Optical anisotropy of CsPbBr3 perovskite nanoplatelets

Abstract

The two-dimensional CsPbBr3 nanoplatelets have a quantum well electronic structure with a band gap tunable with sample thicknesses in discreet steps based upon the number of monolayers. The polarized optical properties of CsPbBr3 nanoplatelets are studied using fluorescence anisotropy and polarized transient absorption spectroscopies. Polarized spectroscopy shows that they have absorption and emission transitions which are strongly plane-polarized. In particular, photoluminescence excitation and transient absorption measurements reveal a band-edge polarization approaching 0.1, the limit of isotropic two-dimensional ensembles. The degree of anisotropy is found to depend on the thickness of the nanoplatelets: multiple measurements show a progressive decrease in optical anisotropy from 2 to 5 monolayer thick nanoplatelets. In turn, larger cuboidal CsPbBr3 nanocrystals, are found to have consistently positive anisotropy which may be attributed to symmetry breaking from ideal perovskite cubes. Optical measurements of anisotropy are described with respect to the theoretical framework developed to describe exciton fine structure in these materials. The observed planar absorption and emission are close to predicted values at thinner nanoplatelet sizes and follow the predicted trend in anisotropy with thickness, but with larger anisotropy than theoretical predictions. Dominant planar emission, albeit confined to the thinnest nanoplatelets, is a valuable attribute for enhanced efficiency of light-emitting devices.

Novel Chiral CsPbBr3 Metal Halide Perovskite Magic-Sized Clusters and Metal Halide Molecular Clusters with Achiral Ligands

“…One possible explanation, as shown in Figure a, is that the clusters are intrinsically chiral due to the twisting of layered structures. Layered structure of the clusters has been suggested in our previous work ,, and by others. ,, As the clusters are very small, they may be distorted or strained, resulting in a twisted structure that happens to be chiral. Another possible explanation is defect-induced chirality, as illustrated in Figure b and found in previous studies of QDs.…”

“…Another possible explanation is defect-induced chirality, as illustrated in Figure b and found in previous studies of QDs. Previous studies have found optical anisotropy within nanoplatelets and nanorods resulting from inherent defects during formation. ,, CsPbBr 3 perovskite nanoparticles were found to aggregate along a helical scaffold formed from either silica or polymers. , …”

“…Fluorescent chiral nanoparticles have been employed as chiral optical probes for determining enantiomeric excess and identifying chiral molecules, attracting increasing research interest. , Most of the work done to date has focused on bulk crystals with chiral building blocks ,,, or QDs with chirality induced by using chiral ligands. ,,,− Similar to QDs, PMSCs and MHMCs could potentially acquire chirality through passivation using chiral ligands. However, it would be more interesting and desired if the clusters could possess intrinsic chirality without the need to use chiral ligands to induce extrinsic chirality.…”

“…To explain the observed CD signal, we propose two possible explanations. The first is structural chirality ,− , as a result of broken mirror symmetry, while the second is magnetism-induced chirality , via a weak magnetic field inherent to the clusters.…”

Correction: Optical anisotropy of CsPbBr3 perovskite nanoplatelets

“…In the original publication of the article [ 1 ], the copyright holder was incorrectly given as ‘© Argonne National Laboratory, under exclusive licence to Korea Nanotechnology Research Society (KoNTRS) and Springer Nature Singapore Pte Ltd. 2023' but should have been ‘© Argonne National Laboratory'. This has now been corrected with this erratum.…”