Blue Long Afterglow and Ultra Broadband Vis‐NIR Emission from All‐Inorganic Copper‐Doped Silver Halide Single Crystals

All-inorganic metal halides with afterglow emission have attracted increasing attention due to their significantly longer afterglow duration and higher stability compared to their organic-inorganic hybrid counterparts. However, their afterglow colors have not yet reached the blue spectral region. Here, we report all-inorganic copper-doped Rb₂AgBr₃ single crystals with ultralong blue afterglow (>300 s) by modulating defect states through doping engineering. The introduction of copper(I) ions into Rb₂AgBr₃ facilitates the formation of bromine vacancies, thus increasing the density of trap states available for charge storage and enabling bright, persistent emission after ceasing the excitation. Moreover, cascade energy transfer between distinct emissive centers in the crystals results in ultra-broadband photoluminescence, not only covering the whole white light with near-unity quantum yield but also extending into the near-infrared region. This 'cocktail' of exotic light-emission properties, in conjunction with the excellent stability of copper-doped Rb₂AgBr₃ crystals, allowed us to demonstrate their implementation to solid-state lighting, night vision, and intelligent anti-counterfeiting.