Microtron electron beam enables post-synthetic defect engineering in ultrasmall ceria nanocrystals

This work explores high-dose MeV beam irradiation as a dopant-free, post-synthetic route to tune defect-related properties in 2-3 nm colloidal CeO₂ nanoparticles. Oleate/oleylamine-stabilised nanoceria were reproducibly prepared via degassing-controlled thermal decomposition in dibenzyl ether. After that, the CeO₂ nanoparticles were irradiated with a 16.5 MeV beam for 10, 40, and 80 min with nominal absorbed doses up to 171 ± 51 MGy while retaining crystalline fluorite cores. XPS and TEM-EELS analyses indicate the presence of irradiation-induced Ce³⁺/oxygen vacancy states, although spectral limitations prevent robust quantitative ranking of Ce³⁺. Surface-sensitive readouts show a non-monotonic response: the apparent optical bandgap narrows at the intermediate dose and partially recovers at the highest dose, accompanied by corresponding changes in the Urbach tail. In contrast, room-temperature magnetisation is substantially enhanced relative to pristine nanoceria and changes only weakly between the two highest-dose conditions. These observations suggest that defect centres persist within the nanoparticle volume even when the near-surface microstructure changes.