A Comprehensive Study on the Impact of Aluminum Doping on X-ray Diffraction Peak Profile Analysis, Structural, Morphological, and Optical Properties of ZnO Nanoparticles Synthesized by Sol–Gel Auto-Combustion

The effect of aluminum doping on the structural, morphological and optical properties of Zn_1-xAl_xO (0 ≤ x ≥ 0.12) nanoparticles synthesized by sol–gel auto-combustion technique has been studied. All the x-ray diffraction patterns were single phase with a wurtzite crystal structure. The Scherrer, Williamson–Hall and Size–Strain plot (SSP) methods have been adopted to estimate the crystallite size, lattice stress, lattice micro-strain, and energy density using x-ray peak profile analysis. The crystallite size decreased, and the lattice strain, lattice stress, and energy density increased for Zn_1-xAl_xO (0 ≤ x ≥ 0.12) nanoparticles. The crystallite sizes obtained from the SSP method are highly intercorrelated with the morphology of aluminum-doped ZnO nanoparticles examined by field-emission scanning electron microscopy. The optical bandgap decreased with increasing the aluminum concentration in the ZnO nanoparticles, which correlated with the Urbach energy (E_u). The E_u values of aluminum-doped ZnO nanoparticles exhibited higher values than those of ZnO nanoparticles, which might be associated with the localized states originating from the contribution of defects and structural disorder. Photoluminescence results indicated the presence of defects in Zn_1-xAl_xO (0 ≤ x ≥ 0.12) nanoparticles, which were interlinked with zinc vacancies (V_Zn), zinc interstitials (Z_in), neutral oxygen vacancies (V_O), and oxygen interstitials (O_I).