The effect of laser energy on the size of WS₂ quantum dots synthesized by pulsed laser ablation in liquid

This study aims to synthesize WS₂ quantum dots (QDs) by pulsed laser ablation in liquid. The synthesis was carried out by varying laser energy in the range of 10-40 mJ and keeping all other parameters unchanged. The quantum dots so formed were characterized using Raman spectroscopy, Field emission transmission electron microscope (FETEM), and Photoluminescence (PL) spectroscopy. The identified prominent Raman peaks are at 356.78 (E¹_2g) and 420.71 cm^− 1 (A_1g) for 10 mJ laser energy, at 351.40 (2LA), 357.03 (E¹_2g) and 421.57 cm^− 1 (A_1g) for 20 mJ laser energy, at 353.21 (E¹_2g) and 419.161 cm^− 1 (A_1g) for 40 mJ laser energy. The Peak frequency difference between A_1g(Γ) & E¹_2g(Γ) increases, peak intensity ratio I E¹_2g/I A_1g, decreases, and the FWHM for E¹_2g(Γ) & A_1g (Γ) increases for laser energies from 10 mJ to 40 mJ. The FETEM images of synthesized quantum dots exhibited the significant influence of laser energy on the size of WS₂ quantum dots; the mean size increased from 3.56 nm to 6.1 nm for laser energy, from 10 to 40 mJ, respectively. The deconvoluted PL spectrum for different laser energies shows multiple peaks, indicating size distribution of WS₂ QDs. The PL peaks having maximum area intensity exhibit red shifts from 3.26 eV to 3.09 eV with increasing laser energy from 10 mJ to 40 mJ, indicating increase in size of WS₂ QDs and narrowing of the band gap energy of the QDs.