Origin of photoluminescence in suzukiite-type BaTiSi2O7

A barium titanosilicate, BaTiSi2O7, with suzukiite (BaVSi2O7)-type structure has a unique Ti-O unit, which consists of mirror-symmetrical TiO5 pyramids pair, and possesses a visible orange photoluminescence (PL) by an ultraviolet excitation at room temperature. However, the origin of orange PL has not been fully understood. Therefore, the purpose of this study is to elucidate the origin and mechanism of orange PL in suzukiite-type BaTiSi2O7. It has been proposed that two types of oxygen-defect in the pyramidal TiO5 unit pair contribute to the efficient orange PL, i.e., the extrinsic oxygen-vacancy due to the lack of oxygen in the TiO5 unit, and the intrinsic oxygen-vacancy, which exists in the TiO5 unit pair due to its structural peculiarity.