Red emitting Sm() phosphors: thermally switchable luminescence in Sm(AlX) (X = Cl, Br) by 5d-4f and intra-4f transitions

Divalent samarium compounds of the constitution Sm(AlX 4 ) 2 , X = Cl, Br, show remarkable luminescence of Sm 2+ . At room temperature, the luminescence is dominated by parity-allowed broad-band 4f 5 5d 1 → 4f 6 emission with additional 5 D 0 → 7 F J narrow-line emission. At 79 K, only the intra-4f-emission is observed, rendering the mechanism thermally switchable. The luminescence processes and their temperature dependence were determined including lifetime investigations for both, room temperature and 79 K, as well as quantum efficiency determinations. In addition, a new pathway for the synthesis of Sm(AlCl 4 ) 2 and the previously unknown Sm(AlBr 4 ) 2 is reported. Sm(AlX 4 ) 2 (X = Cl, Br) show thermally switchable luminescence of Sm 2+ between broad-band 4f 5 5d 1 → 4f 6 emission and thin line intra-4f-emission, rendering the compounds interesting Ln( ii )-based phosphors with samarium.