Developments in the photophysics and photochemistry of actinide ions and their coordination compounds

Actinide coordination chemistry is currently experiencing a renaissance, with the emergence of exciting and less studied oxidation states, and previously unpredicted magnetic properties and reactivities. On one hand, the actinide ions themselves underpin technologies that result in nuclear power production, yet from a scientific viewpoint their fascinating physical and chemical properties are poorly understood, especially when compared with their lanthanide and transition metal counterparts. Although, in principle, all actinide (Ann+) and actinyl (AnO2n+) ions are emissive, it is only in recent years that the luminescence properties of a relatively small number of well defined complexes have begun to be explored and the emission properties of the actinide ions exploited, for example in optical imaging of surface alteration reactions in uranium minerals. Nonetheless, these studies represent a veritable advancement in this important field. In this review, an account of developments in the area of actinide and actinyl luminescence will be presented, focussing on the fundamental optical properties of the ions and their coordination compounds. A discussion of the nature of the emission, including assignments of charge transfer and intra 5f transitions, band position, band shape and emission decay constant(s) is presented, with particular attention on potential applications related to the nuclear fuel cycle, including separation and remediation technologies.

► How the electronic structure relates to the intrinsic photophysical properties of the 5f ions and their coordination complexes. ► Application of emissive uranium complexes in optical imaging. ► Recent progress in understanding the emission from the transuranics. ► Application of emission spectroscopy to lanthanide/actinide separation technologies in the nuclear fuel cycle.