Ag–Ag2S decorated functionalized MWCNTs nanocomposite: A highly efficient optical limiter

Sensitive optical devices require robust protection from intense laser light; however, no single material has fully satisfied this need. In this study, a novel nanocomposite was synthesized by decorating functionalized multi-walled carbon nanotubes (F-MWCNTs) with Ag-Ag₂S alloy nanoparticles (AS NPs) using the hydrothermal method, aiming to enhance optical limiting performance. The nanocomposite's structure was confirmed using standard spectroscopic and microscopic techniques. Nonlinear optical measurements were carried out using a continuous wave (CW) laser with 638 nm wavelength via a Z-scan technique and using nanosecond laser pulses with 532 nm wavelength via a Z-scan and degenerate four-wave mixing (DFWM) techniques. Nonlinear optical measurements reveal a nonlinear absorption coefficient, derived from open-aperture (OA) Z-scan fits at three CW intensities (4.7, 5.6, and 6.5 × 10³ Wcm⁻²), where the nonlinear optical absorption coefficient (β_eff) increases from (4.4 ± 0.2) × 10⁻³ to (10.5 ± 0.5) × 10⁻³ cmW⁻¹. This intensity-dependent growth reflects a sequential 2PA → ESA (RSA-assisted) mechanism rather than material instability, and the values significantly surpass those of previously reported materials. This enhanced performance demonstrates the potential of F-MWCNTs-based nanocomposites for advanced optical limiting applications, paving the way for improved protection of sensitive photonic devices.