The monodisperse spherical SiO2/Y2O3:Tb3+ core/shell particles were prepared by a heterogeneous precipitation coating of the phosphor shell on the surface of the core particles. The shell thickness and the calculated crystallite size were increased with the core size and, thus, the photoluminescence (PL) intensity was also increased. The phosphor photonic crystals (PCs) were fabricated by self-assembly of the core/shell particles.