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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]

• NIR laser triggered UC emissions in glass-stabilized CsPbX 3 perovskites are realized. • The UC mechanism is radiative energy transfer from Tm: KYb 2 F 7 to CsPbX 3. • Tunable DS/UC combined luminescence is demonstrated via tailoring halogens in glass and selecting diverse excitation modes. • Visualized anti-counterfeits using screen-printable CsPbX 3 inks are practically applicable. • The luminescence of anti-counterfeiting patterns is well retained after storing in water for 30 days. Photon upconversion (UC) of perovskite nanocrystals (PeNCs) is an attractive topic and has been recently realized in colloidal solution. However, this scheme suffers from system instability owing to the easy decomposition of PeNCs, which will greatly limit their applications. This work reports the achievement of radiative energy transfer UC of glass-stabilized CsPbX 3 (X = Cl, Br, I) PeNCs triggered by Tm: KYb 2 F 7 NCs upon 980 nm near-infrared (NIR) laser excitation, which shows the advantages of superior long-term stability and enables them to find practical application. Both CsPbX 3 @glass and Tm: KYb 2 F 7 @glass nanocomposites are fabricated by an in-situ glass crystallization method, and their mixtures yield tunable downshifting/upconverting combined luminescence via tailoring halogen components in glass and selecting diverse excitation modes (UV, NIR or concurrent UV and NIR). Consequently, screen-printing multiple anti-counterfeiting patterns containing ultra-stable CsPbX 3 PeNCs with convenient encryption/decryption and excellent water resistance are experimentally demonstrated, providing a very high level of security. [ABSTRACT FROM AUTHOR]