Excitation Energy Dependence of Semiconductor Nanocrystal Emission Quantum Yields - Zhang et al. - 2021 - Unknown

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pubs.acs.org/JPCLLetterExcitationEnergyDependenceofSemiconductorNanocrystalEmissionQuantumYields∥∥ZhuomingZhang,ShubinZhang,IrinaGushchina,TianleGuo,MichaelC.Brennan,IliaM.Pavlovetc,TodA.Grusenmeyer,andMasaruKuno*CiteThis:J.Phys.Chem.Lett.2021,12,4024−4031ReadOnlineACCESSMetrics&MoreArticleRecommendations*sıSupportingInformationABSTRACT:Accuratemeasurementsofsemiconductornanocrystal(NC)emissionquantumyields(QYs)arecriticaltocondensedphaseopticalrefrigeration.OfparticularrelevancetomeasuringNCQYsisalongstandingdebateastowhetheranexcitationenergy-dependent(EED)QYexists.VariousreportsindicateexistenceofNCEEDQYs,suggestingthatthephenomenonislinkedtospecificensembleproperties.WethereforeinvestigateheretheexistenceofEEDQYsintwoNCsystems(CsPbBr3andCdSe)thatarepossiblecandidatesforuseinopticalrefrigeration.TheinfluenceofNCsize,size-distribution,surfaceligand,andas-madeemissionQYsareinvestigated.ExistenceofEEDQYsisassessedusingtwoapproaches(anabsoluteapproachusinganintegratingsphereandarelativeapproachinvolvingexcitationspectroscopy).Altogether,ourresultsshownoevidenceofEEDQYsacrosssamples.ThissuggeststhatparametersbeyondthosementionedaboveareresponsibleforobservationsofNCEEDQYs.emiconductornanocrystals(NCs)representoneofthepossiblewhenNCsurfacesaretreatedtoreducethedensityof6,20−23Smosttangiblesuccessesofnanoscienceandnanotechnol-midgapstates.1Applicationofnear-unityQYNCstodemonstratingogy.Fromanapplicationsstandpoint,colloidalNCsexhibitfavorableopticalresponsessuchaslargeabsorptionefficien-condensedphaselasercooling,however,requiresbettercies,2tunableabsorptionandemissionresponses,3−5andunderstandingofhowNCQYsareimpactedbyexcitation11narrowemissionbandsandlargeemissionquantumyieldsconditionssuchasexcitationintensityand/orexcitation(QYs).6,7TheseemissivepropertiesmakeNCsattractiveforawavelength.Thelatterisofparticularconcerngivenpriorwiderangeofapplications,includingsolarcells,8light-emittingstudies,suggestingthatvaryingNCexcitationenergiesleadsto910differentemissionQYs.24−41Suchexcitationenergy-dependentdiodes,photodetectors,andpossiblyforverifiabledemon-strationsofcondensedphaseopticalrefrigeration.11(EED)emissionQYswerefirstdemonstratedbyHoheiselet24Opticalrefrigerationand,inparticular,demonstrationsofal.whoshowedthroughphotoluminescenceexcitationcoolingsemiconductorsusinglighthaveattractedattention(PLE)measurementsthatCdSeNCemissionQYsdecreasedduetothepossibilityofachievingcryogenfreecoolingwithmonotonicallywhenensembleswereexcitedtotheblueofDownloadedviaUNIVOFCALIFORNIASANTABARBARAonMay16,2021at15:34:24(UTC).Seehttps://pubs.acs.org/sharingguidelinesforoptionsonhowtolegitimatelysharepublishedarticles.temperaturerangeslargerthanthoseofexistingPeltiertheirbandedges.Thiswasrationalizedasexcitingparticlesintotechnologies.11,12Furthermore,∼10Kcoolingfloorsareacontinuumofstates,distinctfromconfinedNCstates.TheliteratureonEEDQYs,however,isconflicted,withpossibleduetocoolingtransitionsbeingpopulatedevenat13suggestionsthatNCEEDQYsaretheresultofmeasurementverylowtemperatures.Unfortunately,materialquality25errors.Inparticular,Tontietal.havesuggestedthatEEDproblemshavepreventedverifiabledemonstrationsofcon-14−16QYsareartifactsduetothepresenceofNCaggregatesaswelldensedphaselasercooling.Inallcases,crucialtoasexcesssurfaceligandspresentinsolution.BothleadtodemonstratingcondensedphaseopticalrefrigerationisthescatteringlossesinPLEmeasurementsatshortexcitationrequirementofhavingnear-unityemissionQYs.Recent17wavelengthsandresultinmisleadingdeviationsbetweenPLEadvancesinNCandNCsurfacepassivationchemistriesandcorrespondingabsorptancespectra.Insupportofthis,nowmakesuchnear-unityemissionQYspossible.LargeNCemissionQYsderivefromwell-developedcolloidalchemistries.3,4,18Theyalsoresultfromtheidenti-Received:March12,2021ficationofdefect-tolerantNCsystemswithpointdefectsAccepted:April14,2021havingenergiesoutsideNCbandgaps.5,19AllinorganicPublished:April21,2021CsPbBr3NCsarethelatestexampleofsuchdefect-tolerantmaterials,showinglargeas-madeQYs,rangingfrom50%to1890%.Subsequentworkhasshownthatnear-unityQYsare©2021AmericanChemicalSocietyhttps://doi.org/10.1021/acs.jpclett.1c008114024J.Phys.Chem.Lett.2021,12,4024−4031

1TheJournalofPhysicalChemistryLetterspubs.acs.org/JPCLLetterFigure1.(a,d,g)TEMimagesforl=10.0nm,l=7.7nm,andl=5.9nmCsPbBr3NCs.Scalebar=20nm.(b,e,h)Correspondingabsorptance(solidblueline),PLE(dashedredline),andPL(dashedgreenline)spectra.Asterisksdenoteturn-onwavelengthsoflongpassfiltersusedinPLEmeasurements.(c,f,i)CorrespondingηPL(openredcircles)andabsoluteQY(solidgreencircles)valuesasfunctionsofλexc.Solidgraylinesin(c,f,i)areguidestotheeye.Tontietal.reportnoevidenceforEEDQYsfollowingToday,conventionalwisdomsuggeststhatobservationsofadditionalwashingofNCensemblestoremovescatteringEEDQYsstemsfromNCsensitivitiestoensemble-specific28sources.Geißleretal.corroboratethis,reportingexcitationparameterssuchasNCsize,size-distribution,choiceofsurfacewavelength-independentQYsinCdSeNCsthroughabsolute,ligand,andstartingemissionQYs.Thiswouldthenrationalizeintegratingsphere-basedQYmeasurements.inaself-consistentfashion,whichiswhysomestudiesreport24,26,27,31−3325,28,31,33Incontrast,Loomisandco-workersshowCdSeNCPLQYsNCEEDQYswhileothersdonot.decreasingwithincreasingexcitationenergieswitha∼90%Becauseoftheirimportanceforverifiabledemonstrationsof263111decrease∼1eVabovethebandgap.Lietal.likewiseshowcondensedphaselasercooling,weassessherewhetherevidenceforEEDQYsthroughconcertedPLEandCsPbBr3andCdSeNCsexhibitEEDQYsandwhetherabsorptancemeasurements.Loomisandco-workerssuggestobservationsofEEDQYsrelatetoensembleparametersthatthatEEDQYsresultfromincreasednonradiativecarrierinvolvetheabove-mentionedparameters(i.e.,NCcomposi-trappingaboveNCbandedgesduetoprogressiveincreasesintion,size,size-distribution,surfacepassivation,andstartingtrap-statedensities.Lietal.similarlysuggestincreasedhotemissionQY).AssessmentsaremadeusingtwoindependentcarriertrappingaboveNCbandedgesduetoincreasesinapproachestomeasuringNCQYs.ThefirstinvolvesabsolutecarriertrappingratesthatstemfromprogressivelylargerfreeQYmeasurementsusinganintegratingsphere.Thesecondenergydifferencesfortrapping.entailsrelativemeasurements,involvingphotoluminescenceSuchmixedresultsexisteveninnewlydevelopedall-excitationspectroscopy,conductedinconjunctionwith31inorganicperovskiteNCs.Specifically,Lietal.showabsorptancemeasurements.evidenceforEEDQYsinCsPbBr3NCsthroughPLEandTwoprimaryapproachesexistformeasuringNCemission32absorptancemeasurements.Mandalandco-workers,how-QYs.Broadlyspeaking,theyentailabsoluteorrelative11ever,reportonlyslightchangestoCsPbBr3NCQYsabovethemeasurements.ThelatterapproachismorecommonlybandedgeandthatonlywhenanexcitationenergythresholdusedsinceitofteninvolvesmeasuringNCemissionintensities∼0.8eVabovethebandgapisreacheddotheQYsdecreaserelativetoaknownQYstandardsuchasanorganicdye.significantly.ExplanationsforthesebehaviorsalsodifferwithNotableissuesunderliesuchrelativemeasurements,though,42Lietal.,suggestingfreeenergydifferencesasresponsibleforandincludeuncertaintiesduetoinstrumentresponse,43increasedhotcarriertrappingrateswhereasMandalandco-referenceQYs,andreferenceQYdependencieswith44workersinvokeasimilarmodeltoLoomisbypositingtheconcentration.AllofthesemakeobtainingaccurateQYs43existenceofamanifoldoftrapstatesaboveCsPbBr3’sproblematic.Incontrast,absolutemeasurementsinvolveconductionbandedge.directlymeasuringtheamountofabsorbed/emittedlightbya4025https://doi.org/10.1021/acs.jpclett.1c00811J.Phys.Chem.Lett.2021,12,4024−4031

2TheJournalofPhysicalChemistryLetterspubs.acs.org/JPCLLetterFigure2.ExperimentalηPLvaluesforal∼8nm(σ=0.8nm)CsPbBr3NCensemble,acquiredusing(a)500nm(openpurplecircles),(b)510nm(openbluecircles),and(c)525nm(openredcircles)turn-onlongpassfilters.Asterisks,diamonds,andsquaresdenotelocalminimaandmaximainthedata.CorrespondingsimulatedηPLdataareshownusingdashedlines.(d)SimulatedηPLvaluesfordifferentassumedsizedistributions.sampleandareconsequentlylesspronetomeasurementfiber-coupledSiphotoreceiverrecordsmeasured,integrated43errors.emissionintensitiesasafunctionofλexc.Forthel∼10nmInthisstudy,webeginbymeasuringCsPbBr3NCQYsusingensemble,a525nmlong-passfilterexcludesanyexcitationanabsoluteapproach.Figure1showsresultsofthesestudieslightfromreachingthephotoreceiver.Forbothl∼8andl∼6onthreedifferentCsPbBr3NCensembles.NCshavebeennmensembles,a510nmlong-passfilterisused.Asterisksin45madeusingamodifiedliteratureapproachwithdetailsoftheFigures1(b,e,h)indicateturn-onwavelengthsforfiltersusedsynthesisprovidedintheSupportingInformation(SI).FiguresinPLEmeasurements.Integratedemissionsignalsare1(a,d,g)showtransmissionelectronmicroscopy(TEM)normalizedforλexcchangestoexcitationintensities,usingimagesofthethreeensembles.DetailsofTEMmeasurementsthereferencechanneloftheabove-mentioned,autobalancedhavebeenprovidedintheSI.Fromanalyzingsuchimages,photoreceiver.correspondingmeanNCedgelengthsarel=10.0±1.5,l=ResultingPLEspectraareshowninFigures1(b,e,h)using7.7±0.8,andl=5.9±0.5nm.Associatedsizedistributionsdashedredlines.OfnoteisthatPLEspectracloselymatch(σ)areoforder10−15%.Sizinghistogramshavebeentheirrespectiveabsorptancespectra,reproducingbothprovidedinFigureS1.structureatthebandedgeandoverallexcited-stateNext,Figures1(b,e,h)showabsorptance(solidbluelines)progressions.Furthermore,PLE-basedStokesshifts(l∼10andbandedgePL(dashedgreenline,excitationwavelengthnm,41meV;l∼8nm,43meV;andl∼6nm,45meV)agreeλexc=460nm)spectraofallthreeensemblesintoluene(bandwiththosederivedfromabovedirectabsorptance/bandedge46,47edgeopticaldensitiesoforder∼0.1)collectedusingaemissionmeasurementsandwithpriorliterature.Slighthomemadeinstrument.AttheheartoftheinstrumentisadecreasesinPLEStokesshiftsrelativetotheabovevaluesarea46tunable,fiber-basedsupercontinuumlaser,whichenablesλexcconsequenceofresidual,ensemblesizedistributions.Suchtobetunedbetween420and750nm.DetectionisachievedresidualsizedistributionsalsocausePLEspectratobeslightlyusingacommercialautobalancedphotoreceiver.Additionalred-shiftedrelativetocorrespondingabsorptancemeasure-detailsoftheinstrumentcanbefoundintheSIwithamentssincePLEsignalsoriginatefromlargerNCswithinaschematicofthesetupshowninFigureS2.Figures1(b,e,h)givenensemble.25revealconfinement-inducedabsorptionblueshiftswithdecreas-IthaspreviouslybeenshownbyTontietal.thataningCsPbBr3NCsizeandsize-dependentStokesshifts[l∼10accurateaccountingofemissionefficiencyrequirescorrectingnm,48meV;l∼8nm,51meV;andl∼6nm,55meV]inPLEdatafortheactualfractionofphotonsabsorbedbya46,47goodagreementwithpriorresults.specimen.Consequently,PLEsignalsaredividedbymeasuredFigures1(c,f,i)showcorrespondingemissionQYsabsorptancespectrainFigures1(b,e,h)(solidbluelines).measuredusinganintegratingsphere.DetailsoftheseWhatresultsaresignalsreferredtointheliteratureasPL24,26,30,33,40,41measurementscanbefoundintheSI.Inallthreecases,as-efficiencies(ηPL).ResultingCsPbBr3NCηPLmadeQYsarearound80%.ThishighlightsthequalityofthevaluesareshowninFigures1(c,f,i)usingopenredcircles.NCs.Morerelevantly,nosignificantQYλexcdependenciesareAcomparisonofηPLspectra(openredcircles)forallthreeseen.QYvaluesremainrelativelyconstantacrossthesampledsamples,relativetotheircorrespondingabsoluteQYs(solidλexcrangewithnomorethana10%decreaseupto∼0.5eVgreencircles),revealstwoobservations.ThefirstisthatηPLabovecorrespondingbandedges.LoweremissionQYsamplesspectraareessentiallyconstantandlikeabsoluteQYwillbediscussedlaterinthemanuscript,givenpriorstudiesmeasurementsdonotshowmonotonicNCQYdecreaseslinkingEEDQYstothepresenceoftrapstates.withdecreasing(increasing)excitationwavelength(energy).BecauseitismorecommontoassessexistenceofEEDQYsIneffect,noapparentEEDQYsareobservedinthesethreeusingrelativeapproaches,wehaveconductedPLEmeasure-ensembles.mentsonthesamethreeensembles.Here,PLEmeasurementsThesecondobservationisthatthereareapparentPLhavebeenconductedusingthesamehome-builtsystem.Aefficiencyvariationsnearthebandedge,whichfollowstructure4026https://doi.org/10.1021/acs.jpclett.1c00811J.Phys.Chem.Lett.2021,12,4024−4031

3TheJournalofPhysicalChemistryLetterspubs.acs.org/JPCLLetter∞inthebandedgeabsorptanceofeachsample.ThesevariationsPLE()EI=[∫PL(Ecutoff,,xxE0)Abssubaremostapparentinthel∼6nmspecimen.Suchvariations026,27,29,33havepreviouslybeenreportedwithsuggestionsofsuchstructurebeingrelatedtotheexistenceoflowlyingtrap−ΔExxxxfxxabs(,)(,)(,,)d0]ε00σx(2)26,33states.Oursuggestion,though,isthatsuch(bandedge)whereweightsreflectintegratedPLintensitiesforagivenηPLstructureistheresultofresidualsizedistributionspresentsubensembleandwhichaccountfortherangeofenergiesinNCensembles.Ineffect,redshiftsofPLEspectrainFiguresmonitoredinourexperiments.Ineq2,theweight,IPL,is1(b,e,h),relativetocorrespondingabsorptancespectrayieldexplicitlyexpressedassuchstructurewhenthetwofunctionsaredivided.ThelinkbetweenbandedgeηPLstructureandsizeEcutoffdistributionisdemonstratedinFigures2(a−c)whereIPL(,Excutoff,x0)=[∫PLsubEEx′−ΔPL(,xE0)]d′0experimentalPLefficiencyspectrahavebeenacquiredusing(3)different,monitoredemissionwavelengths(longpassfilterturn-onwavelengthsof500,510,and525nm)inPLEwhereEcutoffistheenergyassociatedwithlongpassfilterturn-measurementsforagivenl∼8nm(σ=0.8nm)CsPbBr3onwavelengthsusedinPLEmeasurementsandPLsubistheensemble.Theeffectsofsizeselectivitycanthereforebesize-dependentPLspectrumofasubensemblewithNCsizeassessedinacquiredηPLtracessincelargerlongpassfilterturn-equaltox0.MoredetailsaboutPLsubcanbefoundintheSIonwavelengthsprogressivelyselectoutthelargestNCspresentwithaplotshowninFigureS4.ΔEPL(x,x0)isthebandedgewithinanensemble’sresidualsizedistribution.energydifferencebetweentwodifferent-sizedNCs(xandx0).46Figures2(a−c)revealthatincreasingthesizeselectivityofΔEPLisobtainedfromliteratureNCsizingcurveswithPLEmeasurementsintroducesbandedgestructuretospectrallyoffsetbutidenticalPLprofilesassumedforsubensembleswithinalimitedsizerange.OfnoteisthatcorrespondingηPLspectra.Thisisbestseenbycomparingthe500and525nmdatasets.Localmaxima/minimainηΔEPLandΔEAbsarenotidenticalduetoexistenceofasize-PL46,47dependentStokesshift.Additionalinformationaboutthesespectraareadditionallysensitivetothedata’ssizeselectivitywithminimaforthe500nm(525nm)turn-ondataat∼488numericalsimulations,includingplotsofEabsandEPL(FigureS5)fromwhereΔEabsandΔEPLhavebeenobtained,canbenm(492nm)and∼462nm(∼465nm).Ingeneral,Figures2foundintheSI.(a−c)showprogressiveredshiftsofηPLmaxima/minimawithSimulationresultsareshownasdashedlinesinFigures2increasingsizeselectivity.Thesesensitivitiesstronglysuggest(a−c).Itisevidentthatthesimulatedspectranear-thatηPLbandedgestructuresaresize-distributionrelated.quantitativelyreproduceexperimentalbandedgeηPLstructureAbsorptance,PL,andPLEspectraforthel∼8nmensembleinthel∼8nmensemble.Furthermore,localmaxima/minimastudiedinFigures2(a−c)havebeenprovidedinFigureS3.insimulatedηPLtracestrackobservedexperimentalchangesAccompanyingnumericalsimulationscorroboratethiswithincreasingsizeselectivity.Anadditionalsimulation,whichconclusion.Namely,wehaveconductedsimulationsofηPLassumesthatallemissionfromanensembleiscollected,revealsbymodelingaNCensemble’sabsorptionandPLEspectra.thattheηPLbandedgestructuredisappearsintheabsenceofSize-distributioneffectsareconsideredbyexplicitlyincludingsizeselectivityinPLEmeasurements(FigureS6).spectralcontributionsfromdifferent-sizedsubensembleswith-Figure2dcomplementstheseηPLresultsbysimulatingtheintheoverallparentensemble.Inbrief,anensemble’sexpliciteffectsofalteringthel∼8nmensemble’ssizeabsorptionspectrumisfirstconstructedusingthefollowingdistribution.A510nmPLEturn-onwavelengthisassumedinweightedlinearcombinationofsubensemblespectraallcases.Whensizeselectivityinthemeasurementisremovedbyprogressivelydecreasingthepolydispersityoftheensemble∞Abs()EE=[∫Abssub−Δ]σEabs(,xx0)()(,εxfxx0,)dx(i.e.,decreasingσvaluesfromσ=1.2nmtoσ=0.1nm),what0resultsisaprogressivelossofbandedgeηPLstructure.(1)Consequently,thisandthedatainFigures2(a−c)stronglyIneq1,thevariablexdenotesNCsize,andAbssubisthesuggestthatthebandedgestructuresinηPLspectraaremainlyartifactsofanensemble’sresidualsizedistribution.size-dependentabsorptionspectrumofasubensemblewithInfluenceofAs-MadeQYs,Traps,andSurfaceChemistry.NCsizeequaltox0.AdditionaldetailsaboutAbssubcanbeAlthoughCsPbBr3isthoughttobedefecttolerant,anotionfoundintheSIwithaplotshowninFigureS4.ΔEabs(x,x0)issupportedbyelectronicstructurecalculationswhichshowthethebandedgeenergydifferencebetweentwodifferent-sized49−51absenceofmidgapstates,as-madeQYsarenotunity.NCs(xandx0).ΔEabsisobtainedfromknownliteratureNCThissuggeststhatdefectstates,whichinducenonradiative46sizingcurves.Weassumespectrallyoffsetbutidenticalrelaxation,doexist.Theconclusioniscorroboratedbysurfaceexcited-stateprogressionsintheabsorptionofdifferent-sizedchemistrieswhichraiseas-madeQYstounityornearNCswithinalimitedsizerange.Thefunctionε(x)expressesunity.20,45thesize-dependentscalingofNCmolarabsorptivities,whichSincepriorstudieshavelinkedEEDQYstotrapstates,we348hasbeenreportedtogrowwithNCvolume[i.e.,ε(x)∝x].investigatewhetherEEDQYsexistinCsPbBrNCshaving3f(x,x0,σ)representstheensemble’ssize-distributionusingaloweras-madeQYsthanthosestudiedinFigure1.Notethata()xx−218Gaussianprobabilitydensity,i.e.,f(,,)expxxσ∝0differentpreparationforCsPbBr3NCshasbeenusedhere0()2σ2sinceitisdifficulttoaltertheas-madeQYsofNCsinvolvedinwithσthestandarddeviationofNCsizesinthedistribution.Figure1.ThispreparationdiffersfromthefirstinthatNCsareTheensemble’scorrespondingPLEspectrumisdescribedbypassivatedwitholeateligandsasopposedtodidodecyldime-thefollowinglinearcombinationofweighted,subensemblethylammonium.Furthermore,startingQYstendtobelowerabsorptionspectra:andcanempiricallybecontrolledbychangingtheCs/Pb4027https://doi.org/10.1021/acs.jpclett.1c00811J.Phys.Chem.Lett.2021,12,4024−4031

4TheJournalofPhysicalChemistryLetterspubs.acs.org/JPCLLetterFigure3.(a,d,g)TEMimagesford=7.2nm,d=5.9nm,andd=4.0nmCdSeNCs.Scalebar=20nm.(b,e,h)Correspondingabsorptance(solidblueline),PLE(dashedredline),andPL(dashedgreenline)spectra.(c,f,i)CorrespondingηPL(openredcircles)andabsoluteQY(solidgreencircles)valuesasfunctionsofλexc.Solidgraylinesin(c,f,i)areguidestotheeye.4precursorratioduringsynthesis.Detailsofthesyntheticapproach.DetailsofthesynthesishavebeenprovidedintheprocedurehavebeenprovidedintheSI.SI.Figures3(a,d,g)showTEMimagesofresultingCdSeFigureS7showsresultsofQYmeasurementsonthreeNCs.AnalysisoftheseimagesrevealincreasinglyprolateCsPbBr3NCensembleswherestarting(bandedgeexcited)shapeswithincreasingsize.Thisisinlinewithwhathas28QYshavebeenmadeprogressivelysmaller(∼52%,∼35%,andpreviouslybeenreportedintheliterature.TEM-established∼15%).Thedata,likethatinFigure1,showaninvarianceofeffectivediametersared=7.2±0.9,d=5.9±0.7,andd=4.0bothabsoluteQYsandηPLvaluestoexcitationwavelength.±0.7nm.FigureS10showsresultingsizinghistogramswithFigureS8furtherassesseswhetheranyEEDQYsareobservedestimatedsizedistributionsrangingfrom11%to17%.32belowλexc=370nmgivenpriorresultsbyMandaletal.whoFigures3(b,e,h)showcorrespondingabsorptance(solidreportmonotonicQYdecreasesupto25%betweenλexc=370bluelines)andbandedgePL(dashedgreenlines)spectraofand300nm.Here,absoluteQYmeasurementshavebeenCdSeNCsdispersedinhexane(bandedgeopticaldensitiesconductedonthreeCsPbBr3NCensembleswithQYsof20%,∼0.1).AswithCsPbBr3,confinementeffectsareevident,as32%,and41%downtoλexc=310nmusingacommercialseenthroughblueshiftsofboththebandedgeabsorptionandfluorimeterequippedwithanintegratingsphere.DetailsofemissionwithdecreasingNCsize.Figures3(b,e,h)thesemeasurementscanbefoundintheSI.ThedatashownoadditionallyplotassociatedPLEspectra(dashedredlines)apparentEEDQYs.TogetherwithFigureS7,thiscollectivelythathavebeenacquired.ObtainedPLEspectracloselyfollowsuggeststhatas-madeQYsarenotafactorininducingpossiblecorrespondingabsorptancespectraandreproducebothbandEEDQYs.edgestructureandexcited-stateprogressions.OnlyasmallFinally,FigureS9comparesQYandηPLdataforCsPbBr3departureisseeninthed∼7nmensembleatwavelengthsNCswithsimilaraverageQYs(87%and53%)butwithbelow520nm.differentsurfaceligands.SamplesweremadeusingthetwoFigures3(c,f,i)nowplotmeasuredabsoluteQYs(solidsynthesesdescribedabove.Thecomparisonismotivatedbygreencircles)andηPLvalues(openredcircles)asfunctionsofseveralstudieslinkingligandpassivationtothepresence,λexc.ThedataagainshowthatabsoluteQYsareeffectively20,23,45energy,anddensityofmidgapstates.Thiscould,inturn,constantacrosstheinvestigatedspectralrange.OfnoteisthatinfluencetheexistenceofEEDQYs.Aswithpriordata,Figureabsolute(as-made,bandedgeexcited)QYvaluesforallthreeS9showsnoevidenceofEEDQYsineitherabsoluteorηPLsamples(4%,8%,and5%)aremuchsmallerthanthoseformeasurements.CsPbBr3.ThishighlightsthedefecttolerantnatureofCsPbBr3.CdSeNCs.WenowinvestigatewhetherEEDQYsexistinCdSeηPLvaluesarealsorelativelyconstantwithsize-CdSeNCsasthishasbeentheprototypicalsystemfordistribution-inducedstructurenearthebandedge.Onlythe24−29,31,33demonstratingtheirexistence.AswithCsPbBr3,d∼7nmensembleshowsaslight10%ηPLdecreasewhenthreedifferentsizesweremadeusinganexistingliterature∼0.9eVabovethebandedge.Ingeneral,thedatainFigure34028https://doi.org/10.1021/acs.jpclett.1c00811J.Phys.Chem.Lett.2021,12,4024−4031

5TheJournalofPhysicalChemistryLetterspubs.acs.org/JPCLLetterstronglypointtotheabsenceofEEDQYsintheseCdSeShubinZhang−UniversityofNotreDame,Departmentofensembles.TogetherwithFigure1,ourresultssuggestthatPhysics,NotreDame,Indiana46556,UnitedStatesEEDQYsarenotauniversalfeatureofcolloidalNCs.IrinaGushchina−UniversityofNotreDame,DepartmentofInconclusion,wefindnoevidenceofEEDQYsinCsPbBr3ChemistryandBiochemistry,NotreDame,Indiana46556,andCdSeNCsthatwehaveproduced.ThishasentailedUnitedStatesdetailedabsoluteandrelativeQYmeasurements.NCQYsforTianleGuo−UniversityofNotreDame,DepartmentofbothsystemsappearinsensitivetoexcitationenergyacrossChemistryandBiochemistry,NotreDame,Indiana46556,investigatedspectralrangesthatextendupto∼1.6eV(∼0.9UnitedStateseV)abovecorrespondingCsPbBr3(CdSe)NCbandedges.MichaelC.Brennan−AirForceResearchLaboratory,ThesemeasurementsaccountforpossibleNCcomposition,MaterialsandManufacturingDirectorate,Dayton,Ohiosize,sizedistribution,surfaceligand,andstartingQY45433,UnitedStates;orcid.org/0000-0002-4482-5173influencesonwhetherEEDQYsareobserved.OurresultsIliaM.Pavlovetc−UniversityofNotreDame,DepartmentofareofrelevanceaspastworkhassuggestedthatNCChemistryandBiochemistry,NotreDame,Indiana46556,photophysicsand,inparticular,observationsofEEDQYsareUnitedStatesexquisitelysensitivetotheseensembleparameters.OurworkTodA.Grusenmeyer−AirForceResearchLaboratory,thereforesuggeststhatintrabandrelaxationratesinNCcanbeMaterialsandManufacturingDirectorate,Dayton,Ohiofasterthancompetinghotcarriertrappingprocessesthatcould45433,UnitedStates;orcid.org/0000-0002-1842-056XinduceEEDQYs.Moreimportantly,theseresultspointtoCompletecontactinformationisavailableat:factorsbeyondNCcomposition,size,sizedistribution,surfacehttps://pubs.acs.org/10.1021/acs.jpclett.1c00811chemistry,andstartingemissionQYaskeytowhetherNCEEDQYsareobserved.AuthorContributions∥■Z.Z.andS.Z.contributedequallytothiswork.ASSOCIATEDCONTENTNotes*sıSupportingInformationTheauthorsdeclarenocompetingfinancialinterest.TheSupportingInformationisavailablefreeofchargeathttps://pubs.acs.org/doi/10.1021/acs.jpclett.1c00811.■ACKNOWLEDGMENTSDetailsofthesynthesisofhighQYCsPbBr3NCs,detailsWethankD.BaranovandG.AlmeidaforhelpfuldiscussionsofTEMmeasurements,sizinghistogramsforthreehighonthesynthesisofnear-unityemissionQYCsPbBr3NCs.QYCsPbBr3NCensembles,detailsofthehome-builtM.K.thankstheMURI:MARBLeprojectundertheauspicesofinstrumentationforabsorptance,PL,PLE,ηPL,andtheAirForceOfficeofScientificResearch(awardno.FA9550-absoluteQYmeasurements,includingaschematic,16-1-0362)forfinancialsupport.WealsothanktheNDdetailsofabsoluteQYmeasurements,absorptance,PL,EnergyMaterialsCharacterizationFacilityforuseoftheirandPLEspectraforthel∼8nmensemblestudiedinequipment.ResearchattheAirForceResearchLaboratoryFigure2a,additionalinformationaboutnumerical(AFRL)wasperformedwhileM.C.B.heldanNRCResearchsimulationsforbandedgeηPLstructure,includesAbssub,Associateshipaward.M.C.B.andT.A.G.acknowledgefundingPLsub,andplotsofEabsaswellasEPLforCsPbBr3,underAFRL/RXAPcontractFA8650-16-D-5402-0001.additionalsimulationshowingthedisappearanceofηPLbandedgestructureintheabsenceofsize-selectivityin■REFERENCESPLEmeasurements,detailsofthesynthesisoflowerQY(1)Choi,J.-H.;Wang,H.;Oh,S.J.;Paik,T.;Sung,P.;Sung,J.;Ye,CsPbBr3NCs,resultsofQYmeasurementsforthreelowX.;Zhao,T.;Diroll,B.T.;Murray,C.B.;Kagan,C.R.ExploitingtheQYCsPbBr3NCensembles,resultsofQYmeasure-ColloidalNanocrystalLibrarytoConstructElectronicDevices.SciencementsonthreeadditionallowQYCsPbBr3NC2016,352,205−208.ensemblesdowntoλexc=310nm,comparisonofQY(2)Giblin,J.;Kuno,M.NanostructureAbsorption:AComparativeandηPLdatafortwoCsPbBr3NCensembleswithStudyofNanowireandColloidalQuantumDotAbsorptionCrosssimilarQYsbutwithdifferentsurfaceligands,detailsofSections.J.Phys.Chem.Lett.2010,1,3340−3348.thesynthesisofCdSeNCs,andsizinghistogramsfor(3)Murray,C.B.;Norris,D.J.;Bawendi,M.G.SynthesisandCharacterizationofNearlyMonodisperseCdE(E=sulfur,selenium,threeCdSeNCensembles(PDF)tellurium)SemiconductorNanocrystallites.J.Am.Chem.Soc.1993,115,8706−8715.■(4)Peng,Z.A.;Peng,X.FormationofHigh-QualityCdTe,CdSe,AUTHORINFORMATIONandCdSNanocrystalsUsingCdOasPrecursor.J.Am.Chem.Soc.CorrespondingAuthor2001,123,183−184.MasaruKuno−UniversityofNotreDame,Departmentof(5)Wehrenberg,B.L.;Wang,C.;Guyot-Sionnest,P.InterbandandChemistryandBiochemistry,NotreDame,Indiana46556,IntrabandOpticalStudiesofPbSeColloidalQuantumDots.J.Phys.UnitedStates;UniversityofNotreDame,DepartmentofChem.B2002,106,10634−10640.(6)DiStasio,F.;Christodoulou,S.;Huo,N.;Konstantatos,G.Near-Physics,NotreDame,Indiana46556,UnitedStates;UnityPhotoluminescenceQuantumYieldinCsPbBr3Nanocrystalorcid.org/0000-0003-4210-8514;Email:mkuno@Solid-StateFilmsviaPostsynthesisTreatmentwithLeadBromide.nd.eduChem.Mater.2017,29,7663−7667.(7)Greytak,A.B.;Allen,P.M.;Liu,W.;Zhao,J.;Young,E.R.;AuthorsPopovic,Z.;Walker,B.J.;Nocera,D.G.;Bawendi,M.G.AlternatinǵZhuomingZhang−UniversityofNotreDame,DepartmentofLayerAdditionApproachtoCdSe/CdSCore/ShellQuantumDotsChemistry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