Colloidal synthesis and remarkable enhancement of the upconversion luminescence of BaGdF5:Yb3+/Er3+nanoparticles by active-shell modification

Abstract

BaGdF₅:Yb³⁺/Er³⁺ colloidal nanoparticles (NPs) with tunable average particle diameters from 3 to 10 nm in different solvents were first prepared by thermal decomposition method. X-Ray diffraction (XRD), transmission electron microscopy (TEM) and upconversion (UC) luminescence spectra were used to characterize the resulting samples. After coating the active shell (containing Yb³⁺) around the BaGdF₅:Yb³⁺/Er³⁺ NPs, not only their morphology and monodisperse properties were well maintained but also the relative UC luminescence intensity was enhanced remarkably. In contrast to the pure BaGdF₅:Yb³⁺/Er³⁺ core, the luminescence intensity of the active-shell coated NPs can be enhanced several hundred times. Unexpectedly, the luminescence intensity of the active-core/active-shell NPs was about four times as high as that of β-NaYF₄:Yb³⁺/Er³⁺ NPs under the same doping concentration and measurement conditions. Moreover, the luminescence colors of the active-core/active-shell NPs can be tuned from green to yellow by multilayer active-shell coating under 980 nm laser excitation.