High-quality and rod-like single-phase BaSi2O2N2:Eu2+ phosphor was prepared by a solid-state reaction method using Eu2O3@B2O3 core–shell structure as an activator. This technique makes it possible to obtain a rod-like single phase with high luminescence efficiency. The transmittance electron microscope image and electron energy loss spectrum of the Eu2O3@B2O3 core–shell structure particles show that the B2O3 coating and the core–shell structure consisted of Eu and B elements. The BaSi2O2N2:Eu2+ phosphor showed higher emission intensity than commercial β-SiAlON:Eu2+ phosphor. This oxyntiride phosphor and synthesis method are expected to be promising candidates for realizing white LEDs.