Figure 3.

Schematic presentation showing fluorescence imaging approaches of traditional methods versus rare-earth-metal doped nanoparticles. (A) The spectral range of classical fluorescence imaging methods. NIR, near-infrared region. (B) Examples of probes in the NIR-II region: single-walled carbon nanotubes (SWNTs), rare-earth-metal doped nanoparticles (RENPs), organic dyes, conjugated polymers, and quantum dots (QDs). (C) Nanoparticles are doped with rare-earth metals (Nd, Tm, Pr, Ho, Er) [42]. Copyright 2020, Frontiers.