Processes of luminescence quenching in europium aromatic carboxylates with the participation of LMCT states: A brief review

Materials based on Eu3+ coordination compounds thanks to their intense red emission have great potential for applications, and the ability to control the processes of excitation and quenching their luminescence is extremely important. One of the effective processes of Eu3+ luminescence quenching results from the influence of ligand–metal charge transfer (LMCT) states. The widely used luminescence sensitizers are aromatic carboxylic acids, which form a great number of compounds with lanthanide ions. At the same time, the participation of the LMCT states in the luminescence quenching mechanisms in europium aromatic carboxylates competes with sensitization processes. A brief review of luminescence excitation and quenching processes involving LMCT states in europium substituted benzoates: methoxy-, methylthio-, hydroxy-, thio-, aminobenzoates, and fenamates; carboxylates with π-excessive heterocycles: pyrrole- and indolecarboxylates; and phenyl- and naphthylcarboxylates with methylene bridge, as well as other europium compounds, is presented. It is shown how the different substituents on the aromatic ring and modification of ligands affect the LMCT energy. Experimental methods to study this phenomenon are also discussed.