We report on the time development of surface photovoltage ͑SPV͒ and electron paramagnetic resonance ͑EPR͒ spectra for C 60 films irradiated by room light in air. Such exposure is shown to result in the progressive reduction of the SPV signal at 0.9-1.1 eV and in an increase in the signal at approximately 1.3 eV, as well as in the reduction of the signals at about 1.6 and 2.3 eV. A decrease in the dark contact potential difference signal as a result of surface band-bending reduction is also observed after exposure. These results are explained assuming that gap states at E c Ϫ(0.9-1.1) eV in our samples are attributed to nonbonded intercalated O 2 in the C 60 lattice while other states at E v ϩ1.3 eV are related to oxygen chemically bonded to the C 60 molecules. EPR measurements reveal that light/air exposure causes an increase in the number of C 60 ϩ paramagnetic defects. A hypothesis has been suggested that the recombination centers at E v ϩ1.3 eV and the C 60 ϩ paramagnetic centers have the same origin and are attributable to carbon dangling bonds.
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