Core-shell structured NaMnF3: Yb, Er nanoparticles for bioimaging applications

Abstract

NaMnF₃: Yb,Er upconversion nanoparticles (UCNPs) have received considerable attention due to their single-band emission. In this paper, a modified thermal decomposition method to synthesize single or core/shell structured lanthanide-doped NaMnF₃ nanoparticles is proposed. The NaMnF₃: 20% Yb³⁺, 2% Er³⁺ nanoparticles displayed pure red emission under 980 nm laser excitation, and the emission intensity could be significantly enhanced by coating a NaMnF₃ or NaMnF₃: 20% Yb³⁺ shell layer on their surfaces. Moreover, NaMnF₃: 20% Yb³⁺, 2% Er³⁺ nanoparticles shelled with NaMnF₃: 20% Nd³⁺ or NaMnF₃: 20% Yb³⁺, 20% Nd³⁺ were synthesized for the first time, and displayed pure red emission when excited by an 808 nm laser. The core/shell structured NaMnF₃: Yb/Er@NaMnF₃: Yb or NaMnF₃: Yb/Er@NaMnF₃: Yb/Nd nanoparticles were applied to bioimaging. The NaMnF₃ based UCNPs exhibited good photostability and biocompatibility in HeLa cells. The obtained images indicated that the UCNPs could mainly exist in the cytoplasmic regions in the cells. Besides, images from the same region exposed to laser irradiations at 808 nm and 980 nm were found to be comparable. This result indicated that, for NaMnF₃: 20% Yb³⁺, 2% Er³⁺@NaMnF₃: 20% Yb³⁺, 20% Nd³⁺ nanoparticles, laser excitation at 808 nm was as efficient as that at 980 nm for bioimaging.