Multicolor upconversion luminescence in monodispersed Ba2LaF7:Ln3+ (Ln=Yb/Er and Yb/Tm) nanocrystals

Lanthanide-doped Ba2LaF7 nanocrystals have been successfully synthesized via a modified liquid–solid-solution process. The yielded nanocrystals are determined to be pure cubic Ba2LaF7 phase and consist of nearly square-shaped nanoparticles with an average 14 nm in size. The Yb3+/Er3+ (Tm3+) co-doped Ba2LaF7 nanocrystals emit bright multicolor upconversion luminescence following the excitation of 980 nm laser diode. Proposed mechanisms for the emission were analyzed based on the emission spectra and their dependence on pumping power, as well as corresponding energy level diagram.