Luminescent Properties of Ca2 Y8 ( SiO4 ) 6O2:Eu3 + Phosphors Prepared by Spray Pyrolysis Process

JOURNAL OF RARE EARTHSVol.22, Spec. , Dec. 2004, p.122Luminescent Properties of Ca2 Yg ( SiO4 )。O2 :Eu' * PhosphorsPrepared by Spray Pyrolysis ProcessShen Weiying (沈伟英), Lin Jun(林君) .(Key Laboratory of Rare Earh Chemistry and Physics , Changchun Instiute of Applied Chemistry, Chinese Academyof Sciences，Changchun 130022, China)Abstract: Using CaCO3, metal oxides ( all dissolved by nitric acid) and tetraethoxysilane Si( OC2H,)4(TEOS) as themain starting materials, Ca2Yg ( SiO, )。O2: Eu'* phosphors were synthesized by spray pyrolysis. X-ray diffraction( XRD) , scanning electron microscopy ( SEM) and photoluminescence (PL) spectra as well as lifetimes were used tocharacterize the resulting phosphors. The results of XRD indicated that the 1000 C annealed powders crystallize withthe silicate oxyapatite structure. SEM study revealed that the phosphors consist of spherical particles with an averagesize of about 1 ~3 μm. In the crystalline Can Y,( SiO4)。O2 Eu’* phosphor, the Eu' * shows its characteristic emissioncorresponding to 'D。- 'F(J=0, 1, 2, 3, 4) tansitions, with 'D。- 'F2 red emission (613 nm) as the most promi-nent group, agreeing well with the structure of the host material.Key words: silicate oxyapatite; spray pyrolysis ; luminescence; europium; spherical phosphorCLC number :0614.33Document code: AArticle ID: 1002 -0721(2004) -0122 -03Ca2 Yg( Si04)。O2 is a kind of ternary rare- earth-1 Experimentalmetal silicate with the oxyapatite structure ，whichhad been used as host materials for the luminescenceThe starting materials for preparation of theof various rare earth and mercury-like ions'phosphor were CaCO,(A. R. ), Y2O3 (99.99%)，There are two kinds of sites available for the cations,Eu2O3(99. 9% ) and tetraethoxysilane Si( 0C2H,)4i. e., 4f(Cz) site with nine-coordination and 6h(TEOS). The stoichiometric amounts of the starting(Cs) site with seven-coordination for cations to exitmaterials CaCO, Y2O3 and Eu2O, were dissolved inin this compoundIn recent years， Ca2Ygdiluted HNO, and subsequently mixed with ethanol( SiO4)。O2 based powder and thin film phosphorsand Si( OC2Hs)4. The resulting mixture was furtherhave been prepared by the sol-gel techniquestirred for 3 h, then the solution was loaded to theIt is reported that phosphor materials must havespray pyrolysis apparatus ( BiCHI Mini Spray Dryerfine size ( <3 μm), narrow size distribution, non-B-191) to obtain precursor paricles, which were an-agglomeration and spherical morphology for good lu-nealed at 800 ~ 1100 C to produce the final phos-minescent characteristics8. Recently, spray pyroly-phors.sis technique has been applied to prepare sphericalThe X-ray diffraction ( XRD) of the powderphosphor materials[9, 10]In general, luminescentsamples was examined on a Rigaku-Dmax 2500 dif-materials derived from this method have sphericalfractometer using Cu Ka radiation ( λ = 0. 15405morphology and narrow size distribution for good lu-nm). The morphology of the phosphors was inspec-minescence. In this paper, we report the morphologyted using a scanning electron microscope ( SEM, JE-and luminescent properties of the Ca2Yg( SiO4)。O, .OL JXA-840). The excitation and emission spectra: Eu'+ phosphors prepared by spray pyrolysis ( lowwere taken on Hitachi F-4500 spectrofluorimeter e-temperature spray drying followed by slow pyrolysis)quipped with a 150 W xenon lamp as the excitationmethod.source. Luminescence lifetimes were measured witha SPEX 1934D phosphorimeter using a 7 W pulsexenon lamn. as the exritatinn enurre with the pulse中国煤化工Received date: 2004 - 08 -07 ;revised date: 2004- 10 -25JHCNMHGCB3147) and theFoundation item: Project supported by the " Bairen Jihua" of Chinese AcademyNational Natural Science Foundation of China (20271048)Biography: Shen Weiying (1979 - ), Female, BachelorCorresponding author (E - mail:; jlin@ ns. ciac. jl. cn)Shen W Y etal. Luminescent Properties of Ca, Y,( SiO)。O2: Eu'+ Phosphors123width of 3 μs. All the measurements were performedat room temperature( RT).2 Results and Discussion2.1 XRD and SEMFig.1 shows XRD pttemns of the CaY.gE4o.14( SiO。)。O2 powder samples annealed at differenttemperatures from 800 to 1100 C with an interval of3089IveMD39100 C as well as the JCPDS Card (27-0093) forcalcium yttrium oxide silicate as a reference. Forpowders annealed at 800 C, no diffraction peaks areFig.2 SEM micrographs for CaY, 86 Euo 1n( siO, )。O2 powderobserved. This indicates that the powder remains a-morphous below this temperature. For the samplefred at 900 C, a broad band with a weak peak at 20high packing density and the reduction of light scat-=32. 0° is present, which is assigned to (211) re-tering!9!.flection of oxyapatite Ca2Yg( SiO, )。O2, suggesting2.2 Photoluminescent propertiesthe starting of crystallization at this stage. At 1000C, other diffraction peaks at 2θ = 21. 9° (200),The excitation and emission spectra of Ca2Y7.8623.00(111)，26.19(002), 28.49(102)，29. 1°Euo.ua( SiO2)。O2 phosphor are shown in Figs. 3(a,(210), 32.59(112) ,33.10(300) and 47. 10(401)b)，respectively. The excitation spectrum ( Fig. 3belonging to the crystalline oxyapatite have been ob-(a)) consists of abroad intense band with a maxi-served, and no difference in width and intensity ismum at 269 nm and some weak lines in the longerobserved for the 1000 and 1100 C sintered samples，wavelength region. The former is due to the chargeindicating that the crysallization of Ca2Y7.6 Euo.14transfer band (CTB) of Eu'+- 02- , and the latter(SiO2)。O2 is complete at 1000 C.is from f-f transitions within the Eu'+ 4f electronThe SEM micrograph of CaY7.6 Eu, u( SiO,)。O2configuration. Upon excitation into the CTB at 269phosphors prepared by spray pyrolysis is shown innm, the obtained emission spectrum (Fig. 3(b)) isFig. 2. It can be seen that the phosphor particles havecomposed of 'D。- 7F(J=0,I, 2, 3, 4) emissionspherical shape and smooth surface in the size of 1 ~lines of Eu'* ( the locations for the emission lines as3 μm. It has been reported that phosphor particleswell as their assignments are labeled in the figure ).with spherical morphology and the size of 1 ~3 μmIn general, when the Eu' + ion is located at crystallo-could improve the optical performance due to thegraphic site without inversion symmetry, its hyper-sensitive transition ‘D。- 'F, red emission will domi-nate in the emission spectrum, otherwise if the Eu' *site possesses an inversion center, its“D。-'F or-ange emission will dominate'. In this emission1100 Cspectrum of Ca2 Y7.86 Euo,14( SiO, )。O,，because theEu'+ ion replaces theY'+ ion in view of their similar1000 Csizes and valence state, the Eu'+ ion is located at asite with C; and/or Cs point symmetry ( without in-900 Cversion center), so its‘D。- 'F2 red (613 nm) emis-sion presents as the most prominent group.800 CThe emission spectra are recorded as a functionnoratire With the increase of an-2025 30354045505560ne中国煤化Imission intensity in-20/ (°)cre:YHCN M H Gcan be resolved, asshown in Hig.4. Thus IS due to the content of impuri-Fig.1 X-ray dffaction patterns for Ca2 Y, .gEuo.14ties in the phosphor such as - OH, - OR, H2O,( SiO, )。O2 powder samples annealed at differentNO3 and others decreasing with the increase of an-temperatures and JCPDS cards for calcium yttriumnealing temperature. This also agrees with the factoxide silicate (No. 27 0093 )124JOURNAL OF RARE EARTHS, VoL 22, Spec. , Dec. 2004300269613a)(b)250-Round circles: experimenta! dataSolid line: ftting results byλ。 -613nmλ .=269nm2200=I.exp(-/r)150T=1.55 msCTBf50-导61(400500600700Decay time/msWavelength/nmFig.5 Decay curve for Eu'+ ('D。-F, at 613 nm) inFig.3 Excitation (a) and emission (b) spectra of powderCaY.gEuo. u( siO,)。O2 annealed at 1000 CCaY.gEuo. 4(SiO4)。O2 annealed at 1000 C700to1000C,withalifetimeof1.55ms(1000Cannealed sample).1000 CReferences :[1] LinJ, Su Q. A study of site occupation of Eu'+ in900 CMerY,(SiO,)。O2(Me=Mg, Ca, Sr) [J]. Mater.Chem. Phys., 1994, 38: 98.[2] Lin J, Su Q. Luminescence and energy transfer ofrare- earth-metal ions in Mg2Yg ( SiO.)。O2[J]. J. .800 CMater. Chem., 1995, 5: 1151.700 C[3] Lammers M J J， Blasse G. Luminescence of Tb(3+)-and Ce (3+ )-activated rare earth silicates[J]. J. Electrochem. Soc., 1987, 134: 2068.550650[4] LinJ, Su Q. Luminescence and energy migration inthe oxyapatite CaYg ( siO, )。O2 doped with severalrare earth and mercury-like ions [J]. J. Alloys andCompounds, 1994, 159: 210.Fig.4 Emision spectra of Bu'* in Ca2Y.w Euo.14 .[5] Ito J. Silicate apatites and oxyapaties [J]. Am. Min-( Sio, )。02 powder annealed at dfferent tempera-eral, 1968, 53: 890.tures[6] SuQ, LinJ, Li B. A study on the luminescence prop-that the crystallinity of the powder increases with fir-erties of Eu'* and Dy*+ in M,RE, ( SiO,)。O2 (M =ing temperature， as shown in the XRD patternsMg, Ca; RE=Y, Gd, La) [J]. J. Alloys and Com-(Fig. 1)pounds, 1995, 225; 120.The photoluminescence decay curves of Eu'+ in[7] Yu M, Lin J, Wang S B. Sol-gel derived silicateoxyapatite phosphor flms doped with rare earth ionsCaY.gEuo 1+( siO, )。O2 powders sintered at 1000C is[J]. J. Alloys and Compounds , 2002, 344: 212.shown in Fig.5. The curve can be ftted by a single ex-[8] Aron Vecht, Carol Gibbons， Dominic Davies, et al.ponential function as I =Iexp( -t/(r), from which theEngineering phosphors for field emission displays [J].lifetime(r) of Eu'+ is determined to 1. 55 ms.J. Vac. Sci. Technol. B, 1999, 17(2) :750.[9] Kang Y C, LenggoroI w, ParkSB, etal. YAG: Ce3 Conclusionphosphor particles prepared by ultrasonic spray pyroly-sis[J]. Mare. Res. Bull. , 2000, 35(5) :789.Spherical Car Yg(SiO4)。O; Eu'+ phosphor parti-[10]cles with size of 1 ~3 μm were successfully prepared' 中国煤化工咖Mrzsinn o-rosphor particles byby the spray pyrolysis process annealed at 1000 C.0HCNMHGers,2001，50:92.The Eu'* shows its characteristic emissions 'D。- 'F,[11] BrBass U, Uraomae K D L. Luminescent Materials(J=0, 1,2, 3, 4). The PL intensity of Eu'* in-[M]. New York, Berlin: Springer, 1994.creases with the heat treatment temperature from