The lowest triplet state T-1 of Ir(btP)(2)(acac) doped into CH2Cl2 is studied by site-selective and time-resolving emission and by excitation spectroscopy at cryogenic temperatures. Different sites due to different environments of Ir(btP)(2)(acac) show dissimilar intensity distributions of the substate emissions, zero-field splittings, emission decay times, and spin-lattice relaxation (SLR) times. Temperature dependent investigations of the SLR processes reveal the importance of the direct process and the Orbach process. Moreover, the emitting T-1 state is assigned as (LC)-L-3 (ligand-centered) state with significant (MLCT)-M-1,3 (metal-to-ligand charge transfer) perturbation. This classification is related to the usability of phosphorescent emitters in OLEDs. (C) 2007 Elsevier B.V. All rights reserved.