The Influence of Al Doping on the Optical Characteristics of ZnO Nanopowders Obtained by the Low-Cost Sol-Gel Method

Abstract

In this work, the influence of Al (0, 2, 4, and 6 wt.%) on the optical properties of ZnO has been briefly investigated and described. The undoped and doped samples were characterized using a UV-visible spectrophotometer and Photoluminescence (PL). The X-ray diffraction (XRD) data in our preceding study is also indexed, and materials are said to have a wurtzite-structured hexagonal phase and exhibit no impurity phases. The average crystallite sizes of the pure ZnO were found to increase, i.e., from 14.19 nm to 34.17 nm with an increase in temperature, and in the case of Al-doped ZnO, at a constant temperature, from 35.05 nm to 18.89 nm, respectively. The average crystallite size of AZO (Al-doped ZnO) decreases with increasing Al content. With the increasing temperature, increases in crystallinity and size of the pure ZnO have been observed. In the case of Al doping, with an increase in the concentration of doping the crystallite size is seen to be decreased, without any change in the temperature. Al doping improves the formation of the well-ordered crystalline structure of ZnO up to a certain limit of doping. The absorbance spectra were used to determine the optical band gap of the samples. The optical photoluminescence (PL) spectra of both ZnO and AZO nanopowder are obviously influenced by the increasing temperature and Al doping content, respectively. Different optical properties of ZnO and AZO were observed for different contents of Al in ZnO. The band gap of AZO nanopowder with different concentrations has been seen to be lower than that of undoped ZnO (3.10 eV), suggesting broad application potential. Also, the optical properties of ZnO were tailored by Al doping in the near visible region, suggesting various potential uses.