Bimolecular reactions of singlet excitons in tris(8-hydroxyquinoline) aluminum

Abstract:  Abstract We have studied singlet excited state dynamics in thin films of tris(8-hydroxyquinol ine) aluminum (Alq3), a well known emitter for organic electroluminescent devices. Our experimental results show that bimolecular recombination dominates the singlet exciton decay in pristine films at high intensities, thus decreasing the photoluminescence quantum efficiency and the singlet lifetime. Because of the relatively low carrier concentration at which light emitting diodes operate the electroluminescence efficiency is not affected. The measured rate constant of singlet–singlet annihilation in Alq3 films is ?ss=(3.5±2.5)×10-11 cm3?s-1. The diffusion coefficient and the diffusion length of singlet excitons estimated from ?ss are Ds=(1.2±0.8)×10-5 cm2?s-1 and L=98±40 Å, respectively. © 1996 American Institute of Physics.