Electronic relaxation processes in the T1 state of phosphorescent fac-tris(2-phenylpyridine) iridium molecule in 4,4′-N,N′-dicarbazole-biphenyl host

We have analyzed the time-resolved photoluminescence spectra of fac-tris(2-phenylpyridine) iridium [Ir(ppy)(3)] doped in 4,4'-N,N'-dicarbazole-biphenyl (CBP) using the spin-phonon relaxation processes among three zero-field splitting substates of the T-1 triplet state under the Franck-Condon principle. Good agreement was obtained between the calculated and measured results regarding temperature dependence of three decay components, red peak shift during time evolution at 5 K, and luminescence line shape with vibronic structure.