Pressure dependent radiative quantum yields of the prompt and delayed luminescence of polyfluorene films

We have measured the prompt and delayed fluorescence and the phosphorescence quantum yields (PLQYs) of thin spin coated films of the conjugated polymer poly(9,9-di(ethylhexyl)fluorene) (PF2/6) at 20 K either in vacuum or under pressure. Only in the latter case, which was achieved by sandwiching the polymer film between two quartz discs, was the observation of delayed luminescence possible. In this case the PLQYs are of the order of 10−4. Additionally the prompt fluorescence is enhanced by a factor of 2, more resolved and spectrally red shifted when compared to non-sandwiched films. We attribute our observations to pressure induced trap formation preventing excitons from migration to quenching sites.