P. M. Aneesh

Synthesis of ZnO nanoparticles by hydrothermal method

Stable, OH free zinc oxide (ZnO) nanoparticles were synthesized by hydrothermal method by varying the growth temperature and concentration of the precursors. The formation of ZnO nanoparticles were confirmed by x-ray diffraction (XRD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED) studies. The average particle size have been found to be about 7-24 nm and the compositional analysis is done with inductively coupled plasma atomic emission spectroscopy (ICP-AES). Diffuse reflectance spectroscopy (DRS) results shows that the band gap of ZnO nanoparticles is blue shifted with decrease in particle size. Photoluminescence properties of ZnO nanoparticles at room temperature were studied and the green photoluminescent emission from ZnO nanoparticles can originate from the oxygen vacancy or ZnO interstitial related defects.

Hydrothermal Synthesis and Characterization of Undoped and Eu-Doped ZnGa2O4 Nanoparticles

Nanoparticles of ZnGa2O4 and Eu-doped ZnGa2O4 were hydrothermally synthesized varying the process parameters, such as the volume ratio of the cation precursor solutions, temperature and time of growth, and dopant concentration. The nanoparticles were structurally characterized by X-ray diffraction, high-resolution transmission electron microscopy, and selected-area electron diffraction. The studies confirmed the formation of spherically shaped ZnGa2O4 nanoparticles with the standard spinel structure. Photoluminescence (PL) studies show that Eu-doped ZnGa2O4 nanoparticles exhibits a sharp red luminescence due to the intra-4f transitions of Eu3+ ions at an excitation of 397 nm. Luminescence quenching is observed in the nanoparticles at higher Eu concentration. The room-temperature PL measurements of pure ZnGa2O4 nanocrystals monitored at an excitation wavelength of 254 nm gave a peak-shaped spectrum instead of the normally observed bell-shaped spectrum of bulk ZnGa2O4. The bandgap of the ZnGa2O4 nanoparticles is blueshifted compared to the bulk material due to quantum confinement effects. Incorporation of Eu in the nanoparticles was confirmed by inductively coupled plasma atomic emission spectroscopic studies. (c) 2009 The Electrochemical Society. [DOI: 10.1149/1.3070662] All rights reserved.

Size-Dependent Optical Nonlinearity of Au Nanocrystals

Gold nanoparticles of different sizes are prepared by laser ablation of the gold target in deionized water. The UV/visible absorption spectra show surface plasmon resonance bands that are redshifted in wavelength with an increase in particle size. An increase in particle size is observed with increasing laser pulse energy. The optical absorptive nonlinearity of the nanoclusters shows an optical-limiting-type nonlinearity, which finds application in the fabrication of optical-limiting devices. The limiting efficiency decreases with an increase in particle size. The Au nanoparticle shows good nonlinear refraction, which is of a self-defocusing nature. Both the real and imaginary parts of nonlinear susceptibility increase with a decrease in particle size. A stable nonlinear

Synthesis of Highly Luminescent, Bio‐Compatible ZnO Quantum Dots Doped with Na

Na doped ZnO quantum dots of average size 6 nm were prepared using wet chemical route at room temperature without any capping agents and the formation of nanoparticles is confirmed by transmission electron microscope (TEM) and x‐ray diffraction (XRD) analysis. Optical band gap of ZnO: Na is found to be blue shifted with decrease in size due to quantum size effects. Incorporation of Na in ZnO quantum dots is confirmed using inductively coupled plasma atomic emission spectroscopy (ICP‐AES). Strong room temperature photoluminescent emissions in the violet region due to native defects of ZnO and yellow region resulting from substitutional incorporation of Na in the Zn site was observed from the ZnO: Na quantum dots. Both emission wavelength and integral intensity of emission in the visible region can be well controlled by adjusting the concentration of the alkaline precursor used as the dopant. Highly luminescent bio‐friendly Na doped ZnO quantum dots can be used as fluorescent probes in biomedical applications.

Growth of vertically aligned ZnO nanorods on various substrates by hydrothermal method

ZnO has great potential in a wide range of applications such as microelectronics, optoelectronics, and sensors. Hydrothermal method has proven to be an effective method for the growth of nanostructured materials. Vertically aligned ZnO nanorods were grown on various substrates such as glass and Si by low temperature hydrothermal method using ZnO as the seed layer. The thin seed layer on various substrates was deposited by RF magnetron sputtering. The morphology of the ZnO nanorods can be tuned by varying the sputtering conditions and hydrothermal parameters. Scanning electron microscopy images confirm the formation of vertically aligned nanorods and XRD pattern shows the formation of wurtzite structure of ZnO. The sharp (0002) peak in the XRD spectra indicates that the synthesized nanorods are single crystalline, grown along the [0001] direction. These ZnO nanostructures can be considered as a potential candidate for sensor and nanowire transistor applications.