Relaxation processes of point defects in vitreous silica from femtosecondto nanoseconds

We studied ultrafast relaxation of localized excited states at Ge-related oxygen deficient centers insilica using femtosecond transient-absorption spectroscopy. The relaxation dynamics exhibits abiexponential decay, which we ascribe to the departure from the Frank–Condon region of the firstexcited singlet state in 240 fs, followed by cooling in ~10 ps. At later times, a nonexponentialrelaxation spanning up to 40 ns occurs, which is fitted with an inhomogeneous distribution ofnonradiative relaxation rates, following a chi-square distribution with one degree of freedom. Thisreveals several analogies with phenomena such as neutron reactions, quantum dot blinking, orintramolecular vibrational redistribution. © 2008 American Institute of Physics.[DOI: 10.1063/1.2975965]