Establishing the Structural Integrity of Core–Shell Nanoparticles against Elemental Migration using Luminescent Lanthanide Probes

Core–shell structured nanoparticles are increasingly used to host luminescent lanthanide ions but the structural integrity of these nanoparticles still lacks sufficient understanding. Herein, we present a new approach to detect the diffusion of dopant ions in core–shell nanostructures using luminescent lanthanide probes whose emission profile and luminescence lifetime are sensitive to the chemical environment. We show that dopant ions in solution‐synthesized core–shell nanoparticles are firmly confined in the designed locations. However, annealing at certain temperatures (greater than circa 350 °C) promotes diffusion of the dopant ions and leads to degradation of the integrity of the nanoparticles. These insights into core–shell nanostructures should enhance our ability to understand and use lanthanide‐doped luminescent nanoparticles.