Magnetic field effects on electroluminescence in phosphorescence organic light emitting diodes

In this letter, we presented a method to study the MFEs on the triplets in phosphorescent OLEDs. The magnetic electroluminescence (MEL) was obtained by doping a red phosphorescent guest with low concentration into a fluorescent host, where the guest and host can simultaneously emit. Experimentally two different MEL shapes of Lorentz and linear were observed, depending on the used host materials. We presented two different mechanisms to explain their difference. The diffusion process of triplets from host to guest and prolonged lifetime of triplet by magnetic field were attributed to the formation of the Lorentz shape, and it is considered that the linear shape was caused by magnetic field increased Dexter energy transfer rate and determined by the triplet energy difference between guest and host. It can be seen that the competition of two processes lead to the formation of the two different MEL shapes in the phosphorescent OLEDs.