Refining Iron Pyrite Nanomaterials: Advancing Optical Applications with DMII Treatment and Co-Alloying

Over the past decade, there has been a pronounced research emphasis on leveraging the advantageous defect states inherent in metal dichalcogenide nanostructures to intricately modulate and tailor their optoelectronic characteristics. Here, we demonstrate how defects significantly impact the linear and nonlinear optical properties of pristine FeS2 nanomaterials (NMs), ionic liquids (DMII) passivated FeS2 NMs, and CoFeS2 NMs. These NMs were synthesized using a low-cost hot-injection process, and their structure was validated via X-ray diffraction analysis. The oval-like structure of the NMs is revealed by high-resolution transmission electron microscopy, and X-ray photoelectron spectra demonstrate the presence of the divalent oxidation state of iron (Fe) and cobalt (Co). After the treatment of DMII on the pristine NMs, a decrease in the Urbach energy (Eu) was found, with values reducing from 0.77 to 0.27 meV. This phenomenon may potentially be associated with the passivation of surface imperfections in pristine NMs. The treatment of DMII further enhances the lifetime of charge carriers (1.25 ns) and conductivity by one order compared to pristine FeS2 NMs. On the other hand, introducing Co in FeS2 alters the conductivity of pure FeS2 NMs, shifting them from p-type to n-type and significantly enhancing their electrical characteristics by 3 orders of magnitude. The open aperture z-scan study revealed that the CoFeS2 NMs have an effective nonlinear absorption coefficient (βeff) of 160 cm GW–1, which is superior to that of the pristine NMs with a βeff of 130 cm GW–1. The optical limiting threshold value (1.01 J cm–2) of CoFeS2 NMs is much higher than those of both pristine and DMII-treated FeS2 NMs, indicating superior optical limiting performance. The current work presents a comprehensive analysis of pristine, DMII-treated, and Co-alloyed FeS2 NMs, focusing on their potential for linear and nonlinear optoelectronic applications.