Direct surface functionalization of LiYbF4:Tm(III) upconversion nanoparticles with a luminescent Ir(III) complex: a hybrid theranostic nanoplatform

Rare-earth-doped upconversion nanoparticles (UCNPs) are promising theranostic materials due to their ability to convert near-infrared (NIR) excitation into higher-energy emissions, enabling deep tissue penetration and reduced phototoxicity. In this work, LiYbF₄:Tm^III/LiYF₄ core/shell UCNPs were synthesized by thermal decomposition and functionalized with Ir^III complexes to obtain hybrid nanoplatforms. TEM analysis confirmed the formation of well-dispersed bipyramidal core/shell nanoparticles with an epitaxial inert shell. Under 980 nm excitation, the overlap between Tm^III upconversion emission and the Ir-complex absorption promoted energy transfer, resulting in changes in the Tm^III emission profile and the appearance of the characteristic Ir^III phosphorescence. The Ir^III downshifting emission was also observed under direct UV excitation. These findings demonstrate the successful integration of UCNPs and Ir^III complexes, highlighting the potential of this hybrid system for NIR-activated luminescent sensing and future theranostic applications.