A novel mixed-ligand terbium complex Tb(Sal)3(TPPO)2 was synthesized and characterized by elemental, IR and thermal analyses. The film-forming properties of the new Tb(Sal)3(TPPO)2 and the known Tb(Sal)3·H2O complexes in spin-coating process were compared. The study of thin films morphology with NSOM/AFM microscope showed that the RMS roughness for the Tb(Sal)3(TPPO)2 films was 9 nm in contrast to 66 nm for Tb(Sal)3·H2O ones. The electroluminescent (EL) device structure ITO/PEDOT/PVK/Tb(Sal)3(TPPO)2/Al was employed to study the electroluminescence of the terbium carboxylate complex. The EL spectrum with sharp spectral band at 545 nm peak wavelengths confirms that emission comes exclusively from terbium ions. The EL emission was observed at biases higher than 12 V. A considerable difference between the PL and EL spectra was observed and a possible way of explaining the phenomenon has been proposed.