Strong Photoluminescence Enhancement in Molybdenum Disulfide in Aqueous Media

The interface between conventional semiconductors and aqueous ionic solutions is an important target in chemistry and materials science. Recently, a wide variety of research has been done on transition-metal dichalcogenides (TMDCs) for use as 2D layered semiconductors, and their optoelectronic properties have been widely explored. One representative TMDC, monolayer (1L) MoS₂, is known to show a photoluminescence (PL) signal of a direct band gap nature, and the PL intensity is dependent on the carrier concentration. Various methods of 1L MoS₂ carrier modulation have been shown to enhance the PL intensity in dry environments. In contrast, enhancement in an aqueous environment is limited, and a strategy to design an interface with aqueous media has not yet been established. One proposed idea was an aqueous acid interface; however, the enhancement of the PL with this method was usually minimal, about 1 order of magnitude. In this study, we demonstrate a method to achieve strong PL enhancement in 1L MoS₂ in an aqueous media by incorporating bis(trifluoromethane)sulfonyl anion (TFSI^- ion) in an acidic environment. With the addition of the TFSI^- ion in an acidic environment, the enhancement factor of the PL in 1L MoS₂ is more than 100 times greater than its PL intensity in water. The molecular anion is the key factor, as the TFSI^- ion facilitates the oxidation of MoS₂. This anionic effect is the additional factor needed to modulate the optoelectronic properties of 2D semiconductors in aqueous media. The proposed idea could have potential applications for biochemical sensors in aqueous situations.