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Herein, we have investigated the tunability of the photoluminescence (PL) of the monolayer MoS2 (1L-MoS2) by decorating it with WS2 quantum dots (WS2 QD). The direct bandgap 1L-MoS2 and WS2 QDs are grown by chemical vapor deposition and liquid exfoliation methods, respectively. The room temperature PL spectrum of bare 1L-MoS2 is systematically quenched with its decoration with WS2 QDs at different concentrations. A decrease in the work function of 1L-MoS2 with the decoration of WS2 QDs was established from the Kelvin probe force microscopy analysis. A detailed quantitative analysis using the four-energy level model involving coupled charge transfer was employed to explain the redshift and the systematic decrease in the intensity of the PL peak in 1L-MoS2/WS2 QD heterostructure. The modulation of the PL in the heterostructure is attributed to the increase in the formation of negative trions through the charge transfer from WS2 QD to the 1L-MoS2 and thus making the 1L-MoS2 heavily n-type doped, with increase in the electron density by ~1.5 × 1013 cm−2. This study establishes the contribution of defects in the coupled charge transfer dynamics in 1L-MoS2, and it lays out a convenient strategy to manipulate the optical and electrical properties of 1L-MoS2 for various optoelectronic applications.

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Heterostructures (HS) of van der Waals two-dimensional (2D) semiconductors with non-van der Waals 2D semiconductors can be an exciting avenue for exploring their innovative optoelectronic applications. Neutral and charged exciton dynamics play a significant role in understanding the optical interband transitions in two-dimensional monolayer transition-metal dichalcogenides (TMDs). We investigate the effect of non-van der Waals 2D Bi2O2Se quantum dot (QDs) decoration on the monolayer WS2 (1L-WS2) film grown using chemical vapor deposition (CVD). The high photoluminescence (PL) emission of 1L-WS2 gets systematically quenched on the variation of the concentration of the QDs. We study the associated charge transfer dynamics in the system using a four-energy-level model. The PL measurements at different QD concentrations show that the exciton decay becomes faster as the concentration increases. Likewise, the trion formation rate increases. The trion decay involves trapping by defect states, which plays a vital role in the coupled charge transfer. Thus, the evolution of the emission features of 1L-WS2 in the heterostructure (HS) is attributed to the conversion of neutral excitons to negatively charged trions via electron transfer from the Bi2O2Se QDs. The simulation based on a set of decay rate equations replicates the experimental data for different concentrations of QDs. The 1L-WS2 becomes n-type doped, with an increase in the electron density by ∼6.6 × 1013 cm–2. The charge transfer from Bi2O2Se to WS2 due to the type II band alignment is confirmed by Kelvin probe force microscopy (KPFM). The study lays out a suitable approach to tune the optical properties of 1L-WS2 by doping using QDs. The charge transfer potentially enables researchers further to study the fundamentals of light–matter interaction at nanoscale heterostructures.

Bismuth oxyselenide (Bi2O2Se) quantum dots, a new 2D non-van der Waals nanomaterial having unique semiconducting properties, could be favorable for various sensing applications.