High-resolution luminescence and absorption spectroscopy of Cs2GeF6:Os4+

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 T-1(2g) lowest excited electronic state and the Gamma (1), Gamma (4), and Gamma (5)/Gamma (3) spinor levels of the T-3(1g) ground state, respectively. The octahedral OsF62- 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), zeta = 3000 cm(-1). Transition intensities reveal an intermediate coupling situation for OsF62-: 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.