Luminescence spectroscopy of lanthanide(III) ions in solution

Luminescence spectroscopy of Ln(III) ions, characterised by very narrow emission bands and a long decay time, is an important technique for the study of coordination, analytical and photophysical aspects of lanthanide chemistry. Factors affecting the Ln(III) luminescence in solution that can both quench or increase the intensity and lifetime of luminescence, are described. The quenching processes of the Ln(III) excited states, strongly dependent on energy of vibrators resulting from ligands (and/or solvents) and energy gaps, DE, between the emissive state and the highest sublevel of the ground state of Ln(III), are presented. Effectiveness of quenching of the luminescent excited state of the Ln(III) ions by O-H, N-H and a strong deactivating power of the azide ion, N-3(-), are described. The factors which markedly increase luminescence, efficiently reducing nonradiative energy degradation of Ln(III) ions are presented. Highly luminescent Ln(III) systems based on complex and ternary complex formation with several groups of ligands (e.g. crytptands, beta-diketones, macrocyclic ligands, heterobiaryl ligands, etc.) as well as energy transfer processes are discussed. The use of europium luminescence excitation spectroscopy of the F-7(0)-->D-5(0) transition as a unique and sensitive way to characterize the number of Eu(III) species present in solution, binding sites of various ligands and complex stoichiometries, is briefly reviewed. Recent developments in the use of the excitation spectroscopy of Eu(III) and a wealth of information which can be obtained from this method are presented. (C) 2002 Elsevier Science B.V. All rights reserved.