CHEMIJA. 2009. Vol. 20. No. 3. P. 169–174 © Lietuvos mokslų akademija, 2009 © Lietuvos mokslų akademijos leidykla, 2009 Sol–gel synthesis of RE 3+ -activated CaWO 4 phosphores Artūras Žalga 1 *, Rokas Sažinas 1 , Edita Garškaitė 1 , Aivaras Kareiva 1 , Tomas Bareika 2 , Gintautas Tamulaitis 2 , Remigijus Juškėnas 3 , Rimantas Ramanauskas 3 1 Faculty of Chemistry, Vilnius University, Naugarduko 24, LT-03225 Vilnius, Lithuania 2 Institute of Materials Science and Applied Research, Vilnius University, Saulėtekio 9, LT-10222 Vilnius, Lithuania 3 Institute of Chemistry, A. Goštauto 9, LT-01108 Vilnius, Lithuania A series of red-emitting phosphores containing CaWO 4 : RE (RE = Tb 3+ , Eu 3+ , Sm 3+ ) was prepared by an aqueous sol–gel method using tungsten (VI) oxide, WO 3 , calcium nitrate tetrahidrate, Ca(NO 3 ) 2 · 4H 2 O, terbium oxide, Tb 4 O 7 , europium oxide, Eu 2 O 3 , and samar- ium oxide, Sm 2 O 3 as starting materials. Synthesized ceramics were characterized using in- frared spectroscopy (IR), X-ray difraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) measurements. Te obtained results clearly show that only CaWO 4 : Eu phosphor can be efectively excited under photoexcitation at 280, 360 and 460 nm and exhibits red emission in the vicinity of 620 nm. Key words: CaWO 4 phosphores, sol–gel synthesis, lanthanide doping, photolumines- cence * Corresponding author. E-mail: arturas.zalga@chf.vu.lt INTRODUCTION Photoluminescence study of diferent crystalline multinary metal oxide ceramics, either pure or doped, mainly with rare earth ions such as Eu 3+ , Er 3+ , Nd 3+ etc., revealed a considerable potential of these materials in optoelectronic applications [1, 2]. Tese compounds could be widely used as phosphores in cathode-ray tubes, feld emission, vacuum fuorescent and electroluminescent displays as well as scintillators in X-ray and positron emission tomographs [1–5]. Te specifc lumi- nescence behaviour of crystalline ceramics is highly sensitive to the initial composition of the host material, dopant or sub- stitutant concentration and processing conditions. Te opti- cal properties of trivalent rare-earth ions (RE 3+ ) in tungstate materials with scheelite (CaWO 4 ) structure have been widely investigated [6–9], especially due to their attractive third- order nonlinear dielectric susceptibilities [10, 12]. It is well known that rare-earth elements can form a series of isomor- phous tungstates with the general formula RE x (WO 4 ) 3 [13]. Because of their attractive luminescence and structural prop- erties, tungstates have been intensively studied and found ap- plications in many felds such as lasers, fuorescent lamps, and scintilators during the last few decades. Tungstates can be divided into two groups with a diferent crystal structure: scheelites (CaWO 4 , BaWO 4 , SrWO 4 , RE 2 (WO 4 ) 3 and PbWO 4 ) and wolframites (MgWO 4 , CdWO 4 , ZnWO 4 and others) [13, 14]. Calcium tungstate CaWO 4 is a representative example of tungstates with the scheelite structure containing Ca 2+ ions and WO 4 2– groups with the coordination number of eight for Ca 2+ and four for W 6+ , and is considered to be a highly func- tional material due to its prominent luminescence properties. When excited by short-wavelength ultraviolet radiation, X- rays or cathode rays, CaWO 4 shows an efcient blue emission. Moreover, many researchers focused their attention on euro- pium (III) and samarium (III) ions as luminescence centres in red light phosphores with excellent emission properties. Tus, CaWO 4 , whether doped or substituted by rare-earth el- ements, is an important optical material which has already