X-ray-activated UVA long persistent luminescence from defective fluoride elpasolites

Long persistent phosphors have received significant attention owing to their attractive photophysical properties. Here, we report a new long persistent phosphor exhibiting strong ultraviolet A (UVA) afterglow . The phosphors were synthesized by a solid-state reaction method. We find that the obtained phosphors demonstrate super long UVA-afterglow emissions after irradiation by X-ray source, and the afterglow can last more than 50 h. A wide range of experimental characterizations indicate that the Tb 3+ doped fluoride elpasolite phosphors are defective and some fluoride ions are replaced by oxygen ions , which creates electron traps with suitable trap depths. Our results establish that Tb 3+ can act as optical emitters in wide-bandgap hosts that can result in the UVA afterglow. This work enriches the bank of UV long persistent phosphors, and may stimulate more efforts for the design and synthesis of this kind of optical materials .