Photoluminescence spectra of thenardite Na2SO4 activated with rare-earth ions, Ce3+, Sm3+, Tb3+, Dy3+ and Tm3+

Five Na 2 SO 4 :RE 3+ phosphors activated with rare-earth (RE) ions (RE 3+ =Ce 3+ , Sm 3+ , Tb 3+ , Dy 3+ and Tm 3+ ) were synthesized by heating natural thenardite Na 2 SO 4 from Ai-Ding Salt Lake, Xinjiang, China with small amounts of rare-earth fluorides, CeF 3 , SmF 3 , TbF 3 , DyF 3 and TmF 3 , at 920 °C in air. The photoluminescence (PL) and optical excitation spectra of the obtained phosphors were measured at 300 and 10 K. In the PL spectrum of Na 2 SO 4 :Ce 3+ at 300 K, two overlapping bands with peaks at 335 and 356 nm due to Ce 3+ were first observed. Narrow bands observed in PL and excitation spectra of Na 2 SO 4 :RE 3+ (RE 3+ =Sm 3+ , Tb 3+ , Dy 3+ and Tm 3+ ) phosphors were well identified with the electronic transitions within the 4f n ( n =5, 8, 9 and 12) configurations of RE 3+ . The existence of excitation bands with high luminescence efficiency at wavelengths shorter than 230 nm is characteristic of Na 2 SO 4 :RE 3+ (RE 3+ =Sm 3+ , Tb 3+ , Dy 3+ and Tm 3+ ) phosphors. The obtained results suggest that these phosphors are unfavorable as the phosphor for usual fluorescence tubes, i.e., mercury discharge tubes, but may be favorable as the phosphor for UV-LED fluorescent tubes and as cathodoluminescence, X-ray luminescence and thermoluminescence phosphors.