Stable crystalline aluminum doped zinc oxide (AZO) nanopowders were synthesized using hydrothermal treatment processing. Three different aluminum precursors have been used. The Al-precursors were found to affect the morphology of the obtained nanopowders. AZO nanoparticles based on zinc acetate and aluminum nitrate have been prepared with different Al/Zn molar ratios. XRD investigations revealed that all the obtained powders have single phase zincite structure with purity of about 99%. The effect of aluminum doping ratio in AZO nanoparticles (based on Al-nitrate precursor) on structure, phase composition, and particle size has been investigated. The incorporation of Al in ZnO was confirmed by UV-Vis spectroscopy revealing a blue shift due to Burstein-Moss effect. 1. Introduction Zinc oxide ZnO is a wide band gap (3.4？eV) semiconductor which has broad range of potential uses in optical and electrical applications such as in solar energy conversion, thin film transistors, photocatalysis, nonlinear optics, gas sensors, pigments, cosmetic, LED, anti-UV and low-emission coatings, and photoluminescent and sensor materials [1–8]. Undoped ZnO shows n-type conductivity due to the existence of native defects such as oxygen vacancy, zinc interstitials, and hydrogen interstitials in the ZnO lattice [9–11]. Unfortunately, the conductivity of undoped ZnO is thermally unstable. The substitution of Zn2+ ions with group III ions (B3+, Al3+, Ga3+, and In3+) [8–16] generates extra electrons and improves ZnO optical, electrical, thermal, and magnetic properties. Al3+ has been the most used dopant element due to its small ionic radius and low material cost. The substitution of Zn2+ ions with Al3+ in ZnO lattice improves the electrical conductivity through the increase of charge carriers where it is reported that the electron concentration increases from 1016 to 1021/cm？3 [17, 18]. The mobility of the charge carriers is strongly influenced by scattering at the disorder locations created in the crystal structure due to doping. Therefore, well crystalline doped ZnO particles, pure in phase, are very important for obtaining good electrical conducting properties. Accordingly, structural considerations should also be included [19]. The choice of aluminum precursor used for substitution of Al3+ ions in ZnO host lattice is very important. Organic salts are recommended for successful homogenous substitution [20]. On the other hand, doping based on aluminum’s inorganic salts is reported to be not successful [21, 22]. In this work, AZO nanoparticles were synthesized using hydrothermal
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