Surface Plasmon Assisted Enhancement in the Nonlinear Optical Properties of Phenothiazine by Gold Nanoparticle

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.