AN ANOMALOUS HOMOGENEOUS LINEWIDTH OF OPTICAL-TRANSITIONS DUE TO INCOHERENT TUNNELING IN GLASSES

Relaxation due to incoherent tunnelling is shown to be responsible for the anomalous temperature dependence of the homogeneous linewidth of optical transitions in glasses. The distribution function of the tunne lling model for the parameters of the tunnelling systems (TS) is used, and dipole-dipole coupling between the chromophore and the TS is assu med. Within this, a bending from a linear to a quadratic temperature d ependence of the homogeneous linewidth at T approximate to 5 K is der ived. Measurements on SiO2, GeO2 and BeF2 doped with Eu3+ and Pr3+ are quantitatively accounted for by our theory. This interpretation is su pported by acoustic measurements on oxide glasses.