Probing the role of ligand molecules on the thermal stability and optical properties of Tb3+-based complexes

Lanthanide complexes embody the high absorption coefficient of ligand molecules in a wide ultraviolet spectral range and the excellent characteristics of the lanthanide ions that make them attractive for various applications. In this work, we synthesized terbium-based complexes, namely, terbium tris(1,1,1-trifluoro-2,4-pentanedionate) dihydrate Tb(TFAC) 3 2H 2 O, terbium tris(1,1,1-trifluoro-2,4-pentanedionate)(1,10-phenanthroline)Tb(TFAC) 3 Phen, terbium tris (2-chlorobenzonate)(1,10-phenanthroline)Tb(2-CIBA) 3 Phen, and terbium tris(acetylsalicylate)(1,10-phenanthroline)Tb(ASA) 3 Phen and investigated the role of ligand molecules on the luminescence properties, thermal stability, and energy sensitization to Tb 3+ ions. The Raman and FTIR studies reveal that the primary and secondary ligands coordinate with the central Tb 3+ ion. The PLE spectrum does not show a sharp excitation peak corresponding to Tb 3+ ions in all these complexes; it possesses only a broad excitation corresponding to the ligand molecule, indicating an efficient energy transfer from ligand to Tb 3+ ions. The secondary ligand is not an efficient energy sensitizer; however, it reduces the non-radiative channel, thereby helping in increasing the photoluminescence intensity, excited-state lifetime of Tb 3+ ions, and photoluminescence quantum yield (PLQY). Thermogravimetric analysis shows that among these complexes, Tb(2-CIBA) 3 Phen possesses the highest thermal stability. Also, it exhibits maximum photoluminescence intensity and PLQY (61.7 %), which was attributed to the favorable energy alignment between the triplet state of 2-CIBA and the 5 D 4 level of Tb 3+ ions. Further, the CIE coordinates, LER, and color purity of these complexes show that these complexes have pretty similar color parameters. This work successfully demonstrates the role of ligand molecules on the optical properties, energy sensitization, and thermal stability of the lanthanide complexes in general.