The dynamics of gain-narrowing in a ladder-type π-conjugated polymer

Amplified spontaneous emission (ASE) indicated by photoluminescence spectral-narrowing is observed from a ladder-type conjugated polymer at high excitation densities. The narrowed emission shows a distinct blue-shift with respect to the photoluminescence emitted at lower densities. The line-narrowing is examined in detail using picosecond luminescence spectroscopy in conjunction with femtosecond pump–probe spectroscopy. The experiments give insight into the fundamental processes that lead to optical gain in conjugated polymers. Our results provide conclusive evidence that gain-narrowing occurs simultaneously with an energetic relaxation of localized excitations. The spectral properties of the ASE are closely linked to the dynamics of the excited states.