Structural and Optical Properties of CaCuWO Solid Solution Synthesized by Sonochemistry Method at Room Temperature.

In this work, we report the room-temperature synthesis of pure calcium tungstate (CaWO) and copper-doped calcium tungstate solid solution (CaCuWO) by using a sonochemistry method. These materials were structurally characterized by X-ray diffraction (XRD) and Raman spectroscopy. The obtained XRD patterns were submitted to a Rietveld refinement showing, in both materials, a tetragonal phase with space group and point group of 4 and , respectively. Microscopy images of both materials, obtained by field emission scanning electron microscopy, showed spherical agglomerated structures composed by spherical nanoparticles, while calcium and tungstate elements were identified by energy-dispersive X-ray spectroscopy for pure calcium tungstate and copper, calcium, and tungstate for CaCuWO solid solution. The decrease of optical band gap () from 4.0 eV (CaWO) to 3.45 eV (CaCuWO) confirmed the substitution of calcium atoms for copper atoms in the clusters [CaO]. Maximum photoluminescence (PL) emission was shifted from 522 nm in the pure CaWO to 475 nm in the CaCuWO solid solution. Consequently, there was an increase of PL emissions intensity in the blue and green regions of the visible spectrum, due to electronic transitions between the orbitals O 2p, Cu 3d, and W 5d.