Partially conjugated poly(phenylenevinylene) as a blue-emitting laser medium: the suppression of stimulated emission due to chain aggregates

Abstract

A new blue emitting conjugated polymer is studied for Amplified Spontaneous Emission (ASE) and laser action in liquid solutions and solid matrices. Both processes were observed simultaneously when the liquid polymeric sample is placed into a resonator consisting of a mirror and a grating. This observation permits the distinguishing between the main differences of ASE and laser action such as tunability and coherence. The stimulated emission efficiency can be strongly affected by the presence of polymer chain aggregates into the sample. In order to study this effect mixtures of the polymer with good and poor liquid solvents were prepared and the ASE action was examined. The polymer molecules tend to aggregate when they approach the poor solvent molecules. Thus, by varying the poor solvent quantity into the liquid samples, the aggregates concentration can be systematically controlled. It is shown that the ASE behavior exhibits a rapid suppress with the aggregates concentration. Performing spectroscopic and stimulated emission cross section measurements in isolated and aggregated polymer solutions, it is proved that in the latter media ASE is caused by the intrachain excitons while the spontaneous emission is caused by the aggregates. The suppress of the ASE is due to the increase of aggregates at the expense of isolated chains.