Excited-State Absorption Assisted Optical Limiting Action of Potassium Dihydrogen Phosphate (KDP)–Polyethylene Oxide (PEO) Electrospun Nanofibers

By employing different flow rates (0.1 mL/h, 0.4 mL/h, 0.6 mL/h) in an electrospinning route, potassium dihydrogen phosphate (KDP)–polyethylene oxide (PEO) nanofibers with different diameters were successfully prepared. Scanning electron microscopy (SEM) showed the formation of PEO nanofiber morphology with average diameters of 410 nm, 435 nm, and 439 nm for flow rates of 0.1 mL/h, 0.4 mL/h, and 0.6 mL/h, respectively. Using x-ray diffraction (XRD), the presence of KDP in the fiber matrix was confirmed from the intense diffraction peak at 2θ = 24°, which corresponds to the (200) plane of KDP, and the nanofiber exhibited variation in crystallite size, ranging from 30 nm to 41 nm with different flow rates. The lattice strain of the prepared samples decreased with increasing flow rate. A blueshift in the absorption edge and an increase in optical band gap were observed for spun fibers (215 nm, 6.04 eV) with bulk KDP (280 nm, 5.82 eV) due to changes in the dielectric properties of the material. From the recorded photoluminescence (PL) spectra, dominant green emission at 565 nm was observed. Electrospun KDP-PEO nanofibers exhibited a frequency doubling phenomenon with relative SHG efficiency twice that of KDP. In addition, intensity-dependent Z-scan measurements were performed with a Q-switched neodymium-doped yttrium aluminium garnet (Nd:YAG) laser as an excitation source (532 nm, 5 ns, 10 Hz). The excited-state absorption process played a dominant role in the observed nonlinearity in the KDP-PEO nanofibers. The demonstrated sequential two-photon absorption-based optical limiting action makes KDP-PEO nanofibers a versatile optical limiting material for eye safety devices against intense laser pulse.