Spin-relaxation Process of Excited Triplet States of Ir(ppy)₃

Abstract

The phosphorescence intensities of the green phosphor, fac tris(2-phenylpyridine) iridium [Ir(ppy)₃], in a polymethylmethacrylate [PMMA] host matrix are independent of temperature, while the phosphorescence lifetimes increase significantly at temperatures below T ∼ 50 K. In this paper, to rationalize the characteristic temperature dependence of the transient phosphorescence of Ir(ppy₃3, we propose a model where the triplet excited states split by spin-orbital interaction, forming three levels in which mutual energy transfer between the sub-levels of triplet states occurs. We discuss the validity of this numerical model by comparing with the experimental result of the transient phosphorescence in a PMMA host matrix and demonstrate that the model well explains the characteristic temperature dependence.