Advanced optical properties of upconversion nanoparticles

Upconversion nanoparticles (UCNPs) are typically doped with lanthanide ions, capable of converting near-infrared light into visible and ultraviolet emissions. Their unique optical properties have attracted considerable research interests and enabled various applications ranging from molecular detection, bioimaging, nanomedicine, to volumetric displays and microcavity lasers. By overcoming the restraint of concentration quenching and controlled synthesis of heterogeneous structures, UCNPs become sufficiently bright with versatile multifunctions. This article surveys the recent advances in developing UCNPs and highlights their optical properties for emerging applications.