Lanthanide-doped core–shell upconversion nanophosphor

A core–shell upconversion (UC) nanoparticle is typically composed of an upconversion core coated with one or more shell layers, which essentially preserve the properties of core-only nanoparticle. However, when compared with the core-only nanoparticle, core–shell structure provides more rooms for UC studies due to the increased flexibility in nanoparticle design. The core–shell structure can boost the UC efficiency by passivating the surface lattice defects and shielding the core nanoparticles from the surrounding environment. In addition, core–shell structures greatly expand the optical tunability and enable functional integration at single nanoparticle levels. In this chapter, we highlight recent advances in general synthetic strategies and possibility for composing core–shell upconversion nanoparticles. We also bring to the forefront several challenges for future study.