Luminescence investigation of Eu3+ ion in the RE2(WO4)3 matrix (RE = La and Gd) produced using the Pechini method

The preparation, characterization and photoluminescent study of Eu3+ ions doped into the RE2(WO4)(3) matrix (RE = La and Gd), which was produced by the Pechini method at 750degreesC are reported. This method is based on polyesterification between citric acid and ethylene glycol, producing a material at low temperature. The X-ray diffraction patterns of the powder materials show the characteristic lines of the rare-earth tungstates. The infrared data are compatible with a T-d point group symmetry for the tungsten atom units in both compounds. The excitation spectra of these systems (lambda(em) = 615 nm) showed an intense broad band with maximum at 265 nm related to the O --> W ligand-to-metal charge-transfer state. The emission spectra of the Eu3+ ion (lambda(excitation) = 393 nm) presented peaks arising from the D-5(J) --> F-7(J') transitions (J = 0-3 and J' = 0-4) and are compatible with a C-nv symmetry. The values of O-2 experimental intensity parameters (25.8 x 10(-20) and 21.5 x 10(-20) cm(2) for La3+ and Gd3+ ions, respectively), reflect the hypersensitive character of the D-5(0) --> F-7(2) transition and indicate that the Eu3+ ion is in a highly polarizable chemical environment, suggesting a considerable covalent character of the metal-donor atom interaction. The high emission quantum efficiencies of the RE2(WO4)(3):Eu3+ materials (68% for La3+ and 64% for Gd3+) suggest that these systems are promising phosphors. The CIE chromaticity coordinates indicate that they are comparable to those of the commercially available red phosphor in cathode ray tubes. (C) 2003 Elsevier Science (USA). All rights reserved.