Controlled-synthesis, self-assembly behavior, and surface-dependent optical properties of high-quality rare-earth oxide nanocrystals

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 RE2O3 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 RE2O3 catalyzed by the base of OM. The selective adsorption of coordinating OA ligands onto specific crystal planes of cubic RE2O3 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 RE2O3 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 Y2O3:Eu ultrathin nanodisks, which displayed strong surface-dependent, highly pure red emissions that were due to selective incorporation of Eu3+ ions in the surface of the nanodisks.