Superparamagnetism of Green Emissive Cs4PbBr6 Zero-Dimensional Perovskite Crystals

We report the characteristic magnetic behaviors of nonemissive (N416) and green emissive (G416) Cs4PbBr6 perovskite crystals. N416 exhibits a diamagnetic behavior, while G416 shows an additional superparamagnetic behavior, demonstrating the existence of paramagnetic electron spins in the G416. Although G416 and N416 crystals belong to the same rhombohedra unit cell with zero-dimensional (0D) connectivity of the [PbBr6](4-) octahedron, the G416 crystal has a smaller unit cell volume than N416. Cs-133 magic-angle-spinning NMR spectroscopy demonstrated the presence of defects in G416 and the extremely low concentration of a CsPbBr3 phase in both crystals. The DFT calculation results for the defected N416 crystal structure possessing Br vacancies included the experimentally observed blue shift of the high-energy optical band in the G416, which reinforces the existence of intrinsic defects in the G416. Our findings reveal that the unusual green emission and paramagnetic domains stem from structural defects in the 0D perovskites.