Low-power photon upconversion through triplet-triplet annihilation in polymers

Low-power upconversion via sensitized triplet-triplet annihilation (TTA-UC) is a useful and versatile process that allows for the conversion of optical radiation into photons of higher energy. While this effect had been known to occur in solution for some 50 years, it was only very recently realized for the first time in polymers. The possibility to realize the TTA-UC process in solid materials is important for a variety of applications that range from the optimization of photovoltaic devices to bioimaging. This article provides a brief introduction to the field, summarizes the underlying photophysical aspects, reviews the design concepts for TTA-UC in polymers, and summarizes the recent advances in the development of such materials.