Synthesis and Luminescent Properties of GdAlO3:RE by Combustion Process

JOURNAL OF RARE EARTHSVol.22, Spec. , Dec. 2004, p. 268Synthesis and Luminescent Properties of GdAlO3 : RE byCombustion ProcessLuo Lan(罗岚)2°, Liu Qingfeng(刘庆峰)”, Liu Qian(刘茜)2(I. School of Material Science and Engineering , Nanchang University, Nanchang 330047, China;2. State KeyLab of High Performance Ceramics and Superfine Microstructure , Shanghai Institute of Ceramics, Chinese A-cademy of Science，Shanghai 200050, China)Abstract: Pure GdAlO3: RE (RE=Eu, Pr or Tb) crystalline phase was formed at 900 C with the precursor prepar bynitric-citric combustion process. The synthesis process was studied by XRD, TG-DSC and IR spectra. The analysis re-sults show that there are three main stages in combustion process:(1) water evaporation and organic compound pyroly-sis; (2) combusting reaction; (3)pure crystal formation. GdAlO;: RE powder shows good luminescent properties un-der 254 nm excitation and was proved to be a good kind of phosphors.Key words: gadolinium- aluminum perovskite; citrate-nitrate combustion; luminescence; rare earthsCLC number: TB 332Document code: AArticle ID:1002 -0721(2004) -0268 -04Gadolinium-aluminum phosphor( Gd,. A1,O2:temperaturel8-10. Herein we use the nitrate-citrateRE, RE is the rare earth element) has good lumines-method to synthesize GdAlO3: RE (Eu, Tb, Pr)cent properties and stable physical chemical quali-pure phase powders.The powder synthesis tempera-ties' I -3，Compared with yttrium aluminum materialture is 900 C(a very low temperature for perovskitewhich has been well studied, this system of materialgadolinium aluminum) and the powders emit red ortakes great advantage of high absorb modulus andgreen luminescence color.large doping amount, and it is a good candidate ma-1 Experimentalterial for many luminescent materials. Perovskitegadolinium-aluminum single crystal ( GdAlO: RE,1.1 Smaple preparationsabbreviated as GAP: RE) is a novel solid laser andscintillator material!4 -7]. Synthesis and luminescentGd.Al,O; RE,(x=0.01, RE=Eu, Pr or Tb)properties of perovskite gadolinium aluminum inprecursors were prepared by using Gd2O3 (99. 95%，polocrystal and powder form capture the attention ofShanghai Y uelong Non-Ferrous Metals Limited )，researchers.Eu2O,(or Pr。O, Tb,O,, 99%，Shanghai YuelongThe gadolinium-aluminum system includes threeNon Ferrous Metals Limited), Al(NO3); ●(9H2Ocrystalline phases: GdAlO3， GdAl2O, an(A. R. , Beijing Fine Chemical Company ) as startingGdzAl3O12, so it is very difficult to control phasematerials. Citric acid and nitric acid were reagenthomogeneity and purity with the high-temperature-grade purity.solid synthesis method. Therefore, improved chemi-The stoichoimetric amounts of the starting mate-cal routes have been developed to achieve high-purityrials were dissolved in diluted nitric acid ( HNO3 )materials. Among these chemical methods, the ni-under stirring and heating. 50% nitric acid exceedtrate-citrate combustion should show its present adwas in order to provide extra-oxidant. Then twice-vantages. Citric acid acts as the chelating agent andmetal-ion amount of citric acid monohydrate was dis-fuel in this method. It not only allows molecular-solved in the above solution and the resultant mixturemixed constituents to be in chemical homogeneity,wasstiredat75Cfor7~8hwhilepHvalueis3.but also uses the combustion heat to lower synthesisAfter concentrating the solutions by slow evapora-中国煤化工Received date: 2004 -9 -20; rerised date: 2004-11-14JMYHCNMHG1 Technoloay Project)Foundation item: Projeet supported by Science and Technology Developmen(0259nm021)Biography: Luo Lan (1979 -), Female, Master, Teacber, Luminescent materials* Corresponding author (E - mail: luolanl 190@ sina. com. cn)Luo Let al.Synthesis and Luminescent Properties of GdAIO;: RE269tion, an orange transparent sol was obtained. Such( which peak is at 478 C) extended to the highersol was dried in oven overnight to obtain the gel. Af-temperature region and masked the higher tempera-ter an intermediate grinding, the powder was sinteredture heat effect. At 600 C -annealed-powder DSCat900Cinairfor2h.curve, 820 C and 893 C peaks could be seen, andthey stand for Gd, Al2 Al;O12 crstallization and1.2 MeasurementGd, Al2Al,O12-Gd2O-recombining-and-transforing-to-The formation process of its phase was investi-GAP.gated by X-ray diffraction ( XRD, Rigaku D/maxIR analysis made the thermal decomposition2550)，infrared spectra ( IR, Perkin Elmer IR42 )process clearer. At 200 C, carboxyl( --CO2H) andandthermal analysis( TG-DSC ,Netzschaether(C- -0--C) characteristic peak at 1724 , 1080STA449C) , and the luminescent spectra of GdAlO;cm-' indicated excessive citrate acid or citrate existedRE was examined by Perkin Elmer LS55 spectropho-in gel; nitric dumpling (-NO3) and nitric cell (一tometer.NO2 ) characteristic peak 1610,1390 cm -1 evinced ni-tric in gel; At 300 C carboxyl( 一CO2H)peak disap-2 Results and Discussionpeared , and aether(C- -0- -C)peak was not marked,nitric dumpling (一-NO, ) and nitric cell (- -NO2 )2.1 Synthesis of GdAlO;: REwere still obvious, which indicated extra citrate acidPerovskite gadolinium aluminum is a phase irand citrate were decomposed during 200 ~400 C. Ingadolinium-aluminum system; and it is hard to form500 C treated powder IR curve, inorganic-material-a pure perovskite phase by solid reaction at high tem-absorbing-region ( small-wavenumber area) intensityperature ( ~ 1450 C). The XRD patterns of theincreased, but nitric ion and nitric dumpling charac-GdAlO3 precursors sintered at various temperaturesteristic peak intensity decreased. The combusting re-are shown in Fig. 1. No diffraction peak is observedaction of nitric and citric decreased nitric amount.for the sample sintered at 800 C，indicating that the92, 373 C peaks (in Fig. 2) stood for decomposingpowder is amorphous at this temperature. The crys-of extra citric acid and citric; 478 C peak stood fortalline phase of GdAlO3: RE can be obtained at 900combusting reaction of nitric and citric.C temperature, the diffraction patterm at this temper-From the XRD, TG-DSC and IR analyses, weature shows that all the peaks are due to the GAPcan know there are three stages in luminescent powphase and no other crystalline phase can be detected.der synthesized with citric-nitric combustion process.From 800 C to 900 C, the powder changed from aFrom room temperature to 400 C，water evaporationmorphous to crystalline phase, and many metastableand organic compound pyrolysis were assumed in thephases: appeared during this temperature rang ( suchpowder; from 400 C to 500 C, combusting reactionas GdjAlAl,Or, Gd2O3). In order to investigateof nitric and citric happened and output large amountthe thermal decomposition process of the GdAlO;: REof heat; from 500 C to 900 C , powder tumed fromprecursor, the TG-DSC of GdAIO;: RE powder wasamorphous to crystallion.carried out in air with 10 K● min -1 heating rate2.2 GdAlO3: RE luminescent powder( shown in Fig. 2). There was 80% weight lossAt room temperature, the luminescent spectra ofwhen the temperature is≤500 C. The heat effectTG of preousor: 900C10二DSC of preousorGdAIO,GadO,05GdAl.AlO,Q00.850C-05-田800C中国煤化工20~ 304050607cMHCNMHG2θ(° )6 200 " 400~ 600 800~ 1000Temperature/CFig.1 XRD patterms of powder GdAlO3: RE calcined atvarying temperatures for2hFig.2 TG-DSC curves of GdAlO;: RE precursor270JOURNAL OF RARE EARTHS, VoL.22 , Spec. , Dec. 2004900°C_wMA.Tb.Ce500C. GAP.TD°D2→7F。300C~°D-'D。200C°D-7F,500 1000 1500 2000 2500 3000 3500 4000Wavenumbers/ cm'5050055600 650Wavelength/(nm)Fig.3 IR spectra of precursor heated at dfferent temperaue.....EFig.6 Emission spectra of GdAIO, :Tb(Ax =254 nm)'D。2"E2;A....一GAP.EU"D。-F, .55060700Wavelength/ mFig. 4 Emission spectra of GdAlOz: Eu(λe =254 nm)0.02 004 0.05 0.08 0.10 0.12RE concentration /(mol%)°D,→HFig.7 Best RE doping content in GdAlO; RE(λa =254P。- PF:nm)becoming doping contents are 9% ,10% and 7% re-spectively( Fig. 7). GdAlO3: Pr powder emits red lu-minescent light but it emission center (628 nm) isfrom the red color region color( centered at 612nm).Compared GdAlO;: Eu, GdAlO,: Tb with commer-cial red fluorescence powder( Y2O3: Eu), green flu-300620640” 6600 680 700 720orescence powder( Mg Al,O,g: Ce ,Tb), the experi-Wavelenghv mmmental red fluorescence powder emission color isFig.5 Emission spectra of GdAlO;: Pr(λc =254 nm)centered at 615 nm, therefore provids a better red-re-gion-emission powder than Y2O3: Eu (611 nm),GdAlO3: RE has been examined by Perkin Elmerand it has the same or better luminescent intensity;LS55 spectrophotometer, and they have characteristicexperimental green fluorescence powder is also betterion linear spectra( Fgs.4 ~6). The intensities of e-than commercial one by emission color ( which cen-mission peaks and the shapes of emission spectra aretered at 544 nm and green-region-emission centeredalso recorded.at 545 nm) and intensity( more details in Table 1).The luminescent powder absorb the energy of3 Conclusionphoton, the base state electron was excited to higherenergy state. When the electron transisted back toGdAlO;: RE can be prepared by a nitrate-citratebase state , it delivered energy and made the charac-combus中国煤化工:mperature at 900teristic emission. The luminescence intensity depen-C. FCN MH G'and intensity ofded greatly on the activator- doping amount. WhenGdAIOHu UunIVz ●IU au'better than theEu, Tb, Pr doping content increased, Eu 'D。- 'Fcommercial fluorescence powders by 254 nm UV ex-(615 nm), Tb 'D,-7F,(544 nm)and Pr 'D2-H。citation at normal temperature.( 628 nm) emission intensity increased too. And the.LuoLetal..Synthesis and Luminescent Properies of GdAlO;: RE271Table1 Main properties of GdAlO, : RE in comparison[4] Andreeta JP, Jovanie B R. Growth and optical proper-with commercial fluorescence powderties of Cr* doped GdAlO, single crystals [J]. MaterParametersRed powderGreen powderRes, 2000, 3(2): 45.[5] Mares J A, Pedrini C. Optical studies of Ce'+ -dopedGdAIO3MgAlnO,。GdAIO;:NamY2Oj: Eugadolinium aluminium perovskite single crstals [J].3u:Ce,Tb[bChem Phys Lett, 1993, 206: 9.Density/ (g. cm-3)5.24.127.4[6] Mares J A, Nikl M, Development and characterisationCrystal systemCubicPerovskite Hexahedron Perovskiteof Czochralski grown Lux( RE'+ )1-x AIOz: Ce crystalsPeak emission Wave-611(RE'*= Y+ or Gd°*)[A]. Eurodim 94' Seventh615541544length/ nmEurophsical Conference on Defects in Insulating Mate-Half wavelength/am <5<5-10rials[C]. Lyon, France, 1994.Light output/(a.u. ) 100%102%100%110%[7] Dorenbos P, Bougrine E. Scinillation properties ofGdAIO;: Ce crystals[J]. Radiation Effect and DefectsReferences:in Solids, 1995, 135: 321.[8] Matsubara I, Paranthaman M. Preparation of Cr-doped[1] Andreeta JP, Jovanie B R. Growth and optical proper-YzAl3On phosphors by heterogeneous precipitationties of Cr?* doped GdAlO, single crystals [J]. Matermethods and their luminescent properties [J]. Mater.Res. Bull. , 2000, 35: 217.[2] Mares J A, Pedrini C. Optical studies of Ce'+ -doped[9] Veith M, Mathur s. Low Temperature synthesis ofgadolinium aluminium perovskite single crystals [J].nanocrystalline YzAlzOz via different sol-gel methods[]. J. Mater. Chem., 199, 9: 3069.[3] Mares J A, Nikl M. Development and characterisation[10] Bryntse I, Kareiva A. Influence of complexing agentsof Czochralski grown Lu, ( RE'* )1. AIO;: Ce crystalson properties of YBa2 Cu, Og superconductors prepared(RE'* = Y'* or Gd+)[A]. 'Burodim 94' Seventhby the sol-gel method [J]. J. Solid State Chem. ,1996, 121 :356.中国煤化工MYHCNMHG