T. Pandiyarajan

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.

Cr doping induced structural, phonon and excitonic properties of ZnO nanoparticles

We report systematic study of structural, phonon and optical properties of Cr-doped ZnO nanoparticles. These particles are synthesized through simple sol–gel technique. Structural studies carried out by X-ray diffraction method, confirm that the prepared particles are in hexagonal wurtzite structure and lattice parameters change considerably while increasing the doping. Raman and Fourier transform infrared spectral studies show that the intensity of the phonon modes decreased and also blue shift due to ion doping, respectively. Apart from this, transmission electron microscopic studies show reduction in particle size where the particle diameters reduced from 36 to 11xa0nm. Optical absorption spectral measurements show a blue shift in the band-gap and increment in excitonic oscillator strength. Photoluminescence studies show doping altered the near-band edge emission but there is no change in the other emission bands which is due to oxygen vacancy, surface defects and surface dangling bonds.

Optical properties of sol-gel synthesized calcium doped ZnO nanostructures.

Optical properties of Ca doped ZnO nanoparticles prepared at room temperature through wet chemical method have been investigated. X-ray diffraction studies show that particles are crystalline in nature and doping did not induce impurity phases. Optical absorption measurements show an absorption peak at ∼372 nm which is due to excitonic absorption of the ZnO. Photoluminescence studies reveal a broad emission at an excitation wavelength of 335 nm and the bands are attributed to near band edge emission, oxygen vacancies, surface dangling bonds and zinc interstitials. Incorporating Ca(2+) induces reduction in near band edge emission and there is an enhancement in the oxygen vacancy peaks which are attributed to the shape changes in the nanoparticles.

Microstructure and enhanced exciton-phonon coupling in Fe doped ZnO nanoparticles.

We report the microstructure and exciton-phonon coupling properties of Fe doped ZnO nanoparticles. Particles are prepared through sol-gel method at room temperature. Doping of Fe(3+) induces strain in the host lattice. Microstructural properties are analysed through Williamson-Hall analysis. Optical absorption studies show strong free excitonic absorption band at 369 nm. The photoluminescence (PL) studies reveal that ultraviolet, blue and green emission bands are located at 380, 445 and 500 nm respectively. Fe doped ZnO nanoparticles exhibits only ultraviolet and blue emission bands. Increase of Fe concentration makes green emission gradually disappeared. Gaussian fitted photoluminescence spectra show the emission is composed of free exciton (FX) recombination and its higher orders of longitudinal optical (LO) phonon replicas. Doping induced blue shift in FX peak and also increases the exciton-phonon coupling.

Sol–gel prepared Cu2O microspheres: linear and nonlinear optical properties

We report the simple sol–gel based synthesis of size-tunable monodispersed crystalline Cu2O microspheres (CMS) and the measurement of their linear and nonlinear optical properties. Optical absorption spectra show a broad plasmonic absorption band extending from 350 to 1100 nm in general agreement with calculations based on Mie theory, despite the relatively large micron size of the particles. Z-scan measurements (532 nm, 5 ns pulses) reveal that Cu2O microspheres are efficient optical limiters, comparable in strength to nanocarbons and metal/semiconductor nanoparticles. The effective two-photon absorption coefficients are numerically calculated from measured data. These can be tuned systematically by varying the particle size.

Optical properties of annealing induced post growth ZnO:ZnFe2O4 nanocomposites

The effects of annealing on structural and optical properties of Fe doped ZnO nanoparticles have been investigated. XRD analysis reveals that prepared particles are in hexagonal wurtzite structure and formation of secondary phases which are related to the ZnFe2O4 phases. FTIR analysis confirms the wurtzite structure and the presence of Zn-O and Fe-O bonds. UV-visible measurements show free exciton absorption band appeared at 363 nm and red shifted for annealed samples. Room temperature photoluminescence spectrum of the as prepared Fe doped ZnO nanoparticles shows three bands which belongs to the near band edge emission (NBE) at 375 nm, blue emission at 450 nm and green emission at 556 nm. Annealed samples exhibit suppression of green emission band and red shift in the NBE emission band. This is attributed to the decrease in the oxygen vacancies and combined effects of size and exchange interaction between the conduction band electrons of ZnO and localised 3d electrons of the substitutional Fe ions, respectively.

Vibrational, giant dielectric and AC conductivity properties of agglomerated CuO nanostructures

We report frequency, temperature dependent dielectric response and AC conductivity of nanocrystalline CuO. These nanoparticles were prepared using sol–gel technique. Prepared particles were made as a pellet using hydraulic pressure and thermally heat treated at 950xa0°C. X-ray diffraction study showed that the prepared particles were crystalline in nature. Fourier transform infrared (FTIR) studies confirm the presence of Cu–O bond. Force constant and bond length is calculated which are 2.17xa0Nxa0cm−1 and 1.98 Å respectively. Frequency dependent dielectric studies were done at different temperatures. Measurements show the giant dielectric value (~103) and it increases with increase of temperature. AC conductivity measurements reveal that the conduction depends on both frequency and temperature, this agrees well with Correlated Barrier Hopping model.

Simple synthesis and spectroscopic studies on cobalt added ZnO nanocrystals

Cobalt doped zinc oxide nanoparticles were prepared through simple wet chemical method. X-ray diffraction studies confirm the prepared particles are in wurtzite structure. Scanning Electron Microscopy studies show the shape and morphology of the particles. To identify the presence of cobalt in ZnO, Energy Dispersive X-ray analysis was done. Optical absorption measurements show the presence of exciton peak at 375 nm. Photoluminescence studies were done with the excitation wavelength of 330 nm, which shows the emission because of exciton recombination and oxygen vacancy.