Effects of Co/Fe doping on the optical limiting behaviors of copper-based sulfides under low energy densities

Abstract

Abstract Copper-based sulfides have demonstrated excellent potential in optical fields due to their unique optical properties. In this work, heteroatom doping is conducted in copper-based sulfides to regulate their photo-physical properties. The average grain size of CuCo2S4/CuFeS2 is about 15 nm, whereas the average grain sizes of CuCo2S4 and CuFeS2 are 69 and 73 nm, respectively. The as-obtained derivations of CuCo2S4, CuFeS2, and the coprecipitated CuCo2S4/CuFeS2 are systematically characterized, and the nonlinear optical properties (NLO) of the copper-based sulfides are investigated via the Z-scan technique in the low-laser intensity range of 1–4 µJ to avoid the contribution of solvent scattering in nonlinear optical results. All copper-based sulfides exhibit optical limiting effects, and the open aperture Z-scan results suggested the coexistence of both nonlinear absorption and nonlinear refraction in the sulfides. Co or Fe doping can enhance the optical limiting effects of copper sulfides to some extent, and the normalized transmittances in CuCo2S4 and CuFeS2 are reduced to about 72% from the pristine Cu1.8S (85%) at the input energy of 4 µJ. Interestingly, the optical limiting performances of the coprecipitated CuCo2S4/CuFeS2 are enhanced significantly, and the normalized transmittance in CuCo2S4/CuFeS2 is reduced to about 59% at an input energy of 4 µJ, much lower than the counterpart of the physical mixture of CuCo2S4 and CuFeS2. The highest nonlinear absorption coefficient (β) value is achieved in CuCo2S4/CuFeS2, consistent with the Z-scan results. The NLO enhancement in CuCo2S4/CuFeS2 may derive from the more efficient interfacial charge transfer between coprecipitated CuCo2S4 and CuFeS2, which give a higher efficiency in the carrier mobility.