Designing ultraviolet upconversion for photochemistry

Upconversion nanoparticle (UNP) technology has matured to enable cutting edge applications in bioimaging, sensing, and photochemistry. UNPs have garnered wide interest due to the many facets of available material choices, surface modifications and optical properties. With their nonblinking long luminescent lifetimes, large anti-Stokes shift and photostability combined with their relatively small size, they provide a compelling alternative to traditional molecular probes in bioimaging and biosensing applications. In particular, the ability to upconvert photons from near-infrared (NIR) to ultraviolet (UV) allows for the development of site-specific methods of photochemical activation of various functional, theranostic agents. This review summarizes advances in the development of synthetic methods that promote UV luminescence in UNPs. The review is organized into three broad topics: the host, dopants, and architecture. Examples of selected applications that may utilize improved NIR to UV upconversion are included. As the advancements in nanotechnology continue to benefit the fields of biochemistry, medicine, and biology, new paradigms of implementation of UNPs may broaden their clinical appeal.