Unusual Phosphorescence Characteristics of Ir(ppy)3 in a Solid Matrix at Low Temperatures

We observed unusual radiative decay characteristics of a ( fac -tris(2-phenylpyridine)iridium [Ir(ppy) 3 ]) triplet-excited state doped into 4, 4'-N, N'-dicarbazole-biphenyl (CBP) and polymethylmethacrylate (PMMA) host matrices. From a measurement of the temperature dependence on the phosphorescence intensity and the lifetime of Ir(ppy) 3 in these hosts, we observed that phosphorescence intensities are independent of temperature, while the lifetimes significantly increase at temperatures below T ∼50 K. These results lead us to conclude that the non-radiative transition rate ( k nr ) from the triplet excited state is very small compared with the radiative transition rate ( k r ) and that the phosphorescence quantum yield (φ PH ) is nearly 100% even at room temperature. Based on our experimental results, we propose a possible decay mechanism to rationalize the characteristic temperature dependence on the transient phosphorescence.