Negatively Charged and Dark Excitons in CsPbBr Perovskite Nanocrystals Revealed by High Magnetic Fields.

The optical properties of colloidal cesium lead halide perovskite (CsPbBr) nanocrystals are examined by time-resolved and polarization-resolved spectroscopy in high magnetic fields up to 30 T. We unambiguously show that at cryogenic temperatures the emission is dominated by recombination of negatively charged excitons with radiative decay time of 300 ps. The additional long-lived emission, which decay time shortens from 40 down to 8 ns and in which the decay time shortens and relative amplitude increases in high magnetic fields, evidences the presence of a dark exciton. We evaluate g-factors of the bright exciton g = +2.4, the electron g = +2.18, and the hole g = -0.22.