Enhanced upconversion luminescence in NaYF4:Yb, Er nanoparticles by using graphitic carbon shells

Upconversion nanoparticles (UCNPs) have drawn much attention in the past decade due to their superior physicochemical features and great potential in biomedical. However, practical applications of upconversion luminescence are often limited by its relatively low luminescence efficiency. In this paper, we designed and synthesized NaYF4:Yb, Er nanoparticles using a hydrothermal approach, and thereafter it was coated with a thin layer of graphitic carbon to form a core/shell nanostructure via a controlled chemical vapor deposition process. It is shown that Yb and Er doped in the crystal of NaYF4 in the forms ofYb(3+) and Er3+. The thickness of the graphitic carbon shell is close to 0.45 nm, and this corresponds between one and two atomic layers. The graphitic carbon shell not only leads to a significant enhancement in the emission intensity but also provide a longer luminescence decay lifetime compared to bare NaYF4:Yb, Er nanoparticles. Our finding provides a new strategy to remarkably improve fluorescence upconversion, and opportunities for diverse applications requiring high fluorescence intense.