ABSTRACT: Photochemical upconversion is a regenerative process that transforms
lower-energy photons into higher-energy light through two sequential bimolecular
reactions, triplet sensitization of an appropriate acceptor followed by singlet fluorescence
producing triplet−triplet annihilation derived from two energized acceptors. This
laboratory directly investigates this phenomenon using the facile photo-induced triplet−
triplet energy-transfer reaction between the benchmark inorganic chromophore