Preparation, luminescence and structural properties of RE-doped RbLaS2 compounds

Rare-earth (RE = Ce, Pr, Sm, Eu, Tb) doped ternary sulfides having the general formula RbLa0.99RE0.01S2 and undoped RbLaS2 were synthesized in the form of crystalline hexagonal platelets by a chemical reaction in an electric resistance furnace under the flow of hydrogen sulfide. X-ray powder diffraction confirmed the single crystalline phase of the rhombohedral lattice system (space group R-3 m, α-NaFeO2 structure type) with hexagonality c/a = 5.34, consistent with the already reported RbLaS2 structure. Time-resolved luminescence spectroscopy was employed to investigate radioluminescence, photoluminescence, decay kinetics and absorption spectra. An RbLaS2 band edge at 322 nm was found and characteristic Pr3+, Sm3+ and Tb3+ 4f-4f emission lines in the visible spectral range were observed. The charge transfer transitions in the Pr3+- and Sm3+-related excitation spectra in the range 330-350 nm are described and the efficient energy transfer from the host to the emission centers is revealed. We discuss the potential for application of these materials in field emission displays, white LED solid-state lighting and X-ray phosphors.