We report the photophysical method for the synthesis of phenothiazine (PTZ)−gold (Au) nanocomposite (NC), by ablating a Au target in PTZ−dimethylformamide (DMF) solution using a Q-switched Nd:YAG laser delivering 7 ns pulses at 532 nm. The ablation of the Au target as well as the photoionization of PTZ was carried out simultaneously in the same medium with the same laser system. PTZ itself acts as a reducing and stabilizing agent during the formation of Au nanoparticles (NPs). The composite formation was confirmed from the Fourier transform infrared spectroscopy (FTIR) analysis and UV−visible absorption spectrum. The presence of NPs in the composite was evident from the absorption studies and transmission electron microscopy (TEM) analysis. A noticeable reduction in photoluminescence intensity was observed in the composite material, indicating the electron/energy transfer between the constituents. Nonlinear optical (NLO) studies have been done by employing the single beam Z-scan technique that uses 532 nm, 7 ns and 10 Hz laser pulses for excitation. A significant enhancement (∼67 times) in nonlinear optical absorption (NLA) was observed in the composite compared to the constituent moieties, and the reason behind the enhancement could be attributed to both the local field effect and electron/energy transfer. It is observed that the NLA mechanism for pure PTZ (two photon absorption (TPA)) differs from that of PTZ−Au NC (TPA assisted excited state absorption (ESA)). The self-defocusing nature of both the composite and pristine compounds was explored from the closed aperture Z-scan studies. The adopted strategy is found to be useful for designing novel materials with potential applications in photonics.

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Materials with large and quick non-linear optical response, excellent photo thermal stability, cost effectiveness and off resonant non-linear absorption (NLA) are essential requirements for a good optical limiting (OL). Among them, organic systems and π-conjugated polymers are getting special interest because of their flexibility in structural modification that leads to the tuning of optical and electronic properties that are suitable for working under large bandwidth. Here, we report a drastic enhancement of non-linear optical activity and exceptional OL action of two organic-inorganic hybrid system based on BODIPY and Au and Ag nanoparticles (NPs). The organic system taken was certain set of BODIPYs with different substitution at the para and meta positions. All the compounds were found to be exhibiting good reverse saturable absorption (RSA) behaviour and negative non-linear refraction property. An attempt was made to improve the non-linear optical (NLO) property of the BODIPY by forming nanohybrids with Au and Ag NPs, and the best NLO active candidate among the studied system was chosen for it. A significant enhancement in NLO property was observed on hybrid system formation. The optical limiting (OL) threshold of the hybrid (1 J/cm 2) was reduced almost 1/5 times than that of the parent compound (5.2 J/cm 2), and this value is comparable with the benchmark OL materials like C 60. The mechanism behind the NLA is found to be the combination of excited state absorption (ESA) and twophoton absorption (TPA). The enhanced NLA and OL action of C Ag/Au nanohybrids are attributed to the synergetic effect among the two parent components as well as the local field effects of NPs. Enhancement in non-linear optical property is found to be stronger in hybrid system with Au NPs and is due to the resonant charge transfer and intense local field effect on exciting with 532-nm pulse compared with that of Ag NPs. Both the parent compounds and the nanohybrids exhibit negative non-linearity, and the non-linear

Understanding the linear and nonlinear optical responses of two-dimensional nanomaterials is essential to effectively utilize them in various optoelectronic applications. Here, few-layer MoS2 and WS2 nanoflakes with lateral size less than 200 nm were prepared by liquid-phase exfoliation, and their linear and nonlinear optical responses were studied simultaneously using experimental measurements and theoretical simulations. Finite-difference time-domain (FDTD) simulations confirmed the redshift in the excitonic transitions when the thickness was increased above 10 nm indicating the layer-number dependent bandgap of nanoflakes. WS2 nanoflakes exhibited around 5 times higher absorption to scattering cross-section ratio than MoS2 nanoflakes at various wavelengths. Open aperture Z scan analysis of both the MoS2 and WS2 nanoflakes using 532 nm nanosecond laser pulses reveals strong nonlinear absorption activity with effective nonlinear absorption coefficient (βeff) of 120 cm/GW and 180 cm/GW, respectively, which was attributed to the combined contributions of ground, singlet excited and triplet excited state absorption. FDTD simulation results also showed the signature of strong absorption density of few layer nanoflakes which may be account for their excellent nonlinear optical characteristics. Optical limiting threshold values of MoS2 and WS2 nanoflakes were obtained as ~ 1.96 J/cm2 and 0.88 J/cm2, respectively, which is better than many of the reported values. Intensity dependent switching from saturable absorption to reverse saturable absorption was also observed for MoS2 nanoflakes when the laser intensity increased from 0.14 GW/cm2to 0.27 GW/cm2. The present study provides valuable information to improve the selection of two-dimensional nanomaterials for the design of highly efficient linear and nonlinear optoelectronic devices.

Light confinement structures offer tantalizing applications in a wide variety of areas where light–matter interactions play a crucial role. Considering optical nonlinearity, light localization in nanoscale mode volumes may trigger nonlinear optical activity even at relatively low input optical powers. Here, we demonstrate the excitation of the Tamm plasmon mode of a metal–polymer photonic crystal hybrid structure, resonantly invoking absorptive nonlinear behavior of organic BODIPY dye incorporated in the spacer layer. Third-order nonlinear optical measurements are carried out using the z-scan technique with a Q-switched Nd:YAG laser delivering 7 ns pulses at 532 nm. While the bare sample exhibits negligible optical nonlinearity, the sample in the Tamm plasmon structure showed a large nonlinear absorption coefficient of 1.2 × 106 cm/GW at 0.27 GW/cm2 peak excitation intensity. Our results demonstrate a simple and efficient method to create a nonlinear nanophotonic platform valuable for applications in all-optical information processing.