Homogeneous and inhomogeneous contributions to the luminescence linewidth of point defects in amorphous solids: Quantitative assessment based on time-resolved emission spectroscopy

This paper describes an experimental method that allows the estimation of the inhomogeneous and homogeneous linewidths of the photoluminescence band of a point defect in an amorphous solid. We performed low-temperature time-resolved luminescence measurements on two defects chosen as model systems for our analysis: extrinsic oxygen deficient centers [ODC(II)] in amorphous silica and F(3)(+) centers in crystalline lithium fluoride. Measurements evidence that only defects embedded in the amorphous matrix feature a dependence of the radiative decay lifetime on the emission energy and a time dependence of the first moment of the emission band. A theoretical model is developed to link these properties to the structural disorder typical of amorphous solids. Specifically, the observations on ODC(II) are interpreted by introducing a Gaussian statistical distribution of the zero-phonon line energy position. Comparison with the results obtained on F(3)(+) crystalline defects strongly confirms the validity of the model. By analyzing experimental data within this frame, we obtain separate estimations of the homogenous and inhomogeneous contributions to the measured total linewidth of ODC(II), which turns out to be mostly inhomogeneous.