Rare-earth silicon carbonitrides, Y2Si4N6C and Y2Si4N6C:M3+ (M = Ce, Tb), were prepared by a carbothermal reduction and nitridation method. The crystal structure of Y2Si4N6C was determined by Rietveld refinement using the atomic coordinates of Ho2Si4N6C as a starting model. The host lattice was isostructural with Ho2Si4N6C of monoclinic system [P21/c, a = 5.9295(1), b = 9.8957(1), c = 11.8800(2) angstrom, beta = 119.63(4)degrees, and Z = 4]. The photoluminescence properties of doped materials, Y2Si4N6C:Ce3+ and Y2Si4N6C:Tb3+, were characterized on the basis of the detailed structural analysis result. (c) 2006 The Electrochemical Society.