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‐In 2 S 3 is studied. This In 2 S 3 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‐In 2 S 3 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‐In 2 S 3 nanoplatelets similarly to a prolonged air exposure. The work shines light on the optical properties of γ‐In 2 S 3 , paving the way for their control and the use of this material in luminescence sensing.