Investigation of photoluminescence in undoped and Ag-doped ZnO flowerlike nanocrystals

Flower-shaped undoped and Ag-doped ZnO nanocrystals have been synthesized by a hydrothermal method. The nanocrystals have been investigated by x-ray powder diffraction and all the particles are found to show the wurtzite structure. Scanning electron microscopy and high resolution transmission electron microscopy reveal the flower-shaped structures of the samples consist of many pricklelike nanopetals. The x-ray photoelectron spectroscopy results provide evidence that Ag ions are mainly in the monovalent state and incorporated into the ZnO lattice at Zn2+ sites. It was found from the UV–visible spectra that the bandgap of ZnO decreases due to Ag doping. Excellent enhancement of luminescence properties in the green band is observed in Ag-doped ZnO nanocrystals. The origin of this enhancement was discussed. It was demonstrated that oxygen vacancies and a spin-split impurity band are the key factors for deep level emissions. We believe that the present approach is a very simple but effective one for synthesis of novel ZnO complex micro/nanostructures, and these flowerlike Ag-doped ZnO nanocrystals may have good prospects in scientific and industrial applications.