Abstract

Coherent polarization effects in molecular aggregates and semiconductor microstructures such as quantum dots and wells are responsible for enhanced nonlinear optical susceptibilities as well as ultrafast radiative dynamics. Recent experiments on pseudoisocyanine Bromide aggregates [1] and GaAs - AlGaAs multiple quantum wells [2] show an increase of the fluorescence lifetime with temperature; in the aggregate case, the lifetime ranges from the ultrafast T=0 value to the monomer value at room temperature. In order to account for this behavior, we have developed a microscopic model which describes aggregate radiation in the presence of intermolecular vibrations. Exciton - acoustic phonon scattering is shown to limit the polarization coherence volume and thereby increase the radiation lifetime. Acoustic phonons are particularly effective in lifteime enhancement when the dispersion relation satisfies certain resonance conditions. We discuss, in general, how the phonon frequency, exciton - phonon coupling strength, aggregate size and temperature effect the cooperative radiation dynamics.

© 1990 Optical Society of America