Laser‐Synthesized Amorphous PdSe _2‐x Nanoparticles: A Defect‐Rich Platform for High‐Efficiency SERS, Photocatalysis, and Photothermal Conversion

ABSTRACT The control of material properties at the atomic scale remains a central challenge in materials science. Transition metal dichalcogenides (TMDCs) offer remarkable electronic and optical properties, but their functionality is largely dictated by their stable crystalline phases. Here, we demonstrate a single‐step, ligand‐free strategy using femtosecond laser ablation in liquid to transform crystalline, stoichiometric palladium diselenide (PdSe 2 ) into highly stable, amorphous, and non‐stoichiometric nanoparticles (PdSe 2‐x , with 1). This laser‐driven amorphization creates a high density of selenium vacancies and coordinatively unsaturated sites, which unlock a range of emergent functions absent in the crystalline precursor, including plasmon‐free surface‐enhanced Raman scattering with an enhancement factor exceeding 10, a 50‐fold increase in photocatalytic activity, and near‐infrared photothermal conversion efficiency reaching 83%. Our findings establish laser‐induced amorphization as a powerful top‐down approach for defect‐engineered TMDCs and advances their practical usage in optics, catalysis, and nanomedicine.