Size-dependent anisotropy in lattice parameters governs the bright-exciton fine-structure splitting (BEFSS) in ${\mathrm{CsPbI}}_3$ nanocrystals. By using the continuum elastic theory, we demonstrate that an additional lattice anisotropy in a pseudocubic nanocrystal is determined by the elastic coupling between bulk and surfaces. For the ${\mathrm{CsPbI}}_3$ nanocrystal in orthorhombic phase, it reveals that the surface stress anisotropy of the (001) surface plays a more important role than that of the (110) surface in inducing the size-dependent lattice anisotropy. According to the first-principles calculations, the intrinsic surface stress anisotropy is relatively small for either (110) or (001) surface. As organic ligands are always involved in the synthesis of ${\mathrm{CsPbI}}_3$ nanocrystals, they may introduce stochastic surface stress anisotropy and thus result in divergency of BEFSS. Therefore, we further study the surface with typical substitutional short-chain ligands, namely methylammonium and formate ions. It turns out that the surface stress anisotropy is large on the (110) surface but small on the (001) surface due to the cooperative geometric effect of ligand and surface structure. Consequently, the BEFSS variations become negligible at various coverages with the short-chain ligands. These findings enable precise control of the BEFSS through surface stress engineering by carefully selecting the suitable ligands, improving the application of ${\mathrm{CsPbI}}_3$ nanocrystals in quantum optics and information technologies.

Close

PrevNext

View figure in article

• Excitons
• Fine & hyperfine structure
• Surface & interfacial phenomena
• Quantum dots
• Surfaces
• Density functional theory