title: Synthesis of 10 nm β-NaYF4:Yb,Er/NaYF4 Core/Shell Upconversion Nanocrystals with 5 nm Particle Cores.
abstract: A new method is presented for preparing gram amounts of very small core/shell upconversion nanocrystals without additional codoping of the particles. First, ca. 5 nm β-NaYF4:Yb,Er core particles are formed by the reaction of sodium oleate, rare-earth oleate, and ammonium fluoride, thereby making use of the fact that a high ratio of sodium to rare-earth ions promotes the nucleation of a large number of β-phase seeds. Thereafter, a 2 nm thick NaYF4 shell is formed by using 3-4 nm particles of α-NaYF4 as a single-source precursor for the β-phase shell material. In contrast to the core particles, however, these α-phase particles are prepared with a low ratio of sodium to rare-earth ions, which efficiently suppresses an undesired nucleation of β-NaYF4 particles during shell growth.
authors.affiliation: Institute of Chemistry of New Materials, University of Osnabrück, Barbarastrasse 7, 49076, Osnabrück, Germany.
authors.forename: Thorben
authors.initials: T
authors.lastname: Rinkel
authors.affiliation: Institute of Chemistry of New Materials, University of Osnabrück, Barbarastrasse 7, 49076, Osnabrück, Germany.
authors.forename: Athira Naduviledathu
authors.initials: AN
authors.lastname: Raj
authors.affiliation: Institute of Chemistry of New Materials, University of Osnabrück, Barbarastrasse 7, 49076, Osnabrück, Germany.
authors.forename: Simon
authors.initials: S
authors.lastname: Dühnen
authors.affiliation: Institute of Chemistry of New Materials, University of Osnabrück, Barbarastrasse 7, 49076, Osnabrück, Germany. markus.haase@uni-osnabrueck.de.
authors.forename: Markus
authors.initials: M
authors.lastname: Haase
keywords: core/shell nanocrystals; lanthanides; luminescence; nanoparticles; upconversion