LAUSR

Abstract Nanoparticles of xRe2O3 – (100-x)CaWO4 (Re = Eu, Dy, Sm; x = 0, 1, 3, 5, 7 and 10 mol%) were synthesized by solid-state sintering at two annealing temperatures of 800 °C and 1150 °C and characterized by neutron diffraction, Raman and photoluminescence (PL) spectroscopy. The samples are composite materials and contain tetragonal CaWO4 and cubic Re2O3 phases. The unit cell parameters, atomic position co-ordinates, crystallite size, mole-fraction of phases, bond-lengths, bond-angles and cation-oxygen co-ordination numbers were determined by Rietveld analysis of the neutron diffraction data. The short-range structure of CaWO4 consists of snub disphenoid deltahedral CaO8 and tetrahedral WO4 units and the structure of cubic Re2O3 consists of two types of ReO6 units. All the W–O bonds in WO4 units are of equal lengths (1.77–1.79 A) whereas two kinds of slightly different Ca–O bond-lengths (2.41–2.45 A and 2.45–2.47 A) exist in CaO8 units. The neutron pair distribution function of the undoped CaWO4 samples shows the first peak in the range of 1.71–1.74 A due to W–O bonds and the second peak at 2.84 A due to O–O and Ca–O pair correlations. Raman studies of Eu-doped samples show only W–O vibration modes, however, Sm and Dy-doped CaWO4 show weak Raman peaks of Sm2O3 and Dy2O3, along with W–O bond vibrations. PL studies show highest orange-red emission at 1 mol% Sm2O3, green emission at 1 mol% Dy2O3 and red emission at 3 mol% Eu2O3. The light emission intensity in all the samples increases with the increase in annealing temperature from 800 °C to 1150 °C.