Optical–magnetic bifunctional properties and mechanistic insights on upconversion of NaYF4:Yb,Ho,Tm@NaGdF4 with a tunable nanodumbbell morphology

The energy-upconversion of lanthanide-doped nanoparticles with a core–shell structure can be utilized to enhance and tune optical properties and can generate multifunctionality in a single system. Herein, the core–shell nanoparticles NaYF4:Yb,Ho,Tm@NaGdF4 were prepared by thermally decomposing lanthanide acetylacetonate precursors. Through modifying the molar ratio of the core and shell, nanodumbbell-shaped particles with different sizes and morphologies were precisely synthesized. The formation mechanism and the heterogeneous epitaxial growth process of the nanodumbbell-shaped particles were studied. After coating the shell layer, upconversion luminescence intensities, spectral purity and fluorescence lifetimes were improved. Furthermore, the magnetic performance of the core–shell nanoparticles was characterized. The optical–magnetic bifunctional upconversion core–shell particles with programmable shape and multiple properties provide an ideal platform for the preparation of nanodumbbell-shaped particles and the promotion of upconversion materials for biomedical research.