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

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 CuCo 2 S 4 /CuFeS 2 is about 15 nm, whereas the average grain sizes of CuCo 2 S 4 and CuFeS 2 are 69 and 73 nm, respectively. The as-obtained derivations of CuCo 2 S 4 , CuFeS 2 , and the coprecipitated CuCo 2 S 4 /CuFeS 2 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 µ J 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 CuCo 2 S 4 and CuFeS 2 are reduced to about 72% from the pristine Cu 1.8 S (85%) at the input energy of 4 µ J. Interestingly, the optical limiting performances of the coprecipitated CuCo 2 S 4 /CuFeS 2 are enhanced significantly, and the normalized transmittance in CuCo 2 S 4 /CuFeS 2 is reduced to about 59% at an input energy of 4 µ J, much lower than the counterpart of the physical mixture of CuCo 2 S 4 and CuFeS 2 . The highest nonlinear absorption coefficient ( β ) value is achieved in CuCo 2 S 4 /CuFeS 2 , consistent with the Z -scan results. The NLO enhancement in CuCo 2 S 4 /CuFeS 2 may derive from the more efficient interfacial charge transfer between coprecipitated CuCo 2 S 4 and CuFeS 2 , which give a higher efficiency in the carrier mobility.