EVIDENCE FOR EXCIPLEX LASER ACTION IN COUMARIN DYES BY MEASUREMENTS OF STIMULATED FLUORESCENCE

Abstract

Experiments have been performed that measure the time dependence of stimulated fluorescence from acidified solutions of 4‐methylumbelliferone and 7‐hydroxycoumarin. The results show that laser action takes place from excited state complexes. It was found that exciplex emission is delayed after the neutral molecule emission. The delay gives a measure of the exciplex formation time. The measured dependence of exciplex formation time on hydrogen ion concentration, temperature, and pumping power was found to agree qualitatively with a simple model. Evidence for multiple exciplex formation is also presented.