Transition metal dichalcogenides (TMDs) with a typical layered structure are highly sensitive to their layer number in optical and electronic properties. Seeking a simple and effective method for layer number identification is very important to low-dimensional TMD samples. Herein, a rapid and accurate layer number identification of few-layer WS and WSe is proposed via locking their photoluminescence (PL) peak-positions. As the layer number of WS/WSe increases, it is found that indirect transition emission is more thickness-sensitive than direct transition emission, and the PL peak-position differences between the indirect and direct transitions can be regarded as fingerprints to identify their layer number. Theoretical calculation confirms that the notable thickness-sensitivity of indirect transition derives from the variations of electron density of states of W atom d-orbitals and chalcogen atom p-orbitals. Besides, the PL peak-position differences between the indirect and direct transitions are almost independent of different insulating substrates. This work not only proposes a new method for layer number identification via PL studies, but also provides a valuable insight into the thickness-dependent optical and electronic properties of W-based TMDs.

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Flexibly tunable fluorescence intensity and electron concentration of 1L-MoS2 are achieved by forming novel 2D/0D hybrid heterostructures with semiconductor dots.

A high-temperature driven carrier transfer process of multilayer WS2 is proposed and demonstrated for significant fluorescence emission enhancement.

Flexibly manipulating optical and electrical properties of 2D materials is of great importance to extend their functional applications in the advanced optoelectronic field. Herein, a type II 2D/0D hybrid heterostructure is facilely fabricated by spin-coating CdSe quantum dots (CdSe-QDs) onto monolayer WS2 (1L-WS2) flakes, and improved fluorescence emission and electron density of 1L-WS2 have been achieved through effective CdSe-QDs doping. The interfacial charge behavior is explored via X-ray photoelectron spectroscopy, scanning Kelvin probe force microscopy studies, and time-resolved photoluminescence measurements, proving the charge transfer from QDs to 1L-WS2 in these heterostructures. Furthermore, the photocurrent of a photodetector based on this hybrid heterostructure increases significantly due to efficient and fast separation and collection of photocarriers, verifying the validity of our proposed carrier dynamic model. The current work proposes a convenient strategy for tuning the photonic and electronic properties of 2D semiconducting materials, which may pave the way for developing new-type optoelectronic devices based on these newly emerging 2D materials and heterostructures.