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The effect of magnetic fields on electroluminescence of an organic light-emitting device,known as organicmagnetoelectroluminescence,shows the relation between the spin-related exciton dynamics and the mechanism of light-electricity conversion in organic semiconductors.However,a thorough and microscopic description of such an effect is still missing.We present in this talk a two-step model for exciton generation in different ranges of magnetic fields.Our experimental results and theoretical analysis reveal the role of spin scattering in low fields for the first time.By investigating different blends of hole transporting material and electron transporting material,we find that hopping rates of carriers determine the intensity of magnetoelectroluminescence.Decay of magnetoelectroluminescence for a fluorescent dye with a high trapping ability in high fields and totally different behaviors of singlet excitons and triplet excitons in low fields are experimentally observed,as is predicted by our theoretical model.