Structural and optical investigations of pure and Al-doped ZnO nano-aerogels: effects of supercritical organic solvent

Abstract

Undoped (ZnO) and Al-doped ZnO (AZO) aerogels were synthesized in different supercritical alcohols (acetone, ethanol and isopropanol). The effects of supercritical solvent on structural, morphological and optical properties of ZnO and AZO aerogels were studied. XRD patterns reveal that the aerogels were polycrystalline and monophasic, indicating that Al3+ ions have been successfully incorporated into ZnO lattice. SEM images show that morphology and size of the grains are dependent on supercritical drying conditions. FTIR results indicate that the intensity and the position of Zn–O vibration band are dependent on doping atoms and supercritical solvent. The UV–visible studies put into evidence that the optical band gap decreases after Al doping and the absorption intensity is affected by the drying conditions. TGA measurements indicate that Al-doped ZnO aerogels are chemically pure and their thermal behavior is independent on the used supercritical organic alcohol. Room temperature PL studies reveal that the supercritical solvent properties affect considerably the defect concentrations during the elaboration process. Al doping leads to the diminution of the overall PL intensity of ZnO nanostructures elaborated in acetone and ethanol, whereas, the opposite behavior is obtained when isopropanol is used. These results could be of great interest for optical applications.