Polaron–Bipolaron Modulation in Reduced Graphene Oxide/ZnO/PEDOT:PSS-Based Solid-State Filters for Optical Limiting Applications

The rapid advancements in high-intensity laser technologies necessitate the advancement of robust optical limiters to safeguard optical components and human sight. This study presents the fabrication of solid-state-based limiting filters by incorporating reduced graphene oxide–metal oxide nanocomposites into a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) polymer matrix. Precise reduction rate modulation of reduced graphene oxide enables the tailoring of defect densities and electronic structures, thereby optimizing the interplay between polaronic and bipolaronic states to enhance nonlinear optical properties. The fabrication of the filters was carried out by using the dip-coating technique, and their structural integrity and defect characteristics were examined through X-ray diffraction patterns and Raman spectral analysis, respectively. The variations in polaronic and bipolaronic states were analyzed by using near-infrared absorption spectroscopy, while the third-order nonlinear optical properties and optical limiting performance were evaluated with the Z-scan technique. The presence of both polaronic and bipolaronic states facilitates a more controlled charge transport mechanism and enhances excited-state absorption, thereby improving the reverse saturable absorption process, which is crucial for effective optical limiting. The fabricated filters exhibited an optical limiting threshold of 2.69 J/cm2 at a laser input intensity of 4.59 GW/cm2, under excitation with a 5 ns pulse at a repetition rate of 10 Hz and a wavelength of 532 nm. The findings establish a direct correspondence between charge transport modulation and enhanced optical limiting performance, offering valuable insights into the design of next-generation, high-efficiency nonlinear optical devices.