Sensitization and Protection of Lanthanide Ion Emission in In₂O₃:Eu Nanocrystal Quantum Dots

Lanthanide ions are visible to near-infrared ultranarrowband emitters with long luminescence lifetimes and thus have potential applications in lasing, up-conversion, and bioimaging. However, lanthanide ions have specific and narrow absorption bands characterized by small cross sections, and their luminescence is vibrationally quenched in common solvents. To address these limitations, lanthanide ions were incorporated into a semiconductor nanocrystal quantum dot host matrix, where the semiconductor matrix can sensitize the lanthanide ions toward absorption and reduce solvent quenching effects. Specifically, functional, colloidal europium-doped indium(III) oxide nanocrystal quantum dots were synthesized and characterized structurally and optically. Incorporation of the dopant ions into the matrix, rather than simple adhesion to the quantum dot surfaces, was demonstrated by applying a novel chemical extraction procedure utilizing ethylenediaminetetraacetic acid followed by quantitative elemental analysis. Sensitization and protection of europium ion emission by the indium(III) oxide semiconductor host were confirmed using photoluminescence excitation and time-resolved photoluminescence spectroscopies, respectively.