Dual-Emission and Two Charge-Transfer States in Ytterbium-doped Cesium Lead Halide Perovskite Solid Nanocrystals

Some unusual phenomena besides near-infrared emission of Yb3+ ions have been observed in ytterbium-doped perovskite solid nanocrystals. A systematic study on doping kinetic and energy-transfer processes is presented. The observed unique dual-peak photoluminescence (PL) emission of perovskite nanocrystals in the visible region can be attributed to radiative recombination in the near-surface region and the interior region of the perovskite nanocrystals, respectively. Insightful studies based on dual-peak PL emission clarify the kinetic process of doping in perovskite nanocrystals. Once the dopant concentration of rare earth ions in the near-surface region is more than a certain value, the dopant ions start to immerse into the interior region of the host nanocrystals. The unusual excitation spectra of ytterbium-doped perovskite solid nanocrystals could be explained by the presence of two charge-transfer (CT) states at ∼24 000 cm–1 (CT1) and ∼21 460 cm–1 (CT2), and both of them could be observed in the near-surface region of the perovskite host. Furthermore, the lifetime of the near-infrared emission of Yb3+ ions through the CT2 is three orders faster than that through CT1 (in millisecond), which should be fixed on the surface of the perovskite nanocrystals. The results provide essential insights into the dynamic carrier behaviors and surface effects of all inorganic perovskite nanocrystals doped with rare earth ions for expanded functionality.