In this Study, Mg2+ and Ba2+ act to enhance the maximum emission of Sr2.97SiO5:0.03Eu(2+) significantly and redshift the emission band to the orange-red region in Sr2.97-x-yMgxBaySiO5:0.03Eu(2+). Size mismatch between the host and the doped cations tunes the photoluminescence spectra shift systematically. A slight blue shift when increasing the amount of Mg2+ occurs in the Sr2.97-xEu0.03MgxSiO5 lattices, and a rapid red shift occurs when Ba2+ is codoped in the Sr2.57-yEu0.03Mg0.4BaySiO5 lattices. The emission spectra were tuned from 585 to 601 nm by changing the concentration of Ba2+. Accordingly, we propose the underlying mechanisms of the changes in the photoluminescence properties by adjusting the cation composition of phosphors. The influence of the size mismatch on the thermal quenching is also observed. This mechanism could be widely applied to oxide materials and could be useful in tuning the photoluminescence properties, which are sensitive to local coordination environment. The emission bands of Sr2.97-x-yEu0.03MgxBaySiO5 show the blue shift with increasing temperature, which could be described in terms of back tunneling of the excited electrons from the low-energy excited state to the high-energy excited state. Thus, the Sr2.97-x-yEu0.03MgxBaySiO5 phosphors could have potential applications in the daylight LEDs or warm white LEDs.