In this work, 14 ternary Eu(III) complexes were studied by means of spectroscopy. The studied Eu(III) complexes consisted of Lewis bases (4'-(4-diethylaminophenyl)-2,2':6',2 ''-terpyridine (L-8) or 1,10-phenanthroline (L-9)) and differently substituted beta-diketones. The ternary complexes with L-8 show the excitation peak at 405 nm and the quantum yield even 76%. The brightest ternary complex at the 405 nm excitation was Eu(L-3)(3)L-8 while Eu(L-7)(3)L-8 (HL3=4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione, HL7=1-(9-ethyl-9H-carbazol-3-yl)-4,4,5,5,5-pentafluoro-1,3-pentanedione) was found to be the brightest at the ligand-centred excitation maximum. The ternary complexes were studied mainly in toluene as the model environment for the polystyrene nanoparticle cavities. The complexes were successfully loaded into the polystyrene nanoparticles enabling their bioanalytical application in aqueous environment. The encapsulation of the complexes preserved, or even enhanced, their good photophysical features. (C) 2014 Elsevier B.V. All rights reserved.