The luminescence spectrum of ReCl6 2- doped in various host lattices with antifluorite-type structure

The vibrational structure derived from the Γ7(2 T 2g ) → Γ8(4 A 2g ) phosphorescence spectrum at liquid nitrogen temperature of a number of cubic host crystals A2BX6 (A = K, Rb, Cs; B = Pt, Sn, Pb, Te; X = Cl, Br) doped with ReCl6 2- has been investigated. The best resolved spectra were obtained for those host crystals absorbing appreciably more of the exciting light than ReCl6 2-. This suggests an energy transfer mechanism from host molecules to the chromophore. The spectral bands are assigned to normal frequencies of the octahedral chromophore, to lattice vibrations and to various combinations. For a complete assignment, vibrational states must be considered which belong to special points in the Brillouin zone other than the zone centre. The zero phonon transitions vary in a definite pattern for host crystals which have closed electron shells. The shifts, which depend more on the cation A+ than on the host complex BX6 2-, are discussed by means of ligand field theory.