Investigation of the Defect and Intensity-Dependent Optical Limiting Performance of MnO₂ Nanoparticle-Filled...

To enhance the optical limiting behavior triggered by nonlinear absorption (NA), wide-band gap MnO₂ nanoparticles were incorporated into polyvinylpyrrolidone (PVP) polymer nanofibers at various concentrations. SEM images of the composite nanofibers showed that MnO₂ nanoparticles are well entrapped in the nanofibers. With an increase in MnO₂ nanofiller concentration, a widened optical band gap energy and an increased Urbach energy were observed. As the concentration of MnO₂ nanofiller in PVP increased, the NA behavior became more pronounced but weakened with higher input intensity. This behavior was attributed to the filling of the localized defect states by one photon absorption (OPA). The NA mechanisms of the composite nanofibers were examined, considering their band gap energies and localized defect states. Although all of the composite nanofibers had OPA, sequential/simultaneous two photon absorption (TPA), and excited state absorption mechanisms, the higher concentration of the MnO₂ nanofiller led to stronger NA behavior due to its more defective structure. The highest optical limiting behavior was observed for composite nanofibers with the highest concentration of MnO₂ nanofiller. The results obtained show that these composite nanofibers with a high linear transmittance and an extended band gap energy can be used in optoelectronic applications that can operate in a wide spectral range. Furthermore, their robust NA behavior, coupled with their promising optical limiting characteristics, positions them as strong contenders for effective optical limiting applications.