Restructuring and remodeling of NaREF4 nanocrystals by electron irradiation

NaREF4 nanocrystals are found to be highly manipulable by electron beam irradiation. With 200 kV electron beam irradiation, both 14.6 nm spherical NaGdF4 :Yb,Er nanoparticles and 44.7 nm × 34.1 nm ellipsoidal NaYF4 :Yb,Er nanorods form hollow structures and eventually convert to the corresponding REF3 upon prolonged irradiation. Furthermore, the NaYF4 nanorods fractured with irradiation with a 100 kV electron source are found to be subsequently self-healed when irradiated with a 200 kV source. The detailed experimental results, in combination with theoretical analysis, suggest that knock-on effects, specific lattice energy, and the inherently low surface energy of NaREF4 collectively contribute to the formation of the hollow structures. These mechanisms allow controlled engineering and manipulation of RE nanomaterials on the nanometer scale.