Correlation between Sm3+optical absorption and disorder build-up in swift heavy ion-irradiated CeO2nanoparticles.

Diffuse reflectance spectroscopy was used to study undoped and Sm-doped CeO2nanoparticles prepared by sol-gel and ball-milling routes, and to probe radiation damage induced by swift heavy ions. Kubelka-Munk analysis of UV-vis-NIR spectra reveals nine Sm3+4f-4f absorption bands within the wide O 2p-Ce 4f band gap, with intensities that increase with Sm content and remain broad owing to low local symmetry and native disorder. Under 946 MeV Au irradiation up to 5 × 1012cm-2, ball-milled Sm-doped samples exhibit a systematic fluence-dependent decrease of Sm3+band intensities, without significant changes in bandwidth or peak positions, indicating that irradiation primarily weakens the local crystal field rather than altering site multiplicity. In parallel, the Urbach energy of the absorption edge increases, providing an optical measure of disorder build-up and yielding approximate damage cross sections consistent with electronically driven track formation. A weak Ce3+4f-5 d band near 15 000 cm-1appears in irradiated undoped CeO2but is absent in Sm-doped samples, in agreement with oxygen-potential pinning by charge-compensating vacancies. Overall, the data indicate that Sm3+absorption bands are sensitive optical probes of irradiation-induced disorder in nanocrystalline ceria and highlight the utility of rare-earth dopants for tracking radiation damage in fluorite-type oxide nanoparticles.