Crystalline and optical properties of zinc oxide nanoparticles synthesized by a solvent based technique -

Abstract

ZnO nanoparticles were successfully synthesized via simple precipitation method by controlling different parameters of the precipitation process such as solution concentration and calcination temperature. The structural and morphological properties of these samples were investigated by SEM and XRD analysis. SEM images showed uniformity in the particles size and shape for ZnO nanoparticles calcined at different temperatures compared to the other synthesized samples. The average crystallite size increases with increasing the calcination temperature. We used UV-VIS and FTIR spectrophotometers to get the reflectivity data of the selected samples. By using Kramers-Kronig (K-K) method, we then determined the optical constants, n and k with the real and imaginary parts of the dielectric constant in the IR region. The K-K method was then combined with a newly developed technique to compute the optical parameters in the UV-VIS region. A shift in the absorption peak in the extinction coefficients of the samples was observed due to defects by varying the calcination temperature. Green emission was observed from 36 nm grain size ZnO samples and yellow emission was observed from 470 nm grain size ZnO samples. Finally, to verify the validity of our approach, we back calculated the UV-VIS reflectivity spectra from the deduced optical parameters, and good agreement was found between the measured and calculated spectra. This confirms the importance of our approach in developing a new numerical technique for accurate measurement of the optical parameters at the UV-VIS wavelengths. The reflectivity based technique described in this work could be applied to study ZnO nanoparticles of smaller sizes reaching the quantum confinement region.