JP2021130593A - Method for growing single crystal ingot, and single crystal sample - Google Patents

Abstract

To provide a method for growing a new single crystal ingot in order to grow a single crystal including an inclusion reduced as compared with conventional one, having a high light emission amount and having a size practically necessary as radiation detection applications.SOLUTION: A method for growing a single crystal ingot having a composition represented by (A1-xBx)2Si2O7 (A is at least one kind selected from a group consisting of Y, La and Gd, B is at least one kind selected from a group consisting of rare earth elements except Y, La and Gd, and x satisfies 0.005<x<0.30.) comprises: a melting step of obtaining a melt in the state of melting a single crystal raw material in a crucible on the basis of a fusion method; and a cooling and solidification step of growing a crystal along a predetermined crystal plane orientation of a seed crystal by dipping at least a part of the seed crystal in the melt and cooling and solidifying the melt having the dipped seed crystal to obtain a single crystal ingot. The fusion method is the rotating Czochralski method, and a pulling speed is less than 0.3 mm/h.SELECTED DRAWING: Figure 12

Description

The present invention relates to a method for growing a single crystal ingot used for detecting radiation such as X-rays and γ-rays, and a single crystal sample obtained by the growing method.

When a Gd ₂ Si ₂ O ₇ series single crystal (hereinafter, may be referred to as “GPS single crystal”) is used for radiation detection, it is referred to as a Gd ₂ SiO ₅ series single crystal (hereinafter, “GSO single crystal”). It is known that it exhibits far superior light emission amount and temperature characteristics as compared with (for example, Patent Document 1).

Japanese Patent No. 6303146

However, even with such a GPS single crystal having excellent characteristics, what has been reported so far as a single crystal for radiation detection is a single crystal having a high transparency having a size of about 5 mm × 5 mm × 5 mm. .. When an attempt is made to cut out a larger single crystal sample, cracks, bubbles, and the like are likely to be included, and a single crystal sample having a low transmittance as a whole tends to be easily obtained.

At sites such as oil drilling, a detection element (single crystal sample) with a diameter of about 1 inch and a length of about 2 inches is collected for use as a detector in a high temperature environment (about 150 to 250 ° C) with low signal strength. A technique for growing a single crystal ingot that can be produced is required, but it has not been reported that a colorless and transparent single crystal ingot that is practically necessary for this size has been obtained.

Therefore, in the present invention, inventing a new single crystal ingot for growing a single crystal ingot having reduced inclusions, a high amount of light emission, and practically necessary dimensions for radiation detection applications. The purpose is to provide a method. Another object of the present invention is to provide a single crystal sample obtained by the growing method.

The present invention provides a method for growing a single crystal ingot having a composition represented by the following general formula (1).
(A _1-x B _x ) ₂ Si ₂ O ₇ ... (1)
[In formula (1), A is at least one selected from the group consisting of Y, La and Gd, and B is at least one selected from the group consisting of rare earth elements excluding Y, La and Gd. , X satisfies 0.005 <x <0.30. ]
The growing method of the present invention includes a melting step of obtaining a molten liquid in which a single crystal raw material is melted in a pot based on a melting method, and melting in which at least a part of a seed crystal is immersed in the molten liquid and the seed crystal is immersed. It is equipped with a cooling and solidification step in which crystals are grown along the crystal plane of the seed crystal to obtain a single crystal ingot by cooling and solidifying the liquid. It is a breeding method that is less than / h.

According to the growing method of the present invention, inclusions are reduced as compared with the conventional one, the amount of light emitted and the energy resolution are high, and a single crystal sample having dimensions required for radiation detection can be obtained.

In the growing method of the present invention, B is preferably Ce in the above formula (1), and A is preferably Gd in the above formula (1). Thereby, the amount of light emission can be further increased.

In the growing method of the present invention, the rotation speed of the seed crystal in the rotary pulling method is preferably 0.5 to 9 rpm, and the rotation speed of the crucible is preferably 1 to 6 rpm. As a result, the amount of light emitted and the energy resolution can be further increased.

The present invention provides a single crystal sample having a composition represented by the following general formula (1) and having a thickness direction of 75% or more with respect to light having a wavelength of 600 nm when the thickness is 12 mm.
(A _1-x B _x ) ₂ Si ₂ O ₇ ... (1)
[In formula (1), A is at least one selected from the group consisting of Y, La and Gd, and B is at least one selected from the group consisting of rare earth elements excluding Y, La and Gd. , X satisfies 0.005 <x <0.30. ]

The single crystal sample of the present invention has reduced inclusions, high emission amount and energy resolution, and has dimensions necessary for radiation detection applications.

According to the present invention, inclusions are reduced as compared with the conventional case, the amount of light emitted and the energy resolution are high, and the dimensions and shape (for example, the length of any one side is 12 mm or more) practically necessary for radiation detection applications. It is possible to provide a new method for growing a single crystal ingot for growing a single crystal ingot capable of obtaining a single crystal sample having a rectangular parallelepiped or a cylinder having a diameter of 12 mm or more and a length of 12 mm or more. Further, according to the present invention, it is possible to provide a colorless and transparent high-quality single crystal sample in which polycrystalline portions, small grain boundaries, cracks and the like are not observed. It can be said that such a single crystal sample is a single crystal sample in which inclusions are reduced as compared with the conventional one, the amount of light emitted and the energy resolution are high, and the dimensions are practically necessary for radiation detection applications.

The single crystal sample of the present invention has excellent detection characteristics in a wide temperature range from room temperature to high temperature. With such a single crystal sample, it is possible to detect radiation with high accuracy from room temperature to a high temperature environment, which was not possible with a conventional radiation detector.

FIG. 1 is a schematic cross-sectional view showing an example of the basic configuration of the crystal growing apparatus. FIG. 2 is an external photograph of the single crystal ingot obtained in Example 1. FIG. 3 is a diagram showing an XRD diffraction pattern of the single crystal obtained in Example 1. FIG. 4 is an external photograph of the single crystal sample obtained in Example 1. FIG. 5 is a diagram showing a pulse wave height spectrum of a single crystal sample. FIG. 6 is a diagram showing a transmittance curve of a single crystal sample. FIG. 7 is an external photograph of the single crystal ingot obtained in Example 4. FIG. 8 is an external photograph of the single crystal ingot obtained in Example 5. FIG. 9 is a diagram showing inclusions inside the single crystal ingot obtained in Example 5 and their distribution. FIG. 10 is a diagram showing inclusions inside the single crystal ingot obtained in Comparative Example 1 and their distribution. FIG. 11 is an external photograph of the single crystal ingot obtained in Comparative Example 3. FIG. 12 is a diagram showing the relationship between the pulling speed and the average transmittance for light having a wavelength of 600 nm.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings as necessary. Unless otherwise specified, the positional relationship such as up, down, left, and right shall be based on the positional relationship shown in the drawings. Furthermore, the dimensional ratios in the drawings are not limited to the ratios shown.

[Single crystal sample]
The single crystal sample according to the preferred embodiment of the present invention has a composition represented by the following general formula (1).
(A _1-x B _x ) ₂ Si ₂ O ₇ ... (1)
In formula (1), A is at least one selected from the group consisting of Y, La and Gd, and B is at least one selected from the group consisting of rare earth elements excluding Y, La and Gd. x satisfies 0.005 <x <0.30.

Here, in the above formula, from the viewpoint that a high amount of light emission can be easily obtained, A is preferably an element that is not colored in the crystal, and more preferably Gd. From the same viewpoint, B is preferably an element having high luminous efficiency, and more preferably Ce. From the viewpoint that it is easy to obtain a high-quality single crystal sample that is colorless and transparent and has few defects, x is preferably 0.005 <x <0.30, and 0.01 <x <0.10. Is more preferable, 0.015 <x <0.05 is further preferable, and 0.015 <x <0.03 is extremely preferable.

Since such a single crystal sample emits fluorescence when exposed to radiation, it can be used for radiation detection applications, that is, for scintillator applications. In the single crystal sample of the present embodiment, the maximum peak wavelength is observed around 430 nm in the fluorescence intensity spectrum.

Here, "radiation" refers to particle rays or electromagnetic waves (α-rays, β-rays, γ-rays, X-rays, etc.) having sufficient energy to ionize atoms or molecules.

The single crystal sample of the present embodiment has suitable light emission characteristics at room temperature (25 ° C.) to high temperature (300 ° C.). In particular, it is excellent in light emission characteristics in a high temperature region. For example, when the single crystal of the present embodiment is irradiated with 662 keV γ-rays, the light emission amount at 150 ° C. can be made higher than the light emission amount at room temperature. Similarly, the amount of light emitted at 200 ° C. when irradiated with 662 keV γ-rays can be made higher than the amount of light emitted at room temperature. The emission characteristics in the high temperature region can be adjusted by appropriately changing the composition of the single crystal sample. As described above, the single crystal sample of the present embodiment can be suitably used in a wide temperature range from room temperature to high temperature.

The single crystal sample of the present embodiment has extremely excellent transmittance even if the dimensions are practically necessary for radiation detection applications. For example, in a sample obtained by cutting a single crystal ingot so as to have a thickness of 12 mm, the transmittance (25 ° C.) in the thickness direction with respect to light having a wavelength of 600 nm can be 75% or more. The same transmittance (25 ° C.) may be 80% or more. The ideal upper limit of the same transmittance is 85% when the refractive index of the crystal is taken into consideration. The transmittance of a single crystal sample can be measured using, for example, a U4100 Spectrophotometer (manufactured by Hitachi High-Tech Science Co., Ltd.).

The dimensions and shape of the cut-out sample are not particularly limited as long as they are practically necessary dimensions and shapes for, for example, radiation detection applications. For example, a rectangular parallelepiped or cube having a side length of 12 mm or more, preferably 25 mm or more, a cylinder having a diameter of 12 mm or more, preferably 25 mm or more and a length of 12 mm or more, preferably 25 mm or more can be mentioned. .. A sample having such dimensions and shape (single crystal sample) exhibits sufficient performance, but it does not limit its use in dimensions smaller than this or in other shapes.

The single crystal sample of the present embodiment having excellent transmittance can have an energy resolution of 662 keV for γ-rays of 7% or less when, for example, a columnar sample having a diameter of 12 mm and a length of 12 mm is used. That is, by using the sample, it is possible to realize extremely high-precision radiation detection ability. The energy resolution may be 6% or less or 5% or less. The energy resolution can be measured using, for example, the Universal Computer Spectrometer UCS30 (manufactured by Spectrometer Spectrometer).

<How to grow a single crystal ingot>
The method for growing a single crystal ingot of the present embodiment is a method for growing a single crystal having a composition represented by the above general formula (1). The growing method includes a melting step of obtaining a molten liquid in which a single crystal raw material is melted in a pot based on the melting method, and a molten liquid in which at least a part of the seed crystal is immersed in the molten liquid and the seed crystal is immersed. At least a cooling solidification step of growing a crystal along a predetermined crystal plane orientation of the seed crystal to obtain a single crystal ingot by cooling and solidifying is provided. The growing method may further include a cutting step of cutting the obtained single crystal ingot into a desired shape and size.

(Melting process)
From the viewpoint of more reliably obtaining a single crystal ingot having good crystallinity, the melting method in the melting step is a rotary pulling method such as the Czochralski method and the TSSG method (Top Seeded Solution Growth Method). Specifically, it is preferable to perform the work in the melting step and the cooling solidification step by using the pulling device 10 having the structure shown in FIG.

FIG. 1 is a schematic cross-sectional view showing an example of a basic configuration of a crystal manufacturing apparatus. The lifting device 10 shown in FIG. 1 includes a refractory furnace body 14 and a refractory lid 13 provided on the refractory body 14 with a hole in the center. The furnace body 14 is for continuously performing the operations in the melting step and the cooling solidification step described above. Further, the refractory lid 13 is used to adjust the temperature gradient around the single crystal ingot in order to prevent cracks in the growing single crystal ingot.

The furnace body 14 is a bottomed container having a cylindrical side wall and having fire resistance. The shape of the bottomed container itself is similar to that used for crystal production based on the known rotary pulling method. A high frequency induction coil 15 is wound around the outer surface of the bottom of the furnace body 14. A crucible 17 (for example, a crucible made of Ir (iridium)) is arranged on the bottom surface inside the furnace body 14. The crucible 17 also serves as a high-frequency induction heater. When the raw material of the single crystal ingot is put into the crucible 17 and a high frequency current is passed through the high frequency induction coil 15, the crucible 17 is heated by the generated induction current, and the melt 18 in which the raw material of the single crystal ingot is in a molten state. Obtained in the crucible 17.

A through hole (not shown) is provided in the center of the bottom of the furnace body 14, and a crucible support rod 16 is inserted into this hole from the outside. By rotating the crucible support rod 16, the crucible 17 can be rotated in the furnace body 14. The pulling device 10 is isolated from the atmosphere by an airtight container (not shown), and the growing atmosphere is protected from the atmosphere.

Next, a more specific manufacturing method using the pulling device 10 will be described. In the process described later, the transmittance of the single crystal obtained by changing the rotation speed of the crucible at the time of growing the single crystal ingot, the rotation speed of the pulling rod, the pulling speed, the growing atmosphere, the structure of the furnace body, etc. It is possible to adjust the characteristics of.

In the melting step, each raw material of the single crystal ingot is put into the crucible 17 so as to obtain a desired crystal composition, and the crucible 17 is heated by passing a high frequency current through the high frequency induction coil 15 to form the single crystal ingot. A melt 18 made of the material is obtained. The raw materials of the single crystal ingot are not particularly limited as long as the single crystal ingot having the composition represented by the above general formula (1) can be obtained, and for example, Y, La, and Gd constituting the single crystal ingot are not particularly limited. , Ce and other rare earth element single oxides, Si single oxides and the like can be used. If an attempt is made to grow a single crystal ingot with a raw material composition similar to the crystal composition, an apatite-type compound may precipitate in the primary crystal. Therefore, the melt composition is changed and the crystallization experiment is repeated to determine the raw material composition for growing. It is preferable to do so.

(Cooling and solidification process)
Next, the single crystal ingot 1 is obtained by cooling and solidifying the melt in the cooling and solidifying step. The cooling and solidifying step is divided into two steps, a growing step and a cooling step, which will be described later, and the work proceeds.

In the growing step, a pulling rod 12 having the seed crystal 2 fixed to the lower tip is immersed in the melt 18 from the upper part of the furnace body 14. Next, the single crystal ingot 1 is grown while pulling up the pulling rod 12. At this time, in the growing step, the high frequency output of the high frequency induction coil 15 is adjusted, and the single crystal ingot 1 pulled up from the molten liquid 18 is grown until its cross section has a predetermined diameter. From the viewpoint of more reliably obtaining a desired single crystal ingot, the seed crystal 2 that is the core of the single crystal ingot 1 is a single crystal (for example, GPS single crystal or the like) as represented by the above general formula (1). Is preferable.

In the growing step, the crucible support rod 16 rotates the crucible 17 at a predetermined speed (for example, 1 to 6 rpm), and the pulling rod 12 pulls up the seed crystal 2 while rotating it in the direction opposite to the rotation direction of the crucible 17. By rotating both in opposite directions, the heat and atom flow near the crystal precipitation interface becomes smooth, and there is an effect of reducing defects in the crystal. The rotation speed of the seed crystal can be appropriately adjusted according to the composition of the single crystal ingot and the pulling speed (growth speed), but from the viewpoint of obtaining a better single crystal ingot, it may be 0.5 to 9 rpm. It is preferably 2 to 6 rpm, more preferably 2 to 6 rpm. On the other hand, the pulling speed is less than 0.3 mm / h from the viewpoint of obtaining a single crystal sample having reduced inclusions, high light emission amount and energy resolution, and dimensions required for radiation detection applications. It is preferably 0.25 mm / h or less, 0.2 mm / h or less, 0.15 mm / h or less, or 0.1 mm / h or less. The lower limit of the pulling speed is not particularly limited, but may be 0.01 mm / h or 0.05 mm / h from the viewpoint of cost and growing efficiency.

The crystal plane of the seed crystal can be appropriately selected according to the crystal orientation to be grown. The crystal plane can have, for example, <100>, <010>, <001> orientations. In addition, the growing method of the present embodiment can grow a single crystal in almost any direction. Therefore, the crystal plane of the seed crystal may have an orientation inclined by a predetermined angle (for example, 10 to 20 degrees) from the orientations such as <100>, <010>, and <001> described above.

Next, in the cooling step, the high frequency output of the high frequency induction coil 15 is adjusted to cool the grown single crystal ingot obtained after the growing step. After the cooling step is completed, the single crystal ingot is taken out from the pulling device 10.

(Cutting process)
In the cutting step, a single crystal sample having a desired size and shape is cut out from the single crystal ingot. As described above, the dimensions and shape of the cut-out sample can have the dimensions and shape practically necessary for, for example, radiation detection applications.

<Radiation detector>
The radiation detector includes a single crystal sample cut out in this way and a light detection device for detecting light emission from the single crystal sample. Examples of the photodetector include Photomultiplier H7195 (manufactured by Hamamatsu Photonics Co., Ltd.). Such a detector is excellent in radiation detection ability because it includes the single crystal sample of the present embodiment.

<How to use the radiation detector>
The single crystal sample of the present embodiment has excellent luminescence characteristics in a wide temperature range from room temperature to high temperature. Therefore, for example, a radiation detector provided with the single crystal sample of the present embodiment is suitable in a temperature range (for example, an environment of 150 ° C. or higher, 200 ° C. or higher, or 300 ° C. or higher) in which sufficient detection accuracy has not been obtained in the past. Can be used for.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

[Example 1]: Preparation and evaluation of GPS: Ce2.5% 0.1 mm / h- <001> In the following general formula (1), the composition of A = Gd, B = Ce, and x = 0.025, That is, a single crystal ingot was prepared by the following method with the goal of obtaining a single crystal sample having a composition of _{(Gd 0.975} Ce _0.025 ) ₂ Si ₂ O _7.
(A _1-x B _x ) ₂ Si ₂ O ₇ ... (1)

Specifically, the raw material powders of gadolinium oxide (Gd ₂ O ₃ , purity 4N), silicon oxide (SiO _2, purity 5N), and cerium oxide (CeO ₂ , purity 4N) are heated at about 1000 degrees, and then. From the amount of weight loss, the true value of the active ingredient in the reagent was measured, corrected by that value, and the raw materials were weighed so as to have the above chemical formula. The above compound is a decomposition melt compound, and when the raw material having a crystal composition is melted to grow the above compound, an apatite type compound is precipitated in the primary crystal. It was determined. The growth material composition was selected _{0.32 (Gd 0.975 Ce 0.025) 2} O 3 · 0.68Si 2 O 2.

The crystal growth apparatus shown in FIG. 1 was used for crystal growth. The raw materials weighed as described above were mixed with a mixer, molded, reacted at 1600 ° C. for 12 hours, and then used as a growing raw material. The Ir pot installed in the high-frequency Czochralski furnace was filled with the growing material, and a high-frequency voltage was applied to the high-frequency induction coil to melt the growing material. The same procedure was repeated as needed, and about 4400 g of the growing material was filled in the Ir crucible. The volume of the melt at this time was about 75% of the volume of the crucible.

As a seed crystal, a single crystal of GPS: Ce 2.5%, which was separately prepared by a pulling method, was cut out in the <001> direction and prepared. The temperature of the melt in the crucible was adjusted, the seed crystal was immersed in the melt, and the seed crystal was pulled up while rotating while adjusting the temperature by controlling the high frequency power. The rotation speed (rotation speed) of the seed crystal was 3 rpm, and the crucible was rotated at 3 rpm in the opposite direction. The pulling speed was 0.1 mm / h. Single crystal ingots were grown in a nitrogen atmosphere.

FIG. 2 is an external photograph of the single crystal ingot obtained in Example 1. The obtained single crystal ingot was a high-quality crystal that was slightly yellow and transparent without cracks and white turbidity, which had been a problem in the past, and had a columnar size of about 35 mm in diameter and about 40 mm in length.

[Determination of crystal composition]
As described above, this crystal decomposes and melts. Therefore, the composition of the molten raw material and the composition of the crystallized crystals are different. When a part of the obtained crystal was subjected to ICP analysis, the crystal composition was (Gd _0.983 Ce _0.017 ) ₂ Si ₂ O ₇ .

[Identification of crystal structure]
A part of the obtained single crystal sample was pulverized, and the crystal structure was identified by powder X-ray diffraction method. A powder X-ray diffractometer (Rigaku Co., Ltd., MiniFlexII) was used as the X-ray diffractometer, and the structure was identified by comparing the diffraction pattern with the crystal structure database (Joint Committee on Power Diffraction Standards, JCPDS). FIG. 3 is a diagram showing an XRD diffraction pattern of the single crystal sample obtained in Example 1. As a result of the identification, it was found that the single crystal sample obtained in Example 1 had an orthorhombic (space group Pna21) structure.

[Evaluation of light emission characteristics]
In order to evaluate the luminescence characteristics of the scintillator, a columnar single crystal sample having a diameter of about 12 mm and a length of about 12 mm was cut out from the obtained single crystal ingot and mechanically polished on the entire surface. Then, the single crystal sample was annealed in a nitrogen atmosphere at 1450 ° C. for 144 hours using an annealing furnace. FIG. 4 is an external photograph of the single crystal sample obtained in Example 1. As shown in FIG. 4, it was found that this sample was a colorless and transparent high-quality single crystal containing no polycrystalline parts, small grain boundaries, cracks, inclusions and the like. The obtained single crystal sample is referred to as "GPS 0.1 mm / h".

For the purpose of evaluating the scintillator characteristics of "GPS 0.1 mm / h", pulse wave height spectrum measurement was performed for 662 keV γ-rays from ^{137 Cs.} Photomultiplier H7195 (manufactured by Hamamatsu Photonics Co., Ltd., product name) was used as the photodetector, and the applied voltage was -1600 V. FIG. 5 is a diagram showing a pulse wave height spectrum of a single crystal sample. In FIG. 5, single crystal samples “GPS 0.1 mm / h” (Example 1) and single crystal samples “GPS 0.3 mm / h” (Comparative Example 1) having different growth rates, and measurements were taken for comparison. The measurement result of the pulse wave height spectrum of the standard sample "GSO crystal" is shown.

Since a current signal proportional to the amount of light emitted can be obtained from a photomultiplier tube, a multi-channel analyzer USC30 (Spectrum Techniques, manufactured by LLC, product name) is connected to measure the pulse wave height distribution and compare the photoelectric peak positions. , It is possible to evaluate the amount of light emitted by the scintillator relative to the standard sample. The energy resolution is the ratio of the full width at half maximum of the photoelectric peak to the position. The photoelectric peak position of the light emission of the single crystal sample "GPS 0.1 mm / h" was 1440 ch, and the energy resolution was 4.4%, which were very excellent results. Moreover, since the energy resolution of "GSO standard" measured as a standard sample is 9.4%, an excellent result that the energy resolution of "GPS 0.1 mm / h" is more than doubled was obtained. Further, in the single crystal sample "GPS 0.3 mm / h" prepared in Comparative Example 1, the photoelectric peak position is about 760 ch, and the energy resolution is about 8%, which is about half of "GPS 0.1 mm / h". rice field. Since the single crystal "GPS 0.3 mm / h" has white turbid inclusions in the crystal, it is considered that the light emission was inhibited by the inclusions.

As can be seen from the wave height spectrum of FIG. 5, in "GPS 0.1 mm / h", the number of channels forming a valley between the photoelectric peak and the Compton peak is close to zero. This result shows that "GPS 0.1 mm / h" is a practical scintillator having excellent radiation absorption ability. On the other hand, at "GPS 0.3 mm / h", the valley was higher than that at "GPS 0.1 mm / h" due to the close distance between the Compton peak and the photoelectric peak.

[Transmittance measurement]
The transmittance of a sample is greatly affected by cracks and inclusions inside the sample. It is also known that the abundance of cracks, inclusions and the like has a great influence on the above-mentioned value of the wave height spectrum. Therefore, the transmittance was used to evaluate the performance of the grown crystals.

From the obtained single crystal ingot, a single crystal sample was cut out so as to have a thickness of 12 mm, and both sides were mirror-polished to prepare an evaluation sample, and the transmittance thereof was measured. A U-4100 Spectrophotometer (Hitachi High-Tech Science Co., Ltd., product name) was used for the measurement of the transmittance.

FIG. 6 is a diagram showing a transmittance curve of a single crystal sample. FIG. 6 shows the transmittance of "GPS 0.1 mm / h" obtained in Example 1 and the transmittance of "GPS 0.3 mm / h" obtained in Comparative Example 1. .. As can be seen from FIG. 6, "GPS 0.1 mm / h" (thickness 12 mm) had an absorption edge near a wavelength of 350 nm and showed a very high transmittance of about 85% with respect to light having a wavelength of 600 nm. Further, the transmittance changed linearly from 600 nm to around 370 nm, and maintained a transmittance of 80% or more even at 370 nm near the absorption edge, showing very good absorption characteristics. On the other hand, the transmittance of "GPS 0.3 mm / h" was about 50% due to the influence of inclusions. Further, the transmittance curve changed linearly from 600 nm to 500 nm, but the transmittance gradually decreased from 500 nm to the absorption edge.

[Example 2] Preparation and evaluation of GPS: Ce2.5% 0.1 mm / h- <100> As a seed crystal, a single crystal of GPS: Ce separately prepared by a pulling method was cut out in the <100> direction. The single crystal ingot was grown in substantially the same manner as in Example 1 except that it was prepared. The obtained single crystal ingot did not contain polycrystalline portions, small grain boundaries, cracks, inclusions, etc., was pale yellow transparent, and had a circular cross section perpendicular to the growing direction.

A columnar single crystal sample was cut out from the above single crystal ingot, and the transmittance was measured in the same manner as in Example 1. The obtained evaluation sample had an absorption edge near a wavelength of 350 nm and showed a very high transmittance of about 85% with respect to light having a wavelength of 600 nm.

[Example 3] Preparation and evaluation of GPS: Ce2.5% -0.1 mm / h- <010> As a seed crystal, a single crystal of GPS: Ce separately prepared by a pulling method was cut out in the <010> direction. The single crystal ingot was grown in substantially the same manner as in Example 1 except that the above was prepared. The obtained single crystal ingot did not contain polycrystalline portions, small grain boundaries, cracks, inclusions, etc., was pale yellow transparent, and had a circular cross section perpendicular to the growing direction.

A columnar single crystal sample was cut out from the above single crystal ingot, and the transmittance was measured in the same manner as in Example 1. The obtained evaluation sample had an absorption edge near a wavelength of 350 nm and showed a very high transmittance of about 84% with respect to light having a wavelength of 600 nm.

[Example 4] Preparation and evaluation of GPS: Ce2.5% 0.1 mm / h- <010> 15 degrees off As a seed crystal, from a GPS: Ce single crystal separately prepared by a pulling method, from the <010> direction. The single crystal ingot was grown in substantially the same manner as in Example 1 except that the one cut out with the <001> axis as the rotation axis and the <010> direction tilted by about 15 degrees was prepared. .. FIG. 7 is an external photograph of the single crystal ingot obtained in Example 4. The obtained single crystal ingot did not contain polycrystalline portions, small grain boundaries, cracks, inclusions, etc., was pale yellow transparent, and had a circular cross section perpendicular to the growing direction.

A columnar single crystal sample was cut out from the above single crystal ingot, and the transmittance was measured in the same manner as in Example 1. The obtained evaluation sample had an absorption edge near a wavelength of 350 nm and showed a very high transmittance of about 83% with respect to light having a wavelength of 600 nm.

In the above example where the pulling speed was 0.1 mm / h, the average value (average transmittance) of the transmittance for light having a wavelength of 600 nm was 84.1%, and the standard deviation was 0.653. Considering that the transmittance considering the light propagation loss due to the reflection of this substance is about 85% and that the transmittance changes linearly from around 600 to 380 nm, the above result is the emission center of the scintillator. It shows that there is almost no absorption at 430 nm, which is near the wavelength, and it can be said that the single crystal obtained by the above example has an ideal transmittance when used as a scintillator.

[Example 5] Preparation and evaluation of GPS: Ce2.5% 0.2 mm / h- <100> In substantially the same manner as in Example 2 except that the pulling speed was set to 0.2 mm / h. Crystal ingots were cultivated. FIG. 8 is an external photograph of the single crystal ingot obtained in Example 5. FIG. 9 is a diagram showing inclusions inside the single crystal ingot obtained in Example 5 and their distribution. As shown in FIG. 9, the obtained single crystal ingot contained a small amount of small inclusions, but did not contain polycrystalline parts, small grain boundaries, cracks, etc., and was pale yellow transparent and in the growing direction. It was a crystal with a circular vertical cross section.

A columnar single crystal sample was cut out from the above single crystal ingot, and the transmittance was measured in the same manner as in Example 1. The obtained evaluation sample had an absorption edge near a wavelength of 350 nm and showed a high transmittance of about 79% with respect to light having a wavelength of 600 nm.

[Example 6] Preparation and evaluation of GPS: Ce2.5% 0.2 mm / h- <001> In substantially the same manner as in Example 1 except that the pulling speed was set to 0.2 mm / h. Crystal ingots were cultivated. The obtained single crystal ingot contained a small amount of small inclusions, but did not contain polycrystalline parts, small grain boundaries, cracks, etc., was pale yellow transparent, and had a circular cross section perpendicular to the growing direction. Met.

A columnar single crystal sample was cut out from the above single crystal ingot, and the transmittance was measured in the same manner as in Example 1. The obtained evaluation sample had an absorption edge near a wavelength of 350 nm and showed a very high transmittance of about 81% with respect to light having a wavelength of 600 nm.

[Example 7] Preparation and evaluation of GPS: Ce2.5% 0.2 mm / h- <010> In substantially the same manner as in Example 3 except that the pulling speed was set to 0.2 mm / h. Crystal ingots were cultivated. The obtained single crystal ingot contained a small amount of small inclusions, but did not contain polycrystalline parts, small grain boundaries, cracks, etc., was pale yellow transparent, and had a circular cross section perpendicular to the growing direction. Met.

A columnar single crystal sample was cut out from the above single crystal ingot, and the transmittance was measured in the same manner as in Example 1. The obtained evaluation sample had an absorption edge near a wavelength of 350 nm and showed a very high transmittance of about 81% with respect to light having a wavelength of 600 nm.

[Example 8] GPS: Ce2.5% 0.2 mm / h- <010> 15 degree off production and evaluation Except that the pulling speed was set to 0.2 mm / h, it was substantially the same as in Example 4. Then, the single crystal ingot was cultivated. The obtained single crystal ingot contained a small amount of small inclusions, but did not contain polycrystalline parts, small grain boundaries, cracks, etc., was pale yellow transparent, and had a circular cross section perpendicular to the growing direction. Met.

A columnar single crystal sample was cut out from the above single crystal ingot, and the transmittance was measured in the same manner as in Example 1. The obtained evaluation sample had an absorption edge near a wavelength of 350 nm and showed a very high transmittance of about 82% with respect to light having a wavelength of 600 nm.

In the above example where the pulling speed was 0.2 mm / h, the average value of the transmittance for light having a wavelength of 600 nm was 79.9%, and the standard deviation was 1.88. In the crystals grown at 0.2 mm / h, the measured values vary slightly due to the difference in the amount and distribution of small inclusions present, and the effect appears in the standard deviation value.

[Comparative Example 1] Preparation and evaluation of GPS: Ce2.5% 0.3 mm / h- <001> In substantially the same manner as in Example 1 except that the pulling speed was set to 0.3 mm / h. Crystal ingots were cultivated. FIG. 10 is a diagram showing inclusions inside the single crystal ingot obtained in Comparative Example 1 and their distribution. The obtained single crystal ingot had no cracks, but white inclusions were distributed around the crystal axis. The color of the single crystal ingot was pale yellow and transparent, and {100} facets appeared parallel to the growth axis.

A columnar single crystal sample was cut out from the above single crystal ingot, and the transmittance was measured in the same manner as in Example 1. The obtained evaluation sample had an absorption edge near a wavelength of 350 nm, and had a transmittance of about 71% for light having a wavelength of 600 nm.

[Comparative Example 2] Preparation and evaluation of GPS: Ce2.5% 0.3 mm / h- <100> In substantially the same manner as in Example 2 except that the pulling speed was set to 0.3 mm / h. Crystal ingots were cultivated. The obtained single crystal ingot had no cracks, but white inclusions were distributed in layers perpendicular to the growth axis. The color of the single crystal ingot was pale yellow and transparent, and the cross section perpendicular to the growing direction was a crystal having a substantially circular shape.

A columnar single crystal sample was cut out from the above single crystal ingot, and the transmittance was measured in the same manner as in Example 1. The obtained evaluation sample had an absorption edge near a wavelength of 350 nm, and had a transmittance of about 54% for light having a wavelength of 600 nm.

[Comparative Example 3] Preparation and evaluation of GPS: Ce2.5% 0.3 mm / h- <010> In substantially the same manner as in Example 3 except that the pulling speed was set to 0.3 mm / h. Crystal ingots were cultivated. The obtained single crystal ingot had no cracks, but white inclusions were distributed around the crystal axis. The color of the single crystal ingot was pale yellow and transparent, and {100} facets appeared. FIG. 11 is an external photograph of the single crystal ingot obtained in Comparative Example 3. As shown in the figure, inclusions existing inside the crystal are observed through the faceted plane.

A columnar single crystal sample was cut out from the above single crystal ingot, and the transmittance was measured in the same manner as in Example 1. The obtained evaluation sample had an absorption edge near a wavelength of 350 nm, and had a transmittance of about 29% for light having a wavelength of 600 nm.

In the above example where the pulling speed was 0.3 mm / h, the average value of the transmittance for light having a wavelength of 600 nm was 51.5%, and the standard deviation was 18.5%. In the example where the pulling speed was 0.3 mm / h, as shown in FIG. 10, the variation in the measured values became large depending on the degree of distribution of inclusions present in the crystal. The standard deviation increased accordingly. In the evaluation sample, a portion having a transmittance of 10% or less also appeared. It is difficult to cut out a large single crystal such as a cylinder having a diameter of 12 mm and a length of 12 mm from a single crystal ingot grown at a pulling speed of 0.3 mm / h.

FIG. 12 is a diagram showing the relationship between the pulling speed and the average transmittance for light having a wavelength of 600 nm. The horizontal axis of the figure represents the pulling speed, and the vertical axis represents the average transmittance of each crystal. Error bars in the figure indicate values of 3σ.

1 ... Single crystal ingot, 2 ... Seed crystal, 10 ... Pulling device, 12 ... Pulling rod, 13 ... Lid, 14 ... Furnace body, 15 ... High frequency induction coil, 16 ... Crucible support rod, 17 ... Crucible, 18 ... Melt (Melting).

Claims (5)

A method for growing a single crystal having a composition represented by the following general formula (1).
A melting step of obtaining a molten liquid in which the raw material of the single crystal is melted in a crucible based on the melting method, and
By immersing at least a part of the seed crystal in the melt and cooling and solidifying the melt in which the seed crystal is immersed, crystals are grown along the crystal plane orientation of the seed crystal to obtain a single crystal ingot. With a cooling and solidification process,
A method for growing a single crystal ingot in which the melting method is a rotary pulling method and the pulling speed is less than 0.3 mm / h.
(A _1-x B _x ) ₂ Si ₂ O ₇ ... (1)
[In formula (1), A is at least one selected from the group consisting of Y, La and Gd, and B is at least one selected from the group consisting of rare earth elements excluding Y, La and Gd. , X satisfies 0.005 <x <0.30. ] The breeding method according to claim 1, wherein B is Ce in the formula (1). The breeding method according to claim 1 or 2, wherein A is Gd in the formula (1). The growing method according to any one of claims 1 to 3, wherein the rotation speed of the seed crystal in the rotary pulling method is 0.5 to 9 rpm, and the rotation speed of the crucible is 1 to 6 rpm. A single crystal sample having a composition represented by the following general formula (1) and having a thickness of 12 mm and a transmittance of 75% or more in the thickness direction with respect to light having a wavelength of 600 nm.
(A _1-x B _x ) ₂ Si ₂ O ₇ ... (1)
[In formula (1), A is at least one selected from the group consisting of Y, La and Gd, and B is at least one selected from the group consisting of rare earth elements excluding Y, La and Gd. , X satisfies 0.005 <x <0.30. ]

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