Spectral properties and charge transfer luminescence of Yb3+

Correspondingauthor.Tel.:+8602169915174;

fax:+8602159928755.

E-mailaddresses:jiangbx@http://www.77cn.com.cn(B.Jiang),zzw8006@http://www.77cn.com.cn(Z.Zhao).

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laserdiodepumpingnear980nmandthesmallStokesshift(about650cmÀ1)betweenabsorptionandemissionreducesthethermalloadingofthematerialduringlaseroperation.Owingtothisuniquecon guration,Yb3+presentsremarkableproperties.

Chenaisetal.[3]hasreportedthecomparisonbetweenYb:GGGandYb:YAG,whichshowsthatYb:GGGsingle-crystalcanbepotentialmaterialsforhigh-average-powersolidstatelaser.ThereareseveralmainfactorsthatmakeYb:GGGcrystalofinterest:(1)ThethermalconductivityofYb:GGGislargerthanthatofYb:YAGwithYbdopinglevelmorethan4at%.(2)Yb:GGGcrystalhasasmallerStokesshiftbetweenabsorptionandemission,whichcanreducethethermalloading.(3)GGGcrystalscanbegrowncore-freeupto15cminsizeandsuperioropticalquality.AllofthesefeaturesmakeYb:GGGcrystalsattractconsiderableattention.

Recently,Yb3+-dopedcrystalshaveattractedalotofattentionduetoluminescenceofYb3+fromthechargetransfer(CT)statewithnearUV–VISpositionedemissionspectrumandshortradiativelifetime[4–7].Applicationareasofthesecrystalsareverypromisingforneutrinodetection.AndalsotheexcellentpropertiesofgadoliniumgalliumgarnetweretheinitialmotivationforstudyingYb:GGG.

TheaimofthispaperistoreporttheresultsoftheYb:GGGsingle-crystalgrowthaswellasitsopticalandluminescenceproperties.EmphasisislaidonresultsobtainedforlaserandCTluminescenceapplications.

2.Experimentalprocedure

Yb:GGGcrystalwasgrownbytheRF-heatingCzochralskimethodwithaniridiumcrucible(50mmindiameter).ThestartmaterialsusedwereGd2O3(99.999%),Ga2O3(99.99%)andYb2O3(4N).Yb2O3/Gd2O3¼10%and30%(moleratio).Themixturewasgrindedandextrudedtoformpieceswithdiameterclosetotheinnerdiameterofthecrucibleathighpressure,thensinteredinanaluminumcrucibleat13001Cfor24htoobtainGGGsingle-phasepowder.The

245000

GGG polycrystalline samples

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4024043000

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t2344i358866s240

4n4etn2000

IGGG standard card

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50

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2T(o

)

Fig.1.PatternsofX-raydiffractionoftheas-obtainedGGGpolycrystallinesamples.

XRDdatashowedthatithadnearlyasinglephaseofGGG(Fig.1).

Thechargewasthenloadedintotheiridiumcruciblesforcrystalgrowth.Thepullingandrotationrateswere3mm/hand12rpm.TodecreasetheevaporationofGa2O3,thegrowthatmosphereofO2+N2wasadopted.Anatmo-spherewithO2wasrequiredtosuppresstheevaporationofGafromthemeltofthegarnetcontainingGa.

Aftergrowth,theas-grownYb3+:GGGbouleswereannealedinairat15001Cfor24hintheMoSi2furnaceandtherateofheatingandcoolingwas801C/h.ThecrystalbouleswerecolorlessasshowninFig.2;(444)double-crystalrockingcurvesforYb:GGGcrystalisshowninFig.2(b).Thefull-widthathalf-maximum(FWHM)oftherockingcureis40.9s.

3.Resultsanddiscussion3.1.Spectralproperties

Samplesforspectroscopicmeasurementswerecutoutofboulesandthesurfacesperpendiculartothe/111Sgrowthaxiswerepolished.Thethicknessofthesampleswasbelow0.4mm.AJASCOV-570UV/VIS/NIRspectrophotometer

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B.Jiangetal./JournalofCrystalGrowth277(2005)186–191

(a)

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y2000tisnet1000

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Fig.2.(a)photographofas-grownYb:GGGsinglecrystaland(b)(444)rockingcurveofNd:GGGcrystal.

wasemployedforacquisitionoftheabsorptionspectraatroomtemperature.TheabsorptionofYb3+inGGGcrystaloccursinthewavelengthrange850–1100nm,asillustratedinFig.3.Therearenoabsorptionbandscenteringat370and625nmofYb2+ionsandcolorcenters,whichusuallyoccurinYb:YAGcrystals.ThepossiblereasonisthatYb:GGGcrystalsweregrowninO2atmosphereinthiswork,whileYb:YAGcrystalswereinN2atmosphere.FromFig.3.therearefourmainabsorptionbandsinYb:GGG,whichcenterat929,942,971and1024nm,respectively.Theabsorptioncoef cientsof942nmare12and43cmÀ1forYb(10%):GGGandYb(30%):GGG,respectively.Theline-widths(FWHM)ofabsorp-tionbandsat942and971nmareabout25and7nm,respectively.AwideFWHMmeansthatthe

Yb(30%):GGGI

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Fig.3.(a)Absorptionand(b)luminescencespectraofYb:GGGsingle-crystalatroomtemperature.

lasercrystalcanaccommodatesomethermalshiftofthepumplightwavelength,andtheoutputpowerofthelaserremainsstable.Therefore,theFWHMofabsorptionbandatpumpwave-lengthisoneoftheimportantparametersforlasercrystal.

TheluminescencespectraofYb:GGGcrystalsatroomtemperatureareshowninFig.4.ItwasacquiredbyaTRIAX550spectrophotometerwithnGaAsLDasthepumpsource(excitedat940nm).Thedecaytimesof1.7and0.6msfor10%and30%Yb,respectively,weremeasuredbyacomputer-controlledtransientdigitizer.Thestrongestemissionpeakislocatedatwavelength1026nm.Fig.4givesustheabsorptionandluminescencespectraofYb:YAGsinglecrystals.FromitwecanseethatYb:GGGhasaweakerStokesshift,whichleadstosmallenergyloss.

B.Jiangetal./JournalofCrystalGrowth277(2005)186–191

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absorption curve of Yb(30%):YAG28absorption curve of Yb(10%):YAG26Fluorescence curve of Yb(30%):YAG24Fluorescence curve of Yb(10%):YAG

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18u.a16/yt14isn12e10tnI86420-2

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Fig.4.AbsorptionandluminescencespectraofYb:YAGsinglecrystals.

Whyisthemeasuredlifetimelargerthanthatofthetheoreticalvalue?AndwhydoesitbecomeshortwiththeincreaseofYbconcentrations?Auzeletal.[8,9]studiedthesephenomenainY2O3single-crystal ber.Themeasuredlifetimecanbededucedwiththefollowingform …… 此处隐藏：10448字，全部文档内容请下载后查看。喜欢就下载吧 ……