Lanthanide‐Doped Near‐Infrared Nanoparticles for Biophotonics

Abstract Light in the near‐infrared (NIR) spectral region is increasingly utilized in bioapplications, providing deeper penetration in biological tissues owing to the lower absorption and scattering in comparison with light in the visible range. Lanthanide‐doped luminescent nanoparticles with excitation and/or emission in the NIR range have recently attracted tremendous attention as one of the prime candidates for noninvasive biological applications due to their unique optical properties, such as large Stokes shift, spectrally sharp luminescence emissions, long luminescence lifetimes, and excellent photostability. Herein, recent advances of lanthanide‐doped nanoparticles with NIR upconversion or downshifting luminescence and their uses in cutting‐edge biophotonic applications are presented. A set of efficient strategies for overcoming the fundamental limit of low luminescence brightness of lanthanide‐doped nanoparticles is introduced. An in‐depth literature review of their state‐of‐art biophotonics applications is also included, showing their superiority for high‐resolution imaging, single‐nanoparticle‐level detection, and efficacy for tissue‐penetrating diagnostics and therapeutics.