Size-tunable photoluminescence from WS2 nanostructures

Variable size crystalline nanostructures of WS2 have been successfully synthesized in a single-step process using liquid exfoliation in different liquid media. Out of three liquid media chosen in the work, we found that the mixture of de-ionized water and ethanol is most efficient for preparing the nanostructures. The average size of obtained nanostructures (quantum dots) range from 4 nm to 5 nm and that of few layer sheets range from 20 nm to 100 nm or even larger depending upon the choice of liquid media used for exfoilation process. The present work illustrates that choice of liquid media is critical for efficient production of the highly luminescent nanostructures in lesser time. Further, when compared to their bulk counterpart these nanostructures exhibit size dependent photoluminescence in ultraviolet and visible region. Quantum dots displayed absorption features at shorter wavelength and might originate from excitonic transitions in these scaled nanostructures. Highly luminescent nature together with blue shifted absorption feature suggests the presence of quantum confinement effects in the WS2 nanostructures.