Terbium(III)-Doped Silica Surface of Fe(II) Spin Crossover Nanoparticles as a Multifunctional Interface

Spin-crossover (SCO) nanoparticles (NPs) of the ID coordination polymer [Fe-(HTrz)₂(Trz)]·(BF₄), where HTrz = 1H-1,2,4-triazole, have been synthesized with integrated luminescence properties, focusing on the role of dopant trivalent Terbium (Tb) ions. Using a reverse micelle method, three types of nanoparticles were synthesized: pristine NPs (NP1), silica covered (NP2), and Tb-doped (NP3) NPs. Structural and morphological analyses, including TEM, STEM-XEDS, FT-IR, P-XRD, XPS, and XAFS spectroscopy, confirmed the successful incorporation of Tb ions into the silica matrix of NP3 and revealed their bonding environment with SiO₄ tetrahedra and nitrate ions. Magnetic susceptibility measurements demonstrated hysteretic SCO behavior in all nanoparticle types, with NP3 exhibiting the highest thermal hysteresis width and a shift in critical temperatures, indicating enhanced cooperativity and modified magnetic properties due to the presence of Tb ions. Temperature-dependent photoluminescence (PL) measurements of NP3 showed hysteresis during thermal cycling, attributed to SCO transitions between high- and low-spin states. The study highlights the synergy between SCO and luminescence properties, paving the way for the development of multifunctional materials for applications in optoelectronics, sensors, and thermometry. These findings provide valuable insights into the design and optimization of advanced SCO-luminescent nanomaterials.