On the Origin of Circularly Polarized Luminescence in Chiral One-Dimensional (A)PbBr ₃ Single Crystals

With the emergence of chiral hybrid metal-halide and chiral low-dimensional halide perovskite materials, the propensity to generate polarized electroluminescence in LED devices using this new family of hybrid semiconductors is questioned. To evaluate this potential, some efforts have been undertaken in order to reveal their intrinsic circularly polarized luminescence (CPL) either in the single crystal or thin film state. However, the strong anisotropy in the optical properties of such highly crystalline materials can affect CPL measurements, especially in bi-axial compounds, leading to the dominance of artifacts and/or CPL of macroscopic origin which have been sometimes overlooked. Here, we wish to investigate the origins of CPL signals recorded using one-dimensional compounds of general formula (A)PbBr3 (A = monovalent cation). To achieve this, we complement the crystal structure determination with optical properties analysis (photoluminescence, circular dichroism), Raman spectroscopy, and computational modeling. CPL measurements reveal that the circularly polarized signal is dominated by the combination of linearly polarized optical effects from the sample and the detection system (i.e. artifacts), while the combination of two linearly polarized optical phenomena from the sample could give rise to non-reciprocal CPL, i.e. a reproducible CPL which is dependent to the direction of propagation. This study suggests that with a careful choice of organic cation, chiral hybrid metal-halides could afford reciprocal CPL with glum values lying in the 10-3 order of magnitude, a degree of polarization that might be increased in electroluminescence due to the presence of non-reciprocal effects.