STRUCTURE AND LUMINESCENCE OF BARIUM URANIUM DISILICATE (BAUO2SI2O6)

The structure and luminescence of BaUSi2O8 are reported and discussed. BaUSi2O8, orthorhombic, Cmcm, a = 5.7027(4) Angstrom, b = 16.4636(10) Angstrom, c = 7.4956(5) Angstrom, V = 703.74(8) Angstrom(3), Z = 4, D -x = 5.281 Mg m(-3). The structure has been refined by Rietveld analys is of neutron diffraction data recorded at room temperature. R(p) = 4. 43%, R(wp) = 6.24%. The structure is related to SrVSi2O7, haradaite. T he luminescence spectra are characteristic of the uranyl group. At low temperatures the energy migration is hampered by the presence of two sets of uranyl groups and inhomogeneous broadening. At somewhat higher temperature the uranyl traps can be reached by migration, and trap em ission occurs until the temperature is high enough for detrapping. The spectra show a progression in the symmetrical stretching frequency of the uranyl group. The radiative decay time is 1.1 ms. The spectroscop ic results suggests that the proposed structure cannot be correct in a ll details.