Investigation of the wavelength dependent nonlinear absorption mechanisms of polyvinylpyrrolidone and cadmium selenide hybrid nanofibers

In this study, wavelength dependent nonlinear absorption mechanisms, nonlinear absorption and optical limiting behaviors of electrospun polyvinylpyrrolidone/cadmium selenide (PVP/CdSe) hybrid nanofibers were investigated. Scanning electron microscopy showed that homogeneous continuous nanofibers were obtained. Their diameter decreased from 443 nm to 271 nm with CdSe filler content in PVP. Linear absorption analysis revealed that the hybrid nanofibers have a narrow bandgap compared to PVP nanofibers due to the increased localized defect states inside the bandgap. A theoretical fit of the open aperture Z-scan data was performed considering the contributions of one-photon absorption (OPA), two-photon absorption (TPA) and free carrier absorption (FCA) to nonlinear absorption (NA). NA behavior was observed for all hybrid nanofibers at both 1064 and 532 nm excitation wavelengths. The strongest NA property was observed for the highest CdSe filler content at 1064 nm compared to 532 nm. At 1064 nm, the main NA mechanism is the TPA due to its sufficient energy to excite an electron from valance band to conduction band for CdSe filled PVP nanofibers. On the other hand, the excitation light energy at 532 nm (2.32 eV) is sufficient to excite an electron from the valence band to conduction band, making OPA as the dominant NA mechanism as compared to TPA for CdSe filled PVP nanofibers. When the NA mechanisms were examined, it was observed that the presence of TPA accompanying OPA at 1064 nm led to a stronger NA feature than at 532 nm. The lower optical limiting threshold for higher CdSe filler content in PVP at 1064 nm was measured as 0.85 mJ/cm2. In light of the strong NA and strong optical limiting behavior of hybrid nanofibers, they may find use in optoelectronic devices operating in a wide wavelength range.

Automated summary

This study investigated the wavelength dependent nonlinear absorption mechanisms, nonlinear absorption and optical limiting behaviors of electrospun polyvinylpyrrolidone/cadmium selenide (PVP/CdSe) hybrid nanofibers. It was found that all hybrid nanofibers exhibited nonlinear absorption properties at both 1064 and 532 nm excitation wavelengths, with the highest CdSe filler content showing the strongest nonlinear absorption at 1064 nm.