An Eu2+-activated BaSi7N10 cyan phosphor for UV-pumping white light-emitting diodes (LEDs) was successfully synthesized by direct gas reduction and nitridation of the homogeneous oxide precursor of a BaO-SiO2-Eu2O3 system in flowing NH3 and CH4 mixture gas. The phase purity, morphology, chemical composition, and luminescence properties were investigated. The effect of activator concentration on the optical properties of Eu2+ in BaSi7N10 was discussed. The synthesized powders have a nearly pure BaSi7N10 phase and consist of microsized particles. Eu2+-doped BaSi7N10 phosphors absorb strongly in the UV part of the electromagnetic spectrum and exhibit an intense cyan emission band centered at 482-500 nm, which agrees with earlier papers. The optical properties depend greatly on the Eu2+ concentration. Under an UV excitation, BaSi7N10:Eu2+ phosphors doped with a 20 atom % activator give the best luminescent properties, such as high emission intensity, high quantum efficiency, and very low thermal quenching, which suggests that Eu2+-doped BaSi7N10 can be a good green-blue phosphor for UV-pumping white LEDs. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3424899] All rights reserved.