Luminescence properties of nano and bulk ZnWO₄ and their charge transfer transitions

We here investigated the photoluminescence properties of nano and bulk ZnWO₄ phosphors with the aim to understand the observed altered properties of nanoparticles as compared to their bulk counterparts. Their excitation bands were decomposed into three components by Gaussian fitting. The influence of crystalline defects that are present due to the low synthesis temperature of ZnWO₄ nanoparticles on the excitation spectra was studied. The structures of ZnWO₄ samples were refined with the General Structure Analysis System. Making use of the estimated refractive indices and the refined lattice parameters, four chemical bond parameters of W-O bonds were calculated and integrated to give the environmental factor h _e, which can to some extent explain the broadened excitation band in bulk ZnWO₄. A new factor H of every W-O bond was calculated, and based on the results, three components of the excitation band at about 250, 280 and 300 nm were assigned to be from W-O1, W-O2(2) and W-O2(1) charge transfer transitions, respectively.