JP2004137354A - Electroluminescent fluorescent substance - Google Patents

Electroluminescent fluorescent substance Download PDF

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Publication number
JP2004137354A
JP2004137354A JP2002302596A JP2002302596A JP2004137354A JP 2004137354 A JP2004137354 A JP 2004137354A JP 2002302596 A JP2002302596 A JP 2002302596A JP 2002302596 A JP2002302596 A JP 2002302596A JP 2004137354 A JP2004137354 A JP 2004137354A
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peak wavelength
time
wavelength
phosphor
fluorescent substance
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Japanese (ja)
Inventor
Hiroshi Fujimoto
藤本 央
Yosuke Miyashita
宮下 陽介
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Fujifilm Holdings Corp
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Fuji Photo Film Co Ltd
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  • Luminescent Compositions (AREA)
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Abstract

<P>PROBLEM TO BE SOLVED: To obtain an EL fluorescent substance for providing favorable donor acceptor (D-A) type luminescence. <P>SOLUTION: In the EL fluorescent substance composed of a sulfide base material, when PL luminescence of the fluorescent substance is subjected to time-resolved spectral analysis at 25°C, the EL fluorescent substance has results that the peak wavelength of emission spectrum is shifted to a long-wavelength side with time, the peak wavelength after 1 millisecond (ms) delay time is a longer wave than a wavelength being 10 nm shorter wavelength than the peak wavelength of a fluorescence spectrum by continuous excitation and the delay time in which a shift amount reaching the peak wavelength is shorter than 15 microseconds (μs). Or the EL fluorescent substance comprises zinc sulfide containing Cu as an activator. In the EL fluorescent substance, when PL luminescence of the fluorescent substance is subjected to time-resolved spectral analysis at 25°C, the EL fluorescent substance has results that the peak wavelength of emission spectrum is shifted to a long-wavelength side with time, the peak wavelength after 1 millisecond (ms) delay time is a long wave longer than 490 nm and the delay time in which a shift amount reaching the peak wavelength is shorter than 15 microseconds (μs). <P>COPYRIGHT: (C)2004,JPO

Description

【0001】
【発明の属する技術分野】
本発明は、硫化物、特に付活剤としてCuを含む硫化亜鉛を母体材料とするエレクトロルミネッセンス(EL)蛍光体に関し、詳しくは、発光効率が高いエレクトロルミネッセンス(EL)蛍光体(以下、EL蛍光体と略記することがある)に関する。
【0002】
【従来の技術】
EL蛍光体を用いた素子としては、従来より蛍光体粒子を電極に挟んで発光素子とした分散型EL素子と、蛍光体を薄膜層として電極で挟んだ薄膜型EL素子が知られている。分散型EL素子は薄膜型EL素子に比べて輝度が低いなどの欠点があるものの、薄膜型EL素子製造のような大がかりな真空設備を必要とせず、比較的安価かつ大面積の発光素子の作成が可能であることから、出来るだけ輝度を高めることで、各種表示用発光パネル、インテリアやエクステリア用の照明光源あるは補助光源、液晶ディスプレーのバックライトなどの用途への期待が大きい。
【0003】
このような背景から、硫化亜鉛を母体としたEL蛍光体の輝度向上のためにさまざまな改良が試みられてきた。例えば、特開平8−183954号には、積層欠陥を粒子内部に均一にかつ高密度に形成させ付活剤を高密度で該積層欠陥に析出させることで高輝度を得る方法が記載されている。また、特開2000−136381号には、第1焼成と第2焼成の間の中間体を静水圧によるラバープレスを行い、塩酸酸性条件下で洗浄するなどの方法で高輝度の粒子の作成を試みている。
【0004】
硫化亜鉛を母体としたEL蛍光体粒子の発光機構は、一般にClイオンあるいはAlイオンがドナーとして、Cuイオンがアクセプターとして機能するドナー・アクセプター(D−A)型の対発光機構であることが知られている。これらの発光中心を効率よく導入するために、例えば、特開平7−233368号には、共付活剤供給のためのフラックスとして、CuClやMgClを用いてClイオンを十分に粒子内に導入することで輝度を向上させることが記載されている。また特開平6−9954号には、フラックスとしてMgClに加えてNaClを用いD−A発光と共にSA発光(Zn空位とClイオンが発光中心となる発光)を重ねることで輝度向上を図ることが記載されている。
【0005】
しかしながら、これらの方法に従っても、必ずしも高輝度は得られない。多くの場合、高輝度のEL発光を得るための蛍光体の物性などが明確ではないので最終的にはEL素子化して輝度を測定評価することになる。高輝度発光を得るための粒子としては、そのサイズや結晶構造、積層欠陥などの形状が一次的な要件として考えられるが、好ましいD−A発光を得るためには付活剤に関する光特性がより重要な指標になる。硫化亜鉛系のフォトルミネッセンス(PL)発光としての特性は、例えば「蛍光体同学会編、蛍光体ハンドブック、II編第2章p151」にZnS:Cu,Alの4.2KにおけるPL時間分解の波長シフトの現象が記載されている。ここで議論されるPL発光の機構は紫外線励起によるD−A対発光に関するのもであり、EL発光との関係はわかっていない。EL発光の機構は、電界励起によるホットエレクトロンの生成と発光中心へのエネルギー移動が関連し、この特殊な励起過程を支配する光学的な特性はよく理解できていないのが実情である。
【0006】
【特許文献1】
特開平8−183954号
【特許文献2】
特開2000−136381号
【特許文献3】
特開平7−233368号
【特許文献4】
特開平6−9954号
【非特許文献5】
蛍光体同学会編、蛍光体ハンドブック、II編第2章p151
【0007】
【発明が解決しようとする課題】
本発明は、前記従来における諸問題を解決し、以下の目的を達成することを課題とする。即ち、本発明は、好適なD−A発光を得るためのEL蛍光体を提供することを目的とする。
【0008】
【課題を解決するための手段】
EL蛍光体粒子を合成する場合は、積層欠陥に硫化銅の針状結晶を高密度に析出させるといった、他の蛍光体とは異なる発光プロセスである電子供給源の形成に最大の注意が払われる場合が多い。しかしながら電子供給源が硫化銅の針状結晶であることの直接証拠を掴んだ記載の報告は少なく、また積層欠陥の高密度化が発光の必要条件であるか否かも十分には解明されていない。本発明はこのような粒子の外的な構成によらず、D−A発光に関する光学的な特性を基に、目的とする好適なEL蛍光体を得る手段を見いだしたものである。
【0009】
すなわち、上記課題は、以下の手段で達成された。
(1) 硫化物の母体材料からなるエレクトロルミネッセンス蛍光体において、
該蛍光体のフォトルミネッセンス発光を25℃において時間分解のスペクトル解析した際に、発光スペクトルのピーク波長が時間と共に長波長側にシフトし、遅延時間1ミリ秒(ms)後のピーク波長が、連続励起による蛍光スペクトルのピーク波長より10nm短波長となる波長より長波であり、かつ該ピーク波長に至るシフト量が半分になる遅延時間が15マイクロ秒(μs)より短いことを特徴とするエレクトロルミネッセンス蛍光体。
(2) 付活剤としてCuを含む硫化亜鉛からなるエレクトロルミネッセンス蛍光体において、
該蛍光体のフォトルミネッセンス発光を25℃において時間分解のスペクトル解析した際に、発光スペクトルのピーク波長が時間と共に長波長側にシフトし、遅延時間1ミリ秒(ms)後のピーク波長が490nmより長波であり、かつ該ピーク波長に至るシフト量が半分になる遅延時間が15マイクロ秒(μs)より短いことを特徴とするエレクトロルミネッセンス蛍光体。
(3) 上記エレクトロルミネッセンス蛍光体の共付活剤がCl又はAlであることを特徴とする前記(2)に記載のエレクトロルミネッセンス蛍光体。
(4) 上記エレクトロルミネッセンス蛍光体の平均粒子サイズが0.2μm〜15μmであることを特徴とする前記(1)〜(3)のいずれかに記載のエレクトロルミネッセンス蛍光体。
【0010】
【発明の実施の形態】
以下、本発明を詳細に説明する。
本発明のEL蛍光体は、そのフォトルミネッセンス(PL)発光スペクトルの時間分解解析を行うと、発光スペクトルのピーク波長が時間と共に長波化する。これはD−A対発光の場合の特徴と考えられるが、蛍光体の構造によってはこの長波化シフトを起こす時間的タイミングが異なることがわかった。すなわち、PL発光スペクトルの時間分解解析を25℃で行った場合、先ずEL発光として少なくとも10cd/m以上の輝度を得るためには、遅延時間1ミリ秒後のピーク波長が、連続励起による蛍光スペクトルのピーク波長より10nm短波長となる波長より長波側までシフトすること、特に490nmより長波側までシフトすることが重要であることがわかった。さらに、該ピーク波長に至るシフト量が半分になる遅延時間が15マイクロ秒より短い場合に、より高輝度発光が得られることがわかった。
【0011】
ここで、本発明のEL蛍光体は、上記遅延時間1ミリ秒後のピーク波長が、480nmより長波側までシフトすることが好ましく、より好ましくは490nmより長波側までシフトすることである。また、ピーク波長に至るシフト量が半分になる遅延時間は、13マイクロ秒より短いことが好ましく、より好ましくは、11マイクロ秒より短いことである。
【0012】
本発明のEL蛍光体の母体材料は硫化物であるが、具体的には、硫化亜鉛、硫化ストロンチウム、硫化カルシウム、或いはチオガレート系化合物、バリウムチオアルミネートなどの多元素化合物を指す。特に好ましくは硫化亜鉛(ZnS)であり付活剤はCuであり、共付活材はCl又はAlであることが好適である。
【0013】
こような組成の場合、EL発光として重要な波長は490〜510nmの間に存在する。すなわち、連続的な電界励起を行った場合に現れるこの発光波長はD−A間の最も代表的なエネルギーギャップが反映していると考えられる。本発明のD−A対発光のPL時間分解スペクトルは、遅延時間が1μs以内の発光の初期では440nm〜480nm付近の比較的短波長側にスペクトルのピークが存在する。そして、該スペクトルの発光ピーク波長が、次第に長波長側にシフトしてくるが、このとき遅延時間が1msの時のピーク波長が、連続励起による蛍光スペクトルのピーク波長より10nm短波長となる波長より短波長側にある場合、特に490nmより短波側にある場合は、EL発光の輝度が極めて低くなることがわかった。すなわち、より遅い時間でピーク波長が、連続励起による蛍光スペクトルのピーク波長より10nm短波長となる波長にシフト、特に490nmにシフトしたとしても、EL輝度は低い。更に、1ms後のピーク波長に至るシフト量が半分になる遅延時間が15マイクロ秒より長い場合は、490〜510nmに相当するEL発光の輝度が相対的に低下することがわかった。
【0014】
ここで、PL発光の時間分解の測定は、具体的には半値幅3μSの340nmのキセノンランプを用いて25℃にて行う。検出のタイミングは電気的なゲートを利用し遅延時間を調節する。
【0015】
この様にEL発光の輝度がPL発光の時間分解スペクトルの波長シフトタイミングと関連することは興味深い。この光学的特性は、EL蛍光体の母体材料として、硫化物母材材料、特に付活剤がCuイオンのZnS母体材料(好適には、共付活剤がClイオン又はAlイオンである母体材料。)を適用した場合に最も好適な結果が得られる。
【0016】
また、上記関係は、EL蛍光体の平均粒子サイズが0.2μm〜15μmの場合に特に顕著に現れる。粒子サイズが0.2μmより小さい場合はEL発光自体の輝度低下が大きく時間分解のスペクトルピークのずれタイミングの差はさほど優位ではなくなることがある。一方、平均粒子サイズが15μmより大きな場合も本発明の効果は比較的小さくなることがある。平均粒子サイズは好ましくは0.5μm〜12μmであり、この範囲で発光層の厚みは出来るだけ薄くなるように素子を構成することがよい。即ち、発光層の厚みは平均粒子サイズの5倍以下、1倍以上が好ましい。より好ましくは3倍以下、1倍以上である。
【0017】
また、上記関係は、例えば、蛍光体合成時の焼成条件(温度や雰囲気)或いは付活剤や共付活剤(フラックス)の添加量などにより制御することができる。
【0018】
本発明のEL蛍光体は、以下のようにして合成することができる。具体的には、例えば、硫化亜鉛を母体材料とするEL蛍光体の合成方法について説明する。まず、母体材料である硫化亜鉛は焼成法或いは液相法で合成できる。例えば焼成法において合成する場合、先ず硫化亜鉛母体材料に付活剤としてCuがドープされるが、ドープ量は亜鉛のモル量に対し0.03%〜0.5%が好ましい。より好ましくは0.05%〜0.2%である。共付活剤は一般にフラックスから提供される。フラックスとしては例えばCsCl、MgCl、KCl、CaCl、NaCl、BaCl、Al塩の場合はフッ化物、硝酸塩、硫酸塩などが挙げられるが、通常NHIを共存させるのが良い。これらの添加量は、焼成時の雰囲気や温度、時間によって適切に調整する必要があるが、通常硫化亜鉛のモル数に対し、1%〜50%量が好ましい。本発明のより好ましい範囲としては5%〜20%である。
【0019】
焼成温度は750℃〜1200℃の範囲が好ましく、特に多段焼成を行う場合、第1段目の焼成温度は900℃〜1200℃が好ましく、その後の焼成温度は750℃〜1000℃が好ましい。第1焼成時の温度が750℃より低い場合は、原料の硫化亜鉛の焼結が進まず、本発明の好ましい粒子サイズにすることが困難である。一方、1200℃以上の高温の場合は、硫化亜鉛の昇華が激しく、また粒子表面が粗く、均一性の欠ける粒子に成りやすいので好ましくない。焼成時間は1時間〜30時間の範囲で調整するのが好ましい。特に第1焼成時の温度が900℃以下の場合は最低4時間以上の時間が必要である。1100℃以上の高温の場合は、1時間〜8時間が好ましく、8時間以上の焼成を行うと、10μm以上の大粒子同士の融着が発生し、歪な粒子を形成しやすい。
【0020】
焼成時の雰囲気は必要に応じて様々に変えることが出来る。第1焼成時にはHSガスを通気させた還元雰囲気、あるいはカーボンを混在させた還元雰囲気が好ましい。空気雰囲気で焼成する場合は、気密性の高い容器を工夫して硫化亜鉛が簡単に酸化されないようにしなくてはならない。
【0021】
焼成後のEL蛍光体の結晶系は、主に閃亜鉛鉱型であり、一部ウルツ鉱型が含まれても良い。X線構造解析で結晶構造は確認できるが、ウルツ鉱型の閃亜鉛鉱型に対する比率は20%以下にすることが好ましい。ウルツ鉱型が20%を超える比率で存在すると、EL輝度は著しく低下することがある。
【0022】
第1焼成と第2焼成の間に出来る蛍光体の中間体は、種々の処理を施すことができる。例えば、ラバープレスによる静水圧等方プレスやボールミルのような異方性の衝撃を加えることで結晶に積層欠陥を導入して、発光サイトを高密度に分散させることができる。この場合できるだけ粒子を粉砕しないように注意を払う必要がある。
【0023】
焼成の後は、余分な塩の洗浄と、過剰な表面付加物の除去を行うことが好ましい。洗浄方法は蒸留水による水洗と、塩酸、酢酸、クエン酸、シュウ酸などの酸洗浄、あるいはZn及びCuに対する適度な安定度定数を有するキレート剤を用いて洗浄することも好ましい。
【0024】
一方、液相法において合成する場合、母体材料の原料としては、硝酸亜鉛、硫酸亜鉛、酢酸亜鉛などが挙げられるが、特に亜鉛のキレート剤として、エチレンジアミン四酢酸(EDTA)、やEDTA−OHを用いることは合成時の亜鉛徐放効果をもたらし、粒子サイズや形状をコントロールする点で好ましい。硫黄源としては、硫化ナトリウム、チオアセトアミドなどが挙げられる。上記キレート剤を用いる場合は、特に硫化ナトリウムが好ましく用いられる。上記原料の水溶液をオートクレーブ等を用いて高温高圧にして合成することが好ましく、反応温度としては150℃〜350℃が好ましい。反応時間は30分〜100時間で、サイズや粒子の形状に応じて反応条件を選択する。また、反応中に攪拌したり、高温高圧時に、インジェクター等の投入装置を用いて種々の添加剤を添加することも好ましい。この場合、反応の段階(例えば、核形成、粒子成長、表面修飾)に応じて、添加のタイミングを制御するのが良い。
【0025】
本発明のEL蛍光体は、例えば、蛍光表示材料として、各種ディスプレーやバックライトなどの表示装置に使用することができる。また発光色を制御することで各種照明装置に使用することができる。
【0026】
【実施例】
以下に実施例を挙げて本発明の特徴をさらに具体的に説明する。以下の実施例に示す材料、使用量、割合、処理内容、処理手順等は、本発明の趣旨を逸脱しない限り適宜変更することができる。したがって、本発明の範囲は以下に示す具体例により限定的に解釈されるべきものではない。
【0027】
(実施例1)
高純度の硫化亜鉛粉末100gに、蒸留水10mlに溶かした硫酸銅5水塩0.3gを添加してよく攪拌し、150℃で12時間乾燥させた。乾燥後、塩化マグネシウム6水塩を17gと塩化バリウム2水塩及び塩化ナトリウム4gを混ぜ、よく混合してから小型高純度ルツボに充填した。さらに該ルツボごと大型ルツボに入れ、大型ルツボ内にカーボン粉末を適宜量を変更して混在させた数種の水準を作製した。HSガス気流中900〜1150℃で3時間焼成した。焼成後、蒸留水500mlで3回水洗し、次いで塩酸でpH=1.5に調整した酸性水で3回洗浄後、更に蒸留水で8回水洗の後、120℃で4時間乾燥させた。凝集した粒子を除去するために篩いにかけ、平均粒径15〜20μmの蛍光体をそれぞれ得た。
【0028】
得られた各蛍光体は、スリット状の石英セルに入れてPL時間分解スペクトルの測定を行った。更に、30%シアノエチルセルロースのDMF溶液10gに上記各蛍光体12gを分散し、透明電極(ITO)が設けられたガラス板上に塗布した。80℃で乾燥後、同じく30%シアノエチルセルロースのDMF溶液にチタン酸バリウムの粉末を分散させたものを上記乾燥膜上に塗布し、乾燥後アルミニウム電極を蒸着によって設けたEL素子を各々作製した。
【0029】
PL時間分解の測定は、スペックス社製の、フルオロログII型蛍光分光光度計を用いて25℃の条件で実施した。励起光源としては半値幅3μSのキセノンフラッシュランプを用いた。時間分解において、遅延時間が1msの時のスペクトルのピーク波長及び、該ピーク波長までの波長シフトの有無と、シフトした場合のシフト量の半分に至るまでの遅延時間を表1に示す。尚、このときの連続励起による蛍光スペクトルのピーク波長は499nmであった。
【0030】
【表1】

Figure 2004137354
【0031】
表1からわかるように、水準1と2は遅延時間が1msの時のスペクトルのピーク波長がいずれも490nmより長波長であり、スペクトルはシフトしている。且つシフト量の半分に至るまでの遅延時間はいずれも15μs以内の短時間である。一方水準3は1ms後のピーク波長は490nmより長波長であるが、遅延時間が15μsより長い。また水準4は波長シフトするが1ms後のピーク波長が490nmより短波長である。また水準5は波長シフトを殆ど起こしていない。これらのEL発光輝度は、明らかに水準1、2が高く、それ以外は輝度が低いことがわかる。
【0032】
(実施例2)
高純度の硫化亜鉛粉末100gに、蒸留水10mlに溶かした硫酸銅5水塩0.3gを添加してよく攪拌し、150℃で12時間乾燥させた。乾燥後、塩化マグネシウム6水塩を17gと塩化バリウム2水塩及び塩化ナトリウム4gを混ぜ、よく混合してから小型高純度ルツボに充填した。さらに該ルツボごと大型ルツボに入れ、大型ルツボ内にカーボン粉末を適宜量を変更して混在させた数種の水準を作製した。HSガス気流中1100℃で1〜8時間焼成して粒子サイズを変更した。焼成後、蒸留水500mlで3回水洗し、次いで塩酸でpH=1.5に調整した酸性水で3回洗浄後、更に蒸留水で8回水洗の後、120℃で4時間乾燥させた。凝集した粒子を除去するために篩いにかけ、平均粒径1〜20μmの蛍光体をそれぞれ得た。
【0033】
得られた各蛍光体は、スリット状の石英セルに入れてPL時間分解スペクトルの測定を行った。更に、30%シアノエチルセルロースのDMF溶液10gに上記各蛍光体12gを分散し、透明電極(ITO)が設けられたガラス板上に塗布した。80℃で乾燥後、同じく30%シアノエチルセルロースのDMF溶液にチタン酸バリウムの粉末を分散させたものを上記乾燥膜上に塗布し、乾燥後アルミニウム電極を蒸着によって設けたEL素子を各々作製した。
【0034】
PL時間分解の測定において、遅延時間が1msの時のスペクトルのピーク波長及び、該ピーク波長までの波長シフトの有無と、シフトした場合のシフト量の半分に至るまでの遅延時間を表2に示す。なお、波長シフトはいずれの蛍光体にも観測された。
【0035】
【表2】
Figure 2004137354
【0036】
表2からわかるように、平均粒子サイズが15μm以下の蛍光体は、それ以上の平均粒子サイズの蛍光体に比べて本発明の条件を満たした場合に、顕著にEL輝度が向上することがわかる。(水準4,5に対して水準1,2,3)また、本発明の構成を満たさない場合はEL輝度は低いことがわかる。(水準6,7)
【0037】
【発明の効果】
以上、本発明によれば、EL蛍光体の輝度がPL時間分解の光特性でも予想可能となり、また粒子サイズが比較的小さい場合にその効果が顕著になることがわかった。従って、本発明の構成に従えばEL発光輝度の高い蛍光体を得ることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electroluminescence (EL) phosphor having a base material of sulfide, particularly zinc sulfide containing Cu as an activator, and more specifically, an electroluminescence (EL) phosphor (hereinafter referred to as EL fluorescence) having high luminous efficiency. May be abbreviated as body).
[0002]
[Prior art]
As an element using an EL phosphor, a dispersion type EL element in which phosphor particles are sandwiched between electrodes and a light emitting element and a thin film type EL element in which a phosphor is sandwiched between electrodes as a thin film layer are conventionally known. Dispersion type EL devices have disadvantages such as lower brightness than thin film type EL devices, but do not require large vacuum equipment as in the manufacture of thin film type EL devices, and produce light emitting devices that are relatively inexpensive and have a large area. Therefore, by increasing the luminance as much as possible, there are great expectations for applications such as light-emitting panels for various displays, illumination light sources for interiors and exteriors, auxiliary light sources, and backlights for liquid crystal displays.
[0003]
Against this background, various improvements have been attempted to improve the luminance of EL phosphors based on zinc sulfide. For example, Japanese Patent Application Laid-Open No. 8-183955 describes a method of obtaining high brightness by forming stacking faults uniformly and at high density inside the particles and precipitating activator on the stacking faults at high density. . Japanese Patent Laid-Open No. 2000-136381 discloses the production of high-brightness particles by a method such as performing rubber pressing with an isostatic pressure on an intermediate between the first baking and the second baking and washing under an acidic condition of hydrochloric acid. I'm trying.
[0004]
The light emission mechanism of EL phosphor particles based on zinc sulfide is generally known as a donor-acceptor (DA) type counter-light emission mechanism in which Cl ions or Al ions function as donors and Cu ions function as acceptors. It has been. In order to efficiently introduce these luminescent centers, for example, in JP-A-7-233368, CuCl 2 or MgCl 2 is used as a flux for supplying a coactivator, and Cl ions are sufficiently contained in the particles. It is described that the luminance is improved by the introduction. In JP-A-6-9954, brightness is improved by superimposing SA light emission (light emission centered on Zn vacancy and Cl ions) together with DA light emission using NaCl as a flux in addition to MgCl 2. Has been described.
[0005]
However, even with these methods, high brightness is not always obtained. In many cases, since the physical properties of the phosphor for obtaining EL light emission with high luminance are not clear, the luminance is finally measured and evaluated by forming an EL element. As the particles for obtaining high-intensity light emission, the size, crystal structure, shape of stacking faults, and the like are considered as primary requirements. However, in order to obtain preferable DA light emission, the light characteristics relating to the activator are better. It becomes an important indicator. The characteristics of zinc sulfide-based photoluminescence (PL) emission are, for example, the wavelength of PL time-resolved ZnS: Cu, Al at 4.2 K in “Phosphors Society, Phosphor Handbook, Chapter II, p151”. The phenomenon of shift is described. The mechanism of PL emission discussed here relates to DA pair emission by ultraviolet excitation, and the relationship with EL emission is not known. The mechanism of EL emission is related to the generation of hot electrons by electric field excitation and energy transfer to the emission center, and the optical characteristics that govern this special excitation process are not well understood.
[0006]
[Patent Document 1]
Japanese Patent Laid-Open No. 8-183954 [Patent Document 2]
JP 2000-136381 A [Patent Document 3]
JP-A-7-233368 [Patent Document 4]
JP-A-6-9954 [Non-Patent Document 5]
Fluorescent Material Society, Fluorescent Handbook, Chapter II, Chapter 2, p151
[0007]
[Problems to be solved by the invention]
An object of the present invention is to solve the conventional problems and achieve the following objects. That is, an object of the present invention is to provide an EL phosphor for obtaining suitable DA light emission.
[0008]
[Means for Solving the Problems]
When synthesizing EL phosphor particles, the greatest attention is paid to the formation of an electron source, which is a light emission process different from other phosphors, such as high-density deposition of copper sulfide needle crystals on stacking faults. There are many cases. However, there are few reports that have obtained direct evidence that the electron source is a needle-shaped copper sulfide crystal, and it has not been fully clarified whether the density of stacking faults is a necessary condition for light emission. . The present invention has found a means for obtaining a desired suitable EL phosphor on the basis of the optical characteristics relating to DA emission, regardless of the external configuration of such particles.
[0009]
That is, the said subject was achieved by the following means.
(1) In an electroluminescent phosphor made of a sulfide base material,
When the photoluminescence emission of the phosphor is subjected to time-resolved spectrum analysis at 25 ° C., the peak wavelength of the emission spectrum shifts to the longer wavelength side with time, and the peak wavelength after a delay time of 1 millisecond (ms) continues. Electroluminescence fluorescence characterized in that it is longer than a wavelength that is 10 nm shorter than the peak wavelength of the fluorescence spectrum due to excitation, and the delay time for halving the shift amount to the peak wavelength is shorter than 15 microseconds (μs) body.
(2) In an electroluminescent phosphor composed of zinc sulfide containing Cu as an activator,
When the photoluminescence emission of the phosphor was analyzed by time-resolved spectrum at 25 ° C., the peak wavelength of the emission spectrum shifted to the longer wavelength side with time, and the peak wavelength after 1 millisecond (ms) delay time was from 490 nm An electroluminescent phosphor characterized in that it has a long wave and a delay time for halving the shift amount to the peak wavelength is shorter than 15 microseconds (μs).
(3) The electroluminescent phosphor as described in (2) above, wherein the co-activator of the electroluminescent phosphor is Cl or Al.
(4) The electroluminescent phosphor according to any one of (1) to (3), wherein an average particle size of the electroluminescent phosphor is 0.2 μm to 15 μm.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
When the EL phosphor of the present invention is subjected to time-resolved analysis of its photoluminescence (PL) emission spectrum, the peak wavelength of the emission spectrum becomes longer with time. This is considered to be a feature in the case of DA pair emission, but it was found that the time timing for causing this long wave shift differs depending on the structure of the phosphor. That is, when the time-resolved analysis of the PL emission spectrum is performed at 25 ° C., in order to obtain a luminance of at least 10 cd / m 2 or more as EL emission, the peak wavelength after a delay time of 1 millisecond is the fluorescence due to continuous excitation. It has been found that it is important to shift from the wavelength that is 10 nm shorter than the peak wavelength of the spectrum to the longer wave side, particularly from 490 nm to the longer wave side. Furthermore, it has been found that when the delay time at which the shift amount to the peak wavelength is halved is shorter than 15 microseconds, higher luminance emission can be obtained.
[0011]
Here, in the EL phosphor of the present invention, the peak wavelength after the delay time of 1 millisecond is preferably shifted from 480 nm to the long wave side, more preferably from 490 nm to the long wave side. In addition, the delay time for halving the shift amount to the peak wavelength is preferably shorter than 13 microseconds, and more preferably shorter than 11 microseconds.
[0012]
The matrix material of the EL phosphor of the present invention is a sulfide. Specifically, it refers to a multi-element compound such as zinc sulfide, strontium sulfide, calcium sulfide, a thiogallate compound, or barium thioaluminate. Particularly preferred is zinc sulfide (ZnS), the activator is Cu, and the coactivator is Cl or Al.
[0013]
In such a composition, an important wavelength for EL emission exists between 490 and 510 nm. That is, it is considered that the most representative energy gap between DA is reflected in the emission wavelength that appears when continuous electric field excitation is performed. The PL time-resolved spectrum of DA pair emission of the present invention has a spectrum peak on the relatively short wavelength side in the vicinity of 440 nm to 480 nm at the beginning of emission with a delay time of 1 μs or less. The emission peak wavelength of the spectrum gradually shifts to the longer wavelength side. At this time, the peak wavelength when the delay time is 1 ms is shorter than the wavelength at which the peak wavelength of the fluorescence spectrum by continuous excitation is 10 nm shorter. It has been found that the luminance of EL light emission becomes extremely low when it is on the short wavelength side, particularly when it is on the short wave side from 490 nm. That is, even if the peak wavelength is shifted to a wavelength that is shorter by 10 nm than the peak wavelength of the fluorescence spectrum due to continuous excitation in a later time, in particular, the EL luminance is low. Furthermore, it was found that the luminance of EL light emission corresponding to 490 to 510 nm is relatively lowered when the delay time in which the shift amount to the peak wavelength after 1 ms is halved is longer than 15 microseconds.
[0014]
Here, the time-resolved measurement of PL emission is specifically performed at 25 ° C. using a 340 nm xenon lamp having a half width of 3 μS. The timing of detection uses an electrical gate to adjust the delay time.
[0015]
It is interesting that the luminance of EL emission is related to the wavelength shift timing of the time-resolved spectrum of PL emission. This optical characteristic is that a base material of an EL phosphor is a sulfide base material, particularly a ZnS base material in which the activator is Cu ion (preferably, a base material in which the coactivator is Cl ion or Al ion). The most favorable result is obtained when.
[0016]
Further, the above relationship appears particularly prominent when the average particle size of the EL phosphor is 0.2 μm to 15 μm. When the particle size is smaller than 0.2 μm, the luminance decrease of the EL emission itself is large, and the difference in time difference between the time-resolved spectrum peaks may not be so dominant. On the other hand, when the average particle size is larger than 15 μm, the effect of the present invention may be relatively small. The average particle size is preferably 0.5 μm to 12 μm, and it is preferable to configure the device so that the thickness of the light emitting layer is as thin as possible within this range. That is, the thickness of the light emitting layer is preferably 5 times or less and 1 time or more of the average particle size. More preferably, it is 3 times or less and 1 time or more.
[0017]
Further, the above relationship can be controlled by, for example, the firing conditions (temperature and atmosphere) at the time of phosphor synthesis or the amount of activator or coactivator (flux) added.
[0018]
The EL phosphor of the present invention can be synthesized as follows. Specifically, for example, a method for synthesizing an EL phosphor using zinc sulfide as a base material will be described. First, zinc sulfide, which is a base material, can be synthesized by a firing method or a liquid phase method. For example, when synthesizing by a firing method, Cu is first doped into the zinc sulfide base material as an activator, and the doping amount is preferably 0.03% to 0.5% with respect to the molar amount of zinc. More preferably, it is 0.05% to 0.2%. The coactivator is generally provided from a flux. Examples of the flux include fluoride, nitrate and sulfate in the case of CsCl, MgCl 2 , KCl, CaCl 2 , NaCl, BaCl 2 , and Al salt, but NH 4 I is usually preferably present together. These addition amounts need to be appropriately adjusted depending on the atmosphere, temperature, and time during firing, but are usually preferably 1% to 50% with respect to the number of moles of zinc sulfide. A more preferable range of the present invention is 5% to 20%.
[0019]
The firing temperature is preferably in the range of 750 ° C to 1200 ° C. In particular, when performing multi-stage firing, the first stage firing temperature is preferably 900 ° C to 1200 ° C, and the subsequent firing temperature is preferably 750 ° C to 1000 ° C. When the temperature during the first firing is lower than 750 ° C., sintering of the raw material zinc sulfide does not proceed and it is difficult to obtain the preferred particle size of the present invention. On the other hand, a high temperature of 1200 ° C. or higher is not preferable because zinc sulfide is extremely sublimated, and the particle surface is rough and tends to be non-uniform. The firing time is preferably adjusted in the range of 1 hour to 30 hours. In particular, when the temperature during the first firing is 900 ° C. or lower, a time of at least 4 hours is required. In the case of a high temperature of 1100 ° C. or higher, 1 hour to 8 hours are preferable, and when baking is performed for 8 hours or more, fusion of large particles of 10 μm or more is likely to occur and distorted particles are easily formed.
[0020]
The atmosphere during firing can be variously changed as necessary. A reducing atmosphere in which H 2 S gas is passed during the first firing or a reducing atmosphere in which carbon is mixed is preferable. When firing in an air atmosphere, a highly airtight container must be devised so that zinc sulfide is not easily oxidized.
[0021]
The crystal system of the EL phosphor after firing is mainly zinc blende type, and may partially include wurtzite type. Although the crystal structure can be confirmed by X-ray structural analysis, the ratio of wurtzite to zinc blende is preferably 20% or less. If the wurtzite type is present in a proportion exceeding 20%, the EL luminance may be significantly reduced.
[0022]
The phosphor intermediate formed between the first firing and the second firing can be subjected to various treatments. For example, stacking faults can be introduced into the crystal by applying an anisotropic impact such as isostatic pressing with a rubber press or a ball mill to disperse the light emitting sites with high density. In this case, care must be taken not to crush the particles as much as possible.
[0023]
After calcination, it is preferable to wash off excess salt and remove excess surface adducts. The washing method is preferably washing with distilled water and acid washing with hydrochloric acid, acetic acid, citric acid, oxalic acid, or a chelating agent having an appropriate stability constant for Zn and Cu.
[0024]
On the other hand, in the case of synthesizing in the liquid phase method, the raw materials of the base material include zinc nitrate, zinc sulfate, zinc acetate, and the like. In particular, as a chelating agent for zinc, ethylenediaminetetraacetic acid (EDTA) or EDTA-OH is used. The use is preferable in that it provides the effect of sustained release of zinc during synthesis and controls the particle size and shape. Examples of the sulfur source include sodium sulfide and thioacetamide. In the case of using the chelating agent, sodium sulfide is particularly preferably used. It is preferable to synthesize the aqueous solution of the raw material at a high temperature and high pressure using an autoclave or the like, and the reaction temperature is preferably 150 ° C to 350 ° C. The reaction time is 30 minutes to 100 hours, and the reaction conditions are selected according to the size and shape of the particles. It is also preferable to add various additives using a charging device such as an injector at the time of stirring during the reaction or at high temperature and pressure. In this case, the timing of addition may be controlled according to the stage of the reaction (for example, nucleation, particle growth, surface modification).
[0025]
The EL phosphor of the present invention can be used for display devices such as various displays and backlights, for example, as a fluorescent display material. Moreover, it can be used for various lighting devices by controlling the emission color.
[0026]
【Example】
The features of the present invention will be described more specifically with reference to the following examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.
[0027]
(Example 1)
To 100 g of high-purity zinc sulfide powder, 0.3 g of copper sulfate pentahydrate dissolved in 10 ml of distilled water was added and stirred well, and dried at 150 ° C. for 12 hours. After drying, 17 g of magnesium chloride hexahydrate, 4 g of barium chloride dihydrate and 4 g of sodium chloride were mixed and mixed well, and then filled into a small high-purity crucible. Further, the crucible was put together in a large crucible, and several kinds of levels were prepared by mixing carbon powder in the large crucible with appropriate amounts changed. Firing was performed at 900 to 1150 ° C. in a H 2 S gas stream for 3 hours. After calcination, it was washed with 500 ml of distilled water 3 times, then washed 3 times with acidic water adjusted to pH = 1.5 with hydrochloric acid, further washed 8 times with distilled water, and dried at 120 ° C. for 4 hours. In order to remove the aggregated particles, they were sieved to obtain phosphors having an average particle diameter of 15 to 20 μm.
[0028]
Each of the obtained phosphors was placed in a slit-like quartz cell, and PL time-resolved spectrum was measured. Further, 12 g of each phosphor was dispersed in 10 g of a 30% cyanoethyl cellulose DMF solution and applied onto a glass plate provided with a transparent electrode (ITO). After drying at 80 ° C., a dispersion of barium titanate powder in a DMF solution of 30% cyanoethyl cellulose was applied onto the dry film, and after drying, each EL element provided with an aluminum electrode by vapor deposition was produced.
[0029]
The PL time-resolved measurement was carried out at 25 ° C. using a fluorolog II type fluorescence spectrophotometer manufactured by Specs. As the excitation light source, a xenon flash lamp having a half width of 3 μS was used. Table 1 shows the peak wavelength of the spectrum when the delay time is 1 ms, the presence / absence of a wavelength shift to the peak wavelength, and the delay time until the shift amount reaches half when shifted. At this time, the peak wavelength of the fluorescence spectrum by continuous excitation was 499 nm.
[0030]
[Table 1]
Figure 2004137354
[0031]
As can be seen from Table 1, in Levels 1 and 2, the peak wavelength of the spectrum when the delay time is 1 ms is longer than 490 nm, and the spectrum is shifted. In addition, the delay time until reaching half of the shift amount is a short time within 15 μs. On the other hand, in Level 3, the peak wavelength after 1 ms is longer than 490 nm, but the delay time is longer than 15 μs. Level 4 has a wavelength shift, but the peak wavelength after 1 ms is shorter than 490 nm. Level 5 hardly causes a wavelength shift. It can be seen that these EL emission luminances are clearly high in levels 1 and 2 and low in other cases.
[0032]
(Example 2)
To 100 g of high-purity zinc sulfide powder, 0.3 g of copper sulfate pentahydrate dissolved in 10 ml of distilled water was added and stirred well, and dried at 150 ° C. for 12 hours. After drying, 17 g of magnesium chloride hexahydrate, 4 g of barium chloride dihydrate and 4 g of sodium chloride were mixed and mixed well before filling into a small high-purity crucible. Furthermore, the crucible was put in a large crucible, and several kinds of levels were prepared by mixing carbon powder in the large crucible by changing the appropriate amount. The particle size was changed by firing at 1100 ° C. for 1 to 8 hours in a H 2 S gas stream. After calcination, it was washed with 500 ml of distilled water three times, then washed three times with acidic water adjusted to pH = 1.5 with hydrochloric acid, further washed eight times with distilled water, and dried at 120 ° C. for 4 hours. In order to remove the aggregated particles, they were sieved to obtain phosphors having an average particle diameter of 1 to 20 μm.
[0033]
Each of the obtained phosphors was placed in a slit-like quartz cell, and PL time-resolved spectrum was measured. Further, 12 g of each phosphor was dispersed in 10 g of a 30% cyanoethyl cellulose DMF solution and applied onto a glass plate provided with a transparent electrode (ITO). After drying at 80 ° C., a dispersion of barium titanate powder in a DMF solution of 30% cyanoethyl cellulose was applied onto the dry film, and after drying, each EL element provided with an aluminum electrode by vapor deposition was produced.
[0034]
Table 2 shows the peak wavelength of the spectrum when the delay time is 1 ms, the presence / absence of a wavelength shift to the peak wavelength, and the delay time until the shift amount reaches half in the case of the PL time resolution measurement. . Note that wavelength shift was observed in all phosphors.
[0035]
[Table 2]
Figure 2004137354
[0036]
As can be seen from Table 2, a phosphor having an average particle size of 15 μm or less has a significantly improved EL luminance when the conditions of the present invention are satisfied as compared with a phosphor having an average particle size of more than 15 μm. . (Levels 1, 2 and 3 with respect to levels 4 and 5) It can also be seen that the EL luminance is low when the configuration of the present invention is not satisfied. (Level 6, 7)
[0037]
【The invention's effect】
As described above, according to the present invention, it has been found that the luminance of the EL phosphor can be predicted even with PL time-resolved light characteristics, and the effect becomes remarkable when the particle size is relatively small. Therefore, according to the configuration of the present invention, a phosphor with high EL emission luminance can be obtained.

Claims (4)

硫化物の母体材料からなるエレクトロルミネッセンス蛍光体において、
該蛍光体のフォトルミネッセンス発光を25℃において時間分解のスペクトル解析した際に、発光スペクトルのピーク波長が時間と共に長波長側にシフトし、遅延時間1ミリ秒(ms)後のピーク波長が、連続励起による蛍光スペクトルのピーク波長より10nm短波長となる波長より長波であり、かつ該ピーク波長に至るシフト量が半分になる遅延時間が15マイクロ秒(μs)より短いことを特徴とするエレクトロルミネッセンス蛍光体。
In an electroluminescent phosphor made of a sulfide base material,
When the photoluminescence emission of the phosphor is subjected to time-resolved spectrum analysis at 25 ° C., the peak wavelength of the emission spectrum shifts to the longer wavelength side with time, and the peak wavelength after a delay time of 1 millisecond (ms) continues. Electroluminescence fluorescence characterized by being longer than a wavelength that is 10 nm shorter than the peak wavelength of the fluorescence spectrum due to excitation and having a delay time of halving the amount of shift to the peak wavelength less than 15 microseconds (μs) body.
付活剤としてCuを含む硫化亜鉛からなるエレクトロルミネッセンス蛍光体において、
該蛍光体のフォトルミネッセンス発光を25℃において時間分解のスペクトル解析した際に、発光スペクトルのピーク波長が時間と共に長波長側にシフトし、遅延時間1ミリ秒(ms)後のピーク波長が490nmより長波であり、かつ該ピーク波長に至るシフト量が半分になる遅延時間が15マイクロ秒(μs)より短いことを特徴とするエレクトロルミネッセンス蛍光体。
In an electroluminescent phosphor composed of zinc sulfide containing Cu as an activator,
When time-resolved spectrum analysis of the photoluminescence emission of the phosphor was performed at 25 ° C., the peak wavelength of the emission spectrum shifted to the longer wavelength side with time, and the peak wavelength after a delay time of 1 millisecond (ms) was from 490 nm An electroluminescent phosphor characterized by being a long wave and having a delay time of halving the amount of shift to the peak wavelength shorter than 15 microseconds (μs).
上記エレクトロルミネッセンス蛍光体の共付活剤がCl又はAlであることを特徴とする請求項2に記載のエレクトロルミネッセンス蛍光体。The electroluminescent phosphor according to claim 2, wherein the co-activator of the electroluminescent phosphor is Cl or Al. 上記エレクトロルミネッセンス蛍光体の平均粒子サイズが0.2μm〜15μmであることを特徴とする請求項1〜3のいずれかに記載のエレクトロルミネッセンス蛍光体。4. The electroluminescent phosphor according to claim 1, wherein an average particle size of the electroluminescent phosphor is 0.2 μm to 15 μm.
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