One-photon absorption enhanced nonlinear absorption and optical limiting of the electrospun polyvinylpyrrolidone via excitation energy and incorporation of polypyrrole particles

Recently, we have shown defect-assisted nonlinear absorption and optical limiting in semiconducting polymers due to one-photon, two-photon absorption (via the sequential absorption of two photons or simultaneous absorption of two photons) and free-carrier absorption. The strength of the nonlinear absorption and its spectral width may be taken into account as the effective parameters due to an excitation wavelength. In this work, to enhance nonlinear absorption performance with increase in one-photon absorption, we investigated the nonlinear absorption of the doping of the narrow band gap polypyrrole (PPy) into the wide band gap polyvinylpyrrolidone (PVP) nanofiber with increase in PPy particle content. SEM measurements showed PVP/PPy nanofibers with a cylindrical morphology. Linear optical results indicated an improved reflectance and decreased Urbach energy with increase in PPy particle content in PVP nanofibers. Open aperture Z-scan experiments were carried out at 532 nm and 1064 nm excitation wavelengths under various input intensities to evaluate the nonlinear absorption performance of PVP/PPy nanofibers. The nonlinear absorption coefficient increased at 532 nm while it decreased at 1064 nm excitation wavelength with the increase in PPy content. This behavior is attributed to the increase in contribution of one-photon absorption to nonlinear absorption at 532 nm. Saturable absorption which led to decreased nonlinear absorption was induced with the filling of the localized defect states at 1064 nm energy region by one-photon absorption. Our findings indicate that the nonlinear absorption and optical limiting behavior of the PVP/PPy nanofibers can be adjusted depending on the PPy content and energy of the excitation light. Graphical Abstract: [Figure not available: see fulltext.].