JP3694884B2 - Method for growing rare earth silicate single crystals - Google Patents
Method for growing rare earth silicate single crystals Download PDFInfo
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- JP3694884B2 JP3694884B2 JP23022496A JP23022496A JP3694884B2 JP 3694884 B2 JP3694884 B2 JP 3694884B2 JP 23022496 A JP23022496 A JP 23022496A JP 23022496 A JP23022496 A JP 23022496A JP 3694884 B2 JP3694884 B2 JP 3694884B2
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- Prior art keywords
- rare earth
- single crystal
- silicate single
- earth silicate
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Description
【０００１】
【発明の属する技術分野】
本発明は、シンチレ−タ等に用いられる希土類珪酸塩単結晶の育成方法に関する。
【０００２】
【従来の技術】
珪酸ガドリニウム単結晶等の希土類珪酸塩単結晶は、シンチレ−タ、蛍光体等として広く用いられている。
この珪酸ガドリニウム単結晶等は、希土類酸化物の酸化ガドリニウムと珪素酸化物の２酸化珪素を原料として、チョクラルスキ−法等の原料融液から単結晶を育成する方法によって育成される。
一般に、蛍光出力等のシンチレ−タ特性には、構成元素以外の希土類元素及び遷移金属等の不純物が悪影響を与えると考えられ、それらの不純物元素を低減した４Ｎ以上（９９．９９重量％以上）の高純度原料（Ｇｄ2Ｏ5、ＳｉＯ2等）を 使用して結晶育成が行われている。
【０００３】
【発明が解決しようとする課題】
しかし、従来の原料を使用した場合、結晶中にボイドが発生したりすることによって、安定して良好なシンチレ−タ特性が得られないという問題があった。
本発明は、希土類珪酸塩単結晶を育成する場合に、結晶中にボイドの発生しない良好なシンチレ−タ性能を有する希土類珪酸塩単結晶が安定して得られる希土類珪酸塩単結晶の育成方法を提供するものである。
【０００４】
【課題を解決するための手段】
本発明は、希土類珪酸塩単結晶を育成する場合に、特定の不純物元素を低減した希土類酸化物等の原料を使用するものであり、希土類酸化物、珪素酸化物を含む原料の融液から希土類珪酸塩単結晶を育成する方法において、Ａｌの不純物濃度が０．４ｐｐｍ以下の原料を用いることを特徴とする希土類珪酸塩単結晶の育成方法である。
【０００５】
【発明の実施の形態】
本発明者らは、希土類珪酸塩単結晶のボイド発生及びシンチレ−タ特性と、その原料である希土類酸化物等中の不純物濃度係について検討した。その結果、特定の不純物元素の含有量の差が、育成した単結晶の特性に影響することを見いだすことによって、本発明はなされたものである。
珪酸ガドリニウム単結晶を育成する場合において、Ａｌの不純物濃度が少ない希土類酸化物を原料として使用することによって、結晶中のボイド発生が無くなり、シンチレ−タ特性を向上できることがわかった。すなわち結晶中のボイド発生が無くなると、結晶にγ線等の放射線を照射することにより結晶中で生じた蛍光が結晶の一面に接して設けられている光電子増倍管に効率良く到達するため、蛍光出力、エネルギ−分解能が向上し、結果としてシンチレ−タ特性が向上する。
Ａｌの不純物濃度が０．４ｐｐｍ以下の原料を用いる場合、Ａｌの不純物濃度が０．４ｐｐｍ以下の希土類酸化物を使用することが好ましい。
【０００６】
珪酸ガドリニウム単結晶以外の、一般式
Ｒ ＳｉＯ
更に、一般には希土類珪酸塩単結晶に蛍光中心としてＣｅ等の添加物をド−プするが、その場合も効果は同様である。
以上の希土類珪酸塩単結晶は、珪酸ガドリニウム単結晶の結晶構造と同じ結晶構造を持ち、その構造は空間群Ｐ２1／ｃに属する。
【０００７】
【実施例】
比較例
セリウム付活珪酸ガドリニウム単結晶（Ｃｅ：Ｇｄ2ＳｉＯ5、Ｃｅ濃度０．５ｍｏｌ％）の場合の例を説明する。原料として酸化ガドリニウム（Ｇｄ2Ｏ3）４Ｎ（Ａ種）、２酸化珪素（ＳｉＯ2）４Ｎ及び酸化セリウム（ＣｅＯ2）４Ｎを使用して、チョクラルスキ−法によって単結晶を育成した。酸化ガドリニウムを２５７３．５ｇ、２酸化珪素を４２６．５ｇ、そして酸化セリウムを５．９ｇを秤量して混合し、１２００℃で焼成した後直径１００ｍｍのＩｒるつぼにチャ−ジし、原料融液１９５０℃、種結晶の回転数３０ｒｐｍ，引き上げ速度２ｍｍ／ｈの条件で、原料の８０重量％が結晶化した段階で引き上げを完了し、直径５０ｍｍの単結晶を育成した。
育成した単結晶は、インゴット下部に多数のボイドが発生していた。ボイドの発生の度合いには、育成（インゴット）によってばらつきが見られた。育成結晶から１０×１０×３０ｍｍ3の試料を採取して、γ線を照射したときの特性につ いて測定した結果を表１に示すが、安定して良好な結果が得られなかった。酸化ガドリニウム、２酸化珪素、酸化セリウム中のＡｌ不純物測定を行った結果、各々１３．０ｐｐｍ、０．０１６ｐｐｍ、３．５ｐｐｍ未満であった。原料中のＡｌ不純物は１１．１ｐｐｍを越えている。
【０００８】
実施例
比較例と同様に、セリウム付活珪酸ガドリニウム単結晶（Ｃｅ：Ｇｄ2ＳｉＯ 5、Ｃｅ濃度０．５ｍｏｌ％）の場合の例を説明する。原料として酸化ガドリニウム（Ｇｄ2Ｏ5）４Ｎ（Ｂ種）と、比較例で使用したものと全く同じ（精製ロット番号も同じ）２酸化珪素（ＳｉＯ2）４Ｎ及び酸化セリウム（ＣｅＯ2）４Ｎを使用して、チョクラルスキ−法によって単結晶を育成した。酸化ガドリニウム２５７３．５ｇ、２酸化珪素４２６．５ｇ、そして酸化セリウム５．９ｇを秤量し、混合して焼成した後、Ｉｒるつぼに入れて比較例と同様にして育成を行った。育成の結果、安定して着色やボイドの発生が無い結晶が得られた。育成結晶から１０×１０×３０ｍｍ3の試料を採取して、γ線を照射したときの特性につい て測定した結果を同様に表１に示すが、安定して良好な特性を示した。Ａｌ不純物の低減により、結晶特性の改善が明確に観測された。酸化ガドリニウム中のＡｌ不純物測定を行った結果、０．３５ｐｐｍであり、比較例で使用した酸化ガドリニウム原料に比べ、大幅に少ない結果であった。原料中のＡｌ不純物は０．３１ｐｐｍ未満である。
【０００９】
【表１】
【発明の効果】
本発明の希土類珪酸塩単結晶の育成方法により、結晶中のボイドの発生の無い安定して良好なシンチレ−タ性能を有する希土類珪酸塩単結晶を育成することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for growing rare earth silicate single crystals used in scintillators and the like.
[0002]
[Prior art]
Rare earth silicate single crystals such as gadolinium silicate single crystals are widely used as scintillators, phosphors and the like.
The gadolinium silicate single crystal or the like is grown by a method of growing a single crystal from a raw material melt such as the Czochralski method using gadolinium oxide of rare earth oxide and silicon dioxide of silicon oxide as raw materials.
In general, impurities such as rare earth elements other than constituent elements and transition metals are considered to adversely affect the scintillator characteristics such as fluorescence output, and 4N or more (99.99% by weight or more) in which those impurity elements are reduced. Crystal growth is performed using high-purity raw materials (Gd 2 O 5 , SiO 2, etc.).
[0003]
[Problems to be solved by the invention]
However, when conventional raw materials are used, there is a problem in that good scintillator characteristics cannot be obtained stably due to the generation of voids in the crystal.
The present invention provides a method for growing a rare earth silicate single crystal, which can stably obtain a rare earth silicate single crystal having good scintillator performance in which no void is generated in the crystal when the rare earth silicate single crystal is grown. It is to provide.
[0004]
[Means for Solving the Problems]
The present invention uses a raw material such as a rare earth oxide in which a specific impurity element is reduced when growing a rare earth silicate single crystal, and a rare earth from a melt of the raw material containing the rare earth oxide or silicon oxide. The method for growing a silicate single crystal is a method for growing a rare earth silicate single crystal, wherein a raw material having an impurity concentration of Al of 0.4 ppm or less is used.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
The present inventors examined the void generation and scintillator characteristics of the rare earth silicate single crystal and the impurity concentration in the rare earth oxide as the raw material. As a result, the present invention has been made by finding that the difference in the content of specific impurity elements affects the characteristics of the grown single crystal.
When growing a gadolinium silicate single crystal, it was found that by using a rare earth oxide having a low impurity concentration of Al as a raw material, void generation in the crystal is eliminated and scintillator characteristics can be improved. That is, when there is no void generation in the crystal, the fluorescence generated in the crystal by irradiating the crystal with radiation such as γ rays efficiently reaches the photomultiplier tube provided in contact with one surface of the crystal. Fluorescence output and energy resolution are improved, and as a result, scintillator characteristics are improved.
When using a raw material having an Al impurity concentration of 0.4 ppm or less, it is preferable to use a rare earth oxide having an Al impurity concentration of 0.4 ppm or less.
[0006]
General formula R SiO other than gadolinium silicate single crystal
Further, generally, an additive such as Ce as a fluorescent center is doped into a rare earth silicate single crystal, but the effect is the same in that case.
The above rare earth silicate single crystal has the same crystal structure as that of the gadolinium silicate single crystal, and the structure belongs to the space group P2 1 / c.
[0007]
【Example】
Comparative Example An example in the case of a cerium-activated gadolinium silicate single crystal (Ce: Gd 2 SiO 5 , Ce concentration 0.5 mol%) will be described. Single crystals were grown by the Czochralski method using gadolinium oxide (Gd 2 O 3 ) 4N (type A), silicon dioxide (SiO 2 ) 4N and cerium oxide (CeO 2 ) 4N as raw materials. 2573.5 g of gadolinium oxide, 426.5 g of silicon dioxide, and 5.9 g of cerium oxide were weighed and mixed, fired at 1200 ° C., charged into an Ir crucible having a diameter of 100 mm, and the raw material melt 1950 The pulling was completed when 80% by weight of the raw material was crystallized under the conditions of ° C, the number of rotations of the seed crystal of 30 rpm and the pulling speed of 2 mm / h, and a single crystal having a diameter of 50 mm was grown.
In the grown single crystal, many voids were generated at the bottom of the ingot. There was a variation in the degree of void generation due to growth (ingot). A 10 × 10 × 30 mm 3 sample was collected from the grown crystal and measured for characteristics when irradiated with γ rays. The results are shown in Table 1, but stable and good results were not obtained. As a result of measuring Al impurities in gadolinium oxide, silicon dioxide, and cerium oxide, they were 13.0 ppm, 0.016 ppm, and less than 3.5 ppm, respectively. The Al impurity in the raw material exceeds 11.1 ppm.
[0008]
As in the comparative example, an example in the case of a cerium activated gadolinium silicate single crystal (Ce: Gd 2 SiO 5 , Ce concentration 0.5 mol%) will be described. As raw materials, gadolinium oxide (Gd 2 O 5 ) 4N (type B), silicon dioxide (SiO 2 ) 4N and cerium oxide (CeO 2 ) 4N, which are exactly the same as those used in the comparative examples (same purification lot number), In use, single crystals were grown by the Czochralski method. Gadolinium oxide 2573.5 g, silicon dioxide 426.5 g, and cerium oxide 5.9 g were weighed, mixed and fired, and then placed in an Ir crucible and grown in the same manner as in the comparative example. As a result of the growth, a crystal free from coloring and voids was obtained. A 10 × 10 × 30 mm 3 sample was taken from the grown crystal, and the results of measuring the characteristics when irradiated with γ rays are shown in Table 1 in the same manner. A clear improvement in crystal properties was observed due to the reduction of Al impurities. As a result of measuring the Al impurity in gadolinium oxide, it was 0.35 ppm, which was significantly less than the gadolinium oxide raw material used in the comparative example. The Al impurity in the raw material is less than 0.31 ppm.
[0009]
[Table 1]
【The invention's effect】
By the method for growing a rare earth silicate single crystal of the present invention, a rare earth silicate single crystal having stable and good scintillator performance without generation of voids in the crystal can be grown.
Claims (4)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP23022496A JP3694884B2 (en) | 1995-08-31 | 1996-08-30 | Method for growing rare earth silicate single crystals |
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP22344395 | 1995-08-31 | ||
| JP7-223443 | 1995-08-31 | ||
| JP23022496A JP3694884B2 (en) | 1995-08-31 | 1996-08-30 | Method for growing rare earth silicate single crystals |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH09142994A JPH09142994A (en) | 1997-06-03 |
| JP3694884B2 true JP3694884B2 (en) | 2005-09-14 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP23022496A Expired - Lifetime JP3694884B2 (en) | 1995-08-31 | 1996-08-30 | Method for growing rare earth silicate single crystals |
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| Country | Link |
|---|---|
| JP (1) | JP3694884B2 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP4839634B2 (en) * | 2005-03-01 | 2011-12-21 | 日立化成工業株式会社 | Scintillator manufacturing method and scintillator |
| JP5087913B2 (en) * | 2006-05-30 | 2012-12-05 | 日立化成工業株式会社 | Single crystal for scintillator and method for producing the same |
-
1996
- 1996-08-30 JP JP23022496A patent/JP3694884B2/en not_active Expired - Lifetime
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| Publication number | Publication date |
|---|---|
| JPH09142994A (en) | 1997-06-03 |
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