Crystal Growth of Two New Photoluminescent Oxides: Sr₃Li₆Nb₂O₁₁ and Sr₃Li₆Ta₂O₁₁

Single crystals of Sr₃Li₆M₂O₁₁ (M = Nb, Ta) were grown out of a high-temperature Sr(OH)₂/LiOH/KOH flux. The single crystal X-ray diffraction data were indexed to the orthorhombic Pmma system, with a = 10.5834(15) Å, b = 8.3103(13) Å, c = 5.8277(8) Å, V = 512.55(13) ų, and Z = 2 for Sr₃Li₆Nb₂O₁₁ and a = 10.5936(6) Å, b = 8.3452(5) Å, c = 5.8271(4) Å, V = 515.15(6) ų, and Z = 2 for Sr₃Li₆Ta₂O₁₁. The crystal structure consists of sheets of interconnected SrO₈ polyhedra that are separated by M−O layers and an intervening LiO_x polyhedral framework, representing a new structural type. The M−O layers exhibit a rare occurrence of both five- and six-coordinated M⁵⁺ ions in the same structure. The oxides, upon excitation at 250 nm, exhibit violet emission at room temperature.