| Summary: | Antimony sulfide/reduced graphene oxide (Sb<sub>2</sub>S<sub>3</sub>/RGO) nanocomposites were synthesized via a facile, one-step solvothermal method. XRD, SEM, FTIR, and Raman spectroscopy were used to characterize the uniform distribution of Sb<sub>2</sub>S<sub>3</sub> nanoparticles on the surface of graphene through partial chemical bonds. The third-order nonlinear optical (NLO) properties of Sb<sub>2</sub>S<sub>3</sub>, RGO, and Sb<sub>2</sub>S<sub>3</sub>/RGO samples were investigated by using the Z-scan technique under Nd:YAG picosecond pulsed laser at 532 nm. The results showed that pure Sb<sub>2</sub>S<sub>3</sub> particles exhibited two-photon absorption (TPA), while the Sb<sub>2</sub>S<sub>3</sub>/RGO composites switched to variable saturated absorption (SA) properties due to the addition of different concentrations of graphene. Moreover, the third-order nonlinear susceptibilities of the composites were also tunable with the concentration of the graphene. The third-order nonlinear susceptibility of the Sb<sub>2</sub>S<sub>3</sub>/RGO sample can achieve 8.63 × 10<sup>−12</sup> esu. The mechanism for these properties can be attributed to the change of the band gap and the formation of chemical bonds supplying channels for photo-induced charge transfer between Sb<sub>2</sub>S<sub>3</sub> nanoparticles and the graphene. These tunable NLO properties of Sb<sub>2</sub>S<sub>3</sub>/RGO composites can be applicable to photonic devices such as Q-switches, mode-locking devices, and optical switches.
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