Subrata Biswas

Enhanced nonlinear optical properties of graphene oxide–silver nanocomposites measured by Z-scan technique

Nonlinear optical properties (NLO) of a graphene oxide–silver (GO–Ag) nanocomposite have been investigated by the Z-scan setup at Q-switched Nd:YAG laser second harmonic radiation i.e., at 532 nm excitation in a nanosecond regime. A noteworthy enhancement in the NLO properties in the GO–Ag nanocomposite has been reported in comparison with those of the synthesized GO nanosheet. The extracted value of third order nonlinear susceptibility (χ3), at a peak intensity of I0 = 0.2 GW cm−2, for GO–Ag has been found to be 2.8 times larger than that of GO. The enhancement in NLO properties in the GO–Ag nanocomposite may be attributed to the complex energy band structures formed during the synthesis which promote resonant transition to the conduction band via surface plasmon resonance (SPR) at low laser intensities and excited state transition (ESA) to the conduction band of GO at higher intensities. Along with this photogenerated charge carriers in the conduction band of silver or the increase in defect states during the formation of the GO–Ag nanocomposite may contribute to ESA. Open aperture Z-scan measurement indicates reverse saturable absorption (RSA) behavior of the synthesized nanocomposite which is a clear indication of the optical limiting (OL) ability of the nanocomposite.

Synthesis of anisotropic nanostructures of silver for its possible applications in glucose and temperature sensing

Syntheses of anisotropic nanostructures of silver have been demonstrated by using a simple chemical synthesis route and the roles of temperature and reaction time in the anisotropic growth of the material have been reported. The role of multiple twinned particles in the anisotropic shape evolution and branching growth of synthesized silver nanostructures is demonstrated. The optical absorption and photoluminescence (PL) properties of the non-functionalized silver nanostructures have been studied in the UV–visible wavelength region and there exist two surface plasmon resonance (SPR) peaks, one called transverse surface plasmon resonance (TSPR) peak situated at smaller wavelength at ~410–415 nm, and another called longitudinal surface plasmon resonance (LSPR) peak appearing at longer wavelength at ~595–615 nm in the visible region. Intense PL emission spectra centered at ~410 nm have been observed from the synthesized products obtained at lower temperature, whereas the PL spectra of higher temperature materials are divided into two broad peaks staying >100 nm apart at both sides of 410 nm. It has been demonstrated that the synthesized non-functionalized silver nanostructure can further be utilized for sensing of glucose and temperature. Tyndall effect experiment with the synthesized silver nanostructures dispersed in methanol has been performed and demonstrated the stability of the nanostructures.

Template-free hydrothermal synthesis of amphibious fluorescent carbon nanorice towards anti-counterfeiting applications and unleashing its nonlinear optical properties

Anisotropic fluorescent carbon nanostructures, namely carbon nanorice (CNR), has been prepared hydrothermally, without using any template, from a commercially available beef extract (BE) bio-precursor at a temperature of 150 °C. The structural and morphological characterizations of the synthesized sample have been carried out using transmission electron microscopy (TEM) and Raman spectroscopy. It has been proposed that the synthesized CNR structures have been formed due to the coalescence of initially formed small spherical carbon nanocrystals during hydrothermal treatment. The third order nonlinear refractive index (n2) of the synthesized CNR has been measured using the spatial self-phase modulation (SSPM) technique, for the first time, and a high optical nonlinearity with an n2 value of the order of 10−6 cm2 W−1 was obtained. The origin of such high nonlinearity is the reorientation of the sp2 graphitic core of CNR in response to intense laser radiation coupled with the thermal lensing effect. A theoretical simulation has been carried out to explain the formation of experimental optical diffraction ring patterns, which have occured due to SSPM of a continuous wave He–Ne laser beam of 632.8 nm wavelength. Furthermore, the synthesized CNR structures have been found to exhibit excitation-dependent tunable photoluminescence (PL) emission with visible blue light emission in liquid dispersion as well as in a PVA matrix, under 365 nm UV light irradiation. This amphibious nature in PL emission characteristics of the synthesised CNR structures has also been utilized in successful demonstration of using CNR structures as an anti-counterfeiting agent and indicates their potential future applications in photonic devices.

In-situ synthesis of rGO-ZnO nanocomposite for demonstration of sunlight driven enhanced photocatalytic and self-cleaning of organic dyes and tea stains of cotton fabrics

Recently, research activities are focused on development of 2D reduced graphene oxide (rGO) based semiconductor nanocomposite materials for boosting up its catalytic applications. In this work, a rarely reported green synthesis approach has been envisioned to synthesize in-situ 2D rGO-ZnO (rGZn) nanocomposites from Apple juice and zinc acetate. Also the composition of the samples has been optimized to achieve high photocatalytic and self-cleaning properties by the formation of reactive oxidation species. The samples are characterized for their microstructural, optical absorption and photoluminescence properties. It has been tested that rGZn nanocomposites are capable of removing a test dye, namely methylene blue (MB) from water and achieved the highest dye degradation efficiency of ∼91% within only 60 min under UV-vis light irradiation. A smart cotton fabric (CF) coated with rGZn has been prepared and demonstrated its photocatalytic self-cleaning property by degradation of MB, rhodamine B dyes and tea stains on it even under sunlight irradiation, which is scarcely available in the literature. Therefore, this work may open a new avenue of research for low cost and easy synthesis of rGO-semiconductor nanocomposites with high photocatalytic properties for industrial applications as well as for development of rGO based smart fabric for real-life applications.

Measurement of the Nonlinear Optical properties of Silver Nanoparticles and Graphene Oxide Nanocomposite

The nonlinear optical properties of silver nanoparticle and graphene oxide (AgNP/GO) nanocomposites synthesized by solvothermal method have been measured in nanosecond time by using Z-scan technique with Q-switched Nd:YAG laser radiation of 1064 nm wavelength.