Rare-Earth-Based Nanoparticles with Simultaneously Enhanced Near-Infrared (NIR)-Visible (Vis) and NIR-NIR Dual-Conversion Luminescence for Multimodal Imaging.

Multifunctional NaGdF4 :Yb(3+),Er(3+),Nd(3+) @NaGdF4 :Nd(3+) core-shell nanoparticles (called Gd:Yb(3+),Er(3+),Nd(3+) @Gd:Nd(3+) NPs) with simultaneously enhanced near-infrared (NIR)-visible (Vis) and NIR-NIR dual-conversion (up and down) luminescence (UCL/DCL) properties were successfully synthesized. The resulting core-shell NPs simultaneously emitted enhanced UCL at 522, 540, and 660 nm and DCL at 980 and 1060 nm under the excitation of a 793 nm laser. The enhanced UCL and DCL can be explained by complex energy-transfer processes, Nd(3+) →Yb(3+) →Er(3+) and Nd(3+) →Yb(3+) , respectively. The effects of Nd(3+) concentration and shell thickness on the UCL/DCL properties were systematically investigated. The UCL and DCL properties of NPs were observed under the optimal conditions: a shell Nd(3+) content of 20 % and a shell thickness of approximately 5 nm. Moreover, the Gd:Yb(3+) ,Er(3+) ,Nd(3+) @Gd:20 % Nd(3+) NPs exhibited remarkable magnetic resonance imaging (MRI) properties similar to that of a clinical agent, Omniscan. Thus, the core-shell NPs with excellent UCL/DCL/magnetic resonance imaging (MRI) properties have great potential for both in vitro and in vivo multimodal bioimaging.