Studies of transient stimulated emission in DOO-PPV films

We experimentally and theoretically investigated the stimulated emission band in neatly prepared 2,5-dioctyloxy poly(p-phenylene-vinylene) (DOO-PPV) films. We found that at moderately high excitation intensity spectral narrowing (SN) occurs due to the amplified spontaneous emission (ASE). A complex ASE build-up and decay dynamics as a function of excitation intensity and stripe length is observed. We also found that the exciton energy relaxation process within the inhomogenously broadened energy distribution becomes faster when ASE occurs. A theoretical model taking into account the polymer film gain and loss, the propagation effect and the time dependent exciton generation process is developed and used to explain the experimental data.