The role of the synthetic pathways on properties of Ag2S nanoparticles for photothermal applications

Two different synthetic pathways, namely the miniemulsion and hydrothermal approaches, were investigated for the preparation of silver sulfide nanoparticles, also doped with lanthanide ions. It was demonstrated that the synthesis and the choice of the precursors play a fundamental role in determining the crystalline purity, the size, the stability and the functional properties of the AgS nanostructures. The miniemulsion approach leads to the formation of the targeted structures already at room temperature, but the hydrothermal approach yields particles with increased purity and long-term stability against oxidation. Synchrotron XPS performed with different penetration depths evidences the presence of a stable core of the crystallites composed uniquely of AgS and an external shell where residual elemental S demonstrates the first stage of oxidation due to atmospheric exposure. The samples prepared via hydrothermal synthesis also show a high optical density (0.377) and a good laser-to-heat conversion efficiency (29%).