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Diameter tuned NiO microrods have been prepared by a wet chemical route. Individual microrods measured 9 μm in length with a diameter of 350 nm, which could be increased by changing the annealing temperature. Crystalline and microstructural parameters were studied by Williamson-Hall (WH) analysis, showing a reduction of microstrain upon increase of temperature due to lattice relaxation. The absorption spectrum reveals the presence of peaks at 350 nm and 250 nm due to the transition from 2p states of oxygen to 3d states of Ni ions, and the transition from the defect band, respectively. Strong UV emission peaks (361, 392 nm) and visible emission bands (436, 467 and 560 nm) are observed in the steady state luminescence spectra. The time resolved photoluminescence spectra show a fast tri-exponential decay with lifetime components of 26, 74 and 670 ps. Open aperture Z-scan measurements conducted at 532 nm using 5 ns laser pulses reveal that the NiO nanorods are good optical limiters which may have potential device applications.

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.

A controlled synthesis of CuO nanostructures with various morphologies were successfully achieved by presence/absence of low frequency (42 kHz) ultrasound with two different methods. The size, shape and morphology of the CuO nanostructures were tailored by altering the ultrasound, mode of addition and solvent medium. The crystalline structure and molecular vibrational modes of the prepared nanostructures were analysed through X-ray diffraction and FTIR measurement, respectively which confirmed that the nanostructures were phase pure high-quality CuO with monoclinic crystal structure. The morphological evaluation and elemental composition analysis were done using TEM and EDS attached with SEM, respectively. Furthermore, we demonstrated that the prepared CuO nanostructures could be served as an effective photocatalyst towards the degradation of methyl orange (MO) under visible light irradiation. Among the various nanostructures, the spherical shape CuO nanostructures were found to have the better catalytic activities towards MO dye degradation. The catalytic degradation performance of MO in the presence of CuO nanostructures showed the following order: spherical \ nanorod \ layered oval \ nanoleaf \ triangular \ shuttles structures. The influence of loading and reusability of catalyst revealed that the efficiency of visible light assisted degradation of MO was effectively enhanced and more than 95 % of degradation was achieved after 3 cycles.