COOPERATIVE AND STIMULATED-EMISSION IN POLY(P-PHENYLENE-VINYLENE) THIN-FILMS AND SOLUTIONS

We discuss cooperative and stimulated emissions and separate their res pective contributions to the emission spectral narrowing in thin films and solutions of poly(p-phenylene-vinylene) derivatives. Whereas coop erative radiation is favored in films with poor optical confinement, d irectional stimulated emission is dominant in dilute solutions and thi n films with superior optical confinement. Spectral narrowing in the l atter case could be achieved by increasing either the excitation lengt h or excitation intensity, from which we determined the optical gain a nd loss coefficients at the 0-1 emission band assuming a simple amplif ied spontaneous emission model. We found that the threshold excitation intensity for stimulated emission in neat films is mainly determined by self-absorption and that the gain saturates at emission intensities of about 10(7) W/cm(2). [S0163-1829(98)02015-3].