Localized electronic states related to O-2 intercalation and photoirradiation on C-60 films and C-70 films

Deep localized electronic states are created by O-2 intercalation into C-60 films and C-70 films, which causes the Fermi level to shift down to the mi ddle of gap. The states act as a trap level for charge carriers and as nonr adiative recombination centers. It seems that prepared C-60 films and C-70 films have a shallow localized state. The shallow state is located at simil ar to 0.2 eV under the conduction band and affects the electrical and optic al properties. Furthermore, the photoirradiation of C-60 films and C-70 fil ms causes polymerization of the O-2-free sample and oxidization of the O-2- intercalated sample. The quasistable electronic states at room temperature are created as a result of photo-oxidization of C-60 films. C-60 oxides cre ate deep localized electronic states which cannot disappear under thermal a nnealing. The photoluminescence intensity of O-2-free samples increases wit h photoirradiation for 1 h. It is found for the first time that this increa se occurs along with a decrease of localized state density. (C) 2000 Americ an Institute of Physics. [S0021-8979(00)02712-2].