Doping of semiconductors by introducing foreign atoms enables their widespread applications in microelectronics and optoelectronics. We show that this strategy can be applied to direct bandgap lead-halide perovskites, leading to the realization of ultrawide photoluminescence (PL) at new wavelengths enabled by doping bismuth (Bi) into lead-halide perovskites. Structural and photophysical characterization reveals that the PL stems from one class of Bi doping-induced optically active center, which is attributed to distorted [PbI6] units coupled with spatially localized bipolarons. Additionally, we find that compositional engineering of these semiconductors can be employed as an additional way to rationally tune the PL properties of doped perovskites. Finally, we accomplished the electroluminescence at cryogenic temperatures by using this system as an emissive layer, marking the first electrically driven devices using Bi-doped photonic materials. Our results suggest that low-cost, earth-abundant, solution-processable Bi-doped perovskite semiconductors could be promising candidate materials for developing optical sources operating at new wavelengths.

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Bismuth-doped luminescent materials have gained significant attention in the past years owing to their huge potential for the applications in telecommunications, biomedicine, and displays. However, the controlled synthesis of these materials, in particular for those luminescing in the near-infrared (NIR), remains a challenging subject of continuous research effort. Herein, we show that the low-temperature topotactic reduction by using Al metal powders as oxygen getters can be adopted as a powerful technique for the conversion of bismuth-doped red-emitting systems into NIR-emitting cousins as a result of the creation of unique crystalline networks. Thorough experimental characterization indicates that the framework oxygen of hosts can be topotactically extracted, thus producing unique metal-oxygen-metal networks in the reduced phases while preserving the crystalline structure of the precursor. Furthermore, X-ray absorption spectroscopy reveals that Bi atoms substitute for both Ba 2+ and P 5+ /B 3+ in BaBPO5 crystals, and subsequent topotactic treatment preferentially changes the local environment of Bi at P 5+ /B 3+ sites, which results in the occurrence of NIR emission owing to the creation of NIR-luminescent, defective Bi-O polyhedra in which Bi bears lower oxidation states with respect to that in the precursor. The site-specific topotactic reduction reaction reported here helps us create peculiar NIR-luminescent Bi-O units, and simultaneously does not seriously affect the red photoluminescence from Bi 2+ situated at the Ba 2+ sites. Given the long-lived, ultrawide NIR emission covering the second biological windows, the phosphors developed here hold great promise for in vivo luminescence and lifetime bioimaging. We anticipate that this low-temperature topotactic reduction strategy can be applied to the development of more novel Bi-doped luminescent materials in various forms that can find a broad range of functional applications.