De-excitation process and hot luminescence in the FA(type I) center in KCl:Na

The de-excitation process of FA(type I) centers in KCl:Na has been investigated by measuring the hot luminescence spectrum from optically excited FA centers with time-resolved spectroscopy. The experimental results are analyzed by using a model that describes a time evolution of the phonon wave packet during the vibronic relaxation process from the Franck–Condon state to a relaxed excited state. From the analysis of the experimental data, information on the vibronic mixing between 2p and 2s states, whose magnitude varies during the relaxation process, and the adiabatic potential energy curves of 2s and 2p states are extracted. The present results are compared with the already known ones of the FA(type II) centers.