Tailoring Near-Infrared-IIb Fluorescence of Thulium(III) by Nanocrystal Structure Engineering
Feng Ren, Haoying Huang, Hongchao Yang, Bin Xia, Zhiwei Ma, Yejun Zhang, Feng Wu, Chunyan Li, Tao He, Qiangbin Wang
Abstract
Currently, mainstream lanthanide probes with fluorescence located in the second near-infrared subwindow of 1500–1700 nm (NIR-IIb) are predominantly Er(III)-based nanoparticles (NPs). Here we report a newly developed NIR-IIb fluorescent nanoprobe, α-Tm NP (cubic-phase NaYF 4 @NaYF 4:Tm@NaYF 4 ), with an emission at 1630 nm. We activate the 1630 nm emission of Tm(III) in α-Tm NP through the large spread of the Stark split sublevels induced by the crystal-field effect of the α-NaYF 4 host. Further, we systematically investigated the effect of crystalline structure of the host NaYF 4 NP (cubic phase (α) or hexagonal phase (β)), the type and concentrations of dopants (Yb(III), Tm(III), and Ca(II) ions) in the α-phase host, and the thicknesses of the interlayer and inert shell on the NIR-IIb fluorescence of Tm(III). The ultimate nanostructure presents a significant enhancement factor of the NIR-IIb photoluminescence intensity of Tm(III) up to ∼315. With this bright NIR-IIb fluorescent nanoprobe, we demonstrate high-spatial-resolution time-coursing imaging of breast cancer bone metastasis.