Visible orange photoluminescence in a barium titanosilicate BaTiSi2O7

A visible orange photoluminescence (PL) was observed at room temperature from a barium titanosilicate BaTiSi2O7. The diffuse-reflection spectrum revealed the presence of an oxygen defect in the Ti-O polyhedral unit. The broad PL with the peak at 580 nm was observed by ultraviolet (UV) excitation at 321 nm as the PL excitation spectrum maximum, being sufficient for a visual confirmation under UV light. It was suggested that its peculiar PL is related to both the absolutely isolated pyramidal TiO5 unit pair and the oxygen defect in the TiO5 unit in the BaTiSi2O7 phase.