Impact of Symmetry and Donor Set on the Electronic Energy Levels in Nine-coordinated Eu(III) and Sm(III) Crystals Structures Determined from Single Crystal Luminescence Spectra

Lanthanide luminescence is characterised by “forbidden” 4f-4f transitions and a complicated electronic structure. Our understanding of trivalent lanthanide(III) ions luminescence is centered on Eu3+ because absorbing and emitting transition in Eu3+ occur from a single electronic energy levels. In Sm3+ both absorpbing and emitting multiplets have a larger multiplicity. A transition from the first emitting state multiplet to the ground state multiplet will result in nine lines for a Sm3+ complex. In this study, high resolution emission and excitation spectra were used to determine the electronic energy levels for the ground state multiplet and first excited state multiplet in four Sm3+ compounds with varying donor set and site symmetry. This was achieved by the use of Boltzmann distribution population analysis and experimentally determined transition probabilities from emission and excitation spectra. Using this analysis it was possible to show the effect of changing three oxygen atoms with three nitrogen atoms in the tricapping donor set for compounds with the same Trigonal Tricapped Prism (TTP) site symmetry on the crystal field splitting in both Eu3+ and Sm3+ crystals. This work celebrates the 40 year annivesary for the first report of [Eu(ODA)3]3- luminescence by Kirby and Richardson.