Polyethylene Glycol-Mediated Switchable Blue-Green Emissions in Sulfur Nanostructures Controlled through the Surface Chemistry

Metal-free sulfur nanodots are an emerging class of nanoparticles for applications in photonics and nanobiotechnology. Because of the stable photoluminescence (PL) and low toxicity, pure elemental quantum dots, such as S-dots, are excellent candidates for a new generation of 0D nanomaterials. However, they require a proper design to control the PL and obtain an excitation-independent emission. Here, we show that the control of the S nanostructure emission can be achieved by modulating the surface interface with an organic polymer, polyethylene glycol (PEG-400), which is widely used to passivate the nanostructure surface. Blue and green emissions can be switched on or off through PEG-400. The fluorescent S nanomaterials have been synthesized by thermally treating S powders in an alkaline solution and adding controlled amounts of PEG-400. The polymer triggers the formation of organosulfur compounds, with a remarkable modification of the characteristic emission of the S products. The sample emission shifts from blue to green by controlling the polymer concentration in the solution. The intensities of the two emissions can be tuned by adjusting the amount of PEG that favors the surface oxidation of the S nanostructure. A lower degree of oxidation causes an emission in the blue range, and higher oxidation of the sulfur atoms promotes an emission to the green.