ELECTRIC-FIELD-INDUCED LUMINESCENCE QUENCHING IN AN ELECTROLUMINESCENT ORGANIC SEMICONDUCTOR

We report on the effect of a static electric field on the photolumines cence (PL) of laddertype poly(paraphenylene) (m-LPPP) in devices of po lymer-light-emitting diodes. External electric fields of 4.5 MV/cm red uce the integral PL intensity down to 24% of the zero-held value and a lter the shape of the PL spectra. The field-induced PL quenching in th e m-LPPP polymer is ascribed to held dissociation of the emitting spec ies. Time-resolved spectroscopy showed that the emission is composed o f contributions from the radiative recombination of free singlet excit ons and of a second emitting species, which we describe as self-trappe d excitons. The observed field-induced changes of the shape of the PL emission can be attributed to the different field response of these tw o emitting species. Thus the PL emission color can be changed with the electric held in the blue-green spectral range. The magnitude of the binding energy of free singulet excitons is discussed.