PhysicaB308–310(2001)1046–1049

Valence-change-anddefect-inducedwhiteluminescence

ofEu2O3

S.Mochizukia,*,Y.Suzukia,T.Nakanishia,K.Ishib

a

DepartmentofPhysics,CollegeofHumanitiesandSciences,NihonUniversity,3-25-40Sakurajosui,Setagaya-ku,

Tokyo156-8550,Japan

b

InstituteofMultidisciplinaryResearchforAdvancedMaterials,TohokuUniversity,Sendai980-8577,Japan

Abstract

UnderirradiatingwithaCWUVlaserlight(l¼325nm)atroomtemperatureinvacuumandoxygengasatmosphere,the lm,microcrystalsandpowdercompactsofEu2O3exhibitareversiblephotoluminescence(PL)spectralchangebetweenaredsharp-linestructureandawhitebroadone.AfterstoppingtheUVirradiation,theabilityofthewhitePLlastsformorethanseveralmonthsatroomtemperatureunderroomlight,inspiteofchangesofatmosphere.Thereversiblephenomenatobeobservedareinterpretedastheresultsofboththevalence-numberchangeofeuropiumions(Eu3+-Eu2+)andtheoxygenvacancyformation.r2001ElsevierScienceB.V.Allrightsreserved.

Keywords:Defectstructures;Valencechange;White-lightemission

1.Introduction

Eu2O3isstableinairandhas vephasesdesignatedbyX,H,A,BandCatatmosphericpressureinorderofdecreasingtemperatureasfollows[1].Atabout2553K,theXphasetransformsintotheHphasewhichtransformstotheAphaseat2413K.At2313K,theAphase(hexagonalstructure:spacegroupD3d)trans-formsintotheBphase(monoclinicstructure:spacegroupC32h).IntheAphase,theeuropiumatomsareseven-coordinatewithfouroxygenatomscloserthantheotherthree,while,intheBphase,theeuropiumatomsaresix-andseven-coordinate.Atabout1373K,theBphasetransformsintotheCphase(cubicstructure:spacegroupT7h)inwhichtheeuropiumatomsaresix-coordinate.Atroomtemperature,thepresentauthorshaverecentlyobservedthereversibleUV-laser-light-inducedspectraltransitionsbetweenthered-andwhite-luminescencestatesinEu2O3-powdercompactsandF lmsproducedbytheradio-frequencysputtering

*Correspondingauthor.Tel.:+81-3-5317-9733;fax:+81-3-5317-9771.

E-mailaddress:motizuki@physics.chs.nihon-u.ac.jp(S.Mochizuki).

method[2,3].Theinterestinphotoluminescentmaterialsshowingsuchphoto-inducedreversiblespectralchangeatroomtemperaturehassigni cantlygrown,becauseacombinationofthereversiblephenomenonandthenear- eldopticalmicroscope[4]isverypromisingwhenappliedtohigh-densityopticalstoragewithnanometerresolution.Itisalsothehopethatwecan ndwhitePLmaterial,whichisusefulforthewide-bandtunable-lasermedium.Veryrecently,wehavealsoobservedthesimilarphotoinducedspectraltransitioninEu2O3 lmsproducedbythepulsedlaserablationmethodinvacuumandEu2O3microcrystal lmsproducedbythelaserablationinlow-pressureoxygengasatmosphere.

Inthispaper,anoverviewofourresultsobtainedinthepastthreeyearswillbegiven,togetherwithaphenomenalmodelofthephotoinducedspectraltransi-tion.

2.Experimental

AllspecimensweremadefromEu2O3powderof99.98%purity.Powdercompactspecimenswerepre-paredbypressingtheEu2O3powderunderapressureof0.2GPafor1hatroomtemperature.Theywerethen

0921-4526/01/$-seefrontmatterr2001ElsevierScienceB.V.Allrightsreserved.PII:S0921-4526(01)00921-8