Boosting X-Ray-Activated Persistent Luminescence in Nanoparticles Toward Highly Accurate Flexible X-Ray Imaging and Information Security

The X-ray activated persistent luminescence (PersL) observed in lanthanide-doped nanoparticles has recently attracted widespread interest in both basic research and cutting-edge applications. However, how to realize intense, rich, and color-tunable PersL in nanoparticles has remained a challenge. Here a conceptual strategy is reported to enhance the X-ray-activated PersL of nanoparticles by minimizing the hydroxyl impurities inside the host lattice. This study shows that the anhydrides/acids treatment during synthetic procedures is able to reduce the hydroxyl impurities inside fluoride nanocrystal lattice markedly, and promote the formation of Frenkel defects by moving more F⁻ ions from their lattice sites into interstitial sites under X-ray irradiation. A mechanism is proposed to illustrate the enhancement of PersL in hydroxyl-minimized nanoparticles. The radioluminescence is also enhanced, and the multimode luminescence in a single nanoparticle is further obtained by the core-shell nanostructure design with temporally tunable multi-colors output. These findings facilitate the development of small-size X-ray-activated PersL nanomaterials and provide more opportunities for their frontier applications in optical storage, information identification, and flexible optical imaging.