Effect of Heterohalide Composition on the Dopant–Exciton Exchange Interactions in Mn ²⁺ -Doped Cesium Lead Halide Perovskite Nanocrystals

Lead halide perovskite quantum dots hold promise for applications in various quantum technologies, owing to their unique optical and electronic properties. The possibility of inducing excitonic Zeeman splitting in transition-metal-doped lead halide perovskites via dopant–carrier exchange interactions provides a foundation for their potential application in semiconductor spintronics. Therefore, it is crucial to devise different means to tune these exchange interactions and optimize the charge carrier spin polarization. Here, we used variable-field and variable-temperature magnetic circular dichroism spectroscopy to quantitatively probe excitonic Zeeman splitting in Mn2+-doped CsPb(Cl1–xBrx)3 nanocrystals having varying heterohalide compositions. We observed a significant increase in the spin-induced excitonic Zeeman splitting with increasing Br content, which is predominantly associated with anomalous kinetic exchange between Mn2+ d electrons and an s-orbital-derived valence band maximum. This giant kinetic exchange is attributed to admixing of p-like conduction band states into the valence band wave function, resulting in the valence band Zeeman splitting energy as high as 50 meV and the effective excitonic g-value (geff) as high as 550 for nanocrystals containing ca. 10% Br at the halide site. The estimated geff upon 10% Br alloying is nearly an order of magnitude higher than that for analogous Mn2+-doped CsPbCl3 nanocrystals. The results of this work demonstrate that dopant–exciton exchange interactions in diluted magnetic lead halide perovskite nanocrystals are highly sensitive to the host lattice heterohalide composition. The ability to generate a tunable giant excitonic Zeeman splitting in lead halide perovskite nanocrystals by heterohalide composition renders these materials highly promising for spintronic and other quantum technology applications.