Compositionally\nTunable Magneto-optical Properties\nof Lead-Free Halide Perovskite Nanocrystals

Inorganic lead-free metal halide perovskites have garnered\nmuch\nattention as low-toxicity alternatives to lead halide perovskites\nfor luminescence and photovoltaic applications. However, the electronic\nstructure and properties of these materials, including the composition\ndependence of the band structure, spin–orbit coupling, and\nZeeman effects, remain poorly understood. Here, we investigated vacancy-ordered\nCs<sub>3</sub>Bi<sub>2</sub>X<sub>9</sub> (X= Cl, Br) perovskite nanocrystals\nusing magnetic circular dichroism spectroscopy. Our results indicate\nthat the excitonic spectra are predominantly composed of direct and\nindirect band gap transitions and that the Zeeman splitting energy\nof the direct exciton increases from 0.50 to 0.63 meV at 7 T by substituting\nBr for Cl. Comparison with analogous results for Cs<sub>2</sub>AgBiCl<sub>6</sub> nanocrystals, obtained by cation substitution, suggests an\nimportant effect of charge distribution within electronic bands on\nthe excitonic Zeeman splitting. This work demonstrates that the magneto-optical\nproperties of these materials can be effectively manipulated via chemical\ncomposition, suggesting promising applications in photonics, spintronics,\nand optoelectronics.