Particularities of pure and Al-doped ZnO nanostructures aerogels elaborated in supercritical isopropanol

Abstract

Undoped and Al-doped ZnO nanoparticles are synthesized in supercritical isopropanol using zinc acetate di-hydrate, aluminum nitrates and methanol as precursor, dopant source and solvent, respectively. The atomic ratio [Al]/[Zn] is fixed to 3%. X-ray diffraction (XRD) results indicate that the synthesized ZnO nanoparticles possess hexagonal wurtzite structure. Al-doping of ZnO aerogel leads to the improvement of the crystalline quality due to the occupation of Zn2+ sites by Al3+ ions. The crystallites size is found to be 32 nm in pure ZnO and 50 nm in the doped aerogel. Fourier-transform infrared spectroscopy spectra reveal that the intensity of the absorption bands in ZnO decreases and the Zn-O vibration band position shifts towards higher wave numbers upon Al-doping. UV–Visible measurements show a reduction in the band gap and a shift towards long wavelength side of the absorbance with Al-doping. Scanning electron microscopy images reveal that aerogel grains are quasi-spherical in pure ZnO and have different and random forms of morphologies in the doped sample. Room temperature photoluminescence (PL) studies put into evidence that the PL emission peaks are influenced by the Al-doping, in particular, a decrease in the green emission at 535 nm is observed.