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[Display omitted] • Effective Ni2+ doping in CsPbI 3 nanocrystals is achieved. • Ni2+ doping enables to stabilize cubic CsPbI 3 up to 7 months in atmosphere. • Ni2+ doping leads to significantly improve PLQY approaching near-unity. • Ni2+-doped perovskite LED outperforms the device using pristine CsPbI 3 nanocrystals. • The device exhibits a peak EQE of ~7% and a maximal luminance of 830 cd/m2. Room temperature phase instability of cubic CsPbI 3 perovskite nanocrystals is one of the notorious limitations for practical applications in optoelectronic fields. Herein, the incorporation of Ni2+ ions into CsPbI 3 lattice was successfully achieved by a modified hot-injection method using nickel acetate as doping precursor. The as-prepared Ni2+ (3.3 mol%): CsPbI 3 nanocrystals exhibited an improved, near-unity (95%~100%) photoluminescence quantum yield owing to the enhanced radiative decay rate and the decreased non-radiative decay rate. Additionally, Ni-doping was demonstrated to stabilize CsPbI 3 lattice and the Ni2+: CsPbI 3 film and colloidal solution can retain their red luminescence up to 15 days and 7 months in atmosphere, respectively. First-principle calculations verified that the significantly improved optical performance and stability of Ni2+: CsPbI 3 nanocrystals arose primarily from the increased formation energy due to the successful doping of Ni2+ in CsPbI 3. Benefiting from such an effective doping strategy, the as-prepared Ni2+-doped CsPbI 3 perovskite nanocrystals can function well as efficient red-light emitter toward the fabrication of high-performance perovskite LED with a peak external quantum efficiency of ~7%. [ABSTRACT FROM AUTHOR]