1997-PRB-Off-resonant spectral hole burning in CaS Eu by tim(2)

differs ii Thebetweenspectraltheshapemainof 625.5theholesnm andisrathersatellitecomplexlines.

andOn

12994S.A.BASUNetal.FIG.3.PersistentspectralholesburnedatT 2Kwithapowerdensityof60mW/cm2incidentonasinglecrystalofCaS:0.1%Eu.Curvesaandb:irradiationat631.5nmfor3min.Curvescandd:irradiationat625.5nmfor0.5min.Curvesaandcareself-gatedholes,curvescanddaregatedwithatungstenlampthroughtheSchottRG715color lter powerdensity 1W/cm2 .Dashedline—spectralholeburnedinCaF2:Eu2 forcomparisonofholeshape Ref.7

.

themainZPL,aswellasonthesatellitelines,acontourwithafullwidthathalfmaximum FWHM of 5GHz seeFigs.3and4 isobserved,whosespectralshapedoesnotchangemarkedlywithholedepth.Onthe631.5-nmZPL,inadditiontothe5-GHzcontour,therealsooccursamuchnarrowerhole 200-MHzFWHM whichdisappearswithincreasedburningandincreasedoverallholedepth.Astheoverall appear5GHzhole ZPL’sremainsdepthofthepracticallyincreases,theperturbedthe‘‘main’’sitessame,at631.6butholeextendedwidthcontourand641.3wingsnm andbecomedeeper seeFig.4 ,extendingoveraratherbroadspectralrangetobothsidesfromtheresonantfre-quency( 50GHz).Theseextendedwingsaswellasthenarrow200-MHzholearemuchlesspronouncedonthemainZPLat625.5nm.

FIG.4.SequentialburningofaholeatT 2Kandat641.3nm incidentlaserpowerdensityof60mW/cm2,gatingwithatungstenlampthroughtheSchottcolor lterRG715 afteratotaltimeof0.5,2.5,5,and10min.Thetoptraceistheluminescenceexcitationspectrabefore

burning.

FIG.5.Sequentialerasing for5mineach oftheholeburnedafter10min bottomtraceofFig.4 withilluminationfromatung-stenlamp lteredthroughdifferentinterferencebandpass lters 10-nmFWHM :656,650,640,630,620,610,600,and590.

sample iii Theisheatedholesarefromthermally2KtostableT 100andK,persistandkeptwhenatthetheelevatedtemperatureforseveraltensofminutes.Aftersub-sequentcoolingdowntoT 2K,boththewidthanddepthofthethe ivsample holeTheremainholesunchanged.

inthecanspectralbeeffectivelyregionoferasedtheEuby2 irradiationabsorption.ofFigure5showstheprocessoftheerasureforthe641.3-nmsiteundersuccessiveirradiation,eachfor5min,withlightofdifferentwavelengths tungstenlampplusinterferenceband lters,10-nmFWHM .Itisseenthateffectiveerasingoc-cursonlyforwavelengthsshorterthantheEu2 ZPLregion.Althoughtheerasureisdonesuccessively,themainpointwhichisillustratedisthewavelengthdependenceoftheera-sureef ciency.Ingeneral,duringerasurethenarrow200-MHzfeaturedisappears rst,thenthe5-GHzholefadesbutalmostnochangeintheextendedwingsisobserved Fig.5 ,i.e.,theluminescenceremainsatalevelwhichislessthan65%ofthatbeforeholeburningoverthewhole20-GHzscanrange. Fig.625.5-nmIn5,ispresentedZPLFig. ,6,calculatedthespectraltogetherfromef ciencyoftheerasingwithdatathephotoluminescencesimilartothatgivenex-incitationspectrum.ThereisaclearcorrelationbetweentheerasurespectrumandtheEu2 absorptionspectrum.ThisfactsuggeststhattheEu3 actastrapswhichbecomecon-vertedtoEu2 bycapturingthephotoionizedelectrons.Itisimportanttonotethattheerasureratewasdirectlypropor-tionaltothepoweroftheerasinglight,i.e.,aone-photonexcitationprocessofEu2 tothe4f65dstateisresponsibleforfrom thev theBurningerasure.

rstoneofresultsadeepinsecondthedisappearanceholeatadifferentofthefrequency rstholeincludingthe 100-GHz-widepedestal.Thissupportstheionizationcharacteroftheholesandtheproposedredistribu-tionofEuionsbetweentheirchargestates,Eu2 andEu3 ,whichoccursduringirradiation seebelow

.

OFF-RESONANTSPECTRALHOLEBURNINGIN...12995

parisonoferasureef ciencyandEu2 excitationspectrum.Squares—relativeerasureef ciencymeasuredonaholeburnedonthemainsiteat625.5nmandatT 2Kbysequentialerasureatdifferentwavelengths 5mineach withabroadbandtunabledyelaser powerdensity10mW/cm2 .Solidline—photoluminescenceexcitationspectrumfromFig.

1.

IV.DISCUSSION

TheseobservationsofPSHBonthef-dEu2 ZPL’spro-videclearevidenceofatwo-stepphotoionizationmechanismofholeburninginCaS:Eucrystals.Thesecondstep,promo-tionofelectronstotheCB,isaccomplishedeitherbythesame monochromaticlight self-gating orbylievegatingare .PhotoelectronspredominantlyareEu3captured ions.Indeed,bytrapsIRthewhichirradiationpresencewebe-ofelectrontrapsshallowerthanEu3 ions—iftheydominated—wouldresultinafasterasureofholesunderirradiationatthewavelengthslongerthanEu2 ZPL’s,con-trarytoobservations.Thus,selectiveexcitationresultspre-dominantlyinaspatialredistributionofEuionsbetweentheirchargestates,Eu2 andEu3 tionofrelativelyshallowelectrontraps althoughshouldsomenotcontribu-beruledout .Thelargebindingenergyofthedominant traps Eu3 ions equaltotheionizationenergyofEu2, 2.3eV(EZPL ECB),explainsthethermalstabilityoftheholes.Thespectralshapeoftheholeshasacomplicatedstruc-turewhichcontainsbothrathernarrowfeatures central200-MHzholeanda5-GHz-wideunderlyingstructure andaverybroad( 100GHz)wings.TheХ5-GHzwidestruc-tureofboththemainholeandholesburnedintheperturbedsites,webelieve,isassociatedwithsideholeswhichresultfromthesmallcrystal- eldsplittinginthegroundstateandhyper neinteractionsoftheEu2 inboththe4f7(8SgroundstateandexcitedstateasobservedinCaF7/2)theholespectrumobservedinCaF2:Eu2 .7Forcomparison,2:Eu2isreproducedasthedashedlineinFig.3,wherethewidthofthesideholestructureisseentobeabout5GHz.TheabsenceofresolvedstructurecomparedtothatofCaF2:Eu2 isas-cribedtotheroleofchanginginternalCoulomb eldswhichalter duetotheStarkeffect theEu2 opticaltransitionen-ergiesduetothephotoionizationandtrappingoftheresult-ingphotoelectronsasdescribedbelow.Zero- eldcrystal- eld2 splittingsof 2–5GHzforthe8Scubicsitesinanumber7/2groundstateofEuarecommoninofhosts.AsinthecaseofCaF2:Eu2 ,7thecontributionofallionstotheholeatthelaserfrequencyresultsintheobservationofthenarrow 200MHz centralfeatureintheholespectrum.Theobservationofthebroad( 100GHz)wingsonthephotoionizationholeisadirectmanifestationofthephoto-

FIG.7.Schematicillustrationoftheroleofchanginginternalelectric eldsintheburningofphotoionizationspectralholes.IonA,whichinitiallycontributestotheholeatfrequency i,h …… 此处隐藏：6090字，全部文档内容请下载后查看。喜欢就下载吧 ……