Tauc-plot scale and extrapolation effect on bandgap estimation from UV–vis–NIR data – A case study of β-Ga2O3

Use and misuse of the Kubelka-Munk function to obtain the band gap energy from diffuse reflectance measurements

/pdf/use-and-misuse-of-the-kubelka-munk-function-to-obtain-the-1p724881.pdf

Copper oxide nanoflowers (CuO-NFs) have been synthesized through a novel green route using Tulsi leaves-extracted eugenol (4-allyl-2-methoxyphenol) as reducing agent. Characterizations results reveal the growth of crystalline single-phase CuO-NFs with monoclinic structure. The prepared CuO-NFs can effectively degrade methylene blue with 90% efficiency. They also show strong barrier against E. coli (27 ± 2 mm) at the concentration of 100 µg mL−1, while at the concentration of 25 µg mL−1 weak barrier has been found against all examined bacterial organisms. The results provide important evidence that CuO-NFs have sustainable performance in methylene blue degradation as well as bacterial organisms.

/pdf/biosynthesis-of-flower-shaped-cuo-nanostructures-and-their-2161unmkj9.pdf

Biosynthesis of Flower-Shaped CuO Nanostructures and Their Photocatalytic and Antibacterial Activities

This study provides a critical analysis on the use of diffuse reflectance spectroscopy and Tauc equation to estimate the optical energy bandgap of semiconductor/carbon composites and amorphous porous carbons. Determination of the energy gap from diffuse reflectance is strongly dependent on the analyst’s experience, due to uncertainties related to establish the adequate range to fit the experimental data to Tauc equation, and to identify the type of electronic transitions. Furthermore, its application to strong light absorbing or multiphase materials with several absorbing components is not straightforward, due to the appearance of various curvatures/linear ranges. For such, reporting the linear fitting range used in the diffuse reflectance spectra is recommended to avoid miscalculation of a gap value. For materials absorbing in the visible range (e.g., displaced onset in Tauc representation), a double-linear fitting must be used in the extrapolation of [F(R∞)hv]1/n to avoid underestimation of Eg values. For amorphous porous carbons, different optical responses were obtained from the diffuse reflectance spectra recorded upon dilution with a non-absorbing matrix. The application of Tauc equation (indirect transitions) to data rendered bandgap values ranging between 1.5–2.3 eV for fourteen carbons, which are in agreement with those reported for these materials.

https://hal.archives-ouvertes.fr/hal-02746386/document

L. Tepech-Carrillo

Papers

Automated method for the determination of the band gap energy of pure and mixed powder samples using diffuse reflectance spectroscopy.