Bicationic MxCa2−2xSiO4:xEu2+ [M = Mg, Sr, (x = 0.005–0.16)] phosphors were prepared by high temperature solid-state method. The evolution of luminescence structure, space occupying mechanism and energy transfer were studied by XRD and PL spectra. Mg2+/Sr2+ cationic sites induced the matrix phases as β-Ca2SiO4 (Mg, Sr = 0.005–0.04), β-Ca2SiO4 mixed with Ca14Mg2(SiO4)8 (Mg = 0.08–0.16), or αHʹ-Ca2SiO4 (Sr = 0.08–0.16), Mg occupied Ca2 position in β-Ca2SiO4 to form structural unit 1, and Sr occupied Ca1 position in β-Ca2SiO4 to form structural unit 2. β-Ca2SiO4 is the preferred host site for Eu2+ within the matrix, and Eu2+ ions preferentially occupy the Sr/Ca2 site. For MxCa2−2xSiO4:xEu2+ [M = Mg, Sr, (x = 0.005–0.16)] phosphors, due to the 4f65d1 → 4f7 jump of Eu2+ ions, it exhibits 450–650 nm broadband yellow-green emission under 345 nm excitation, and the redshift of the emission spectra is attributed to the contraction of CaO7 polyhedra by the movement of the SiO4 tetrahedra leading to a weakened crystal field of the Eu2+ ion crystal field weakening. Sr2+ cationic sites provide an improvement in the luminescence thermal stability of MxCa2−2xSiO4:xEu2+ [M = Mg, Sr (x = 0.005–0.04)], as is demonstrated by its energy level potential barrier ΔE > 0.34 eV at 150 °C. The Mg2+/Sr2+ cationic sites are provided to enable phosphors to achieve green to yellow light, promising applications for multicolor tunable WLED lighting.