Defect based violet–blue emission of Mg doped ZnO annealed at different temperatures Zein K. Heiba 1,3 • Mohamed Bakr Mohamed 2,3 • N. G. Imam 4 Received: 2 April 2015 / Accepted: 18 May 2015 Ó Springer Science+Business Media New York 2015 Abstract This paper describes structural and optical characterization of Mg doped ZnO nanoparticles. The system Zn 1-x Mg x O with x = 0.0, 0.01, 0.03, 0.05, 0.1 were prepared by a simple chemical method and annealing at different temperatures, T = 500, 700 and 900 °C. XRD spectra and the Rietveld refinement show that the crys- talline phase of these samples belongs to the wurtzite hexagonal structure of space group P6 3 mc. The PL results show three main emission bands in the violet and blue emission regions. The presence of several emission bands are attributed to free excitation transitions, interstitial Zn, local zinc vacancy, single ionized oxygen vacancy, and deep level emissions. PL studies at 500 °C revealed that visible PL emission was enhanced with doping concen- tration (x). Mg doped ZnO structures have changed the optical properties significantly. 1 Introduction Environmentally friendly and inexpensive ZnO is an at- tractive direct band gap semiconductor material with a direct band gap of 3.37 eV and with a large excitonic binding energy (60 meV) [1, 2]. ZnO nanomaterial has shown a great potential for applications in solid state blue to UV optoelectronics, including laser development, quantum wells with superior interface morphologies, cell imaging, solar cells, photoconductors, chemical sensors, electronics, luminescent devices, varistors, cosmetics, optoelectronics, photocatalysis, bactericides and biomarkers [3]. Transparency to visible light provides opportunities to develop transparent electronics, UV op- toelectronics, and integrated sensors, all from the same material system [1]. The band gap of ZnO can be tuned via divalent substitution on the cation site. Doping of Mg in ZnO permits the band gap to be tailored and decrease the oxygen vacancies and electron density [4]. So, Mg doping will have considerable influence on the optical properties of ZnO and it paves the way to obtain tunable optical and electrical properties. The wurtzite-type Zn 1-x MgxO alloys possess attractive properties for possible applications in optoelec- tronic and display devices. Alloying of wurtzite ZnO with cubic MgO results in metastable wurtzite (x \ 0.5) or zincblende (x [ 0.5) crystals [5]. The big difference be- tween the crystal structure of wurtzite-hexgonal ZnO and that of rock-salt-cubic MgO may cause unstable phase mixing and limits the solubility of Mg in ZnO lattice [6]. Furthermore, by doping of ZnO NPs with Group II ele- ments (Cd, Mg) the band gap of ZnO NPs can be tuned for manufacturing light-emitting diode (LED) operating in a wider wavelength range and enhance the emission in UV region [7–9]. The main aim of the present work is to in- vestigate the effect of magnesium doping and annealing & Mohamed Bakr Mohamed mbm1977@yahoo.com 1 Physics Department, Faculty of Science, Taif University, Taif, Saudi Arabia 2 Physics Department, Taibah University, Al-Madinah Al-Munawara, Saudi Arabia 3 Physics Department, Faculty of Science, Ain Shams University, Cairo, Egypt 4 Experimental Physics Department, Nuclear Research Center, Atomic Energy Authority, Cairo 13759, Egypt 123 J Mater Sci: Mater Electron DOI 10.1007/s10854-015-3222-x