title: Simultaneous phase and size control of upconversion nanocrystals through lanthanide doping.
abstract: Doping is a widely applied technological process in materials science that involves incorporating atoms or ions of appropriate elements into host lattices to yield hybrid materials with desirable properties and functions. For nanocrystalline materials, doping is of fundamental importance in stabilizing a specific crystallographic phase, modifying electronic properties, modulating magnetism as well as tuning emission properties. Here we describe a material system in which doping influences the growth process to give simultaneous control over the crystallographic phase, size and optical emission properties of the resulting nanocrystals. We show that NaYF(4) nanocrystals can be rationally tuned in size (down to ten nanometres), phase (cubic or hexagonal) and upconversion emission colour (green to blue) through use of trivalent lanthanide dopant ions introduced at precisely defined concentrations. We use first-principles calculations to confirm that the influence of lanthanide doping on crystal phase and size arises from a strong dependence on the size and dipole polarizability of the substitutional dopant ion. Our results suggest that the doping-induced structural and size transition, demonstrated here in NaYF(4) upconversion nanocrystals, could be extended to other lanthanide-doped nanocrystal systems for applications ranging from luminescent biological labels to volumetric three-dimensional displays.
authors.affiliation: Department of Chemistry, National University of Singapore, 117543, Singapore.
authors.forename: Feng
authors.initials: F
authors.lastname: Wang
authors.forename: Yu
authors.initials: Y
authors.lastname: Han
authors.forename: Chin Seong
authors.initials: CS
authors.lastname: Lim
authors.forename: Yunhao
authors.initials: Y
authors.lastname: Lu
authors.forename: Juan
authors.initials: J
authors.lastname: Wang
authors.forename: Jun
authors.initials: J
authors.lastname: Xu
authors.forename: Hongyu
authors.initials: H
authors.lastname: Chen
authors.forename: Chun
authors.initials: C
authors.lastname: Zhang
authors.forename: Minghui
authors.initials: M
authors.lastname: Hong
authors.forename: Xiaogang
authors.initials: X
authors.lastname: Liu
mesh_terms: D003116:Color; D003460:Crystallization; D005459:Fluorides / Q000737:chemistry; D028581:Lanthanoid Series Elements / Q000032:analysis / Q000737:chemistry*; D049449:Luminescence; D008163:Luminescent Measurements; D046529:Microscopy, Electron, Transmission; D053758:Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D055620:Optical Phenomena; D010316:Particle Size; D015019:Yttrium / Q000737:chemistry
chemical_list: D028581:Lanthanoid Series Elements; C525362:sodium yttriumtetrafluoride; D015019:Yttrium; D005459:Fluorides