JP3702863B2 - White light emitting device - Google Patents

Description

【００２４】
のようなスペクトルを持っている。ｅｘｐ（）の中に１／λがあるから、すぐに立ち上がり最大値λ_ｍａｘにいたるが、その後１／λ^５のなだらかな減衰になる。そのように広いスペクトルをもち多様な色を含むので目に優しい白色となる。演色性というのは白色発光素子の発光スペクトルがどれほど式（１）の分布に近いかということである。蛍光灯は当然白熱電球よりも演色性は劣り８６％程度である。ということは８６％を越えないと蛍光灯以上に優れた白色とは言えない訳である。
【００２５】
従来例のＡやＢのように青色発光ＬＥＤの青色光の一部を黄色光に変換することによる白色発光素子では高い演色性を得る事は難しい。その理由は二つある。
【００２６】
［理由１］ 青色光発光素子（ＺｎＳｅ−ＬＥＤ、ＩｎＧａＮ−ＬＥＤ）が発光するのは青色光の単色であるから本来狭いスペクトル幅しか持っていない。その狭スペクトル青色光が一方にあるから演色性が悪い。
【００２７】
［理由２］ 青色光を変換して得られた黄色光に、緑色成分や赤色成分が不足している。ＹＡＧで変換した蛍光は黄色であって緑や赤が欠ける。また不純物ドープＺｎＳｅで変換した蛍光も黄色であって緑成分を全く含まない。赤成分も不足している。やはり白熱電球にとって代わろうとするのであれば、赤や緑など広範な範囲のスペクトルを平等に含むものでなければならない、と思う。
【００２８】
【課題を解決するための手段】
本発明の白色発光素子は、紫外光を発生するＩｎＧａＮ−ＬＥＤと、塊状のＺｎＳ第１蛍光板と、塊状のＺｎＳＳｅ又はＺｎＳｅ第２蛍光板とよりなり、ＩｎＧａＮ−ＬＥＤの紫外光によって、ＺｎＳ第１蛍光板を励起して青色光蛍光を発生させ、青色光蛍光によってＺｎＳｅ又はＺｎＳＳｅ第２蛍光板を励起して黄色蛍光を発生させ、外部に青色光蛍光と黄色光蛍光を放出することによって白色を合成する。ＺｎＳＳｅというのは正確にはＺｎＳ_ｘＳｅ_１−ｘのことであるが本明細書においては簡単のため混晶比ｘを省略することもある。
【００２９】
つまり本発明には３種類の発光部分がある。
Ａ．紫外光（ＵＶ）発光ＩｎＧａＮ−ＬＥＤ
Ｂ．青色光（Ｂ）蛍光発生ＺｎＳ第１蛍光板
Ｃ．黄色光（Ｙ）蛍光発生ＺｎＳＳｅ（ＺｎＳｅ）第２蛍光板
そして外部へ出る光Ｗは青色光と黄色光だけとする。つまりＷ＝Ｂ＋Ｙとする。
【００３０】
紫外光用のＬＥＤを使う。それが一つの特徴である。紫外光は可視光ではないから外部に出てはいけない。紫外光は外部に出ないようにし第１蛍光板で全部を青色の蛍光に変換させるようにする。青色光の蛍光によって第２蛍光板を励起して黄色光を発生させる。だから蛍光現象を２段階で利用するのである。多くの準位からの電子遷移に基づく蛍光はもともとブロードなスペクトルをもつ。ＬＥＤ光のような急峻なスペクトルを持たない。青色光も黄色光も蛍光なのでスペクトルが広い。広いスペクトルが重なり合うので広い分布の白色ができる。当然に白熱電球の分布に似てくる。だから演色性も高揚する。
【００３１】
紫外光の発光波長は３４０ｎｍ〜４００ｎｍのものとする。ＩｎＧａＮのＬＥＤでもＧａＮの比率の高いＬＥＤを用いる必要がある。そのような短波長の紫外光はＺｎＳｅ系のＬＥＤでは発生させることができない。ＩｎＧａＮに限定される。
【００３２】
蛍光は励起光より必ず波長が長くなるのであるから、青色光の蛍光を得るためには青色光のＬＥＤでは役に立たない。それよりもエネルギーの高い、紫外光の光源が不可欠である。幸いな事に赤色発光素子として開発されたＩｎＧａＮのＬＥＤは青色紫色など可視光を発光することもできるがＧａの混晶比を増やすことによって紫外光をも出す事ができる。本発明はＩｎＧａＮ系で紫外光を発光する白色発光素子を根元的な光源として２段階蛍光現象を利用して演色性の優れた白色を作り出そうとするものである。
【００３３】
紫外光ＬＥＤ＋２段階蛍光が本発明の骨子である。紫外光は外部に出ず蛍光の二種類（青蛍光、黄蛍光）が外部に出てゆく。蛍光はもともとスペクトル幅が広いので演色性という点では有利なのである。そのように２段階蛍光によって白色を創造するというのは本発明が最初である。真に優れた着想であると言わねばならない。
【００３４】
【発明の実施の形態】
本発明者は上記の課題を解決するために蛍光材を検討した。その結果、３族元素または７族元素が混入したＺｎＳ結晶を紫外線で励起して、青色光を発光させ、その青色光で３族または７族元素が混入したＺｎＳｅ（またはＺｎＳＳｅ混晶）を励起して黄色光を発生させ、青色光と黄色光を混ぜ合わせるようにした白色発光素子を発明した。
【００３５】
本発明は、一つのＬＥＤ光源と２種類の蛍光を利用している。→によって蛍光板の変換作用を表現すると本発明の素子の作用は以下のように略記できる。

【００３６】
第１の蛍光材はバンドギャップの広い半導体であるＺｎＳであり、第２の蛍光材はよりバンドギャップの狭い半導体であるＺｎＳ_ｘＳｅ_１−ｘ（０≦ｘ＜１）である。
【００３７】
図７はその原理を説明するための略図である。下からＩｎＧａＮ−ＬＥＤ／ＺｎＳ／ＺｎＳＳｅよりなる構造である。ＬＥＤの紫外光でＺｎＳを励起して青色光蛍光を発生させ、青色光によってＺｎＳＳｅを励起して黄色光蛍光を発生させる２段階蛍光を示す。
【００３８】
図８は下からＩｎＧａＮ−ＬＥＤ／ＺｎＳ／ＺｎＳｅ（ＺｎＳＳｅ）よりなる構造で、発光波長の領域を略示したものである。３４０ｎｍ〜４００ｎｍのＩｎＧａＮ・ＬＥＤ紫外光を、ＺｎＳで４８０ｎｍ中心の青色光に変え、青色光をＺｎＳＳｅによって５８５ｎｍ中心の黄色光に変換している。３４０ｎｍはＺｎＳのバンドギャップであり、それ以上の波長でＺｎＳを励起すべきだということを意味する。４６５ｎｍはＺｎＳｅのバンドギャップ波長で、それ以上の波長でＺｎＳｅを励起すべきだということを意味する。
【００３９】
［１．第１蛍光板（ＺｎＳ）］
ＺｎＳの結晶にＡｌ、Ｉｎ、Ｇａ、Ｃｌ、Ｂｒ、Ｉの何れかの不純物を添加すると蛍光を生ずるようになる。それはバンドギャップエネルギーより低いエネルギーの蛍光であり伝導帯の下にできるドナーと価電子帯の上にできるアクセプタの間で電子が遷移することによっておこる蛍光だと考えられる。上記の不純物はそのような比較的深いドナー、アクセプタを形成するのであろうと考えられる。浅いレベルであれば単に伝導性を与えるだけであるが深いレベルなので電子、正孔が安定して存在し光照射によってやっと励起されてドナー・アクセプタ遷移を引き起こすのであろう。レベルがたくさんできるので蛍光の準位も多数あり、それがスペクトルの幅を広くしているのであろう。
【００４０】
ＺｎＳからの青色光（蛍光）は中心波長が４８０ｎｍ近辺の光であるが、波長スペクトルは青−緑−黄緑に及ぶ広い波長分布を持っている。それは多数のレベル間の遷移が重畳したものであるからである。
【００４１】
ＺｎＳは４００ｎｍ以下のエネルギーの高い紫外光よって励起されて先述の４８０ｎｍに中心をもち青・緑・黄緑に広がる蛍光を発生する。それよりエネルギーの低い青色光のＬＥＤ光ではＺｎＳから蛍光を引き出すことができない。だからＬＥＤは４００ｎｍ以下の紫外光とする。励起光の波長の下限（エネルギーの上限）は３４０ｎｍである。その理由については後に詳しく述べる。
【００４２】
紫外光の定義であるが、厳密に定義するものもあり厳密でないものもある。１３ｎｍ〜３９３ｎｍが紫外光だという定義もある。そうなると本発明が励起光として用いる波長帯（３４０ｎｍ〜４００ｎｍ）の内３９３ｎｍ〜４００ｎｍの７ｎｍ分は紫外光でなく紫色と言うべきである。しかし、それは面倒なので、本明細書では４００ｎｍまでを紫外光と表現することもある。
【００４３】
［２．第２蛍光板（ＺｎＳ_ｘＳｅ_１−ｘ）］
ＺｎＳ_ｘＳｅ_１−ｘ（０≦ｘ＜１；ＺｎＳｅを含む）の結晶にＡｌ、Ｉｎ、Ｇａ、Ｃｌ、Ｂｒ、Ｉの何れかの不純物を添加すると蛍光を生ずるようになる。それはバンドギャップエネルギーより低いエネルギーの蛍光であり伝導帯の下にできるドナーと価電子帯の上にできるアクセプタの間で電子が遷移することによっておこる蛍光だと考えられる。上記の不純物はそのような比較的深いドナー、アクセプタを形成するのであろうと考えられる。浅いレベルであれば単に伝導性を与えるだけであるが深いレベルなので電子、正孔が安定して存在し光照射によってやっと励起されてドナー・アクセプタ遷移を引き起こすのであろう。レベルがたくさんできるので蛍光の準位も多数あり、それがスペクトルの幅を広くしている。そのようなことは第１蛍光材のＺｎＳと同様である。しかしＺｎＳよりバンドギャップが狭いから蛍光のエネルギーも低く（波長が長く）なる。
【００４４】
蛍光材としてのＺｎＳｅ（ＺｎＳＳｅ）は４８０ｎｍ近辺の波長の光で効率よく励起され中心波長５８５ｎｍの黄色光を発する。中心波長は５８５ｎｍであるが実際はその両側に幅広く広がっている。ＺｎＳｅ蛍光の波長スペクトルは黄緑−黄色−赤色に及ぶ広い波長分布を持っている。
【００４５】
ＺｎＳｅに比率ｘでＺｎＳを混合したＺｎＳＳｅはバンドギャップがＺｎＳｅより広いので不純物ドープによるドナー・アクセプタの高さの差も広くなり蛍光の波長が短くなる。ＺｎＳＳｅの場合は、４８０ｎｍより短い光でよく励起されて５８５ｎｍより短い波長にピークをもつ蛍光を発生する。つまり赤成分が弱くなり黄色成分が増える。目的とする白色のスペクトルによって第２蛍光板の硫黄Ｓの混晶比ｘを０から増やすことにすればよい。
【００４６】
［３．二つの蛍光の合成］
第１蛍光板のＺｎＳからの青色光と第２蛍光板ＺｎＳｅ（又はＺｎＳＳｅ）からの黄色光を合わせると、可視領域の全域をカバーする波長スペクトルを持つ白色となる。いずれもスペクトル幅の広い蛍光を組み合わせたものだから演色性の高い白色を実現することができる。
【００４７】
そのために第１蛍光板（ＺｎＳ）の厚みＦ、第２蛍光板（ＺｎＳＳｅ）の厚みＨには、ある制限が課されることになる。
【００４８】
それはＩｎＧａＮ−ＬＥＤの紫外光が第１蛍光板で完全に吸収されること、青色光蛍光が第２蛍光板で完全に吸収されない事という二重の条件が必要だからである。
【００４９】
ＬＥＤからの光、第１蛍光板からの光は二次元的な広がりを持つが、ここでは簡単に一次元の問題として考える。ＬＥＤの紫外光のＺｎＳ第１蛍光板での吸収係数をαとする。ＺｎＳ蛍光板の端から内部に向けて縦方向に座標ｚを考える。第１蛍光板の始端での強度を１とすると第１蛍光板内部ｚ点での紫外光の強度はｅｘｐ（−αｚ）によって表現される。蛍光板の裏側では（ｚ＝Ｆ）紫外線強度はｅｘｐ（−αＦ）となる。
【００５０】
紫外線が全部吸収されて青色光蛍光に変換されるのが最も良い。しかし上の値が０にはならないから、せいぜい０．１以下あるいは０．０１以下というように決める。例えば第１蛍光板の終わりでの紫外線強度が０．１以下だとするべきならば、
【００５１】
ｅｘｐ（−αＦ）≦０．１ （２）
【００５２】
となって、第１蛍光板の厚みの範囲が決まる。
【００５３】
Ｆ≧２．３／α （３）
【００５４】
となるし、０．０１以下だとすべきならば
【００５５】
Ｆ≧４．６／α （４）
【００５６】
となる。そのように第１蛍光板の厚みの下限は決まるが上限は決まらない。厚すぎるとコスト高になるので上限は経済性などから決めれば良いことである。
【００５７】
第２蛍光板は少し事情が異なる。第２蛍光板（ＺｎＳＳｅまたはＺｎＳｅ）青色光蛍光の吸収係数をβとする。第２蛍光板の始端ｚ＝Ｆでの青色光蛍光の強度をＢ_０とすると、蛍光板内部の点（Ｆ＜ｚ≦Ｆ＋Ｈ）での青色光蛍光の強度は、Ｂ_０ｅｘｐ（−β（ｚ−Ｆ））によって表現される。青色光蛍光から黄色光蛍光への第２蛍光板での変換効率をγとする。黄色光生成は青色光の強度に比例するから、黄色光蛍光の強度Ｙ（ｚ）は
【００５８】
ｄＹ＝γＢ_０ｅｘｐ（−β（ｚ−Ｆ））ｄｚ （５）
【００５９】
という微分方程式を満足する筈である。これは簡単に積分することができて
【００６０】
Ｙ＝（γＢ_０／β）｛１−ｅｘｐ（−β（ｚ−Ｆ））｝ （６）
【００６１】
となる。第２蛍光板（ＺｎＳｅまたはＺｎＳＳｅ）の終端ｚ＝Ｆ＋Ｈでの青色光蛍光Ｂと、黄色光蛍光Ｙの強度はそれぞれ
【００６２】
Ｂ＝Ｂ_０ｅｘｐ（−βＨ） （７）
【００６３】
Ｙ＝（γＢ_０／β）｛１−ｅｘｐ（−βＨ）｝ （８）
【００６４】
となる訳である。本発明の白色は、青色光蛍光Ｂと黄色光蛍光Ｙを適当な比率で加え合わせることによって合成される。その比率は
【００６５】
【数２】

【００６６】
によって与えられる。
【００６７】
β、γは不純物ドープ量などで変化させる事ができるパラメータである。Ｈは第２蛍光板の厚みである。Ｂ／Ｙ比（青／黄の比率）を変更したいという場合、ドープ量を変化させることも有効であるが第２蛍光板厚みＨを変化させることによっても可能である。
【００６８】
逆に言えば、予め所望のＢ／Ｙ比が与えられ、変換効率β、γも決まっているのであれば、式（９）が第２蛍光板の厚みＨを決める決定方程式だということになる。
【００６９】
［４．耐水性の問題］
ＹＡＧの場合でもそうであるが蛍光剤というのはできるだけ光を受け易いように微小な粉末にして透明の媒体の中に薄く分散する。それが普通の使い方である。しかしＺｎＳ系やＺｎＳｅ系の蛍光剤は耐水性に欠ける。つまり粉末にすると水を吸収してしまい劣化する。ＺｎＳ、ＺｎＳｅが蛍光剤としてこれまで利用されなかったのは不純物添加によって蛍光を発生するということが分かっても強い吸収性のため信頼性が低く蛍光剤として使いにくいという問題があったからである。
【００７０】
だからＺｎＳｅやＺｎＳはＹＡＧのような蛍光剤としての実績がない。しかし考えてみれば蛍光剤を微小粉末にしなければならないのは、それが光に対し不透明だからである。不透明な蛍光剤で光が中へ入って行かないので、できるだけ直径の小さい微粉末とする必要があったのである。微小粉末にするとプラスチックやガラスに分散してあっても容易に吸水して急速に劣化する。そのような理由で蛍光剤は吸水性があってはならないとされて来たのである。
【００７１】
［５．塊状の蛍光板］
粉末は実効的な表面積が広いので水が容易に滲みる。表面積が狭ければ水が内部へ入りにくいはずである。ＺｎＳやＺｎＳｅの著しい吸水性を克服するには微小粉末にせず、その反対で粒径の大きい多結晶にする、あるいは全体を単結晶にすれば良いのである。粒界から水が入り浸透するのだから多結晶でも粒径が大きいと吸水性は減るはずである。単結晶にすれば、より吸水性は減少するであろう。表面から水が浸透するとしても内部まで水が入るのには時間がかかるし充分に厚いと最早内部まで水が浸透できない。
【００７２】
本発明者は、粉末状の蛍光剤を使用する代わりに、塊状の単結晶もしくは多結晶ＺｎＳ（若しくはＺｎＳｅ）から構成される蛍光板を使用すればよい、ということに気付いた。そうすれば、蛍光材体積に対する表面積の割合が非常に小さくなるので、耐水性が格段に向上する。塊状の蛍光材をプラスチックやガラスで被覆すれば容易に水が浸透できないはずである。
【００７３】
［６．励起光の波長の制限］
従来の蛍光物質のように微粉末として分散したのは励起光に対し、それが不透明であり内部へ入って行かないものだからである。本発明では吸収性を克服するため塊状の蛍光材を用いる。塊状とすると光に対して不透明であってはいけない。不透明だと励起光が内部へ入らず蛍光物質の大部分が無駄になるからである。ということは励起光に対し蛍光材を透明としなければならないということである。それは新しい拘束条件となる。
【００７４】
どうすればよいのか？もともとＺｎＳｅやＺｎＳは可視光に対して透明に近く（わずかに黄色を帯びる）て、ある程度の紫外光に対しても透明である。しかしＺｎＳ、ＺｎＳｅの吸収端波長（バンドギャップ波長）より短い紫外光はすぐに吸収してしまう。それはどのようなものでも共通の性質である。そこで本発明は励起光の波長を蛍光材の方から限定する。励起光波長をΛｒとすると、それを蛍光材のバンドギャップ波長（吸収端波長）λｇよりも長いものとする。
【００７５】
Λｒ＞λｇ （１０）
【００７６】
とするのである。これは励起光のエネルギーの下限を決定する。上限は先ほど述べたように、それを励起して蛍光を発生しうるという点で決定する。
【００７７】
両方の蛍光材について共通に言えば、蛍光板を構成するＺｎＳ結晶やＺｎＳｅ結晶の禁制帯幅（バンドギャップ）より小さなエネルギーを持った励起光を使用するということである。
【００７８】
そうすれば、励起光に対する蛍光板の吸収係数が小さくなり、蛍光板内部まで励起光が進入し、蛍光板全体で発光することになる。だから表面の影響が小さくなる。それは吸収性を克服するために課されることになった条件である。
【００７９】
室温でのＺｎＳＳｅのバンドギャップＥｇは
【００８０】
Ｅｇ＝２．７＋１．６３ｘ−０．６３ｘ^２ （ｅＶ） （１１）
【００８１】
によって近似される。単位はｅＶである。１２３９をバンドギャップで割ったものが吸収端波長（バンドギャップ波長）λｇ（ｎｍ）である。
【００８２】
λｇ（ｎｍ）＝１２３９／Ｅｇ （１２）
【００８３】
（１１）式によってＺｎＳｅ、ＺｎＳや、ＺｎＳＳｅのバンドギャップＥｇが分かる。
【００８４】
［７．ＩｎＧａＮ−ＬＥＤの波長の制限］
ＺｎＳ結晶の禁制帯幅は室温で３．７ｅＶであるから吸収端波長は約３４０ｎｍ（λｇ１とする）である。塊の内部まで励起光が浸透するようにするため（Λｒ＞λｇ１という制限）ＺｎＳ結晶は３４０ｎｍより長波長で励起すれば良いということが分かる。それが励起光波長の下限を与える。上限は先述のようにＺｎＳから蛍光を出させるという条件で４００ｎｍ以下だというように決まる。だからＺｎＳを励起するＩｎＧａＮ−ＬＥＤの励起波長Λｒは、
【００８５】
３４０ｎｍ≦Λｒ≦４００ｎｍ （１３）
【００８６】
ということになる。これは紫外（３４０〜３９３ｎｍ）と紫（３９４〜４００ｎｍ）を含むが簡便に紫外光と呼ぶことにする。ＩｎＧａＮのＧａの比率を上げることによって、そのような短い波長の紫外光を発生することができるようになる。
【００８７】
［８．ＺｎＳ蛍光板の波長の制限］
青色光蛍光波長をΛｑによって表現する。それはＺｎＳｅ蛍光板では励起光だからΛによって表現している。ＺｎＳｅ蛍光板がどのような波長の光を出せばよいのか？それは第２蛍光板の材料によるわけである。第２蛍光材としてＺｎＳｅを用いる場合を考える。ＺｎＳｅ結晶の禁制帯幅は室温で２．７ｅＶであり対応する吸収端波長は４６０ｎｍ（λｇ２とする）である。内部まで励起光が入るという条件（Λｑ＞λｇ２）を満足するため、ＺｎＳｅ蛍光板は４６５ｎｍより長波長で励起すれば良い。
【００８８】
第１のＺｎＳ蛍光板から発せられた青色光の中心波長は約４８０ｎｍ（Λｑ）である。これは４６５ｎｍ（λｇ２）より長波長である要件（Λｑ＞λｇ２）を満たしている。４８０ｎｍ中心といっても広がりがあり、第１蛍光板ＺｎＳが発生する蛍光は４６５ｎｍより短い波長成分をも含むのであるが、それは少ない。
【００８９】
そもそもＺｎＳｅは４８０ｎｍ程度の青色で良く励起され黄色の蛍光を発生する。だからＺｎＳの発生する蛍光が４８０ｎｍ中心だというのは好都合なことである。
【００９０】
第２蛍光板をＺｎＳＳｅ混晶にするとバンドギャップ波長（λｇ３とする）が４６５ｎｍより短くなる（λｇ２＞λｇ３）。だからＺｎＳの青色光蛍光（４８０ｎｍ中心；Λｑ＞λｇ２）は依然としてΛｑ＞λｇ３という条件を満足し第２蛍光板の内部まで深く浸透することができる。混晶の第２蛍光板も黄色の蛍光を発生するが中心波長が５８５ｎｍよりも短波長側へよる。そうすると、緑がかった白色ができる。
【００９１】
［９．蛍光材にドープする不純物濃度］
ＺｎＳ結晶やＺｎＳｅ結晶が青色光や黄色光を発するためには、Ａｌ、Ｉｎ、Ｇａ、Ｃｌ、Ｂｒ、Ｉの何れかの不純物をドープ（混入）する必要がある。その濃度が小さすぎるとあまり発光しない。少なくとも１×１０^１７ｃｍ^−３以上の濃度の不純物の混入が必要である。変換効率βは不純物濃度に比例して増大する。不純物濃度は重要な設計パラメータとなる。これらの不純物は意図的に添加することもできる。そうでなくてＺｎＳｅ、ＺｎＳの製造方法によっては、製造工程でいずれかの不純物が前記の濃度以上に含まれるという場合もある。その場合は意図的にその不純物を添加する必要はない訳である。
【００９２】
［１０．蛍光板の熱処理］
ＺｎＳｅ結晶、ＺｎＳＳｅ結晶、ＺｎＳ結晶は粒界が大きい方が吸水しないので良いと説明した。平均粒径が蛍光板の厚み以上にすると一層良い。単結晶とすると粒界がないから、より好ましい。それは結晶の態様のことである。ヨウ素輸送法でこれらの多結晶や単結晶ができるが、そのままでは欠陥が多くて品質が悪い。そこで、Ｚｎ雰囲気で、ＺｎＳｅ結晶、ＺｎＳＳｅ結晶、ＺｎＳ結晶を、１０００℃程度の高温で熱処理して結晶の欠陥を減少させる。そうすることによって蛍光を強化することができる。非発光損失をも抑制できる。
【００９３】
［１１．蛍光板のミラー研磨］
ＺｎＳ蛍光板やＺｎＳｅ蛍光板の励起光が入射する側の面は、入射効率を高めるためにミラー研磨することが望ましい。加えて、反射防止膜を形成すれば、より好ましいと考えられる。蛍光板のそれ以外の面に関しては、必ずしもミラー研磨する必要はないが、加工上の必要に応じてミラー研磨しても構わない。
また蛍光板内で発生した青色光や黄色光の出射効率を高めるための表面加工を施すのも有用である。
【００９４】
【実施例】
［実施例１（図１）］
図１に本発明の実施例にかかる白色発光素子の断面図を示す。Γ型リード３０とＬ型リード３２を組み合わせた２本のリードがある。組み合わせのためにΓ型リード３０の壁面には狭い通し穴３３が穿孔してある。その通し穴にＬ型リード３２の先端を挿入するようにして組み合わせる。Γ型リード３０は上方に開口する広い凹部３４を有する。凹部３４の底部にサファイヤ基板上にＩｎＧａＮ層を形成した紫外光ＬＥＤ３５を電極３６、３７を下にして実装してある。だからサファイヤ／ＩｎＧａＮ−ＬＥＤ３５はサファイヤ基板が上にエピタキシャル層が下にある。二つの電極３６、３７も下向きになっている。一方の電極３６はΓ型リード３０に接合される。他方の電極３７は他方のＬ型リード３２に接合されている。そのように裏返しにＩｎＧａＮ−ＬＥＤ３５を取り付けているからワイヤは不要である。しかしそれに限らずサファイヤ基板を下向きにして電極が上を向くように取り付け２本のワイヤで電極とリードを接続してもよい（図３のように）。電極、リードの接続形式は自由である。
【００９５】
ＩｎＧａＮ−ＬＥＤ３５のすぐ上にＺｎＳよりなる第１蛍光板３８が載せられている。ＩｎＧａＮ−ＬＥＤの紫外光を青色光に変換するための第１蛍光板３８である。第１蛍光板３８の上に、ＺｎＳｅ第２蛍光板３９が搭載してある。第２蛍光板は青色光を黄色光蛍光に変換するためのものである。この例ではＺｎＳｅ第２蛍光板３９が少し狭いが、その外側から直接に青色光が上方へ出てゆくようにしているのである。第２蛍光板３９／第１蛍光板３８／ＬＥＤ３５の上を覆うように拡散剤を分散させた透明樹脂４０が凹部３４に充填されている。第１蛍光板で青色光蛍光が、第２蛍光板で黄色光蛍光が生成され、それが上向きに放射される。拡散剤でその光が散乱されて適度に青色光と黄色光が混合して上から見ると白色に見えるのである。
【００９６】
次にそのような白色発光素子の製造方法を述べる。ヨウ素を輸送媒体とする化学輸送法（ＣＶＴ）でＺｎＳ単結晶とＺｎＳｅ単結晶を作製した。化学輸送法というのは容器の下に置いたＺｎＳ、ＺｎＳｅ多結晶をヨウ素雰囲気で加熱しＳｅとＺｎＩ_２またはＳとＺｎＩ_２として蒸発させ、上部に置いたより低温の種結晶の上に固化させ単結晶を成長させる方法である。図５に化学輸送法を示す。
【００９７】
反応炉８６の下方にＺｎＳｅ（またはＺｎＳ）多結晶８７を置く。反応炉８６の上方にサセプタ８８を介してＺｎＳｅ（またはＺｎＳ）種結晶８９を取り付ける。反応炉８６の雰囲気はヨウ素である。多結晶８７のある下方を高温Ｔ１に、種結晶８９のある上方を低温Ｔ２にする。高温（Ｔ１）側で
【００９８】
２ＺｎＳｅ＋２Ｉ_２→２ＺｎＩ_２＋Ｓｅ_２ （１４）
【００９９】
という反応が起こる。ＺｎＩ_２、Ｓｅ_２は拡散によって上昇し天井の種結晶８９に至る。これは低温Ｔ２であるから反対の反応が起こり、
【０１００】
２ＺｎＩ_２＋Ｓｅ_２→２ＺｎＳｅ＋２Ｉ_２ （１５）
【０１０１】
となる。生成したＺｎＳｅが種結晶８９の下面に堆積してゆく。気体であるヨウ素Ｉ_２は拡散によって下方へ戻りＺｎＳｅ多結晶８７に再び接触し式（１４）の反応を引き起こす。そのような繰り返しによって単結晶のＺｎＳｅを成長させることができる。その手法はＺｎＳやＺｎＳＳｅの混晶にも用いることができる。成長速度は１ｍｍ／日といった程度である。
【０１０２】
得られたＺｎＳ単結晶から切り出した厚み３００μｍ、面方位（１００）のＺｎＳ結晶基板をＺｎ雰囲気中、１０００℃で熱処理をした。
【０１０３】
Ｚｎ中の熱処理は結晶欠陥を減らすために行う。それはＺｎＳｅ、ＺｎＳ、ＺｎＳＳｅのどれでも同じ装置で行うことができる。図６は熱処理室９０を示す。ＺｎＳｅ単結晶基板８９をその中に置いてＺｎ雰囲気で１０００℃、５０時間熱処理する。その後−６０℃／分の割合で降温して常温に到る。ＺｎＳの場合はそれより少し高い温度で熱処理する。その方法や効果はほぼ同じである。
【０１０４】
そのＺｎＳ結晶基板の両面をミラー研磨した後、スクライブブレークし、４００μｍ角、厚み２００μｍのＺｎＳ蛍光板３８を作製した。
【０１０５】
同様に、ＺｎＳｅ単結晶から切り出した厚み２００μｍ、面方位（１００）のＺｎＳｅ基板をＺｎ雰囲気１０００℃で熱処理した。このＺｎＳｅ基板を両面ミラー研磨した後、スクライブブレークして３００μｍ角、厚み１００μｍのＺｎＳｅ蛍光板３９を作製した。
【０１０６】
またサファイヤ基板を使用したＩｎＧａＮ活性層を持つ発光波長３８０ｎｍの青色ＬＥＤチップ３５を準備した。このＬＥＤチップ３５を図１にあるようにフリップチップ型に実装し、ＬＥＤの上側（サファイヤ基板の上側）にＺｎＳ蛍光板３８を透明樹脂を介して貼り付けた。
【０１０７】
さらにＺｎＳ蛍光板３８の上にＺｎＳｅ蛍光板３９を透明樹脂を介して貼り付けた。ＬＥＤチップ３５とＺｎＳ蛍光板３８とＺｎＳｅ蛍光板３９全体を、拡散剤（ＳｉＣ粉末）を分散させた透明樹脂４０で覆ってやり、更に全体を透明樹脂によって樹脂モールドして砲弾型の白色発光素子を作製した。この白色発光素子に通電して発光させたところ、色温度５０００Ｋの白色を得ることができた。色温度の低い白色を生成できるということである。
【０１０８】
分光してスペクトルを調べた。発光スペクトルを図２に示す。横軸は波長（ｎｍ）、縦軸は相対発光強度である。発光強度は４００ｎｍから立ち上がり、４５０ｎｍ〜４９０ｎｍに高い分布をもつ。それが第１蛍光板ＺｎＳによる蛍光の分布である。ＺｎＳの蛍光は青色光から緑まで広がっている。
【０１０９】
それらより長波長側に、５８５ｎｍに中心をもち、５３０ｎｍ〜６５０ｎｍに渡るなだらかなピークがある。それは第２蛍光材ＺｎＳｅによる蛍光のスペクトルである。これは黄色が中心であるが、赤にも緑にも広がりがある。両方の蛍光板からの発光は互いに重なり合い可視領域全体に及ぶ発光が得られている。４５０ｎｍ〜４８０ｎｍの青色光の強度を１として４９５ｎｍ〜５２０ｎｍの緑が少し弱いが、それでも０．７８以上の強度がある。だから４４０ｎｍ〜６５０ｎｍに広がった理想的な白色のスペクトルを与える。平均演色評価係数を計算すると８９となった。３波長型の蛍光灯並みの高い演色性を有しているということが判明した。
【０１１０】
【発明の効果】
紫外線発光ＬＥＤを使用した白色発光素子の作製において、演色性が高い白色発光素子が製造可能になった。演色性が良いので照明用にできる白色である。一つの素子では照明として不十分であるが、本発明の白色発光素子を多数マトリックス状に配列すれば充分な光量を作り出すことができる。実績のあるサファイヤ基板ＩｎＧａＮ−ＬＥＤのｐｎ接合によって発光するのだから長寿命である。蛍光材は吸水性のあるＺｎＳｅ、ＺｎＳ、ＺｎＳＳｅを用いるが塊としており内部まで水が入らないようにしている。だから蛍光板も長寿命となる。その点で白熱電球や蛍光灯に勝る。
【０１１１】
２段階の蛍光現象を利用したものであるが励起光は蛍光板のバンドギャップよりも低いエネルギーを持つものとするから蛍光板の内部まで浸透して蛍光を発生する。内部まで到達できるような波長であるから、その一部は蛍光板を透過することもできる。だから２段階蛍光で両方の蛍光を足し合わせたものを外部へ放射するようにできる。発光ダイオードと同じ形状にできるから一つの素子は軽量小型である。
【図面の簡単な説明】
【図１】Γ型リードとＬ型リードを組み合わせてなるΓ型リードの凹部に紫外線発光ＩｎＧａＮ−ＬＥＤ、ＺｎＳ第１蛍光板、ＺｎＳｅ第２蛍光板を積層し、上部を拡散剤を分散した透明樹脂によって覆い全体を透明の樹脂でモールドした本発明の実施例にかかる砲弾型白色発光素子の縦断面図。
【図２】紫外線発光ＩｎＧａＮ−ＬＥＤ、ＺｎＳ第１蛍光板、ＺｎＳｅ第２蛍光板を積層してなる本発明の実施例にかかる白色発光素子の発光スペクトル図。横軸は波長（ｎｍ）、縦軸は相対発光強度である。
【図３】▲１▼「光機能材料マニュアル」光機能材料マニュアル編集幹事会編、オプトエレクトロニクス社刊、ｐ４５７、１９９７年６月、によって提案されたＹＡＧ／ＩｎＧａＮ白色発光素子の断面図。
【図４】▲２▼特願平１０−３１６１６９号「白色ＬＥＤ」によって初めて提案された不純物ドープＺｎＳｅ基板の上にＺｎＣｄＳｅエピタキシャル発光層を設けＺｎＣｄＳｅの青色光発光をＺｎＳｅ基板で黄色光蛍光に変え青色光と黄色光を合成して白色を得るようにしたＺｎＣｄＳｅ／ＺｎＳｅ白色発光素子の概略構造図。
【図５】ＺｎＳｅ多結晶からＺｎＳｅ単結晶を製造する化学輸送法を説明するための断面図。
【図６】熱処理室においてＺｎＳｅ単結晶をＺｎ雰囲気で熱処理している状態を説明するための断面図。
【図７】ＺｎＳＳｅ／ＺｎＳ／ＩｎＧａＮ−ＬＥＤよりなる本発明の白色発光素子において、ＩｎＧａＮ−ＬＥＤの紫外光をＺｎＳ蛍光板によって青色光蛍光に変換し、その一部の青色光によって、ＺｎＳＳｅ蛍光板によって黄色光蛍光に変換し、青色光と黄色光を合成することによって白色とする本発明の原理を示す説明図。
【図８】ＺｎＳｅ／ＺｎＳ／ＩｎＧａＮ−ＬＥＤよりなる本発明の実施例にかかる白色発光素子において、３４０ｎｍ〜４００ｎｍのＩｎＧａＮ−ＬＥＤの紫外光によって、ＺｎＳ蛍光板を励起し４８０ｎｍ中心波長の青色光蛍光を発生させ、その青色光蛍光によってＺｎＳｅ蛍光板を励起して５８５ｎｍ中心波長の黄色光蛍光を発生させ、中心波長４８０ｎｍの青色光蛍光と、中心波長５８５ｎｍの黄色光蛍光を合成して白色とする原理を説明する図。
【符号の説明】
２ Γ型リード
３ 凹部
４ 青色光ＩｎＧａＮ−ＬＥＤ
５ 蛍光剤を分散させた透明樹脂
６ 電極
７ 電極
８ ワイヤ
９ ワイヤ
１０ Ｉ型リード
２０ 透明樹脂
２２ 不純物ドープＺｎＳｅ基板
２３ ＺｎＣｄＳｅ発光層
３０ Γ型リード
３２ Ｌ型リード
３３ 通し穴
３４ 凹部
３５ 紫外光ＩｎＧａＮ−ＬＥＤ
３６ 電極
３７ 電極
３８ ＺｎＳ第１蛍光板
３９ ＺｎＳｅ第２蛍光板
４０ 拡散剤を分散させた透明樹脂
４２ 透明モールド樹脂
８６ 反応炉
８７ ＺｎＳｅ（ＺｎＳ）多結晶
８８ サセプタ
８９ ＺｎＳｅ（ＺｎＳ）種結晶
９０ 熱処理室[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a lightweight, small, and long-life white light-emitting element capable of generating a white color with excellent color rendering that can be used for illumination, display, liquid crystal backlight, and the like with a single element structure. .
[0002]
Many light emitting diodes (LEDs) and semiconductor lasers (LDs) are manufactured and sold as small light emitting elements. As LEDs having high luminance, red LEDs, yellow LEDs, green LEDs, blue LEDs, and the like are commercially available. The red LED is an LED having AlGaAs, GaAsP or the like as an active layer. Yellow and green are LEDs having GaP as a light emitting layer. Orange and yellow can be produced by an LED having a light emitting layer of AlGaInP.
[0003]
The blue color requiring wide band gap interband transition was the most difficult and difficult. SiC, ZnSe, and GaN-based materials have been tried and competed. However, it has been found that GaN-based materials with high brightness and long life are overwhelmingly superior, and wins and losses are already attached. Since the GaN-based LED actually has an active layer of InGaN, it will be referred to as an InGaN-based LED, InGaN-LED, etc., but the substrate is sapphire and the main layer structure is GaN. Since these semiconductor light emitting elements such as LEDs and LD use band gap transition, naturally they emit light of a single color with a narrow spectrum width. If it is as it is, it is not possible to make a complex color with semiconductor elements.
[0004]
[Prior art]
Illumination light sources are useless with monochromatic light sources. A liquid crystal backlight cannot be a monochromatic light source. A white light source is required for illumination. In particular, white with high color rendering properties is desirable. A liquid crystal backlight also requires a white light source. Incandescent bulbs and fluorescent lamps are still used exclusively as lighting sources. Incandescent light bulbs are suitable for lighting because of their high color rendering properties, but they have the disadvantages of poor efficiency and short life. Fluorescent lamps have a short life span, require heavy objects, and are large and heavy equipment.
[0005]
The appearance of a white light source that is smaller, has a longer life, is more efficient, and is less expensive is awaited. If it is light weight, small size, long life, and high efficiency, it seems that it is already only a semiconductor element.
[0006]
In fact, there are blue LEDs, green LEDs, and red LEDs, so if these three light colors are combined, white should be synthesized. If three types of LEDs of blue, green, and red are uniformly attached to the panel and light is emitted at the same time, it should be white. It seems that such a three-color mixed LED has already been proposed and implemented in part. Three colors can produce a white color, but it must not appear as a separate single color, so the three types of LEDs must be distributed at a high density.
[0007]
In addition, since the three types of LEDs have different current, voltage, and light emission characteristics, they must be separated from each other, resulting in three power sources. Difficult to align due to variations in brightness. Although there is such a problem, above all, a large number of three kinds of LEDs are densely arranged in parallel, so that it becomes an expensive light source.
[0008]
Expensive light sources are not widespread and useless. We would like to make a low-cost small white light emitting element as a semiconductor device. There are two known technologies for semiconductor light-emitting devices using a single light-emitting device. One is a composite LED in which an InGaN-LED (light emitting element on a GaN substrate) is surrounded by a YAG phosphor. The other is that the ZnSe substrate of ZnSe-LED is doped with impurities to form a phosphor, and the ZnSe fluorescent part is excited by the blue color of the ZnSe-LED light emitting part (ZnCdSe) (referred to as SA emission) to generate yellow and orange colors. White is obtained by combining yellow and orange. For simplicity, the former will be referred to as a GaN-based white light-emitting element (A), and the latter will be referred to as a ZnSe-based white light-emitting element (B). Each will be described.
[0009]
(A) GaN-based white light emitting device (YAG + InGaN-LED; FIG. 3)
This uses InGaN-LED, for example,
(1) “Optical Functional Materials Manual”, edited by the Executive Committee for Optical Functional Materials Manual, published by Optoelectronics, p457, June 1997. FIG. 3 shows the structure.
[0010]
A recess 3 is provided in the horizontal portion of the Γ-type lead 2, and an InGaN-LED 4 is attached to the bottom of the recess 3. The recess 3 accommodates a resin 5 in which a Ce-added YAG fluorescent material is dispersed. YAG fluorescent materials have the property of absorbing blue light and generating a lower energy yellow. Such a material that absorbs light with high energy and is excited to be excited to return to the original level, and light with low energy emitted is called fluorescence. The material that produces it is called a fluorescent material. Since it returns to the original level via various levels, the energy spreads and the fluorescence spectrum is wide. The energy loss becomes heat.
[0011]
The electrodes 6 and 7 of the InGaN-LED 4 are connected to the lead 2 and the lead 10 by wires 8 and 9. The upper portions of the leads 2 and 10 and the fluorescent agent resin 5 are covered with a transparent resin 20. Thereby, a bullet-type white light emitting element is manufactured. Since InGaN-LED uses an insulating sapphire substrate, an n-electrode cannot be provided on the bottom surface, and an n-electrode and a p-electrode are formed at two locations on the top surface, and two wires are required.
[0012]
This surrounds the InGaN-based blue LED 4 with a resin layer 5 in which a YAG fluorescent agent is dispersed, and a part of the blue light B is converted into yellow light Y by the fluorescent agent, and the original blue light B and yellow light Y are converted. Is combined to realize white W (= B + Y). White can be produced with a single light-emitting element. Here, Ce-activated one is used as the YAG fluorescent agent. The light of 460 nm is used as the blue light B of the InGaN-LED. The center wavelength of yellow light Y converted by YAG is about 570 nm. That is, YAG absorbs blue light of 460 nm and converts it into yellow light having a broad peak at about 570 nm.
[0013]
Since the light-emitting element InGaN-LED has high luminance and long life, this white light-emitting element also has an advantage of long life. However, since YAG is an opaque material, blue light is strongly absorbed, and the conversion efficiency is not good. This realizes a white light emitting element having a color temperature of about 7000K.
[0014]
(B) ZnSe-based white light emitting device (ZnCdSe light emission, ZnSe substrate fluorescent agent; FIG. 4)
This uses ZnCdSe-LED instead of InGaN-LED as a blue light source. Fluorescence is used but no separate fluorescent material is used. Excellent and clever element. Become the applicant,
[0015]
(2) Japanese Patent Application No. 10-316169 "White LED"
[0016]
It was first proposed by The structure of LED shown in FIG. 4 is shown. A ZnSe substrate 22 is used instead of the GaN substrate. A light emitting layer made of the ZnCdSe epitaxial layer 23 is provided on the impurity-doped ZnSe substrate 22. The ZnCdSe layer 23 emits a blue color of 485 nm. The ZnSe substrate 22 is doped with any one of I, Al, In, Ga, Cl, and Br as the emission center. The impurity-doped ZnSe substrate 22 absorbs a part of blue and generates broad yellow light having a center at 585 nm. Blue light B and yellow light Y are combined to produce white W (W = B + Y).
[0017]
Actually, the ZnCdSe-LED of FIG. 4 is also attached to the lead and surrounded by a transparent resin to form a bullet-type light emitting device like the device of FIG. 3, but this is not shown. In this method, an n-type ZnSe substrate is doped with impurities and the n-type substrate itself is used as a fluorescent plate. The epilayer ZnCdSe emits blue, and the ZnSe substrate emits yellow fluorescence. Together, they become white W.
[0018]
Since it is LED, a board | substrate is essential. The substrate functions as a fluorescent plate in addition to the physical holding function of the light emitting layer. That is, it has an elaborate structure that effectively uses the substrate twice. An independent fluorescent agent such as YAG is unnecessary. That is a great advantage.
[0019]
The emission of impurity-doped ZnSe is called SA emission (self activated). This uses blue light with a wavelength of 485 nm and yellow light with a center wavelength of 585 nm, and realizes white having an arbitrary color temperature between 10,000 K and 2500 K. When the ZnSe substrate is thinned or the impurity concentration is lowered, the fluorescence becomes inferior and the blue light of the ZnCdSe light emitting layer becomes dominant. A white color having a high color temperature is obtained. When the ZnSe substrate is thickened or the impurity concentration is increased, the fluorescence becomes superior, so that white having a low color temperature can be obtained. With such a little ingenuity, whites with various color temperatures can be obtained.
[0020]
As described above, there are three semiconductors with wide band gaps: ZnSe, SiC, and GaN. SiC is indirect transition and is not efficient and does not compete from the beginning. ZnSe, which can produce a single crystal substrate, was primary. Currently, InGaN blue light from GaN and InGaN thin films on sapphire substrates is winning as a long-life, high-brightness, low-cost blue LED. InGaN / Sapphire-LEDs can generate blue light with a shorter wavelength (higher energy), have a longer lifetime, and have higher brightness.
[0021]
Since ZnSe has a short life and low energy (long wavelength), it has been delayed as a blue light LED. However, in this white light emitting element B, the substrate itself is a fluorescent plate, a special fluorescent agent is not required, and it is excellent in economic efficiency and low cost. There is a possibility of growing into a light emitting device.
The present invention relates to a white light emitting device. In particular, the present invention relates to a white light emitting device having excellent color rendering properties and a long life, light weight and small size.
[0022]
[Problems to be solved by the invention]
When the white light emitting element is used as an illumination light source, color rendering is important. The color rendering property is a parameter for evaluating white color defined by how close the light emission spectrum shape of an incandescent bulb is to 100%. Incandescent light bulbs have a distribution function written at a wavelength λ
[0023]
[Expression 1]

[0024]
Have a spectrum like Since exp () has 1 / λ, the maximum value λ rises immediately. _max But then 1 / λ ⁵ Becomes a gentle attenuation. Since it has such a wide spectrum and includes various colors, it is white that is kind to the eyes. The color rendering property is how close the emission spectrum of the white light emitting element is to the distribution of the formula (1). Naturally, fluorescent lamps are inferior in color rendering to incandescent bulbs and are about 86%. This means that it cannot be said that white is superior to fluorescent lamps unless it exceeds 86%.
[0025]
It is difficult to obtain high color rendering properties with a white light emitting element by converting a part of blue light of a blue light emitting LED into yellow light as in A and B of the conventional example. There are two reasons for this.
[0026]
[Reason 1] The blue light emitting element (ZnSe-LED, InGaN-LED) emits a single color of blue light, so that it originally has only a narrow spectral width. The color rendering is poor because the narrow spectrum blue light is on one side.
[0027]
[Reason 2] The yellow light obtained by converting the blue light lacks the green component and the red component. The fluorescence converted with YAG is yellow and lacks green and red. The fluorescence converted with the impurity-doped ZnSe is also yellow and does not contain any green component. The red component is also lacking. If we are going to replace incandescent light bulbs, I think that they should include a wide range of spectrums such as red and green.
[0028]
[Means for Solving the Problems]
The white light emitting device of the present invention includes an InGaN-LED that generates ultraviolet light, a bulk ZnS first fluorescent plate, and a bulk ZnSSe or ZnSe second fluorescent plate, and the ZnS first fluorescent plate is obtained by the ultraviolet light of the InGaN-LED. Is excited to generate blue light fluorescence, the ZnSe or ZnSSe second fluorescent plate is excited by blue light fluorescence to generate yellow fluorescence, and white light is synthesized by emitting blue light fluorescence and yellow light fluorescence to the outside. ZnSSe is exactly ZnS _x Se _1-x However, in the present specification, the mixed crystal ratio x may be omitted for simplicity.
[0029]
That is, the present invention has three types of light emitting portions.
A. Ultraviolet (UV) light emitting InGaN-LED
B. Blue light (B) fluorescence generating ZnS first phosphor plate
C. Yellow light (Y) fluorescence generating ZnSSe (ZnSe) second fluorescent plate
The light W emitted to the outside is only blue light and yellow light. That is, W = B + Y.
[0030]
Use LED for ultraviolet light. That is one feature. Ultraviolet light is not visible light, so do not go outside. Ultraviolet light is prevented from going outside, and the first fluorescent plate converts all into blue fluorescence. The second fluorescent plate is excited by blue light fluorescence to generate yellow light. Therefore, the fluorescence phenomenon is used in two stages. Fluorescence based on electronic transitions from many levels originally has a broad spectrum. It does not have a steep spectrum like LED light. Since both blue and yellow light are fluorescent, the spectrum is wide. Wide spectrum overlaps, so a wide distribution of whites is produced. Naturally it resembles the distribution of incandescent bulbs. Therefore, color rendering properties are enhanced.
[0031]
The emission wavelength of ultraviolet light is 340 nm to 400 nm. It is necessary to use an LED having a high GaN ratio even for an InGaN LED. Such short-wavelength ultraviolet light cannot be generated in a ZnSe-based LED. Limited to InGaN.
[0032]
Since the fluorescence always has a longer wavelength than the excitation light, a blue light LED is not useful for obtaining blue light fluorescence. An ultraviolet light source with higher energy is indispensable. Fortunately, an InGaN LED developed as a red light emitting element can emit visible light such as blue-violet, but can also emit ultraviolet light by increasing the Ga mixed crystal ratio. The present invention intends to create a white color having excellent color rendering properties by utilizing a two-step fluorescence phenomenon using an InGaN-based white light emitting element that emits ultraviolet light as a fundamental light source.
[0033]
Ultraviolet LED + 2 step fluorescence is the gist of the present invention. Two types of fluorescence (blue fluorescence and yellow fluorescence) are emitted outside without ultraviolet light. Fluorescence is advantageous in terms of color rendering properties because it originally has a wide spectral width. The present invention is the first to create white color by two-step fluorescence. It must be said that it is a truly excellent idea.
[0034]
DETAILED DESCRIPTION OF THE INVENTION
The present inventor has studied fluorescent materials in order to solve the above problems. As a result, a ZnS crystal mixed with a group 3 element or a group 7 element is excited with ultraviolet light to emit blue light, and the blue light is used to excite ZnSe (or a ZnSSe mixed crystal) mixed with a group 3 or group 7 element. Thus, a white light emitting device was invented which generates yellow light and mixes blue light and yellow light.
[0035]
The present invention utilizes one LED light source and two types of fluorescence. The action of the element of the present invention can be abbreviated as follows when the conversion action of the fluorescent plate is expressed by

[0036]
The first fluorescent material is ZnS, which is a semiconductor with a wide band gap, and the second fluorescent material is ZnS, which is a semiconductor with a narrower band gap. _x Se _1-x (0 ≦ x <1).
[0037]
FIG. 7 is a schematic diagram for explaining the principle. From the bottom, the structure is composed of InGaN-LED / ZnS / ZnSSe. Two-stage fluorescence is shown in which ZnS is excited by ultraviolet light of an LED to generate blue light fluorescence, and ZnSSe is excited by blue light to generate yellow light fluorescence.
[0038]
FIG. 8 shows a structure composed of InGaN-LED / ZnS / ZnSe (ZnSSe) from the bottom, and schematically shows the emission wavelength region. InGaN LED ultraviolet light of 340 nm to 400 nm is converted into blue light centered on 480 nm with ZnS, and blue light is converted into yellow light centered on 585 nm with ZnSSe. 340 nm is the band gap of ZnS, which means that ZnS should be excited at a wavelength longer than that. 465 nm is the band gap wavelength of ZnSe, which means that ZnSe should be excited at higher wavelengths.
[0039]
[1. First fluorescent plate (ZnS)]
When any impurity of Al, In, Ga, Cl, Br, or I is added to the ZnS crystal, fluorescence is generated. It is considered that the fluorescence is lower than the bandgap energy and is generated by the transition of electrons between a donor formed below the conduction band and an acceptor formed above the valence band. It is believed that the above impurities will form such relatively deep donors and acceptors. If it is at a shallow level, it only gives conductivity, but since it is at a deep level, electrons and holes will exist stably and will be finally excited by light irradiation to cause donor-acceptor transition. Since there are many levels, there are a lot of fluorescence levels, which probably broadens the spectrum.
[0040]
Blue light (fluorescence) from ZnS is light having a central wavelength around 480 nm, but the wavelength spectrum has a wide wavelength distribution ranging from blue-green-yellow-green. This is because transitions between multiple levels are superimposed.
[0041]
ZnS is excited by ultraviolet light having a high energy of 400 nm or less and generates fluorescence having a center at 480 nm and spreading in blue, green, and yellowish green. The blue LED light with lower energy cannot extract fluorescence from ZnS. Therefore, the LED has an ultraviolet light of 400 nm or less. The lower limit (upper limit of energy) of the wavelength of the excitation light is 340 nm. The reason will be described in detail later.
[0042]
The definition of ultraviolet light, but some are strictly defined and some are not. There is also a definition that 13 nm to 393 nm is ultraviolet light. In that case, 7 nm of 393 nm to 400 nm in the wavelength band (340 nm to 400 nm) used as excitation light by the present invention should be said to be purple instead of ultraviolet light. However, since it is troublesome, in this specification, up to 400 nm may be expressed as ultraviolet light.
[0043]
[2. Second fluorescent screen (ZnS _x Se _1-x ]]
ZnS _x Se _1-x When an impurity of Al, In, Ga, Cl, Br, or I is added to a crystal (0 ≦ x <1; containing ZnSe), fluorescence is generated. It is considered that the fluorescence is lower than the bandgap energy and is generated by the transition of electrons between a donor formed below the conduction band and an acceptor formed above the valence band. It is believed that the above impurities will form such relatively deep donors and acceptors. If it is at a shallow level, it merely gives conductivity, but since it is at a deep level, electrons and holes will exist stably and will be finally excited by light irradiation to cause donor-acceptor transition. Since there are many levels, there are many levels of fluorescence, which broadens the spectrum. Such a thing is the same as that of ZnS of a 1st fluorescent material. However, since the band gap is narrower than that of ZnS, the energy of fluorescence is low (the wavelength is long).
[0044]
ZnSe (ZnSSe) as a fluorescent material is efficiently excited by light having a wavelength around 480 nm and emits yellow light having a central wavelength of 585 nm. The center wavelength is 585 nm, but actually spreads widely on both sides. The wavelength spectrum of ZnSe fluorescence has a wide wavelength distribution ranging from yellowish green to yellow to red.
[0045]
ZnSSe in which ZnS is mixed with ZnSe at a ratio x has a wider band gap than ZnSe. Therefore, the difference in height between donor and acceptor due to impurity doping is widened, and the fluorescence wavelength is shortened. In the case of ZnSSe, it is well excited by light shorter than 480 nm and generates fluorescence having a peak at a wavelength shorter than 585 nm. That is, the red component is weakened and the yellow component is increased. What is necessary is just to increase the mixed-crystal ratio x of sulfur S of a 2nd fluorescent screen from 0 with the target white spectrum.
[0046]
[3. Synthesis of two fluorescences]
When the blue light from ZnS of the first fluorescent plate and the yellow light from the second fluorescent plate ZnSe (or ZnSSe) are combined, the color becomes white with a wavelength spectrum covering the entire visible region. Since both are combined with fluorescence having a wide spectral width, white with high color rendering can be realized.
[0047]
Therefore, a certain restriction is imposed on the thickness F of the first fluorescent plate (ZnS) and the thickness H of the second fluorescent plate (ZnSSe).
[0048]
This is because the double condition that the ultraviolet light of the InGaN-LED is completely absorbed by the first fluorescent plate and that the blue light fluorescence is not completely absorbed by the second fluorescent plate is necessary.
[0049]
Although the light from the LED and the light from the first fluorescent plate have a two-dimensional spread, it is considered here as a one-dimensional problem simply. Let α be the absorption coefficient of the ultraviolet light of the LED at the ZnS first fluorescent plate. A coordinate z is considered in the vertical direction from the end of the ZnS phosphor plate to the inside. Assuming that the intensity at the start of the first fluorescent plate is 1, the intensity of the ultraviolet light at the z point inside the first fluorescent plate is expressed by exp (−αz). On the back side of the fluorescent plate (z = F), the ultraviolet intensity is exp (−αF).
[0050]
It is best that all ultraviolet light is absorbed and converted into blue light fluorescence. However, since the above value does not become 0, it is determined to be 0.1 or less or 0.01 or less at most. For example, if the UV intensity at the end of the first fluorescent plate should be 0.1 or less,
[0051]
exp (−αF) ≦ 0.1 (2)
[0052]
Thus, the thickness range of the first fluorescent screen is determined.
[0053]
F ≧ 2.3 / α (3)
[0054]
And if it should be less than 0.01
[0055]
F ≧ 4.6 / α (4)
[0056]
It becomes. As such, the lower limit of the thickness of the first fluorescent screen is determined, but the upper limit is not determined. If it is too thick, the cost will be high, so the upper limit should be determined from economics.
[0057]
The second fluorescent screen is slightly different. The absorption coefficient of the second fluorescent plate (ZnSSe or ZnSe) blue light fluorescence is β. The intensity of blue light fluorescence at the starting edge z = F of the second fluorescent plate is represented by B ₀ Then, the intensity of blue light fluorescence at a point (F <z ≦ F + H) inside the fluorescent plate is B ₀ It is expressed by exp (−β (z−F)). The conversion efficiency on the second fluorescent screen from blue light fluorescence to yellow light fluorescence is γ. Since the generation of yellow light is proportional to the intensity of blue light, the intensity Y (z) of yellow light fluorescence is
[0058]
dY = γB ₀ exp (−β (z−F)) dz (5)
[0059]
It should satisfy the differential equation. This can be easily integrated
[0060]
Y = (γB ₀ / Β) {1-exp (−β (z−F))} (6)
[0061]
It becomes. The intensity of blue light fluorescence B and yellow light fluorescence Y at the end z = F + H of the second phosphor plate (ZnSe or ZnSSe) is respectively
[0062]
B = B ₀ exp (-βH) (7)
[0063]
Y = (γB ₀ / Β) {1-exp (−βH)} (8)
[0064]
That is why. The white color of the present invention is synthesized by adding blue light fluorescence B and yellow light fluorescence Y at an appropriate ratio. The ratio is
[0065]
[Expression 2]

[0066]
Given by.
[0067]
β and γ are parameters that can be changed by the impurity doping amount. H is the thickness of the second fluorescent screen. When it is desired to change the B / Y ratio (ratio of blue / yellow), it is effective to change the doping amount, but it is also possible to change the second fluorescent plate thickness H.
[0068]
In other words, if a desired B / Y ratio is given in advance and the conversion efficiencies β and γ are determined, equation (9) is a decision equation that determines the thickness H of the second fluorescent screen.
[0069]
[4. Water resistance problem]
As in the case of YAG, the fluorescent agent is made into a fine powder and dispersed thinly in a transparent medium so as to receive light as much as possible. That is normal usage. However, ZnS-based and ZnSe-based fluorescent agents lack water resistance. That is, when powdered, it absorbs water and deteriorates. The reason why ZnS and ZnSe have not been used as fluorescent agents so far is that there is a problem that even if it is understood that fluorescence is generated by addition of impurities, there is a problem that reliability is low and it is difficult to use as a fluorescent agent because of strong absorption.
[0070]
Therefore, ZnSe and ZnS have no track record as fluorescent agents such as YAG. However, if you think about it, the fluorescent agent must be made into a fine powder because it is opaque to light. Since opaque fluorescent material does not allow light to enter, it was necessary to make the powder as small in diameter as possible. When it is made into a fine powder, even if dispersed in plastic or glass, it easily absorbs water and deteriorates rapidly. For this reason, it has been said that fluorescent agents should not absorb water.
[0071]
[5. Lumped fluorescent screen]
Since the powder has a large effective surface area, water easily oozes out. If the surface area is small, water should be difficult to enter. In order to overcome the remarkable water absorption of ZnS and ZnSe, it is not necessary to use a fine powder, but on the contrary, it is necessary to use a polycrystal having a large particle size or a single crystal as a whole. Since water enters and penetrates from the grain boundary, water absorption should decrease if the particle size is large even if it is polycrystalline. A single crystal will reduce water absorption more. Even if water permeates from the surface, it takes time for the water to enter the interior, and if it is thick enough, it can no longer penetrate the interior.
[0072]
The present inventor has noticed that instead of using a powdery fluorescent agent, a fluorescent plate made of massive single crystal or polycrystalline ZnS (or ZnSe) may be used. If it does so, since the ratio of the surface area with respect to a fluorescent material volume becomes very small, water resistance improves markedly. If the fluorescent material is covered with plastic or glass, water should not easily penetrate.
[0073]
[6. Limitation of excitation light wavelength]
The reason why it is dispersed as a fine powder like conventional fluorescent materials is that it is opaque to excitation light and does not enter the interior. In the present invention, a bulky fluorescent material is used to overcome the absorption. If it is a lump, it must not be opaque to light. If it is opaque, excitation light does not enter the inside, and most of the fluorescent material is wasted. This means that the fluorescent material must be transparent to the excitation light. It becomes a new constraint.
[0074]
What should i do? Originally, ZnSe and ZnS are nearly transparent (slightly yellowish) to visible light, and are also transparent to some degree of ultraviolet light. However, ultraviolet light shorter than the absorption edge wavelength (band gap wavelength) of ZnS and ZnSe is immediately absorbed. It's a common property for everything. Therefore, the present invention limits the wavelength of excitation light from the fluorescent material. If the excitation light wavelength is Λr, it is longer than the band gap wavelength (absorption edge wavelength) λg of the fluorescent material.
[0075]
Λr> λg (10)
[0076]
It is. This determines the lower limit of the energy of the excitation light. As described above, the upper limit is determined in that it can be excited to generate fluorescence.
[0077]
In general, both fluorescent materials use excitation light having energy smaller than the forbidden band width (band gap) of the ZnS crystal or ZnSe crystal constituting the fluorescent plate.
[0078]
If it does so, the absorption coefficient of the fluorescent plate with respect to excitation light will become small, excitation light will approach into the inside of a fluorescent plate, and it will light-emit on the whole fluorescent plate. Therefore, the influence of the surface becomes small. It is a condition that has been imposed to overcome absorbency.
[0079]
The band gap Eg of ZnSSe at room temperature is
[0080]
Eg = 2.7 + 1.63x-0.63x ² (EV) (11)
[0081]
Is approximated by The unit is eV. Absorption edge wavelength (band gap wavelength) λg (nm) is obtained by dividing 1239 by the band gap.
[0082]
λg (nm) = 1239 / Eg (12)
[0083]
The band gap Eg of ZnSe, ZnS, or ZnSSe can be found from the equation (11).
[0084]
[7. Limitation of wavelength of InGaN-LED]
Since the forbidden band width of the ZnS crystal is 3.7 eV at room temperature, the absorption edge wavelength is about 340 nm (referred to as λg1). It can be seen that the ZnS crystal may be excited at a wavelength longer than 340 nm in order to allow the excitation light to penetrate into the inside of the mass (limitation of Λr> λg1). This gives the lower limit of the excitation light wavelength. The upper limit is determined to be 400 nm or less under the condition that fluorescence is emitted from ZnS as described above. Therefore, the excitation wavelength Λr of the InGaN-LED that excites ZnS is
[0085]
340 nm ≦ Λr ≦ 400 nm (13)
[0086]
It turns out that. This includes ultraviolet (340 to 393 nm) and purple (394 to 400 nm), but is simply referred to as ultraviolet light. By increasing the Ga ratio of InGaN, ultraviolet light having such a short wavelength can be generated.
[0087]
[8. Limitation of wavelength of ZnS phosphor plate]
The blue light fluorescence wavelength is expressed by Λq. It is expressed by Λ because it is excitation light in the ZnSe fluorescent plate. What wavelength should the ZnSe phosphor plate emit? This is due to the material of the second fluorescent screen. Consider the case of using ZnSe as the second fluorescent material. The forbidden band width of the ZnSe crystal is 2.7 eV at room temperature, and the corresponding absorption edge wavelength is 460 nm (referred to as λg2). In order to satisfy the condition (Λq> λg2) that the excitation light enters inside, the ZnSe phosphor plate may be excited at a wavelength longer than 465 nm.
[0088]
The center wavelength of blue light emitted from the first ZnS phosphor plate is about 480 nm (Λq). This satisfies the requirement (Λq> λg2) that is longer than 465 nm (λg2). Even if it is the center of 480 nm, there is a spread, and the fluorescence generated by the first phosphor plate ZnS includes a wavelength component shorter than 465 nm, but it is small.
[0089]
In the first place, ZnSe is well excited by a blue color of about 480 nm and generates yellow fluorescence. Therefore, it is convenient that the fluorescence generated by ZnS is centered at 480 nm.
[0090]
When the second fluorescent plate is made of ZnSSe mixed crystal, the band gap wavelength (λg3) becomes shorter than 465 nm (λg2> λg3). Therefore, the blue light fluorescence of ZnS (480 nm center; Λq> λg2) still satisfies the condition of Λq> λg3 and can penetrate deeply into the second fluorescent plate. The mixed crystal second fluorescent plate also emits yellow fluorescence, but the center wavelength is shorter than 585 nm. This gives a greenish white.
[0091]
[9. Impurity concentration doped in fluorescent material]
In order for the ZnS crystal or ZnSe crystal to emit blue light or yellow light, it is necessary to dope (mix) any of Al, In, Ga, Cl, Br, and I. If the concentration is too small, it does not emit much light. At least 1x10 ¹⁷ cm ^-3 It is necessary to mix impurities with the above concentrations. The conversion efficiency β increases in proportion to the impurity concentration. Impurity concentration is an important design parameter. These impurities can also be added intentionally. Otherwise, depending on the manufacturing method of ZnSe and ZnS, any impurity may be contained in the manufacturing process at a concentration higher than the above-described concentration. In that case, it is not necessary to intentionally add the impurities.
[0092]
[10. Heat treatment of fluorescent screen]
It has been explained that ZnSe crystals, ZnSSe crystals, and ZnS crystals are better because the larger grain boundaries do not absorb water. It is even better if the average particle size is greater than the thickness of the fluorescent screen. A single crystal is more preferable because there is no grain boundary. It is a crystalline embodiment. These polycrystals and single crystals can be produced by the iodine transport method, but the quality is poor as it is with many defects. Therefore, the ZnSe crystal, ZnSSe crystal, and ZnS crystal are heat-treated at a high temperature of about 1000 ° C. in a Zn atmosphere to reduce crystal defects. By doing so, fluorescence can be enhanced. Non-emission loss can also be suppressed.
[0093]
[11. Mirror polishing of fluorescent screen]
The surface of the ZnS phosphor plate or ZnSe phosphor plate on which excitation light is incident is preferably mirror-polished in order to increase the incidence efficiency. In addition, it is more preferable to form an antireflection film. The other surface of the fluorescent plate is not necessarily mirror-polished, but may be mirror-polished according to processing needs.
It is also useful to perform surface processing to increase the emission efficiency of blue light and yellow light generated in the fluorescent screen.
[0094]
【Example】
[Example 1 (FIG. 1)]
FIG. 1 is a sectional view of a white light emitting device according to an embodiment of the present invention. There are two leads combining the Γ-type lead 30 and the L-type lead 32. A narrow through hole 33 is formed in the wall surface of the Γ-type lead 30 for combination. The L-shaped lead 32 is combined in such a way that the tip of the L-shaped lead 32 is inserted into the through hole. The Γ-type lead 30 has a wide recess 34 that opens upward. An ultraviolet LED 35 having an InGaN layer formed on a sapphire substrate is mounted on the bottom of the recess 34 with the electrodes 36 and 37 facing down. Therefore, the sapphire / InGaN-LED 35 has a sapphire substrate on top and an epitaxial layer on the bottom. The two electrodes 36 and 37 are also facing downward. One electrode 36 is joined to the Γ-type lead 30. The other electrode 37 is joined to the other L-shaped lead 32. Since the InGaN-LED 35 is attached so as to be reversed, no wire is required. However, the present invention is not limited to this, and the electrode and the lead may be connected with two wires attached with the sapphire substrate facing downward and the electrode facing upward (as shown in FIG. 3). The connection form of electrodes and leads is free.
[0095]
A first fluorescent plate 38 made of ZnS is placed immediately above the InGaN-LED 35. It is the 1st fluorescent plate 38 for converting the ultraviolet light of InGaN-LED into blue light. A ZnSe second fluorescent plate 39 is mounted on the first fluorescent plate 38. The second fluorescent plate is for converting blue light into yellow light fluorescence. In this example, the ZnSe second fluorescent plate 39 is a little narrow, but the blue light is directly emitted upward from the outside thereof. The concave portion 34 is filled with a transparent resin 40 in which a diffusing agent is dispersed so as to cover the second fluorescent plate 39 / first fluorescent plate 38 / LED 35. Blue fluorescent light is generated by the first fluorescent plate and yellow fluorescent light is generated by the second fluorescent plate, which is emitted upward. The light is scattered by the diffusing agent, and blue light and yellow light are mixed appropriately, and it looks white when viewed from above.
[0096]
Next, a method for manufacturing such a white light emitting element will be described. A ZnS single crystal and a ZnSe single crystal were produced by a chemical transport method (CVT) using iodine as a transport medium. The chemical transport method is a method in which ZnS and ZnSe polycrystals placed under a container are heated in an iodine atmosphere to produce Se and ZnI. ₂ Or S and ZnI ₂ Is evaporated and solidified on a lower temperature seed crystal placed on the top to grow a single crystal. FIG. 5 shows the chemical transport method.
[0097]
A ZnSe (or ZnS) polycrystal 87 is placed below the reaction furnace 86. A ZnSe (or ZnS) seed crystal 89 is attached above the reaction furnace 86 via a susceptor 88. The atmosphere of the reaction furnace 86 is iodine. The lower part with the polycrystal 87 is set to the high temperature T1, and the upper part with the seed crystal 89 is set to the low temperature T2. On the high temperature (T1) side
[0098]
2ZnSe + 2I ₂ → 2ZnI ₂ + Se ₂ (14)
[0099]
This happens. ZnI ₂ , Se ₂ Rises by diffusion and reaches the seed crystal 89 on the ceiling. Since this is a low temperature T2, the opposite reaction occurs,
[0100]
2ZnI ₂ + Se ₂ → 2ZnSe + 2I ₂ (15)
[0101]
It becomes. The generated ZnSe is deposited on the lower surface of the seed crystal 89. Iodine I, which is a gas ₂ Returns downward by diffusion and contacts the ZnSe polycrystal 87 again to cause the reaction of the formula (14). Single crystal ZnSe can be grown by such repetition. This method can also be used for ZnS or ZnSSe mixed crystals. The growth rate is about 1 mm / day.
[0102]
A ZnS crystal substrate having a thickness of 300 μm and a plane orientation (100) cut out from the obtained ZnS single crystal was heat-treated at 1000 ° C. in a Zn atmosphere.
[0103]
Heat treatment in Zn is performed to reduce crystal defects. Any of ZnSe, ZnS, and ZnSSe can be performed in the same apparatus. FIG. 6 shows the heat treatment chamber 90. A ZnSe single crystal substrate 89 is placed therein and heat-treated in a Zn atmosphere at 1000 ° C. for 50 hours. Thereafter, the temperature is lowered at a rate of −60 ° C./min to reach room temperature. In the case of ZnS, heat treatment is performed at a slightly higher temperature. The method and effect are almost the same.
[0104]
Both surfaces of the ZnS crystal substrate were mirror-polished and then scribe-breaked to produce a 400 μm square ZnS phosphor plate 38 having a thickness of 200 μm.
[0105]
Similarly, a ZnSe substrate having a thickness of 200 μm and a plane orientation (100) cut out from a ZnSe single crystal was heat-treated at a Zn atmosphere of 1000 ° C. After polishing this ZnSe substrate by double-sided mirror polishing, a scribe break was performed to prepare a ZnSe phosphor plate 39 having a 300 μm square and a thickness of 100 μm.
[0106]
A blue LED chip 35 having an emission wavelength of 380 nm and having an InGaN active layer using a sapphire substrate was prepared. The LED chip 35 was mounted in a flip chip type as shown in FIG. 1, and a ZnS phosphor plate 38 was attached to the upper side of the LED (upper side of the sapphire substrate) via a transparent resin.
[0107]
Further, a ZnSe fluorescent plate 39 was pasted on the ZnS fluorescent plate 38 via a transparent resin. The entire LED chip 35, ZnS phosphor plate 38, and ZnSe phosphor plate 39 are covered with a transparent resin 40 in which a diffusing agent (SiC powder) is dispersed, and the whole is resin-molded with a transparent resin to produce a bullet-type white light emitting device. did. When the white light emitting element was energized to emit light, white having a color temperature of 5000K could be obtained. This means that white having a low color temperature can be generated.
[0108]
The spectrum was examined by spectroscopy. The emission spectrum is shown in FIG. The horizontal axis represents wavelength (nm), and the vertical axis represents relative emission intensity. The emission intensity rises from 400 nm and has a high distribution between 450 nm and 490 nm. That is the distribution of fluorescence by the first phosphor plate ZnS. The fluorescence of ZnS extends from blue light to green.
[0109]
On the longer wavelength side, there is a gentle peak centered at 585 nm and extending from 530 nm to 650 nm. It is a spectrum of fluorescence by the second fluorescent material ZnSe. This is mainly yellow, but there is a spread in red and green. Light emission from both fluorescent plates overlaps each other, and light emission over the entire visible region is obtained. The intensity of blue light of 450 nm to 480 nm is 1, and green of 495 nm to 520 nm is slightly weak, but still has an intensity of 0.78 or more. Therefore, an ideal white spectrum extending from 440 nm to 650 nm is given. The average color rendering evaluation coefficient was 89. It has been found that the color rendering property is as high as that of a three-wavelength fluorescent lamp.
[0110]
【The invention's effect】
In the production of a white light emitting device using an ultraviolet light emitting LED, a white light emitting device having high color rendering properties can be produced. White color that can be used for lighting due to good color rendering. One element is insufficient as illumination, but a sufficient amount of light can be produced by arranging a number of white light emitting elements of the present invention in a matrix. Since the pn junction of the sapphire substrate InGaN-LED with proven results emits light, it has a long lifetime. The fluorescent material uses water-absorbing ZnSe, ZnS, and ZnSSe, but it is a lump that prevents water from entering the interior. Therefore, the fluorescent screen also has a long life. In that respect, it is superior to incandescent bulbs and fluorescent lamps.
[0111]
Although it uses a two-stage fluorescence phenomenon, the excitation light has an energy lower than the band gap of the fluorescent plate, so that it penetrates into the fluorescent plate and generates fluorescence. Since the wavelength can reach the inside, a part of the wavelength can be transmitted through the fluorescent screen. Therefore, it is possible to emit the sum of both fluorescences in a two-stage fluorescence. One element is light and small because it can be made the same shape as a light emitting diode.
[Brief description of the drawings]
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 A UV light emitting InGaN-LED, a ZnS first fluorescent plate, and a ZnSe second fluorescent plate are stacked in a concave portion of a Γ type lead formed by combining a Γ type lead and an L type lead, and the upper part is made of a transparent resin in which a diffusing agent is dispersed. The longitudinal cross-sectional view of the bullet-type white light emitting element concerning the Example of this invention which molded the whole cover with transparent resin.
FIG. 2 is an emission spectrum diagram of a white light emitting device according to an embodiment of the present invention, in which an ultraviolet light emitting InGaN-LED, a ZnS first fluorescent plate, and a ZnSe second fluorescent plate are stacked. The horizontal axis represents wavelength (nm), and the vertical axis represents relative emission intensity.
FIG. 3 is a cross-sectional view of a YAG / InGaN white light-emitting element proposed by (1) “Optical Functional Material Manual” edited by the Executive Committee for Optical Functional Material Manual, published by Optoelectronics, p457, June 1997.
(2) A ZnCdSe epitaxial light-emitting layer is provided on an impurity-doped ZnSe substrate first proposed by Japanese Patent Application No. 10-316169 “White LED”, and the blue light emission of ZnCdSe is changed to yellow light fluorescence on the ZnSe substrate. The schematic structure figure of the ZnCdSe / ZnSe white light emitting element which synthesize | combined blue light and yellow light and was made to obtain white.
FIG. 5 is a cross-sectional view for explaining a chemical transport method for producing a ZnSe single crystal from ZnSe polycrystal.
FIG. 6 is a cross-sectional view for explaining a state in which a ZnSe single crystal is heat-treated in a Zn atmosphere in a heat treatment chamber.
FIG. 7 shows a white light emitting device of the present invention composed of ZnSSe / ZnS / InGaN-LED, in which ultraviolet light of InGaN-LED is converted into blue light fluorescence by a ZnS phosphor plate, and a part of blue light is converted into yellow by a ZnSSe phosphor plate. Explanatory drawing which shows the principle of this invention which converts it into photofluorescence and makes white by synthesize | combining blue light and yellow light.
8 shows a white light emitting device according to an embodiment of the present invention composed of ZnSe / ZnS / InGaN-LEDs, which excites a ZnS phosphor plate with ultraviolet light of InGaN-LEDs having a wavelength of 340 nm to 400 nm to emit blue light fluorescence having a central wavelength of 480 nm. FIG. The blue light fluorescence excites the ZnSe phosphor plate to generate yellow light fluorescence with a central wavelength of 585 nm, and the blue light fluorescence with a central wavelength of 480 nm and the yellow light fluorescence with a central wavelength of 585 nm are combined to make white. Illustration to explain.
[Explanation of symbols]
2 Γ type lead
3 recess
4 Blue light InGaN-LED
5 Transparent resin with dispersed fluorescent agent
6 electrodes
7 electrodes
8 wires
9 wire
10 Type I lead
20 Transparent resin
22 Impurity doped ZnSe substrate
23 ZnCdSe light emitting layer
30 Γ type lead
32 L-type lead
33 through holes
34 recess
35 UV InGaN-LED
36 electrodes
37 electrodes
38 ZnS first phosphor screen
39 ZnSe second fluorescent screen
40 Transparent resin with diffusing agent dispersed
42 Transparent mold resin
86 reactor
87 ZnSe (ZnS) polycrystal
88 Susceptor
89 ZnSe (ZnS) seed crystal
90 Heat treatment room

Claims (5)

From an InGaN-LED that emits ultraviolet light of 340 nm to 400 nm and an InGaN-LED that contains at least one element of Al, In, Ga, Cl, Br, and I as an impurity at a concentration of 1 × 10 ¹⁷ cm ⁻³ or more. A first fluorescent plate made of ZnS crystal that is a polycrystal or a single crystal that is a lump that has an average particle diameter larger than the thickness, and is a lump that converts the ultraviolet light into blue light that spreads from 400 nm to 490 nm at the center of 480 nm , Agglomerated ZnSe that contains at least one element of Al, In, Ga, Cl, Br, I as an impurity at a concentration of 1 × 10 ¹⁷ cm ⁻³ or more and converts part of the blue light into yellow light centered at 585 nm. becomes more and second fluorescent plate made of crystalline or ZnSSe crystal, can be used in air, the blue light of the fluorescent leaving from ZnS crystals and ZnSe / Zn White light emitting device, characterized in that synthesizing white by mixing yellow light fluorescence emitted from Se crystals.   2. The white light emitting device according to claim 1, wherein an average particle diameter of a ZnSe crystal or a ZnSSe crystal constituting the second fluorescent plate is made larger than a thickness of the fluorescent plate.   3. The white light emitting element according to claim 1, wherein the second phosphor plate, the ZnSe phosphor plate or the ZnSSe phosphor plate, is composed of single crystal ZnSe or single crystal ZnSSe. 4.   The white light-emitting element according to claim 1, wherein a ZnS crystal that has been heat-treated in a Zn atmosphere is used as the first fluorescent plate.   The white light-emitting element according to claim 1, wherein a ZnSe crystal or a ZnSSe crystal that has been heat-treated in a Zn atmosphere is used as the second fluorescent plate.

Images