Surface Oxidation of 2D γ-Indium Sulfide Nanoplatelets and Its Impact on Photoluminescence

Two-dimensional (2D) semiconductor materials are being explored for applications including photocatalysis and optoelectronic devices. This class of materials features high surface-to-volume ratio that imparts unique physical properties. Yet, this feature makes 2D semiconductor materials prone to chemical changes that translate to variations in their photophysical behavior. Large-scale application of these materials requires an understanding of degradation processes toward developing strategies to increase their stability. Here, the effect of air exposure on underexplored 2D semiconductor material γ-In₂S₃ is studied. This In₂S₃ polymorph is stabilized as nanoplatelets, which are then characterizes before and after exposure to air. A marked surface oxidation , accompanied by drastic variations in photoluminescence is observed. Temperature-dependent spectroscopic measurements show that the emission spectrum of fresh γ-In₂S₃ nanoplatelets is dominated by two defect-related bands, while oxidation enhances the contribution of a third band. An energy level scheme is proposed based on the analysis of the spectroscopic data. This study finally portrays how a postsynthesis treatment with an oxygen-containing molecule (oleic acid) changes the photoluminescence of γ-In₂S₃ nanoplatelets similarly to a prolonged air exposure. The work shines light on the optical properties of γ-In₂S₃, paving the way for their control and the use of this material in luminescence sensing.