Influence of NaYF(4) Inert and Active Layer on Upconversion Luminescence

NaYF(4):Yb,Er@NaYF(4) core–shell nanostructures were prepared to investigate their influence on upconversion (UC) luminescence. Tests revealed green radiation ((4)S(3/2)→(4)I(15/2)) and red radiation ((4)F(9/2)→(4)I(15/2)) first increased and then gradually decreased as Yb concentration increased in the NaYF(4) shell. The strongest fluorescent radiation occurred at an Yb concentration of 5%. To investigate the complicated variation of luminescence, we designed a set of experiments to study the impact of Yb ion concentration on luminescence intensity, and we analyzed the corresponding enhancement mechanism. It is probable that the energy transfers between both Yb and Er ions and Yb and Yb ions are involved in the UC processes. The enhancement of hybrid nanostructures has huge potential in biological detection and solar cells.