Synthesis and luminescence properties of Mg4Nb2O9 nanocrystals by citric gel process were investigated in this work. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL). The excitation band at about 241 and 341 nm originates from the regular and defect octahedra group [NbO6](7-). The room-temperature PL spectra under 241 and 341 nm excitations show a broad violet and a very strong emission peaks located at 390 and 402 turn, respectively. (C) 2008 Elsevier B.V. All rights reserved.