Magnetic hyperfine modulation of charge photogeneration in solid films of Alq3

Magnetic fields were found to increase photoconduction in tris-(8-hydroxyquinolinato) aluminum (III) (Alq3) by up to 6% at about 100 mT. The effect was found either to saturate or to decrease as magnetic field increased and revealed a non-monotonic evolution with applied voltage. These observations are explained in terms of a hyperfine scale magnetic-field-dependent mixing of singlet and triplet electron–hole pair states formed prior to the separation of charge carriers, taking into account a statistical distribution of the inter-carrier distance in the charge pairs.