Interface Effects on Optical Nonlinearity in Au/MoS ₂ Nanohybrids

Tuning nonlinear optical (NLO) phenomena are crucial for next‐generation light modulation technologies like optical limiting and switching as well as quantum photonics. To that end, metal–semiconductor nanohybrids have emerged as important systems. Herein, the NLO behavior of Au/MoS 2 hybrids is investigated using the Z‐scan technique in the nanosecond regime. A key observation is a pronounced reverse saturable absorption (RSA) response in strongly coupled Au/MoS 2 , markedly distinct from the behavior of weakly coupled Au/MoS 2 , as well as pristine MoS 2 nanosheets and Au nanoparticles (NPs), which give saturable absorption (SA). The RSA in strongly coupled Au/MoS 2 is attributed to strong interplay between the semiconductor electronic states and localized surface plasmon resonances of the metal NPs, enabling an excited‐state absorption (ESA) process following one‐photon excitation. A field‐assisted carrier trapping model is proposed to account for this unique noninstantaneous RSA, where charge separation across the hybrid interface enhances excited‐state population. Further, comparison with a weakly coupled hybrid structure underscores the critical role of interfacial interactions in switching between SA and RSA regimes. These findings demonstrate the importance of controlling the interfacial interactions at metal‐semiconductor hybrids in NLO applications where dynamic range, noninstantaneity, and broadband control are critical.