JP3915482B2 - Method for producing inorganic phosphor - Google Patents
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【０００１】
【発明の属する技術分野】
本発明は、無機蛍光体の製造方法に関し、詳しくは生産性及び発光特性に優れた無機蛍光体の製造方法に関する。
【０００２】
【従来の技術】
従来から、様々な分野で、種々の蛍光体が用いられている。
【０００３】
例えば、照明装置の一例である三波長発光型の蛍光ランプにおいては、蛍光体として青色、緑色、赤色の三波長に発光する蛍光体が用いられ、青色蛍光体としては、ＢａＭｇＡｌ10Ｏ17：Ｅｕ2+や（Ｓｒ，Ｂａ，Ｃａ，Ｍｇ）10（ＰＯ4）6Ｃｌ2：Ｅｕ2+などのＥｕ2+を発光中心とするユーロピウム付活蛍光体が、緑色蛍光体としてはＣｅＭｇＡｌ11Ｏ19：Ｔｂ3+やＬａＰＯ4：Ｃｅ3+，Ｔｂ3+や（Ｃｅ，Ｇｄ）ＭｇＢ5Ｏ10：Ｔｂ3+などのＴｂ3+イオンを発光中心とするテルビウム付活蛍光体やＣｅ（Ｍｇ，Ｚｎ）Ａｌ11Ｏ19：Ｍｎ2+などのＭｎ2+を発光中心とするマンガン付活蛍光体が、また、赤色蛍光体としては、Ｙ2Ｏ3：Ｅｕ3+や３．５ＭｇＯ・ＭｇＦ2・ＧｅＯ2：Ｍｎ4+などのＥｕ3+イオンやＭｎ4+イオンを発光中心とするユーロピウム付活蛍光体やマンガン付活蛍光体が用いられている。さらに、蛍光ランプの光の演色性を高める目的で、（Ｂａ，Ｓｒ）ＭｇＡｌ10Ｏ17：Ｅｕ2+，Ｍｎ2+やＳｒ4Ａｌ14Ｏ25：Ｅｕ2+などのＥｕ2+を発光中心とするユーロピウム付活蛍光体も用いられている。
【０００４】
また、表示装置の一例であるＰＤＰにおいては、青色蛍光体として、ＢａＭｇＡｌ10Ｏ17：Ｅｕ2+などのＥｕ2+を発光中心とするユーロピウム付活蛍光体が、緑色蛍光体として、Ｚｎ2ＳｉＯ4：Ｍｎ2+やＢａＡｌ12Ｏ19：Ｍｎ2+やＹＢＯ4：Ｔｂ3+などのＭｎ2+イオンを発光中心とするマンガン付活蛍光体やＴｂ3+イオンを発光中心とするテルビウム付活蛍光体が、また、赤色蛍光体として、Ｙ2Ｏ3：Ｅｕ3+、（Ｙ，Ｇｄ）ＢＯ3：Ｅｕ3+、ＹＢＯ3：Ｅｕ3+などのＥｕ3+イオンを発光中心とするユーロピウム付活蛍光体が用いられている。さらに、カラー陰極線管（ＣＲＴ）においては、青色蛍光体として、ＺｎＳ：Ａｇ+，Ａｌ3+やＺｎＳ：Ａｇ+，Ｃｌ-などの銀イオンをアクセプタとする非局在発光中心型の硫化亜鉛蛍光体が、緑色蛍光体として、ＺｎＳ：Ｃｕ+，Ａｌ3+などの銅イオンをアクセプタとする非局在発光中心型の硫化亜鉛蛍光体や、Ｙ3Ａｌ5Ｏ12：Ｔｂ3+やＩｎＢＯ3：Ｔｂ3+やＧｄ4Ａｌ2Ｏ9：Ｔｂ3+などのＴｂ3+イオンを発光中心とするテルビウム付活蛍光体や、Ｚｎ2ＳｉＯ4：Ｍｎ2+などのＭｎ2+イオンを発光中心とするマンガン付活蛍光体が、また、赤色蛍光体として、Ｙ2Ｏ3：Ｅｕ3+やＹ2Ｏ2Ｓ：Ｅｕ3+などのＥｕ3+イオンを発光中心とするユーロピウム付活蛍光体が用いられている。
【０００５】
エレクトロルミネッセンス装置、能動発光液晶装置においても各種の蛍光体が用いられている。
【０００６】
また、蛍光体としては長残光を有する長残光蛍光体がある。これら長残光蛍光体は、タイル、灰皿、粘着テープ、シール、ロープや下敷き、筆箱などの文房具など各種の器具に用いられる。
【０００７】
このような長残光蛍光体としては、例えば、Ｓｒ4Ａｌ14Ｏ25：Ｅｕ2+，Ｄｙ3+やＳｒＡｌ2Ｏ4：Ｅｕ2+，Ｄｙ3+やＣａＡｌ2Ｏ：Ｅｕ2+，Ｄｙ3+、Ｓｒ4Ａｌ14Ｏ25：Ｅｕ2+，Ｎｄ3+やＳｒＡｌ2Ｏ4：Ｅｕ2+，Ｎｄ3+やＣａＡｌ2Ｏ4：Ｅｕ2+，Ｎｄ3+などのＥｕ2+およびＤｙ3+やＮｄ3+イオンを共付活したアルミニウム含有酸化物蛍光体が用いられている。
【０００８】
通常これらの蛍光体は、蛍光体原料混合物の高温での焼成により合成される。この焼成工程は、蛍光体の母体が結晶化すると同時に、母体結晶中に付活剤元素が拡散する工程であり、得られる蛍光体の発光特性に影響を及ぼす重要な工程である。また焼成は空気中で行える場合と還元を必要とする場合とがあり、Ｔｌ+、Ｐｂ2+、Ｓｂ3+、Ｍｎ2+、Ｍｎ4+、Ｅｕ3+などを付活剤とする蛍光体は空気中で焼成すれば良いが、Ｓｎ2+、Ｅｕ2+、Ｃｅ3+、Ｔｂ3+などの場合には還元雰囲気中で焼成を行う還元焼成が必要である。その際、還元が不十分であると得られる蛍光体の発光特性が著しく低下するなど、還元工程も重要な工程である。
【０００９】
焼成工程において用いられる焼成装置としては、一般的に電気炉が使用される。前記電気炉の加熱方式としては、石英やアルミナ等のセラミックス系の材料からなる焼成管の外部に熱源が配されている外熱タイプと、焼成管がなく熱源が露出した直熱タイプがある。一般的に、還元焼成においては、還元ガスによる熱源の劣化防止のため外熱タイプが使用される。あるいは直熱タイプを還元焼成で使用する場合には、最高温度などを制限した範囲で使用される。
【００１０】
前記外熱タイプでは、蛍光体原料混合物を収容し得る焼成容器が焼成管内部に出し入れ可能に備えられ、焼成管内部の焼成雰囲気を調整するためのガス導入排気管が焼成管に接続されている。焼成時には、前記焼成容器に蛍光体原料混合物を収容し、これを焼成管内部に投入し、前記ガス導入排気管により焼成管内部の焼成雰囲気を調整しつつ、熱源からの熱により焼成管内部を高温にして、前記蛍光体原料混合物の焼成を行う。
【００１１】
さらに、前記外熱タイプにおいては、焼成管が回転可能に設計されている場合もある。回転可能な焼成管に直接蛍光体原料混合物を収容し、焼成管を回転することで前記蛍光体原料混合物を流動させながら焼成を行うことで、焼成における温度むら、還元むらの低減を意図したものである。
【００１２】
還元焼成を行う場合には外熱タイプを用いることが一般的であるが、外熱タイプに使用されるセラミックス系の材料からなる焼成管において、特に１１００℃以上の高温焼成で使用可能な焼成管においては、熱衝撃に弱く、熱衝撃によって割れてしまうといった耐久性に関する問題があった。かかる弊害を防止するため焼成炉のヒートサイクルを緩やかにすることで割れを防いでいたが、ヒートサイクルを緩やかにすると生産効率が低下するという問題があった。
【００１３】
また、蛍光体原料混合物を還元焼成し、得られた焼成物を冷却する際に、急加熱及び急冷却をすると、発光特性の優れた蛍光体が得られる場合が知られているが、特に１１００℃以上の高温焼成を行う場合、用いる焼成管の材質によっては、急加熱及び急冷却によって割れが発生する等の問題があるし、かといって焼成管のない直熱タイプを用いた場合には熱源の劣化という問題があった。
【００１４】
また、焼成における温度むら、還元むらの低減を目的とした回転可能なセラミック系の材料からなる焼成管においては、１１００℃以上の高温では物理的強度の低下により、回転などの操作が困難であるという問題があった。
【００１５】
さらに、焼成時において、焼成管や焼成容器に焼成物が付着することで収率の低下や、温度むら、還元むら等の問題があった。
【００１６】
上記のように、蛍光体の製造方法等に工夫を施した技術が多く開示されているが、十分に満足できるものは得られていない。今日、十分な発光特性を有するとともに、生産効率および製造安定性に優れた蛍光体の製造方法が望まれているのが現状である。
【００１７】
【発明が解決しようとする課題】
本発明は、上記のような問題点を解消し、生産効率を損なうことなく、また、熱源の劣化を引き起こすことなく、さらに、温度むら、還元むらなどの焼成むらが発生することなく、生産性や発光特性に優れた無機蛍光体の製造方法を提供することを目的とする。
【００１８】
【課題を解決するための手段】
本発明者等は、無機蛍光体の製造方法に関し鋭意検討を重ねた結果、還元焼成において、蛍光体の結晶化と還元の機能を分離し各々を別々に行うことや、焼成時における焼成容器への蛍光体の付着を防止することなどにより、無機蛍光体の製造について生産性や発光特性の向上が可能であることを見出し、本発明を完成するに至った。前記課題を解決するための手段は、以下の通りである。即ち、
１．無機蛍光体の原料混合物を還元焼成して焼成物を得る無機蛍光体の製造方法において、該還元焼成が、１５〜１００℃／分の昇温速度で加熱し、１５〜１００℃／分の降温速度で冷却する結晶化工程と、１５〜１００℃／分の昇温速度で加熱し、１５〜１００℃／分の降温速度で冷却する還元工程を別々に有し、結晶化工程の後に還元工程を経て該焼成物を得ることを特徴とする無機蛍光体の製造方法。
【００１９】
２．還元工程の焼成温度が結晶化工程の焼成温度より低いことを特徴とする前記１に記載の無機蛍光体の製造方法。
【００２０】
３．還元工程の焼成温度が６００℃から１１００℃であることを特徴とする前記１または２に記載の無機蛍光体の製造方法。
【００２１】
４．還元工程の焼成温度が８００℃から１１００℃であることを特徴とする前記１または２に記載の無機蛍光体の製造方法。
【００２２】
５．結晶化工程と還元工程が各々異なる焼成装置を用いて行うことを特徴とする前記１〜４のいずれか１項に記載の無機蛍光体の製造方法。
【００２３】
６．還元工程を熱膨張係数が１×１０-6／℃以下の材質からなる焼成管を用いて行うことを特徴とする前記１〜５のいずれか１項に記載の無機蛍光体の製造方法。
【００２４】
７．還元工程を回転可能な焼成管を用いて行うことを特徴とする前記１〜６のいずれか１項に記載の無機蛍光体の製造方法。
【００２５】
８．無機蛍光体が紫外線励起蛍光体であることを特徴とする前記１〜７のいずれか１項に記載の無機蛍光体の製造方法。
【００３２】
本発明を更に詳しく説明する。最初に本発明の無機蛍光体について説明する。本発明の無機蛍光体は紫外線励起蛍光体であることが好ましい。励起光のピーク波長は紫外領域にあることが好ましく、より好ましくは３３０ｎｍから４００ｎｍである。
【００３３】
本発明で用いられる無機蛍光体の原料混合物について説明する。本発明の無機蛍光体の原料混合物は、目的とする蛍光体組成を構成するような粉体原料を混合した物でも良いし、予めゾルゲル法や晶析法で合成した前駆体を用いても良い。ここでいうゾルゲル法とは、一般的には母体または付活剤または共付活剤に用いる元素（金属）を、例えば、Ｓｉ（ＯＣＨ3）4やＥｕ3+（ＣＨ3ＣＯＣＨＣＯＣＨ3）3等の金属アルコキシドや金属錯体またはそれらの有機溶媒溶液に金属単体を加えて作るダブルアルコキシド（例えば、Ａｌ（ＯＣ4Ｈ9）3の２−ブタノール溶液に金属マグネシウムを加えて作るＭｇ［Ａｌ（ＯＣ4Ｈ9）3］2等）、金属ハロゲン化物、有機酸の金属塩、金属単体として必要量混合し、熱的または化学的に重縮合することによる製造方法を意味する。また晶析法とは、冷却、蒸発、ｐＨ調節、濃縮等による物理的または化学的な環境の変化、或は化学反応によって混合系の状態に変化を生じる場合等において液相中から固相が析出してくることがあり、一般に晶析現象と言われているが、この様な晶析現象発生の誘因となりえる物理的、化学的操作による製造方法を意味する。
【００３４】
次に本発明の焼成工程について説明する。本発明の焼成工程は、前記無機蛍光体の原料混合物を焼成して焼成物を得る工程である。本発明の無機蛍光体の製造方法は、焼成工程において、焼成しようとする無機蛍光体を収容するボート型、ルツボ型又は円柱管型等の容器（以下、「焼成容器」と呼ぶことがある。）に、無機蛍光体の原料混合物を充填して焼成する。円柱管型の容器の場合は回転させながら焼成することで焼成むらなく焼成物を得ることができる。
【００３５】
前記焼成工程の焼成時間としては、無機蛍光体の原料混合物の充填量、焼成温度又は炉からの取出温度等によっても異なるが、一般に、０．５〜６時間が好ましく、１〜３時間がより好ましい。
【００３６】
前記焼成容器は、熱膨張係数が１×１０-6／℃以下の材質からなるが、０．７×１０-6／℃以下の材質からなることが好ましい。前記熱膨張係数が１×１０-6／℃を超える場合、焼成工程において、焼成容器を急激に加熱すると、即ち、焼成容器を除々に昇温せずに、高温に設定された焼成空間にいきなり入れると、焼成容器が熱膨張して割れやすい。一方、前記熱膨張係数が１×１０-6／℃以下であれば、焼成工程において、焼成容器を急激に加熱させることができ、発光特性の優れた無機蛍光体を得ることができる。熱膨張係数が１×１０-6／℃以下の材質としては、石英ガラス（熱膨張係数が５．５×１０-7／℃）、チタン酸アルミナ（Ａｌ2ＴｉＯ5）（熱膨張係数が５．２×１０-7／℃）が特に好ましい。
【００３７】
本発明の結晶化工程について説明する。本発明の結晶化工程とは、前記無機蛍光体の原料混合物を焼成して反応させ、目的組成物へ蛍光体の母体を結晶化させる工程である。本発明の結晶化工程においては、１５〜１００℃／分の昇温速度で加熱することが好ましく、また、１５〜１００℃／分の降温速度で冷却することが好ましい。１５〜１００℃／分の昇降温速度で急加熱、急冷却することにより、発光特性の優れた無機蛍光体を得ることができる。
【００３８】
前記結晶化工程の温度は、蛍光体の母体により異なり、りん酸塩では９００〜１４００℃、けい酸塩では１０００〜１５００℃、アルミン酸塩では１２００〜１７００℃が好ましい。
【００３９】
本発明の還元工程について説明する。本発明の還元工程とは、前記無機蛍光体の原料混合物を還元雰囲気下で焼成することにより、原料混合物中に含まれる付活剤を還元させる工程である。本発明の還元工程においては、１５〜１００℃／分の昇温速度で加熱することが好ましく、また、１５〜１００℃／分の降温速度で冷却することが好ましい。１５〜１００℃／分の昇降温速度で急加熱、急冷却することにより、発光特性の優れた無機蛍光体を得ることができる。
【００４０】
前記還元工程の温度は、６００〜１１００℃、より好ましくは８００〜１１００℃である。
【００４１】
本発明の焼成装置について説明する。本発明で用いられる焼成装置としては、急速昇降温が可能な焼成炉が好ましい。すなわち、大気中で焼成を行う結晶化工程においては、熱源が露出した直熱タイプが好ましい。また還元工程においては、焼成管の外部に熱源が配されている外熱タイプが好ましい。前記焼成管は、熱膨張係数が１×１０-6／℃以下の材質からなるが、０．７×１０-6／℃以下の材質からなることが好ましい。前記熱膨張係数が１×１０-6／℃を超える場合、焼成管を急激に加熱すると、焼成管が熱膨張して割れやすい。一方、前記熱膨張係数が１×１０-6／℃以下であれば、焼成管を急激に加熱させることができ、発光特性の優れた無機蛍光体を得ることができる。熱膨張係数が１×１０-6／℃以下の材質としては、石英ガラス（熱膨張係数が５．５×１０-7／℃）、チタン酸アルミナ（Ａｌ2ＴｉＯ5）（熱膨張係数が５．２×１０-7／℃）が特に好ましい。前記焼成管は、固定式でも良いが、回転可能であることがより好ましい。
【００４２】
本発明の焼結防止剤について説明する。本発明の焼結防止剤とは、前記無機蛍光体の原料混合物を焼成する際、蛍光体と焼成容器との融着を防止するためのものである。用いられる焼結防止剤としては特に限定はなく、蛍光体の種類、焼成条件によって適宜選択される。例えば、蛍光体の焼成温度域によって８００℃以下での焼成にはＴｉＯ2等の金属酸化物が、１０００℃以下での焼成にはＳｉＯ2が、１７００℃以下での焼成にはＡｌ2Ｏ3が各々好ましく使用される。
【００４３】
【実施例】
以下に、本発明を実施例により具体的に説明するが、本発明はこれらの実施例によって限定されるものではない。
【００４４】
実施例１
《無機蛍光体１（Ｓｒ10（ＰＯ4）6Ｃｌ2：Ｅｕ2+）の前駆体合成》
下記、晶析法にて無機蛍光体１の前駆体を製造した。
【００４５】
ＳｒＣｌ2・６Ｈ2Ｏ ０．５６ｍｏｌ
Ｅｕ（ＮＯ3）3・６Ｈ2Ｏ ５．６×１０-3ｍｏｌ
ＫＨ2（ＰＯ）4 ０．３４ｍｏｌ
をそれぞれ純水５００ｍｌに溶解し、６０℃で混合した。その際、混合液のｐＨ９を保つようにアンモニア水を添加した。混合と同時に沈殿が生じ、得られた沈殿を濾過、洗浄後、分取した。その後５０℃、１０時間で乾燥して無機蛍光体１の前駆体を得た。
【００４６】
《無機蛍光体１の還元焼成》
［試料１の作製］
（結晶化工程）
無機蛍光体１の前駆体をチタン酸アルミナ製の焼成容器に入れ、焼成装置として株式会社モトヤマ製ＳＢＴ−２０２５Ｄ（焼成管非装着）を用いて１４００℃で３時間、大気中で熱処理を施し、焼成を行った。その後、２００℃以下まで冷却し、焼成物を大気中に取り出した。その際、室温から１４００℃までの昇温時間は６０分、１４００℃から２００℃までの降温時間は６０分の急速昇降温を行った。
【００４７】
（還元工程）
次に、結晶化工程を経て得られた焼成物を、焼成装置として株式会社モトヤマ製ＳＢＴ−２０２５Ｄに石英ガラス製の焼成管を装着したものを用いて６００℃で３時間、還元雰囲気中で熱処理を施し、還元焼成を行った。その後、２００℃以下まで冷却し、焼成物を大気中に取り出した。その際、室温から６００℃までの昇温時間は３０分、６００℃から２００℃までの降温時間は２０分の急速昇降温を行った。また焼成管に使用した石英ガラスの熱膨張係数は５．５×１０-7／℃であった。得られた蛍光体の最大励起波長２８３ｎｍ、最大発光波長４４７ｎｍであった。
【００４８】
［試料２〜４の作製］
還元工程の焼成温度を８００℃、１１００℃、５００℃とし、それ以外は試料１と同様にして試料２〜４を作製した。
【００４９】
比較例１
［試料５の作製］
無機蛍光体１の前駆体をチタン酸アルミナ製の焼成容器に入れ、焼成装置として株式会社モトヤマ製ＳＢＴ−２０２５Ｄにアルミナ製の焼成管を装着したものを用いて１４００℃で３時間、還元雰囲気中で熱処理を施し、還元焼成を行った。その後、２００℃以下まで冷却し、焼成物を大気中に取り出した。その際、急速昇降温を行うと焼成管が割れるので、室温から１４００℃までの昇温時間は９時間、１４００℃から２００℃までの降温時間は８時間とゆっくり昇降温を行った。焼成管に使用したアルミナの熱膨張係数は５．７×１０-6／℃であった。得られた蛍光体の最大励起波長２８３ｎｍ、最大発光波長４４７ｎｍであった。
【００５０】
《評価》
得られた蛍光体を分光蛍光光度計（日立製作所 Ｆ−４５００）を用いて励起波長３５０ｎｍでの発光強度を測定した。得られた結果を試料１の発光強度を１００とした相対強度で示した。焼成に要した時間もあわせて表１に示した。
【００５１】
【表１】
表１より、本発明による無機蛍光体の製造方法は発光強度及び生産性に優れていることがわかる。
【００５３】
参考例
《無機蛍光体２（Ｂａ2ＳｉＯ4：Ｅｕ2+）の前駆体合成》
下記、ゾルゲル法にて無機蛍光体２の前駆体を製造した。
【００５４】
Ｓｉ（ＯＣ2Ｈ5）4 ４×１０-2ｍｏｌ
Ｅｕ（ＣＨ3ＣＯＣＨＣＯＣＨ3）3・２Ｈ2Ｏ ２×１０-4ｍｏｌ
をエタノール１５０ｍｌに溶解し、これをアンモニア１．６×１０-2ｍｏｌを加えた水（１５０ｍｌ）−エタノール（１５０ｍｌ）中に約１ｍｌ／ｍｉｎの速度で撹拌しながら滴下し、ゾルを調製した。得られたゾルをエバポレーターで約１５倍の濃度になるように濃縮し、０．３ｍｏｌ／Ｌの硝酸バリウム水溶液を２９５ｍｌ添加しゲル化させ、湿潤ゲルを得た。得られた湿潤ゲルを、密閉容器中、６０℃で１５時間熟成させた。
【００５５】
その後、撹拌を行っているエタノール（３００ｍｌ）中に、１ｍｌ／ｍｉｎの添加速度で添加し、析出した無機蛍光体前駆体を濾過分取し、５０℃で１０時間乾燥して無機蛍光体２の前駆体を得た。
【００５６】
《無機蛍光体２の還元焼成》
［試料６の作製］
焼成装置として石英ガラス製の焼成管を装着したバッチ式ロータリーキルン（ＡＤＶＡＮＴＥＣ製）を使用した。蛍光体の焼成に先立ち、焼成管内の表面処理を実施した。酸化アルミナ粉体を焼成管に投入し、焼成管を１２０ｒｐｍの速度で回転させながら１１００℃で３０分、大気中で空焼きを行った。その後、２００℃以下まで冷却し、余分な酸化アルミナを取り出した。続いて、無機蛍光体２の前駆体を酸化アルミナで表面処理した焼成管に投入し、焼成管を１２０ｒｐｍの速度で回転させながら１１００℃で３時間、還元雰囲気中で焼成を行った。得られた蛍光体の最大励起波長３５０ｎｍ、最大発光波長５０１ｎｍであった。
【００５７】
比較例２
［試料７の作製］
酸化アルミナで焼成管を表面処理しない以外は試料６と同様にして試料７を得た。
【００５８】
《評価》
得られた試料の回収率を測定した。予め焼成管のみの質量を測定する（Ａ）。次に焼成終了後、蛍光体試料が焼成管内に入った状態での質量を測定する（Ｂ）。焼成管を傾けて中身を回収し、焼成管の質量を測定する（Ｃ）。以下の式により、蛍光体の回収率を計算し比較した。
【００５９】
（Ｂ−Ｃ）／（Ｂ−Ａ）×１００
次に焼成管に付着しているものをスパーテル等でこそぎ落として回収し、先ほど回収したものと混合した。こうして得られた蛍光体の励起波長３５０ｎｍでの発光強度を分光蛍光光度計（日立製作所 Ｆ−４５００）を用いて測定した。得られた結果を試料６の発光強度を１００とした相対強度で示した。
【００６０】
回収率と発光強度をあわせて表２に示した。
【００６１】
【表２】
【発明の効果】
本発明によれば、生産効率を損なうことなく、また、熱源の劣化を引き起こすことなく、さらに、温度むら、還元むらなどの焼成むらが発生することなく、生産性や発光特性に優れた無機蛍光体の製造方法を提供することが可能である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing an inorganic phosphor, and more particularly to a method for producing an inorganic phosphor excellent in productivity and light emission characteristics.
[0002]
[Prior art]
Conventionally, various phosphors are used in various fields.
[0003]
For example, in a three-wavelength emission type fluorescent lamp that is an example of an illumination device, a phosphor that emits light of three wavelengths of blue, green, and red is used as a phosphor, and the blue phosphor includes BaMgAl 10 O 17 : Eu. Europium-activated phosphors having an emission center of Eu 2+ such as 2+ and (Sr, Ba, Ca, Mg) 10 (PO 4 ) 6 Cl 2 : Eu 2+ are CeMgAl 11 O 19 as green phosphors. : Tb 3+ and LaPO 4: Ce 3+, Tb 3+ and (Ce, Gd) MgB 5 O 10: terbium-activated phosphor is a luminescent center of Tb 3+ ions such as Tb 3+ and Ce (Mg, Zn) Al 11 O 19: manganese activated phosphor to an emission center Mn 2+, such as Mn 2+ are also as the red phosphor, Y 2 O 3: Eu 3+ and 3.5MgO.0.5MgF · MgF 2 · GeO 2: Eu 3+ ions and Mn 4+ ions emission center such as Mn 4+ Europium-activated phosphor and manganese-activated phosphors which have been used. Further, for the purpose of enhancing the color rendering properties of the fluorescent lamp light, the emission centers of Eu 2+ such as (Ba, Sr) MgAl 10 O 17 : Eu 2+ , Mn 2+ and Sr 4 Al 14 O 25 : Eu 2+ are used. The europium activated phosphor is also used.
[0004]
In addition, in a PDP which is an example of a display device, a europium activated phosphor having an emission center of Eu 2+ such as BaMgAl 10 O 17 : Eu 2+ is used as a blue phosphor, and a Zn 2 SiO is used as a green phosphor. 4: Mn 2+ and BaAl 12 O 19: Mn 2+ and YBO 4: Tb 3+ terbium activated to an emission center manganese activated phosphor or Tb 3+ ions an emission center Mn 2+ ions, such as The phosphor is also a red phosphor, europium having an emission center of Eu 3+ ions such as Y 2 O 3 : Eu 3+ , (Y, Gd) BO 3 : Eu 3+ , YBO 3 : Eu 3+. An activated phosphor is used. Further, in a color cathode ray tube (CRT), as a blue phosphor, a delocalized emission center type zinc sulfide fluorescence using silver ions such as ZnS: Ag + , Al 3+ or ZnS: Ag + , Cl − as an acceptor. The body is a green phosphor, a delocalized emission center type zinc sulfide phosphor that accepts copper ions such as ZnS: Cu + , Al 3+ , Y 3 Al 5 O 12 : Tb 3+ , InBO 3 : Tb 3+ and Gd 4 Al 2 O 9: Tb 3+ and terbium-activated phosphors of the Tb 3+ ion to an emission center such as, Zn 2 SiO 4: emission center Mn 2+ ions, such as Mn 2+ Further, the manganese-activated phosphor is an europium-activated phosphor having an emission center of Eu 3+ ions such as Y 2 O 3 : Eu 3+ and Y 2 O 2 S: Eu 3+ as a red phosphor. Is used.
[0005]
Various phosphors are also used in electroluminescence devices and active light-emitting liquid crystal devices.
[0006]
Further, as the phosphor, there is a long afterglow phosphor having a long afterglow. These long afterglow phosphors are used in various instruments such as tiles, ashtrays, adhesive tapes, seals, ropes, underlays, and stationery such as pencil cases.
[0007]
Examples of such long afterglow phosphors include Sr 4 Al 14 O 25 : Eu 2+ , Dy 3+ , SrAl 2 O 4 : Eu 2+ , Dy 3+, and CaAl 2 O: Eu 2+ , Dy. 3+, Sr 4 Al 14 O 25 : Eu 2+, Nd 3+ or SrAl 2 O 4: Eu 2+, Nd 3+ and CaAl 2 O 4: Eu 2+, Eu 2+ and Dy such Nd 3+ Aluminum-containing oxide phosphors co-activated with 3+ and Nd 3+ ions are used.
[0008]
Usually, these phosphors are synthesized by baking the phosphor raw material mixture at a high temperature. This firing step is a step in which the activator element diffuses into the host crystal at the same time that the host material of the phosphor crystallizes, and is an important step that affects the light emission characteristics of the resulting phosphor. There are cases where firing can be performed in air and cases where reduction is required, and phosphors using Tl + , Pb 2+ , Sb 3+ , Mn 2+ , Mn 4+ , Eu 3+, etc. as activators May be fired in air, but in the case of Sn 2+ , Eu 2+ , Ce 3+ , Tb 3+, etc., reductive calcination is required in which calcination is performed in a reducing atmosphere. At that time, the reduction process is also an important process, for example, if the reduction is insufficient, the emission characteristics of the phosphor obtained are significantly reduced.
[0009]
As a baking apparatus used in the baking process, an electric furnace is generally used. As a heating method of the electric furnace, there are an external heat type in which a heat source is arranged outside a firing tube made of a ceramic material such as quartz and alumina, and a direct heat type in which there is no firing tube and the heat source is exposed. In general, in reduction firing, an external heat type is used to prevent deterioration of a heat source due to a reducing gas. Alternatively, when the direct heat type is used for reduction firing, it is used in a range where the maximum temperature is limited.
[0010]
In the external heat type, a firing container capable of accommodating the phosphor raw material mixture is provided so that it can be taken in and out of the firing tube, and a gas introduction exhaust pipe for adjusting the firing atmosphere inside the firing tube is connected to the firing tube. . At the time of firing, the phosphor raw material mixture is accommodated in the firing container, and this is put into the firing tube, and the inside of the firing tube is adjusted by the heat from the heat source while adjusting the firing atmosphere inside the firing tube by the gas introduction exhaust tube. The phosphor raw material mixture is fired at a high temperature.
[0011]
Furthermore, in the external heat type, the firing tube may be designed to be rotatable. The phosphor raw material mixture is directly stored in a rotatable firing tube, and the firing is performed while the phosphor raw material mixture is made to flow by rotating the firing tube, thereby reducing temperature unevenness and reduction unevenness in firing. It is.
[0012]
In the case of reducing firing, it is common to use an external heat type, but in a fired tube made of a ceramic material used for the external heat type, a fired tube that can be used particularly at a high temperature firing of 1100 ° C. or higher. However, there was a problem regarding durability, such as being susceptible to thermal shock and being broken by thermal shock. In order to prevent such harmful effects, cracking was prevented by slowing down the heat cycle of the baking furnace, but there was a problem that when the heat cycle was slowed down, production efficiency was lowered.
[0013]
Further, it is known that a phosphor having excellent emission characteristics can be obtained by rapid heating and rapid cooling when the phosphor raw material mixture is reduced and fired and the obtained fired product is cooled. When firing at a high temperature of ℃ or higher, depending on the material of the firing tube used, there are problems such as cracking due to rapid heating and rapid cooling, but when using a direct heating type without firing tube There was a problem of deterioration of the heat source.
[0014]
Moreover, in a firing tube made of a rotatable ceramic material for the purpose of reducing uneven temperature and reduction unevenness in firing, operations such as rotation are difficult due to a decrease in physical strength at a high temperature of 1100 ° C. or higher. There was a problem.
[0015]
Furthermore, there are problems such as a decrease in yield, uneven temperature, and uneven reduction due to the fired product adhering to the firing tube or firing container during firing.
[0016]
As described above, many techniques have been disclosed in which a method for manufacturing a phosphor is devised, but no sufficiently satisfactory one has been obtained. Today, there is a demand for a method for producing a phosphor having sufficient light emission characteristics and excellent production efficiency and production stability.
[0017]
[Problems to be solved by the invention]
The present invention eliminates the above-mentioned problems, does not impair production efficiency, does not cause deterioration of the heat source, and does not cause uneven firing such as temperature unevenness or reduction unevenness. Another object is to provide a method for producing an inorganic phosphor excellent in emission characteristics.
[0018]
[Means for Solving the Problems]
As a result of intensive studies on the production method of the inorganic phosphor, the present inventors have separated the functions of crystallization and reduction of the phosphor in the reduction firing and performed each separately, or to the firing container at the time of firing. It has been found that productivity and light emission characteristics can be improved in the production of inorganic phosphors by preventing adhesion of phosphors, and the present invention has been completed. Means for solving the above problems are as follows. That is,
1. In the method for producing an inorganic phosphor, in which a raw material mixture of the inorganic phosphor is reduced and fired to obtain a fired product, the reduction firing is performed at a temperature rising rate of 15 to 100 ° C./min, and the temperature is lowered to 15 to 100 ° C./min. A crystallization process that cools at a rate and a reduction process that heats at a rate of temperature increase of 15 to 100 ° C./min and cools at a rate of temperature decrease of 15 to 100 ° C./min are separately provided. A method for producing an inorganic phosphor, wherein the fired product is obtained through
[0019]
2. 2. The method for producing an inorganic phosphor as described in 1 above, wherein the firing temperature in the reduction step is lower than the firing temperature in the crystallization step.
[0020]
3. 3. The method for producing an inorganic phosphor according to 1 or 2 above, wherein the firing temperature in the reduction step is 600 ° C. to 1100 ° C.
[0021]
4). 3. The method for producing an inorganic phosphor according to 1 or 2 above, wherein the firing temperature in the reduction step is 800 ° C. to 1100 ° C.
[0022]
5. 5. The method for producing an inorganic phosphor according to any one of 1 to 4, wherein the crystallization step and the reduction step are performed using different firing apparatuses.
[0023]
6). 6. The method for producing an inorganic phosphor according to any one of 1 to 5, wherein the reduction step is performed using a fired tube made of a material having a thermal expansion coefficient of 1 × 10 −6 / ° C. or less.
[0024]
7). 7. The method for producing an inorganic phosphor according to any one of 1 to 6, wherein the reduction step is performed using a rotatable firing tube.
[0025]
8). 8. The method for producing an inorganic phosphor according to any one of 1 to 7, wherein the inorganic phosphor is an ultraviolet-excited phosphor.
[0032]
The present invention will be described in more detail. First, the inorganic phosphor of the present invention will be described. The inorganic phosphor of the present invention is preferably an ultraviolet excitation phosphor. The peak wavelength of the excitation light is preferably in the ultraviolet region, more preferably from 330 nm to 400 nm.
[0033]
The raw material mixture of the inorganic phosphor used in the present invention will be described. The raw material mixture of the inorganic phosphor of the present invention may be a mixture of powder raw materials constituting the target phosphor composition, or a precursor synthesized in advance by a sol-gel method or a crystallization method may be used. . The term “sol-gel method” as used herein generally refers to an element (metal) used for a base material, an activator, or a coactivator, such as Si (OCH 3 ) 4 or Eu 3+ (CH 3 COCHCOCH 3 ) 3. Metal alkoxide, metal complex or double alkoxide prepared by adding a metal simple substance to an organic solvent solution thereof (for example, Mg [Al (OC 4 ) prepared by adding metal magnesium to a 2-butanol solution of Al (OC 4 H 9 ) 3 H 9 ) 3 ] 2 etc.), a metal halide, a metal salt of an organic acid, a necessary amount as a simple metal, and a thermal or chemical polycondensation method. The crystallization method refers to a change in the physical or chemical environment due to cooling, evaporation, pH adjustment, concentration, etc., or a change in the state of the mixed system due to a chemical reaction. Although it may precipitate, it is generally said to be a crystallization phenomenon, and means a production method by physical and chemical operations that can cause the occurrence of such a crystallization phenomenon.
[0034]
Next, the firing process of the present invention will be described. The firing step of the present invention is a step of obtaining a fired product by firing the raw material mixture of the inorganic phosphor. The method for producing an inorganic phosphor of the present invention may be referred to as a boat type, crucible type or cylindrical tube type container (hereinafter referred to as a “baking vessel”) that accommodates the inorganic phosphor to be fired in the firing step. ) Is filled with an inorganic phosphor raw material mixture and fired. In the case of a cylindrical tube type container, a fired product can be obtained without firing unevenness by firing while rotating.
[0035]
The firing time of the firing step varies depending on the filling amount of the raw material mixture of the inorganic phosphor, the firing temperature or the temperature of taking out from the furnace, but generally 0.5 to 6 hours is preferable, and 1 to 3 hours is more preferable. preferable.
[0036]
The firing container is made of a material having a coefficient of thermal expansion of 1 × 10 −6 / ° C. or less, and preferably made of a material of 0.7 × 10 −6 / ° C. or less. When the thermal expansion coefficient exceeds 1 × 10 −6 / ° C., when the baking container is rapidly heated in the baking process, that is, the baking container is not heated gradually, but suddenly enters a baking space set at a high temperature. If it puts in, a baking container will thermally expand and it will be easy to crack. On the other hand, if the thermal expansion coefficient is 1 × 10 −6 / ° C. or less, the firing container can be rapidly heated in the firing step, and an inorganic phosphor having excellent light emission characteristics can be obtained. Examples of the material having a thermal expansion coefficient of 1 × 10 −6 / ° C. or less include quartz glass (thermal expansion coefficient 5.5 × 10 −7 / ° C.), alumina titanate (Al 2 TiO 5 ) (thermal expansion coefficient 5 .2 × 10 −7 / ° C.) is particularly preferable.
[0037]
The crystallization process of the present invention will be described. The crystallization process of the present invention is a process in which the inorganic phosphor raw material mixture is baked and reacted to crystallize the phosphor matrix into the target composition. In the crystallization step of the present invention, it is preferable to heat at a rate of temperature increase of 15 to 100 ° C./min, and it is preferable to cool at a rate of temperature decrease of 15 to 100 ° C./min. By rapidly heating and rapidly cooling at a temperature increase / decrease rate of 15 to 100 ° C./min, an inorganic phosphor having excellent light emission characteristics can be obtained.
[0038]
The temperature of the crystallization step varies depending on the phosphor matrix, and is preferably 900 to 1400 ° C. for phosphate, 1000 to 1500 ° C. for silicate, and 1200 to 1700 ° C. for aluminate.
[0039]
The reduction process of the present invention will be described. The reduction step of the present invention is a step of reducing the activator contained in the raw material mixture by firing the raw material mixture of the inorganic phosphor in a reducing atmosphere. In the reduction step of the present invention, it is preferable to heat at a rate of temperature increase of 15 to 100 ° C./min, and it is preferable to cool at a rate of temperature decrease of 15 to 100 ° C./min. By rapidly heating and rapidly cooling at a temperature increase / decrease rate of 15 to 100 ° C./min, an inorganic phosphor having excellent light emission characteristics can be obtained.
[0040]
The temperature of the reduction step is 600 to 1100 ° C, more preferably 800 to 1100 ° C.
[0041]
The firing apparatus of the present invention will be described. As the baking apparatus used in the present invention, a baking furnace capable of rapidly raising and lowering the temperature is preferable. That is, in the crystallization process in which baking is performed in the air, a direct heating type in which a heat source is exposed is preferable. In the reduction step, an external heat type in which a heat source is arranged outside the firing tube is preferable. The calcined tube is made of a material having a thermal expansion coefficient of 1 × 10 −6 / ° C. or less, and is preferably made of a material having a coefficient of 0.7 × 10 −6 / ° C. or less. When the thermal expansion coefficient exceeds 1 × 10 −6 / ° C., when the firing tube is heated rapidly, the firing tube is thermally expanded and easily broken. On the other hand, if the thermal expansion coefficient is 1 × 10 −6 / ° C. or less, the calcined tube can be rapidly heated, and an inorganic phosphor excellent in emission characteristics can be obtained. Examples of the material having a thermal expansion coefficient of 1 × 10 −6 / ° C. or less include quartz glass (thermal expansion coefficient 5.5 × 10 −7 / ° C.), alumina titanate (Al 2 TiO 5 ) (thermal expansion coefficient 5 .2 × 10 −7 / ° C.) is particularly preferable. The firing tube may be fixed, but is more preferably rotatable.
[0042]
The sintering inhibitor of the present invention will be described. The sintering inhibitor of the present invention is for preventing fusion between the phosphor and the firing container when firing the raw material mixture of the inorganic phosphor. The sintering inhibitor to be used is not particularly limited, and is appropriately selected depending on the type of phosphor and firing conditions. For example, depending on the firing temperature range of the phosphor, a metal oxide such as TiO 2 is used for baking at 800 ° C. or lower, SiO 2 is used for baking at 1000 ° C. or lower, and Al 2 O 3 is used for baking at 1700 ° C. or lower. Are preferably used.
[0043]
【Example】
EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
[0044]
Example 1
<< Precursor Synthesis of Inorganic Phosphor 1 (Sr 10 (PO 4 ) 6 Cl 2 : Eu 2+ ) >>
The precursor of the inorganic fluorescent substance 1 was manufactured by the following crystallization method.
[0045]
SrCl 2 · 6H 2 O 0.56 mol
Eu (NO 3 ) 3 · 6H 2 O 5.6 × 10 −3 mol
KH 2 (PO) 4 0.34 mol
Were dissolved in 500 ml of pure water and mixed at 60 ° C. At that time, aqueous ammonia was added so as to maintain the pH of the mixed solution. Precipitation occurred simultaneously with mixing, and the resulting precipitate was filtered, washed and collected. Thereafter, drying was performed at 50 ° C. for 10 hours to obtain a precursor of inorganic phosphor 1.
[0046]
<< Reduction firing of inorganic phosphor 1 >>
[Preparation of Sample 1]
(Crystallization process)
The precursor of the inorganic phosphor 1 is placed in a firing container made of alumina titanate, and heat treatment is performed in the atmosphere at 1400 ° C. for 3 hours using SBT-2025D (not equipped with a firing tube) manufactured by Motoyama Co., Ltd. as a firing device. Firing was performed. Then, it cooled to 200 degrees C or less, and took out the baked product in air | atmosphere. At that time, the temperature rising time from room temperature to 1400 ° C. was 60 minutes, and the temperature falling time from 1400 ° C. to 200 ° C. was 60 minutes.
[0047]
(Reduction process)
Next, the fired product obtained through the crystallization process was heat-treated in a reducing atmosphere at 600 ° C. for 3 hours using a SBT-2025D manufactured by Motoyama Co., Ltd. and a fired tube made of quartz glass as a firing device. Then, reduction firing was performed. Then, it cooled to 200 degrees C or less, and took out the baked product in air | atmosphere. At that time, the temperature was raised rapidly from room temperature to 600 ° C. for 30 minutes, and the temperature drop time from 600 ° C. to 200 ° C. was 20 minutes. Moreover, the thermal expansion coefficient of the quartz glass used for the firing tube was 5.5 × 10 −7 / ° C. The phosphor obtained had a maximum excitation wavelength of 283 nm and a maximum emission wavelength of 447 nm.
[0048]
[Preparation of Samples 2 to 4]
Samples 2 to 4 were produced in the same manner as Sample 1 except that the firing temperature in the reduction step was 800 ° C., 1100 ° C., and 500 ° C.
[0049]
Comparative Example 1
[Preparation of Sample 5]
The precursor of the inorganic phosphor 1 is put in a firing container made of alumina titanate, and a firing apparatus equipped with SBT-2025D manufactured by Motoyama Co., Ltd. and an alumina firing tube is mounted at 1400 ° C. for 3 hours in a reducing atmosphere. Then, heat treatment was performed and reduction firing was performed. Then, it cooled to 200 degrees C or less, and took out the baked product in air | atmosphere. At that time, the firing tube was cracked when rapid temperature increase / decrease was performed, so the temperature increase time from room temperature to 1400 ° C. was 9 hours, and the temperature decrease time from 1400 ° C. to 200 ° C. was 8 hours. The thermal expansion coefficient of alumina used for the calcined tube was 5.7 × 10 −6 / ° C. The phosphor obtained had a maximum excitation wavelength of 283 nm and a maximum emission wavelength of 447 nm.
[0050]
<Evaluation>
The phosphor obtained was measured for emission intensity at an excitation wavelength of 350 nm using a spectrofluorometer (Hitachi F-4500). The obtained results are shown as relative intensities where the emission intensity of Sample 1 is 100. Table 1 also shows the time required for firing.
[0051]
[Table 1]
From Table 1, it can be seen that the method for producing an inorganic phosphor according to the present invention is excellent in emission intensity and productivity.
[0053]
Reference Example << Precursor Synthesis of Inorganic Phosphor 2 (Ba 2 SiO 4 : Eu 2+ ) >>
A precursor of inorganic phosphor 2 was produced by the following sol-gel method.
[0054]
Si (OC 2 H 5 ) 4 4 × 10 -2 mol
Eu (CH 3 COCHCOCH 3 ) 3 · 2H 2 O 2 × 10 −4 mol
Was dissolved in water (150 ml) -ethanol (150 ml) added with 1.6 × 10 −2 mol of ammonia at a rate of about 1 ml / min with stirring to prepare a sol. The obtained sol was concentrated by an evaporator so as to have a concentration of about 15 times, and 295 ml of 0.3 mol / L barium nitrate aqueous solution was added for gelation to obtain a wet gel. The obtained wet gel was aged in a sealed container at 60 ° C. for 15 hours.
[0055]
Thereafter, the mixture was added to stirring ethanol (300 ml) at an addition rate of 1 ml / min, and the precipitated inorganic phosphor precursor was collected by filtration and dried at 50 ° C. for 10 hours to form the inorganic phosphor 2. A precursor was obtained.
[0056]
<< Reduction firing of inorganic phosphor 2 >>
[Preparation of Sample 6]
A batch type rotary kiln (manufactured by ADVANTEC) equipped with a quartz glass firing tube was used as a firing device. Prior to the firing of the phosphor, the surface treatment in the firing tube was performed. The alumina oxide powder was put into a firing tube, and baked in the air at 1100 ° C. for 30 minutes while rotating the firing tube at a speed of 120 rpm. Then, it cooled to 200 degrees C or less, and took out the excess alumina oxide. Subsequently, the precursor of the inorganic phosphor 2 was put into a firing tube surface-treated with alumina oxide, and was fired in a reducing atmosphere at 1100 ° C. for 3 hours while rotating the firing tube at a speed of 120 rpm. The phosphor obtained had a maximum excitation wavelength of 350 nm and a maximum emission wavelength of 501 nm.
[0057]
Comparative Example 2
[Preparation of Sample 7]
Sample 7 was obtained in the same manner as Sample 6 except that the calcined tube was not surface-treated with alumina oxide.
[0058]
<Evaluation>
The recovery rate of the obtained sample was measured. The mass of only the firing tube is measured in advance (A). Next, after the firing, the mass of the phosphor sample in a state where it enters the firing tube is measured (B). Tilt the firing tube to collect the contents, and measure the mass of the firing tube (C). The phosphor recovery rates were calculated and compared using the following formula.
[0059]
(BC) / (BA) × 100
Next, the material adhering to the firing tube was scraped off with a spatula or the like and collected, and mixed with the material collected earlier. The emission intensity of the phosphor thus obtained at an excitation wavelength of 350 nm was measured using a spectrofluorometer (Hitachi F-4500). The obtained results are shown as relative intensities with the emission intensity of Sample 6 as 100.
[0060]
The recovery and emission intensity are shown together in Table 2.
[0061]
[Table 2]
【The invention's effect】
According to the present invention, an inorganic fluorescent material excellent in productivity and light emission characteristics is produced without impairing production efficiency, causing deterioration of a heat source, and without causing uneven firing such as uneven temperature and reduced unevenness. It is possible to provide a method for manufacturing a body.
Claims (8)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2001348389A JP3915482B2 (en) | 2001-11-14 | 2001-11-14 | Method for producing inorganic phosphor |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2001348389A JP3915482B2 (en) | 2001-11-14 | 2001-11-14 | Method for producing inorganic phosphor |
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| JP3915482B2 true JP3915482B2 (en) | 2007-05-16 |
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