Markus Wermuth, Christian Reber and Hans U. Güdel
High-Resolution Luminescence and Absorption Spectroscopy of Cs₂GeF₆:Os⁴⁺
Inorg. Chem. 40, 3693-3703 (2001)                 

Abstract: The luminescence spectrum of the Os⁴⁺ dopant ion occupying O_h sites of the Cs₂GeF₆ host shows three sets of resolved transitions in the near-infrared at approximately 12000, 9000, and 6700 cm^–1, corresponding to intraconfigurational transitions between the ¹T_2g lowest excited electronic state and the G₁, G₄, and G₅/G₃ spinor levels of the ³T_1g ground state, respectively. The octahedral OsF₆^2- chromophore does not emit from higher excited states, in contrast to related chloride and bromide host lattices, where several excited states show luminescence. The highly resolved single-crystal luminescence and absorption spectra are rationalized with ligand field parameters 10 Dq = 24570 cm^–1, B = 500 cm^–1, C = 2380 cm^–1, z = 3000 cm^–1. Transition intensities reveal an intermediate coupling situation for OsF₆^2-: Whereas they generally follow the selection rules derived in the L-S coupling scheme, additional information can be gained from the j-j coupling limit. The resolved vibronic structure allows the identification of the most efficient ungerade parity enabling modes (vibronic origins) and shows that progressions along the a_1g, e_g, and t_2g modes occur for some transitions.