The effect of Mg incorporation on structural and optical characteristics of rhombohedral Zn2GeO4 doped with manganese was systematically studied, fixing the concentration of manganese at 2 atom %. The phosphors were prepared by a high-temperature solid-state-reaction technique. The structural properties were studied using X-ray diffraction (XRD) and optical properties were characterized by diffuse reflectance spectra (DRS), photoluminescent excitation (PLE), and photoluminescent (PL) emission spectra. The XRD and DRS analyses reveal that Mg can be successfully alloyed in Zn1.96-1.96xMg1.96xGeO4:Mn-0.04 up to x = 0.30 and forms a solid solution. The PL emission was maximum when 5 atom % Zn was replaced with Mg in comparison to an Mg-free Zn1.96GeO4:Mn0.04 sample. The mechanism of luminescence is identified as resonant transfer from a subbandgap state in the host to Mn2+. The PLE and DRS spectra of Zn1.96-1.96xMg1.96xGeO4: Mn-0.04 (0 <= x <= 0.5) exhibited a blue shift with an increase in Mg concentration. The cell volume was found to be a monotonously increasing function of Mg concentration up to x = 0.25, beyond which it varied randomly. (c) 2007 The Electrochemical Society.