Reversible vs irreversible photodarkening in a-Se: the kinetics study

The kinetics of photodarkening (PD) in amorphous selenium has been studied experimentally at different intensities of optical excitation. Comparison between the experimental results and a proposed phenomenological model reveals the characteristic rates for conversion of structural units into reversible and irreversible states. Our results show that the relaxation of the irreversible PD states occurs over a barrier of about 0.9 eV and is described by much longer characteristic times (more that one order of magnitude) than that for the reversible states.