Structural, Spectroscopic, and Electronic Properties of Cubic G0-Rb2KTiOF5 Oxyfluoride

The G0-Rb2KTiOF5 single crystals with dimensions up to nearly a centimeter in size have been prepared by slow solidification method. The elpasolite-related crystal structure of G0-Rb2KTiOF5 has been refined by Rietveld method at T = 298 K (space group Fm (3) over barm, Z = 4, a = 8.880(1) angstrom, V = 700.16(2) angstrom(3); R-B = 2.66%). The wide optical transparency range of 0.25-9 mu m and forbidden band gap of E-g = 3.87 eV have been obtained for the G0-Rb2KTiOF5 crystal. Dominating photoluminescence bands at 3.36 and 2.33 eV are related to free and self-trapped excitons, respectively. The electronic structure of G0-Rb2KTiOF5 has been evaluated by X-ray photoelectron spectroscopy and calculated with the first-principles methods. A good agreement between theoretical and experimental results has been achieved. Chemical bonding effects have been discussed for all metal ions using binding energy difference parameters and a wide comparison with related oxides and fluorides. The competition between O2- and F- ions for metal valence electrons has been found.