Relaxation processes of point defects in vitreous silica from femtosecond to nanoseconds

The authors studied ultrafast relaxation of localized excited states at Ge-related O deficient centers in SiO2 using femtosecond transient-absorption spectroscopy. The relaxation dynamics exhibits a biexponential decay, which the authors ascribe to the departure from the Frank-Condon region of the 1st excited singlet state in 240 fs, followed by cooling in .apprx.10 ps. At later times, a nonexponential relaxation spanning up to 40 ns occurs, which is fitted with an inhomogeneous distribution of nonradiative relaxation rates, following a chi-square distribution with one degree of freedom. This reveals several analogies with phenomena such as neutron reactions, quantum dot blinking, or intramol. vibrational redistribution. (c) 2008 American Institute of Physics.