Frenkel Defect Responsive Upconversion Through High‐Energy Radiation

Abstract Near‐infrared light excitable upconversion nanocrystals are extensively applied in anticounterfeiting, optical imaging, and biomedicine, wherein many mechanistic endeavors are made to manipulate energy transfer through chemical engineering. However, how external stimuli such as high‐energy radiation (X‐ray) influence the energy transfer of these upconversion nanoparticles remains poorly understood. Here a new strategy for energy transfer modulation through X‐ray irradiation in Yb³⁺ and Tm³⁺ co‐doped nanoparticles is reported. Mechanistic studies indicate that X‐ray induced Frenkel defects in crystal lattices, other than the variation of lanthanide valence or crystal symmetry, lead to energy mismatch between adjacent Yb³⁺ sensitizers and the resultant inefficient energy transfer from sensitizers to activators. Based on these findings, high‐contrast X‐ray imaging and long‐term information storage (over 50 days) using nanoparticle‐containing flexible films are demonstrated. This work offers insights into the understanding of light‐matter interaction by high‐energy radiation and provides a promising methodology for long‐term information storage and X‐ray imaging.