A green-emitting phosphor, Ca₁₄-xEuxMg₂[SiO₄]₈ (CMS:Eu²⁺), has been synthesized as a component of white light emitting diodes (WLEDs). The emission spectrum is broad, with a maximum at about 505 nm under 400 nm excitation due to the transition from the 4f⁶5d excited state to the 4f⁷-ground state of a Eu²⁺ ion. The dipole-dipole interaction was a dominant energy transfer mechanism of the electric multipolar character of CMS:Eu²⁺. The critical distance was calculated as 12.9 Å and 14.9 Å using a critical concentration of Eu²⁺ and Dexter's theory for energy transfer. When CMS:Eu²⁺ and red phosphor are incorporated with an encapsulant on an ultraviolet (λmax = 395 nm) light emitting diodes (LEDs), white light with a color rendering index of 91 under a forward bias current of 20 mA was obtained. The structural and optical characterization of the phosphor is described.