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

Electronic Structure and Optical Properties of CdWO4 with Oxygen Vacancy Studied from First Principles. X.Zhou, T.Liu, Q.Zhang, F.Cheng, H.Qiao: Solid State Communications, 2010, 150[1-2], 5-8