Charge Transfer, Luminescence, and Phonon Bottleneck in TiO₂ Nanowires Computed by Eigenvectors of Liouville Superoperator

A nonadiabatic excited state dynamics study of ⟨001⟩ anatase TiO₂ nanowire is obtained by combining density matrix in Liouville–Redfield formalism and ab initio electronic structure calculations. The properties of eigenvectors of Liouville–Redfield superoperator are investigated. The time evolutions of Kohn–Sham orbital populations are obtained for different electronic excitations. The numerical solutions of the population changes over time are in agreement with the analytical results. The analytical and numerical results on the electron and hole relaxation rates are compared. The electron nonradiative relaxation to the bottom of conduction band involves Ti 3d orbitals, whereas the hole nonradiative relaxation to the top of valence band is mainly localized in surface O 2p orbitals. The rate of relaxation in nanowire is slower than in bulk TiO₂ demonstrating phonon-bottleneck effect. Calculated emission spectrum has vanishing contribution from lowest energy excitation, which indicates charge transfer.