Effect of Aluminium Doping on Structural and Optical Properties of ZnO Nanoparticles Prepared by Mechanochemical Synthesis

Optical properties of metal ion doped zinc oxide (ZnO) nanoparticles synthesized by various methods were reported to display different properties. Nevertheless, there are limited reports on metal ion doped ZnO prepared by mechanochemical synthesis. This paper reports the effect of aluminium doping on structural and optical properties of ZnO (Zn1-xAlxO, x = 0, 0.02, 0.04, 0.06, 0.08, 0.1) nanoparticles prepared by mechanochemical synthesis in a high-energy ball mill. The samples were synthesized by milling corresponding chemical precursors in a planetary ball mill for 5 h. Diluents were used to control the agglomeration and reaction kinetics during the milling. The shifting of X-Ray Diffraction (XRD) peaks indicated that Al ions have been successfully doped into the crystal lattice of ZnO host. Average crystallite size, was calculated based on Scherrer's equation, was found to vary from 22 to 29 nm. Blue shift in energy gap (E-g) with increasing Al concentration (x <= 0.08) could be attributed to either the Burstein-Moss effect in which higher carrier concentration leads to E-g broadening, or to the decreasing crystallite size of the ZnO nanoparticles. The red shift in E-g at x>0.08 was possibly due to excess oxygen and also may be affected by sudden increase in crystallite size. The quantum confinement effect was suggested to be the dominant reason for the changes in E-g.