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) Å3, 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) Å3, 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 LiOx 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.