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
CloudCone（12.95美元/月CN2 GT线路，KVM架构1 Gbps带宽
整理一下CloudCone商家之前推送的闪购VPS云服务器产品，数量有限，活动推出可能很快机器就售罄了，有需要美国便宜VPS云服务器的朋友可以关注一下。CloudCone怎么样？CloudCone服务器好不好？CloudCone值不值得购买？CloudCone是一家成立于2017年的美国服务器提供商，国外实力大厂，自己开发的主机系统面板，CloudCone主要销售美国洛杉矶云服务器产品，优势特点是...
宝塔面板批量设置站点404页面
今天遇到一个网友，他在一个服务器中搭建有十几个网站，但是他之前都是采集站点数据很大，但是现在他删除数据之后希望设置可能有索引的文章给予404跳转页面。虽然他程序有默认的404页面，但是达不到他引流的目的，他希望设置统一的404页面。实际上设置还是很简单的，我们找到他是Nginx还是Apache，直接在引擎配置文件中设置即可。这里有看到他采用的是宝塔面板，直接在他的Nginx中设置。这里我们找到当前...
港云网络(￥1/月活动机器)，香港CN2 4核4G 1元/月 美国CN2
港云网络官方网站商家简介港云网络成立于2016年，拥有IDC/ISP/云计算资质，是正规的IDC公司，我们采用优质硬件和网络，为客户提供高速、稳定的云计算服务。公司拥有一流的技术团队，提供7*24小时1对1售后服务，让您无后顾之忧。我们目前提供高防空间、云服务器、物理服务器，高防IP等众多产品，为您提供轻松上云、安全防护。点击进入港云网络官方网站港云网络中秋福利1元领【每人限量1台】，售完下架，活...
数据库为你推荐
-
有趣的广告有趣的广告易pc华硕的易PC怎么样，能流畅运行的游戏大概是什么水平的？如何免费开通黄钻怎么免费开黄钻？网站联盟怎样进入网站联盟显卡温度多少正常显卡温度多少正常硬盘人克隆一个人需要多少人多长时间啊硬盘人什么叫“软盘人”和“硬盘人”？人人逛街人人逛街网是正品吗商标注册查询官网全国商标注册查询在哪里查呀？二层交换机什么是二层交换机