The relaxation of FH(OH-) centers, after optical excitation, was studied by using a technique which involved time-resolved induced transparency measurements. A rapid electronic relaxation, which occurred within a few ps, was observed. A slower, and markedly temperature-dependent component, was attributed to the restoration of thermal equilibrium between the configurations of the FH center. A third component was attributed to a vibrational relaxation of the OH- stretching vibration which was excited by E-V energy transfer during electronic relaxation. On the basis of the data, a tentative description was proposed for the relaxation of the FH center. It was suggested that, following optical excitation, the FH center probably did not reach a relaxed excited state but instead underwent a rapid transition to the electronic ground state during lattice relaxation in the excited state, together with excitation of the OH- stretching vibration.
E.Gustin, M.Leblans, A.Bouwen, D.Schoemaker: Materials Science Forum, 1997, 239-241, 465-8