Dynamics of Exciton Diffusion in PVK:Phosphorescent Materials/Al Hetero-Structures

Exciton quenching dynamics in a polymer PVK doped with FirPic, Ir(piq)₂(acac) and Ir(ppy)₃ phosphorescent guest materials, respectively, due to the presence of metal films is analyzed using time−resolved photoluminescence. The quenching is directly governed by radiationless energy transfer to the metal and is further enhanced by diffusion of excitons into the depletion region of the exciton population at the polymer/metal interface. The influence of polymer layer thickness on the luminescence decay is described by a one-dimensional diffusion model. The energy transfer distance and exciton diffusion length are 10 nm, 9 nm, 15 nm and 29.3 nm, 30.1 nm, 30.9 nm for PVK doped with phosphorescent guest materials FirPic, Ir(piq)₂(acac) and Ir(ppy)₃, respectively. This can disentangle the contributions from direct energy transfer to the metal and exciton migration to the exciton quenching process. The lengths of the exciton quenching region of the three doping systems are 39.3 nm, 39.1 nm and 45.9 nm, respectively.