Luminescence as a Tool for the Detection of Uranyl(VI) in Biogeochemical Scenarios: Direct and Indirect Sensors

Abstract

Uranyl(VI) is the most common form of soluble uranium in the environment, and as such is a major analytical target for experiments looking to explore the behaviour of uranium in biogeochemical scenarios. Examples include understanding the interactions of uranyl(VI) with microorganisms, its absorption onto mineral phases, or the coordination chemistry with proteins on a molecular level. Analytical methods based on luminescence benefit from high sensitivity, good spatial resolution, and multiple output parameters (wavelength, intensity, lifetime) which can be used to locate uranyl(VI) at low concentrations and fingerprint local coordination environments. In this chapter, we discuss first the photophysical origins of the characteristically green uranyl(VI) emission, and its application in environmental fingerprinting and analysis. This is followed by a brief discussion of alternative indirect optical sensors, based on specific interactions between uranyl(VI) and another coloured or luminescent species. Both direct and indirect luminescence systems are discussed using select examples from the literature.