ORIGINAL PAPER Nanorods www.crt-journal.org Band Gap Engineering of Mg Doped ZnO Nanorods Prepared by a Hydrothermal Method Sevim D. Senol, Cihat Boyraz, Ersin Ozugurlu, Ali Gungor, and Lutﬁ Arda* The eﬀect of band gap on the structure, magnetic, and optical properties of Zn 1−x Mg x O nanorods synthesized by hydrothermal method using varying x-values from 0.00 to 0.05 with 0.01 step increment is studied. The structural phases of Zn 1−x Mg x O samples are determined by X-ray diﬀraction tool. The Rietveld analysis is performed for the selected Zn 0.95 Mg 0.05 O sample and all samples’ phases are found as single phase. The concentration-dependent of lattice parameters, cell volumes, microstrain, and dislocation density, locality of the atoms and their displacement, and bond length in Zn 1- x Mg x O structures are detailed. Electron Spin Resonance (ESR) measurements are performed and analyzed through concentration dependence of the g-factor and the line-widths of pike to pike (H PP ) of ESR spectra. A ferromagnetic behavior of the Zn 0.95 Mg 0.05 O nanorods is observed. The optical band gaps (E g ) of Zn 1- x Mg x O nanorods are obtained by the data taken from Ultraviolet–Visible (UV–VIS) diﬀuse reﬂectance spectroscopy. It is found that the E g -values increased with increasing amount of Mg elements in the structure. 1. Introduction The zinc oxide (ZnO) nanostructure comes forward from among the II-VI semiconductors with very attractive properties such as the exciting binding energy of 60 meV at room temperature and a direct wide band gap of 3.37 eV. These properties have been used for the development of optoelectronic materials and applications. [1–11] Electro-optical and structural properties of ZnO nanomaterials can be controlled and improved by doping process with various elements. According to ref. [9] silver doping not only improves the absorption of the photocatalysts but also causes red-shift in the absorption band. Band gap reduction means that lower energy is required for the electron-hole pair generation. An- other doping element lowering the band gap of ZnO is cerium Dr. S. D. Senol Abant Izzet Baysal University Faculty of Arts and Science Department of Chemistry 14280 Bolu, Turkey Dr. C. Boyraz Marmara University Faculty of Technology Department of Mechanical Engineering Goztepe, 34722 Istanbul, Turkey The ORCID identiﬁcation number(s) for the author(s) of this article can be found under https://doi.org/10.1002/crat.201800233 DOI: 10.1002/crat.201800233 which was studied by Sinha et al. [4] who revealed that cerium doping decreased size of nanorods, increased the intensity of green emission peak in photolumi- nescence, and decreased the band gap energy to 3.18 eV from 3.37 eV. More- over, gallium-doped ZnO is also an im- portant material due to its high carrier concentration and electrical conductiv- ity, especially higher gallium doping pro- duces a decrease of the band gap values of ZnO. Among these various doping el- ements, cadmium decreases to approxi- mately 3 eV [5] and magnesium increases the band gap to 4 eV and higher. [2,11] In addition, magnesium doping might be suitable for enhancement of structural, electrical, and optical properties of ZnO. Moreover, the Mg 2+ ions can also be suc- cessfully incorporated into the lattice of ZnO nanostructures due to its ionic ra- dius (0.57 ˚ A) close to the ionic radius of Zn 2+ (0.60 ˚ A). [12] The wurtzite-type ZnMgO alloys have important applications in optoelectronic and display devices. Alloying of wurtzite ZnO with cubic MgO develops metastable wurtzite (x < 0.5) or zincblende (x > 0.5) crystals. Recent optical studies of ZnMgO indicated that with increasing Mg content the energies of the fundamental band-to-band transitions were found to be strongly blue shifted. Heiba and Arda [2] reported that magnesium content in ZnO must be high to achieve the true blindness and to extend the band gap energy. However, they found out that unstable phase mixing could occur because of the large crystal structure dissimilarity between wurtzite-hexagonal ZnO and rock-salt- cubic MgO. Dr. E. Ozugurlu Istanbul Technical University Faculty of Science and Arts Department of Mathematical Engineering 34467 Maslak, Istanbul, Turkey Prof. A. Gungor Bahcesehir University Faculty of Medicine Department of Biophysics 34734 Kadikoy, Istanbul, Turkey Prof. L. Arda Bahcesehir University Faculty of Engineering and Natural Sciences Department of Mechatronic Engineering 34349 Besiktas, Istanbul, Turkey E-mail: lutﬁ.arda@eng.bau.edu.tr Cryst. Res. Technol. 2019, 1800233 C  2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1800233 (1 of 7)