Controlled-Synthesis, Self-Assembly Behavior, and Surface-Dependent Optical Properties of High-Quality Rare-Earth Oxide Nanocrystals

Abstract

Single-crystalline and monodisperse cubic rare-earth (RE = La to Lu, Y) oxide nanocrystals (ultrathin nanoplates and nanodisks) have been synthesized via a nonhydrolytic approach in oleic acid (OA)/oleylamine (OM)/1-octadecene (ODE) using various rare-earth complexes, including acetylacetonate, benzoylacetonate, and acetate, as the precursors. The transformation from the complex precursors to RE 2 O 3 was proposed to occur in two stages: first, the formation of rare-earth oleates by ligand exchange in solution, and second, the subsequent decomposition of the oleates into RE 2 O 3 catalyzed by the base of OM. The selective adsorption of coordinating OA ligands onto specific crystal planes of cubic RE 2 O 3 nanocrystals made them adopt a plate shape with the confined growth of {100} facets and/or a disk shape with the confined growth of {111} facets. Along with delicately tuning the polarity of the dispersant, the RE 2 O 3 nanocrystals could be aligned to form “side-to-side” or “face-to-face” self-assembly nanoarrays on carbon-coated copper grids. With the developed synthetic method, we also obtained high-quality luminescent Y 2 O 3:Eu ultrathin nanodisks, which displayed strong surface-dependent, highly pure red emissions that were due to selective incorporation of Eu 3+ ions in the surface of the nanodisks.