Europium complexes general structure

Examples of europium complexes 30-32 that have been applied in temperature sensors or dual pressure- and temperature-sensitive paints are listed in Table 5. The respective ligand structures are shown in Scheme 7. The temperature dependency is quantified as average luminescence intensity temperature coefficient 7 [%/°C]. Usually, it is determined in a temperature range from 1 to 40 or 50°C. These examples exceed the intensity temperatiue coefficients of other established temperature sensitive probes such as ruthenium(II)-tris-(l,10-phenanthroline) [121]. Generally, the lifetime temperature coefficients are significantly lower. This indicates that thermal quenching of the triplet state of the antenna chromophore plays an important role. Due to the narrow emission band of europium complexes at 615 nm even triple sensors for temperature, oxygen, and pH are achievable [122]. 

A large number of rare-earth adducts have been synthesized and characterized (see Gmelin Handbook of Inorganic Chemistry, Part D4, 1986 for a general review or Cunha et al. (1992) for a review on europium trigonal complexes). However, the molecular structure of only a few compounds has been established by means of single-crystal X-ray diffraction. In table 16, we compare the coordination numbers in the solid state and in solution for the solvates for which extensive data are at hand, that is, adducts with DMSO. Solid solvates R(N03)3 nDMSO display a CN change from 10 to 9 between Eu and Tb. X-ray diffraction data for 1M solutions of Er(N03)3 in DMSO yield the same coordination number (CN=9) and similar distances as in the crystalline phase (Johansson et al. 1991). 

---