Comparative Study of Single and Dual Gain-Narrowed Emission in Thiophene/Furan/Phenylene Co-Oligomer Single Crystals

Three organic semiconductors consisting of thiophene, furan, and phenylene groups showed either one or two gain-narrowed emission peaks by excitation with a laser pulse. The two gain-narrowed emission peaks are optically studied and assigned to 0 → 1 and 0 → 2 vibronic transitions. The number of gain-narrowed emission peaks is determined by a degree of overlap of the vibronic emissions with ground-state and excited-state absorption of the material. Dependence of the gained emission intensity both on the total input energy and the density of the excited states shows that the two gain-narrowed peaks are attributed to two different decay processes: amplified spontaneous emission (ASE) and superfluorescence (SF). The input energy to be conserved in total is distributed between ASE and SF processes strongly dependent on the transition probability and the self-absorption of organic semiconductors as a gain media.