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

Abstract

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) Å, b = 11.7091(1) Å, c = 5.1429(2) Å and β = 91.0452(2)° and can be described as an original member of the A₃BC₁₀O₂₀ family. Atypical for this A₃BC₁₀O₂₀ 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.