Morphology-dependent fluorescence of europium-doped cerium oxide nanomaterials

Europium-doped CeO₂ nanomaterials have been investigated for a variety of sensing and biological applications, as doping enhances the catalytic activity of CeO₂ and contributes visible fluorescence to the nanomaterial. However, scant evidence is available that directly compares Eu³⁺ fluorescence from multiple morphologies establishing useful correlation(s) between physical and optical trends in such structures. To address this shortcoming, Eu³⁺-doped CeO₂ nanorods, nanowires, nanocubes, and annealed nanorods were synthesized and characterized, representing a range of crystalline defect sizes, defect concentrations, and surface moieties. Morphologies rich with oxygen defects and hydroxyl groups (assessed via X-ray photoelectron spectroscopy) quenched the Eu³⁺ fluorescence, while samples with larger crystalline domains and lower Ce³⁺ concentrations have relatively stronger emission intensities. Of the four morphologies, nanocubes exhibit the strongest emission, as each structure is monocrystalline with few oxygen defects and associated quenching sites. Furthermore, the Eu³⁺ hypersensitive transition is more responsive to the dopant concentration in the nanocubes, as defects induced by the dopant are not removed by thermal annealing.