A novel reddish-orange emitting phosphor Eu-activated KLaSiO 4 was synthesized by the conventional solid-state reaction at 1200°C. The luminescence properties of KLaSiO 4 :Eu phosphor were investigated, and the critical concentration of the activator ion (Eu 3+ ) was established as 0.02 mol per formula unit. Chromaticity coordinates of a typical KLa 0.98 SiO 4 :0.02Eu phosphor were x = 0.614 and y = 0.385. The phosphor exhibited reddish-orange luminescence with dominating emission at 612 nm, corresponding to 5 D 0 → 7 F 2 of Eu 3+ . Furthermore, the phosphor was characterized by excellent thermal stability, implying its potential use in white light emitting diodes.