Lead-Sulfide-Based Hybrid Inorganic-Organic Superlattice Particles for Prominent Nonlinear Optical Absorption

Simultaneously optimizing nonlinear absorption coefficient and modulation depth is a considerable challenge for nonlinear optical materials. Here we present an effective solution through constructing PbS₂-based inorganic-organic superlattice. PbS₂/C_n superlattice particles are synthesized, where n (4, 6, and 8) denotes the number of carbon atoms in the organic component. First-principles simulations indicate the formation of covalent bonds and van der Waals interaction between PbS₂ unit and interlayer organic molecules. All samples exhibit strong nonlinear absorption under femtosecond laser excitation with a wavelength range between 515 nm and 900 nm, and the nonlinear absorption coefficient increases with interlayer distance. The optimized sample, PbS₂/C₈, demonstrates outstanding nonlinear absorption and substantial modulation depth under 800 nm (the third-order nonlinear absorption coefficient β_eff, 10449 ± 609 cm GW⁻¹; modulation depth, 39.1%) and 900 nm (the fifth-order nonlinear absorption coefficient γ_eff, 6465 ± 68 cm³ GW⁻²; modulation depth, 88.1%), which exhibits saturable absorption under 515 nm (β_eff, -4932 ± 818 cm GW⁻¹; modulation depth, 48.1%). It exhibits a small optical limiting threshold of 1.23 mJ cm⁻². These performances surpass those of typical single-/few-layer metal chalcogenides. Structural and spectral analyses elucidate that the remarkable optical nonlinearity can be attributed to quantum confinement in the inorganic layer and the dielectric enhancement of the superlattice.