Ultrafast stimulated emission dynamics in poly(p-phenylenevinylene) films

Femtosecond time-resolved studies of photoluminescence (PL) and stimulated emission (SE) have been conducted, for the first time, in neat thin films of poly(p-phenylenevinylene) derivatives. We found that the SE spectral narrowing is accompanied by a dramatic lifetime shortening from similar to 250 to similar to 3 ps, which enhances energy migration within the inhomogeneously broadened exciton distribution. In addition, the SE is delayed with respect to the PL onset by a few picoseconds depending on excitation intensity and the illumination stripe length. In some cases, a second, delayed SE is formed in the film due to the continuing energy migration into exciton states with superior radiative coupling. A set of coupled rate equations, which take into account the time-dependent exciton generation, propagation effect, optical gain and absorption loss, can simulate correctly all the observed SE dynamics. (C) 2000 Elsevier Science S.A. All rights reserved.