Uncovering the Influence of Ni²⁺ Doping in Lead-Halide Perovskite Nanocrystals Using Optically Detected Magnetic Resonance Spectroscopy

Magnetic doping in halide perovskite semiconductors is of timely interest in the pursuit of new optical and magnetic properties that surpass those of the existing undoped materials. Here, we report a thorough investigation of the optical and magneto-optical properties of Ni2+-doped cesium lead halide perovskite with a chemical formula CsPb(Br1–xClx)3, implementing steady-state and transient photoluminescence (PL), polarized magneto-PL, and optically detected magnetic resonance (ODMR) spectroscopies. The magneto-PL measurements revealed three PL features with different degrees of circular polarization, associated with recombination from band-edge and trapping states. The ODMR measurements probed magnetic resonance transitions of photogenerated electrons and holes with phenomenological g-factors that deviate from those of band-edge states. Simulations of the ODMR spectra suggested carriers’ trapping in shallow traps with a slight anisotropic surrounding and with weak electron–hole exchange coupling. Furthermore, we observed substantial broadening of the hole resonance, due to its spin-exchange coupling with the Ni2+ unpaired spins. Overall, these ODMR measurements uncovered the role of the dopant in localizing photogenerated carriers by stiffening (becoming more rigid by decreasing the structural dynamics) the crystal structure and, for the first time, provide a direct observation of carrier-dopant spin exchange interactions in metal-halide perovskite nanocrystals. These results offer insight into the influence of magnetic dopants on the electronic structures of metal-halide perovskites, with a view toward emerging spin-based devices made from perovskites.