The ability of upconverting nanoparticles (UCNPs) to emit visible upconverted luminescence upon excitation by near-infrared light (NIR) has made UCNPs hold great promise as probes for various biological applications including imaging and sensing. Ytterbium, Yb3+, ions are commonly doped as sensitizers in upconverting (UC) rare earth sodium fluoride nanocrystals. However, the Yb3+ -sensitized UC process suffers from 980 nm absorption overlap with water, the most abundant NIR absorber in the body. Substitution of Neodymium, Nd3+, for Yb3+ ions allows for the utilization of 808 nm absorption that minimizes signal attenuation in biological tissue and reduces overheating observed at 980 nm. Previous reports have attempted to integrate Nd3+ either by direct doping into the core or introducing a core-shell structure; however, these designs were limited to 1-20 mol % Nd [1][2]. Herein we report the synthesis of NaYF4:Yb3+/Er3+ @ NaLuF4: Nd3+ nanocrystals via thermal decomposition and self-focusing by Ostwald ripening. The previously described tunable layer-by-layer epitaxial shell growth overcomes the limitations of conventional shell growth techniques thus allowing for larger shell thicknesses that ensures spatially confined doping of Nd3+ ions within a concentric shell [3] [4]. More importantly, the Nd3+ sensitized core-shell design enabled higher concentration doping of Nd3+ in the shell than previously reported and thus, significantly enhanced UC emission from the emitter, Er. With the new ability to grow shells in a highly controlled manner, we were able to tune the thickness and Nd3+ concentration of the shell to achieve maximum UC efficiency. [1] Wang, Y.F. et. al., ACS Nano (2013); [2] Xie, X. et. al., JACS (2013); [3] Johnson, N. et. al., JACS (2012); [4] Johnson, N. et. al., ACS Nano (2014);

Designed synthesis of lanthanide doped core-shell nanoparticles with excitation at a benign wavelength

251st National Meeting (2016)

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