The present invention relates to organic light-emitting devices comprising (a) an anode, (i) a cathode, and (e) an emitting layer between the anode and cathode, comprising 2 to 40% by weight of a triplet emitter X having a difference of the singlet energy (ES1(X)) and the triplet energy (ET1(X)) of less than or equal to 0.4 eV [Δ(ES1(X))−(ET1(X))≤0.4 eV], 0.05 to 5.0% by weight of a fluorescent emitter Y and 55 to 97.95% by weight of a host compound(s), wherein the amount of the triplet emitter X, the fluorescent emitter Y and the host compound(s) adds up to a total of 100% by weight and the singlet energy of the triplet emitter X (ES1(X)) is greater than the singlet energy of the fluorescent emitter Y (ES1(Y)) [(ES1(X))>ES1(Y)]. By doping, for example, an emitting layer containing a luminescent organometallic complex having a small S1-T1 splitting, with a fluorescent emitter the emission decay time can significantly be shortened without sacrificing external quantum efficiency (EQE) because of very efficient energy transfer.