On the Excitonic Nature of the Photoluminescence in Polythiophene Revealed by ODMR Spectroscopy

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Abstract
We used the photoluminescence (PL) and photoinduced absorption (PA) techniques, as well as their respective versions of optically detected magnetic resonance (ODMR), to elucidate the photoexcitation properties and the origin of the PL emission in films of poly(3 octhyl-thiophene). We identified the various PA bands in the PA spectrum as due to triplets, bipolarons and excitons, respectively. We show that the previous models used to explain the ODMR spectra in conjugated polymers are incompatible with our data. We offer a new model, in which the long-lived photoexcitations such as polarons, bipolarons, and triplets are non-radiative centers which compete with the excitonic PL emission.