Abstract
We demonstrate the phosphorescence (PH) from neat Pt (II) porphyrin (PtOEP) films to be quenched by bimolecular reactions of monomeric (M) and dimeric (D) triplet (T) excitons. Their respective rate constants, γTT(M)≅8×10−12cm3∕s and γTT(D)≅8×10−15cm3∕s, were found from the kinetics fits to the excitation intensity dependence of the relative PH yield. The exciton decay becomes dominated by mutual annihilation above a critical concentrations of TMcrit≅6.3×1017cm−3 for M, and TDcrit≅1.2×1019cm−3 for D triplet excited states. These data allow us to exclude T–T annihilation as the nonradiative pathway quenching the emission from guest aggregates in PtOEP-doped emitters, and predict the onset of the current roll-off in electrophosphorescence efficiency at a current that exceeds four orders of magnitude the values observed experimentally with light-emitting-diodes based on thin PtOEP-doped emitting layers.
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