Luminescence properties of layered chalcogenide oxides Ba3RE2Ag2Se2O5

Abstract New layered chalcogenide oxides, Ba 3 RE 2 Ag 2 Se 2 O 5 ( RE = Y, Lu), were successfully synthesized. The crystals of these compounds are isostructural with that of Sr 3 Fe 2 Cu 2 S 2 O 5 , and are composed of alternate stacks of anti-fluorite-type silver selenide and perovskite-like oxide layers. Direct band gaps of ∼2.6 eV at room temperature were estimated by the diffuse reflectance measurements of the powdered samples. Exciton absorption peaks near the band gap were observed, and the splitting of the peaks was probably due to spin–orbit interactions. Sharp luminescence at 2.5–2.7 eV with very fast decay times was observed in both compounds, even at room temperature. It was found that excitonic luminescence can be observed in several layered compounds having semiconducting and insulating layers.