Synthetic Control over the Electron-Beam Stability of Upconverting Nanoparticles

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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 NaYb0.8Er0.2F4 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.
Funding Information
  • Chemical Sciences, Geosciences, and Biosciences Division (DE-AC02-05CH11231)
  • Defense Sciences Office, DARPA (HR0011365551)
  • Biological and Environmental Research (DE-AC02-05CH11231)
  • Biological and Environmental Research (DE-SC0025297)

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