Effect of pH variation on structural and optical properties of Zn0.95Co0.05O nanoparticles

We have synthesized the Zn0.95Co0.05O nanoparticles using a sol-gel method with different pH values under acid base and basic base reactions. The structural properties were characterized using powder X-ray diffraction (XRD) and scanning electron microscope (SEM) while the optical properties were characterized using Ultraviolet/Visible (UV/Vis) spectroscopy, Fourier transform infra red (FTIR) spectroscopy and Raman spectroscopy. Both samples are found in single phase with wurtzite structure. SEM micrographs show spherical nanoparticles for the sample synthesized under acid base reaction (pH=6) and nanorods for the sample synthesized under basic base reaction (pH=9). The band gap estimated using UV/Vis spectra shows an increase with the increase in pH value. FTIR spectra show that typical stretching mode peak of ZnO at 497 cm−1. On Co doping this absorption peak shifted to 446 cm−1 (for pH=6 sample) and to 478 cm−1 (for pH=9 sample). Raman spectra of cobalt doped samples reveal presence of small amounts of ZnCo2O4 and Co3O4. Fluorescence spectra display blue shift in near band emission peak of ZnO with cobalt doping and pH variation.