Pulsed electrical discharge synthesis of red photoluminescence zinc oxide nanoparticles

Zinc oxide (ZnO) nanoparticles have been prepared using a pulsed electrical discharge in a liquid medium. The effects of the processing parameters, including liquid media, current, frequency of the electrical discharge and electrode gap distance exert significant effects on the characteristic and properties of ZnO nanoparticles. The synthesized ZnO nanoparticles are characterized using a combination of transmission electron microscopy (TEM), energy dispersive X-ray (EDS) and photoluminescence (PL) spectroscopy. The average size of ZnO nanoparticles varies between 10–25 nm depending on the processing parameters. It is found that an increase in the arc current plays a great role in particle growth and results in a significant increase in average particles size. Both frequency of discharge and electrode gap distance can influence the average particle size and distribution due to the variation in the cooling rate. The PL spectrum for all as-synthesized ZnO nanoparticles exhibits an ultraviolet emission (~3.4 eV) and a red visible emission (~1.98 eV). The blue shift is independent of the average size of the ZnO nanoparticles. However, the intensity of visible emission is significantly enhanced with the decrease of the particle sizes. The porous structure and irregular particle surface are suggested to contribute significantly to the visible red emission.