Time-resolved excited state dynamics of super-exciplex in the coumarin dye laser

Abstract It has been known for a few decades that laser dye, 7-diethylamino 4-methyl coumarin (DAMC) exhibits one absorption and one fluorescence peak but produces dual amplified spontaneous emission (ASE) bands (at 427 and 460 nm) in certain solvents, under high power pulsed laser pumping. The appearance of the new peak manifested only under high pump energy excitation, is attributed to a rare excited state species, called a “superexciplex” (SX). This is a transient excited state bimolecular association in which two excited state molecules get bonded with the help of an unexcited solvent molecule acting as an intermediary. In principle, the formation of excited state species would take a time of the order of a few hundred picoseconds or even nanoseconds. The objective of this paper is to delineate the formation of such super - exciplex employing time resolved ASE spectra where the three-dimensional display gives clearer perspectives. Since the formation of the SX depends on dye concentration, pump energy, and temperature, in the present time-resolved spectroscopy (TRS) paper all the above factors had been studied in some detail.