Lanthanide-based inorganic-organic hybrid materials for photon-upconversion

Photon-upconversion materials are capable of converting low energy infrared light into higher energy visible or ultraviolet light. Such materials are demanded for applications such as deep-tissue imaging, cancer therapy, nano-thermometry, biosensing, display and solar-cell technologies, and beyond. Trivalent lanthanide ions are promising materials for upconversion due to their suitable f-orbital energy levels allowing absorption in the near-infrared and emission in the visible wavelength range. The major obstacle in realizing the full potential of the Ln-based upconverters is their characteristically small absorption cross-sections. As many organic molecules possess much larger absorption cross-sections, their combination with Ln³⁺ions could bring about remarkable mutual benefits. Additionally, the organic ligands can also function as spacers to yield metal-organic framework type upconverting materials. Indeed, superior upconverting properties have already been reported for a diverse family of Ln-based inorganic-organic hybrids. Here we present an account of the recent developments in the field of Ln-based inorganic-organic upconverting materials and their emerging applications.