Spectral diffusion broadening by soft local modes in Sm2+-doped sodium borate glass

An explanation for the anomalous temperature broadening of zero-phonon transition corresponding to 7F0↔5D0 electronic transition in Sm2+–doped sodium borate glasses is given. The main broadening mechanism is spectral diffusion induced by thermal fluctuation of long-living soft localized modes over the whole studied temperature region 5–293 K.