Homogeneous Broadening of Zero-Phonon Lines in the Impurity Spectra of Crystals and Glasses

Abstract

The broadening of zero-phonon lines (ZPL) in the light absorption spectra of impurity crystals, caused by the interaction of the electrons of impurity centres with phonons and localized vibrations, is considered. The peculiarities of the homogeneous broadening of ZPL in the impurity spectra of glasses, studied by selective spectroscopy methods, are discussed. The resulting average spectral distribution of a ZPL that is broadened by the interaction with low-frequency two-level modes or quasilocal vibrations has been found. It is shown that in glasses the ZPL broadening, Ω, is usually caused by dynamical shifts of electronic levels in fluctuational transitions between the modes’ states during the lifetime of the excited electronic state or during the hole existence. The temperature dependence of Ω is connected with the decrease of the concentration of excited modes with the fall of temperature. The dependences Ω(T) obtained allow one to explain the experimental results on ZPL in glasses.