Microwave-assisted synthesis and single particle spectroscopy of infrared down-and visible up-conversion in Er3+ and Yb3+ co-doped fluoride nanowires

We report a comprehensive study on the influence of solvent and organic ligands on the up-converted emission characteristics of NaYF4 nanowires. We have modified the hydrothermal reaction procedure, and used a microwave flash heating method'' to obtain 1.5 mu m long and 100 nm wide up-converting NaYF4 nanowires. As-synthesized particles were dispersed in cyclohexane, and a ligand removal procedure has been performed leading to nanowires soluble in water and heavy water. The infrared emission of Er3+ ions was quenched through coupling to the vibrational modes of water molecules and the values of slopes of double logarithmic plots of power dependencies were changed. Besides the spectroscopic characterization of colloidal solutions of NaYF4 up-converting nanowires, we have also performed single particle studies of steady-state emission and luminescence kinetics. In the case of solvent-free separated particles, the ligand molecules provided the main nonradiative depopulation channels, and efficiently shortened the luminescence lifetimes. The output luminescence color also varied for colloidal solutions and single particle studies, which can be of importance for imaging and single particle tracking applications.