Multiphoton and upconverted excitation of lanthanide(III) ions in coordination complexes

The unique optical profiles exhibited by trivalent lanthanide ions and their coordination compounds has resulted in their emergence as excellent candidates for a wide range of optical applications. However, methods for exciting lanthanide compounds more often than not involve excitation in the UV and visible regions of the electromagnetic spectrum, where many biological molecules and materials also strongly absorb. In this Chapter, we discuss developments in the use of alternative approaches to excitation of trivalent lanthanides using near infra-red light in both multiphoton and upconversion processes, focusing on the underlying principles and recent developments in the coordination chemistry enabling such processes to operate in solution.