Enhancement of near-infrared to near-infrared upconversion luminescence in sub-10-nm ultra-small LaF(3):Yb(3+)/Tm(3+) nanoparticles through lanthanide doping.

Abstract

In this Letter, I present a versatile strategy to enhance the near-infrared to near-infrared (NIR-to-NIR) upconversion luminescence from sub-10-nm ultra-small LaF(3):Yb(3+)/Tm(3+) colloidal nanoparticles through lanthanide doping under 980 nm laser excitation. It is interesting that the NIR-to-NIR upconversion emission at 801 nm of LaF(3):Yb(3+)Tm(3+) nanoparticles can be improved by increasing the Tm(3+) doping concentration or by introducing another lanthanide activator (Er(3+) or Ho(3+)) as a sensitizer. The luminescence enhancement effect showed a strong dependence on the doping concentrations of activator ions (Tm(3+), Er(3+), or Ho(3+)). Particularly, adding 1 mol. % Ho(3+) ions into LaF(3):Yb(3+)Tm(3+) nanoparticles induced a 2.85-fold enhancement in NIR 801 nm emission of Tm(3+) ions. The related upconversion emission mechanisms were investigated and discussed.