One-center trapping of the holes in alkali halide crystals

The geometric and electronic structures and electron excitation energies for the one-center hole polaron state and several possible intermediate states corresponding to the hole relaxation in KI are calculated using the static embedded molecular cluster method. The calculated optical transition energies are close to the maxima of the transient optical-absorption spectra in KI which were observed experimentally using femto-second spectroscopy. The mechanism of the self-trapping of the holes in KI is discussed. It is demonstrated that the experimental spectra can be reasonably understood if we consider that the hole first localizes in the one-center state which then transforms into the two-center state, and finally into the VK center. {} 1996 The American Physical Society.