[en] Highly efficient green phosphors SrSi₂O₂N₂ : Eu²⁺, suitable for white light emitting diodes (LEDs), was synthesized by solid-state reaction and their photoluminescence properties were investigated. SrSi₂O₂N₂ : Eu²⁺ phosphors can be effectively excited by ultraviolet (UV)-Vis light (300-460 nm) and yield green emission with a single, intense, broad band centred at around 540 nm. Concentration quenching occurs in the phosphors when the Eu²⁺ concentration exceeds 2 at%. The mechanism of concentration quenching is confirmed to be dipole-dipole interaction of Eu²⁺. With an increase in the Eu²⁺ concentration, the emission band of Eu²⁺ shifts to a longer wavelength due to the 5d-orbit hybridization of Eu²⁺ with the host crystal and the energy transfer between adjacent Eu²⁺ ions. All the results indicate that SrSi₂O₂N₂ : Eu²⁺ is a promising green phosphor for UV or blue chip based white LEDs.