Influence of composition on luminescence properties of Cd1-xZnxWO4 solid solutions

Abstract

A set of single-phase Cd1-xZnxWO4 (x = 0–1) solid solutions synthesized by spontaneous crystallization technique was studied by the methods of luminescence and electron paramagnetic resonance (EPR) spectroscopy. Luminescence spectra of all studied solutions are characterised by a single emission band related to the intrinsic emission of self-trapped excitons. The dependence of luminescence spectra and thermostimulated luminescence (TSL) curves on solution composition was investigated, and the origin of TSL peaks was analysed on the basis of the EPR data. It is shown that the values of optical bandgap and activation energy of luminescence thermal quenching gradually change with solution composition. Several phenomena are observed in solid solutions predominantly at intermediate concentrations of Cd and Zn cations that can be connected with the structural disorder of the solid solutions. In particular, the deviation of lattice parameters from the Vegard's law, the redshift and broadening of the emission band, the suppression of low-temperature (T < 80 K) TSL peaks related to self-trapped holes and the broadening of high-temperature (100–200 K) TSL peaks related to structural defects. The structural disorder arises due to the non-homogeneous distribution of substitutional atoms in cation lattice sites, pronounced because of the mismatch in ionic radii of substitutional cations, which reaches 28.3 % for Cd2+ and Zn2+.