The role of cobalt doping in tuning the band gap, surface morphology and third-order optical nonlinearities of ZnO nanostructures for NLO device applications.

The work presented here reported the effect of doping cobalt (Co) in ZnO thin films. The thin films were prepared using the spray pyrolysis technique with 0, 1, 5 and 10 wt% cobalt doping concentrations to study the morphological, optical and third-order nonlinear optical (NLO) properties. X-ray diffraction revealed the crystalline nature of the prepared thin films, and the crystallite size was found to increase with the concentration of doped Co. The morphology and surface topography of the films were largely influenced by doping, as indicated by field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). With an increase in Co-doping concentration, the direct optical energy band-gap value increased from 3.21 eV to 3.45 eV for pure to 10 at% of Co concentrations respectively. To study the NLO properties of the prepared thin films, the Z-scan technique was adopted; it was observed that with an increase in the doping concentration from 0 to 10 wt%, the nonlinear absorption coefficient (ß) was enhanced from 4.68 × 10-3 to 9.92 × 10-3 (cm W-1), the nonlinear refractive index (n 2) increased from 1.37 × 10-8 to 2.90 × 10-8 (cm2 W-1), and the third-order NLO susceptibility (χ (3)) values also increased from 0.79 × 10-6 to 1.88 × 10-6 (esu). At the experimental wavelength, the optical limiting (OL) features of the prepared films were explored, and the limiting thresholds were calculated. The encouraging results of the NLO studies suggest that the Co : ZnO thin film is a capable and promising material for nonlinear optical devices and optical power limiting applications.

Optical properties and ionic conductivity studies of an 8 MeV electron beam irradiated poly(vinylidene fluoride-co-hexafluoropropylene)/LiClO4 electrolyte film for opto-electronic applications.

The influence of 8 MeV energy electron beam (EB) irradiation on optical properties and ionic conductivity of PVDF-HFP/LiClO4 (90 : 10 PHL10) electrolyte film with 40, 80 and 120 kGy doses. The FT-IR results show that C[double bond, length as m-dash]O bond stretching at 1654 cm-1 is due to the degradation of polymer chains and the CH2 bond wagging intensity at 1405 cm-1 corresponds to C-H bond scissioning in the 120 kGy dose irradiated film. 1H and 13C NMR spectroscopy was performed and the 13C NMR spectra confirm the effect of EB irradiation of the PHL10 polymer electrolyte by sharpening and splitting the spectral lines with increasing EB dose and revealing a new spectral line at 162.80 ppm with a 120 kGy EB dose. The size and shape of the porous morphology was drastically changed, becoming deeply porous with a visible inner hollow shaped structure, suggesting increased amorphous character upon irradiation. The absorption band of the unirradiated film observed at 202 nm in the ultraviolet region is shifted to 274 nm after irradiation due to inter band transition of electrons from the valence band to the conduction band and the optical band gap decreasing from 3.49 eV in the unirradiated film to 2.64 eV with a 120 kGy EB dose. Segmental motion in the polymer matrix leads to a decrease in the local viscosity by increasing the mobility of ions upon irradiation. Nyquist plots show semicircles at high frequency due to Li-ion migration through the porous surface of the electrolyte film. A maximum ionic conductivity of 8.28 × 10-4 S cm-1 was obtained with a 120 kGy EB dose and the observed cyclic voltammetry of the irradiated polymer electrolyte suggests it is electrochemically stable.

Flexible and high energy density solid-state asymmetric supercapacitor based on polythiophene nanocomposites and charcoal.

An asymmetric supercapacitor (ASC) was constructed using a polythiophene/aluminium oxide (PTHA) nanocomposite as an anode electrode and charcoal as a cathode electrode. The highest specific capacitance (C sp) of the PTHA electrode was found to be 554.03 F g-1 at a current density (CD) of 1 A g-1 and that of the charcoal electrode was 374.71 F g-1 at 1.4 A g-1, measured using a three electrode system. The maximum C sp obtained for the assembled PTHA//charcoal asymmetric supercapacitor (ASC) was 265.14 F g-1 at 2 A g-1. It also showed a high energy density of 42.0 W h kg-1 at a power density of 735.86 W kg-1 and capacitance retention of 94.61% even after 2000 cycles. Moreover, it is worth mentioning that the asymmetric device was used to illuminate a light emitting diode (LED) for more than 15 minutes. This PTHA//charcoal ASC also possesses stable electrochemical properties in different bending positions and hence finds a promising application in flexible, wearable and portable energy storage electronic devices.