The role of the β-phase content on the stimulated emission of poly(9,9-dioctylfluorene) thin films

We investigated the optical gain properties of poly(9,9-dioctylfluorene) thin films as a function of the β-phase content. We demonstrate that the product between the gain cross section and the excited state lifetime of the β-phase is about 3.2 times larger than the glassy-phase one, indicating that the β-phase molecules, for a given pump density, have higher gain than the glassy-phase ones. The dependence of the amplified spontaneous emission threshold on the molecular properties, on the waveguide losses, and on the β-phase content is also quantitatively discussed.