Excited-State Absorption in Silver Nanoclusters
Gowri U. Kuda-Singappulige, Christine M. Aikens
Abstract
To understand the decay mechanisms of plasmon resonances, we study the excited-state dynamics in atomistic silver clusters─Ag102+ (Td), Ag135+ (Ih), Ag131– (Oh), Ag191+ (D5h), Ag20 (Td), and Ag553– (Ih)─using real-time time-dependent density functional theory (RT-TDDFT). Excited-state absorption (ESA), particularly multiple-photon absorption, was observed regardless of the shape and size of the cluster. Double-photon absorption was prominent in all cases, while strong higher-order ESAs were also detected in Ag135+ (Ih). The strong plasmon-like state in Ag20 (Td) drastically decayed into a weak state near twice the resonant energy, as confirmed by a comparison of the time-dependent difference density and the transition densities calculated from linear-response time-dependent density functional theory (LR-TDDFT). In addition to the nonlinear optical activation, excited-state dynamics in Ag191+ (D5h) and Ag553– (Ih) indicate that interference between neighboring states occurs in systems with densely packed excited states. The multiple-photon absorption that results in a rapid decay of the dipolar plasmon offers fundamental insights about dynamical light–matter interactions in silver materials not only in the direction of plasmon conversion but also in enhancing nonlinear optical properties.