Orbital-dependent photodynamics of strongly correlated nickel oxide clusters

Abstract

The ultrafast electronic relaxation dynamics of neutral nickel oxide clusters were investigated with femtosecond pump–probe spectroscopy and supported with theoretical calculations to reveal that their excited state lifetimes are strongly dependent on the nature of the electronic transition. Absorption of a UV photon produces short-lived (lifetime ∼ 110 fs) dynamics in stoichiometric (NiO)_n clusters (n < 6) that are attributed to a ligand to metal charge transfer (LMCT) and produces metallic-like electron–electron scattering. Oxygen vacancies introduce excitations with Ni-3d → Ni-4s and 3d → 4p character, which increases the lifetimes of the sub-picosecond response by up to 80% and enables the formation of long-lived (lifetimes >2.5 ps) states. The atomic precision and tunability of gas phase clusters are employed to highlight a unique reliance on the Ni orbital contributions to the photoexcited lifetimes, providing new insights to the analogous band edge excitation dynamics of strongly correlated bulk-scale NiO materials.