Ultrafast Direct Charge Transfers Mediated Modification of Third Order Nonlinear Optical Response in Sb2Se3–Au Core Shell Nanorods

Realization of the direct charge transfer at metal–semiconductor interfaces is a long-standing goal of both fundamental and technological significance. Here we report the synthesis of a colloidal Sb2Se3–Au core–shell nanorod as a model system to demonstrate an efficient direct charge transfer from an Au shell to Sb2Se3 core when the metal is selectively excited at the plasmonic wavelength. In our experiments, direct charge transfer by the Landau damping of the plasmons of metal shell significantly enhances the excited state population that results in an unprecedented ultrafast third-order nonlinear optical response as a function of the plasmon-excitation detuning wavelength. The single step photo-induced charge transfer analogous to the intramolecular electronic transition in molecules is probed by ultrafast transient absorption, which reveals that the electrons are directly transferred from the Fermi level of Au to the unoccupied levels of Sb2Se3 in less than 150 fs. First principles density functional theory calculations indicate that the hybridized eigenstates of the strongly coupled system are delocalized across the metal–semiconductor interfaces. By formulating the theoretical models, we connect our experimental results to the theory.