Emission properties of [Os(phen)(2)(dppene)](2+) were investigated from 1.4 to 300 K in ethanol, PMMA, and PVK, a matrix which is frequently applied in OLEDs. These data provide the zero-field splitting values of the emitting T-1 state and the individual decay times of its substates. The T-1 state is assigned to be largely of MLCT character. The splittings change only moderately due to variation of the matrix, whereas the individual decay times are substantially affected. Further, energy transfer from the triplet state of PVK to [Os(phen)(2)(dppene)](2+) was studied by applying time-resolved emission spectroscopy and is assigned to be dominantly of Dexter type. (C) 2008 Elsevier B.V. All rights reserved.