Presence of excited electronic state in CaWO4 crystals provoked by a tetrahedral distortion: An experimental and theoretical investigation

By combining experimental techniques such as x-ray diffraction, Fourier transform Raman, ultraviolet-visible, x-ray absorption near edge structure, extended x-ray absorption fine structure spectroscopy, and theoretical models, a general approach to understand the relationship among photoluminescence (PL) emissions and excited electronic states in CaWO4 crystals is presented. First-principles calculations of model systems point out that the presence of stable electronic excited states (singlet) allow us to propose one specific way in which PL behavior can be achieved. In light of this result, we reexamine prior experiments on PL emissions of CaWO4.