Role of dielectric medium on optical behaviour of blue emitting colloidal MoS2 quantum Dots

Abstract

In this work, we report colloidal synthesis of blue emitting MoS2 quantum dots (QDs). The emission characteristics, being dependent on the surface defect states, can be tuned by engineering the QD – dielectric interface. We have reported an investigation of interaction between dispersing medium and MoS2 QDs. The MoS2 QDs have shown different optical behaviour in three different dispersing dielectric media: non-polar (hexane), electron acceptor (chloroform) and an electron donor (dimethylformamide). As synthesized MoS2 QDs absorb in the UV and emit in the UV–Vis wavelength range from 2 to 4 eV with emission maxima at ∼3 eV. A significant decrease to ∼62 nm in the FWHM value of emission spectra has been obtained for QDs dispersed in DMF along with no shift in the maxima at various excitation wavelengths due to quenched surface dangling states and sulfur (S2−) vacancies leading to decreased non-radiative decay pathways. Our synthesized MoS2 QDs have shown the excitation dependent photoluminescence behaviour with a redshift in the emission peak with increasing excitation wavelength. This redshift can be attributed to the polydisperse nature of the MoS2 QDs as well as the presence of surface defect states.