  The magnetic field effects on the carrier mobilities and recombination in
tri-(8-hydroxyquinoline)-aluminum (Alq3) based light-emitting diodes have been
measured by the method of transient electroluminescence. It is confirmed that
the magnetic field has no effect on the electron and hole mobilities in Alq3
layers and can decrease the electron-hole recombination coefficient. The
results imply that the dominant mechanism for the magnetic field effects in
Alq3 based light-emitting diodes is the interconversion between singlet e-h
pairs and triplet e-h pairs modulated by the magnetic field when the driving
voltage is larger than the onset voltage of the electroluminescence.
