Phosphors emitting visible and near-infrared persistent luminescence have been explored extensively owing to their unusual properties and commercial interest in their applications such as glow-in-the-dark paints,optical information storage,and in vivo bioimaging.However,no persistent phosphor that features emissions in the ultraviolet C range (200-280 nm) has been known to exist so far.Here,we demonstrate a strategy for creating a new generation of persistent phosphor that exhibits strong ultraviolet C emission with an initial power density over 10 milliwatts per square meter and an afterglow of more than 2 h.Experimental characterizations coupled with first-principles calculations have revealed that structural defects associated with oxygen introduction-induced anion vacancies in fluoride elpasolite can function as electron traps,which capture and store a large number of electrons triggered by X-ray irradiation.Notably,we show that the ultraviolet C afterglow intensity of the yielded phosphor is sufficiently strong for sterilization.Our discovery of this ultraviolet C afterglow opens up new avenues for research on persistent phosphors,and it offers new perspectives on their applications in terms of sterilization,disinfection,drug release,cancer treatment,anti-counterfeiting,and beyond.