Au–WS2 Nanohybrids with Enhanced Optical Nonlinearity for Optical Limiting Applications

Abstract

Utilizing plasmonic effects of metal nanostructures on tailoring the properties of semiconducting materials has gained substantial research attention in the past 10 years. Here, we report the plasmon resonance-induced enhanced optical nonlinearity of Au–WS2 nanohybrids prepared via the blending of liquid phase exfoliated few-layer WS2 nanosheets with chemically synthesized spherical gold nanoparticles (NPs). Nonlinear optical properties were studied using the open aperture Z-scan technique with nanosecond laser pulses of wavelength 532 nm, which lie in the plasmonic band of Au NPs (480–550 nm) and B-excitonic transition range of WS2 nanosheets (520–535 nm). Au–WS2 nanohybrids exhibited an enhanced nonlinear absorption and optical limiting activity with an effective nonlinear absorption coefficient of 182 cm/GW at an on-axis input intensity of 0.14 GW/cm2, which is 3.87 times higher than that of bare WS2 nanosheets. The improved NLO response of nanohybrids is due to the plasmon resonance-induced local field effects, which significantly enhance B-excitonic transitions in WS2 nanosheets. The simulated field intensity enhancement profile also confirmed the effect of formation, where a strong interaction of plasmonic fields with WS2 nanosheets is clearly visible. The enhancement observed in simulated absorption density profiles indicated improved B-excitonic transitions in WS2 nanosheets due to the resonant plasmonic field. Au–WS2 nanohybrids exhibited a low limiting threshold of 0.55 J/cm2, which is better than that of many eminent nanohybrids reported so far. The strategy followed in this work for attaining superior nonlinear optical responses in Au–WS2 nanohybrids will be useful to develop novel nonlinear optical materials for photonic device applications.