The phosphors Y0.95-x M (x) Eu0.05B1-y R (y) O-3:Eu3+ (M = Ca, Sr, Ba, Zn, Al, 0 <= x <= 0.1; R = Si, P, 0 <= y <= 0.1) are successfully synthesized by solid-state reaction. All the solid samples are identified as isomorphs. Their luminescent properties are studied under UV and VUV excitation. With the incorporation of metallic or nonmetallic cations, the chromaticity of YBO3:Eu3+ is remarkably improved as well as the luminescent intensity increased. When 10% of Al3+ is doped into YBO3 host lattice, the best ratio of the red emission at 610 nm to the orange one at 591 nm is obtained and the luminescent intensity increased simultaneously. The reason is analyzed, and can be explained by the decrease of the symmetry around Eu3+ site in YBO3 host lattice.