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Doping lithium fluoride (LiF) in the fluorescent layer of conventional organic light-emitting diode is able to effectively tune the magnetic field effects (MFEs) on the current and electroluminescence. As compared with the undoped device, the line-shape and amplitude of MFEs in LiF-doped device showed apparent variation. At room temperature, when the applied external magnetic field reached several hundreds mili-Tesla, the MFEs in conventional device slowly increased and tended to be saturated. However, the MFEs in doped device almost linearly increased with the increasing field, displaying the abnormal and unsaturated high-field effects. Additionally, the amplitudes of high-field effects in current and fluorescence all went up firstly and down later when increasing the doping concentration of LiF. The differences between the MFEs in doped and undoped devices can be attributed to the dielectric polarization of LiF particles in the devices internal electric field. The reaction between the excitons in fluorescent layer and polarization charges on the surface of LiF particles resulted in the special MFEs in doped device.

By utilizing singlet fission property of 5, 6, 11, 12-tetraphenylnaphthacene (Rubrene), i.e., a singlet exciton can convert into two triplet excitons (STT), the Rubrene doped organic light emitting diodes (OLEDs) were fabricated in this work. The magneto-electroluminescence (MEL) and transient electroluminescent were measured in our devices. We found that the strength of singlet fission decreases with decreasing Rubrene concentration (increasing molecular space of Rubrene), i.e. singlet fission can be regulated through modifying the molecular space in Rubrene. This was manifested in two aspects: first is the magnitude of MEL in higher fields (~500 mT) decrease with decreasing Rubrene concentration. When the doping concentration was 20wt%, the MEL curves in higher fields show a decline; another is that the values of the MEL at B =20 mT change from negative to positive with decreasing Rubrene concentration. In addition, the fast decay component of transient electroluminescence after turning off the voltage pulse has a more rapid decline in lower doped concentration. A qualitative discussion is made by analyzing the relation between singlet fission and molecular space of Rubrene, and exploiting magnetic field dependence of singlet fission.