Structural and optical characterizations of ZnO aerogel nanopowder synthesized from zinc acetate ethanolic solution

• Synthesis of ZnO aerogel nanopowder in supercritical ethanol.
• The supercritical ethanol decreases the ZnO lattice parameters.
• Annealing increases the ZnO lattice parameters and decreases the optical gap.
• Annealing shifts the ZnO infrared absorption band and increases the Zn–O bond length.
• The UV emission of ZnO aerogel disappears after annealing.

ZnO aerogel powder has been synthesized by a modified sol–gel process using zinc acetate ethanolic solution. XRD, SEM, EDAX, FTIR, UV–visible absorption and photoluminescence (PL) techniques have been used to characterize the as-prepared and the annealed ZnO aerogel powders. The as-prepared ZnO powder has a well-defined polycrystalline hexagonal wurtzite structure. This measurement has demonstrated that the lattice parameters are lower than the standard ones indicating that drying in supercritical conditions of ethanol does not affect the crystallinity but acts as a compressive agent. EDAX measurements show that the obtained aerogel contains only O and Zn elements. Annealing improves the crystallinity in the low DRX angles and decreases the crystalline quality in the high diffraction angles. Also, annealing acts as a tensile agent and increases the lattice parameters. FTIR spectra confirm the annealing effect by the apparition of the strong Zn–O vibration band. The ZnO absorption band shifts to lower wave numbers after annealing indicating an increase in the Zn–O bond length and confirms the XRD results. UV–visible results show a decrease of the ZnO aerogel optical band gap after annealing and confirm the thermal decompression effect on the lattice parameters. The photoluminescence measurements show that the annealing of ZnO aerogel favors the thermal generation of zinc interstitials and oxygen vacancies defects existing in the as-prepared zinc oxide aerogel and shifts the emission toward lower energies.

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