Photoluminescence time decay of surface oxygen deficient centers in un-doped and Ge-doped silica

We report a study of the emission decay from the singlet excited state of two fold coordinated Si and Ge centers stabilized on the surface of silica and Ge-doped silica. The PL lifetimes are of the order of nano-seconds and increase on decreasing the temperature. The results suggest that, for the surface centers, the phonon assisted intersystem-crossing process linking the excited states affects the decay rates, is effective down to low temperatures and is distributed because of the inhomogeneity of the defects.