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1、WhiteLightEmittingDiodesJ.Baur,P.SchlotterandJ.SchneiderFraunhofer-lnstitutforAngewandteFestk6rperphysik,Tullastr.72,D-79108FreiburgAbstract:Usingblue-emittingGaNLEDsonSiCsubstratechipsasprimarylightsources,wehavefabricatedgreen,yellow,redandwhitelightemittingdiodes
2、(LUCOLEDs).Thegenerationofmixedcolors,asturquoiseandmagenta,isalsodemonstrated.Theunderlyingphysicalprincipleisthatofluminescencedown-conversion(Stokesshift),astypicalfororganicdyemoleculesandmanyinorganicphosphors.ForwhitelightgenerationviatheLUCOLEDprinciple,theph
3、osphorY3AIsO12:Ce3+(4fI)isideallysuited.TheopticalcharacteristicsofCe3+(4f1)inY3AIsOI2(YAG)arediscussedindetail.Possibilitiesto"tune"thewhitecolorbyvarioussubstitutionsinthegarnetlatticeareshortlyoutlined.1IntroductionDifferentbluelightemittingdiodes(LEDs)basedongal
4、liumnitride(GaN)arenowcommerciallyavailable:TheNichia[1]SQWdiode,grownonsapphire(o~-A1203)substrate,availablewithdifferentwavelengthsbetween~,max----450nmand~s=520rim,andtheCree[2]"bluechip",grownonsiliconcarbide(6H-SiC)substrate,Lmax=430nm.Theseprimarylightsourcesc
5、anbeusedasefficientpumpstoexciteorganicandinorganicluminescentmaterialsforsubsequentphotonemissionatlowerenergies.ThenameLUCOLED(LuminescenceConversionLED)hasbeencoinedforsuchadevice[3].Ifluminescentorganicdyesareembeddedinorganicmatrices,asepoxyresinorpolymethylmet
6、acrylate(PMMA)theluminescentspeciesis,ingeneral,incorporatedinmolecularform.ThespectralshiftoftheluminescencetowardlongerwavelengthisamanifestationofthewellknownStokes-shift(foundin1853).Asatypicalexam-pleFig.1showstheabsorptionandemissionspectrumofacommercialgreen-
7、emittingperylene-baseddyeembeddedinepoxyresin.AlsoshowninFig.1istheelectrolu-minescencespectrumofaCreeLED,usedasapumpforourLUCOI.EDs.AstrongspectraloverlapoftheblueLED-emissionwiththeabsorptionspectrumofthegreen-emittingdyeconverterisapparent.Thisenablesthefabricati
8、onofgreen-emittingLU-COLEDs.Aslightlydifferentsituationarises,ifinorganicphosphorsareusedforLUCOLEDs.Here,theluminescentpowderswill,ingene
