Distinct nonlinear absorption behaviors in Cu1.8S nanocrystals influenced by geometry features

Spherical and lamellar Cu1.8S nanocrystals with radial dimension of about 40 nm were synthesized by the thermal injection method. Combining the crystal and morphological analysis with the photo physical property, the lamellar Cu1.8S nanocrystals displayed the typical features of 2D metal sulfides which can be ultrasonically exfoliated into single or few layers of Cu1.8S nanosheets due to the fact that the atomic layers were bonded by interlayer van der Waals forces. While in the spherical Cu1.8S nanocrystals, no exfoliation or morphological change occurred after sonication. The nonlinear optical properties of spherical and lamellar Cu1.8S nanocrystals after sonication were investigated by the Z- scanning technique using a 532-nm nanosecond laser pulse. The lamellar Cu1.8S nanocrystals showed saturation absorption, reaching a normalized transmittance of 1.58 at 60 mu J with a I- s value of 1.65 GW/cm(2) and beta value of -16 cm GW(-1). While the spherical Cu1.8S nanocrystals exhibited optical limiting effects, reaching the normalized transmittance of 0.38, with a beta value of 8 cm/GW. Distinct nonlinear absorption behaviors in Cu1.8S nanocrystals with the similar lateral size were observed in the spherical and lamellar Cu1.8S nanocrystals, showing significant geometry feature-dependent nonlinear absorption behaviors.