Kasilingam Senthilkumar

Hydrogen related defect complexes in ZnO nanoparticles

Hydrogen related local vibrational modes (LVMs) of ZnO nanoparticles have been studied using Fourier transform infrared spectroscopy and Raman spectroscopy in as prepared and high temperature annealed samples. The obtained experimental results confirm the presence of cationic vacancies (VZn) in addition to unintentional hydrogen doping and their complex defects such as VZn–Hi and VZn–HO. After high temperature annealing, hydrogen related LVMs and multiphonon modes disappear. The presence of these complex defects determines the nonradiative and multiphonon recombination processes in the band gap of ZnO due to carrier trapping at deep levels.

Optimization of nonlinear optical properties of ZnO micro and nanocrystals for biophotonics

The defect and impurity states in ZnO nanocrystals synthesized using the plasma arc technique can be modified to optimize the nonlinear optical properties for optoelectronic and biophotonic applications. Highly efficient second harmonic signals over a wide range of near-infrared wavelengths, spanning from 735 nm-980 nm, has been observed and can be used in biological imaging. The use of further high energy excitation ranging from 700 nm-755 nm leads to two-photon absorption and yields broadband two photon emission extending from the 370 nm-450 nm wavelength regime which can be useful for therapeutic applications.

Bioimaging Using the Optimized Nonlinear Optical Properties of ZnO Nanoparticles

Nonlinear imaging using nanocrystals has advantages over fluorescent dyes. Highly nonlinear optically susceptible ZnO was synthesized for the purpose of bioimaging. ZnO nanoparticles with enhanced second and third order nolinearity have been utilized for nonlinear in vitro imaging of living cells. Highly efficient nonlinear processes in noncentrosymmetric ZnO nanoparticles was used to generate second harmonic signal within nanoparticles at extremely low-input light intensities in order to track and image live cells and thrombocytes infiltrated with ZnO.

Deposition of Nanoparticle-Aggregated ZnO Thin Films by Drop Coating Method

Nitrogen-doped ZnO nanoparticles were prepared by a gas evaporation method. We chose a drop coating method for the deposition of thin films from a dispersion of the nanoparticles in water. The drop coating method appears to be the optimum method for the deposition of thin films from the dispersions. Sintering at 300 °C improved the deposition of a thin film compared with that of films dried at room temperature. Photoluminescence spectroscopy and scanning electron microscopy showed that high-density aggregated films were formed by the drop coating method.