Enhancement in the Optical Properties of ZnO:Al Nanopowders by Sn Codoping

(Al,Sn)-codoped ZnO powders with a constant molar ratio of Zn: Al (99:1) and various molar ratios of Sn/Al (0–0.02) were synthesized by a sol–gel process and characterized by x-ray diffraction, field emission scanning electron microscopy, and ultraviolet (UV)-vis and luminescent spectrophotometries. The experiments indicated that the powders have random orientation and decreased particle size with increasing Sn content. The Sn codoping decreased absorbance in the UV-visible light range and widened the band gap. The molar ratio of Sn/Al = 0.01 showed an optimal effect. The Sn codoping also increased the native defect concentration of ZnO, thereby enhancing the emissions in the range of visible light.