High yield production of photoluminescent tungsten disulphide nanoparticles.

Single and few layered tungsten disulphide (WS2) nanoparticles were prepared using a surfactant assisted ultrasonication exfoliation technique with concentrations of up to 0.4 mg/mL. The lateral dimension of the particles was in the range of 100-250 nm. The exfoliated WS2 was stabilised against re-aggregation through adsorption of a tri-block non-ionic polymeric surfactant (PEO-PPO-PEO). These nanoparticles were characterised by absorption, Raman and photoluminescence spectroscopy (PL). Broadening of the E2g peak in the Raman spectrum was observed due to phonon confinement within a single layer of WS2. The exfoliated particles have significantly different properties than the bulk WS2 material, in particular, the emergence of strong photoluminescence at 1.97 eV in energy coincidental with the excitonic peak in the UV-Vis spectrum. The emergent PL emission suggests that the monolayer WS2 is a direct gap material analogous to other dichalcogenides such as MoS2.