EFFECT OF GAMMA IRRADIATION ON THE STRUCTURAL AND OPTICAL PROPERTIES OF MG-DOPED ZNO NANOSTRUCTURES GROWN VIA AQUEOUS CHEMICAL GROWTH (ACG) METHOD

Abstract

One of the most current and actively studied fields of modern materials research is the fabrication of nanostructured materials for optoelectronic and photonic devices. This is because Zinc Oxide (ZnO) is one of the semiconductor oxides that has received special interest due to its large exciton binding energy (60 meV), low processing cost, environmentally friendly processing, and a wide, direct band-gap (3.37 eV), which makes it an attractive alternative to GaN and GaAs for use in next-generation photonic devices. Pure and magnesium (Mg)-doped ZnO nanostructures with three different Mg concentrations of 5, 10, and 15 at. % have been successfully prepared using the low-temperature aqueous chemical growth (ACG) technique. Successful doping was confirmed by energy-dispersive X-ray spectroscopy (EDX) that revealed the hexagonal, rod-like morphology of ZnO remained after incorporation of Mg and there was minor change in the aspect ratio. Scanning electron microscopy (SEM) was also used to confirm the retention of the hexagonal, rod-like morphology of ZnO after Mg incorporation with a slight change in aspect ratio. The X-ray diffraction (XRD) revealed that all samples crystallized in the hexagonal wurtzite phase (JCPDS card No. 36-1451) having a strong (002) reflection showing that the growth was along the c-axis direction. The optical absorption edge blue shifted with increasing magnesium concentration as seen from the UV-Visible spectroscopy, which concluded that the optical band gap of the specimen increased from 3.31 eV (pure ZnO) to 3.357 eV at 15% Mg concentration. The as-grown and Mg-doped samples were then subjected to 100 and 500 Gray doses of gamma radiation from 60Co source. The XRD peaks shifted towards higher diffraction angles and the SEM pictures showed visible surface disruption that were found to be dependent on the dose of the gamma irradiation process compared to that of the as-grown material, suggesting changes in d-spacing and crystallite size with increasing dose. Photoluminescence (PL) spectroscopy revealed the NBE ultraviolet emission of the Mg-doped ZnO became stronger after the irradiation, which corresponds to the improvement of the crystalline quality, while the two visible deep-level emission bands at about 480 nm and 690 nm, linked to the presence of zinc interstitials and oxygen vacancies, respectively, remained post-irradiation. These findings show that the Mg doping and gamma irradiation are effective and complementary methods to engineer structural and optical tunability of ACG grown ZnO nanostructures.

Keywords:

ZnO nanostructures; Magnesium doping; Aqueous chemical growth; Optical energy band gap; Gamma irradiation; Photoluminescence