Red emitting Sm(ii) phosphors: thermally switchable luminescence in Sm(AlX4)2 (X = Cl, Br) by 5d–4f and intra-4f transitions

Abstract

Divalent samarium compounds of the constitution Sm(AlX₄)₂, X = Cl, Br, show remarkable luminescence of Sm²⁺. At room temperature, the luminescence is dominated by parity-allowed broad-band 4f⁵5d¹ → 4f⁶ emission with additional ⁵D₀ → ⁷F_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(AlCl₄)₂ and the previously unknown Sm(AlBr₄)₂ is reported.