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We present excitation spectra, picosecond decay time, and quantum efficiency measurements of the photoluminescence (PL) signal in poly (p-phenylenevinylene) (PPV). In pristine PPV we observe a constant efficiency with excitation wavelength for singlet intrachain exciton generation, which we model to be close to unity. In contrast, photo-oxidized PPV samples contain a distribution of quenching centers following the profile of the absorption depth, which causes the PL efficiency to decrease with increasing excitation energy, and the PL efficiency and decay time to be no longer simply related.
Harrison et al. (Mon,) studied this question.