Synthesis of Li1−xNaxYF4:Yb3+/Ln3+ (0 ≤ x ≤ 0.3, Ln = Er, Tm, Ho) nanocrystals with multicolor up-conversion luminescence properties for in vitro cell imaging

Abstract

In this paper, we demonstrated the synthesis of Li1−xNaxYF4:Yb3+/Ln3+ (0 ≤ x ≤ 0.3, Ln = Er, Tm, Ho) upconversion nanocrystals (UCNCs) via a simple high boiling solvent process. The size and morphology of the Li1−xNaxYF4 NCs can be tuned by varying the doping amount of Na+. Furthermore, the introduction of Na+ also affects their upconversion luminescence properties. By changing the dopant's species (Ln3+) and the doping concentration of Na+, multicolor (green, blue, red, yellow, orange and white) upconversion emissions can be obtained. In addition, the as-prepared OA-capped hydrophobic LiYF4:Yb3+/Er3+ nanocrystals were modified with sodium dodecylsulfate (SDS) to convert them into hydrophilic ones. MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay indicates that the SDS-modified LiYF4:Yb3+/Er3+ NCs exhibit good biocompatibility. Meanwhile, the application of these hydrophilic LiYF4:20%Yb3+/2%Er3+ and Li0.7Na0.3YF4:20%Yb3+/2%Er3+ NCs in the luminescence imaging of cells were also investigated, which showed bright green and red emissions without background noise, respectively. So these UCNCs are promising for multiple cell imaging.