Enhanced afterglow blue emissions from atomically confined excitons in Pb(II)-doped cadmium-based metal halides

All-inorganic metal halide perovskites possess significant potentiality in lighting, bioimaging, and optical anti-counterfeiting due to their exceptional and unique properties. However, the exploration of efficient, robustly stable, and long-persistent luminescent blue light-emitting materials poses huge challenges, especially in understanding their electronic structure and photophysical processes. In this work, high-purity Pb2+-doped CsCdCl3 crystals were synthesized using a straightforward hydrothermal method. Parts of Pb2+ ions replaced partial Cd2+ sites in the face-sharing octahedra and formed atomically confined excitons around the Pb(II) octahedra. This exciton could emit blue light (423 nm) at room temperature with an enhanced radiation transition probability at a nearly 90% quantum yield. The incorporation of Pb2+ and confined exciton formation not only shifted the emission color region from weak orange to strong blue but also exhibited intrinsic afterglow behavior as CsCdCl3 perovskite. The Raman spectra and TL spectra indicated their polaronic states corresponding to the A1g 244 cm−1 phonon mode coupling to electron, which dominated their afterglow processes in undoped and doped CsCdCl3. These findings could not only facilitate the understanding of atomically confined excitons around dopant ions as dominant emission centers to tune emission color in halide semiconductors, unveiling the nature of afterglow phenomena in this halide material, but could also find unique applications in optical devices.