ELECTROLUMINESCENCE-DETECTED, CONDUCTIVITY-DETECTED, AND PHOTOCONDUCTIVITY-DETECTED MAGNETIC-RESONANCE STUDY OF POLY(P-PHENYLENEVINYLENE)-BASED LIGHT-EMITTING-DIODES

The strong electroluminescence (EL)-detected magnetic resonance of poly(p-phenylenevinylene) (PPV)-based light emitting diodes is compared to the conductivity (sigma)-, photoconductivity (sigma(ph))- and photoluminescence (PL)-detected resonances. In contrast to the narrow PL-enhancing resonance assigned to polaron fusion into singlet excitons, strong EL- and sigma-quenching resonances are attributed to the spin-dependent polaron-to-bipolaron decay. While the half-field PL-detected resonance reveals only one triplet exciton resonance, believed to result from triplet-triplet fusion into singlets, the half-field EL- and sigma-detected resonances yield two distinct triplets. While both are sigma-enhancing, one is EL-quenching. The nature of the two triplet states is discussed.