Investigation of band gap effect and dephasing on Raman line broadening for the highest-frequency Ag mode in comparison with SrWO4 and SrMoO4

The phonon dispersions of SrWO4 crystal were calculated using the lattice dynamical calculations approach. Spontaneous Raman spectra in SrWO4 were measured in the temperature range from 15 K to 295 K, and the temperature dependence of the linewidth of the Ag (921-cm↙1) Raman mode was analyzed using the lattice dynamical perturbative treatment. The experimental temperature dependence of the linewidth was well described by the calculated one which included both the cubic and the dephasing relaxation terms. The bands for internal modes in SrWO4 are broader than that in SrMoO4. The number of the up-conversion relaxation processes in SrWO4 is determined by the interaction between higher vibronic bands with lower bands. So the relative impact of the dephasing process in the linewidth broadening on SrWO4 crystal is smaller than that in SrMoO4.