Recently, organo-metal halide perovskites (OMHP) gained major research interest due to their fascinating electro-optical porperties, rendering them promising candidates for light harvesting as well as light emitting devices.
In spite of the huge research effort, fundamental properties of these materials are not yet fully understood. One particular issue is the origin of the optical transitions behind the wide semiconductor-like band. Theoretical calculations predict that the optical absorption spectrum originates from a combination of several transitions between several valence and conduction bands formed from individual and hybridized orbitals of lead and iodide. A versatile tool to shed light on these transitions are light polarization measurements. However, the photoluminescence anisotropy of bulk OMHP samples is practically zero, due to the general absence of photselection in semiconductors and ensemble averaging over randomly oriented disordered crystals in bulk samples.
Investigation of individual perovskite nanocrystals allows us to detect polarization of photoluminescence (PL) and photoluminescence excitation hidden in bulk samples by ensemble averaging.
From individual methylammonium lead iodide (CH3MH3PbI3) nanocrystals we obtained PL polarization at room temperature up to 35%, while even higher PL polarization (≤ 70%) was observed at low temperatures .
Additional to the investigation of OMHP, we also study fully anorganic perovskites as CsPbBr3 and CsPbI3.
 D. Täuber, A. Dobrovolsky, R. Camacho, I. Scheblykin: Exploring the electronic band structure of lead-iodide perovskite via photoluminescence anisotropy of individual nanocrystals, Nano Letters, 16(8), 5087–5094, 2016.
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