Shell-thickness-mediated anomalous thermal enhancement of core-shell-shell structured nanoparticles for...

Modern nanotechnology increasingly demands multifunctional nanomaterials, motivating rational core-shell designs to integrate diverse capabilities within a single nanostructure. Herein, core-shell-shell structured NaYF₄:20%Yb³⁺@NaErF₄:0.5%Tm³⁺@NaGdF₄:20%Yb³⁺ nanoparticles are developed through a layer-by-layer epitaxial growth strategy. The key novelty of this synthesis lies in the precise spatial organization of functional ions: an inner core and an outer shell rich in Yb³⁺ sensitizers collaboratively pump a central energy-migrating erbium sublattice. This unique architecture exhibits intense red upconversion luminescence under 980 nm excitation while enabling multimodal nanothermometry and dual-modal bioimaging (optical imaging and T₁-weighted magnetic resonance imaging). Aberration-corrected transmission electron microscopy (AC-TEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) analyses confirm the precise layered architecture and high crystallinity. Significantly, the outer thin shell induces anomalous thermal enhancement at 544 nm. This phenomenon is governed by a shell-thickness-mediated energy migration process, which modulates the interaction between the erbium sublattice and surface ligands, thereby facilitating enhanced performance in multimodal nanothermometry. HAADF-STEM provides direct visualization of shell thickness variations, offering mechanistic evidence for this phenomenon. Crucially, dual-modal bioimaging capability is validated in vivo. This core-shell design strategy advances the development of multifunctional nanoparticles for nanothermometry and bioimaging applications.