Lanthanide-induced magnetic functionality and conductivity enhancement in MAPbI3 via water-assisted recrystallization

Abstract Lanthanide incorporation into hybrid halide perovskites offers a promising route to introduce magnetic functionality while tuning charge-transport behavior. Here, we report the incorporation of paramagnetic rare-earth ions (Gd ³ ⁺, Tb ³ ⁺, and Dy ³ ⁺) into MAPbI₃ through a water-assisted dissociation-recrystallization strategy that enables trapping of 4f ions within the restored 3D perovskite-derived lattice. Powder X-ray diffraction confirms preservation of the tetragonal I4/mcm structure, while ICP-MS verifies the presence of lanthanides in the final materials. Magnetic susceptibility measurements reveal robust paramagnetic behavior governed by the 4f electronic configuration, with effective magnetic moments of μ _eff = 9.12 μ _B for MAPbI₃:Tb and 20.22 μ _B for MAPbI₃:Dy. Electrical measurements show a pronounced reduction in dark resistance, decreasing from approximately 7.7 × 10⁷ Ω for pristine MAPbI₃ to about 1.0 × 10 ⁴ Ω for the most conductive Ln-doped sample, indicating a substantial enhancement of charge transport upon lanthanide incorporation. Under illumination, all samples exhibit reversible photoconductive behavior. Density functional theory calculations, performed using simplified substitutional models, provide exploratory electronic-structure scenarios: Gd-related unoccupied 4f states may lie within or near the conduction band, whereas Tb and Dy can introduce localized f-derived states within the bandgap, which may contribute to carrier trapping and modified recombination dynamics. Optical absorption measurements indicate subtle bandgap modulation without significant changes in the radiative band-to-band emission. These results demonstrate that water-assisted recrystallization is a viable strategy to introduce magnetic functionality into MAPbI₃ while substantially modifying its electrical response, and they identify lanthanide-doped MAPbI₃ as a promising multifunctional platform for future optoelectronic and spintronic studies. Graphical abstract A significant conductivity enhancement is observed when rare-earth ions are incorporated into an iodine-based 3D perovskite matrix. The results also reveal the emergence of magnetic functionality associated with the inclusion of 4f paramagnetic ions. Although the photoluminescence spectra of the doped samples remain similar to that of pristine MAPbI₃, clear changes in optical absorption and electrical transport are observed.