Nonlinear Optical Activities in Van der Waals Ternary Transition Metal Dichalcogenides

In recent years, low-dimensional van der Waals (vdW) materials have been extensively investigated due to their unique characteristics, including atomically thin structures, broad absorption spectra, pronounced layer-dependent optoelectronic properties, and strong light-matter interactions. Ternary low-dimensional vdW materials are gaining prominence in the two-dimensional (2D) domain, attracting considerable attention for their exceptional physical, chemical, and optical properties. This study explores a ternary 2D transition metal dichalcogenide (TMDC) comprising molybdenum (Mo) and niobium (Nb) coexisting with selenium (Se) chalcogenide for nonlinear optics applications. The nonlinear optical responses of the prepared nanoflakes were examined in the near-infrared (NIR) regime, demonstrating notable nonlinear optical absorption that transitions from saturable absorption (−580 × 10³ to −55 × 10³ cm/GW at 1068 nm and −170 × 10³ to −67 × 10³ cm/GW at 1558 nm) to reverse saturable absorption (14 × 10³ to 15 × 10³ cm/GW at 1068 nm and 8 × 10³ to 10.9 × 10³ cm/GW at 1558 nm) with increasing pump intensity (40.86 to 64.42 MW/cm² for 1068 nm and 11.48 to 161.78 MW/cm² for 1558 nm). Additionally, the material's self-defocusing nature was revealed using the closed aperture (CA) z-scan technique. Furthermore, broadband second harmonic generation (SHG) was observed in the even-numbered layers, indicating a non-centrosymmetric structure exclusively in these layers. The remarkable findings highlight the potential of Mo and Nb-based ternary TMDC as effective nonlinear optical materials, thereby presenting significant opportunities for various advanced photonics and optoelectronics applications.