As heavy metal-free quantum dots, transition metal dichalcogenides (TMDs) and boron nitride (BN) quantum dots (QDs) have aroused great interest due to features such as good thermal conductivity, chemical stability, and unique optical properties. Although TMDs have been synthesized using different methods, most of these methods require time-consuming or complex steps, limiting the applications of TMDs. We propose a fast and simple method for the synthesis of high-quality molybdenum disulfide (MoS₂) QDs and tungsten disulfide (WS₂) QDs based on femtosecond laser ablation and sonication-assisted liquid exfoliation. The prepared MoS₂ QDs and WS₂ QDs were characterized by transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. The resulting products possessed few-layered thickness with an average size of 3.7 nm and 2.1 nm. Due to the abundance of functional groups on their surface, the MoS₂ QDs and WS₂ QDs showed bright blue-green luminescence under UV irradiation. Our method offers a facile and novel synthetic strategy for TMDs QDs and other two-dimensional nanomaterial quantum dots, such as boron nitride quantum dots (BNQDs).

Photoluminescent carbon nanodots (C-dots) with size tunability and uniformity were fabricated in polyethylene glycol (PEG_200N) solution using femtosecond laser ablation method. The size distributions and photoluminescence (PL) properties of C-dots are well controlled by adjusting the combined parameters of laser fluence, spot size, and irradiation time. The size reduction efficiency of the C-dots progressively increases with decreasing laser fluence and spot size. The optimal PL spectra are red-shifted and the quantum yields decrease with the increase in C-dots size, which could be attributed to the more complex surface functional groups attached on C-dots induced at higher laser fluence and larger spot size. Moreover, an increase in irradiation time leads to a decrease in size of C-dots, but long-time irradiation will result in the generation of complex functional groups on C-dots, subsequently the PL spectra are red-shifted.

Carbon nanodots (C-dots) with ultrasmall size possessing large surface-to-volume ratio are expected to improve their performance in sensing and catalytic applications. Here, we present a simple strategy to synthesis ultrasmall C-dots using double-pulse femtosecond laser ablation in solution. The size of C-dots reaches minimum value of ∼1 nm when the delay between the pulses was approaching the electron-ion relaxation time. In this case, the mean sizes of C-dots in double-pulse ablation are even smaller than that obtained in single-pulse ablation with the same laser fluence due to the suppression of rarefaction wave by the shock wave created by the second pulse. Furthermore, abundant functional groups are created on the surface of C-dots in double-pulse ablation because of reheating the nascent ablated materials by the second pulse. These results demonstrate that the double-pulse technique is therefore an effective strategy beyond single-pulse ablation to synthesis ultrasmall C-dots with abundant surface functional groups as well as other nanoparticle for catalytic and sensing applications.