Perovskite-type Metal Halides as Luminescent Materials*

Halide semiconductors and insulators broadly belonging to perovskite-type crystal structures have received considerable attention due to their range of properties which are suitable for a variety of applications. If electronic band gap is taken as one metric, these materials span values that are relevant for solar absorbers, semiconductor radiation detectors and scintillators, obtainable by virtue of different metal-halogen combinations. Here, we concern ourselves with luminescent materials covering 3-dimensional (3-D) ABX₃-type compounds and the 0-D perovskite, Cs₄PbBr₆. The former consist of corner or edge-sharing octahedra such as in CsCaI₃ and KCaI₃, while the latter is obtained from almost disjointed octahedra connected only by Cs-Br bridges. Employing density functional methods, we study their structural differences which is reflected in distinctive electronic properties and formation of self-trapped carriers. We discuss these properties as they relate to radiative decay and light yield in gamma scintillator applications. We also speculate on the observed green emission in CsPbBr₃/Cs₄PbBr₆ composites which may be related to excitonic luminescence.