Thermoluminescence and electroluminescence of annealed polyfluorene layers

As-prepared and annealed layers of polyfluorene were studied by thermoluminescence (TL), photoluminescence (PL) and electroluminescence (EL). Upon annealing at the transition to the liquid-crystalline phase, the green emission in PL and EL becomes more pronounced. At the same time the TL spectrum broadens towards higher temperatures, indicating the introduction of additional trapping sites. In contrast, photooxidation does not broaden the TL spectrum, even so it significantly affects the emission spectra. We conclude that annealing causes the formation of non-/weakly emitting aggregates which compete with the undisturbed chains with respect to charge carrier capture and exciton recombination.