Localized optical absorption in Cs4PbBr6

The fundamental optical absorption of Cs4PbBr6 crystals, which are built up of nearly regular Pb2+(Br-)(6) octahedra mutually bound by Cs+ ions, exhibits novel features: despite the crystalline entity of Cs4PbBr6, it shows oscillator-like absorption peaks and a wide window just above the first peak. The Cs+ ions prevent the Pb2+ 6s and 6p states from taking part in the construction of extended states. These states form a set of localized states confined to within respective octahedra, similar to the case of isolated Pb2+ ions doped in face-centred cubic alkali halide crystals.