Synthesis and Characterization of Upconversion Fluorescent Yb3+, Er3+ Doped RbY2F7 Nano- and Microcrystals

Lanthanide-doped RbY2F7 nanocrystals with a mean diameter of approximately 10 rim were synthesized at 185 degrees C in the high boiling organic solvent N-(2-hydroxyethyl)-ethylenediamine (HEEDA) using ammonium fluoride, rare earth chlorides, and a solution of rubidium alkoxide of N-(2-hydroxyethyl)-ethylenediamine in HEEDA as precursors. Transmission electron microscopy images of the particles reveal that they are separated but have a broad size distribution ranging from 6 to 22 nm. Heat-treatment of these nanocrystals (600 degrees C for 45 min) led to bulk material which shows highly efficient light emission upon continuous wave (CW) excitation at 978 nm. As an alternative to the synthesis procedure carried out in the organic solvent HEEDA, we performed a microwave synthesis under hydrothermal conditions. This procedure led to the same composition of the material, but we obtained a marked increase of the particle size (60 nm). Apart from the optical properties, the structure and the morphology as well as the constitution of the three products were investigated by means of powder X-ray diffraction and X-ray fluorescence spectroscopy.