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.

ZnO nanoparticles were prepared by using a gas evaporation method. As ZnO is a luminescent and less toxic material, it can be useful in imaging applications. The nanoparticles prepared in our laboratory showed intense exciton emission in the UV‐blue region. They were processed and surface treated to be compatible for bio‐conjugation. We were able to prepare good dispersions and water‐soluble ZnO nanoparticles from our experiments. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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.

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