Impurity spectroscopy in glasses and disordered crystals: Inhomogeneous broadening and electron phonon coupling

Parameters of optical impurity spectra in disordered solids were calculated using the potential energy distribution of the ground state and the guest–host interaction potentials of the lower and upper states. The model can yield inhomogeneous band shapes, pressure shift coefficients of zero phonon lines, (pseudo)local phonon frequencies, and linear and quadratic coupling constants to phonons. Results are compared to properties of Shpolʹskii multiplets and zero phonon holes burned over the broad spectra in glasses. Crystal spectra contain discrete lines, but the overall width of multiplets and the bands in weakly polar solvent glasses is similar, and so are the pressure shift coefficients. A decrease of zero phonon transition probability (Debye–Waller factor) with increasing (negative) solvent shift was predicted and confirmed for crystal spectra. In general, no correlation exists between the strength of the first- and second-order couplings, and the vibrational modes involved can be different. Moreover, no relationship was established between the line shift and broadening in a temperature interval from 5 to 100 K.