Publication date: 15th December 2025
Lead-halide perovskites have rapidly established themselves as a new class of semiconductor materials with outstanding optical properties and technological promise [1,2]. Nanoplatelets (NPLs) of these materials exhibit extreme quantum and dielectric confinement, resulting in strongly modified exciton manifolds compared to their bulk and nanocrystal counterparts. Understanding the fine structure and optical selection rules of these excitons is essential for advancing perovskite-based quantum photonic devices.
Here, we investigate the electronic structure and excitonic emission pathways of single 2-monolayer CsPbBr₃ nanoplatelets, combining polarization-resolved micro-PL spectroscopy at 10 K with variational and k·p modeling that explicitly incorporates finite-well confinement, dielectric contrast, Coulomb interaction, and crystal-field contributions.
Our calculations predict a four-level band-edge exciton manifold composed of one dark state and three bright states, split by a combination of orthorhombic crystal field terms, extreme confinement, and anisotropic dielectric screening. The bright manifold divides into two strongly allowed in-plane dipole states and a suppressed out-of-plane exciton whose oscillator strength is quenched by dielectric screening effects [3-5].
Experimentally, single-NPL µ-PL spectra reveal polarization-orthogonal bright doublets with ≈2 meV splitting, unambiguously resolving the in-plane exciton states in the orthorhombic phase. Temperature-dependent time-resolved PL, interpreted through a two-phonon bright–dark mixing model, yields bright–dark splittings consistent with our theoretical predictions and recent high-resolution studies [6].
This combined theoretical–experimental approach provides a comprehensive picture of exciton fine structure under ultra-strong confinement, revealing the emergence of anisotropic emission channels and the suppression of out-of-plane excitonic transitions. These insights establish atomically thin CsPbBr₃ nanoplatelets as promising platforms for polarization-defined light sources, quantum emitters, and engineered excitonic materials in next-generation optoelectronic and quantum technologies.
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