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 BaLuF₅:Yb3+,Er3+ NPs by way of combining doping Ce3+ ions and coating multiple BaLuF₅: Yb3+ active-shells. We prepared the BaLuF₅:18%Yb3+,2%Er3+,2%Ce3+ NPs through a high-boiling solvent method. The effect of Ce3+ concentration on the DC luminescence was systematically investigated in the BaLuF₅:Yb3+,Er3+ NPs. Under a 980 nm laser excitation, the intensities of 1.53 μm emission of BaLuF₅:18%Yb3+,2%Er3+,2%Ce3+ NPs was enhanced by 2.6 times comparing to that of BaLuF₅:18%Yb3+,2%Er3+ NPs since the energy transfer between Er3+ and Ce3+ ions: Er3+:⁴I11/2 (Er3+) + ²F5/2 (Ce3+) → ⁴I13/2 (Er3+) + ²F7/2 (Ce3+). Then, we synthesized BaLuF₅:18%Yb3+,2%Er3+,2%Ce3+@BaLuF₅:5%Yb3+@BaLuF₅:5%Yb3+ core-active-shell-active-shell NPs via a layer-by-layer strategy. After coating two BaLuF₅:Yb3+ active-shell around BaLuF₅:Yb3+,Er3+,Ce3+ NPs, the intensities of the 1.53 μm emission was enhanced by 44 times compared to that of BaLuF₅:Yb3+,Er3+ 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 Yb3+ ions inside the active-shells.
Keywords: 1.5 μm; BaLuF5; active-shell; core-shell; down conversion luminescence; nanoparticles.