Synthesis and characterization monodisperse core-shell lanthanide up-conversion nanoparticles NaYF4: Yb Er/Tm
Robeth Viktoria Manurung1, Pradip Kumar Roy1*, Chia Min Wang1, Surojit Chattopadhyay1,2
1Institute of biophotonics, National Yang Ming University, Taipei, Taiwan
2Biophotonics and Molecular Imaging Research Center, National Yang Ming University, Taipei, Taiwan
* presenting author:Robeth Manurung,
Lanthanide doped up-converting luminescent nanoparticles (UCNPs) are promising materials for optical bioimaging and therapy due to their unique optical and chemical properties. UCNPs absorb low energy near-infrared (NIR) light and emit high-energy shorter wavelength photons. The excitation energy being in the biological transparency window, ~1000 nm, these UCNPs offer deep tissue imaging possibilities Their special features provide a nanoplatform with both imaging and therapeutic modalities.
The synthesis of the UCNPs, NaYF4:Yb/Er and NaYF4:Yb/Tm, was done by thermal decomposition process which involves dissolving organic precursors in high-boiling-point solvents oleic acid (OA) and octadecene (ODE). This paper reports a core–shell structure NaYF4:Yb/Er@SiO2, and NaYF4:Yb/Tm@SiO2 microspheres prepared by coating the NaYF4:Yb/Er and NaYF4:Yb/Tm phosphors by silica via microemulsion process. Scanning electron microscopy, transmission electron microscopy, specific area electron diffraction, and photoluminescence were applied to characterize these samples. The obtained core–shell structured NaYF4:Ln@SiO2 phosphors exhibit a perfect cubic morphology with narrow size distribution and smooth surface. Upon IR excitation at 980 nm, the NaYF4:Yb/Er@SiO2 and NaYF4:Yb/Tm@SiO2 samples exhibit bright green and whitish blue up-conversion (UC) luminescence, respectively. Although the efficiency of the upconversion process is small, but the luminescence intensity could be modulated in presence of metallic surfaces for which the core-shell structure was necessary. We show a simple method to modulate the luminescence intensity in these UCNPs.

Acknowledgments: National Science Council, Taiwan, under grant # NSC-101-2112-M-010-003-MY3.

Keywords: Lanthanide, up-converting luminescent, deep tissue imaging, core–shell structure, thermal decomposition