Emission Quenching and Recovery of Illuminated Perovskite Quantum Dots Due to Iodide Ion Migration.

All-inorganic lead halide perovskite quantum dots (PQDs) are wellknown to easily lose their luminescence emission under light illumination, which is often attributed to a photoinduced degradation mechanism. Here, we demonstrate that such quenched emission of PQDs can completely recover in the dark at room temperature, which occurs through a spontaneous "self-healing" mechanism. Our findings indicate that the loss of emission under light illumination is not due to the generally accepted photoinduced degradation, as otherwise the complete recovery would not be possible. Instead, we attribute the emission loss and its subsequent recovery to the migration of iodide ions on the PQD surface. Under illumination, the iodide ions migrate out and associate to adjacent lead ions on the PQD surface, leading to halide vacancies, lattice distortions, and fluorescence quenching. During the recovery process, the migrated iodide ions spontaneously migrate back and fill halide vacancies, resulting in fluorescence recovery. The results of this study offer a useful solution on how to improve the emission and photostability of PQDs.