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 optica l excitations. The effect is explained by field-assisted dissociation of on -chain excitons into short metastable off-chain geminate pairs of charge ca rriers, Some of the surviving geminate pairs can recombine again into on-ch ain singlet excitations after turning off the external electric field. This gives rise to a spike of the field-delayed photoluminescence with the spec trum identical to that of prompt fluorescence. (C) 1999 Elsevier Science B. V. All rights reserved.