Plasmon-enhanced nonlinear optical response in Au-SnS₂ nanohybrids for optical limiting applications

Integrating plasmonic metal nanoparticles (NPs) with semiconductor nanostructures is widely used as an invaluable tool for tailoring the light-matter interaction and thereby improving the nonlinear optical activity of the latter. In the present work, inherent plasmonic effects of spherical Au NPs of size 20 nm were utilized to enhance the nonlinear optical absorption of SnS₂ nanoplates of lateral size 890 nm. The pristine SnS₂ nanoplates exhibited significant reverse saturable absorption with an effective nonlinear absorption coefficient (β _eff) of 50 cm GW^-1, which increased to 85 cm GW^-1 after incorporation of Au NPs, when their nonlinear optical characteristics were investigated using an open-aperture Z-scan technique with a nanosecond pulsed laser operating at a wavelength of 532 nm. The enhancement in nonlinear optical absorption is mainly attributed to the strong influence of plasmonic hotspots of Au NPs, whose characteristic resonance range (450-600 nm) aligns with the laser wavelength. The interaction of such intense plasmonic fields with SnS₂ nanoplates was further confirmed by simulating E-field intensity enhancement profiles using the finite-difference time-domain (FDTD) method. Furthermore, Au-SnS₂ nanohybrids exhibited excellent optical limiting behavior with an onset value of 0.07 J cm^-2 and a low limiting threshold of 1.16 J cm^-2, which are found to be very significant compared to the values previously reported for eminent 2D materials and their nanohybrids. These findings highlight the significance of the present strategy in developing nanohybrids to enhance the nonlinear optical activity of conventional semiconductor nanosystems.