A phosphor based on a phosphate host matrix, RbSrPO4:Eu2+ (RSP), was synthesized by a conventional solid-state reaction, and the crystal structure of the RSP host material was investigated by Rietveld refinement. The RSP phosphor could be excited efficiently by light in the 220–430 nm UV/Vis range and exhibited a highly intense emission peak at 450 nm. We discovered the effect of the activated Eu2+ concentration and the concentration quenching mechanism. Also, light absorption and quantum efficiency of the RSP phosphor were measured when excited in the near-UV region. Finally, the effect of temperature on the photoluminescence emission intensity of the RSP phosphor and its thermal activation energy were investigated. All of these characteristics indicate that this phosphor has potential for use in near-UV-based white LEDs.