THE STUDY OF DYNAMICAL PROCESS IN OPTICALLY EXCITED STATES USING TIME-RESOLVED POLARIZATION SPECTROSCOPY

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We investigated the features of relaxation dynamics in optical excited states by using picosecond time-resolved polarization spectroscopy. Particularly, we investigated an F center in alkali halides which is typical defect in solid state and a porous silicon in its application.In the former case, we measured and analyzed the spectrum of resonant secondary radiation for the F center in KCl and RbCl. In our results, from the behavior of linear depolarization for the hot-luminescence (HL), we found that the de-excitation mechanism of the optically excited F center occurs solely through lattice relaxation in a 2p adiabatic potential energy trough (APET) until the energy of ordinary luminescence. Moreover, we measured the excitation energy dependence and temperature dependence for HL in OL region to clarify the origin of the depolarization. In this result, we found that the HL in the OL region separates into two elements, that is, one is the same value of P of the HL in the excitation (lattice relaxation in a 2p-APET from high to low energy after excitation) and the emission with P=0 (OL from bottom in 2P<thermodynamics> potential). This result consists with the time evolution of P calculated by KayanumaIn latter case, we investigated the dynamics of the blue-green photoluminescence from porous silicon oxidized in vacuum-annealing and desorpted hydrogen in terms of excitation energy dependence. We explained phenomenologicaly by a localized exciton model which takes into account the phonon coupling and tunneling processes.