Rare earth elements (Pr,Ce) doped ternary sulfides of formula RbGd 1−x RE x S 2 were synthesized in the form of crystalline hexagonal platelets by chemical reaction under the flow of hydrogen sulfide. The X-ray powder diffraction detected only a single crystalline phase of rhombohedral lattice system. Optical properties of studied systems are investigated by methods of time-resolved luminescence spectroscopy. Thermal stability of the Pr 3+ emission is demonstrated. Application potential in the white light-emitting diode solid state lighting or X-ray phosphors is discussed.