Luminescent Hybrids of Halloysite and Eu3+ and Tb3+ β-Diketonate Complexes: Immobilization, Colloidal and Photophysical Properties

Halloysite nanotubes (HNT) are naturally occurring tubular aluminosilicates whose distinct inner and outer surfaces make them attractive supports for hybrid luminescent materials. In this work, HNT-[Eu(dbm)₄] and HNT-[Tb(dpm)₃] were synthesized and characterized by X-ray diffraction (XRD), electrophoretic and dynamic light scattering (ELS/DLS), FT-IR, and photoluminescence spectroscopy. XRD confirmed preservation of the HNT crystalline structure after immobilization. ELS revealed that HNT-[Eu(dbm)₄] retained the negative zeta potential of pristine HNT, whereas HNT-[Tb(dpm)₃] exhibited positive values. Hydrodynamic particle sizes were approximately 335 nm and 230 nm, respectively, with no significant differences among independent analyses (n = 7, p > 0.05). Both hybrids displayed the characteristic Eu³⁺ and Tb³⁺ emissions with efficient ligand-to-metal energy transfer. Luminescence lifetimes were 0.34 and 0.24 ms for Eu³⁺ and 0.44 and 0.67 ms for Tb³⁺ at 298 and 77 K, respectively, demonstrating that HNT effectively immobilizes β-diketonate lanthanide complexes while preserving their structural, colloidal, and luminescent properties.