INTERMOLECULAR CHARGE-TRANSFER EXCITATION IN C-60 FILMS - EVIDENCE FROM LUMINESCENCE AND PHOTOCONDUCTIVITY

C-60 films have been investigated by means of optical absorption, lumi nescence, and electric-field-induced luminescence quenching, as well a s with steady-state photoconductivity spectroscopies. The drop of the luminescence yield, the increase of the electric-field-induced lumines cence-quenching efficiency, and the sharp increase of the photocarrier -generation efficiency above 2.3 eV, are interpreted in terms of branc hing either in the excitation or relaxation processes involving interm olecular charge-transfer excited states.