Lattice relaxation study on self-trapped exciton and biexciton in neutral and charged fullerenes

The formation and dynamical properties of ${\mathit{D}}_{5\mathit{a}}$-symmetry self-trapped exciton (STE) derived from the electronic ${\mathit{h}}_{\mathit{u}}$→${\mathit{t}}_{1\mathit{u}}$ parity-forbidden transition of neutral buckyball are studied in the presence of Coulomb interactions using the Bogoliubov–de Gennes formalism. Within the lattice relaxation theory, the multimode vibronic structures in the luminescene and absorption spectra related to STEs are elucidated in good agreement with experiments. The STEs arising from the allowed ${\mathit{t}}_{1\mathit{u}}$→${\mathit{t}}_{1\mathit{g}}$ transition of ${\mathit{C}}_{60}^{1\mathrm{-}}$ and ${\mathit{C}}_{60}^{2\mathrm{-}}$ as well as the possibility of forming a self-trapped biexciton in ${\mathit{C}}_{60}^{1\mathrm{-}}$ are also considered.