Impact of photoinduced energy transfer and LSPR of Au and Ag nanoparticles on nonlinear optical response of methyl orange

In order to realize effective optical limiting (OL), it is necessary to utilize materials that exhibit distinct traits, such as a large and rapid nonlinear optical (NLO) response, high photothermal stability, and cost-effectiveness. In this work, the NLO properties of methyl orange (MO), a popular pH indicator, a potential nonlinear material, and an azo dye of great industrial importance are modulated by forming nanohybrids with Ag and Au nanoparticles. The NLO properties of the samples were investigated via the Z-scan technique using 7 ns laser pulses at a wavelength of 532 nm. A huge enhancement is observed in the nonlinear absorption (NLA) and OL performance MO-Ag and MO-Au nanohybrid compared to its constituent compounds, and it is attributable to photoinduced energy transfer between MO and metal NPs as well as the local field effect of NPs. The mechanisms responsible for the NLA and OL activity are primarily Excited State Absorption (ESA) with contributions from a weak TwoPhoton Absorption (TPA). Notably, the nanohybrid system incorporating Au NPs outperforms the one with Ag NPs in terms of nonlinear optical properties under 532 nm excitation, primarily due to the better resonant energy transfer of Au compared to the Ag nanoparticle and intense local field effects of Au on exciting at 532 nm due to resonant absorption. The Closed Aperture (CA) Z-scan measurements were employed to investigate the nonlinear refraction property of the compounds, and both the pristine MO and its nanohybrid exhibited negative nonlinear refraction. These findings indicate that forming nanohybrids is an efficient way to modify the NLO response of MO. It also suggests MO has the potential for a diverse array of nonlinear optical applications, including but not limited to optical limiting.