Enhanced near-infrared II luminescence in NaErF4 based core/shell nanocrystals via incorporating high Ce3+ ions concentration.

Near-infrared II (NIR-II, 1000–1700 nm) fluorescent probes have received extensive attention in the field of biomedicine due to their deep tissue penetration, high spatial resolution and superior signal-to-noise ratio. In this work, the Ce3+ ions with high concentration were doped into both the core and shell layer of the NaErF 4 @NaYF 4 NCs. Compared to the NaErF 4 @NaYF 4 NCs, the NIR-II emission intensities of the NaErF 4 :20Ce@NaYF 4 :20Ce core@shell NCs increases about 5.1 times under 808 nm excitation. We verify that doping part of Ce3+ ions in the shell could not only preserve the high concentration of Er3+ ions in the core, but also facilitate the nonradiative relaxations of 4I 11/2 → 4I 13/2 followed by the enhanced NIR-II emission intensity. The emission light could be clearly observed even at the depth of 6 mm, which show promising application in deep tissue imaging. • Uniform NaErF 4 :Ce@NaYF 4 :Ce active-core@active-shell NCs was prepared. • The NIR-II luminescence intensity was significantly improved by Ce3+ ions doping. • The emission light was clearly observed at the depth of 6 mm. [ABSTRACT FROM AUTHOR]