Photoluminescent properties of Mg doped ZnO by microwave combustion and microwave polyol method

Microwave assisted combustion (MAC) route holds potential to achieve a substantial degree of Mg doping, > 15-25% in bulk ZnO, which is evident from a blue shifted optical band edge and a shift in emission towards lower wavelength. In contrast, microwave-assisted polyol (MAP) route shows no pronounced effect on the photoluminescence features due to a segregated amorphous Mg(OH)(2) phase. Two factors underlie the substitution of Mg in Zn sites viz: (i) heats of formation of ZnO is -350.5 kJ/mol which is remarkably lower compared to MgO, -601.6 kJ/mol and (ii) the decomposition temperatures of the respective hydroxides are distinctly different, 125 and 350 degrees C, respectively. These thermodynamic requirements play an important role in the mechanism underlying the formation of Mg:ZnO solid solutions. (C) 2009 Elsevier B.V. All rights reserved.