Syntheses, crystal structures and photophysical properties of three lanthanoid mercury or lanthanoid zinc complexes with different structures

Abstract

Three lanthanoid–IIB metal hybrid complexes, namely, [Dy(HIA)₂(H₂O)₂Hg₂Cl₅(IA)]_nn(HgCl₂)·2nH₂O·nCl (1), [Sm(HIA)₃(H₂O)₂]_n(nHg₂Br₆) (nHgBr₃)·2nH₂O (2), and [Sm(HNA)₃(H₂O)₂]_nn(ZnCl₄)·3nH₂O·nCl (3) (HIA = isonicotinic acid; HNA = nicotinic acid), have been successfully synthesized and characterized. Complex 1 exhibits a two-dimensional (2-D) cationic layer architecture, while complexes 2 and 3 feature one-dimensional (1-D) cationic chains. All three complexes display intense solid-state photoluminescence in the visible region. Complex 1 shows bright yellow emission, which is attributed to the ⁴F_9/2 → ⁶H_13/2 transition of Dy³⁺ ions. Notably, this represents an anti-Stokes upconversion process, as the emission energy exceeds that of the excitation photons, highlighting its potential for near-infrared-to-visible photon conversion. Complexes 2 and 3 exhibit characteristic Sm³⁺-based emissions: dual yellow bands at 568 nm and 603 nm (⁴G_5/2 → ⁶H_5/2 and ⁴G_5/2 → ⁶H_7/2) for 2, and a dominant red emission at 610 nm (⁴G_5/2 → ⁶H_7/2) for 3. The CIE chromaticity coordinates are (0.4942, 0.5045), (0.5175, 0.4814), and (0.6242, 0.3753), with corresponding correlated color temperatures (CCT) of 2834 K, 2425 K, and 3902 K, respectively, indicating tunable warm-to-cool luminescence suitable for lighting and display applications. UV/Vis diffuse reflectance spectroscopy reveals wide semiconductor band gaps of 2.18 eV (1), 2.66 eV (2), and 2.78 eV (3), classifying them as wide-bandgap semiconducting materials. The indirect nature of the optical transitions suggests favorable charge carrier lifetimes for optoelectronic applications. These results demonstrate that the combination of lanthanoid ions with IIB metals and aromatic carboxylate ligands enables the rational design of multifunctional materials exhibiting both efficient luminescence and semiconductive behavior. This work expands the structural and functional diversity of lanthanoid-based hybrid materials and highlights their potential in advanced photonic devices, luminescent semiconductors, and energy-conversion technologies.