title: Prevalence of anisotropic shell growth in rare earth core-shell upconversion nanocrystals.
abstract: Through a series of carefully executed experiments, we discovered the prevalence of anisotropic shell growth in many upconversion NaREF4 systems caused by a combination of factors: selective adsorption of ligands on the core surface due to the core crystal structure, ligand etching, and the lattice mismatch between core and shell components. This could lead to incomplete shell formation in core-shell nanocrystals under certain conditions. Shell growth is always faster in the a and b crystallographic directions than in the c direction. In the case of a larger lattice mismatch between the core and shell, shell growth only occurs in the a and b directions resulting in an oblong core-shell structure. These findings are useful for rationalizing shell-dependent emission properties, understanding the emission mechanisms in complex core-shell nanostructures, and for creating accurate models of core-shell designs for multifunctionality and optimal performance in applications.
authors.affiliation: Department of Chemical and Biomolecular Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260, Republic of Singapore.
authors.forename: Chao
authors.initials: C
authors.lastname: Zhang
authors.forename: Jim Yang
authors.initials: JY
authors.lastname: Lee
mesh_terms: D016880:Anisotropy; D008163:Luminescent Measurements; D008674:Metals, Rare Earth / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D053758:Nanoparticles / Q000737:chemistry*
chemical_list: D008674:Metals, Rare Earth