For the first time, we observed positronium formation in Eu(III) complexes more specifically in Eu(BZO)(3)bipy, Eu(DBM)(3)phen, PipEu(DBM)(4), PipEu(bZC)(4), and Eu(Ph2NCS2)(3)Phen, where bipy stands for 2,2'-bipyridine, phen for 1,10-phenanthroline, Pip for piperidinium cation, BzO for benzoate, bzc for benzoylacetonate and DBM for dibenzoyl methide. From the comparison between the positron annihilation parameters for these complexes and for other lanthanide complexes investigated in previous works, correlations between the probability of positronium formation and luminescence properties of Eu(III) complexes could be established. (c) 2006 Elsevier B.V. All rights reserved.