Circularly Polarized Luminescence in Chiral Potassium Europium Nitrate

Emissive chiral compounds exhibit circularly polarized luminescence (CPL), characterized by the emission intensity of right- and left-circularly polarized light. Unlike chiral organic molecules, inorganic compounds that emit CPL have rarely been reported because of the challenges in controlling the symmetry of inorganic crystals. In this study, we present an all-inorganic crystal with CPL. Single crystals of both enantiomorphs of double nitrate of europium, K₃[Eu₂(NO₃)₉], are obtained through spontaneous resolution. The optical rotation is directly confirmed by polarized microscopy. K₃[Eu₂(NO₃)₉] possesses an enantiomorphic crystal structure in which europium ions are surrounded by a dissymmetric environment. This compound exhibits sharp red CPL with a high photoluminescence quantum yield, originating from its chiral crystal structure. The arrangement of ions in inorganic crystals induces chiroptical properties, such as CPL.