Crystal growth of Sr3NaNbO6 and Sr3NaTaO6:: New photoluminescent oxides

Single crystals of Sr3NaNbO6 and Sr3NaTaO6 were grown out of high-temperature Sr(OH)(2)/NaOH melts contained in silver reaction vessels. Block- and rod-shaped crystals of Sr3NaNbO6 and Sr3NaTaO6 were isolated from sealed silver tubes and open crucibles, respectively. The structures were determined by single-crystal X-ray diffraction. Both Sr3NaNbO6 and Sr3NaTaO6 crystallize in the trigonal (rhombohedral) system, R-3c with a 9.7853(12) angstrom, c = 11.606(3) angstrom, V = 962.4(3) angstrom(3), Z = 6 (Sr3NaNbO6), and a = 9.7867(4) angstrom, c = 11.6109(7) angstrom, V = 963.10(8) angstrom(3), Z = 6, (Sr3NaTaO6). The oxides are isostructural with the 2H-perovskite related K4CdCl6 structure type and consist of one-dimensional chains containing face-sharing NbO6 (TaO6) octahedra and NaO6 trigonal prisms. These chains in turn are separated from one another by infinite chains of strontium cations located in a distorted square antiprismatic environment. Interestingly, depending on the exact synthetic conditions, either green or brown crystals with distinct UV-visible spectra were obtained for both Sr3NaNbO6 and Sr3NaTaO6. All crystals luminesce at room temperature with violet emissions upon excitation at 250 nm. To better understand the luminescence of these oxides, we performed semiempirical calculations to ascertain the nature of the excited state.