Electric field induced ionization of the exciton in poly(phenylene vinylene)

The exciton binding energy (E-b) and the band gap energy (E-g) of poly(phen ylene vinylene), PPV, have been determined by photoconductivity excitation profile spectroscopy as a function of applied electric field. The spectral signature of the exciton is a narrow peak (100 meV full width at half maxim um) that emerges just below the band edge upon increasing the external fiel d or the defect density. The exciton peak is observed only for light polari zed parallel to the chain axis. The exciton binding energy is obtained from the energy of the exciton peak with respect to the band edge and, independ ently, from analysis of the field dependence of the exciton dissociation: E -b approximate to 55 meV.