Controlled optical characteristics of lanthanide doped upconversion nanoparticles for emerging applications.

Lanthanide-doped upconversion nanoparticles (UCNPs) can convert long wavelength excitation radiation in the near-infrared region to higher energy emission radiation from ultraviolet to near-infrared. The anti-Stokes luminescence process will result in high tissue penetration depth, low background noise and low photo-damage in bioimaging applications. Considering these excellent optical performances, UCNPs have been considered as the next generation of fluorescent probes for sensing and bioimaging based on near-infrared light stimulation. In this mini review, we highlight the recent advances of UCNPs in the field of emerging applications, such as dye sensitized UCNPs, photogene regulation, anti-counterfeiting, and super-resolution imaging, which depend on the optical modulation. Finally, we discuss the challenges and opportunities in the development of these new applications.