Eu3+-doped LiMgPO4 was prepared by a high temperature solid-state reaction. The phase formation was confirmed by X-ray powder diffraction measurements. The site-selective excitation and emission spectra were investigated in the D-5(0)-> F-7(0) region by using a pulsed, tunable, and narrowband dye laser. Two crystallographic sites for Eu3+ ions doped in LiMgPO4 were observed from the luminescence and structure features. Absorption and emission peaks at 579.0 nm were caused by the Eu3+ site, which substitutes the Li+ ion located in the channel of the LiMgPO4 structure along the [010] direction, creating cation vacancies V-Li', while absorption and emission peaks at 579.9 nm were caused by a cluster of Eu3+ ions. The decay times of the two Eu3+ sites were measured. The defect structures and charge compensation mechanism of Eu3+ doping in LiMgPO4 were discussed. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3356975] All rights reserved.