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The light output and the current driving tris-(8-hydroxyquinolinato) aluminum (III) (Alq3)-based light-emitting diodes were found to increase by up to 5% and 3%, respectively, as an external magnetic fiel increased to 300 mT. The positive magnetic field effects were sensitive to the applied voltage. These observations made clear that the emissive singlet exciton formation proceeds via a correlated electron–hole pair state and the excitonic injection of electrons contributes to the driving current, the concentration of singlet excitons being modulated by the hyperfine scale magnetic- field-dependent mixing of singlet and triplet pair states constituting precursors of molecular excitons.