碱金属和三价Eu离子共掺杂的碱土钼酸盐荧光粉发光性能_英文_

人 工 晶 体 学 报 V o.l 36 N o .5 2007年10月 J OURNAL O F S YNTH ET IC CRYSTALS O ctobe r ,2007

Lu m i nescent Properties of A l kaliM etal Ion

and Trivalent Europi u m Ion Co acti vated

A l kali ne Eart hM ol ybdate Phosphors

LI Xu 1,YA NG Zh i p ing 1,GUAN L i 1,GUO Q i n g lin 1,LI Pan lai 1

,

HUAI Su fang 1,LIU Chong 2(1.College ofPhysics S ci en ce and Technol ogy,H ebeiUn i versity ,B aod i ng 071002,Ch i na ;

2.C oll ege of Gradu ate,H ebeiUn i versity ,B aod i ng 071002,Ch i na)

(R e ce i ved 18M arc h 2007)

Abst ract :A ser i e s of triva lent eur opium ions (Eu 3+)and alka li m etal i o ns (L i +,N a +,K +

)co acti v ated m o lybdate phosphorAM o O 4(A =C a ,Sr)w as fabricated by so li d state reaction ,wh ich cou l d be

used as supple m entary li g hting m a terial for wh ite light e m itti n g diodes (LEDs).X ray diffraction (XRD )

patterns sho w that the lattice para m eters decrease and the diffraction i n tensity re m ar kably i n crease w hen

Eu 3+and N a +

ions are doped i n to the phosphor .The excitation and e m ission spectra o f sa mp les are i n vesti g ated .The excitation spectra cover the reg i o n fro m 240nm to 500n m and have an exc itati o n peak a t

470nm ,w hich i n d icate that t h is phosphor can be excited effectively by the e m ission of Ga N based LED;

the e m issi o n spectra sho w the sa m p l e s can e m it red light whose peaks are l o cated at 616nm and 624n m.

The i n fl u ence of al k alim eta l i o ns dosage (m olar fracti o n)on the lum i n escent properti e s ofAM oO 4:Eu

3+is investigated and the resu lts i n d icate that 0.25i s the appr opriated dosage .The reacti v e ti m e and

te mperature have obv i o us effect on the l u m i n escent properties .The lum i n escent i n tensity w ill reach the

m ax i m um w hen it w as si n tered at 800 for 3h .

K ey w ords :LEDs ;red phosphor ;m olybdate ;XRD;lum i n escent i n tensity

CLC nu m ber :TF 12 D ocu m ent code :A Art i c le I D :1000 985X (1000)05 1192 05 R ecei ved date :2007 03 18

Foundati on ite m:Pro j ect s upported by t h eH eb eiFoundati on ofN atura lS ci en ce (F200601023)

Bi ography :L I Xu(1978 ),M al e ,fro m H eb ei provi nce ,M aster .E m ai:l li xcn@si n a .com

碱金属和三价Eu 离子共掺杂的碱土钼酸盐荧光粉发光性能

李 旭1,杨志平1,关 丽1,郭庆林1,李盼来1,怀素芳1,刘 冲2

(1.河北大学物理科学与技术学院,保定071002;2.河北大学研究生学院,保定071002)

摘要:采用固相法制备了用于白光LED 的Eu 3+和碱土离子(L i +,N a +,K +)共激活的钼酸盐荧光粉AM o O 4(A =

Ca ,Sr)。通过X 射线衍射图片看出,Eu 3+和N a +的掺入降低了晶格参数,同时衍射峰强度明显增加。本文研究了

荧光粉的激发光谱和发射光谱。它的激发谱覆盖了从240n m 到500n m 的范围,在470n m 处有一个激发峰,这说明

它能够被G a N LED 发出的蓝光有效激发。发射谱表明它能够发射峰值位于616nm 和624n m 的红光。实验研究了

碱土离子的量(摩尔分数)对AM oO 4:Eu 3+发光性能的影响,0.25是最合适的掺杂量。反应时间和反应温度对发光

Ion Co activated A l ka li ne E art h M o l ybda te Phosphors

1193

性能也有很大的影响。搅拌均匀的反应物在800 灼烧3h得到的样品发光强度最强。

关键词:LED s;红色荧光粉;钼酸盐;XRD;发光强度

1 Introducti on

In1993,the first blue li g h t e m itti n g diodes(LEDs)w as i n ven ted by S.Naka mura of N ich ia Che m ical Co., w hich m ade the LEDs beca m e a whole syste m w ith trico lor basa l color.Subsequen tl y,t h e firstw hite li g ht e m itting diodes beca m e co mm erc ially available i n1997[1 3],w hich w as co m posed of a Ga N based LED and the cerium doped yttri u m a l u m inu m gar net(YAG:Ce).The G a N based LED belongs to solid state li g hting,wh ich has the properties of long lifeti m e,h i g h effic iency,reliab ility,s m a ll vo l u m e and w ithoutm ercur y po ll u ti o n.So this wh ite LED w as regar ded as the ne w genera ti o n illu m i n a te source after the conventional incandescent la m ps and fluorescent la mps.H o w ever,its lum i n escence,color coord i n ate and color rend ition index shou l d be i m proved if t h e w hite LED is p l a nned to enter the ill u m inati o n field[4,5].

Rece ntl y,the e m ission bands of LEDs are shifted to about400nm w ith the developm ent o f se m iconductor technology.Consequently,the m i x t u re o f b l u e g reen and red phosphors exc ited by one LED can be used to buil d up w hite LEDs.An efficiency and stab le phosphor that can be exc ited fro m400 470nm is needed i n t h is k i n d of wh ite LEDs.I n the last decades,rare earth i o n doped lum i n escentm ateria ls have been ex tensively i n vestigated because the spec ial ato m ic characters of rare earth ions.Eu3+is a fa m iliar activator in the red phosphor[6,7].As i m portant optical m ateria,l m olybdate have attracted particular i n terest because of the ir stable str ucture,wh ich belongs to sc hee lite co m pound;the central M o i o n is coordi n ated by four O2-i o ns in tetrahedral sy mm etry.The red phosphors N a M (WO4)2-x(M oO4)x:Eu3+(M=Gd,Y,B i),Ca M o O4:Eu3+and Ca M oO4:Sm3+had been successfu lly prepared[8 10].

In order to obta i n m ore efficient phosphors,a l k ali m eta l ion and Eu3+w ere co doped i n to t h e Ca M o O4and Sr M oO4hos.t The novel red phosphors C a M o O4:Eu3+,N+and Sr M o O4:Eu3+,N3+(N is L i+,Na+or K+)w as obtai n ed and the ir l u m i n escent properties w ere i n vesti g ated i n th is paper.

2 Experi m ental

The phosphors doped w ith different alka lim etal ions concentration w ere prepared by so li d state m ethod in the a ir.The reactants:stronti u m carbonate(Sr CO3, A.R.),ca lciu m car bonate(C a CO3, A.R.),sodium carbonate (N a2CO3, A.R.),lithiu m car bonate(L i2C O3, A.R.),ka li u m carbonate(K2C O3, A.R.),europi u m ox ide (Eu2O3,99.99%)and m o l y bdenu m ox i d e(M o O3, A.R.)w ere w eighted i n appropriate sto ich i o m etric ratio. These powders w ere blended w ith abso lute ethy l alcoho l and g round thoroughly i n an agate m ortar.Then,the ho m ogeneous m ixture w as filled i n to an alu m i n a cruc i b le and sintered i n a m uffle fur nace at800 for3h i n air. The sintered m ass w as grounded i n to powders and dried at80 after w ashed by deion ized w ater i n order to re m ove t h e residua l reactan.t Fina ll y,the efficient and stable phosphor w as obta i n ed.

The cr ystal str ucture w as characterized by po w der X ray diffraction co llected by D/m ax r A X ray d iffractm e ter usi n g Cu K a rad iation a t40kV and100mA.The exc itati o n spectr um w as m easured by a S H I M ADZU RF 540 ultrav io l e t spectrophoto m eter.The e m ission spectrum w as m easured by the SPEX1404spectrophoto m eter.A ll the l u m inescence properties of t h e phosphorsw ere stud i e d at roo m te m perature.

3 R esults and d i scussi ons

3.1 The cryst al struct ure

F i g.1show s the d i m ensi o na l structure of stronti u m m o lybdate(Sr M o O

4

)un ite ce ll(The b i g ball represen t the1194

人工晶体学报 第36卷Sr ions,the little ba ll located at apex ang le of tetrahedra l represent the oxygen ions).A s isw e ll kno w n,t h e space structure of Sr M o O4is a typ ica l scheelite str ucture w ith space g r oup I41/a and a=0.5226n m c=1.143nm;M o and Sr take up the W yckoff4a and W yckoff4b position in t h e crysta l respectively.Besides,the sy mm etr y group o f Sr M oO4is S4.The whole crystal structure can be regarded as a k i n d of three d i m ensional str ucture co m posed o f iso latedM o O4tetrahedron and Sr,i n w hich the central ions Sr is e i g h t coordinate and it fo r m s an ano m alistic po l y hedra l Sr O8[11].

F i g.1 The struct ure of Sr M o O

un it ce ll F i g.2 T he XRD pa tterns of sa m ples

4

3.2 X ray diffracti o n analysis

In so m e phosphors doped by Eu3+,a l k ali n e m etal i o ns is o ften used to act as charge co m pensation in or der to i m pr ove t h e lu m i n escent properti e s.In our i n vestigation,Li2CO3,N a2CO3and K2CO3are added to the ra w m aterials respectively.F i g.2i n dicates Sr1 x M o O4:Eu3+x and Sr1 2x M oO4:Eu3+x,Na+x(x=0.25,m o lar content)are of si n gle phase,w h i c h consistent w ith JCPDS27 0841[Sr0.4Eu0.4M o O4];Ca1 x M oO4:Eu3+x and C a1 2x M o O4: Eu3+x,N a+x(x=0.25,m o l a r content)are of si n g le phase,wh ich consisten t w ith JCPDS29 0351[Ca M oO4]. W ithoutN a+cop i n g,Sr1 x M o O4:Eu3+x and C a1 x M oO4:Eu3+x are no t perfect in crystalli n e because there is an i m ba lance i n charge bet w een Eu3+and Ca2+(Sr2+),w hich are i n d icated by relati v ely w eak diffracti o n peaks. Correspondi n g l y,t h e diffraction i n tensity ofN a+co doped sa m ples re m ar kab l y i n creases.The reacti o n m echan is m can be express by t w o equations:N a++Eu3+=2C a2+,Na++Eu3+=Sr2+.

Eu3+and N a+prefer to occupy eigh t coo r d i n ated sites instead of Ca2+or Sr2+.B ecause t h e i o nic rad iio fEu3+ (0.113n m)and N a+(0.105n m)are s m aller t h an that of Sr2+(0.118n m),the diffracti o n peaks sh ifts to the s m a ll e r diffraction angle.In the contras,t the d iffraction peaks sh ifts to the b i g ger diffraction ang le due to the i o nic radii o f Eu3+and Na+are bigger t h an that o f Ca2+(0.100n m).

3.3 The excit ation and e m ission spectra

F i g.3i n dicates the e m ission and exc itati o n spectra for Ca1 2x M o O4:Eu3+x,N a+x(F i g.3(a))and Sr1 2x M o O4: Eu3+x,Na+x(F i g.3(b))respecti v e l y(x=0.25,m olar content).These t w o kinds of phosphors not on l y have si m ilar e m issi o n and excitation spectra,but a lso have the sa m e l u m inescen t m echan is m because the outer space electr onic confi g uration of C a2+is si m ilar to that o f Sr2+.The ex citation spectru m for m on itori n g614n m e m ission peak of the phosphor is co m posed of a broad band located240 350nm and a series of sharp li n es.The broad band is a ttri b uted to the charge transfer sta te absorption o f Eu3+-O2-and M o O2-4.M oreover,the shar p lines above 350nm m ight due to the f f transition absorption o fEu3+ions[12].E spec iall y,there is an obv ious exc itati o n peak at 470nm,so this novel phosphor can be ex cited we ll by

G a N based b l u e LED ch i p s.

第5期L I Xu et a:l The Lum inescent P rope rties o f A l kaliM e tal Ion and T ri v alent Europiu m

Ion Co activated A l ka li ne E art h M o l ybda te Phosphors 1195 The e m issi o n spectrum m on itoring 470nm inc l u des a series of narro w lines ,w hich belong to the characteristic

peaks of Eu 3+.There are t w o m a i n e m issi o n peaks :one is the red peaks around 610 625n m (616and 624nm )

attr i b uting to the e lectric dipo le transition 5D 0 7F 2;the o ther is the orange peaks around 590nm attri b uti n g to the m agnetic dipo le transition 5D 0 7F 1.As is w ell known ,the m agnetic dipo le transiti o n 5D 0 7F 1is in the h i g hest flight if Eu 3+i n hab its the sy mm etr y centre of lattice in the host crysta.l On t h e contrary ,the electric dipo le transition 5D 0 7F 2w ill beco m e the m ain if Eu 3+takes up the asy mm etry centre o f lattice i n the host crystal [13].Thus ,the e m issi o n i n tensity ratio of the 5D 0 7F 1to 5D 0 7F 2str ong ly depends on the locality of the Eu 3+i o ns in t h e host lattice .In F i g .3,the e m issi o n spectra o f the sa m ples sho w a strong e m ission at red peaks ,wh ich i n d icates that Eu 3+ions i s located the asy mm etr y centre .

The transiti o ns correspond i n g w ith t h e rest w eak e m ission peaks are 5D 1 7F 1(539n m,545nm ),

5D 1 7

F 2(579nm,582nm ),5D 0 7F 3(654n m,660n m ),5D 0 7F 4(703nm,709nm )respecti v e l y .F ig .3 The exc itati on and e m i ssi on spectra of sa m ples

(a)Ca M oO 4:Eu 3+,N a +,(b)Sr M oO 4:Eu 3+,N a +

F i g .4 T he e m i ssi on spectra of al ka li me tal i on and Eu 3+co doped Sr M oO 43.4 Em ission spectra of alkalim etal and Eu 3+co doped Sr M oO 4

The e m issi o n spectra o f different alkalim eta l ions (L i +,Na +and K +)and Eu

3+co doped Sr M o O 4are g i v en i n Fig .4,i n w h i c h the m o lar contents of alka li m eta l ions are equal to Eu

3+(0.1m o lar fracti o n).A s is w ell kno w n ,a l k alim etal i o ns have one outer she ll electron and it tend to beco m e e l e ctricity positive electric ity i o n after loss th is e lectron .Thus ,they can be used for co m pensati n g charge for Eu

3+i n Sr M o O 4phosphor .Co m paring w ith lith i u m (0.078nm )and sod i u m (0.105nm ),t h e i o nic rad i u s of kali u m (0.151n m )is bigger ,w hich is 1.3ti m es of Sr

2+i o nic radius .It is difficult for K +to enter crysta l lattice and it tends to bri n g the crysta l lattice fla w .The l u m inescent i n tensity of Li +,Eu 3+and N a +,Eu 3+co doped Sr M oO 4is stronger than that of co doped by K +,Eu 3+

.H o w ever ,the rig i d ity of Sr M o O 4co doped by Li +,Eu

3+is stronger than the phospho r co doped by N a +,Eu 3+.Considering the processi n g of grinding w ill a ffect the l u m i n escent i n tensity o f phosphor ,N a +is regard as the

opti m al charge co m pensation for m o l y bdate phosphor .3.5 The i n fl u ence of N a +dosage on t he lu m inescent i n tensity

The pho to l u m i n escence spectra o f the Eu

3+doped Ca M o O 4and Eu 3+,N a +co doped Ca M o O 4phosphors exc ited at 470nm are i n d icated i n Fig .5.It can be seen tha t the e m ission i n tensity at 616nm and 624nm obv iously enhance about 0.5ti m es after Na +added.Because the i o nic radius o fNa

+i s si m il a r to that o f Sr 2+,it can o ffer a lattice site for Eu 3+.Thus t h e e ffective concentration o f Eu

3+increase and the l u m i n escent i n tensity enhance w ith t h e doped dosage (m o lar fraction)of Eu 3+and N a +

.H o w ever ,t h e o t h er peaks have little change .The i n set ill u strates the change of Ca 1 2x M o O 4:Eu 3+x ,N a +x lum i n escent i n tensity w ith the N a +concentration [14].W hen the

人工晶体学报 第36卷

F i g.5 T he em issi on spec tra o f Ca

1 2x M oO

4

:Eu

x

,

N a

x and Ca

1 x

M oO

4

:Eux

equal a m ount o fNa+and Eu3+(x=0.25m o lar con tent)

are added i n to t h e phospho r,the i n tensity w ill reach the

m ax i m um,wh ile no concentration obv i o us quenching

appears.

N a2C O3is regarded as flux i n the reaction process

because it can reduce the synthesizing te m perature and

shorten the reacti o n ti m e so so m e N a2CO3added in the

reactan.t I n add ition,the N a2CO3can i m prove the

crysta lline and the d istri b uti n g of granu larity.

4 Concl usi ons

A series of Eu3+,Na+co acti v ated m o lybdate

phosphors AM oO4(A i s Ca or Sr)w ere fabricated by

solid state reacti o n m ethod.XRD patterns sho w that the doping of Eu3+and N a+reduce the cr ystal para m eter,but t h e structure of unit cell has no change.Co m pared w ith the Eu3+doped m o lybdate phosphor,the l u m inescent i n tensity of Eu3+,N a+co acti v ated phosphor enhances by50%.Our resu lts sho w that N a+is a good char ge co m pensate reagent for Eu3+activated m olybdate phospho r.

R eferences

[1] Yang Z P,LiX,Y angY,et a.l The In fl uen ce ofD ifferen tCond iti ons on the Lum i n escen tP roperti es ofYAG:Ce Phos phor For m ed by C o m bu stion

[J].Lum in.,2007,122 123:707 709.

[2] S chlotter P,Schm i dt R,Schnei der J.Lum i n escen ce C onversi on of B lue L i gh t Em i tti ng D iodes[J].Appl.Phys.A,1997,(4):417 418.

[3] Naka m ura S,M ukaiT,Sen oh M.C andela C lass H i gh B ri gh t n ess InGa N/A l G a N Doub le het erostruct u re B l ue L i gh t Em itti ng D i od es[J].Appl.

P hys.L ett.,1994,:1687 16.

[4] Sakum a K,H irosak iN,X i e R J,et a.l Lum i n escen ce Properties of(C a,Y) S i A l ON:Eu Phosphors[J].M a t er.L ett.,2007,61(2):547

550.

[5] W u Z C,Sh i J X,W ang J,et a.l A Novel B l ue e m itting Phosphor L i SrPO4:Eu2+forW h ite LEDs[J].Soli d.S t a t e Ch e m.,2006,179(8):2356

2360.

[6] PangM L,L i n J,Yu M.Fab ri cati on and Lum i n escen t Properti es of Rare Eart hs doped Gd2(W O4)3Th i n Fil m Phosphors by Pech i n i Sol gel

P rocess[J].Soli d S t a te C he m.,2004,177(7):2237 2241.

[7] J ubera V,Cha m i nad e J P,Garci a A,et a.l Fouassier Lum i n escen t Properties of Eu3+ Acti vated L it h i um Rare Eart h B orates and Oxyborates[J].

Lum in.,2003,101(1 2):1 10.

[8] Neeraj S,K iji m a N,C heet h a m A K.N ovelRed Phosphors f or Soli d st ate L i gh ti ng:the Syste m N a M(W O4)2 x(M o O4)x:Eu3+(M=Gd,Y,B i)

[J].Che m.P hys.L ett.,2004,387(1 3):2 6.

[9] H u Y S,ZhuangW D,Ye H Q,et. a.l A Novel red Phosphor forW h ite L i ght Em itti ng D i odes[J].A lloys and C o mp.,2005,390(1 2):226

229.

[10] H u Y S,ZhuangW D,Y eH Q.Lu m i nescen tP roperti es of Sa m ari um Ion i n Calci um M ol ybdat e[J].Journa l of R are Ea rt hs,2004,22(6):821

824.

[11] L i n Q S,Feng X Q.Progres s on the S truct ure i n P W O4S ci ntill ati on C rystals[J].Journa l of Inorgan icM a t erials,2000,15(2):193 199.

[12] PangM L,L i n J,Yu M.Fab ri cati on and Lum i n escen t Properti es of Rare Eart hs doped Gd2(W O4)3Th i n Fil m Phosphors by Pech i n i Sol gel

P rocess[J].Soli d S t a te C he m.,2004,177(7):2237 2241.

[13] K ott aisa my M,Jagannat han R,et a.l On the For m ati on of F l ux Y2O2S:Eu3+Red Phos phor[J].E lectroc h e m.Soc.,1995,142(9):3205 3209.

[14] Y ang Z P,L iX,Li X M,et. a.l E ff ect of D ifferentH ost on t h e Lum i n escen t Property of YAG:C e3+C ryst a llit e For m ed by Co m busti on[J].

Journa l of Synthetic Crystals,2007,36(1):191 194.