Weak Magnetic Field-Dependent Optical Properties of Lead Bromide Perovskites*

The strong spin-orbit coupling in lead halide perovskites, when inversion symmetry is lifted, has provided opportunities for investigating the Rashba effect in these systems. Moreover, the strong orbital moment plays a significant role in enhancing the optoelectronic properties in the presence of external magnetic fields in lead halide perovskites. Here, we evaluate the effect of weak magnetic fields (< 1 T) on the photoluminescence (PL) properties of CsPbBr₃ nanocrystals (NCs) and single crystal of CH₃NH₃PbBr₃. Along with an enhancement in the PL intensity as a function of an external magnetic field, which is observed in both lead bromide perovskites, the PL emission red-shifts in CsPbBr₃ NCs. Density-functional theory calculations of the electronic band-edge in CsPbBr₃ show almost no change in the energy gap as a function of the external magnetic field. The experimental results thus suggest the role of mixing of the triplet and singlet excitonic states under weak magnetic fields. This is further deduced from an enhancement in PL lifetimes as a function of the field in CsPbBr₃. In CH₃NH₃PbBr₃, an increase in PL intensity is observed under weak magnetic fields; however, no changes in the peak energy or PL lifetimes are observed.