Orthogonal Upconversion Luminescence from Core/Shell-Structured Upconversion Nanophosphors

Abstract

Upconversion nanophosphors (UCNPs) are lanthanide ion-doped nanocrystals that exhibit anti-Stokes shift luminescence. Typically, UCNPs such as NaYF 4 :Yb,Er and NaYF 4 :Yb,Tm emit green and blue light under 980 nm near-infrared (NIR) light excitation. The emission color of lanthanide ion-doped UCNPs depends on the dopant ions in the host nanocrystals. Thus, one can adjust the dopant ions to control the upconversion (UC) luminescence color. For example, UC luminescence color can be tuned by co-doping activator ions into a single host nanocrystal and adjusting the ratio of two different activator ions. In addition, UC luminescence color can be tuned through energy migration UC process in core/shell-structured nanoparticles and by controlling the pulse of an NIR laser. Recently, orthogonal UC luminescence has been reported. In this study, UC luminescence color tuning is shown from the orthogonal UC luminescent UCNPs. To achieve orthogonal UC luminescence, core/multishell-structured UCNPs are synthesized. Depending on the excitation wavelength of NIR light, the UC luminescence color changes, and the core/multishell-structured UCNPs exhibit various UC luminescence colors by adjusting the excitation conditions. Finally, the feasibility of applying core/multishell-structured UCNPs in transparent displays is investigated.