Vibronic coupling parameters and Stokes shift in thiogallate phosphors

This article is devoted to the problem of the electron-vibrational interaction in 4f-5d optical transitions and the calculation of the Stokes shift in thiogallate materials. Usually 4f-5d transitions give rise to the broad vibronic bands whose shape-function have been described and found, including terms corresponding to the emission (absorption) from both ground and first excited levels. This approximation can be applied not only at low temperatures, but at high temperatures also, including room temperature, when the most photoluminescence (PL) measurements are carried out. We estimate vibronic coupling parameters and make the fitting of experimental data for Ba, Ca and Sr thiogallates. The peculiarity of Stokes shift is discussed. The theoretical results are in good agreement with the experimental data.