A mechanism of the influence of Gd(III) and other Ln(III) ions on sensitized luminescence of Eu(III) and Tb(III) ions in aqueous and ethanol solutions: The role of hydroxyl bridges

We studied sensitization of Eu(III) and Tb(III) ions by molecules of 1,10-p henanthroline and 2,2-bipyridil in D2O and d(6)-ethanol and the influence o f Nd(III), Pr(III), Sm(III), Gd(III), and Ho(III) ions on the luminescence intensity I-lum, and lifetime tau (lum) of Eu(III) and Tb(III) in solutions . The stability constants of complexes of Eu(III) and Gd(III) with 2,2'-bip yridil are measured by spectrophotometric and luminescence methods. It is s hown that luminescence of Eu(III) is quenched by Gd(III) ions at the ion co ncentration equal to 10(-2)-10(-1) M, which is caused by competing between these ions for a sensitizer. At the concentration of Ln(III) ions equal to 10(-6)-10(-3) M, the sensitized luminescence of Eu(III) and Tb(III) was que nched and tau (lum) decreased in the presence of Nd(III) ions, whereas in t he presence of Gd(III) the luminescence intensity increased. It is proved t hat a bridge that connects the two ions upon energy transfer is formed by h ydroxyl groups, The intensity of luminescence of Eu(III) and Tb(III) in aqu eous solutions and its lifetime decreased in the presence of hydroxyl group s, while upon addition of Gd(III) to these solutions these quantities were restored. We also found that the addition of Gd(III) to deoxygenated ethano l solutions of 2,2'-bipyridil and Eu(III) slows down photochemical and ther mal reactions between bipyridil and Eu(III), resulting in the increase in t he luminescence intensity of Eu(III). (C) 2000 MAIK "Nauka/Interperiodica".