Near infrared to visible upconversion emission in Er3+/Yb3+ co-doped NaGd(WO4)2 nanoparticles obtained by hydrothermal method

The Er3+/Yb3+ co-doped NaGd(WO4)2 nanoparticles have been prepared by a simply hydrothermal synthesis procedure. The crystal structures and morphologies of the products were characterized by XRD, SEM and FT-IR spectroscopy. The average grain size of these samples depended on the annealing temperature, increasing with the increase of the temperature. The intense visible upconversion and near infrared luminescence of the Er3+/Yb3+ co-doped NaGd(WO4)2 nanoparticles under 975 nm excitation could be observed. The luminescence intensities of the samples depended on the size of the nanoparticles and Yb3+ concentration. The transition mechanisms of the upconversion emission can be ascribed to a two-photon absorption process.