Optical Bandgap Definition via a Modified Form of Urbach’s Rule

We are reporting an esoteric method to determine the optical bandgap of direct gap materials by employing Urbach’s rule. The latter, which describes the slope of the band tail absorption in semiconductors, in its original version, cannot be employed to pinpoint the optical bandgap. Herein, however, we show that a modified form of Urbach’s rule defines the optical bandgap, and therefore, enables the accurate determination of the optical bandgap energy, which turns out to be identical with the threshold energy for the band tail absorption. The model further produces an explicit expression for the absorption coefficient at the optical bandgap energy.

Structural, Optical and Electrical Properties of Cu0.6CoxZn0.4−xFe2O4 (x = 0.0, 0.1, 0.2, 0.3, 0.4) Soft Ferrites

A series of cobalt-inserted copper zinc ferrites, Cu0.6CoxZn0.4−xFe2O4 (x = 0.0, 0.1, 0.2, 0.3, 0.4) having cubic spinel structure were prepared by the coprecipitation method. Various characterization techniques, including XRD, FTIR, UV-vis and I–V were used to investigate structural optical and electrical properties, respectively. The lattice constant was observed to be decreased as smaller ionic radii Co2+ (0.74 Å) replaced the higher ionic radii Zn2+ (0.82 Å). The presence of tetrahedral and octahedral bands was confirmed by FTIR spectra. Optical bandgap energy was determined in the range of 4.44–2.05 eV for x = 0.0 to 0.4 nanoferrites, respectively. DC electrical resistivity was measured and showed an increasing trend (5.42 × 108 to 6.48 × 108 Ω·cm) with the addition of cobalt contents as cobalt is more conductive than zinc. The range of DC electrical resistivity (108 ohm-cm) makes these nanomaterials potential candidates for telecommunication devices.

Optical, Thermal and Radiation Shielding Properties of B2O3 - NaF - PbO – BaO - La2O3 Glasses

The techniques of melt-quenching were used to generate 53B2O3 - 2NaF - 27PbO – (20 - x)BaO - La2O3 (0 ≤ x ≥ 15) glass system. XRD patterns have established the amorphous character of glass samples. There is clear evidence of the role of La2O3 modifier in the glass network. The thermal characteristics were identified to increase with an increase in La2O3 content. Increasing La2O3 increases the linear and non-linear optical bandgap energy and the Urbach energy. By adding La2O3 to the glass samples, the refractive index, molar polarizability, polarizability, and optical basicity are increased. Theoretically, the bulk modulus and the glass transition temperature increase because of the increase in bond strength. The number of bonds per unit increased with the increase in La2O3 content because of the modifier character of La2O3 in the glass samples. Multiple optical parameters (ε∞), (εo), X(1), (X(3)) and (n2) as a function of linear and non-linear Eopt were obtained. The extent of shielding in this article was examined with the increment in La2O3 at the expense of BaO. The results correspond with similar studies conducted previously.

Characterization of As-Prepared (PMMA-PVA)/CuO-NPs Hybrid Nanocomposite Thin Films

We report the synthesis and characterization of Poly Methyl-Meth-Acrylate (PMMA)/Poly vinylalcohol (PVA) polymeric blend doped with different concentrations of Copper oxide (CuO) nanoparticles (NPs). The (PMMA-PVA)/CuO nanocomposite hybrid thin films (wt. % = 0%, 2%, 4%, 8%, and 16%) of CuO NPs are deposited on glass substrates via dip-coating technique. The transmittance (T%), reflectance (R%), the absorption coefficient (α), the optical constants [refractive index (n), extinction coefficient (k)], optical dielectric functions [ɛ',ɛ''] are investigated and interpreted. Tauc, Urbach, Spitzer-Fan, and Drude models are employed to calculate the optical bandgap energy (Eg) and the optoelectronic parameters of the nanocomposite thin films. The refractive index and optical bandgap energy of of (PMMA-PVA) polymeric thin film are found to be (1.5 to 1.85) and 4.101 eV, respectively. Incorporation of specific concentrations of CuO-NPs in (PMMA-PVA) polymeric thin films leads to a noticeable decrease in the optical bandgap energy and to an increase of the refractive index. Moreover, Fourier Transform Infrared Spectroscopy (FTIR) transmittance spectra are measured and analyzed for undoped and doped polymeric thin films to pinpoint the major vibrational modes in the spectral range (500 and 4000 cm-1), as well as, the nature of network bonding in both systems. Thermal stability of thin films is investigated by performing thermogravimetric analysis (TGA). The TGA thermograms confirm that both doped polymeric thin films are thermally stable at temperatures below 110°C which enables them to be attractive for a wide range of optical and optoelectronic applications. Our results indicate that optical, vibrational and thermal properties of both polymeric thin films can be tuned for specific applications by the appropriate corporation of particular concentrations of CuO-NPs.

Chemical and Plant Mediated Synthesis of La2O3 Nanoparticles and Comparison of their Structural, Antibacterial, Photocatalytic and Optical Properties

The La2O3 nanoparticles have been synthesized successfully with a chemical and biosynthesized method. The optical bandgap energy and of chemically synthesized or biosynthesized (M. oppositifolia and T. portlacaustrum leaf extract) La2O3 nanoparticles was calculated from UV-visible absorption between 5.10, 4.26 and 4.46 eV. The good polycrystalline cubic nature of synthesized La2O3 nanoparticles was evident from the bright circular SAED pattern, consistent with the XRD outcome. It is clear that the non-polar extracts could function as stabilizers for La2O3 nanoparticles through attachment to the counterions. The La2O3 nanoparticles have been used as efficient photocatalyst to degrade acid black 1 dye under sunlight irradiation. Besides, this biocatalyst showed excellent ability to degrade biosynthesized La2O3 nanoparticles (T. portlacaustrum) under visible light irradiation 87%. Synthesis of La2O3 nanoparticles by green chemistry process presented good antibacterial activity against Gram-negative and Gram-positive bacteria.

Effect of substrate placement in schott vial to hematite properties

In the present study, hematite (α-Fe2O3) nanostructures were deposited on fluorine doped tin oxide (FTO) coated glass substrate using sonicated immersion synthesis method. The effect of FTO glass substrate placement in Schott vial during immersion process was studied on the growth of the hematite nanostructure and its properties. XRD pattern has revealed seven diffraction peaks of α-Fe2O3 for both hematite nanostructures samples attributed to polycrystalline with rhombohedral lattice structure. The surface morphologies from FESEM have shown that the hematite nanostructures were grown uniformly in both samples with FTO conductive layer facing up and down. Hematite sample with FTO facing down exhibits a smaller size of nanorod, 26.7 nm average diameter, compared to the hematite sample that FTO face up with 53.8nm average diameter. Optical properties revealed higher transmittance in the sample with FTO facing down, probably due to smaller size of nanostructure. The optical band gap energy plotted and extrapolated at 2.50eV and 2.55eV for FTO face up and FTO face down hematite samples respectively, presenting the sample with FTO face up has a lower optical bandgap energy.