Photoexcited Charge Dynamics in Plasmonic Copper Nanoparticles Combined with Copper Oxides Studied by Transient Absorption Spectroscopy

The steady-state and ultrafast optical properties of Cu2O and CuO thin films─both as standalone materials and in combination with Cu nanoparticles to form metallic-core@oxide-shell structures─are studied. By combining transient absorption spectroscopy and steady-state optical measurements, the carrier and plasmon dynamics governing these oxide and oxide–metal hybrid systems have been elucidated. For Cu2O, above-bandgap excitation reveals photobleaching and photoinduced absorption associated with the 1s-like violet exciton. The transient response exhibits a biexponential decay that suggests an ultrafast relaxation into dark excitons, which are long-lived and from which the recombination takes place. In Cu@Cu2O, excitation of the localized surface plasmon resonance induces a transfer of excitation from the Cu core to the Cu2O shell, resulting in a perturbation of the excitonic signal of Cu2O. In CuO and Cu@CuO, complex transient spectral features indicate the presence of short- and long-lived components, while enhanced CuO-related photoinduced absorption in Cu@CuO following visible light excitation is ascribed to the presence of Cu nanoparticles. Overall, these findings demonstrate that coupling Cu nanoparticles with their oxides in a core–shell geometry enhances light–matter interaction across visible wavelengths, enabling a more efficient coupling of the visible and IR ranges to these semiconductors.