Rapid synthesis of blue emitting ZnO nanoparticles for fluorescent applications

ZnO nanoparticles (NPs), with size ∼16–20 nm were produced using simple, cost effective and rapid synthesis method. In this method zinc salt (typically zinc acetate dehydrate) is directly annealed in air at a temperature from 200°C to 500°C for 2 h to form ZnO (NPs). This synthesis method, only requires zinc precursor to produce NPs that can emit visible emission without external doping. X-ray diffraction (XRD) patterns confirm the prepared ZnO NPs is polycrystalline structure with wurtzite phase. The observed variation in scanning electron microscopy (SEM) images showed spherical shape of the ZnO NPs. It was found that the NPs exhibited the estimated direct bandgap (Eg) of 3.28 eV, 3.29 eV, 3.33 eV and 3.39 eV for a decomposition temperature of 500, 400, 300 and 200°C. Energy dispersive X-ray (EDX) analysis showed that carbon is the only impurity at lower temperature which was most likely originated from the acetate group. The photoluminescence (PL) spectra of ZnO NPs showed the appearance of a blue emission, attributed to Zn interstitials, whose intensity reduces with increase in decomposition temperature and the underlying mechanism are discussed. For the samples prepared at 200°C and 300 °C a temperature dependent PL was studied and found out that there are about three transition lines at ∼3.01 eV, ∼3.21 eV and ∼3.33 eV, which are ascribed to zinc vacancy (Vzn), donor–acceptor pairs(DAP) and excitons bound to structural defects respectively. It is hoped that ZnO NPs produced using this method would be ideal for blue light emitting fluorescent application as it is catalyst free growth, uses simple equipment, less hazardous and easy to control particle size and morphologies by scalable temperature.