Luminescence from defect centers with monomolecular- and bimolecular-type configurations in C70 crystals

We have investigated luminescence spectra, decay behaviors and their temperature dependence in C70 crystals prepared by different annealing procedures. The spectra have been measured with one-photon excitation, two-photon excitations and excitation below the HOMO–LUMO band gap. We have found two types of defect-related luminescence band with different activation energies: the radiative recombination of Frenkel-like excitons weakly localized at monomolecular-type defects existing near the sample surface and the radiative recombination of excitons trapped at bimolecular-type defects.