Absorption–emission study of hydrothermally grown Al:ZnO nanostructures

The preparation, structural characterization and optical properties of aluminum doped ZnO (Al:ZnO) nanostructures grown under hydrothermal method are reported. One-dimensional (1-D) growth is achieved by the controlled addition of metal nitrate as precursors in the presence of long chain surfactant, poly-ethylene glycol (PEG) at 160 °C for 20 h. The as-synthesized ZnO rods are single crystalline, exhibiting an oriented growth along [001] direction. The Al6 rod has an aspect ratio of 3.2, which can be effectively applied in optoelectronic devices. Comprehensive structural analysis using X-ray diffraction method (XRD) and Energy dispersive X-ray analysis (EDX) indicate that the dopant Al atom occupies Zn sites in ZnO and the elemental composition of Al is consistent with the amount utilized in the hydrothermal synthesis. XRD shows that the Al:ZnO nanostructures from 1 to 9 atomic percent (at.%) has hexagonal wurtzite structure of ZnO. The Al dopant effects on lattice vibration and electronic transitions of the ZnO nanostructures have been investigated by Fourier transform Infrared spectroscopy (FT-IR), Ultraviolet–visible (UV–vis) absorption spectroscopy and photoluminescence (PL) emission recorded at room temperature. The correlation existing between absorption and emission study tell that their characteristic band edge peak of doped ZnO shifts towards higher wavelength side for 3–9 at.% with respect to Al0 thus, exhibiting a red shift phenomenon with decrease in optical bandgap. The observed PL reveals two emission peaks centered at 374 nm and 530 nm. The near band edge (NBE) to defect emission ratio increases with dopant concentration indicating the linear enhancement in crystal quality and declination in zinc vacancies from 3 to 9 at.% of Al.

The NBE to defect emission ratio increases with dopant concentration indicating the linear enhancement in crystal quality and declination in zinc vacancies.Figure optionsDownload as PowerPoint slideHighlights
► Single crystalline Al:ZnO rods in micron scale is synthesized through PEG-assisted hydrothermal method.
► It is worth to highlighting that the UV absorption is red shifted for 3–9 at.% Al:ZnO nanostructures, deviating from the usual bandgap widening explained on the basis of Burstein–Moss shift.
► The intensity ratio, calculated between the NBE emission and defect related visible luminescence is increased, implying that the crystallinity increases with higher doping concentration (3–9 at.%).
► From the results of absorption and emission study, the bandgap and electronic transition properties of ZnO can be modified with controlled doping of Al.