Transient Spectroscopy of Excitons and Polarons inC60Films from Femtoseconds to Milliseconds

We have studied photoexcitations in ${\mathrm{C}}_{60}$ films using transient photomodulation and photoluminescence from 100 fs to 50 ms and absorption-detected magnetic resonance (ADMR). We show that singlet Frenkel excitons are the primary photoexcitations; their recombination kinetics in the picosecond time domain are dispersive as a result of inhomogeneity. The long-lived photoexcitations, however, are shown to be triplet excitons and charged polarons (${\mathrm{C}}_{60}^{\pm }$), identified by the correlation found between their associated optical transitions and ADMR signals with spin 1 and ½, respectively.