Nonlinear absorption properties of two-dimensional PtSe2 and PtTe2 nanosheets

As transition metal dichalcogenides (TMDCs), PtSe₂ and PtTe₂ exhibit promising nonlinear optical (NLO) properties but lack systematic studies on their nonlinear absorption (NLA) properties. Given that PtSe₂ and PtTe₂ possess an identical hexagonal crystal structure. In this study, we systematically evaluate their NLO properties using open-aperture (OA) Z-scan technique performed at wavelengths of 355, 532, and 1064 nm. Both materials showed significant two-photon absorption (TPA), with their TPA cross-sections (σ_TPA) increasing trend as decreasing wavelength. The σ_TPA of two-dimensional (2D) PtTe₂ exhibited around one order of magnitude larger than that of 2D PtSe₂ in the ultraviolet (UV) band (355 nm), particularly, indicating a stronger optical limiting (OL) effect. Considering that the structural difference between the two materials primarily arises from anion substitution, we further investigated the superior OL performance of 2D PtTe₂ from the perspective of band structure. This analysis elucidates the underlying physical mechanism associated with band splitting induced by spin-orbit coupling (SOC) effects. This study not only advances TMDCs as promising candidates for high-power laser protection, OL devices, and UV photodetection in the NLO field. It also offers valuable insights for the design and development of high-performance NLO materials.