Enhancing NIR-II luminescence of erbium sublattice through lanthanide-mediated energy modulation

Lanthanide-doped near-infrared-II (NIR-II) luminescent nanoparticles have shown great potential in many fields. However, most previous studies were focused on the sensitizer-activator coupled systems in which the NIR-II luminescence intensity is seriously restricted by the low dopants concentration. Improving the NIR-II emission intensity in lanthanide-doped nanoparticles has remained a daunting challenge. Herein, we report a systematic research on the enhancement of the NIR-II luminescence of Er3+ through lanthanide-mediated energy modulation. It is found that introducing proper content of Yb3+, Ce3+, Tm3+, and Ho3+ in the erbium sublattice can indeed enhance the NIR-II emission under 980 and 808 nm excitations by mediating the energy transfer processes. Doping of other lanthanide ions (e.g., Pr3+, Tb3+, Dy3+, and Sm3+) only led to a quick decline in luminescence intensity. The NIR-II emission was further enhanced by designing a core-shell-shell nanostructure which consists of an NaYbF4 interlayer to maximize the absorption of 980 nm excitation. The NIR-II luminescence exhibits superior penetration depth in biological tissue, showing great promise in biological applications.