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(Anhui Key Laboratory of Information Materials and Devices, School of Physics and Materials Science,Anhui University, Hefei 230039, China)

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PhotoluminescencepropertiesofBa2+-dopedSr2.4Y0.2Eu0.2V2O8:Ba2+phosphors

DAIZhenxiang,WANGWeiwei,PENGZhangwan,ZHUYanan,ZHENGGanhong

(AnhuiKeyLaboratoryofInformationMaterialsandDevices,SchoolofPhysicsandMaterialsScience,AnhuiUniversity,Hefei230039,China)

TheBa2+-dopedSr2.4Y0.2Eu0.2V2O8phosphorsweresynthesizedbytheconventionalsolid-statereaction.Uponexcitationwith416nmirradiation,theemissionspectrafortheBa2+-dopedSr2.4Y0.2Eu0.2V2O8sampleswerecomposedofthewell-knownlinelocatingat595nm(5D0→7F1), 619nm(5D0→7F2), 652nm(5D0→7F3),and700nm(5D0→7F4)resultingfromtheemissionofEu3+duetotransitionof5D0→7FJ.TheemissionintensityincreasedandthendecreasedwithincreasingBacontent,andthemaximumemissionintensitywasachievedwhenxwas0.15.TheseresultsindicatedthattheBadopantactsasonesensitizerandenhancedthephotoluminescenceintensity.

solid-statereaction;Ba2+-doped;luminescence

0　Introduction

Alargenumberofvanadateshavebeenfound,suchas(Y,Gd,Lu)VO4[1],Sr3V2O8[2],Ca9Dy(VO4)7[3],whichcanbeeffectivelyexcitedbyultraviolet(UV)andconvertUVradiationtobroadbandemissioninthevisiblelightregion.Asinterestingcandidatesforredphosphors,materialscontainingEu3+,whichhave5D0→7F2transitionat619nmasionsarelocatedinanon-centrosymmetricsite,showbettercolorpuritythanthosephosphorswithbroademissionband.GreatattentionshavebeenpaidtoEu3+-dopedmanganites,borosilicate,andtitanate,whichshowtheeffectivef-ftransitionofEu3+underexcitationintheUVspectralregion,suchasBaGa2(MnO4)4:Eu3+[4],Eu0.14Mg0.18Ca0.07Ba0.12-B0.17Si0.32Oδ[5],(K,Li,Na)x(Y,Gd,La,Eu)yTizOδ[6].

Asweknow,theopticalpropertiesofphosphorscanbetunedwiththelocalenvironmentsaroundluminescenceions.Recently,Wangetal.[7]usedahydrothermalmethodtoprepareYVO4:Ln3+(Ln=Eu,Dy,Sm,Ce)nano-crystalsco-dopedwithBa2+,andreportedalargeenhancementintheirluminescence.Similarly,Zhangetal.foundthatthephotoluminescenceofSr3Al2O6:Eu3+phosphorscanbegreatlyincreasedbydopingBa2+ions[8].Jiaetal.usingasolvothermalmethodtosynthesizeYVO4:Ln3+(Ln=Eu,Dy)andreportedthatthereisalargeenhancementintheluminescencebyco-dopingBa2+[9].

Inthispaper,wesynthesizedBa2+-dopedSr2.4Y0.2Eu0.2V2O8phosphorsbytheconventionalanddescribedthephotoluminescentpropertieswithBaindetail.

1　Experimental

ThephosphorsSr2.4Y0.2Eu0.2V2O8:xBa2+(0≤x≤0.20)werepreparedbyconventionalsolid-satereaction.ThereactantsincludeSrCO3(99.99%),Y2O3(99.9%),Eu2O3(99.99%),NH4VO3(99.0%),andBaCO3(99%).Thestartingmaterialsweremixedtogetherinanagatemortarandfinelyground.Theobtainedmixturewasheatedinanaluminacrucible(inair)at680 ℃for10h.Afternaturalcooling,grindcarefullyandpressitintotablets.Thentheobtainedmixturewasheatedinanaluminacrucible(inair)at850 ℃for10h.Afternaturalcooling,grindcarefullyandpressitintotablets.Finallytheobtainedmixturewasheatedinanaluminacrucible(inair)at1 000 ℃for12h.

ThecrystalstructureofthephosphorpowderswascharacterizedbyX-raydiffraction(XRD)analysis.IntheprocessofXRDanalysis,oneX-raydiffractometerDX-2000SSCwithCuKαirradiation(λ=0.154 06nm)isused,withoperatingvoltagebeing36kVandtheoperatingcurrentbeing25mA.TheelementcontentsarealsodetectedusingX-rayspectrometry(PHI5702).TheactivationandemissionspectraweremeasuredonanFLfluorescencespectrophotometer(F-4500).Theweightofeverysamplewasequalto0.8g.Alltheseoperationswerecarriedoutatroomtemperature.

2　Results and Discussion

2.1The crystal structure and Ba content of Sr2.4Y0.2Eu0.2V2O8:xBa2+

Fig.1　XRD patterns of Sr2.4Y0.2Eu0.2V2O8:xBa (0≤x≤0.20)

2.2Emission spectra of Sr2.4Y0.2Eu0.2V2O8:xBa+(0≤x≤0.20) phosphor

TheemissionspectraofSr2.4Y0.2Eu0.2V2O8:xBa2+(x=0, 0.05, 0.10, 0.15, 0.18, 0.20)phosphor(λex=416nm)areshowninFig.2.Uponexcitationwith416nmirradiation,theemissionspectraconsistofthewell-known5D0→7FJ(J=0, 1, 2,etc.)ofthe4f6configurationforEu3+ions.Theemissionlineat619nm,correspondingtotheforcedelectricdipole5D0→7F2transitionofEu3+,ismuchstrongerthantheemissionlineat595nm.The595nmemissionlineisknowntobeassignedtothemagneticdipole5D0→7F1transitionofEu3+.Accordingly,wecanconcludethatEu3+occupiedtheasymmetrylatticesites.Theothertwopeaksfromthe5D0→7F3and5D0→7F4,whicharelocatedat652nmand700nm,arealsoobserved.

Fig.2　　　　The emission spectra under excitation at λex=416 nm excitation of theSr2.4Y0.2Eu0.2V2O8:xBa (0≤x≤0.20) phosphors

Despitedifferentcompositions,allthesesamplesSr2.4Y0.2Eu0.2V2O8:xBa2+(x=0, 0.05, 0.10, 0.15, 0.18, 0.20)showsimilaremissionspectra.TheemissionwavelengthsarealsofoundtobeindependentofBaaddition,indicatingthattheBa2+-dopingdoesnotchangethehoststructure.However,therelativeemissionintensityatthehighest5D0→7F2transitionofEu3+ischangedwiththedopedBa2+content,asshowninFig.3.

Fig.3　　　　The emission intensity at 595, 619, 652 and 700 nm ofSr2.4Y0.2Eu0.2V2O8:xBa (0≤x≤0.20) versus the Ba concentration

Thephotoluminescenceintensityat595， 619, 652，700nmisalsofoundtochangewithincreasingBacontent,andthehighestvalueisobservedatx=0.15.WithfurtherincreaseofBaconcentration,thephotoluminescenceintensitygraduallydecreases.Thus,theoptimalBa2+dopedcontentinSr2.4Y0.2Eu0.2V2O8:xBa2+phosphoris0.15.Inthiscase,theemissionintensityat619nmofSr2.4Y0.2-Eu0.2V2O8:xBa2+isincreasedbyfivetimesduetotheBadopant.ThissuggeststhattheefficientenergytransferprocessbetweenBa2+andEu3+ionoccurs[10].TheemissionintensityincreaseswithincreasingBadopant.Thesimilarphenomenonisalsoreportedinotheralkalimetal[11-12].Ontheotherhand,consideringtheionicradiiBa2+being0.135nmandSr2+being0.112nm,whenSr2+ionissubstitutedbyBa2+,theionicradiidifferenceisnoticeablewithBadopant.Certainly,thecrystalfieldsurroundingEu3+ionsishighlychangedcorrespondingly.Asdiscussedabove,5D0→7F2isanelectricdipoletransitionandhypersensitivetothelocalsymmetry.Therefore,incaseofx≤0.15,theemissionintensityincreaseswiththeincreaseofBadopantcontent.However,theexcessdistortioncausedbytheadditionofBa2+inthecaseofx≥0.15maybeanotherreasonfordecreasingtheemissionintensity,asreportedinthereference[13].WhenBacontentismorethan0.15,moreandmoreBaionsareintroducedintotheSr2.4Y0.2Eu0.2V2O8samples.Subsequently,thedistancebetweentwoBaionswouldbedecreasedgraduallyandbecloseenough.ThiswillresultinoneefficientanddirectenergytransferprocessbetweenBaions,whichreducestheprobabilityofenergytransferfromBatoSr.ThesensitizedeffectivenessofBa2+ontheSr2+emissionintensityisreduced.Andeventually,theemissionintensityofSr2.4Y0.2Eu0.2V2O8:xBa2+systemislimitedasshowninFig.3.

2.3Excitation spectra of Sr2.4Y0.2Eu0.2V2O8:xBa2+(0≤x≤0.20) phosphor

TheexcitationspectraofSr2.4Y0.2Eu0.2V2O8:xBa2+(0≤x≤0.20)formonitoringthe5D0→7F2transitionofEu3+(λem=619nm)areshowninFig.4.Theintensityofactivationbandistoostrongtoexceedtherangeofmeasurement,therefore,weonlypresenttheresultsoftherepresentativesamples(x=0， 0.05)here.Inaddition,itexhibitssomebandsinthereignof400-550nm,resultingfromthef-ftransitionswithinEu3+4f6electronconfiguration,andthepeaksat416, 468，539nmarecorrespondingtotheelectrontransitionsfromthe7F0,1groundstateto5D3,5D2and5D1,consistentwithspectralcharacterizationsobservedinpreviouswork[14-15].

Fig.4　　　　The excitation spectra for monitoring the emission at λex=619 nm of theSr2.4Y0.2Eu0.2V2O8:xBa (x=0, 0.05)

3　Conclusions

TheSr2.4Y0.2Eu0.2V2O8:xBa2+(0≤x≤0.20)phosphorshavebeensynthesizedbysolid-statereactionmethod.Thecorrespondingphotoluminescepropertiesarealsoprobed.TheemissionintensityisenhancedfirstlywithincreasingtheBaconcentration,andthendecreasesgradually.Thestrongestemissionintensityisachievedatx=0.15.Thistendencyisascribedtothefollowingtwofactors.OneistheenergytransferprocessbetweenBa+ionsandEu3+ions,theotherisrelatedtothedistortionofthecrystalfieldsurroundingEu3+ions.SuchadistortionisenhancedbysubstitutingBa2+.Asforthefirstfactor,theenergyisabsorbedbyBa2+ionsandthentransferredtoEu3+,consequentlytheemissionintensityisenhanced.However,whenBacontentisabove0.15,thedistancebetweenBaionsisshortenoughtocauseoneefficientBa-Baenergytransferprocess,theprobabilityofenergytransferfromBatoEuiscorrespondinglydecreased.Asforthesecondfactor,thecrystalfieldsurroundingEu3+ionsislocallydistorted,withsubstitutingBa2+,thentheasymmetryofsuchacrystalfieldisincreased.Thisdistortionleadstotheenhancementoftheemissionintensity.However,theexcessdistortioncausedbytheadditionofBa2+over0.15mayresultintheemissionintensitydecreases.

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(責(zé)任編輯鄭小虎)

10.3969/j.issn.1000-2162.2016.02.008

Sr2.4Y.Eu.V2O8:Ba2+發(fā)光性能的研究

戴振翔,汪偉偉,彭張皖,朱亞男,鄭贛鴻

(安徽大學(xué) 物理與材料科學(xué)學(xué)院,安徽省信息材料與器件重點(diǎn)實(shí)驗(yàn)室, 安徽 合肥 230039)

固相反應(yīng);Ba2+摻雜;發(fā)光性質(zhì)

date:2015-10-15

SupportedbytheNationalNaturalScienceFoundationofChina(11204001,11174004),AnhuiProvincialNaturalScienceFoundation(1208085QA07,1308085MA04),theHigherEducationalNaturalScienceFoundationofAnhuiProvince(KJ2013A031),AnhuiUniversityScientificResearchFund(201410357005,KYXL2013009), “211Project”ofAnhuiUniversity(SZJYKC2013020,XJGXKC1401)

Author’sbrief:DAIZhenxiang(1975-),male,borninShaoyangofHunanProvince,associateprofessorofAnhuiUniversity,E-mail:physdai@ahu.edu.cn.

O433.2Documentcode:AArticleID:1000-2162(2016)02-0043-06