Field-induced delayed photoluminescence in a conjugated polymer

Field-assisted delayed fluorescence is observed in photoexcited ladder-type poly-(para-phenylene) samples which exceeds the lifetime of primary optical excitations. The effect is explained by field-assisted dissociation of on-chain excitons into short metastable off-chain geminate pairs of charge carriers. Some of the surviving geminate pairs can recombine again into on-chain singlet excitations after turning off the external electric field. This gives rise to a spike of the field-delayed photoluminescence with the spectrum identical to that of prompt fluorescence.