Band gap engineering, enhanced morphology and photoluminescence of un-doped, Ga and/or Al-doped ZnO nanoparticles by reflux precipitation method

In this study, un-doped ZnO, Ga/Al-doped and co-doped ZnO nanoparticles (NPs) at 2 mol% Ga doping (GZO), 2 mol% Al doping and combined Ga and Al doping concentrations summing up to 2 mol% (ranging from 1:1 to 1.9:0.1 mol% Ga/Al) were synthesized using the reflux precipitation method. The effects of increasing the mole ratios of Ga in the ZnO host material or reducing Al mol%, on the structural, luminescence and optical properties of impurity-doped ZnO were investigated along with the properties of ZnO NPs. The X-ray diffraction patterns for all samples exhibit highly crystalline NPs with a hexagonal wurtzite structure. The crystallite size and average relative intensity of the diffraction peaks of the samples increased with increasing Ga doping indicating improved crystallinity with an increase in the content of gallium in the ratio. Photoluminescence spectra also displayed an increase in exciton peak emission with increasing Ga doping levels and reached a maximum at a doping concentration of 2.0 mol% Ga, as well as a corresponding decrease in the deep level emission intensity, indicative that the best optical quality was obtained at the 2 mol% Ga level. It was observed a blue shift in the PL exciton emission peak position and the band edge emission of the reflectance spectra with increasing concentration of Ga in the sample. The optical band gap calculated from the reflectance data also increased with increasing Ga concentration. These GZO NPs with improved crystallinity, minimum lattice stress, and enhanced luminescence intensity and optical properties would be suitable for deposition on a glass substrate to form the seed layer to produce a transparent conducting oxide for a dye- sensitized solar cell based thin films.