title: The effect of surface coating on energy migration-mediated upconversion.
abstract: Lanthanide-doped upconversion nanoparticles have been the focus of a growing body of investigation because of their promising applications ranging from data storage to biological imaging and drug delivery. Here we present the rational design, synthesis, and characterization of a new class of core-shell upconversion nanoparticles displaying unprecedented optical properties. Specifically, we show that the epitaxial growth of an optically inert NaYF(4) layer around a lanthanide-doped NaGdF(4)@NaGdF(4) core-shell nanoparticle effectively prevents surface quenching of excitation energy. At room temperature, the energy migrates over Gd sublattices and is adequately trapped by the activator ions embedded in host lattices. Importantly, the NaYF(4) shell-coating strategy gives access to tunable upconversion emissions from a variety of activators (Dy(3+), Sm(3+), Tb(3+), and Eu(3+)) doped at very low concentrations (down to 1 mol %). Our mechanistic investigations make possible, for the first time, the realization of efficient emissions from Tb(3+) and Eu(3+) activators that are doped homogeneously with Yb(3+)/Tm(3+) ions. The advances on these luminescent nanomaterials offer exciting opportunities for important biological and energy applications.
authors.affiliation: Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore.
authors.forename: Qianqian
authors.initials: Q
authors.lastname: Su
authors.forename: Sanyang
authors.initials: S
authors.lastname: Han
authors.forename: Xiaoji
authors.initials: X
authors.lastname: Xie
authors.forename: Haomiao
authors.initials: H
authors.lastname: Zhu
authors.forename: Hongyu
authors.initials: H
authors.lastname: Chen
authors.forename: Chih-Kai
authors.initials: CK
authors.lastname: Chen
authors.forename: Ru-Shi
authors.initials: RS
authors.lastname: Liu
authors.forename: Xueyuan
authors.initials: X
authors.lastname: Chen
authors.forename: Feng
authors.initials: F
authors.lastname: Wang
authors.forename: Xiaogang
authors.initials: X
authors.lastname: Liu
mesh_terms: D004735:Energy Transfer; D005459:Fluorides / Q000737:chemistry*; D056945:Hep G2 Cells; D006801:Humans; D028581:Lanthanoid Series Elements / Q000737:chemistry*; D049408:Luminescent Agents / Q000737:chemistry*; D053758:Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D013499:Surface Properties; D015019:Yttrium / Q000737:chemistry*
chemical_list: D028581:Lanthanoid Series Elements; D049408:Luminescent Agents; C525362:sodium yttriumtetrafluoride; D015019:Yttrium; D005459:Fluorides