Pump-power tunable white upconversion emission in lanthanide-doped hexagonal NaYF4 nanorods

Pump-power tunable white upconversion (UC) emission under the excitation of a 980 nm laser diode from lanthanide-doped hexagonal NaYF4 nanorods synthesized by a hydrothermal method is reported. The calculated color coordinates reveal that the UC white color output from both the Yb3+–Ho3+–Tm3+ and Yb3+–Er3+–Tm3+ triply-doped systems can be fine-tuned for a wide range of pump-power densities, but each has its own superiority. The former has a broader response scope to pump-power densities for white emission and the simulated white color output can be tuned more precisely, whereas the latter has a much broader range of white color output under the same pump-power densities. These desirable properties make these Ln3+ doped hexagonal NaYF4 nanostructures promising in applications such as miniaturized solid-state light sources, multicolor three-dimensional display devices, optical processing sensors and multicolor labels for bioprobe and bioimaging.

Research highlights
► Yb3+-Er3+-Tm3+ and Yb3+-Ho3+-Tm3+ triply doped hexagonal NaYF4 nanorods were synthesized via a hydrothermal method.
► Bright white UC emissions were observed under the excitation of a 980 nm laser diode.
► White color output can be fine-tuned in a wide range of pump power densities.