JP3840360B2

JP3840360B2 - Blue phosphor for color plasma display panel

Info

Publication number: JP3840360B2
Application number: JP2000122235A
Authority: JP
Inventors: 英貴藤井; 孝之大西; 正孝國分; 書秀張; 勝昭木村; 振華王; 健平蒋; 競涛顧; 徳源張
Original assignee: Daiden Co Inc
Current assignee: Daiden Co Inc
Priority date: 2000-04-24
Filing date: 2000-04-24
Publication date: 2006-11-01
Anticipated expiration: 2020-04-24
Also published as: JP2001303037A

Description

【０００１】
【発明の属する技術分野】
本発明は、プラズマディスプレイパネル（以下、ＰＤＰと略称することがある）に用いられる蛍光体の技術分野に属し、特に、発光強度の経時劣化が改良されたカラーＰＤＰ用青色蛍光体に関する。
【０００２】
【従来の技術】
カラーＰＤＰは、ガス放電によって出る真空紫外線を赤、緑および青色の蛍光体に当てて励起発光させカラー表示するディスプレイであり、薄形で大画面が可能で高速表示ができるなどの特徴があり、壁掛け用や高品位テレビジョンなどへの用途が期待されている。
【０００３】
ＰＤＰ用青色蛍光体としては、主としてアルミン酸系蛍光体が用いられているが、このＰＤＰ用アルミン酸系青色蛍光体は、パネル制作時の熱処理（一般的な条件：５００℃×３０分）による熱劣化とパネル駆動時の真空紫外線（ＶＵＶ）によるＶＵＶ劣化に起因する発光特性の劣化、特に発光強度の劣化の改善が切望されている。このような背景において、アルミン酸蛍光体の組成そのものの最適化等も行われているが特性改善に至ってない。
【０００４】
蛍光体の発光特性を維持しまたは向上させるためには蛍光体の表面をＳｉＯ₂（シリカ）等の各種の物質で保護しようとする試みが従来から提示されている。例えば、特開平１０−２０４４２９（特願平９−９６４５）には、蛍光ランプに用いられるアルミン酸系青色蛍光体の粒子表面にＳｉＯ₂粉末を付着させることによって発光効率等が高められる旨記述されている。このような蛍光体の表面に設けられる保護物質は、励起発光によって生じる蛍光を透過させるとともに、励起光も充分に透過させて高い励起効率が得られるものでなければならない。蛍光ランプの場合は、Ｈｇ（水銀）による２５４ｎｍの紫外線でアルミン酸青色蛍光体を励起発光させ、この紫外線はＳｉＯ₂を透過するので、ＳｉＯ₂が付着しても励起光を透過させ所望の目的はある程度達成されるであろう。
【０００５】
しかしながら、ＰＤＰの場合は、Ｈｅ−ＸｅまたはＮｅによる１４７ｎｍまたは１７２ｎｍの真空紫外線で励起してアルミン酸系青色蛍光体を発光させる。紫外線はＳｉＯ₂を透過するが、真空紫外線はＳｉＯ₂を透過せずにＳｉＯ₂に吸収されてしまう。したがって、ＳｉＯ₂は、真空紫外線を用いるＰＤＰ用青色蛍光体の保護物質としては、不適であると考えられている。真空紫外線を透過させる物質としては、フッ化マグネシウム、フッ化カルシウム、フッ化リチウム等のフッ化物が知られているが、これらの物質を蛍光体粉末（粒子）に均一にコーティングする技術は未だ存在していない。
【０００６】
【発明が解決しようとする課題】
本発明の目的は、真空紫外線で励起発光させるＰＤＰ用青色蛍光体の経時的な発光特性の劣化を防止できる新しい技術を確立することにある。
【０００７】
【課題を解決するための手段】
本発明者は、検討を重ねた結果、真空紫外線が極力吸収されずに透過するような薄い緻密な膜から成る保護膜層を設けることにより上記の課題が解決されることを見出し、本発明を導き出したものである。
【０００８】
かくして、本発明に従えば、アルミン酸系青色蛍光体の粉末表面にＳｉＯ₂被覆膜が１００ｎｍ以下の厚さで成膜されていることを特徴とするカラープラズマディスプレイパネル用青色蛍光体が提供される。本発明が適用されるアルミン酸系青色蛍光体の好ましい例は、（Ｂａ，Ｅｕ）Ｏ・ＭｇＯ・５Ａｌ₂Ｏ₃系蛍光体または（Ｂａ，Ｅｕ）Ｏ・ＭｇＯ・７Ａｌ₂Ｏ₃系蛍光体である。
【０００９】
さらに、本発明は、上記のごときカラープラズマディスプレイパネル用青色蛍光体を製造する方法の１つとして、ケイ素ポリマーを有機溶媒に溶かした溶液中にアルミン酸系青色蛍光体の粉末を浸漬し攪拌する工程、浸漬後の蛍光体と溶液を分離する工程、分離後の蛍光体を乾燥する工程、および乾燥後の蛍光体を酸素存在下に１０００℃以下で加熱する工程、を含むことを特徴とする方法を提供する。本発明のカラーＰＤＰ用青色蛍光体の製造方法の特に好ましい態様に従えば、加熱工程は、１５０℃〜６００℃で加熱する一次処理と、さらに、５００℃〜１０００℃で加熱する二次処理とから成る。また、本発明のＰＤＰ用青色蛍光体の製造方法において用いられるのに特に好ましいケイ素ポリマーはペルヒドロポリシラザンである。
【００１０】
【発明の実施の形態】
本発明においてＰＤＰ用アルミン酸系青色蛍光体の粉末（粒子）を保護するのに用いられるＳｉＯ₂は、従来より専ら実施されていた粉末付着法によるもの、例えば、上記の特開平１０−２０４４２９に記載された蛍光ランプ用青色蛍光体の場合のように蛍光体粒子表面にＳｉＯ₂の粉末が散在的に付着しているものではなく、ＳｉＯ₂被覆膜が１００ｎｍ以下の薄い厚さの緻密（均一）な膜を形成していることに特徴がある。本発明におけるＳｉＯ₂膜がこのような構造を有していることは、Ｘ線回折およびＥＰＭＡによる面分析によって確認されている（後述の実施例参照）。
【００１１】
このようにＳｉＯ₂被覆膜が１００ｎｍ以下の厚さで緻密に成膜されて蛍光体粉末を保護している本発明のアルミン酸系青色蛍光体は、真空紫外線の透過率７０％以上を有することが確認されている。かくして、本発明の蛍光体は、真空紫外線照射の高エネルギー環境下においても真空紫外線の透過率を可及的に損なわず且つ発光強度の経時変化を軽減し蛍光体の長寿命化を実現する。
【００１２】
このアルミン酸系青色蛍光体の粉末表面にＳｉＯ₂被覆膜が１００ｎｍ以下の厚さで緻密に成膜されているＰＤＰ用青色蛍光体は、本発明に従い、ケイ素ポリマーの溶液に原料蛍光体を浸漬してから１０００℃以下の比較的温和な条件でポリマーを加熱分解処理することによって得ることができる。すなわち、本発明に従うカラーＰＤＰ用青色蛍光体の製造方法は、上記の特開平１０−２０４４２９に記述されているように蛍光体粉末（粒子）に粉末状態でＳｉＯ₂を付着させ熱処理を行うのではなく、ケイ素ポリマーを有機溶媒に溶かした溶液中にアルミン酸系青色蛍光体の粉末を浸漬し攪拌し、次いで蛍光体と溶液の分離および蛍光体の乾燥を行った後、蛍光体を酸素存在下（すなわち、大気中または酸素含有ガス雰囲気下）に１０００℃以下で加熱する各工程を含むものである。
【００１３】
ここで、本発明の方法の特に好ましい態様に従えば、加熱処理を１５０℃〜６００℃（好ましくは１５０℃〜５００℃）で加熱する一次処理と、さらに、５００℃〜１０００℃（好ましくは５００℃〜７００℃）で加熱する二次処理とによって行う。これによって、顕著な熱劣化を引き起こさない温度領域でＳｉＯ₂膜を作成し（一次処理）このＳｉＯ₂被覆膜を高温熱処理により緻密化する（二次処理）ことができる。
【００１４】
膜厚の制御は、必要に応じて、上記のごとき工程を繰り返すことによって容易に行うことができる。すなわち、一次処理後、または、一次処理および二次処理後の蛍光体を再びケイ素ポリマーの有機溶媒溶液に浸漬し攪拌した後、分離工程および乾燥工程に供してから、一次処理、または一次処理と二次処理とから成る加熱工程に供する。勿論、最終的には、二次処理を行いＳｉＯ₂の緻密化を図る。
【００１５】
このようにして、本発明に従えば、ケイ素ポリマーの溶液に蛍光体を浸漬してＳｉＯ₂膜を被覆することにより、膜厚を制御が可能となり真空紫外線を透過することのできる緻密なＳｉＯ₂の薄膜を形成することができる。ここで、本発明において用いられるケイ素ポリマーとは、ケイ素化合物のポリマーであって適当な有機溶媒中の溶液状態でアルミン酸系青色蛍光体の粉末に付着するとともに、上記のごとき酸素存在下の加熱処理に供されると分解してＳｉＯ₂を生成し得るものを指称する。そのようなケイ素ポリマーは、一般に、分子構造として、Ｓｉ−Ｈ、Ｓｉ−Ｏ−Ｈ、またはＳｉ−Ｎ−Ｈで表わされるような化学式を含み、その好ましい例はＳｉＨ_aＮ_b（ａ＝１〜３、ｂ＝０または１）で表わされる反復単位を有するペルヒドロポリシラザンである。
【００１６】
本発明の方法においては、このようなケイ素ポリマーを適当な有機溶媒（例えば、キシレン、ジブチルエーテル等）で必要な濃度（一般には、０．００１〜２．０重量％）までに稀釈した後、その溶液に一定量の蛍光体粉末を入れ（一般的にはケイ素ポリマー溶液に対して重量比で１／１０〜１．０）、均一になるように攪拌する。このようにして、蛍光体粉末（粒子）とケイ素ポリマー溶液とを一定時間（一般的には、１０〜３０分間）接触させた後、蛍光体を溶液から分離し（一般的には、ろ過、スプレードライ等による）、蛍光体を乾燥（一般的には、１００〜１２０℃）した後、上記のごとき加熱工程に供する。
【００１７】
【実施例】
以下に、本発明の特徴を更に明らかにするために実施例に沿って本発明を説明するが、本発明はこれらの実施例によって制限されるものではない。
実施例１：膜厚と真空紫外線透過率
キシレンで５ｗｔ％（重量％）および１０ｗｔ％に稀釈されたポリシラザン(ＳｉＨ₂ＮＨ)_n（商標：東燃株式会社）をＣａＦ₂板上にスピンコーティングし、溶媒のキシレンを蒸散させて除去し、３５０℃で焼成（一次処理）後、再度６００℃にて焼成（二次処理）を行い、ＣａＦ₂板上にＳｉＯ₂被覆膜を形成した。スピンコーティングするときの回転数は１０００、２０００、４０００回転とした。
【００１８】
以上のようにして得られた複数の試料を走査型触針式膜厚計を用いて膜厚を測定し、その値を膜厚とした。真空紫外線の透過率はコーティング前後のＣａＦ₂板の透過強度の比から求めた。真空紫外線の透過強度は日本分光製の真空紫外線分光システムを用いて測定した。
【００１９】
膜厚と透過率の関係を表１および図１に示す。図１から理解されるように、紫外線は膜厚が厚くなってもＳｉＯ₂膜を透過するが、真空紫外線の場合はＳｉＯ₂膜を１００ｎｍ以下の膜厚にすることによって透過率の顕著な上昇が認められ、７０％以上の透過率が得られる。膜質の確認はＸＲＤ（Ｘ線回折）を用いて行い、ＳｉＯ₂膜であることを確認した。
【００２０】
【表１】

【００２１】
実施例２：ＳｉＯ ₂ 被覆膜で成膜された蛍光体の調製
試料２：膜厚１００ｎｍ以下のＳｉＯ₂被膜膜で成膜された蛍光体試料を得るために、（Ｂａ，Ｅｕ）Ｏ・ＭｇＯ・５Ａｌ₂Ｏ₃系青色蛍光体粉末を秤量し、キシレンにて濃度０．１ｗｔ％に調整したポリシラザン溶液に浸漬した。このときポリシラザン溶液は蛍光体重量の１０倍とし、混合後１０分程度攪拌した後、ろ過法にて、蛍光体と溶液を分離した。分離した蛍光体を１２０℃の乾燥器中でキシレンを蒸散させて完全に除去し、ポリシラザンを蛍光体に被着させた。この蛍光体を大気中にて、３５０℃の焼成（一次処理）後、再度６００℃の焼成（二次処理）を行い、膜厚約５ｎｍ以下の緻密なＳｉＯ₂の被覆膜を蛍光体表面に形成させた。
【００２２】
試料３：上記と同様の蛍光体を秤量し、キシレンにて濃度０．１ｗｔ％に調整したポリシラザン溶液に浸漬させた。このときポリシラザン溶液は蛍光体重量の２倍とした。１０分程度攪拌後、１２０℃の乾燥器中でキシレンを蒸散させて完全に除去し、ポリシラザンを蛍光体に被着させた。この蛍光体を上記と同様の条件にて焼成し、膜厚約５ｎｍの緻密なＳｉＯ₂の被覆膜を蛍光体表面に形成させた。
【００２３】
試料４〜６：ポリシラザン濃度を０．３ｗｔ％にし、処理（一次処理）を繰り返した後、最後に上記と同様の二次処理を行うことで、膜厚２０，５０，１００ｎｍ以下の緻密なＳｉＯ₂の被覆膜を蛍光体に形成させた。
【００２４】
上記のように作成した試料と、被覆を施していない試料とを有機バインダーで塗料化、塗布、焼成（５００℃）を行った。これらの試料に真空紫外線を照射し、真空紫外線照射での発光強度の経時変化（ＶＵＶ劣化）の評価を行った。
【００２５】
測定結果を表２に示す。但し、発光強度はＳｉＯ₂被覆前の試料を基準にそれぞれの強度発光の割合で示す。なお、発光強度はミノルタ分光放射輝度計を用いて測定した。また、膜厚は、シラザン添加量と比表面積から算出した膜厚を膜厚Ａ、ＳｉＯ₂被覆後の蛍光強度の低下率と実施例１のＳｉＯ₂被覆膜の透過率から算出した膜厚を膜厚Ｂとした。
【００２６】
膜厚ＡとＢはほぼ一致し、真空紫外線を励起光として使用するＰＤＰ用としては１００ｎｍ以下、望ましくは２０ｎｍ以下の膜厚が適切であることが立証された。また、真空紫外線による劣化での維持率（照射０時間に対する照射２２時間の強度）はＳｉＯ₂の被覆により、４３％から６０％以上に向上することが立証された。
【００２７】
【表２】

【００２８】
実施例３：熱処理温度の比較試験
アルミン酸青色蛍光体は、ＶＵＶ劣化の他に、熱処理による熱劣化が起こる。そのため、高温での熱処理は初期値の低下をまねき、熱処理温度を考慮する必要がある。ＳｉＯ₂被覆膜の作成時においても、顕著な熱劣化を引き起こさない温度領域（一次処理）でＳｉＯ₂被覆膜を作成しこのＳｉＯ₂被覆膜を高温熱処理（二次処理）にて緻密化する必要があり、一次処理と二次処理の熱処理温度の比較試験を行った。
【００２９】
試料７：（Ｂａ，Ｅｕ）Ｏ・ＭｇＯ・５Ａｌ₂Ｏ₃系青色蛍光体をキシレン溶液に稀釈した０．１ｗｔ％のポリシラザン溶液に浸漬、ろ過、蒸散後、一次処理温度として３５０℃で焼成を行い、ＳｉＯ₂被覆膜を形成した青色蛍光体粉末を作成した。
【００３０】
試料８：（Ｂａ，Ｅｕ）Ｏ・ＭｇＯ・５Ａｌ₂Ｏ₃系青色蛍光体をキシレン溶液に稀釈した０．１ｗｔ％のポリシラザン溶液に浸漬、ろ過、蒸散後、一次処理温度として６００℃で焼成を行い、ＳｉＯ₂被覆膜を形成した青色蛍光体粉末を作成した。
【００３１】
試料９：（Ｂａ，Ｅｕ）Ｏ・ＭｇＯ・５Ａｌ₂Ｏ₃系青色蛍光体をキシレン溶液に稀釈した０．１ｗｔ％のポリシラザン溶液に浸漬、ろ過、蒸散後、一次処理温度として３５０℃で焼成を行い、その後さらに３５０℃にて二次焼成を施し、ＳｉＯ₂被覆膜を形成した青色蛍光体粉末を作成した。
【００３２】
試料１０〜１６：（Ｂａ，Ｅｕ）Ｏ・ＭｇＯ・５Ａｌ₂Ｏ₃系青色蛍光体をキシレン溶液に稀釈した０．１ｗｔ％のポリシラザン溶液に浸漬、ろ過、蒸散後、一次処理温度として１５０℃〜６００℃で焼成を行い、その後さらに５００℃〜１１００℃にて二次焼成を施し、ＳｉＯ₂被覆膜を形成した青色蛍光体粉末を作成した。
【００３３】
上記のように作成した各蛍光体試料と、被覆を施していない蛍光体試料とを有機バインダーで塗料化、塗布、焼成（５００℃×３０ｍｉｎ）後、真空紫外線照射での発光強度の経時変化（ＶＵＶ劣化）の評価を行った。なお、これらの試料の膜厚は、いずれも、シラザン添加量と比表面積から算出した場合（膜厚Ａ）は５ｎｍ、ＳｉＯ₂被覆後の蛍光強度の低下率と実施例１のＳｉＯ₂被覆膜の透過率から算出した場合（膜厚Ｂ）は１０ｎｍ以下であった。
【００３４】
表３にこれらの青色蛍光体の真空紫外線照射前と真空紫外線２２時間照射後の結果を示す。用いた青色蛍光体の未処理粉体試料（塗料化前）の発光強度を１００％とした。
【００３５】
表３よりポリシラザン処理を施した試料は、真空紫外線２２時間照射後、ポリシラザン処理を施していない試料と比べ相対発光強度が６０％以上の維持率が見られるが、一次処理温度１５０℃〜５００℃で処理後、二次処理温度５００℃〜７００℃で処理した試料は、真空紫外線２２時間照射後、相対発光強度７０％以上の高い維持率を示した。
【００３６】
【表３】

【００３７】
実施例４：表面処理法の比較
蛍光体の表面をＳｉＯ₂で保護する表面処理の手法を比較するために、本発明に従いポリシラザンの溶液を蛍光体に浸漬して加熱（焼成）を行うことによりＳｉＯ₂被覆膜をアルミン酸青色蛍光体表面に作成した試料と、従来のように蛍光体にＳｉＯ₂粉体を付着させて加熱したアルミン酸青色蛍光体試料との比較試験を行った。
【００３８】
試料１７：（Ｂａ，Ｅｕ）Ｏ・ＭｇＯ・５Ａｌ₂Ｏ₃系青色蛍光体に粒子径２００ｎｍのＳｉＯ₂を０．０１ｗｔ％で加え、水中にて分散、十分に攪拌した後、蛍光体粉体をろ過により回収、乾燥後、ふるい分けしＳｉＯ₂を付着させた後、３５０℃に加熱してアルミン酸青色蛍光体を得た。
【００３９】
試料１８〜１９：（Ｂａ，Ｅｕ）Ｏ・ＭｇＯ・５Ａｌ₂Ｏ₃系青色蛍光体に粒子径２００ｎｍのＳｉＯ₂を０．１〜１ｗｔ％で加え、水中にて分散、十分に攪拌した後、蛍光体粉体をろ過により回収、乾燥後、ふるい分けしＳｉＯ₂を付着させた後、３５０℃に加熱してアルミン酸青色蛍光体を得た。
【００４０】
上記のように作成した試料と、被覆を施していない試料とを有機バインダーで塗料化、塗布、焼成（５００℃×３０ｍｉｎ）後、真空紫外線照射での発光強度の経時変化（ＶＵＶ劣化）の評価を行った。また、蛍光体の表面状態の評価を行うために、走査電子顕微鏡写真による観察およびＥＰＭＡによる面分析を行った。
【００４１】
表４にこれらの青色蛍光体試料の真空紫外線照射前と真空紫外線２２時間照射後の結果を示す。表４には、既述の本発明に従いポリシラザン溶液に浸漬した場合の結果をあわせて示している。用いた青色蛍光体の未処理粉体試料（塗料化前）を１００％とした。
【００４２】
表４から理解されるように試料１７，１８および１９のＳｉＯ₂粉体の付着による手法で作成した試料は、真空紫外線２２時間照射後の相対発光強度は低く、耐ＶＵＶ効果は見られない。また、図２の電子顕微鏡写真に示されるように蛍光体の表面にＳｉＯ₂粉体の付着が確認された。さらに図４に示すように、ＥＰＭＡによる面分析により蛍光体を構成する元素の存在分布を調べた。図４の右側は、メイン元素であるＡｌの存在分布を示し、図中の暗色部分（黒い部分）を除いてＡｌが全体的に分布していることを示す。図４の左側はＳｉの存在分布を示すものであり、Ｓｉが均一に分布していれば、Ａｌの存在分布に対応するが、部分的な対応しか認められずＳｉは均一（緻密）に存在していないことが理解される。
【００４３】
一方、本発明に従いポリシラザンを用いてＳｉＯ₂被覆膜を作成した試料（試料１１）は、図３の電子顕微鏡写真に示されるようにＳｉＯ₂粉体の付着は確認されない。さらに、図５のＥＰＭＡ面分析が示すように、蛍光体のメイン元素であるＡｌの存在分布（図５の右）とＳｉの存在分布が対応していることから、蛍光体状にＳｉＯ₂膜が均一（緻密）に存在していることが理解される。試料７についてもほぼ同じ結果が得られる。以上の結果は、単にＳｉＯ₂が蛍光体の表面に付着していればよいということでなく、ポリシラザンのようなケイ素ポリマーの溶液中への浸漬を含む処理による均一（緻密）なＳｉＯ₂被覆膜の形成が必要であることを示している。
【００４４】
【表４】

【００４５】
実施例５：他の蛍光体への適用
本発明によるＳｉＯ₂被覆の薄膜の形成がある特有の蛍光体のみの効果かを確認するために、プラズマディスプレイ用蛍光体として用いられる緑色蛍光体についても、ポリシラザンを用いたＳｉＯ₂被覆膜の形成を行いＶＵＶ評価を行った。
【００４６】
緑色蛍光体としてプラズマディスプレイに用いられている２（Ｚｎ，Ｍｎ）Ｏ・ＳｉＯ₂系を用い、実施例３の試料１１を作成した条件で０．１ｗｔ％のポリシラザン溶液を用いてＳｉＯ₂被覆膜を形成した緑色蛍光体（試料２０）を得た。また、比較のために、実施例３の試料１１のアルミン酸青色蛍光体も調製した。
【００４７】
これらの試料と、被覆を施していない各色試料を有機バインダーで塗料化、塗布、焼成（５００℃×３０ｍｉｎ）後、真空紫外線照射での発光強度の経時変化（ＶＵＶ劣化）の評価を行った。
【００４８】
表５に上記のように作成した青色蛍光体と緑色蛍光体の真空紫外線照射前と真空紫外線２２時間照射後の結果を示す。各色とも未処理粉体試料（塗料化前）を１００％とした。
【００４９】
２（Ｚｎ，Ｍｎ）Ｏ・ＳｉＯ₂系の緑色蛍光体においては、ポリシラザン処理によるＳｉＯ₂被覆膜の形成は逆効果であり、アルミン酸系青色蛍光体のみ有効であった。
【００５０】
【表５】

【図面の簡単な説明】
【図１】本発明によって得られるＳｉＯ₂膜の膜厚と紫外線および真空紫外線の透過率との関係を示す。
【図２】従来法に従いＳｉＯ₂粉末が表面に付着した蛍光体の粒子構造を示す走査電子顕微鏡写真である。
【図３】本発明の蛍光体の粒子構造を示す走査顕微鏡写真である。
【図４】従来法に従いＳｉＯ₂粉末が表面に付着した蛍光体の粒子構造を示すＥＰＭＡ面分析写真である。右側がメイン元素であるＡｌの面分析結果を示し、左側がＳｉの面分析結果を示す。
【図５】本発明の蛍光体の粒子構造を示すＥＰＭＡ面分析写真である。右側がメイン元素であるＡｌの面分析結果を示し、左側がＳｉの面分析結果を示す。[0001]
BACKGROUND OF THE INVENTION
The present invention belongs to the technical field of phosphors used in plasma display panels (hereinafter, may be abbreviated as PDP), and particularly relates to a blue phosphor for a color PDP with improved deterioration over time in emission intensity.
[0002]
[Prior art]
The color PDP is a display that emits and emits color by applying vacuum ultraviolet rays emitted by gas discharge to red, green, and blue phosphors, and has a feature such as being thin and capable of large screens and high-speed display. It is expected to be used for wall mounting and high-definition television.
[0003]
As the blue phosphor for PDP, an aluminate phosphor is mainly used. This aluminate blue phosphor for PDP is subjected to heat treatment during the panel production (general conditions: 500 ° C. × 30 minutes). There is an urgent need for improvement in light emission characteristics caused by thermal deterioration and VUV deterioration caused by vacuum ultraviolet rays (VUV) when driving the panel, particularly improvement in light emission intensity. Against this background, optimization of the composition of the aluminate phosphor itself has been carried out, but the characteristics have not been improved.
[0004]
In order to maintain or improve the light emission characteristics of the phosphor, attempts have been conventionally made to protect the surface of the phosphor with various substances such as SiO ₂ (silica). For example, Japanese Patent Application Laid-Open No. 10-204429 (Japanese Patent Application No. 9-9645) describes that luminous efficiency and the like can be improved by attaching SiO ₂ powder to the particle surface of an aluminate-based blue phosphor used in a fluorescent lamp. ing. Such a protective material provided on the surface of the phosphor must transmit fluorescence generated by excitation light emission and sufficiently transmit excitation light to obtain high excitation efficiency. For fluorescent lamps, the aluminate blue phosphor was excited to emit light by ultraviolet rays of 254nm by Hg (mercury), the ultraviolet is transmitted through the SiO _2, the desired object even SiO ₂ is deposited by transmitting excitation light Will be achieved to some extent.
[0005]
However, in the case of PDP, the aluminate blue phosphor is caused to emit light by being excited by vacuum ultraviolet light of 147 nm or 172 nm with He—Xe or Ne. UV is transmitted through the SiO _2, the vacuum ultraviolet light is absorbed by the SiO ₂ without passing through the SiO _2. Therefore, SiO ₂ is considered to be unsuitable as a protective material for the blue phosphor for PDP using vacuum ultraviolet rays. Fluorides such as magnesium fluoride, calcium fluoride, and lithium fluoride are known as substances that transmit vacuum ultraviolet rays, but there is still a technology to uniformly coat these substances on phosphor powder (particles). Not done.
[0006]
[Problems to be solved by the invention]
An object of the present invention is to establish a new technique capable of preventing deterioration of light emission characteristics over time of a blue phosphor for PDP that emits light by excitation with vacuum ultraviolet rays.
[0007]
[Means for Solving the Problems]
As a result of repeated studies, the present inventor has found that the above problem can be solved by providing a protective film layer made of a thin and dense film that allows vacuum ultraviolet rays to pass through without being absorbed as much as possible. It has been derived.
[0008]
Thus, according to the present invention, there is provided a blue phosphor for a color plasma display panel, characterized in that the SiO ₂ coating film is formed to a thickness of 100 nm or less on the powder surface of the aluminate-based blue phosphor. Is done. Preferred examples of the aluminate-based blue phosphor to which the present invention is applied include a (Ba, Eu) O · MgO · 5Al ₂ O ₃ phosphor or a (Ba, Eu) O · MgO · 7Al ₂ O ₃ phosphor. It is.
[0009]
Furthermore, in the present invention, as one of the methods for producing the blue phosphor for a color plasma display panel as described above, the aluminate-based blue phosphor powder is immersed in a solution in which a silicon polymer is dissolved in an organic solvent and stirred. And a step of separating the phosphor and the solution after immersion, a step of drying the phosphor after separation, and a step of heating the phosphor after drying at 1000 ° C. or less in the presence of oxygen. Provide a method. According to a particularly preferred embodiment of the method for producing a blue phosphor for a color PDP of the present invention, the heating step includes a primary treatment heated at 150 ° C. to 600 ° C., and a secondary treatment heated at 500 ° C. to 1000 ° C. Consists of. A particularly preferred silicon polymer for use in the method for producing a blue phosphor for PDP of the present invention is perhydropolysilazane.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, the SiO ₂ used to protect the powder (particles) of the aluminate-based blue phosphor for PDP is based on a powder adhesion method that has been carried out exclusively, for example, in the above-mentioned JP-A-10-204429. The SiO ₂ powder is not scattered on the surface of the phosphor particles as in the case of the blue phosphor for the fluorescent lamp described, and the SiO ₂ coating film is dense with a thin thickness of 100 nm or less ( It is characterized by forming a uniform film. It has been confirmed by X-ray diffraction and surface analysis by EPMA that the SiO ₂ film in the present invention has such a structure (see Examples described later).
[0011]
Thus, the aluminate blue phosphor of the present invention in which the SiO ₂ coating film is densely formed with a thickness of 100 nm or less to protect the phosphor powder has a vacuum ultraviolet ray transmittance of 70% or more. It has been confirmed. Thus, the phosphor of the present invention realizes a long lifetime of the phosphor without reducing the transmittance of the vacuum ultraviolet ray as much as possible even in a high energy environment of the vacuum ultraviolet ray irradiation, and reducing the change in emission intensity with time.
[0012]
According to the present invention, the blue phosphor for PDP in which the SiO ₂ coating film is densely formed with a thickness of 100 nm or less on the powder surface of the aluminate-based blue phosphor, the raw phosphor is added to the silicon polymer solution according to the present invention. It can be obtained by subjecting the polymer to thermal decomposition under relatively mild conditions of 1000 ° C. or less after immersion. That is, in the method for producing a blue phosphor for a color PDP according to the present invention, as described in JP-A-10-204429, SiO ₂ is adhered to the phosphor powder (particles) in a powder state and heat treatment is performed. In addition, the aluminate-based blue phosphor powder is immersed in a solution in which a silicon polymer is dissolved in an organic solvent and stirred. Then, the phosphor and the solution are separated and the phosphor is dried. Each process includes heating at 1000 ° C. or lower (that is, in the air or in an oxygen-containing gas atmosphere).
[0013]
Here, according to a particularly preferable embodiment of the method of the present invention, a primary treatment in which the heat treatment is performed at 150 ° C. to 600 ° C. (preferably 150 ° C. to 500 ° C.), and further 500 ° C. to 1000 ° C. (preferably 500 ° C.). And a secondary treatment heated at a temperature of from 700 ° C. to 700 ° C. As a result, an SiO ₂ film can be formed in a temperature region that does not cause significant thermal degradation (primary treatment), and the SiO ₂ coating film can be densified by a high-temperature heat treatment (secondary treatment).
[0014]
The film thickness can be easily controlled by repeating the steps as described above as necessary. That is, after the primary treatment or the phosphor after the primary treatment and the secondary treatment is again immersed in an organic solvent solution of silicon polymer and stirred, and then subjected to the separation step and the drying step, the primary treatment or the primary treatment It uses for the heating process which consists of a secondary process. Of course, in the end, secondary treatment is performed to make the SiO ₂ dense.
[0015]
Thus, according to the present invention, the dense SiO ₂ capable of controlling the film thickness and transmitting vacuum ultraviolet rays by immersing the phosphor in the silicon polymer solution and coating the SiO ₂ film. The thin film can be formed. Here, the silicon polymer used in the present invention is a polymer of a silicon compound and adheres to the aluminate-based blue phosphor powder in a solution in an appropriate organic solvent, and is heated in the presence of oxygen as described above. A substance that can be decomposed to produce SiO ₂ when subjected to treatment is designated. Such a silicon polymer generally includes a chemical formula represented by Si—H, Si—O—H, or Si—N—H as a molecular structure, and preferred examples thereof include SiH _a N _b (a = 1). A perhydropolysilazane having a repeating unit represented by ˜3, b = 0 or 1).
[0016]
In the method of the present invention, after diluting such a silicon polymer with a suitable organic solvent (for example, xylene, dibutyl ether, etc.) to a required concentration (generally 0.001 to 2.0% by weight), A certain amount of phosphor powder is put into the solution (generally 1/10 to 1.0 by weight with respect to the silicon polymer solution) and stirred so as to be uniform. In this way, after bringing the phosphor powder (particles) and the silicon polymer solution into contact with each other for a certain time (generally, 10 to 30 minutes), the phosphor is separated from the solution (generally, filtration, After the phosphor is dried (generally, 100 to 120 ° C.), it is subjected to the heating step as described above.
[0017]
【Example】
Hereinafter, the present invention will be described with reference to examples in order to further clarify the features of the present invention, but the present invention is not limited to these examples.
Example 1: Film thickness and 5 wt% in a vacuum ultraviolet transmittance <br/> xylene (wt%) and 10 wt% in diluted been polysilazane (SiH ₂ NH) _n (Trademark: Tonen Corporation) was on CaF ₂ plate Spin coating, solvent xylene is removed by evaporation, firing at 350 ° C. (primary treatment), then firing again at 600 ° C. (secondary treatment) to form a SiO ₂ coating on the CaF ₂ plate did. The number of rotations during spin coating was 1000, 2000, and 4000.
[0018]
A plurality of samples obtained as described above were measured for film thickness using a scanning stylus thickness meter, and the value was defined as the film thickness. The transmittance of vacuum ultraviolet rays was determined from the ratio of the transmission intensity of the CaF ₂ plate before and after coating. The transmission intensity of vacuum ultraviolet rays was measured using a vacuum ultraviolet spectroscopy system manufactured by JASCO.
[0019]
The relationship between film thickness and transmittance is shown in Table 1 and FIG. As can be seen from FIG. 1, ultraviolet rays pass through the SiO ₂ film even when the film thickness increases, but in the case of vacuum ultraviolet rays, the transmittance increases significantly by making the SiO ₂ film 100 nm or less. And a transmittance of 70% or more is obtained. The film quality was confirmed using XRD (X-ray diffraction), and confirmed to be a SiO ₂ film.
[0020]
[Table 1]

[0021]
Example 2: SiO ₂ coating film Preparation of the formed phosphor <br/> Sample 2: To obtain the formed phosphor sample thickness 100nm or less of the SiO ₂ coating film, (Ba, Eu) O · MgO · 5Al ₂ O ₃ -based blue phosphor powder was weighed and immersed in a polysilazane solution adjusted to a concentration of 0.1 wt% with xylene. At this time, the polysilazane solution was 10 times the weight of the phosphor, stirred for about 10 minutes after mixing, and then the phosphor and the solution were separated by a filtration method. The separated phosphor was completely removed by evaporating xylene in a dryer at 120 ° C., and polysilazane was deposited on the phosphor. This phosphor is baked at 350 ° C. (primary treatment) in the atmosphere, and then again baked at 600 ° C. (secondary treatment) to form a dense SiO ₂ coating film having a film thickness of about 5 nm or less. To form.
[0022]
Sample 3: A phosphor similar to that described above was weighed and immersed in a polysilazane solution adjusted to a concentration of 0.1 wt% with xylene. At this time, the polysilazane solution was twice the weight of the phosphor. After stirring for about 10 minutes, xylene was evaporated and completely removed in a dryer at 120 ° C., and polysilazane was deposited on the phosphor. This phosphor was fired under the same conditions as described above, and a dense SiO ₂ coating film having a thickness of about 5 nm was formed on the phosphor surface.
[0023]
Samples 4 to 6: After the polysilazane concentration was set to 0.3 wt% and the treatment (primary treatment) was repeated, the secondary treatment similar to the above was finally performed, so that dense SiO having a film thickness of 20, 50, 100 nm or less _Two coating films were formed on the phosphor.
[0024]
The sample prepared as described above and the sample not coated were formed into a paint with an organic binder, applied, and fired (500 ° C.). These samples were irradiated with vacuum ultraviolet rays, and the change over time (VUV degradation) of the emission intensity by the vacuum ultraviolet irradiation was evaluated.
[0025]
The measurement results are shown in Table 2. However, the luminescence intensity is shown by the ratio of each luminescence intensity based on the sample before coating with SiO ₂ . The emission intensity was measured using a Minolta spectroradiometer. Thickness The film thickness, which was calculated thickness calculated from silazane amount and the specific surface area thickness A, the transmittance of the reduction rate and the SiO ₂ coating film of Example 1 of the fluorescence intensity after SiO ₂ coating Was defined as film thickness B.
[0026]
The film thicknesses A and B are almost the same, and it has been proved that a film thickness of 100 nm or less, preferably 20 nm or less is suitable for PDP using vacuum ultraviolet light as excitation light. In addition, it was proved that the maintenance ratio (deterioration by vacuum ultraviolet rays) (strength of irradiation for 22 hours with respect to irradiation for 0 hours) was improved from 43% to 60% or more by coating with SiO ₂ .
[0027]
[Table 2]

[0028]
Example 3: Comparative test of heat treatment temperature The aluminate blue phosphor undergoes thermal degradation due to heat treatment in addition to VUV degradation. Therefore, heat treatment at a high temperature leads to a decrease in the initial value, and it is necessary to consider the heat treatment temperature. Even when creating a SiO ₂ coating film, to create a SiO ₂ coating film at a temperature range that does not cause significant thermal degradation (primary treatment) dense the SiO ₂ coating film at a high temperature heat treatment (secondary treatment) A comparative test of the heat treatment temperature of the primary treatment and the secondary treatment was conducted.
[0029]
Sample 7: (Ba, Eu) O · MgO · 5Al ₂ O ₃ blue phosphor was immersed in a 0.1 wt% polysilazane solution diluted in a xylene solution, filtered and evaporated, then fired at 350 ° C as the primary treatment temperature A blue phosphor powder having a SiO ₂ coating film formed thereon was prepared.
[0030]
Sample 8: (Ba, Eu) O · MgO · 5Al ₂ O ₃ blue phosphor was immersed in a 0.1 wt% polysilazane solution diluted in a xylene solution, filtered and evaporated, and then fired at 600 ° C as the primary treatment temperature. A blue phosphor powder having a SiO ₂ coating film formed thereon was prepared.
[0031]
Sample 9: (Ba, Eu) O · MgO · 5Al ₂ O ₃ blue phosphor was immersed in a 0.1 wt% polysilazane solution diluted in a xylene solution, filtered and evaporated, then fired at 350 ° C as the primary treatment temperature After that, secondary firing was performed at 350 ° C. to prepare a blue phosphor powder on which an SiO ₂ coating film was formed.
[0032]
Samples 10 to 16: (Ba, Eu) O · MgO · 5Al ₂ O ₃ -based blue phosphor was immersed in a 0.1 wt% polysilazane solution diluted in a xylene solution, filtered, and evaporated, and the primary treatment temperature was 150 ° C to Firing was performed at 600 ° C., and then secondary firing was performed at 500 ° C. to 1100 ° C. to prepare a blue phosphor powder on which an SiO ₂ coating film was formed.
[0033]
Each phosphor sample prepared as described above and a phosphor sample not coated are coated with an organic binder, applied, and baked (500 ° C. × 30 min), and the change in emission intensity with vacuum ultraviolet irradiation over time ( (VUV degradation) was evaluated. The thickness of these samples are all, when calculated from silazane amount and the specific surface area (thickness A) is 5 nm, SiO ₂ coating of Example 1 and reduction rate of the fluorescence intensity after SiO ₂ coating When calculated from the transmittance of the film (film thickness B), it was 10 nm or less.
[0034]
Table 3 shows the results of these blue phosphors before irradiation with vacuum ultraviolet rays and after irradiation with vacuum ultraviolet rays for 22 hours. The emission intensity of the used blue phosphor untreated powder sample (before coating) was set to 100%.
[0035]
From Table 3, the sample subjected to the polysilazane treatment shows a maintenance rate of 60% or more relative emission intensity after irradiation with vacuum ultraviolet rays for 22 hours, compared with the sample not subjected to the polysilazane treatment. After the treatment with the sample, the sample treated at the secondary treatment temperature of 500 ° C. to 700 ° C. showed a high maintenance rate of 70% or more of the relative light emission intensity after being irradiated with vacuum ultraviolet rays for 22 hours.
[0036]
[Table 3]

[0037]
Example 4: The surface of the comparison <br/> phosphor surface treatment in order to compare the technique of surface treatment to be protected by SiO _2, heated by immersing the phosphor solution of polysilazane in accordance with the present invention (sintering) A comparison test between a sample in which the SiO ₂ coating film was prepared on the surface of the blue aluminate phosphor and the aluminate blue phosphor sample heated by attaching SiO ₂ powder to the phosphor as in the past went.
[0038]
Sample 17: (Ba, Eu) O · MgO · 5Al ₂ O ₃ series blue phosphor was added with 0.01 wt% of SiO ₂ having a particle size of 200 nm, dispersed in water, sufficiently stirred, and then phosphor powder Was collected by filtration, dried, sieved to deposit SiO ₂ and heated to 350 ° C. to obtain a blue aluminate phosphor.
[0039]
Samples 18 to 19: (Ba, Eu) O · MgO · 5Al ₂ O ₃ -based blue phosphor was added with SiO ₂ having a particle diameter of 200 nm at 0.1 to 1 wt%, dispersed in water, and sufficiently stirred, The phosphor powder was collected by filtration, dried, sieved and SiO ₂ was deposited, and then heated to 350 ° C. to obtain a blue aluminate phosphor.
[0040]
The sample prepared as described above and the uncoated sample were made into a paint with an organic binder, applied and fired (500 ° C. × 30 min), and then the change in emission intensity with vacuum ultraviolet irradiation (VUV degradation) was evaluated. Went. In order to evaluate the surface state of the phosphor, observation with a scanning electron micrograph and surface analysis with EPMA were performed.
[0041]
Table 4 shows the results of these blue phosphor samples before irradiation with vacuum ultraviolet rays and after irradiation with vacuum ultraviolet rays for 22 hours. Table 4 also shows the results when immersed in a polysilazane solution according to the present invention described above. The untreated powder sample of the blue phosphor used (before coating) was taken as 100%.
[0042]
As can be seen from Table 4, the samples 17, 18 and 19 prepared by the technique based on the adhesion of SiO ₂ powder have a low relative emission intensity after 22 hours of vacuum ultraviolet irradiation, and no VUV resistance is observed. Further, as shown in the electron micrograph of FIG. 2, adhesion of SiO ₂ powder was confirmed on the surface of the phosphor. Furthermore, as shown in FIG. 4, the distribution of elements constituting the phosphor was examined by surface analysis using EPMA. The right side of FIG. 4 shows the presence distribution of Al as a main element, and shows that Al is distributed as a whole except for dark portions (black portions) in the drawing. The left side of FIG. 4 shows the presence distribution of Si. If Si is evenly distributed, it corresponds to the presence distribution of Al, but only a partial correspondence is recognized, and Si exists uniformly (dense). It is understood that they are not.
[0043]
On the other hand, the sample (sample 11) created a SiO ₂ coating film by using polysilazane according to the present invention, deposition of SiO ₂ powder as shown in the electron micrograph of FIG. 3 is not confirmed. Further, as shown by EPMA surface analysis of Figure 5, SiO ₂ film since the presence distribution of Al is a main element of the phosphor (the right in FIG. 5) with the presence distribution of Si corresponds to the phosphor shape It is understood that exists uniformly (dense). Almost the same result is obtained for the sample 7. The above results do not simply mean that SiO ₂ needs to be adhered to the surface of the phosphor, but uniform (dense) SiO ₂ coating by treatment including immersion in a solution of a silicon polymer such as polysilazane. This indicates that film formation is necessary.
[0044]
[Table 4]

[0045]
Example 5: Other applications of the phosphor <br/> to confirm whether the effect of only specific phosphor with the formation of a thin film of SiO ₂ coatings according to the invention, the green used as a phosphor for a plasma display The phosphor was also subjected to VUV evaluation by forming a SiO ₂ coating film using polysilazane.
[0046]
Using a 2 (Zn, Mn) O.SiO ₂ system used for plasma displays as a green phosphor, a SiO ₂ coating is made using a 0.1 wt% polysilazane solution under the conditions for preparing the sample 11 of Example 3. A green phosphor (sample 20) having a film formed thereon was obtained. For comparison, a blue aluminate phosphor of Sample 11 of Example 3 was also prepared.
[0047]
These samples and each color sample that was not coated were made into a paint with an organic binder, applied, and baked (500 ° C. × 30 min), and then the change over time (VUV deterioration) of the emission intensity by vacuum ultraviolet irradiation was evaluated.
[0048]
Table 5 shows the results of the blue phosphor and the green phosphor prepared as described above before irradiation with vacuum ultraviolet rays and after irradiation with vacuum ultraviolet rays for 22 hours. For each color, the untreated powder sample (before coating) was taken as 100%.
[0049]
In the 2 (Zn, Mn) O.SiO ₂ -based green phosphor, the formation of the SiO ₂ coating film by the polysilazane treatment has an adverse effect, and only the aluminate-based blue phosphor is effective.
[0050]
[Table 5]

[Brief description of the drawings]
FIG. 1 shows the relationship between the film thickness of a SiO ₂ film obtained by the present invention and the transmittance of ultraviolet rays and vacuum ultraviolet rays.
FIG. 2 is a scanning electron micrograph showing the particle structure of a phosphor having SiO ₂ powder adhered to the surface in accordance with a conventional method.
FIG. 3 is a scanning micrograph showing the particle structure of the phosphor of the present invention.
FIG. 4 is an EPMA surface analysis photograph showing the particle structure of a phosphor having SiO ₂ powder adhered to the surface in accordance with a conventional method. The right side shows the surface analysis result of Al, which is the main element, and the left side shows the surface analysis result of Si.
FIG. 5 is an EPMA surface analysis photograph showing the particle structure of the phosphor of the present invention. The right side shows the surface analysis result of Al, which is the main element, and the left side shows the surface analysis result of Si.

Claims

A method for producing a blue phosphor for a color plasma display panel in which a SiO ₂ coating film is formed to a thickness of 100 nm or less on a powder surface of an aluminate-based blue phosphor, wherein a silicon polymer is dissolved in an organic solvent. A step of immersing and stirring the aluminate-based blue phosphor powder in the solution, a step of separating the phosphor from the soaked solution, a step of drying the phosphor after separation, and a phosphor present after drying in the presence of oxygen. Heating the substrate at 1000 ° C. or lower, wherein the silicon polymer is perhydropolysilazane.

2. The blue phosphor for a color plasma display according to claim 1, wherein the heating step comprises a primary treatment for heating at 150 to 600 ° C. and a secondary treatment for heating at 500 to 1000 ° C. 3. Production method.