Back Energy Transfer in Nonanuclear Terbium Clusters
Energy transfer from organic ligands to a lanthanide ion is the main concept of sensitized luminescence in lanthanide complexes. Back energy transfer is the reverse process, which occur when the energy of the triplet excited state is close to the emitting excited state of the lanthanide ion and can lead to decrease in sensitization efficiency and therefore the quantum yield as well. Generally, the back energy transfer rate constant is proportional to the energy gap between the triplet excited state and the emitting excited state of the lanthanide, but there are some compounds that deviate from this trend. This chapter focuses on [Tb9(μ-OH)10(L)16]NO3 where ligand L is a derivative of methyl salicylate ligands to change the triplet excited state energy without significantly changing the structure so that direct comparison of back energy transfer rate constant can be performed. The conclusion of this chapter is that back energy transfer rate constant is determined not only by the energy gap but also by the activation energy and the frequency factor (electronic correlation) of the process.
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