O oxysulfides as a probe of covalency and chemical composition*

Rare-earth oxysulfides have been studied in a wide range of applications due to their multiple optoelectronic properties arising from their abundant excited electronic energy levels. Herein, we present the solid-state synthesis and systematic analysis of the lanthanoid (Ln) 3d X-ray photoelectron absorption region for the early lanthanoid oxysulfides Ln₁₀S₁₄O (Ln = La, Ce, Pr, Nd and Sm). The multiplet structure is estimated to originate in the excitation of 3d electrons in addition to a ligand-to-metal charge transfer process, for both 3d_5/2 and 3d_3/2 photoelectron regions. As the atomic number, and 4f electron count, increases from Ce to Sm, the satellite and 3d signal energy separation tends to decrease for the same ligand environment, in conjunction with an increase in the 3d-to-satellite ratio, indicating a lower orbital overlap between Ln 4f and ligand orbitals. Furthermore, analysis of the La(III) 3d region, demonstrates its unique sensitivity to chemical environment based on the covalency of the ligand environment.