BaGa4O7, a new A3BC10O20 crystalline phase: synthesis, structural determination and luminescence properties

The synthesis, structural determination and luminescence properties of a new barium gallate, BaGa4O7, are reported. This crystalline material can uniquely be obtained by direct cooling from the molten state. The crystallographic structure was determined using a combination of electron, synchrotron and neutron powder diffraction data. BaGa4O7 crystallizes in the monoclinic I2/m space group with a = 15.0688(1) angstrom, b = 11.7091(1) angstrom, c = 5.1429(2) angstrom and beta = 91.0452(2)degrees and can be described as an original member of the A(3)BC(10)O(20) family. Atypical for this A(3)BC(10)O(20) structural framework, BaGa4O7 is found to contain exclusively divalent and trivalent cations. In order to maintain overall electroneutrality, disordered defect-type partial substitution of gallium and oxygen ions on barium sites occurs within the pentagonal channels of BaGa4O7. Thanks to the flexibility of this structural framework, BaGa4O7 can be heavily doped with europium and thus is shown to exhibit strong orange-red luminescence emission at 618 nm under 393 nm excitation.