  We investigated the magnetic field effects (MFEs) in organic light-emitting
diodes (OLEDs) through the transient electroluminescence (EL) method. The
time-resolved MFEs on the emission were obtained for the first time, which
would be a useful method to clarify the underlying mechanisms of the MFEs. The
fluorescent dye doped tri-(8-hydroxyquinoline)-aluminum (Alq3) based OLEDs were
fabricated. Then, the transient EL was measured both with and without a
magnetic field. To explore the time-resolved MFEs on the emission of the
device, the excitons population dynamics in the device have been analyzed by a
kinetic model. Our results suggest that both the intersystem crossing between
the singlet and triplet electron-hole pairs and the triplet-triplet
annihilation perturbed by the external magnetic field cause the time-resolved
MFEs.
