Two Eu3+ and Tb3+ homodinuclear complexes with 1,3-diphenyl-1,3- propanedione have been synthesized and characterized by single crystal X-ray crystallography, vibrational analysis, calorimetric, magnetic and optical studies. The two isostructural complexes consist of two tetrakis units bridged by two potassium ions, thus affording a neutral charge. The photoluminescence measurements reveal that efficient energy transfer from the β-diketonate ligand to the central Ln3+ ion by antenna effect is achieved for Eu3+, leading to intense red emission with an intrinsic quantum yield of 48%. The Eu3+-based material has been assessed as the active layer in a solution-processed OLED with glass/ITO/PEDOT:PSS/PVK:Eu-dimer/TiO2/Al structure and its electroluminescent properties have been inspected, showing a threshold voltage of 6 V.