Crystal Anisotropy Implications on the Magneto‐Optical Properties of van der Waals FePS 3

Antiferromagnetic FePS 3 has recently gained significant interest in its potential applications in spin‐related devices. Here, we show that in‐plane structural anisotropy has a major impact in shaping the optical responses of FePS 3 single‐crystals from the bulk form down to the monolayer limit. X‐ray diffraction on a bulk FePS 3 crystal confirms a distorted FeS 6 octahedron causing inequivalent Fe‐Fe distances and consequently resulting in a higher a/b lattice parameter ratio. Micro‐photoluminescence observations on bulk and monolayer FePS 3 reveal four emissions: one intra‐atomic d‐d transition (band A, centered at ∼1.24 eV) and three p‐d charge transfer transitions (bands B, C, and D, centered around ∼1.79, ∼2.3, and ∼2.56 eV, respectively). These bands exhibit different polarization behaviors, which persist down to the monolayer limit. Density functional theory calculations from bulk to monolayer FePS 3 reveal the underlying electronic structure, assign the observed emissions, and indicate why these peaks have contrasting linear and circular polarization responses. These results establish a direct structure‐optics relation in FePS 3 , highlighting the strong coupling between lattice anisotropy, electronic transitions, and symmetry‐selective optical selection rules.