引文数据库
数据库 时间:2021-02-21 阅读:()
登录我的EndNoteWeb我的ResearcherID我的引文跟踪我已保存的检索注销帮助检索检索历史标记结果列表(0)所有数据库数据库中查看此记录:z查看引文数据(来自WebofScience)z查看医疗数据(来自Medline)页码,1/2ISIWebofKnowledge[v.
4.
8]-所有数据库全记录2010-12-21http://apps.
isiknowledge.
com/full_record.
doproduct=UA&search_mode.
.
.
(NNSFC)50672030[显示基金资助信息]出版商:AMERSCIENTIFICPUBLISHERS,25650NORTHLEWISWAY,STEVENSONRANCH,CA91381-1439USAIDS号:548RVISSN:1533-4880DOI:10.
1166/jnn.
2010.
2085数据库全记录2010-12-21http://apps.
isiknowledge.
com/full_record.
doproduct=UA&search_mode.
.
.
RESEARCHARTICLECopyright2010AmericanScienticPublishersAllrightsreservedPrintedintheUnitedStatesofAmericaJournalofNanoscienceandNanotechnologyVol.
10,1–4,2010BrightGreenUpconversionFluorescenceofYb3+,Er3+-CodopedNaYF4NanocrystalsLiliWang12,WeipingQin1,YanWang1,GuofengWang1,ChunyanCao1,GuodongWei1,RyongjinKim1,DaishengZhang1,FuhengDing1,andChunfengHe11StateKeyLaboratoryonIntegratedOptoelectronics,CollegeofElectronicScienceandEngineering,JilinUniversity,Changchun130012,China2SchoolofBasicSciences,ChangchunUniversityofTechnology,Changchun130012,ChinaUniformhexagonalNaYF4:Yb3+,Er3+nanocrystals(NCs)withbrightgreenupconversionuores-cencewereprepared.
Thenanocrystalswerehighlyhydrophobicanddispersedincyclohexaneformingatransparentcolloidalsolutionduetotheuseofoleicacidasacappingligand.
Temper-aturedependenceforemissionofEr3+ionsinthissamplewasalsostudied.
ThegreenemissionintensityofEr3+ionshadamaximumat160Kunder980nmexcitation,whichwasattributedtothethermallyactivateddistributionofelectronsandthethermalquenchingeffect.
Thetransparentcolloidalsolutionisexpectedtobeagoodcandidateforresearchinbiologicalimagingordisplayapplications.
Keywords:NaYF4,RareEarth,NonradiativeRelaxation.
1.
INTRODUCTIONAnumberofrare-earth-dopeduoridenanocrystalsandsubmicrocrystalswithefcientinfrared(IR)radiationintovisiblelightthroughfrequencyupconversion(UC)atroomtemperaturehavebeenproduced.
1–6Duetothelowphotonenergy,therelativelyhighefciencyoftheUCprocessintheseuoridecrystals,andtheinexpensive980nmnear-IR(NIR)diodelasers,therealizationofefcientNIRtovisi-bleupconvertingnanocrystalsandsubmicrocrystalsshouldunlockarealmofnewpossibilitiesintheeldofbiosen-sors,displays,andshort-wavelengthlasers.
Itiswell-knownthatthesizeandshapeofinorganicnanocrystalshavegreatinuenceontheirphysicalproperties.
78Thus,furtherexplorationsofnovelnanomorphology,withcon-trolledsizeandshapebyconvenientsynthesismethods,isofgreatimportanceforthedevelopmentofnewfunctionaldevices.
Simultaneously,inordertorealizethebiologicalimagingordisplayapplicationsbasedontheUCprinci-pleinauid,itiscrucialtoinvestigatelanthanide-dopedUCnanocrystallinecolloidalsolutions.
Todate,thesuc-cessfulpreparationoftransparentcolloidalsolutionshasbeendemonstratedinafewNaYF4nanocrystals.
However,itstemperature-dependentluminescencebehaviorwassel-domstudied.
Inthisletter,wereportastudyonthetrans-parentNaYF4:Yb3+,Er3+nanocrystalcolloidalsolution.
Authortowhomcorrespondenceshouldbeaddressed.
Under980nmexcitationfromalaserdiode,thetrans-parentsolutionpresentedbrightgreenUCuorescence.
Itisexpectedtobeagoodcandidateforresearchinbio-logicalimagingordisplayapplications.
Wealsoinves-tigatedthetemperature-dependentcharacteristicsofEr3+ionemissions.
Theunderstandingofthisprocessishelpfulinthesearchforhighefciencyphosphors.
Thermalizationeffectsbetweenthe2H11/2and4S3/2levelsseparatedby765cm1intheseuoridenanocrystalswerealsoreported.
Theresultsshowthat520nmemissionisfavoredathightemperaturesbyitshigheremissioncrosssectionandthattheoverallgreenuorescenceincreasesconsequently.
2.
EXPERIMENTALDETAILSInatypicalpreparation,0.
6gNaOHwasdissolvedinasolutioncontainingoleicacid,ethanol,anddeionizedwater(10/5/4,v/v/v).
Then1.
5mmolKF,0.
39mmolY(NO33·6H2O,0.
10mmolYb(NO33·6H2Oand0.
01mmolEr(NO3)3·6H2Owereaddedtothesolu-tionundervigorousstirring.
Themixturewasagitatedfor30minandthentransferredintoa50-mLautoclave,sealed,andtreatedat180Cfor16h.
Subsequently,themixturewasallowedtocooltoroomtemperature,andthepowderwasobtainedbycentrifuging,rinsing,anddrying.
PhaseidenticationwasperformedviaX-raydiffrac-tion(XRD,modelRigakuRU-200b),usingnickel-lteredJ.
Nanosci.
Nanotechnol.
2010,Vol.
10,No.
xx1533-4880/2010/10/001/004doi:10.
1166/jnn.
2010.
20851Vol.
10,1825–1828,201031533-4880/2010/10/1825/0051825RESEARCHARTICLEBrightGreenUpconversionFluorescenceofYb3+,Er3+-CodopedNaYF4NanocrystalsWangetal.
CuKradiation(=15406).
Thesizeandmorphol-ogyofthenanocrystalswerecharacterizedbytransmissionelectronmicroscopy(TEM,JEM,2000EX200kV).
High-resolutionemissionspectrawereobtainedat13–300Kwiththesamplemountedinaheliumexchangegascham-berofaclosedcyclerefrigerationsystem.
A980nmlaserdiodewasusedastheexcitationsource.
Theuorescencephotoofthecolloidalsolutionwith0.
2mg/mLconcen-trationincyclohexanewasacquiredwithadigitalcameraunder980nmexcitationfromalaserdiode.
3.
RESULTSANDDISCUSSIONThecrystalstructureandthephasepurityofthematerialwasobtainedbyXRD,asshowninFigure1.
AccordingtoJCPDSstandardcards,theNaYF4:Yb3+,Er3+nano-crystalsexhibitapurehexagonalstructure.
TheXRDpat-ternalsodemonstratesthattheNaionscanbeincorporatedintotheframeworkofYFn,formingNaYF4.
Figure2(a)showstheTEMimageofhexagonal-phaseNaYF4:Yb3+,Er3+nanocrystals.
Theimageclearlyrevealsthatthemorphologyoftheas-synthesizednano-crystalsishexagonalnanoplateswithameansizeof200nm.
Intheimage,thereisnoaggregationofnano-crystals,whichindicatesthegooddispersionofthissam-ple.
Inaddition,thesenanocrystalsarehighlycrystalline.
Theirhighcrystallinityisalsoinferredfromtheelec-trondiffractionimages(insertinFig.
2(a)).
Figure2(b)illustratesphotographsofhexagonal-phaseNaYF4:Yb3+,Er3+dispersedincyclohexanewiththeconcentrationof2mg/mL.
Wecanseethatthecolloidalsolutionisfullytransparentintheleftpicture,andtherightpictureshowsthatthecolloidalsolutionemitseye-visibleUClumines-cenceunder980nmexcitation.
Thissolutionisstableformonthswithoutanyvisibleprecipitate.
ThesurfacesofthesynthesizedNaYF4nanocrystalswerecoveredbyFig.
1.
PowderXRDpatternofhexagonal-phaseNaYF4:Yb3+,Er3+nanocrystals.
Fig.
2.
(a)TEMimageofthemonodispersedNaYF4:Yb3+,Er3+nano-crystals.
Insert:Theelectronicdiffractionpatternsofthesample.
(b)Pho-tographofhexagonal-phaseNaYF4:Yb3+,Er3+dispersedincyclohexaneshowseye-visibleupconversionluminescenceunder980nmexcitationwiththeconcentrationof2mg/mL.
Theleftcellshowsthatthecolloidalsolutionisfullytransparent.
thesurfactantoleicacid,sothenanocrystalswerehighlyhydrophobicanddispersedincyclohexane.
ThenormalizedUCemissionspectraofhexagonal-phaseNaYF4:Yb3+,Er3+nanocrystalsatthreediffer-enttemperaturesunder980nmexcitationareshowninFigure3.
Thelaserpoweris400mW.
Inthespectra,thegreenemissionspeaksareobservedintherangeof515–560nm,correspondingtothe2H11/2,4S3/2→4I15/2transitions,whiletheredemissionpeaksareobservedbetween640and680,correspondingtothe4F9/2→4I15/2transitions.
At13K,the2H11/2uorescenceintensityisnegligible,anditprogressivelyincreaseswithincreas-ingtemperature.
Thisisarepresentativebehaviorofpro-cessesinvolvingthethermallycoupled4S3/2and2H11/2asreportedelsewhere.
910Theupconversionluminescencemechanismandpopula-tionprocessinEr3+/Yb3+-codopedsystemsarepresentedFig.
3.
Upconversionemissionspectraofhexagonal-phaseNaYF4:Yb3+,Er3+nanocrystalsat13,190,and300K.
2J.
Nanosci.
Nanotechnol.
10,1–4,20101826J.
Nanosci.
Nanotechnol.
10,1825–1828,2010RESEARCHARTICLEWangetal.
BrightGreenUpconversionFluorescenceofYb3+,Er3+-CodopedNaYF4NanocrystalsinFigure4.
Following980nmirradiation,theEr3+ionisexcitedtothe4F7/2stateviatwosuccessiveenergytrans-fersfromtheYb3+ionsinthe2F5/2state.
Thus,oneYb3+ionwilltransferitsenergytoanEr3+ioninthegroundstate,therebyexcitingittothe4I11/2state.
ThisprocessisfollowedbyatransferofenergyfromanotherYb3+ionalsoinitsexcitedstate,resultinginthepopulationofthe4F7/2stateoftheerbiumion.
Theloweremittinglevelsarethenpopulatedviamultiphononrelaxation,andgreenandredemissionsarethenobserved.
Ofcourse,interactionsbetweentwoEr3+ionscannotnecessarilybeignored.
Anearinfrared(NIR)photonfromthepumpbeamwillalsoexciteanEr3+iontoits4I11/2state.
AnotherEr3+ionalsointhe4I11/2stateandincloseproximitywilltransferitsenergytotheinitialion,therebyexcitingittothe4F7/2state.
However,followingtheadditionofYb3+ions,thisprocessisgreatlydiminishedduetothelargeabsorptioncross-sectionoftheytterbiumions.
Thus,thesimultaneoustransferofenergyfromYb3+,whichpopulatesthe4F7/2state,isdominant.
Thedependenceoftheupconversionefciencyupontemperaturewasexamined,andtheresultsaredepictedinFigure5.
Ascanbeinferredfromexperimentaldata,thevisibleemissionefciencyincreasedbyafactorof4whenthesamplewascooledfromroomtemper-atureto160K.
Thisbehaviorreectsthecompetitionbetweenthetwomajorthermaleffectsactinginthesys-temasfollows.
Onethermaleffectisthetemperature-enhancedsidebandanti-Stokesexcitationofthesensitizer,whichisresponsiblefortheincreaseintheupconver-sionemissionefciency.
Theexpressionoftheabsorp-tioncross-sectionrelatedtothetemperatureiswrittenasT=0exp/kBT1E/,where0istheabsorptioncrosssectionat0Kandisthephotonenergy.
Theotherthermaleffectisthethermallyenhancednonradiativedecayratethatinhibitsradiativeemission.
ThenonradiativetransitionprobabilitybetweenlevelsforlowconcentrationsofEr3+ionsisduetomultiphononFig.
4.
SchematicdiagramofYb3+-sensitizedEr3+upconversionunder980nmexcitation.
Thesolidlinesrepresentradiativetransitions,andthedashedlinesrepresentnonradiativetransitions.
relaxationprocesses,andcanberelatedtothetemperaturethroughWNR=WNR01exp/kBTE/,1112whereWNR0isthenonradiativerelaxationrateat0K.
ItalsocanbeseenfromFigure5(b)thatthegreenemissionfrom4S3/2decreasesfasterthantheredemis-sionfrom4F9/2above180Kastemperatureincreases.
Asmentionedabove,therearetwomainfactors.
Onefactoristhethermalquenchingeffectofluminescence.
Theinter-mediatelevelofthegreenemissionis4I11/2,whilethatoftheredemissionis4I13/2.
Fortheredaswellasthegreenemission,thenonradiativerelaxationof4I11/2→4I13/2and4S3/2→4F9/2isinvolved,whichincreasestheelectronpopulationon4F9/2whiledecreasingthaton4S3/2.
Thatmakestheredemissionsdecreaseslowerthanthatofgreenemissions.
Asiswellknown,thenonradiativerelax-ationprobabilityissize-dependent.
Astheparticlesize(a)(b)Fig.
5.
(a)VisibleUCluminescencespectrainNaYF4:Yb3+,Er3+nanocrystalsatdifferenttemperatures.
(b)Theupconversionemissionintensityof4S3/2→4I15/2,4F9/2→4I15/2inNaYF4:Yb3+,Er3+nano-crystalsasafunctionoftemperature.
J.
Nanosci.
Nanotechnol.
10,1–4,20103J.
Nanosci.
Nanotechnol.
10,1825–1828,20101827RESEARCHARTICLEBrightGreenUpconversionFluorescenceofYb3+,Er3+-CodopedNaYF4NanocrystalsWangetal.
decreases,duetotheincreaseofthesurface-to-volumeratiocomparedwiththebulk,alargenumberofNO23andOHareinvolved,withvibrationalenergiesof1350and3350cm1,respectively,andhaveavailablelargevibrationalquantatoefcientlydepopulatetheexcitedstates4I11/2and4S3/2nonradiatively.
1314Thus,thenon-radiativerelaxationbecomesmoreefcientthanthermalexcitation.
Theotherfactoristhethermallyactivateddis-tributionofelectronsamong4S3/2.
Someofelectronscanbethermallyexcitedinto2H11/2from4S3/2asthetemper-atureincreases.
Thatalsodecreasesthegreenemissionsfrom4S3/2.
4.
SUMMARYInconclusion,Yb3+,Er3+-codopeduoridenanocrystalsweresynthesized.
Thesecrystalsdemonstratehighcrys-talqualityandexcellentdispersivityandcanbetrans-parentlydispersedinnonpolarsolvents.
Atthesametime,thetransparentcolloidalsolutionshowsefcientinfrared-to-visibleUCemission.
Thegreenupconversionluminescenceexhibitedafour-foldintensityenhancementwhenthetemperatureofthesamplewasvariedintherangebetween20Kand300Kwiththemaximumintensityattainedaround160K.
Theexcellentlumines-cenceofhexagonal-phaseNaYF4:Yb3+,Er3+nanocrystalsprovidesthebasisforamorethoroughinvestigationoftheiropticalandtemperaturepropertiesandmightenableapplicationsinnanoscalebiologicalimagingordisplays.
Acknowledgments:ThisworkwassupportedbytheNationalNaturalScienceFoundationofChina(NNSFC)(grants10874058and50672030).
ReferencesandNotes1.
El-SayedandM.
A.
Acc,Chem.
Rev.
34,257(2001).
2.
J.
C.
Boyer,F.
Vetrone,L.
A.
Cuccia,andJ.
A.
Capobianco,J.
Am.
Chem.
Soc.
128,7444(2006).
3.
G.
F.
Wang,W.
P.
Qin,J.
S.
Zhang,J.
S.
Zhang,Y.
Wang,C.
Y.
Cao,L.
L.
Wang,G.
D.
Wei,P.
F.
Zhu,andR.
Kim,J.
Phys.
Chem.
C112,12161(2008).
4.
A.
Shalav,A.
S.
Richards,T.
Trupke,K.
W.
Krmer,andH.
U.
Güdel,Appl.
Phys.
Lett.
86,013505(2005).
5.
Y.
Wang,W.
P.
Qin,J.
S.
Zhang,C.
Y.
Cao,J.
S.
Zhang,Y.
Jin,P.
F.
Zhu,G.
D.
Wei,G.
F.
Wang,andL.
L.
Wang,Chem.
Lett.
36,912(2007).
6.
Y.
Wang,W.
P.
Qin,J.
S.
Zhang,C.
Y.
Cao,J.
S.
Zhang,Y.
Jin,P.
F.
Zhu,G.
D.
Wei,G.
F.
Wang,andL.
L.
Wang,J.
SolidStateChem.
180,2268(2007).
7.
W.
Chen,J.
Nanosci.
Nanotechnol.
8,1019(2008);W.
Chen,J.
Z.
Zhang,andA.
G.
Joly,J.
Nanosci.
Nanotechnol.
4,919(2004).
8.
J.
B.
LiandL.
W.
Wang,NanoLett.
3,1357(2003).
9.
E.
Maurice,G.
Monnom,B.
Dussardier,A.
Saissy,andD.
B.
Ostrowsky,Opt.
Lett.
19,990(1994).
10.
X.
Bai,H.
W.
Song,G.
H.
Pan,Y.
Lei,T.
Wang,X.
Ren,S.
Z.
Lu,B.
Dong,Q.
L.
Dai,andL.
Fan,J.
Phys.
Chem.
C111,13611(2007).
11.
F.
Auzel,Phys.
Rev.
B13,2809(1976).
12.
M.
J.
Weber,Phys.
Rev.
B8,54(1973).
13.
G.
J.
H.
De,W.
P.
Qin,J.
S.
Zhang,J.
S.
Zhang,Y.
Wang,C.
Y.
Cao,andY.
Cui,Solid.
State.
Commun.
137,483(2006).
14.
J.
S.
Zhang,W.
P.
Qin,C.
Y.
Cao,J.
S.
Zhang,Y.
Wang,Y.
Jin,G.
D.
Wei,G.
F.
Wang,andL.
L.
Wang,J.
Nanosci.
Nanotechnol.
8,1258(2008).
Received:9September2008.
Accepted:5April2009.
4J.
Nanosci.
Nanotechnol.
10,1–4,20101828J.
Nanosci.
Nanotechnol.
10,1825–1828,2010
4.
8]-所有数据库全记录2010-12-21http://apps.
isiknowledge.
com/full_record.
doproduct=UA&search_mode.
.
.
(NNSFC)50672030[显示基金资助信息]出版商:AMERSCIENTIFICPUBLISHERS,25650NORTHLEWISWAY,STEVENSONRANCH,CA91381-1439USAIDS号:548RVISSN:1533-4880DOI:10.
1166/jnn.
2010.
2085数据库全记录2010-12-21http://apps.
isiknowledge.
com/full_record.
doproduct=UA&search_mode.
.
.
RESEARCHARTICLECopyright2010AmericanScienticPublishersAllrightsreservedPrintedintheUnitedStatesofAmericaJournalofNanoscienceandNanotechnologyVol.
10,1–4,2010BrightGreenUpconversionFluorescenceofYb3+,Er3+-CodopedNaYF4NanocrystalsLiliWang12,WeipingQin1,YanWang1,GuofengWang1,ChunyanCao1,GuodongWei1,RyongjinKim1,DaishengZhang1,FuhengDing1,andChunfengHe11StateKeyLaboratoryonIntegratedOptoelectronics,CollegeofElectronicScienceandEngineering,JilinUniversity,Changchun130012,China2SchoolofBasicSciences,ChangchunUniversityofTechnology,Changchun130012,ChinaUniformhexagonalNaYF4:Yb3+,Er3+nanocrystals(NCs)withbrightgreenupconversionuores-cencewereprepared.
Thenanocrystalswerehighlyhydrophobicanddispersedincyclohexaneformingatransparentcolloidalsolutionduetotheuseofoleicacidasacappingligand.
Temper-aturedependenceforemissionofEr3+ionsinthissamplewasalsostudied.
ThegreenemissionintensityofEr3+ionshadamaximumat160Kunder980nmexcitation,whichwasattributedtothethermallyactivateddistributionofelectronsandthethermalquenchingeffect.
Thetransparentcolloidalsolutionisexpectedtobeagoodcandidateforresearchinbiologicalimagingordisplayapplications.
Keywords:NaYF4,RareEarth,NonradiativeRelaxation.
1.
INTRODUCTIONAnumberofrare-earth-dopeduoridenanocrystalsandsubmicrocrystalswithefcientinfrared(IR)radiationintovisiblelightthroughfrequencyupconversion(UC)atroomtemperaturehavebeenproduced.
1–6Duetothelowphotonenergy,therelativelyhighefciencyoftheUCprocessintheseuoridecrystals,andtheinexpensive980nmnear-IR(NIR)diodelasers,therealizationofefcientNIRtovisi-bleupconvertingnanocrystalsandsubmicrocrystalsshouldunlockarealmofnewpossibilitiesintheeldofbiosen-sors,displays,andshort-wavelengthlasers.
Itiswell-knownthatthesizeandshapeofinorganicnanocrystalshavegreatinuenceontheirphysicalproperties.
78Thus,furtherexplorationsofnovelnanomorphology,withcon-trolledsizeandshapebyconvenientsynthesismethods,isofgreatimportanceforthedevelopmentofnewfunctionaldevices.
Simultaneously,inordertorealizethebiologicalimagingordisplayapplicationsbasedontheUCprinci-pleinauid,itiscrucialtoinvestigatelanthanide-dopedUCnanocrystallinecolloidalsolutions.
Todate,thesuc-cessfulpreparationoftransparentcolloidalsolutionshasbeendemonstratedinafewNaYF4nanocrystals.
However,itstemperature-dependentluminescencebehaviorwassel-domstudied.
Inthisletter,wereportastudyonthetrans-parentNaYF4:Yb3+,Er3+nanocrystalcolloidalsolution.
Authortowhomcorrespondenceshouldbeaddressed.
Under980nmexcitationfromalaserdiode,thetrans-parentsolutionpresentedbrightgreenUCuorescence.
Itisexpectedtobeagoodcandidateforresearchinbio-logicalimagingordisplayapplications.
Wealsoinves-tigatedthetemperature-dependentcharacteristicsofEr3+ionemissions.
Theunderstandingofthisprocessishelpfulinthesearchforhighefciencyphosphors.
Thermalizationeffectsbetweenthe2H11/2and4S3/2levelsseparatedby765cm1intheseuoridenanocrystalswerealsoreported.
Theresultsshowthat520nmemissionisfavoredathightemperaturesbyitshigheremissioncrosssectionandthattheoverallgreenuorescenceincreasesconsequently.
2.
EXPERIMENTALDETAILSInatypicalpreparation,0.
6gNaOHwasdissolvedinasolutioncontainingoleicacid,ethanol,anddeionizedwater(10/5/4,v/v/v).
Then1.
5mmolKF,0.
39mmolY(NO33·6H2O,0.
10mmolYb(NO33·6H2Oand0.
01mmolEr(NO3)3·6H2Owereaddedtothesolu-tionundervigorousstirring.
Themixturewasagitatedfor30minandthentransferredintoa50-mLautoclave,sealed,andtreatedat180Cfor16h.
Subsequently,themixturewasallowedtocooltoroomtemperature,andthepowderwasobtainedbycentrifuging,rinsing,anddrying.
PhaseidenticationwasperformedviaX-raydiffrac-tion(XRD,modelRigakuRU-200b),usingnickel-lteredJ.
Nanosci.
Nanotechnol.
2010,Vol.
10,No.
xx1533-4880/2010/10/001/004doi:10.
1166/jnn.
2010.
20851Vol.
10,1825–1828,201031533-4880/2010/10/1825/0051825RESEARCHARTICLEBrightGreenUpconversionFluorescenceofYb3+,Er3+-CodopedNaYF4NanocrystalsWangetal.
CuKradiation(=15406).
Thesizeandmorphol-ogyofthenanocrystalswerecharacterizedbytransmissionelectronmicroscopy(TEM,JEM,2000EX200kV).
High-resolutionemissionspectrawereobtainedat13–300Kwiththesamplemountedinaheliumexchangegascham-berofaclosedcyclerefrigerationsystem.
A980nmlaserdiodewasusedastheexcitationsource.
Theuorescencephotoofthecolloidalsolutionwith0.
2mg/mLconcen-trationincyclohexanewasacquiredwithadigitalcameraunder980nmexcitationfromalaserdiode.
3.
RESULTSANDDISCUSSIONThecrystalstructureandthephasepurityofthematerialwasobtainedbyXRD,asshowninFigure1.
AccordingtoJCPDSstandardcards,theNaYF4:Yb3+,Er3+nano-crystalsexhibitapurehexagonalstructure.
TheXRDpat-ternalsodemonstratesthattheNaionscanbeincorporatedintotheframeworkofYFn,formingNaYF4.
Figure2(a)showstheTEMimageofhexagonal-phaseNaYF4:Yb3+,Er3+nanocrystals.
Theimageclearlyrevealsthatthemorphologyoftheas-synthesizednano-crystalsishexagonalnanoplateswithameansizeof200nm.
Intheimage,thereisnoaggregationofnano-crystals,whichindicatesthegooddispersionofthissam-ple.
Inaddition,thesenanocrystalsarehighlycrystalline.
Theirhighcrystallinityisalsoinferredfromtheelec-trondiffractionimages(insertinFig.
2(a)).
Figure2(b)illustratesphotographsofhexagonal-phaseNaYF4:Yb3+,Er3+dispersedincyclohexanewiththeconcentrationof2mg/mL.
Wecanseethatthecolloidalsolutionisfullytransparentintheleftpicture,andtherightpictureshowsthatthecolloidalsolutionemitseye-visibleUClumines-cenceunder980nmexcitation.
Thissolutionisstableformonthswithoutanyvisibleprecipitate.
ThesurfacesofthesynthesizedNaYF4nanocrystalswerecoveredbyFig.
1.
PowderXRDpatternofhexagonal-phaseNaYF4:Yb3+,Er3+nanocrystals.
Fig.
2.
(a)TEMimageofthemonodispersedNaYF4:Yb3+,Er3+nano-crystals.
Insert:Theelectronicdiffractionpatternsofthesample.
(b)Pho-tographofhexagonal-phaseNaYF4:Yb3+,Er3+dispersedincyclohexaneshowseye-visibleupconversionluminescenceunder980nmexcitationwiththeconcentrationof2mg/mL.
Theleftcellshowsthatthecolloidalsolutionisfullytransparent.
thesurfactantoleicacid,sothenanocrystalswerehighlyhydrophobicanddispersedincyclohexane.
ThenormalizedUCemissionspectraofhexagonal-phaseNaYF4:Yb3+,Er3+nanocrystalsatthreediffer-enttemperaturesunder980nmexcitationareshowninFigure3.
Thelaserpoweris400mW.
Inthespectra,thegreenemissionspeaksareobservedintherangeof515–560nm,correspondingtothe2H11/2,4S3/2→4I15/2transitions,whiletheredemissionpeaksareobservedbetween640and680,correspondingtothe4F9/2→4I15/2transitions.
At13K,the2H11/2uorescenceintensityisnegligible,anditprogressivelyincreaseswithincreas-ingtemperature.
Thisisarepresentativebehaviorofpro-cessesinvolvingthethermallycoupled4S3/2and2H11/2asreportedelsewhere.
910Theupconversionluminescencemechanismandpopula-tionprocessinEr3+/Yb3+-codopedsystemsarepresentedFig.
3.
Upconversionemissionspectraofhexagonal-phaseNaYF4:Yb3+,Er3+nanocrystalsat13,190,and300K.
2J.
Nanosci.
Nanotechnol.
10,1–4,20101826J.
Nanosci.
Nanotechnol.
10,1825–1828,2010RESEARCHARTICLEWangetal.
BrightGreenUpconversionFluorescenceofYb3+,Er3+-CodopedNaYF4NanocrystalsinFigure4.
Following980nmirradiation,theEr3+ionisexcitedtothe4F7/2stateviatwosuccessiveenergytrans-fersfromtheYb3+ionsinthe2F5/2state.
Thus,oneYb3+ionwilltransferitsenergytoanEr3+ioninthegroundstate,therebyexcitingittothe4I11/2state.
ThisprocessisfollowedbyatransferofenergyfromanotherYb3+ionalsoinitsexcitedstate,resultinginthepopulationofthe4F7/2stateoftheerbiumion.
Theloweremittinglevelsarethenpopulatedviamultiphononrelaxation,andgreenandredemissionsarethenobserved.
Ofcourse,interactionsbetweentwoEr3+ionscannotnecessarilybeignored.
Anearinfrared(NIR)photonfromthepumpbeamwillalsoexciteanEr3+iontoits4I11/2state.
AnotherEr3+ionalsointhe4I11/2stateandincloseproximitywilltransferitsenergytotheinitialion,therebyexcitingittothe4F7/2state.
However,followingtheadditionofYb3+ions,thisprocessisgreatlydiminishedduetothelargeabsorptioncross-sectionoftheytterbiumions.
Thus,thesimultaneoustransferofenergyfromYb3+,whichpopulatesthe4F7/2state,isdominant.
Thedependenceoftheupconversionefciencyupontemperaturewasexamined,andtheresultsaredepictedinFigure5.
Ascanbeinferredfromexperimentaldata,thevisibleemissionefciencyincreasedbyafactorof4whenthesamplewascooledfromroomtemper-atureto160K.
Thisbehaviorreectsthecompetitionbetweenthetwomajorthermaleffectsactinginthesys-temasfollows.
Onethermaleffectisthetemperature-enhancedsidebandanti-Stokesexcitationofthesensitizer,whichisresponsiblefortheincreaseintheupconver-sionemissionefciency.
Theexpressionoftheabsorp-tioncross-sectionrelatedtothetemperatureiswrittenasT=0exp/kBT1E/,where0istheabsorptioncrosssectionat0Kandisthephotonenergy.
Theotherthermaleffectisthethermallyenhancednonradiativedecayratethatinhibitsradiativeemission.
ThenonradiativetransitionprobabilitybetweenlevelsforlowconcentrationsofEr3+ionsisduetomultiphononFig.
4.
SchematicdiagramofYb3+-sensitizedEr3+upconversionunder980nmexcitation.
Thesolidlinesrepresentradiativetransitions,andthedashedlinesrepresentnonradiativetransitions.
relaxationprocesses,andcanberelatedtothetemperaturethroughWNR=WNR01exp/kBTE/,1112whereWNR0isthenonradiativerelaxationrateat0K.
ItalsocanbeseenfromFigure5(b)thatthegreenemissionfrom4S3/2decreasesfasterthantheredemis-sionfrom4F9/2above180Kastemperatureincreases.
Asmentionedabove,therearetwomainfactors.
Onefactoristhethermalquenchingeffectofluminescence.
Theinter-mediatelevelofthegreenemissionis4I11/2,whilethatoftheredemissionis4I13/2.
Fortheredaswellasthegreenemission,thenonradiativerelaxationof4I11/2→4I13/2and4S3/2→4F9/2isinvolved,whichincreasestheelectronpopulationon4F9/2whiledecreasingthaton4S3/2.
Thatmakestheredemissionsdecreaseslowerthanthatofgreenemissions.
Asiswellknown,thenonradiativerelax-ationprobabilityissize-dependent.
Astheparticlesize(a)(b)Fig.
5.
(a)VisibleUCluminescencespectrainNaYF4:Yb3+,Er3+nanocrystalsatdifferenttemperatures.
(b)Theupconversionemissionintensityof4S3/2→4I15/2,4F9/2→4I15/2inNaYF4:Yb3+,Er3+nano-crystalsasafunctionoftemperature.
J.
Nanosci.
Nanotechnol.
10,1–4,20103J.
Nanosci.
Nanotechnol.
10,1825–1828,20101827RESEARCHARTICLEBrightGreenUpconversionFluorescenceofYb3+,Er3+-CodopedNaYF4NanocrystalsWangetal.
decreases,duetotheincreaseofthesurface-to-volumeratiocomparedwiththebulk,alargenumberofNO23andOHareinvolved,withvibrationalenergiesof1350and3350cm1,respectively,andhaveavailablelargevibrationalquantatoefcientlydepopulatetheexcitedstates4I11/2and4S3/2nonradiatively.
1314Thus,thenon-radiativerelaxationbecomesmoreefcientthanthermalexcitation.
Theotherfactoristhethermallyactivateddis-tributionofelectronsamong4S3/2.
Someofelectronscanbethermallyexcitedinto2H11/2from4S3/2asthetemper-atureincreases.
Thatalsodecreasesthegreenemissionsfrom4S3/2.
4.
SUMMARYInconclusion,Yb3+,Er3+-codopeduoridenanocrystalsweresynthesized.
Thesecrystalsdemonstratehighcrys-talqualityandexcellentdispersivityandcanbetrans-parentlydispersedinnonpolarsolvents.
Atthesametime,thetransparentcolloidalsolutionshowsefcientinfrared-to-visibleUCemission.
Thegreenupconversionluminescenceexhibitedafour-foldintensityenhancementwhenthetemperatureofthesamplewasvariedintherangebetween20Kand300Kwiththemaximumintensityattainedaround160K.
Theexcellentlumines-cenceofhexagonal-phaseNaYF4:Yb3+,Er3+nanocrystalsprovidesthebasisforamorethoroughinvestigationoftheiropticalandtemperaturepropertiesandmightenableapplicationsinnanoscalebiologicalimagingordisplays.
Acknowledgments:ThisworkwassupportedbytheNationalNaturalScienceFoundationofChina(NNSFC)(grants10874058and50672030).
ReferencesandNotes1.
El-SayedandM.
A.
Acc,Chem.
Rev.
34,257(2001).
2.
J.
C.
Boyer,F.
Vetrone,L.
A.
Cuccia,andJ.
A.
Capobianco,J.
Am.
Chem.
Soc.
128,7444(2006).
3.
G.
F.
Wang,W.
P.
Qin,J.
S.
Zhang,J.
S.
Zhang,Y.
Wang,C.
Y.
Cao,L.
L.
Wang,G.
D.
Wei,P.
F.
Zhu,andR.
Kim,J.
Phys.
Chem.
C112,12161(2008).
4.
A.
Shalav,A.
S.
Richards,T.
Trupke,K.
W.
Krmer,andH.
U.
Güdel,Appl.
Phys.
Lett.
86,013505(2005).
5.
Y.
Wang,W.
P.
Qin,J.
S.
Zhang,C.
Y.
Cao,J.
S.
Zhang,Y.
Jin,P.
F.
Zhu,G.
D.
Wei,G.
F.
Wang,andL.
L.
Wang,Chem.
Lett.
36,912(2007).
6.
Y.
Wang,W.
P.
Qin,J.
S.
Zhang,C.
Y.
Cao,J.
S.
Zhang,Y.
Jin,P.
F.
Zhu,G.
D.
Wei,G.
F.
Wang,andL.
L.
Wang,J.
SolidStateChem.
180,2268(2007).
7.
W.
Chen,J.
Nanosci.
Nanotechnol.
8,1019(2008);W.
Chen,J.
Z.
Zhang,andA.
G.
Joly,J.
Nanosci.
Nanotechnol.
4,919(2004).
8.
J.
B.
LiandL.
W.
Wang,NanoLett.
3,1357(2003).
9.
E.
Maurice,G.
Monnom,B.
Dussardier,A.
Saissy,andD.
B.
Ostrowsky,Opt.
Lett.
19,990(1994).
10.
X.
Bai,H.
W.
Song,G.
H.
Pan,Y.
Lei,T.
Wang,X.
Ren,S.
Z.
Lu,B.
Dong,Q.
L.
Dai,andL.
Fan,J.
Phys.
Chem.
C111,13611(2007).
11.
F.
Auzel,Phys.
Rev.
B13,2809(1976).
12.
M.
J.
Weber,Phys.
Rev.
B8,54(1973).
13.
G.
J.
H.
De,W.
P.
Qin,J.
S.
Zhang,J.
S.
Zhang,Y.
Wang,C.
Y.
Cao,andY.
Cui,Solid.
State.
Commun.
137,483(2006).
14.
J.
S.
Zhang,W.
P.
Qin,C.
Y.
Cao,J.
S.
Zhang,Y.
Wang,Y.
Jin,G.
D.
Wei,G.
F.
Wang,andL.
L.
Wang,J.
Nanosci.
Nanotechnol.
8,1258(2008).
Received:9September2008.
Accepted:5April2009.
4J.
Nanosci.
Nanotechnol.
10,1–4,20101828J.
Nanosci.
Nanotechnol.
10,1825–1828,2010
金山云：618年中促销,企业云服务器2核4G仅401.28元/年,827.64元/3年
金山云618年中促销活动正在进行中!金山云针对企业级新用户优惠力度比普通个人用户优惠力度要大，所以我们也是推荐企业新用户身份购买金山云企业级云服务器，尽量购买3年配置的，而不是限时秒杀活动中1年的机型。企业级用户购买金山云服务器推荐企业专区：云服务器N3 2核4G云服务器，1-5M带宽，827.64元/3年，性价比高，性能稳定!点击进入：金山云618年中促销活动目前，金山云基础型E1云服务器2核4...
Hostiger发布哥伦布日提供VPS主机首月七折优惠 月费2.79美元
Hostiger商家我们可能以前也是有见过的，以前他们的域名是Hostigger，后来进行微调后包装成现在的。而且推出Columbus Day哥伦布日优惠活动，提供全场的VPS主机首月7折月付2.79美元起的优惠。这里我们普及一下基础知识，Columbus Day ，即为每年10月12日，是一些美洲国家的节日，纪念克里斯托弗·哥伦布在北美登陆，为美国的联邦假日。Hostiger 商家是一个成立于2...
VPSMS：53元/月KVM-512MB/15G SSD/1TB/洛杉矶CN2 GIA
VPSMS最近在做两周年活动，加上双十一也不久了，商家针对美国洛杉矶CN2 GIA线路VPS主机提供月付6.8折，季付6.2折优惠码，同时活动期间充值800元送150元。这是一家由港人和国人合资开办的VPS主机商，提供基于KVM架构的VPS主机，美国洛杉矶安畅的机器，线路方面电信联通CN2 GIA，移动直连，国内访问速度不错。下面分享几款VPS主机配置信息。CPU：1core内存：512MB硬盘：...
数据库为你推荐
-
u盘无法读取U盘为什么不能显示google竞价排名谷歌SEO与谷歌竞价的区别和联系快速美白好方法脸部快速美白有什么好方法啊bluestacksbluestacks怎么用？照片转手绘照片转手绘用什么APP网站联盟网盟跟b2b平台有什么区别镜像文件是什么镜像文件是什么意思？中小企业信息化什么是中小企业信息化途径天天酷跑刷金币如何使用八门神器给天天酷跑刷钻刷金币开机滚动条怎么减少开机滚动条？