L Journal of Alloys and Compounds 341 (2002) 45–50 www.elsevier.com / locate / jallcom Luminescence spectroscopy of lanthanide(III) ions in solution * Stefan Lis Department of Rare Earths, Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland Abstract 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 2 the luminescent excited state of the Ln(III) ions by O–H, N–H and a strong deactivating power of the azide ion, N , are described. The 3 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, b-diketones, macrocyclic ligands, heterobiaryl ligands, etc.) as well as energy transfer processes are discussed. The use of europium 7 5 luminescence excitation spectroscopy of the F → D transition as a unique and sensitive way to characterize the number of Eu(III) 0 0 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.  2002 Elsevier Science B.V. All rights reserved. Keywords: Europium(III); Complexes; Luminescence; Quenching; Energy transfer 1. Introduction Luminescence from f-element ions provides a variety of convenient and theoretically challenging features. The Several trivalent lanthanides, Ln(III), show characteris- luminescence intensity and lifetime of Eu(III) and Tb(III) tic luminescence spectra in the visible and near-IR region. ions have been used to gain information on the com- Unlike d-transition metal ion complexes for which the position and structure of the first coordination sphere of electronic excited states are strongly coupled to the en- these ions in solution, in materials ranging from inorganic vironment via the ligand field providing an efficient de- compounds to systems of biological interest [3–6]. Diverse excitation mechanism, in the case of lanthanide complexes experimental studies including elucidation of factors in- the coupling between f-excited electronic states and the fluencing non-radiative decay, speciation of metal com- environment is very small. Among the luminescent Ln(III) plexes and determination of f-element have been widely ions, europium and terbium are the two most extensively applied in solution phase chemistry [2,5,7,8]. studied in solution. The emission bands of Eu(III) origi- Previously, we reported the use of Eu(III) lifetime nate from electronic transitions from the lowest excited measurements to identify the residual hydration of the 5 7 state, D , to the ground state manifold, F (J56–0) and Eu(III) ion in inorganic complexes [9], and in complexes 0 J 5 those of Tb(III) from the lowest excited state, D , to the extracted into the organic phase [10], and to characterize 4 7 ground state manifold, F (J56–0). In the case of both the bonding properties of the nitrogen, oxygen and sulfur J metal ions, the intensity, splitting and energy of the donors to lanthanide ions [11,12] and binding properties of luminescence bands as well as the relative intensities of the polyelectrolytes with lanthanide ions in aqueous solution different bands are very sensitive to the symmetry and the [13]. We also used the luminescence properties of Eu(III) detailed nature of the ligand environment. Other members or Tb(III) to study the complexation of the lanthanides of the lanthanide series emit luminescence much less with polyoxometalates [14–17] and for characterization of efficiently unless in the solid state [1–3]. luminescent complexes based on an antenna effect en- trapped into xerogel matrix [18–20]. *E-mail address: blis@main.amu.edu.pl (S. Lis). Spectroscopic properties of Eu(III) and Tb(III) ions 0925-8388 / 02 / $ – see front matter  2002 Elsevier Science B.V. All rights reserved. PII: S0925-8388(02)00055-5