Electronic structure and optical properties of CdWO4 with oxygen vacancy studied from first principles

The electronic structures, dielectric functions and absorption coefficient of both perfect CdWO4 crystal (CWO) and the CWO crystal containing oxygen vacancy (CWO: V O) have been studied using the CASTEP code with the lattice structure optimized. The calculated total density of states (TDOS) of CWO: V O indicates that the oxygen vacancy would introduce a new electronic state within the band gap compared with that of perfect CWO. The dielectric functions are calculated since the imaginary part of the dielectric function can reduce the optical absorption of a certain crystal, and then the absorption coefficient is calculated. The calculated absorption spectra show that CWO: V O exhibits two absorption bands in the ultraviolet and visible region, peaking at about 3.0 eV (413 nm) and 3.5 eV (354 nm), respectively, which are in agreement with the experimental results showing that the yellow CWO has two optical absorption bands in this region peaking at around 350 nm and 400 nm respectively. It can be concluded that oxygen vacancy causes these two absorption bands. The calculations also indicate that the optical properties of CWO exhibit anisotropy, and can be explained by the anisotropy of the crystal lattice.