Room Temperature Micro-Photoluminescence Studies of Colloidal WS2 Nanosheets

Wet-chemical syntheses of quasi two-dimensional (2D) transition metal dichalcogenides (TMDs) have emerged as promising methods for straightforward solution-processing of these materials. However, the photoluminescence (PL) properties of colloidal TMDs are virtually unexplored due to the typically nonemitting synthesis products. In this work, we demonstrate room temperature micro-PL of delicate ultrathin colloidal WS2 nanosheets synthesized from WCl6 and elemental sulfur in oleic acid and oleylamine at 320 degrees C for the first time. Both mono- and multilayer PL are observed, revealing comparable characteristics to exfoliated TMD monolayers and underpinning the high quality of colloidal WS2 nanosheets. In addition, promising long-term air stability of colloidal WS2 nanosheets is found, and the control of photodegradation of the structures under laser excitation is identified as a challenge for further advancing the nanosheet monolayers. Our results render colloidal TMDs as easily synthesized and highly promising 2D semiconductors with optical properties fully competitive with conventionally fabricated ultrathin TMDs.