator single crystal material is obtained through a solidification step and a cutting step of cutting the single crystal obtained as necessary into a desired shape and size.

Here, the Lu raw material and the M ¹ element raw material may be a compound containing a component that evaporates while raising the temperature, such as an oxide such as Lu ₂ O ₃ or Sc ₂ O ₃ , or a carbonate or hydroxide. .
Examples of the boron oxygen raw material include H ₃ BO ₃ and B ₂ O ₃ . Since these are hygroscopic, it is preferable to use raw materials manufactured and controlled so as not to contain moisture.
The M ² element (light emitting element) raw material may be a single element or oxide of the light emitting element (M ² ), or a compound containing a component that evaporates while raising the temperature, such as carbonate or hydroxide.

  The mixing ratio of each raw material may be weighed so as to be within the above composition range based on the stoichiometry and technical common sense. However, since the boron oxygen raw material easily evaporates after firing or preliminary firing, It is necessary to mix so that the amount of boron is larger than the calculated amount.

  The mixing method of the raw materials is not particularly limited as long as the mixing can be performed sufficiently. For example, it may be mixed overnight with a V-type mixer. It is not necessary to become nervous to the extent of mixing because all of it will eventually melt in the subsequent process.

In the melting step, the Lu raw material, the M ¹ element raw material, the boron oxygen raw material, and the M ² element (light emitting element) raw material are mixed in advance and heated and pre-baked before heating and melting. It is preferable that a reactant having a melting point higher than that of the boron oxygen raw material is calcined and the reactant is heated and melted. The preliminary firing at this time is preferably performed at 800 to 1300 ° C., although it depends on the type of boron oxygen raw material.
By pre-firing in this way, it can be baked and hardened to reduce the bulk, and the handling becomes easy, and the evaporation of boron can be suppressed. For example, the melting point of Lu ₂ O ₃ is around 2400 ° C., whereas the melting point of B ₂ O ₃ is around 577 ° C. to several hundreds of degrees C. Unless a method for preventing the evaporation of B ₂ O ₃ is prepared separately. Although B ₂ O ₃ gradually evaporates, a reaction product having a melting point higher than that of B ₂ O ₃ can be obtained by pre-baking in this way, so that the evaporation of boron during heating and melting is suppressed. be able to.
Note that the preliminary firing may be performed in either an oxygen atmosphere (including air) or an oxygen-free atmosphere (including a vacuum atmosphere and an inert gas atmosphere). In an air or oxygen atmosphere, for example, when M ² (light emitting element) is Ce, the ionic valence is oxidized to an ionic valence that does not emit light. In addition, since the base material is an oxide, oxygen deficiency occurs and coloring occurs in a strong reducing atmosphere such as hydrogen. Further, in a vacuum, a nitrogen atmosphere is particularly preferable because boron easily evaporates and the manufacturing cost increases.

In the heat melting, the raw material mixture may be put in a crucible and heated and melted by a heating means suitable for the melting temperature and equipment.
At this time, a molding press may be performed in accordance with the crucible shape so as to facilitate filling.
The crucible is preferably a noble metal crucible such as iridium or platinum.
The melting of the raw material (in the case of pre-baking, melting after the pre-firing) may be performed by raising the temperature to near the melting point and melting all the raw materials. At this time, it is preferable to heat from room temperature to a predetermined temperature not exceeding the melting point or a predetermined temperature exceeding the melting point. Specifically, it may be heated to about 1650 ° C. to 1700 ° C., for example. At this time, when the crucible is heated by high frequency induction heating, it is preferable to use an iridium crucible having a higher melting point without using the platinum crucible because it is close to the melting point of platinum. However, it is not limited to the melting temperature range.
Heating and melting may be performed in any atmosphere of an oxygen atmosphere (including in the air) or an oxygen-free atmosphere (including a vacuum atmosphere and an inert gas atmosphere), but a nitrogen atmosphere is preferable for the same reason as the preliminary firing.

As a method for obtaining a single crystal by cooling and solidifying the melt, known methods such as the Czochralski method, the Bridgeman method, and the slow cooling method can be employed.
In the Czochralski method, the seed crystal is brought into contact with the molten liquid surface in the crucible and slowly pulled up while rotating. When a predetermined amount of crystals grows following the seed crystal, it is separated from the liquid surface and slowly cooled to room temperature. It is a method to do.
On the other hand, the Bridgman method and the slow cooling method are methods of slowly solidifying from the end face of the crucible and cooling when the solidification is completed.
In any method, at least part of the seed crystal is immersed in the melt, and the melt in which the seed crystal is immersed is cooled and solidified to grow a crystal along a predetermined crystal plane of the seed crystal, thereby producing a single crystal ingot. Can be obtained.

  The cutting process may be performed using a known method.

  Hereinafter, experiments related to the present invention (including examples and comparative examples) will be described. However, the present invention is not limited to the contents described below.

(Experiment 1)
A rare earth borate represented by a composition formula: Lu _0.796 Sc _0.199 Ce _0.005 BO ₃ was prepared.

First, 25.34g of 4N Lu ₂ O ₃ made by Yttrium Japan, 2.20g of 4N Sc ₂ O ₃ made by the company, 0.14g made by 4N CeO ₂ made by the company, 4N made by High Purity Chemical Laboratory 5.85 g of B ₂ O ₃ was weighed. Since B ₂ O ₃ tends to evaporate during firing, it was weighed 5% more in molar ratio than the ratio calculated from stoichiometry.

The weighed raw materials were put in an agate mortar, mixed for 30 minutes, then transferred to a platinum crucible, and lightly covered with a platinum lid. In a nitrogen atmosphere, the temperature was raised to 1500 ° C. at 200 ° C./hour, held for 24 hours, and fired. Thereafter, the temperature was returned to room temperature at 200 ° C./hour, and the fired product was taken out and pulverized in an agate mortar for 30 minutes.
The XRD, photoluminescence, and DTA of the rare earth borate powder thus obtained were measured as follows.

In XRD measurement, Mac Science MXP18 was used as a measuring device, a Cu target was used as a radiation source, and an XRD pattern was obtained in the range of 2θ from 5 degrees to 80 degrees.
The obtained pattern was identified and found to have the same structure as the LuBO ₃ Calcite phase (JCPDS13-0477). (Figure 1: XRD measurement results)

Photoluminescence measurement was performed using a Hitachi spectrofluorometer F4500.
Depending on the excitation wavelength and fluorescence intensity, a filter for suppressing detection of excitation light and a filter for appropriately maintaining the range of fluorescence intensity were used.
As a result, emission having a maximum intensity around 370 nm was confirmed at an excitation wavelength of 333 nm. (Figure 2: Photoluminescence measurement results)

Thermal analysis used SEIKO EXSTAR6000 TG / DTA.
A 30 mg sample is placed in a platinum container, heated to a maximum temperature of 1400 ° C. at a heating rate of + 20 ° C./min, and then cooled to around 100 ° C. at a cooling rate of −20 ° C./min to measure DTA. did.
As a result, no phase transition was observed from room temperature to 1400 ° C. (Figure 3: DTA measurement results)

Furthermore, in order to confirm the presence or absence of a phase transition from 1400 ° C. to the melting point, a simple thermal analyzer that can be used at a high temperature was produced. Briefly, a JIS 10 cc platinum crucible filled with a sample is placed in a firing furnace capable of high-temperature firing, and a PR20-40 thermocouple is inserted into the crucible. The temperature of the firing furnace is raised to around 1700 ° C., the sample is melted, and the output of the thermocouple in the process of cooling and solidifying is recorded. When there is a sudden heat in / out such as a phase transition, it can be detected as a peak.
When such a simple thermal analyzer was used to examine the presence or absence of a phase transition from 1400 ° C. to 1700 ° C., no phase transition was observed in the range from 1400 ° C. to the melting point of 1660 ° C. (Figure 4: Results of high-temperature thermal analysis)

From the above results, it was found that the rare earth borate represented by the composition formula: Lu _0.796 Sc _0.199 Ce _0.005 BO ₃ has no phase transition from room temperature to the melting point. From this, it was found that single crystals can be grown from the melt by adding Sc.

(Experiment 2)
Similar to Experiment 1, the composition formula: (Lu _1-x Sc _x ) _0.995 Ce _0.005 BO ₃ (x = 1, 0.75, 0.5, 0.25, 0.05, 0.03, 0.02 Or a rare earth borate represented by 0.01).

  The XRD, DTA, and photoluminescence of the obtained rare earth borate powder were measured in the same manner as in Experiment 1. The XRD and DTA measurement results are shown in Table 1, and the photoluminescence measurement results are shown in Table 2. It was shown to.

From the XRD measurement results, when x = 0.02, it contains a very small amount of Vaterite phase (JCPDS13-0481) as the main phase, and when x = 0.01, it becomes a mixture of Calcite phase and Vatirite phase. I found out.
Further, it has been found that the emission wavelength shifts to the longer wavelength side as the Sc addition amount x increases. For x = 0.01, the main phase is different (Vatirite phase). Therefore, the comparison of emission wavelength was not performed.
From the DTA measurement result, in the range of x = 1 to 0.02, no peak due to the phase transition was confirmed in the range from room temperature to 1400 ° C.
From the above results, the rare earth borate represented by the composition formula: (Lu _1-x Sc _x ) _0.995 Ce _0.005 BO ₃ where x is 0.02 ≦ x <1 does not have a phase transition from room temperature to the melting point. I found out.

(Experiment 3)
In order to compare with the effect of addition of Sc, a rare earth element other than Sc, Gd, is added to the composition formula: (Lu _1-x Gd _x ) _0.995 Ce _0.005 BO ₃ (where x = 1, 0.75, 0. The rare earth borate represented by 5 or 0.25) was prepared.

For example, when x = 0.25, 23.76 g of 4N Lu ₂ O ₃ made by Yttrium Japan, 7.21 g of 4N Gd ₂ O ₃ made by the company, 0.14 g of 4N CeO ₂ made by the company, high purity chemical 5.85 g each of 4N B ₂ O ₃ manufactured by Research Laboratory was weighed. However, since B ₂ O ₃ tends to evaporate during firing, it was weighed 5% more in molar ratio than stoichiometric.
The weighed raw materials were put in an agate mortar, mixed for 30 minutes, then transferred to a platinum crucible, and lightly covered with a platinum lid. In a nitrogen atmosphere, the temperature was raised to 1500 ° C. at 200 ° C./hour and held for 24 hours for firing. Thereafter, the temperature was returned to room temperature at 200 ° C./hour, and the fired product was taken out and pulverized in an agate mortar for 30 minutes.
The XRD and DTA of the rare earth borate powder thus obtained were measured, and the results are summarized in Table 3.

In XRD measurement, Mac Science MXP18 was used as a measuring device, a Cu target was used as a radiation source, and an XRD pattern was obtained in the range of 2θ from 5 degrees to 80 degrees.
When the obtained pattern was identified, it was found that it had the same structure as the LuBO ₃ Vaterite phase.

Thermal analysis was performed using SEIKO EXSTAR6000 TG / DTA.
A 30 mg sample is placed in a platinum container, heated to a maximum temperature of 1400 ° C. at a heating rate of + 20 ° C./min, and then cooled to around 100 ° C. at a cooling rate of −20 ° C./min to measure DTA. did.
As a result, it was confirmed that there were two phase transitions from room temperature to 1400 ° C.

From the above results, the rare earth borate represented by (Lu _1-x Gd _x ) _0.995 Ce _0.005 BO ₃ (x = 1, 0.75, 0.5 or 0.25) It was found that it was difficult to grow a single crystal from

(Experiment 4)
As in Experiment 1, a rare earth borate represented by the composition formula: Lu _0.8955 M ¹ _0.0995 Ce _0.005 BO ₃ (M ¹ is ^one of Al, Ga, and In) was prepared.

In the same manner as in Experiment 1, the XRD of the rare earth borate powder was measured.
For XRD measurement, Mac Science MXP18 was used as a measuring device, a Cu target was used as a radiation source, and an XRD pattern was obtained in the range of 2θ from 5 degrees to 80 degrees.
When the obtained pattern was identified, a slight amount of Calcite phase was observed with Al addition as the main phase of Vaterite phase. When Ga was added, a slight Vaterite phase was observed with the Calcite phase as the main phase. When In was added, it was a single phase of Calcite phase. (Table 4)

Thermal analysis was performed on the Ga-added sample under the same conditions as in Experiment 1.
A 30 mg sample is placed in a platinum container, heated to a maximum temperature of 1400 ° C. at a heating rate of + 20 ° C./min, and then cooled to around 100 ° C. at a cooling rate of −20 ° C./min to measure DTA. did.
As a result, an endothermic peak due to dehydration was observed from 100 ° C. to 200 ° C., but no phase transition was observed from room temperature to 1400 ° C. (Figure 5: DTA measurement results)

From the above results, the rare earth borate represented by the composition formula: Lu _0.8955 M ¹ _0.0995 Ce _0.005 BO ₃ (M ¹ is ^one of Al, Ga, and In), when M ¹ is Ga or In, It has been found that there is a possibility of exhibiting the effect of suppressing the phase transition similarly to Sc.
It is also possible to combine these elements.

(Experiment 5)
In the same manner as in Experiment 1, a rare earth borate represented by the composition formula: Lu _0.995 Ce _0.005 BO ₃ was prepared.
XRD, photoluminescence and DTA of the obtained rare earth borate powder were measured.

In XRD measurement, Mac Science MXP18 was used as a measuring device, a Cu target was used as a radiation source, and an XRD pattern was obtained in the range of 2θ from 5 degrees to 80 degrees.
When the obtained pattern was identified, it was found that it had the same Vaterite phase as LuBO ₃ . (Figure 6: XRD measurement results)

Photoluminescence measurement was performed using a Hitachi spectrofluorometer F4500. Depending on the excitation wavelength and fluorescence intensity, a filter for suppressing detection of excitation light and a filter for appropriately maintaining the range of fluorescence intensity were used.
As a result, emission having the maximum intensity was confirmed around 394 nm and 419 nm at an excitation wavelength of 363 nm. (Figure 7: Photoluminescence measurement results)

Thermal analysis was performed using SEIKO EXSTAR6000 TG / DTA.
A 30 mg sample is placed in a platinum container, heated to a maximum temperature of 1400 ° C. at a heating rate of + 20 ° C./min, and then cooled to around 100 ° C. at a cooling rate of −20 ° C./min to measure DTA. did.
As a result, a phase transition was confirmed at 1030 ° C. during the temperature raising process and around 530 ° C. during the temperature lowering process. (Figure 8: DTA measurement results)

From the above results, it was found that the rare-earth borate represented by the composition formula: Lu _0.995 Ce _0.005 BO ₃ has a phase transition, so that it is very difficult to grow a single crystal from the melt.

(Experiment 6)
A single crystal of rare earth borate represented by a composition formula: Lu _0.796 Sc _0.199 Ce _0.005 BO ₃ was prepared.

First, as raw materials, 142.53g of 4N Lu ₂ O ₃ from Yttrium Japan, 12.35g from 4N Sc ₂ O ₃ from the company, 0.78g from 4N CeO ₂ from the company, 4N from High Purity Chemical Laboratory 43.86 g of B ₂ O ₃ was weighed. Since B ₂ O ₃ always evaporates during crystal growth, it was weighed 40% in excess of the stoichiometric molar ratio.

All the weighed raw materials were put in a plastic container, capped, and then mixed for 12 hours using a V-type mixer.
The mixed raw material was transferred to a platinum crucible, heated to 1000 ° C. at 200 ° C./hour in a nitrogen atmosphere, and maintained for 24 hours for preliminary firing. Then, it cooled to room temperature at 200 degreeC / hour, and took out the prebaked raw material.
At this time, it was confirmed by XRD measurement that the pre-fired raw material was completely reacted and became a rare earth borate (JCPDS13-0477).

The pre-baked raw material taken out was enclosed in a vinyl chuck bag and pulverized until it became smooth while tapping lightly.
Next, the raw material was sealed in a dedicated rubber bag and compressed using a cold isostatic press (CIP) at a pressure of 2 t / cm ² for 2 minutes to obtain a compact raw material.

This compact material was placed in an Ir crucible having a diameter of 40 mmφ and a height of 35 mm, and set in a crystal growth apparatus. This crystal growth apparatus is an apparatus for performing growth by the Czochralski method.
Crystal growth was performed in a nitrogen atmosphere while heating the rare earth borate to the melting point or higher to melt the raw material and maintaining the melt. Ir wire was attached to the melt, and it was grown by rotating at a rotational speed of 15 rpm and a speed of 5 mm / hour. When the length of the crystal reached about 30 mm, the growth was terminated, and it was cooled sufficiently over time.

Further, a part of the obtained crystal was pulverized and XRD measurement was performed (FIG. 9).
Moreover, it cut | disconnected along the growth direction of the obtained crystal | crystallization, and exposed the cross section. With respect to this cross section, an evaluation of crystallinity by the back reflection Laue method was attempted.

  The back reflection Laue method was performed by converging X-rays emitted from a Mo target of an X-ray source at 30 kV-15 mA with a 1 mmφ collimator and irradiating the sample, and taking the reflected X-rays on a film. At this time, the distance between the film and the sample was 50 mm, the exposure time was 3 minutes, and Polaroid Type 57 was used for the film.

As a result of examining the crystal orientation distribution by dividing the crystal cross section by 2 mm × 2 mm, it was confirmed that a single crystal having a width of 20 mm and a width of 6 mm was grown in the latter half of the crystal growth.
Therefore, the above experiment confirmed that a single crystal of rare earth borate represented by the composition formula: Lu _0.796 Sc _0.199 Ce _0.005 BO ₃ was grown.

The XRD measurement result (XRD pattern) of Lu _0.796 Sc _0.199 Ce _0.005 BO ₃ obtained in Experiment 1 is shown. The results of the photoluminescence measurement of Lu _0.796 Sc _0.199 Ce _0.005 BO ₃ obtained in Experiment 1 are shown. It shows the DTA measurement results of the Lu _0.796 Sc _0.199 Ce _0.005 BO ₃ in Experiment 1. It shows the high-temperature thermal analysis results of the obtained Lu _0.796 Sc _0.199 Ce _0.005 BO ₃ in Experiment 1. It shows the DTA measurement results of the Lu _0.8955 Ga _0.0995 Ce _0.005 BO ₃ in Experiment 4. It shows the XRD pattern of the obtained Lu _0.995 Ce _0.005 BO ₃ in Experiment 5. The photoluminescence measurement result of Lu _0.995 Ce _0.005 BO ₃ obtained in Experiment 5 is shown. The DTA measurement result of Lu _0.995 Ce _0.005 BO ₃ obtained in Experiment 5 is shown. The XRD measurement result (XRD pattern) of the crystal obtained in Experiment 6 is shown.

Claims (11)

Composition formula: (Lu _1-x M ¹ _x ) _1-y M ² _y BO ₃ (where 0.02 ≦ x < ¹ , 0.0001 ≦ y ≦ 0.1, M ¹ : from Sc, Ga and In A single crystal material for a scintillator represented by one or a combination of two or more elements selected from the group consisting of M ² : a luminescent element. A scintillator represented by a composition formula: (Lu _1-x Sc) _1-y M ² _y BO ₃ (where 0.02 ≦ x <1, 0.0001 ≦ y ≦ 0.1, M ² : luminescent element) Single crystal material.   The single-crystal material for scintillators according to claim 1 or 2, wherein the single-crystal material is a calcite phase single-phase single crystal. M ² in the above composition formula is one or a combination of two or more selected from the group consisting of Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, Cr, Bi, and Tl. The single crystal material for scintillators according to any one of claims 1 to 3, wherein   The single crystal material for a scintillator according to any one of claims 1 to 4, wherein 0.02≤x≤0.5 in the composition formula.   A radiation detector comprising the scintillator single crystal material according to claim 1 as a scintillator.   In a method for producing a scintillator material comprising a step of obtaining a scintillator crystal material by melting and cooling and solidifying a mixture containing a Lu raw material and a raw material containing boron and oxygen, at least one of Sc, Ga and In A method for producing a scintillator material, characterized in that a single crystal material for a scintillator is obtained by adding the elemental raw material to suppress phase transition of the material to be added.   A melting step of mixing and heating and melting a Lu raw material, an elemental raw material of at least one of Sc, Ga and In, a raw material containing boron and oxygen, and a light emitting element raw material; The manufacturing method of the material for scintillators of Claim 7 provided with the cooling solidification process obtained.   A Lu raw material, an element raw material of at least one of Sc, Ga and In, a raw material containing boron and oxygen, and a light emitting element raw material are mixed, heated, and pre-fired to include at least the boron and oxygen. The method for producing a scintillator material according to claim 7 or 8, wherein a reactant having a melting point higher than that of the raw material is fired and the reactant is heated and melted.   The method for producing a scintillator material according to any one of claims 7 to 9, wherein the raw material containing boron and oxygen is mixed so that the amount of boron is larger than the amount calculated from stoichiometry. . Composition formula: (Lu _1-x M ¹ _x ) _1-y M ² _y BO ₃ (where 0.02 ≦ x < ¹ , 0.0001 ≦ y ≦ 0.1, M ¹ : from Sc, Ga and In The scintillator single crystal material represented by one or a combination of two or more selected from the group, M ² : luminescent element) is obtained. A method for manufacturing a scintillator material.

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