Comprehensive analysis of intermolecular charge-transfer excited states in C60 and C70 films

We have investigated intermolecular charge transfer (CT) excited states and demonstrated their contribution to the excitation-relaxation and photocarrier generation mechanisms for both C-60 and C-70 Polycrystalline films. This has been done (1) experimentally, using UV-visible absorption (Abs) and electroabsorption (EA), luminescence and its modulation by external electric-field and steady-state photoconductivity; (2) semiempirically, analyzing the Abs and EA spectra in order to determine the CT state energies and to estimate the variation of the average polarizability tensor and the dipole moment; and (3) theoretically, by performing calculations of polarization energies and electrostatic stabilization energies. The most significant CT states have been identified at approximately 2.43 and 3.50 eV for C-60 films and at 2.26 and 3.60 eV for C-70 films (data from the semiempirical analysis). Their properties have been discussed in terms of crystallographic and electronic structure, with special emphasis on their mixing with Frenkel states. [S0163-1829(98)08836-5].