Electroluminescence (EL) transient turn-on peaks with more than twice the brightness of the steady-state EL are observed in fluorescent organic light emitting diodes with a doped emission layer. By modeling both the singlet and triplet population dynamics, we identify the EL drop after the peak as due to singlet-triplet (ST) quenching. The peak recovery following a double voltage pulse sequence is explained in terms of triplet population relaxation through triplet-triplet quenching. A mechanism of using phosphors in the emission region is proposed for reducing ST quenching. (C) 2010 Elsevier B.V. All rights reserved.