Magneto-Optical Response and Luminescence Properties of Lanthanide-Titanium-Oxo Clusters Eu₂Ti₇ and Sm₂Ti₇

The study of magneto-optical effects based on the f-f emission and absorption of lanthanide ions has attracted considerable interest. In this work, we present a series of isostructural lanthanide-titanium-oxo clusters (LTOCs) Ln2Ti7 (Ln = La, Sm, Eu) using 3,5-di-tert-butylbenzoic acid as the ligand. A detailed comparison of the luminescence properties of Sm₂Ti₇ and Eu₂Ti₇ shows that Eu₂Ti₇ displays superior luminescence intensity, higher color purity red light, longer lifetime, and significantly higher quantum yield. These properties, along with its high stability in solution, make Eu₂Ti₇ an excellent candidate for magnetic circularly polarized luminescence (MCPL) studies. Under an external magnetic field, Eu₂Ti₇ exhibited strong MCPL signals, with the maximum |gMCPL| value being 0.04 T-1 from the 5D0→7F4 transition. In contrast, the weaker luminescence of Sm₂Ti₇ rendered MCPL analysis ineffective; however, its strong near-infrared absorption allowed for magnetic circular dichroism (MCD) studies. The MCD spectra of Sm₂Ti₇ revealed significant signals corresponding to f-f transitions in the 900-1600 nm range, with the maximum |gMCD| value observed at 1102 nm. This work provides valuable insights into the magneto-optical properties of Ln-based clusters, emphasizing the role of energy-level analysis for further research into their potential applications in magneto-optical devices.