Upconversion nanoparticles (UCNPs) are a unique class of nanomaterials that absorb low-energy photons and emit higher-energy photons. This process is known as upconversion. Typically, UCNPs are composed of a host lattice doped with rare-earth ions, such as yttrium, erbium, ytterbium, or thulium. These rare-earth ions facilitate the upconversion process, making UCNPs valuable for a variety of applications.
