Facile synthesis of photoluminescent MoS2 and WS2 quantum dots with strong surface-state emission

Highlights: • Quantum dots possess intense and excellent photostability photoluminescence. • Abundant surface functional groups result in the bright photoluminescence. • Direct excitation-recombination of carriers on surface states is fast and dominant. -- Abstract: Transition metal dichalcogenides quantum dots (QDs), especially molybdenum disulfide (MoS₂) and tungsten disulfide (WS₂) QDs, have attracted great attention as a potential candidate for the application of fluorescent materials. However, the photoluminescence quantum yield (PLQY) of these QDs is still very low, which severely limits their availability for practical applications. Here, we present a simple and green strategy to synthesis highly photoluminescent MoS₂/WS₂ QDs using femtosecond laser ablation of raw MoS₂/WS₂ powders in solution. The as-prepared MoS₂/WS₂ QDs exhibit intense and excellent photostability photoluminescence in blue region with a satisfying PLQY of 22.5%. By detailed characterization and spectroscopic study, we find that abundant surface functional groups, such as C–O, CO, and C–N, can efficiently introduce new surface-state emission centers and result in their intense fluorescent emission. A simplified energy level and electron transition diagram has been proposed to help understand the surface-state emission mechanism.