Synthesis of ultra-small BaLuF5:Yb3+, Er3+@BaLuF5:Yb3+ active-core-activeshell nanoparticles with enhanced up-conversion and down-conversion luminescence by a layer-by-layer strategy

摘要

Ultra-small luminescent nanoparticles (NPs) are quite desirable for optoelectronic and biomedical applications. However, it is still a challenge to synthesize ultra-small NPs with high brightness owing to non-radiative energy losses caused by the surface defects as well as from vibrational deactivation ascribed to solvent molecules and ligands absorbed on the NPs. In this paper, we reported a strategy to improve up-and down-conversion luminescence of ultra-small BaLuF5:Yb3+, Er3+ NPs by using multilayer active-shells (containing Yb3+). Sub-10 nm BaLuF5:Yb3+, Er3+@(X-shell, X = 1-5) BaLuF5:Yb3+ NPs were synthesized via a high boiling solvent process through a layer-by-layer strategy. Up-and downconversion fluorescence spectra of the NPs were recorded and analyzed by using a 980 nm laser diode as the excitation source. In comparison with optical properties of BaLuF5:Yb3+, Er3+ NPs, the intensities of up-(similar to 545 nm) and down-conversion (similar to 1530 nm) fluorescence were enhanced by 52 and 9.8 times after coating 5-layer active-shells (BaLuF5: Yb3+) on the BaLuF5: Yb3+, Er3+ NPs, respectively. In addition, the intensities of up-and down-conversion fluorescence of the BaLuF5: Yb3+, Er3+ NPs with multi-layer active-shells were 1.3 and 1.1 times larger than those of the BaLuF5:Yb3+, Er3+ NPs with a one thick-layer active shell, respectively. These results showed that multi-layer active-shells could be used to not only suppress surface quenching but also transfer the pump light to the core region efficiently through Yb3+ ions inside the active-shells.