Characterization and spectroscopic studies of 'Eu POT.3+' and 'Tb POT.3+' complexes with 2,2'-bipyridine-4,4'-dicarboxylic acid - Calefi, Paulo Sérgio; Ribeiro, Anderson Orzari; Pires, Ana Maria; Serra, Osvaldo Antonio (Journal of Alloys and Compounds, 2002)