Phonon Processes in Disordered Systems, Probed by Spectral Hole Burning and Refilling of Dyes

Abstract

With heat pulse technique (pulse duration Δt ≧ 20 ns) we measured the effects of phonons on the persistent spectral holes of dye molecules in thin organic films, e.g. Langmuir-Blodgett films, or of dye molecules adsorbed at the surface of crystals. The measurements include phonon memory1 and real time effects of phonons, i.e., the irreversible and the reversible phonon-induced filling in the center of the spectral hole. In particular we measured the dependence on the duration and on the power density or calculated temperature TH of the heat pulses. The dependence of the fluorescence intensity IO of the first vibronic zero phonon line on the number N of the irradiated heat pulses (or to be precise on the time t = N•Δt) in the case of the phonon memory is demonstrated in Fig. 1. The observed logarithmic time dependence is explained by a theory based on thermally activated processes in double well potentials2with constant density of states concerning their barrier heights.