Comment on "Yield of singlet excitons in organic light-emitting devices: a double modulation photoluminescence-detected magnetic resonance study"

In a recent Letter [1] Lee et al. studied the spin 1/2 photoluminescence-detected magnetic resonance (PLDMR) of a soluble derivative of poly-phenylene vinylene [MEH-PPV] using a double modulation scheme, where both the laser excitation intensity and the microwave power were modulated at ?ex and ?? (?? ??ex), respectively. The obtained results were used to attempt differentiating between the quenching and the spin dependent recombination (SDR) models for PLDMR [2]. Also, an alternative model to the SDR was introduced [1] in which triplet excitons interact with polarons, (T-P model) leading to a reduction of both species. It was concluded [1] from the ?? dependence of PLDMR that the polaron recombination time is ~30 ?s.