Giant nonlinearity in VS₂-black phosphorus nanohybrid under femtosecond pulses

Generating a large optical nonlinearity from hybrid nanoparticles is beneficial for a wide range of applications, such as optical limiting, optical switching, all-optical data processing, and quantum information. A complex vanadium disulphide−black phosphorus (VS₂/BP) nanohybrid with strong interlayer coupling was synthesized by a one-pot hydrothermal method to achieve enhanced third-order nonlinearity for optical limiting applications. In this strongly coupled VS₂/BP nanohybrid, we demonstrate experimentally and theoretically a highly efficient scheme of excited-state absorption (ESA) and refraction by charge transfer. Due to the highly efficient charge transfer at ultrafast time scales between VS₂ and BP, we observed the enhancement in the third-order nonlinear optical response by orders of magnitude compared to VS₂, which shows saturable absorption and one order of magnitude compared to BP, which shows weak two-photon absorption. Moreover, first-principle-based calculations using the density functional theory and Bader charge analysis show the electrons are transferred from VS₂ to BP, verified by steady-state and time-resolved photoluminescence measurements. By using the nonlinear optical response of the nanohybrid, we have designed a high-performance liquid cell-based ultrafast optical limiter with important device parameters such as the optical limiting onset of 5 mJ/cm² along with low limiting differential transmittance 0.6 in the femtosecond regime.