Designing bimetallic lanthanide complexes with composition controlled white-light luminescence for advanced...

Luminescent complexes containing Tb³⁺ and Sm³⁺ ions were prepared through a solution precipitation method, using ligand L and bathophenanthroline (batho) as an auxiliary ligand. Systematically adjusting the Tb³⁺ to Sm³⁺ ratio enabled precise tailoring of the emission characteristics, resulting in emission profiles that approached white light. The elemental analysis verified the elemental composition. Scanning electron microscopy (SEM) and powder X-ray diffraction (PXRD) confirmed the nanoscale morphology and crystalline structure of the complexes. Fourier-transform infrared (FT-IR) spectroscopy revealed details of the coordination environment, indicating that the ligand L adopts a zwitterionic form upon complexation. Thermogravimetric (TG) and differential thermogravimetric (DTG) analyses showed that the complexes are thermally stable up to 255 °C. Optical band gap analysis confirmed semiconducting behavior. Photoluminescence measurements showed tunable emission features, with the optimal composition (Tb_0.65 Sm_0.35) producing white-light emission marked by CIE coordinates of (0.337, 0.371) and a correlated color temperature of 5346.10. Judd-Ofelt analysis (Ω ₂ > Ω ₄ > Ω ₆) indicated notable ligand field asymmetry and rigidity, resulting from cooperative energy transfer between Tb³⁺ and Sm³⁺ ions. Overall, these results suggest that Tb³⁺/Sm³⁺ complexes are strong candidates for multifunctional luminescent materials in optoelectronic and photonic applications.