Synthesis of Small Ce(3+)-Er(3+)-Yb(3+) Tri-Doped BaLuF(5) Active-Core-Active-Shell-Active-Shell Nanoparticles with Strong Down Conversion Luminescence at 1.5 μm

Small fluoride nanoparticles (NPs) with strong down-conversion (DC) luminescence at 1.5 μm are quite desirable for optical fiber communication systems. Nevertheless, a problem exists regarding how to synthesize small fluoride NPs with strong DC emission at 1.5 μm. Herein, we propose an approach to improve 1.5 μm emission of BaLuF(5):Yb(3+),Er(3+) NPs by way of combining doping Ce(3+) ions and coating multiple BaLuF(5): Yb(3+) active-shells. We prepared the BaLuF(5):18%Yb(3+),2%Er(3+),2%Ce(3+) NPs through a high-boiling solvent method. The effect of Ce(3+) concentration on the DC luminescence was systematically investigated in the BaLuF(5):Yb(3+),Er(3+) NPs. Under a 980 nm laser excitation, the intensities of 1.53 μm emission of BaLuF(5):18%Yb(3+),2%Er(3+),2%Ce(3+) NPs was enhanced by 2.6 times comparing to that of BaLuF(5):18%Yb(3+),2%Er(3+) NPs since the energy transfer between Er(3+) and Ce(3+) ions: Er(3+):(4)I(11/2) (Er(3+)) + (2)F(5/2) (Ce(3+)) → (4)I(13/2) (Er(3+)) + (2)F(7/2) (Ce(3+)). Then, we synthesized BaLuF(5):18%Yb(3+),2%Er(3+),2%Ce(3+)@BaLuF(5):5%Yb(3+)@BaLuF(5):5%Yb(3+) core-active-shell-active-shell NPs via a layer-by-layer strategy. After coating two BaLuF(5):Yb(3+) active-shell around BaLuF(5):Yb(3+),Er(3+),Ce(3+) NPs, the intensities of the 1.53 μm emission was enhanced by 44 times compared to that of BaLuF(5):Yb(3+),Er(3+) core NPs, since the active-shells could be used to not only suppress surface quenching but also to transfer the pump light to the core region efficiently through Yb(3+) ions inside the active-shells.