Long-lasting far-UVC persistent luminescence for solar-blind optical tagging†

Far ultraviolet-C (far-UVC; 200–230 nm) luminescent materials have garnered significant interest in recent years, driven by the growing demands for applications such as disinfection and solar-blind imaging due to their distinct wavelength features. However, the research and development of far-UVC persistent phosphors are lacking. Here, we report the realization of far-UVC persistent luminescence in CaSO₄:Pr³⁺ and CaSO₄:Pb²⁺ phosphors, which show emissions peaking at 220 nm and 230 nm with a long persistence time of >24 h after ceasing X-ray excitation. This is by far the shortest UVC afterglow emission to the best of our knowledge. The far-UVC afterglow from the charged phosphors can be readily detected using a solar-blind UV camera in both indoor-lighting and outdoor environments owing to the absence of background noise from ambient light. The continuous photostimulation of indoor white LED light and outdoor sunlight has different impacts on the far-UVC afterglow performance of CaSO₄:Pr³⁺ and CaSO₄:Pb²⁺ phosphors, which is elucidated by the decay time-dependent thermoluminescence (TL) curves under different light conditions. This study expands the field of persistent luminescence to the far-UVC spectral region and will inspire the discovery of more excellent far-UVC persistent phosphors.