Epitaxial growth of ultrathin layers on the surface of sub-10 nm nanoparticles: the case of β-NaGdF4:Yb/Er@NaDyF4 nanoparticles

Abstract

Upconversion core–shell nanoparticles have attracted a large amount of attention due to their multifunctionality and specific applications. In this work, based on a NaGdF₄ sub-10 nm ultrasmall nanocore, a series of core–shell upconversion nanoparticles with uniform size doped with Yb³⁺, Er³⁺ and NaDyF₄ shells with different thicknesses were synthesized by a facile sequential growth process. NaDyF₄ coated upconversion luminescent nanoparticles showed an obvious fluorescence quenching under excitation at 980 nm as a result of energy resonance transfer between Yb³⁺, Er³⁺ and Dy³⁺. NaGdF₄:Yb,Er@NaDyF₄ core–shell nanoparticles with ultrathin layer shells exhibited a better T₁-weighted MR contrast.