Up- and Down-Conversion in Molecules and Materials

The conversion of excited-state energy in molecules and materials, for example by quantum cutting, singlet fission or upconversion, allows for optical functionality well beyond that of conventional semiconductors. In this special issue we focus on such processes in organic, inorganic and hybrid systems, in which processes including singlet fission, triplet-triplet fusion, and quantum cutting represent highly efficient means for energy conversion. We encourage contributions from theory and experiment with particular focus on new materials, for example rare-earth doped perovskite materials; materials for energy harvesting and injection, such as inorganic-organic hybrids; and emerging building blocks for upconversion and singlet fission. We also encourage contributions that report characterization of energy conversion schemes, for example analysis of triplet exciton diffusion by spectroscopy and imaging, and contributions that report new applications of non-linear optical processes, such as near-infrared optogenetics by upconversion, infrared sensitization for imaging, solar cell integration, and photocatalysis.