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High‐quality backlit display puts forward urgent demand for color‐converting materials. Recently, metal halide perovskites (MHPs) with full spectral tunability, high photoluminescence quantum yields (PLQYs), and high color purity have found potential application in wide‐color‐gamut display. Regrettably, naked MHPs suffer from long‐term instable issue and cannot pass harsh stability tests. Herein, amorphous‐glass‐protected green/red CsPbX3 quantum dots (QDs) are prepared by elaborately optimizing glass structure, perovskite concentration, and in situ crystallization. PLQYs of green CsPbBr3@glass and red CsPbBr1.5I1.5@glass reach 94% and 78%, respectively, which are the highest ones of CsPbX3@glass composites reported so far and comparable to colloidal counterparts. Benefited from complete isolation of QDs from external environment by glass network, CsPbX3@glass can endure harsh commercial standard aging tests of 85 °C/85%RH and blue‐light‐irradiation, which are applied to construct white light‐emitting diodes (wLEDs) with high external quantum efficiency of 13.8% and ultra‐high luminance of 500 000 cd m−2. Accordingly, the perovskite wLED arrays‐based backlit unit and a prototype display device are designed for the first time, showing more vivid and wide‐color‐gamut feature benefited from narrowband emissions of CsPbX3 QDs. This work highlights practical application of CsPbX3@glass composite as an efficient and stable light color converter in backlit display. [ABSTRACT FROM AUTHOR]

[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]