Synthesis and Characterization of Upconversion Fluorescent Yb3+, Er3+ Doped CsY2F7 Nano‐ and Microcrystals

Cs Y 2 F 7 : 78% Y 3+ , 20% Yb 3+ , 2% Er 3+ nanocrystals with a mean diameter of approximately 8 nm were synthesized at 185 ° C in the high boiling organic solvent N ‐(2‐hydroxyethyl)‐ethylenediamine (HEEDA) using ammonium fluoride, the rare earth chlorides and a solution of caesium alkoxide of N ‐(2‐hydroxyethyl)‐ethylenediamine in HEEDA. In parallel with this approach, a microwave assisted synthesis was carried out which forms nanocrystals of the same material, about 50 nm in size, in aqueous solution at 200 ∘ C/8 bar starting from ammonium fluoride, the rare earth chlorides, and caesium fluoride. In case of the nanocrystals, derived from the HEEDA synthesis, TEM images reveal that the particles are separated but have a broad size distribution. Also an occurred heat‐treatment of these nanocrystals (600 ∘ C for 45 minutes) led to bulk material which shows highly efficient light emission upon continuous wave (CW) excitation at 978 nm. Besides the optical properties, the structure and the morphology of the three products were investigated by means of powder XRD and Rietveld method.