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 °C, respectively. These thermodynamic requirements play an important role in the mechanism underlying the formation of Mg:ZnO solid solutions.