Morphology dependent fluorescence in alpha-sexithienyl thin film at 4.2K

We investigated by fluorescence spectroscopy at 4.2K high vacuum sublimated thin films of alpha-sexithienyl grown on mica upon a systematic variation of the growth parameters. We studied how the film morphology, induced by di fferent conditions of growth (thickness and substrate temperature), acts on the emission properties at the early stages of growth. We show how the inc reased molecular order corresponds to a less efficient excitation energy tr ansfer to low energy levels (due to the presence of defects and aggregates) and to an enhanced excitonic character of the fluorescence.