B. Karthikeyan

Structural, optical and glass transition studies on Nd3+-doped lead bismuth borate glasses

Abstract Nd3+-doped lead bismuth borate (PbO–Bi2O3–B2O3) glasses were prepared with different concentrations of Nd3+. The structural studies were done through FTIR spectral analysis. The glass transition studies were done through differential scanning calorimetry. The optical analysis was done by using Judd–Ofelt theory. The structural study reveals that the glass has [BiO3], BO4, BO3 and PbO4 units as the local structures.

In situ synthesis and nonlinear optical properties of Au:Ag nanocomposite polymer films

We report a simple in situ synthesis procedure for Au:Ag nanocomposite polymer (NCP) films using polyvinyl alcohol as the reducing agent. Optical measurements show absorption bands of varying strengths around 530 and 410 nm. The presence of nanoparticles is confirmed from Transmission Electron Microscopy (TEM). Nonlinear optical response is studied using 7 ns laser pulses, for near-resonant and off-resonant excitation wavelengths (532 and 1064 nm, respectively). Samples exhibit saturable as well as induced absorption. These materials have the potential to be used as saturable absorbers and optical limiters.

Synthesis and concentration dependent antibacterial activities of CuO nanoflakes

We report, synthesis and antibacterial activities of CuO nanoflakes. CuO nanoparticles are prepared at room temperature through sol-gel method. X-ray diffraction studies show the particles are monoclinic (crystalline) in nature. Scanning electron microscopy (SEM) images clearly show that the prepared particles are flake like in structure. Fourier transform infrared (FTIR) spectra exhibits three different bands that correspond to the Au and Bu modes. Antibacterial studies were performed on Shigella flexneri, Staphylococcus aureus, Staphylococcus epidermidis, Salmonella typhimurium, Bacillus subtilis, Escherichia coli, Vibrio cholera, Pseudomonas aeruginosa and Aeromonas liquefaciens bacterial strains. Among these bacterial strains, S. flexneri and B. subtilis are most sensitive to copper oxide nanoparticles than the positive control (Penicillin G) and S. typhimurium strain shows the less sensitive. Results show that sensitivity is highly dependent on the concentrations of CuO nanoflakes.

Optical and nonlinear absorption properties of Na doped ZnO nanoparticle dispersions

We report linear and nonlinear optical properties of the biologically important Na doped ZnO nanoparticle dispersions. Interesting morphological changes involving a spherical to flowerlike transition have been observed with Na doping. Optical absorption measurements show an exciton absorption around 368 nm. Photoluminescence measurements reveal exciton recombination emission, along with shallow and deep trap emissions. The increased intensity of shallow trap emission with Na doping is attributed to oxygen deficiency and shape changes associated with doping. Nonlinear optical measurements show a predominantly two-photon induced, excited state absorption, when excited with 532 nm, 5 ns laser pulses, indicating potential optical limiting applications.

Enhanced blue light emission in transparent ZnO:PVA nanocomposite free standing polymer films

ZnO:PVA nanocomposite films were prepared and their fluorescence and time resolved photoluminescence properties were discussed. X-ray diffraction and infrared spectroscopy results confirmed the ZnO:PVA interaction. Optical absorption spectra showed two bands at 280 and 367nm which were ascribed to PVA and excitonic absorption band, respectively. Fluorescence spectra showed that the blue emission of ZnO was enhanced about tenfold through chemical interface electron transfer. The electron transfer from ZnO to PVA and its decay dynamics were experimentally analyzed through time resolved fluorescence measurements. The study revealed that the excited electrons found pathway through PVA to ground state which was slower than the pure ZnO nanoparticles.

Study of optical properties and effective three-photon absorption in Bi-doped ZnO nanoparticles

In this paper we report the linear and nonlinear optical properties of Bi-doped ZnO nanoparticles. Bi-doped ZnO nanoparticles were prepared through the wet chemical method at room temperature. Optical absorption measurements show that the exciton peaks are situated at 272 and 368 nm, which are attributed to the n=2 and n=1 exciton states, respectively. Transmission electron microscopy measurements reveal the size and shape of the particles and energy dispersive X-ray measurements confirm the doping of Bi in ZnO. Steady state photoluminescence measurements show that the emission is composed of five peaks. Open aperture z-scan measurements done at 532 nm using 5 ns, 300 μJ laser pulses reveal nonlinear absorption which arises from an effective three-photon absorption process.

Optical and EPR studies on Cu2+-doped sodium borobismuthate glasses

Abstract Heavy metal oxide glasses are becoming a good infrared (IR) transmitting windows. The optical, differential scanning calorimeter (DSC), FTIR and EPR studies of Cu 2+ -doped sodium borobismuthate glasses have been investigated. The FTIR studies show that the glassy system contains BO 3 and BO 4 units in the disordered manner. The optical studies confirm the presence of Cu 2+ ions in the glassy network. The EPR studies show that the Cu 2+ ions are deposited in the distorted octahedral sites elongated on the z -axis.

Enhanced multi-phonon Raman scattering and nonlinear optical power limiting in ZnO:Au nanostructures

We report the synthesis of ZnO:Au hetero structures, their Raman scattering and optical power limiting efficiencies. ZnO:Au nanostructures with flower-like morphology were obtained by the self-assembly of ZnO nano entities using Au nanoparticles as seeds. Compared to ZnO nanostructures, ZnO:Au nanocomposites show enhanced UV emission and decrease in green emission. Increases in the intensities of Raman bands and multiphonon Raman bands of nano ZnO are observed substantially in the nanocomposites. Raman results further indicate that lattice vibrations of semiconductors are sensitive to the presence of metal nanoparticles. Open aperture Z-scan measurements carried out at 532 nm using 5 ns laser pulses reveal metal nanoparticle induced changes in the optical limiting properties of the nanocomposites.

Synthesis and Antifungal Studies on CuO Nanostructures

We report, synthesis and antifungal activities of CuO nanoparticles. Particles are prepared through sol-gel method. X-ray diffraction studies show the particles are monoclinic (crystalline) in nature. Scanning electron microscopic measurements are carried out to understand the morphology of the prepared particles. Energy-dispersive X-ray spectroscopic measurements show that the prepared particles containing Cu and O. To identify the local structure of the particles Fourier transform infra red (FTIR) spectroscopic measurements were carried out showing vibrational bands of Cu-O and O-H band. Anti fungal studies were performed on the set of fungal using disk diffusion method and found that the prepared particles are suitable for antifungal activities.

Fluorescence quenching of rhodamine-6G in Au nanocomposite polymers

Nanocomposite polymers are gaining interest because of their ease of preparation and device applications. In this report, synthesis of Au-polyvinyl alcohol nanocomposite and rhodamine-6G doped Au-polyvinyl alcohol nanocomposite polymer films which are prepared at room temperature have been reported. The role of nanosized gold on fluorescence properties of rhodamine-6G has been analyzed. Steady state fluorescence studies show that the nanoparticles quench the fluorescence of rhodamine-6G. Fluoresence quenching were analyzed using all possible mechanisms like Forster resonant energy transfer, nanometal surface energy transfer and electron transfer to metallic conduction bands. Time resolved fluorescence studies reveal that the decay rate changes because of the addition of Au nanoparticles and also depends on the size of the nanoparticles.