Green-emitting phosphors of Rb₃La_1−xTb_xSi₂O₇ with a K₃NdSi₂O₇-type structure were synthesized via a solid-state reaction technique. Their crystal structures and photoluminescence properties were investigated. Crystal structural analyses of Rb₃LaSi₂O₇ and Rb₃TbSi₂O₇ were carried out for the first time and revealed that the rare-earth sites (La or Tb) were separated by the RbO₆ and SiO₄ units. According to photoluminescence spectroscopy of Rb₃La_1−xTb_xSi₂O₇ monitored at 249 and 481 nm, the highest emission intensity was obtained for the Rb₃TbSi₂O₇ phosphor under the 481-nm excitation, which indicates that the satisfactory separation of the Tb³⁺ ions suppressed the concentration quenching. The intensity of Rb₃TbSi₂O₇ was 32 % in comparison to that of the commercial green-emitting (La_0.52Ce_0.31Tb_0.17)PO₄ phosphor.