Electroluminescence-detected magnetic-resonance study of polyparaphenylenevinylene (PPV)-based light-emitting diodes.

The strong electroluminescence (EL)-detected magnetic resonance of PPV-based light emitting diodes is compared to the conductivity ([sigma])- and photoluminescence (PL)-detected resonances. It provides direct evidence that polaron-to-singlet exciton conversion is responsible for the EL. In contrast to the narrow PL-enhancing resonance assigned to polaron recombination, strong EL- and [sigma]-quenching resonances are attributed to the spin-dependent polaron-to-bipolaron decay. The half-field EL- and [sigma]-detected resonances of two distinct triplet excitons is believed to result from triplet-triplet fusion to singlets.