Luminescence properties of Eu³⁺ complexes based on macrocyclic ligands and its colorimetric analysis for white warm phosphor

The development of phosphors for warm white light plays a decisive role in the quest for energy-efficient and environmentally friendly lighting technologies. Lanthanide-based phosphors, especially those containing europium ions (Eu³⁺), offer promising possibilities as they can emit light in the entire visible spectrum. In this study, the luminescence properties of two Eu³⁺ complexes, specifically [Eucy1a] and [Eu2cy2], synthesized with macrocyclic ligands are presented. The macrocyclic ligands (cy1a)H₃ and (cy2)H₆ provide a stable coordination environment that allows fine-tuning of photophysical properties, which are crucial for warm white phosphors. Synthesis, molecular modeling using density functional theory (DFT) and spectroscopic characterization of the complexes were performed. Notably, the complexes showed an inefficient energy transfer from the ligands to the Eu³⁺ ions, resulting in a broad blue emission spectrum corresponding to the ligand emission and the red 4f–4f transitions of Eu³⁺,which is important for the generation of white light. Photometric evaluation revealed favorable properties, including correlated color temperatures (CCT) indicative of warm white light, high color rendering index (CRI) values and exceptional Luminous Efficacy of Radiation (LER). In addition, the presence of coordinated water molecules influenced the luminescence lifetime and quantum efficiency of the complexes. Overall, the synthesized Eu³⁺ complexes show promising prospects for applications in solid-state lighting, LED designs and emergency technologies that offer high performance and energy efficiency. Graphical Abstract: (Figure presented.)