Nr. 4 / 2015
11. Dezember 2015 : Synthesis of 10 nm β-NaYF4:Yb,Er/NaYF4 Core/Shell // Upconversion Nanocrystals with 5 nm Particle Cores
Thorben Rinkel, Athira Naduviledathu Raj, Simon Dühnen and Markus Haase*
A new method is presented for preparing gram amounts of very small core/shell upconversion nanocrystals without additional codoping of the particles. First, ~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 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.
[*] T. Rinkel, A. N. Raj, S. Dühnen, Prof. Dr. M. Haase
Institute of Chemistry of New Materials
University of Osnabrück
Barbarastraße 7, 49076 Osnabrück (Germany)
[**] We thank Dr. K. Kömpe and H. Eickmeier for the TEM investigations and Dr. B. Herden and Prof. Dr. T. Jüstel for the solid-state synthesis of NaYF4:Yb(18%),Er(2%) powder phosphor.
Angew. Chem. Int. Ed., (2015) DOI: 10.1002/anie.201508838
Angew. Chem., (2015) DOI: 10.1002/ange.201508838