Electronic excitations in ZnWO4 and ZnxNi1-xWO4 (x = 0.1 - 0.9) using VUV synchrotron radiation

Abstract

The photoluminescence spectra and luminescence excitation spectra of pure microcrystalline and nano-sized ZnWO4 as well as the ZnxNi1-xWO4 solid solutions were studied using vacuum ultraviolet (VUV) synchrotron radiation. The samples were also characterized by x-ray powder diffraction. We found that: (i) the shape of the photoluminescence band at 2. 5 eV, being due to radiative electron transitions within the [WO6]6- anions, becomes modulated by the optical absorption of Ni2+ ions in the ZnxNi1-xWO4 solid solutions; and (ii) no significant change in the excitation spectra of Zn0. 9Ni0. 1WO4 is observed compared to pure ZnWO4. At the same time, a shift of the excitonic bands to smaller energies and a set of peaks, attributed to the one-electron transitions from the top of the valence band to quasi-localized states, were observed in the excitation spectrum of nano-sized ZnWO4. © 2011 Versita Warsaw and Springer-Verlag Wien.