Synthetic Control over the Electron-Beam Stability of Upconverting Nanoparticles

alloyed upconverting nanoparticles (UCNPs) with enhanced structural stability and optical properties. Using an automated synthesis platform to control precursor delivery and annealing cycles, high rare-earth ion concentrations are maintained during shell growth and annealing at high temperature, reducing luminescence quenching and degradation under electron beams. This in situ annealing layer-by-layer (ISA-LBL) approach gives rise to alloyed UCNPs (aUCNPs) with exceptional electron-beam stability, reducing beam-induced fractures and voids by >90% compared to conventionally synthesized aUCNPs. ISA-LBL aUCNPs also exhibit enhanced photoluminescence intensity and extended lifetimes, consistent with fewer quenching defects. This demonstrates a synthetic route to nanocrystals with enhanced structural integrity, increasing their compatibility with EM studies and their utility in ionizing environments.