Exciton dissociation in tris(2-phenylpyridine) iridium (III) probed by electric field-assisted time-resolved photoluminescence

We have investigated the mechanism of exciton dissociation in organometallic phosphorescent emitters by measuring the electric field-dependent time-resolved photoluminescence for thin vacuum-evaporated films of a model compound-tris(2-phenylpyridine) iridium (III) [Ir (ppy) 3]. We have shown that the dissociation occurs from higher lying spin-mixed states before their relaxation to the lowest emissive levels, the lifetime of the latter not being significantly affected by external electric field. Knowledge about the mechanism of exciton dissociation in this class of materials is relevant for theoretical simulations of exciton kinetics in phosphorescent diodes as well as for optimization of the performances of these devices. © 2008 American Institute of Physics.