Tailored NIR‐II Lanthanide Luminescent Nanocrystals for Improved Biomedical Application

Abstract Recently, in vivo optical imaging in the second‐near‐infrared window (NIR‐II, 1000–1700 nm) that allows high spatiotemporal resolution and imaging depth due to reduced photon scattering and weak auto‐fluorescence has drawn more and more attention. Among various NIR‐II optical probes, lanthanide‐doped nanoparticles show several great advantages including abundant energy levels transitions for multi‐emissions, ultra‐stable emissions for long‐term detection, and long luminescence lifetime for background‐free imaging. These merits have inspired researchers to make great efforts to develop superior lanthanide‐doped nanoparticles for in vivo bio‐imaging and bio‐sensing. In this review, NIR‐II luminescent emissions and absorption spectra of several lanthanide ions are outlined, and the recent advances in designing NIR‐II lanthanide‐doped nanocrystals with optimized quantum yields are summarized. Then their significant concerns for in vivo imaging and sensing including assembly and disassembly, clearance, and responsiveness of lanthanide‐based nanoparticles are discussed. Major challenges and future opportunities in the NIR‐II bio‐imaging using lanthanide nanocrystals are finally proposed to direct new solutions and interdisciplinary research.