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International audience; We have calculated the exciton fine structure splittings (FSS) of asymmetric GaAs/AlGaAs quantum dots (QDs) obtained after Al droplet epitaxy and subsequent nanoholes formation followed by annealing and GaAs filling of nanoholes. We used a k • p model and considered the heavy-hole and light-hole mixing to calculate the electron-hole exchange interaction (EI). The two components, long-range (LR) and short-range (SR) of the EI, were deduced. The exciton fine structure is organized, as usual in zinc-blende compounds, into two groups of states: bright (optically active) and dark states. The bright-dark and bright-bright splittings contain LR and SR contributions, the LR part representing 5 to 68% of the total bright-dark splitting and 69 to 76% of the total bright-bright splitting for sizes experimentally explored. In QDs having C 2v symmetry, LR and SR contributions to dark-dark splitting have to be calculated at the second order of perturbation theory. A good agreement between the theory and experiment is obtained for QDs with different degrees of asymmetry, from QD having an isotropic shape to QD with a very anisotropic shape.

We investigate the theoretical band structure of organic–inorganic perovskites APbX3 with tetragonal crystal structure. Using D4h point group symmetry properties, we derive a general 16-band Hamilt...

International audience; Since their first synthesis in 2015, the all-inorganic lead halide perovskite nanocrystals CsPbX3(X=Cl,Br,I) have attracted a great deal of attention due to their outstanding electronic and optical properties as well as their performances, which outclass the ones of their II–VI conterparts in many application fields. In addition to these properties, the understanding of the emission features in these systems at the single object scale is crucial, e.g., for nanophotonics and quantum optics devices. Here, the details of the band-edge excitonic emission are theoretically explored. The contribution of the long-range exchange interaction to the bright-exciton splittings is computed in strong and weak confinement regimes using group theory arguments and k⋅p approximation. We show that the shape anisotropy with the real crystalline (cubic, tetragonal, or orthorhombic) structures of nanocrystals explain well their emission properties. In the weak confinement regime, splittings are inversely proportional to the cube of the exciton Bohr radius and we observe an increase of the splittings from iodide, to bromide, and then to chloride perovskite compounds. However, in the strong confinement regime, splittings increase inversely proportional to the nanocrystal volume and, for a given nanocrystal size, the splitting values are comparable for the three-halide-perovskite materials. The present theoretical developments lead to quantitative contributions in good agreement with available experimental data mainly in the weak confinement regime.