Synthesis of hollow and aggregated CeO₂:Sm³⁺ microspheres and their redox-responsive luminescence

Hollow and aggregated microspheres of an Sm³⁺-doped CeO₂ phosphor material were synthesized by liquid processes using organic materials as a template and a structure-directing agent, respectively The microstructure of both the microspheres obtained were characterized as their crystallite size and specific surface area because they were comprised of CeO₂:Sm³⁺ nanocrystals approximately 20 nm in size. The microspheres showed orange luminescence due to electronic transitions of the Sm³⁺ ions upon excitation with ultraviolet light. The luminescence intensity was decreased when the microspheres were treated with an aqueous L(+)-ascorbic acid solution as a reductant. The intensity was then recovered by treating the microspheres with an H₂O₂ solution as an oxidant. Such the redox-responsive luminescence switching is promising for sensing applications if the sensitivity can be controlled well. The relationship between the structural features of the microspheres and the luminescence switching property was then examined in detail.