JP4228610B2 - Rare earth silicate single crystal - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、シンチレータ等に用いられる希土類珪酸塩単結晶に関する。
【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、シンチレータ、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二酸化珪素を原料として、チョクラルスキー法等の原料融液から単結晶を育成する方法によって製造される。更に、一般には希土類珪酸塩単結晶に蛍光中心としてＣｅ等の添加物をドープしている。従来の珪酸ガドリニウム単結晶等の希土類珪酸塩単結晶をシンチレータとして用いた場合の発光減衰曲線は２成分系からなり、減衰の速い成分（Ｆａｓｔ成分）は３０〜６０ｎｓ、遅い成分（Ｓｌｏｗ成分）は４００〜６００ｎｓであり、その減衰の速い成分（Ｆａｓｔ成分）と遅い成分（Ｓｌｏｗ成分）の出力比（存在比）はそれぞれ７０〜８０％：３０〜２０％程度であった。このため蛍光減衰時間の短縮化が望まれるＰＥＴ（陽電子放出核種断層撮像装置、Ｐｏｓｉｔｒｏｎ ｅｍｉｓｓｉｏｎ ｃｏｍｐｕｔｅｄ ｔｏｍｏｇｒａｐｈｙ）用シンチレータでは、他のシンチレータに必要な諸特性を損なうことなく、発光減衰曲線の遅い成分（Ｓｌｏｗ成分）のみを高速化させ、その出力比（存在比）を低減することが望まれていた。蛍光減衰時間の短縮化には、Ｃｅ濃度を従来の濃度より高めに添加する方法があった。
【０００３】
【発明が解決しようとする課題】
しかし、蛍光中心となるＣｅ濃度を０．６ｍｏｌ％以上とした珪酸ガドリニウム単結晶では、淡黄色の着色が発生し、着色は蛍光出力、エネルギー分解能を劣化させ、シンチレータの特性が低下してしまうため好ましくなかった。着色は、発光に寄与しない４価のＣｅが原因と考えられる。蛍光減衰時間の短縮化と蛍光出力の維持の両立を図る方法として、蛍光減衰時間の短縮化が図れるＣｅ濃度を高くしながら、着色の原因と推定される４価のＣｅを減らす事ができる対策が必要とされる。
本発明は、Ｃｅ濃度が従来より高い濃度域すなわち淡黄色の着色が発生する濃度でも、着色の発生が小さく、蛍光減衰時間を短縮することができ、ＰＥＴ用シンチレータの高速化に寄与する希土類珪酸塩単結晶、及び希土類成分がガドリニウムである希土類珪酸塩単結晶を提供することを目的とした。
【０００４】
【課題を解決するための手段】
本発明は、淡黄色の着色が発生する０．６ｍｏｌ％以上、５ｍｏｌ％以下のＣｅ濃度であり、特定の不純物元素すなわちＡｌの含有率が０．４ｐｐｍを超えて５０ｐｐｍ以下であり、波長４５０ｎｍにおける透過率が７５％以上であり、希土類成分がガドリニウムである希土類珪酸塩単結晶である。
【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Ｃｅ濃度、着色状態及び透過率特性、不純物添加について検討した結果、特定の不純物元素を含有させることにより、育成した単結晶のＣｅ濃度を従来より高めても、着色の発生が抑制され透過率が高くなることを見出し本発明に達した。すなわち珪酸ガドリニウム単結晶中にＡｌを０．４ｐｐｍを超えて５０ｐｐｍ以下含有させることにより、淡黄色の着色の発生原因と考えられるＣｅ濃度が従来より高い濃度域でも、着色の発生が小さく透明性の高い希土類珪酸塩単結晶が得られ、蛍光出力が高くなりシンチレータ特性を向上できることがわかった。
【０００６】
本発明における希土類珪酸塩単結晶中のＣｅの添加量は０．６ｍｏｌ％以上、５ｍｏｌ％以下の濃度で波長４５０ｎｍにおける透過率が７５％以上である事が必要であり、好ましくは１ｍｏｌ％〜３ｍｏｌ％の範囲、最も好ましくは１．５ｍｏｌ％〜２ｍｏｌ％の範囲である。上記を達成するためには、Ｃｅを０．６〜５ｍｏｌ％ドープした希土類珪酸塩単結晶中のＡｌの含有量が０．４ｐｐｍを超えて５０ｐｐｍ以下とすることが好ましい。
【０００７】
不純物Ａｌの含有量が０．４ｐｐｍ以下の場合、単結晶の着色の発生を防ぐ効果はなく、単結晶は淡黄色を呈し、透過率が悪くなる。一方、不純物Ａｌの含有量が５０ｐｐｍを超えると単結晶内部にボイドが発生し、透過率が悪くなる。これは珪酸ガドリニウム単結晶中に微少な異相の形成が増加することによって生じるためと思われる。しかしＡｌの含有量が０．４ｐｐｍを超えて５０ｐｐｍ以下含有する場合、Ｃｅ濃度が０．６ｍｏｌ％以上の高濃度である時は異相形成が抑制されボイドは発生しないと考えられる。
【０００８】
本発明におけるＡｌ不純物含有量としては、０．４ｐｐｍを超えて５０ｐｐｍ以下であることが必要であるが、２ｐｐｍ〜３０ｐｐｍの範囲がより好ましく、５ｐｐｍ〜２０ｐｐｍの範囲が最も好ましい。
【０００９】
本発明の希土類珪酸塩単結晶は、珪酸ガドリニウム単結晶以外の、一般式Ｌｎ２−ｘＣｅｘＳｉＯ５（但し、Ｌｎ＝Ｓｃ、Ｙ、Ｌａ、Ｃｅ、Ｐｒ、Ｎｄ、Ｐｍ、Ｓｍ、Ｅｕ、Ｔｂ、Ｄｙ、Ｈｏ、Ｅｒ、Ｔｍ、Ｙｂ及びＬｕからなる群より選ばれる少なくとも１種の元素を表し、ｘ＝０〜２の値である）で示される希土類珪酸塩単結晶についても、同様の結果となる。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。
【００１０】
【実施例】
本発明を実施例に基づいて具体的に説明する。原料として酸化ガドリニウム（Ｇｄ２Ｏ３、９９．９９重量％）、二酸化珪素（ＳｉＯ２、９９．９９重量％）、酸化セリウム（ＣｅＯ２、９９．９９重量％）、及び酸化アルミニウム（Ａｌ２Ｏ３、９９．９９重量％）を使用して、チョクラルスキー法によって単結晶を育成した。単結晶から１０×１０×１０ｍｍ３の試料を採取して、波長４５０ｎｍでの透過率を測定した。また単結晶の外観を目視により観察し、それらの結果をまとめて表１に示した。ただし、それぞれの実施例について３本の単結晶を育成し、その平均値を示した。なお、本実施例は好適な一例を示すもので、本発明はこれらの実施例に限定されるものではない。
【００１１】
（実施例１）
Ｃｅ濃度１．４５ｍｏｌ％の珪酸ガドリニウム単結晶を以下のようにして作製した。酸化ガドリニウムを２５７３．５ｇ、二酸化珪素を４２６．５ｇ、酸化セリウムを１７．７ｇ、そして酸化アルミニウムを０．００７５ｇ秤量して混合し、１２００℃で焼成した後直径１００ｍｍのＩｒるつぼにチャージし、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。育成した単結晶は僅かだけ淡黄色であった。また作製した結晶中のＡｌ濃度測定を、誘導結合プラズマ（ＩＣＰ：Ｉｎｄｕｃｔｉｖｅｌｙ Ｃｏｕｐｌｅｄ Ｐｌａｓｍａ）質量分析法を用いて測定した結果、０．５ｐｐｍであった。
【００１２】
（実施例２）
Ｃｅ濃度１．４５ｍｏｌ％の珪酸ガドリニウム単結晶を以下のようにして作製した。酸化ガドリニウムを２５７３．５ｇ、二酸化珪素を４２６．５ｇ、酸化セリウムを１７．７ｇ、そして酸化アルミニウムを０．１５ｇ秤量して混合し、１２００℃で焼成した後直径１００ｍｍのＩｒるつぼにチャージし、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。育成した単結晶は無色透明であった。また作製した結晶中のＡｌ濃度を、誘導結合プラズマ（ＩＣＰ）質量分析法を用いて測定した結果、１４ｐｐｍであった。
【００１３】
（実施例３）
Ｃｅ濃度１．４５ｍｏｌ％の珪酸ガドリニウム単結晶を以下のようにして作製した。酸化ガドリニウムを２５７３．５ｇ、二酸化珪素を４２６．５ｇ、酸化セリウムを１７．７ｇ、そして酸化アルミニウムを０．５６２５ｇ秤量して混合し、１２００℃で焼成した後直径１００ｍｍのＩｒるつぼにチャージし、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。育成した単結晶は無色透明であった。また作製した結晶中のＡｌ濃度を、誘導結合プラズマ（ＩＣＰ）質量分析法を用いて測定した結果、４７ｐｐｍであった。
【００１４】
（実施例４）
Ｃｅ濃度１．９３ｍｏｌ％の珪酸ガドリニウム単結晶を以下のようにして作製した。酸化ガドリニウムを２５７３．５ｇ、二酸化珪素を４２６．５ｇ、酸化セリウムを２３．６ｇ、そして酸化アルミニウムを０．００７５ｇ秤量して混合し、１２００℃で焼成した後直径１００ｍｍのＩｒるつぼにチャージし、原料融液１９５０℃、種結晶の回転数３ｒｐｍ、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。育成した単結晶は僅かに淡黄色であった。また作製した結晶中のＡｌ濃度を、誘導結合プラズマ（ＩＣＰ）質量分析法を用いて測定した結果、０．６ｐｐｍであった。
【００１５】
（実施例５）
Ｃｅ濃度１．９３ｍｏｌ％の珪酸ガドリニウム単結晶を以下のようにして作製した。酸化ガドリニウムを２５７３．５ｇ、二酸化珪素を４２６．５ｇ、酸化セリウムを２３．６ｇ、そして酸化アルミニウムを０．１５ｇ秤量して混合し、１２００℃で焼成した後直径１００ｍｍのＩｒるつぼにチャージし、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。育成した単結晶は無色透明であった。また作製した結晶中のＡｌ濃度を、誘導結合プラズマ（ＩＣＰ）質量分析法を用いて測定した結果、１２ｐｐｍであった。
【００１６】
（実施例６）
Ｃｅ濃度１．９３ｍｏｌ％の珪酸ガドリニウム単結晶を以下のようにして作製した。酸化ガドリニウムを２５７３．５ｇ、二酸化珪素を４２６．５ｇ、酸化セリウムを２３．６ｇ、そして酸化アルミニウムを０．５６２５ｇ秤量して混合し、１２００℃で焼成した後直径１００ｍｍのＩｒるつぼにチャージし、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。育成した単結晶は無色透明であった。また作製した結晶中のＡｌ濃度を、誘導結合プラズマ（ＩＣＰ）質量分析法を用いて測定した結果、４５ｐｐｍであった。
【００１７】
比較例として、実施例と同様にセリウム賦活珪酸ガドリニウム単結晶（Ｃｅ：Ｇｄ２ＳｉＯ５）の場合の例を説明する。原料として実施例で使用したものと全く同じ（精製ロット番号も同じ）酸化ガドリニウム（Ｇｄ２Ｏ３、９９．９９重量％）と、二酸化珪素（ＳｉＯ２、９９．９９重量％）及び酸化セリウム（ＣｅＯ２、９９．９９重量％）を使用して、チョクラルスキー法によって単結晶を育成した。単結晶から１０×１０×１０ｍｍ３の試料を採取して、波長４５０ｎｍでの透過率を測定し、また単結晶の外観を目視により観察し、それらの結果をまとめて表１に示した。ただし、それぞれの条件について３本の単結晶を育成し、その平均値を示した。
【００１８】
（比較例１）
Ｃｅ濃度１．４５ｍｏｌ％の珪酸ガドリニウム単結晶を以下のようにして作製した。酸化ガドリニウム２５７３．５ｇ、二酸化珪素４２６．５ｇ、そして酸化セリウム１７．７ｇを秤量し、混同して焼成した後、Ｉｒるつぼに入れて実施例１と同様にして育成を行った。育成した単結晶は強い淡黄色であった。また作製した結晶中のＡｌ濃度を、誘導結合プラズマ（ＩＣＰ）質量分析法を用いて測定した結果、０ｐｐｍであった。
【００１９】
（比較例２）
Ｃｅ濃度１．４５ｍｏｌ％の珪酸ガドリニウム単結晶を以下のようにして作製した。酸化ガドリニウム２５７３．５ｇ、二酸化珪素４２６．５ｇ、酸化セリウム１７．７ｇ、そして酸化アルミニウムを０．００２５ｇ秤量して混合し、焼成した後、Ｉｒるつぼに入れて実施例１と同様にして育成を行った。育成した単結晶は強い淡黄色であった。また作製した結晶中のＡｌ濃度を、誘導結合プラズマ（ＩＣＰ）質量分析法を用いて測定した結果、０．２ｐｐｍであった。
【００２０】
（比較例３）
Ｃｅ濃度１．４５ｍｏｌ％の珪酸ガドリニウム単結晶を以下のようにして作製した。酸化ガドリニウム２５７３．５ｇ、二酸化珪素４２６．５ｇ、酸化セリウム１７．７ｇ、そして酸化アルミニウムを０．６５ｇ秤量して混合し、焼成した後、Ｉｒるつぼに入れて実施例１と同様にして育成を行った。育成した単結晶にはボイドが多く存在した。また作製した結晶中のＡｌ濃度を、誘導結合プラズマ（ＩＣＰ）質量分析法を用いて測定した結果、５２ｐｐｍであった。
【００２１】
（比較例４）
Ｃｅ濃度１．４５ｍｏｌ％の珪酸ガドリニウム単結晶を以下のようにして作製した。酸化ガドリニウム２５７３．５ｇ、二酸化珪素４２６．５ｇ、酸化セリウム１７．７ｇ、そして酸化アルミニウムを０．８７５ｇ秤量して混合し、焼成した後、Ｉｒるつぼに入れて実施例１と同様にして育成を行った。育成した単結晶にはボイドが多く存在した。また作製した結晶中のＡｌ濃度を、誘導結合プラズマ（ＩＣＰ）質量分析法を用いて測定した結果、７０ｐｐｍであった。
【００２２】
（比較例５）
Ｃｅ濃度１．９３ｍｏｌ％の珪酸ガドリニウム単結晶を以下のようにして作製した。酸化ガドリニウム２５７３．５ｇ、二酸化珪素４２６．５ｇ、そして酸化セリウム２３．６ｇを秤量し、混同して焼成した後、Ｉｒるつぼに入れて実施例４と同様にして育成を行った。育成した単結晶は強い淡黄色であった。また作製した結晶中のＡｌ濃度を誘導結合プラズマ（ＩＣＰ）質量分析法を用いて測定した結果、０ｐｐｍであった。
【００２３】
（比較例６）
Ｃｅ濃度１．９３ｍｏｌ％の珪酸ガドリニウム単結晶を以下のようにして作製した。酸化ガドリニウム２５７３．５ｇ、二酸化珪素４２６．５ｇ、酸化セリウム２３．６ｇ、そして酸化アルミニウムを０．００２５ｇ秤量して混合し、焼成した後、Ｉｒるつぼに入れて実施例４と同様にして育成を行った。育成した単結晶は強い淡黄色であった。また作製した結晶中のＡｌ濃度を、誘導結合プラズマ（ＩＣＰ）質量分析法を用いて測定した結果、０．３ｐｐｍであった。
【００２４】
（比較例７）
Ｃｅ濃度１．９３ｍｏｌ％の珪酸ガドリニウム単結晶を以下のようにして作製した。酸化ガドリニウム２５７３．５ｇ、二酸化珪素４２６．５ｇ、酸化セリウム２３．６ｇ、そして酸化アルミニウムを０．６５ｇ秤量して混合し、焼成した後、Ｉｒるつぼに入れて実施例４と同様にして育成を行った。育成した単結晶にはボイドが多く存在した。また作製した結晶中のＡｌ濃度を、誘導結合プラズマ（ＩＣＰ）質量分析法を用いて測定した結果、５３ｐｐｍであった。
【００２５】
（比較例８）
Ｃｅ濃度１．９３ｍｏｌ％の珪酸ガドリニウム単結晶を以下のようにして作製した。酸化ガドリニウム２５７３．５ｇ、二酸化珪素４２６．５ｇ、酸化セリウム２３．６ｇ、そして酸化アルミニウムを０．８７５ｇ秤量して混合し、焼成した後、Ｉｒるつぼに入れて実施例４と同様にして育成を行った。育成した単結晶にはボイドが多く存在した。また作製した結晶中のＡｌ濃度を、誘導結合プラズマ（ＩＣＰ）質量分析法を用いて測定した結果、６９ｐｐｍであった。
【００２６】
【表１】
比較例１、５に示したように、Ｃｅ濃度が高くなると単結晶が強く淡黄色に着色し、透過率が低下する。このＣｅ高濃度の単結晶中にＡｌを０．４ｐｐｍを超えて５０ｐｐｍの範囲に存在させた実施例１〜６においては、４５０ｎｍでの透過率が高く、しかも着色が非常に少ない。これに対し、単結晶中のＡｌ濃度が０．４ｐｐｍ以下、あるいは５０ｐｐｍを超えた比較例では、Ａｌ濃度が低いと透過率が低く、強く着色するようになる。そしてＡｌ濃度が高いとボイドが発生し透過率は著しく低下する。このように、本発明は、蛍光減衰時間を短縮化するためにＣｅ濃度を高めた場合の欠点となっていた着色の低減や透過率向上の課題を、不純物としてＡｌを特定範囲での濃度とする事により単結晶の着色を抑制し、透過率を高めることができる。これによりＰＥＴ装置の高速診断化を図ることができる。
【００２８】
【発明の効果】
本発明による希土類珪酸塩単結晶は淡黄色の着色が発生するＣｅ濃度が従来より高い濃度域でも、淡黄色の発生が小さく透明性を高くすることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a rare earth silicate single crystal used for 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 manufactured by a method of growing a single crystal from a raw material melt such as the Czochralski method using gadolinium oxide as a rare earth oxide and silicon dioxide as a silicon oxide as raw materials. Further, generally, a rare earth silicate single crystal is doped with an additive such as Ce as a fluorescent center. When a rare earth silicate single crystal such as a conventional gadolinium silicate single crystal is used as a scintillator, the emission decay curve is composed of two components, the fast decay component (Fast component) is 30-60 ns, and the slow component (Slow component) is The output ratio (existence ratio) of the fast-damping component (Fast component) and the slow component (Slow component) was about 70 to 80%: 30 to 20%, respectively. For this reason, in a scintillator for PET (Positron emission computed tomography) for which shortening of the fluorescence decay time is desired, a slow component (Slow) of the emission decay curve is obtained without impairing various characteristics necessary for other scintillators. It has been desired to speed up only the component) and reduce its output ratio (existence ratio). In order to shorten the fluorescence decay time, there has been a method of adding Ce concentration higher than the conventional concentration.
[0003]
[Problems to be solved by the invention]
However, in a gadolinium silicate single crystal having a Ce concentration of 0.6 mol% or more as a fluorescence center, light yellow coloration occurs, and the coloration deteriorates the fluorescence output and energy resolution, thereby reducing the scintillator characteristics. It was not preferable. The coloring is considered to be caused by tetravalent Ce that does not contribute to light emission. As a method for achieving both reduction of the fluorescence decay time and maintenance of the fluorescence output, a measure capable of reducing the tetravalent Ce, which is estimated to be the cause of coloring, while increasing the Ce concentration capable of shortening the fluorescence decay time. Is needed.
The present invention is a rare earth silicic acid that contributes to speeding up of a scintillator for PET, which can reduce the occurrence of coloration and shorten the fluorescence decay time even in a concentration range where Ce concentration is higher than that in the prior art, that is, a concentration where pale yellow coloring occurs. An object of the present invention is to provide a salt single crystal and a rare earth silicate single crystal whose rare earth component is gadolinium.
[0004]
[Means for Solving the Problems]
The present invention has a Ce concentration of 0.6 mol% or more and 5 mol% or less in which pale yellow coloring occurs, the specific impurity element, that is, the content of Al is more than 0.4 ppm and 50 ppm or less, at a wavelength of 450 nm. der transmittance of 75% or more is, rare earth component is gadolinium der Ru rare earth silicate single crystal.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
As a result of studying the Ce concentration, coloring state and transmittance characteristics, and impurity addition of the rare earth silicate single crystal, the present inventors have increased the Ce concentration of the grown single crystal as compared with the conventional case by including a specific impurity element. However, the present inventors have found that the occurrence of coloring is suppressed and the transmittance is increased, and the present invention has been achieved. That is, by including Al in the gadolinium silicate single crystal in an amount of more than 0.4 ppm to 50 ppm or less, even when the Ce concentration, which is considered to be the cause of pale yellow coloring, is higher than the conventional concentration, the occurrence of coloring is small and transparent. It was found that a high rare earth silicate single crystal was obtained, the fluorescence output was increased, and the scintillator characteristics could be improved.
[0006]
The addition amount of Ce in the rare earth silicate single crystal in the present invention is required to have a transmittance of 75% or more at a wavelength of 450 nm at a concentration of 0.6 mol% or more and 5 mol% or less, preferably 1 mol% to 3 mol. % Range, most preferably in the range of 1.5 mol% to 2 mol%. In order to achieve the above, it is preferable that the Al content in the rare earth silicate single crystal doped with 0.6 to 5 mol% of Ce exceeds 0.4 ppm and is 50 ppm or less.
[0007]
When the content of impurity Al is 0.4 ppm or less, there is no effect of preventing the occurrence of coloration of the single crystal, and the single crystal exhibits a light yellow color, resulting in poor transmittance. On the other hand, when the content of the impurity Al exceeds 50 ppm, voids are generated inside the single crystal and the transmittance is deteriorated. This seems to be caused by an increase in the formation of minute heterogeneous phases in the gadolinium silicate single crystal. However, when the Al content exceeds 0.4 ppm and is 50 ppm or less, it is considered that the heterogeneous phase formation is suppressed and voids are not generated when the Ce concentration is a high concentration of 0.6 mol% or more.
[0008]
The Al impurity content in the present invention needs to be more than 0.4 ppm and 50 ppm or less, more preferably in the range of 2 ppm to 30 ppm, and most preferably in the range of 5 ppm to 20 ppm.
[0009]
Rare earth silicate single crystal of the present invention, other than gadolinium silicate single crystal, the formula Ln 2-x Ce x SiO 5 ( where, Ln = Sc, Y, La , Ce, Pr, Nd, Pm, Sm, Eu, The same applies to the rare earth silicate single crystal represented by at least one element selected from the group consisting of Tb, Dy, Ho, Er, Tm, Yb, and Lu, where x = 0 to 2. Result. 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 P21 / c.
[0010]
【Example】
The present invention will be specifically described based on examples. As raw materials, gadolinium oxide (Gd 2 O 3 , 99.99% by weight), silicon dioxide (SiO 2 , 99.99% by weight), cerium oxide (CeO 2 , 99.99% by weight), and aluminum oxide (Al 2 O) 3 , 99.99 wt%) were used to grow single crystals by the Czochralski method. A sample of 10 × 10 × 10 mm 3 was taken from the single crystal, and the transmittance at a wavelength of 450 nm was measured. The appearance of the single crystal was visually observed, and the results are summarized in Table 1. However, three single crystals were grown for each example, and the average value was shown. In addition, a present Example shows a suitable example, This invention is not limited to these Examples.
[0011]
Example 1
A gadolinium silicate single crystal having a Ce concentration of 1.45 mol% was prepared as follows. 2573.5 g of gadolinium oxide, 426.5 g of silicon dioxide, 17.7 g of cerium oxide, and 0.0075 g of aluminum oxide were weighed and mixed, fired at 1200 ° C., and charged into an Ir crucible having a diameter of 100 mm. Pulling was completed when 80 wt% of the raw material was crystallized under the conditions of the melt at 1950 ° C., the seed crystal rotation speed of 30 rpm, and the pulling speed of 2 mm / h, and a single crystal having a diameter of 50 mm was grown. The grown single crystal was slightly pale yellow. The Al concentration in the produced crystal was measured using an inductively coupled plasma (ICP) mass spectrometry and found to be 0.5 ppm.
[0012]
(Example 2)
A gadolinium silicate single crystal having a Ce concentration of 1.45 mol% was prepared as follows. 2573.5 g of gadolinium oxide, 426.5 g of silicon dioxide, 17.7 g of cerium oxide, and 0.15 g of aluminum oxide were weighed and mixed, fired at 1200 ° C., and charged into an Ir crucible having a diameter of 100 mm. Pulling was completed when 80 wt% of the raw material was crystallized under the conditions of the melt at 1950 ° C., the seed crystal rotation speed of 30 rpm, and the pulling speed of 2 mm / h, and a single crystal having a diameter of 50 mm was grown. The grown single crystal was colorless and transparent. The Al concentration in the produced crystal was 14 ppm as a result of measurement using inductively coupled plasma (ICP) mass spectrometry.
[0013]
(Example 3)
A gadolinium silicate single crystal having a Ce concentration of 1.45 mol% was prepared as follows. 2573.5 g of gadolinium oxide, 426.5 g of silicon dioxide, 17.7 g of cerium oxide, and 0.5625 g of aluminum oxide were weighed and mixed, fired at 1200 ° C., and charged into an Ir crucible having a diameter of 100 mm. Pulling was completed when 80 wt% of the raw material was crystallized under the conditions of the melt at 1950 ° C., the seed crystal rotation speed of 30 rpm, and the pulling speed of 2 mm / h, and a single crystal having a diameter of 50 mm was grown. The grown single crystal was colorless and transparent. The Al concentration in the produced crystal was 47 ppm as a result of measurement using inductively coupled plasma (ICP) mass spectrometry.
[0014]
(Example 4)
A gadolinium silicate single crystal having a Ce concentration of 1.93 mol% was prepared as follows. 2573.5 g of gadolinium oxide, 426.5 g of silicon dioxide, 23.6 g of cerium oxide, and 0.0075 g of aluminum oxide were weighed and mixed, fired at 1200 ° C., and charged into an Ir crucible having a diameter of 100 mm. Pulling was completed when 80% by weight of the raw material was crystallized under the conditions of the melt at 1950 ° C., the seed crystal rotation speed of 3 rpm, and the pulling speed of 2 mm / h, and a single crystal having a diameter of 50 mm was grown. The grown single crystal was slightly pale yellow. Moreover, as a result of measuring the Al concentration in the produced crystal using inductively coupled plasma (ICP) mass spectrometry, it was 0.6 ppm.
[0015]
(Example 5)
A gadolinium silicate single crystal having a Ce concentration of 1.93 mol% was prepared as follows. 2573.5 g of gadolinium oxide, 426.5 g of silicon dioxide, 23.6 g of cerium oxide, and 0.15 g of aluminum oxide were weighed and mixed, fired at 1200 ° C., and charged into an Ir crucible having a diameter of 100 mm. Pulling was completed when 80 wt% of the raw material was crystallized under the conditions of the melt at 1950 ° C., the seed crystal rotation speed of 30 rpm, and the pulling speed of 2 mm / h, and a single crystal having a diameter of 50 mm was grown. The grown single crystal was colorless and transparent. Further, the Al concentration in the produced crystal was measured using inductively coupled plasma (ICP) mass spectrometry, and as a result, it was 12 ppm.
[0016]
(Example 6)
A gadolinium silicate single crystal having a Ce concentration of 1.93 mol% was prepared as follows. 2573.5 g of gadolinium oxide, 426.5 g of silicon dioxide, 23.6 g of cerium oxide, and 0.5625 g of aluminum oxide were weighed and mixed, fired at 1200 ° C., and charged into an Ir crucible having a diameter of 100 mm. Pulling was completed when 80 wt% of the raw material was crystallized under the conditions of the melt at 1950 ° C., the seed crystal rotation speed of 30 rpm, and the pulling speed of 2 mm / h, and a single crystal having a diameter of 50 mm was grown. The grown single crystal was colorless and transparent. Further, the Al concentration in the produced crystal was measured by using inductively coupled plasma (ICP) mass spectrometry, and found to be 45 ppm.
[0017]
As a comparative example, an example in the case of a cerium-activated gadolinium silicate single crystal (Ce: Gd 2 SiO 5 ) will be described as in the example. Gadolinium oxide (Gd 2 O 3 , 99.99% by weight), silicon dioxide (SiO 2 , 99.99% by weight), and cerium oxide (same as those used in the examples as raw materials) A single crystal was grown by the Czochralski method using CeO 2 , 99.99 wt%). A sample of 10 × 10 × 10 mm 3 was taken from the single crystal, the transmittance at a wavelength of 450 nm was measured, and the appearance of the single crystal was visually observed. The results are summarized in Table 1. However, three single crystals were grown for each condition and the average value was shown.
[0018]
(Comparative Example 1)
A gadolinium silicate single crystal having a Ce concentration of 1.45 mol% was prepared as follows. 2573.5 g of gadolinium oxide, 426.5 g of silicon dioxide, and 17.7 g of cerium oxide were weighed, mixed and fired, and then placed in an Ir crucible and grown in the same manner as in Example 1. The grown single crystal was a strong pale yellow. Moreover, as a result of measuring Al concentration in the produced crystal using inductively coupled plasma (ICP) mass spectrometry, it was 0 ppm.
[0019]
(Comparative Example 2)
A gadolinium silicate single crystal having a Ce concentration of 1.45 mol% was prepared as follows. 2573.5 g of gadolinium oxide, 426.5 g of silicon dioxide, 17.7 g of cerium oxide, and 0.0025 g of aluminum oxide were weighed and mixed, baked, and then placed in an Ir crucible and grown in the same manner as in Example 1. It was. The grown single crystal was a strong pale yellow. The Al concentration in the produced crystal was 0.2 ppm as a result of measurement using inductively coupled plasma (ICP) mass spectrometry.
[0020]
(Comparative Example 3)
A gadolinium silicate single crystal having a Ce concentration of 1.45 mol% was prepared as follows. 2573.5 g of gadolinium oxide, 426.5 g of silicon dioxide, 17.7 g of cerium oxide, and 0.65 g of aluminum oxide were weighed and mixed, baked, and then placed in an Ir crucible and grown in the same manner as in Example 1. It was. There were many voids in the grown single crystal. The Al concentration in the produced crystal was 52 ppm as a result of measurement using inductively coupled plasma (ICP) mass spectrometry.
[0021]
(Comparative Example 4)
A gadolinium silicate single crystal having a Ce concentration of 1.45 mol% was prepared as follows. Gadolinium oxide 2573.5 g, silicon dioxide 426.5 g, cerium oxide 17.7 g, and aluminum oxide 0.875 g were weighed and mixed, fired, and then placed in an Ir crucible and grown in the same manner as in Example 1. It was. There were many voids in the grown single crystal. The Al concentration in the produced crystal was 70 ppm as a result of measurement using inductively coupled plasma (ICP) mass spectrometry.
[0022]
(Comparative Example 5)
A gadolinium silicate single crystal having a Ce concentration of 1.93 mol% was prepared as follows. 2573.5 g of gadolinium oxide, 426.5 g of silicon dioxide, and 23.6 g of cerium oxide were weighed, mixed and fired, and then placed in an Ir crucible and grown in the same manner as in Example 4. The grown single crystal was a strong pale yellow. Further, the Al concentration in the produced crystal was measured by using inductively coupled plasma (ICP) mass spectrometry, and found to be 0 ppm.
[0023]
(Comparative Example 6)
A gadolinium silicate single crystal having a Ce concentration of 1.93 mol% was prepared as follows. 2573.5 g of gadolinium oxide, 426.5 g of silicon dioxide, 23.6 g of cerium oxide, and 0.0025 g of aluminum oxide were weighed and mixed, baked, and then placed in an Ir crucible and grown in the same manner as in Example 4. It was. The grown single crystal was a strong pale yellow. Further, the Al concentration in the produced crystal was measured by using inductively coupled plasma (ICP) mass spectrometry, and found to be 0.3 ppm.
[0024]
(Comparative Example 7)
A gadolinium silicate single crystal having a Ce concentration of 1.93 mol% was prepared as follows. 2573.5 g of gadolinium oxide, 426.5 g of silicon dioxide, 23.6 g of cerium oxide, and 0.65 g of aluminum oxide were weighed and mixed, baked, and then placed in an Ir crucible and grown in the same manner as in Example 4. It was. There were many voids in the grown single crystal. The Al concentration in the produced crystal was 53 ppm as a result of measurement using inductively coupled plasma (ICP) mass spectrometry.
[0025]
(Comparative Example 8)
A gadolinium silicate single crystal having a Ce concentration of 1.93 mol% was prepared as follows. 2573.5 g of gadolinium oxide, 426.5 g of silicon dioxide, 23.6 g of cerium oxide, and 0.875 g of aluminum oxide were weighed and mixed, baked, and then placed in an Ir crucible and grown in the same manner as in Example 4. It was. There were many voids in the grown single crystal. Further, the Al concentration in the produced crystal was measured by inductively coupled plasma (ICP) mass spectrometry, and found to be 69 ppm.
[0026]
[Table 1]
As shown in Comparative Examples 1 and 5, when the Ce concentration is increased, the single crystal is strongly colored in pale yellow, and the transmittance is decreased. In Examples 1 to 6 in which Al is present in the range of 50 ppm to more than 0.4 ppm in this Ce high concentration single crystal, the transmittance at 450 nm is high and the coloring is very small. On the other hand, in the comparative example in which the Al concentration in the single crystal is 0.4 ppm or less or exceeds 50 ppm, if the Al concentration is low, the transmittance is low and the color is strongly colored. If the Al concentration is high, voids are generated and the transmittance is significantly reduced. As described above, the present invention addresses the problem of reduction in coloration and improvement in transmittance, which has been a drawback when the Ce concentration is increased in order to shorten the fluorescence decay time. By doing so, coloring of the single crystal can be suppressed and the transmittance can be increased. Thereby, high-speed diagnosis of the PET apparatus can be achieved.
[0028]
【The invention's effect】
In the rare earth silicate single crystal according to the present invention, the occurrence of light yellow is small and the transparency can be increased even in the concentration range where Ce concentration at which light yellow coloration is generated is higher than the conventional one.
Claims (1)
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| JP2002221537A JP4228610B2 (en) | 2002-07-30 | 2002-07-30 | Rare earth silicate single crystal |
| US10/621,350 US6926847B2 (en) | 2002-07-30 | 2003-07-18 | Single crystals of silicates of rare earth elements |
| DE10334513A DE10334513B4 (en) | 2002-07-30 | 2003-07-29 | A process for producing a single crystal of a cerium-doped gadolinium silicate |
| FR0309375A FR2843131B1 (en) | 2002-07-30 | 2003-07-30 | RARE EARTH ELEMENTS SILICATE MONOCRYSTAL AND SCINTILLATOR CONTAINING SAME |
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