White light upconversion of nanocrystalline Er/Tm/Yb doped tetragonal Gd4O3F6

Er³⁺, Tm³⁺ and Yb³⁺ codoped gadolinium oxyfluoride nanoparticles were prepared in aqueous solution by a simple coprecipitation method, under alkaline conditions. After a suitable heat treatment at 500 °C, the nanocrystalline powders were found to be single phase tetragonal Gd₄O₃F₆ after a structural characterization using X-ray powder diffraction. Transmission electron microscopy images showed that the average size of the nanoparticles was approximately 50 nm. Following appropriate lanthanide ion doping, the nanocrystals show bright white light upconversion upon excitation at 980 nm using a diode laser as the excitation source.