THE EU SITE SYMMETRY IN AEU(MOO4)2 (A = CS OR RB) GENERATING SATURATED RED LUMINESCENCE

The luminescence spectrum of CsEu(MoO4)2 is characterized by a single line at 614.5 nm, which has an intensity more than 10 times larger than any other visible line. This spectral feature can be ascribed to D4 site symmetry, which is higher than the exact symmetry, D2, derived from the space group. The apparent inconsistency results from the fact that Cs ions are located between layers consisting of (EuO8) and (MoO4) polyhedra with a long nearest-neighbor distance (0.475 nm) from Eu. A similar luminescence spectrum is observed also for RbEu(MoO4)2 except for line broadening due to random distribution of Rb and Eu ions. The luminescence of these compounds has high colorimetric purity resulting from the high probability of electric dipole transitions including the strong line at 614.5 nm. © 1991.