Quantum efficiency study of photoexcited states in fullerenes

We present a comparative study of photoluminescence (PL) and photoinduced absorption (PA) excitation spectroscopy, resonant Raman (RR) spectroscopy and electroabsorption (EA) of C60 and C70 from 1.5 eV to 4.5 eV. In C60 solid-state films, a salient feature at 2.3 eV was observed, which manifests itself as a peak in the PL excitation and RR spectra, as an onset in the excitation spectra of charge carriers and triplet excitons, and as the first prominent derivative feature in the EA spectrum. In contrast, these features are absent in the case of isolated C60 molecules. We attribute the 2.3 eV feature to a charge transfer state in solid C60. A similar charge transfer state was also observed in solid C70 at 2.15 eV.