The photoluminescence and electroluminescence (EL) spectral characteristics of two phosphorescent dyes, green fac-tris(2-phenylpyridine) iridium(III) [Ir(ppy)3] and red tris-(4,7-diphenyl-1,10-phenanthroline)rhenium dications [Ru(4,7-Ph2-phen)3]2+, doubly doped poly(N-vinylcarbazol) (PVK) films were investigated. The efficient energy transfers from PVK host to both Ir(ppy)3 and [Ru(4,7-Ph2-phen)3]2+ dopants were observed in photoexcitation and EL devices. The intensity ratio (Ri) of red emission versus green emission as function of doping ratio (Rc) of [Ru(4,7-Ph2-phen)3]2+ and Ir(ppy)3 in PVK host is found according to a power-law function with the slopes of 2.28±0.2 for PL which obey the power-law with Ri–Rc2 predicated by Förster energy transfer model. EL spectra show a driving voltage depentent power law of Ri–Rc1.53±0.14 at low voltage and Ri–Rc1.16±0.08 at high voltage, respectively. The shift in the power law of Förster energy transfer is likely due to additional emission mechanisms such as carrier trapping and triplet exciton saturation at high current density. © 2004 American Institute of Physics.