Synthetic Control over the Electron-Beam Stability of Upconverting Nanoparticles.

Qi, Xiao; Ercius, Peter; Schuck, P James; Cohen, Bruce E; Chan, Emory M · Nano Lett · 2026

basic_science · Level V

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Abstract

Electron microscopy (EM) is fundamental to nanocrystal characterization, but some structures degrade quickly under electron beams, limiting advanced structural characterization. Here, we introduce a synthetic strategy that combines layer-by-layer shell growth with in situ annealing to produce NaYb<sub>0.8</sub>Er<sub>0.2</sub>F<sub>4</sub> 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.