Effect of tin on bandgap narrowing and optical properties of ZnO–Zn₂SnO₄ electrospun nanofibre composite

Abstract

The quest for improved visible light absorption in ZnO-based photocatalysts and photodetectors is a prevailing research problem. One method of solving this problem is by narrowing the band gap of this material well into the range of visible light energy. In this work, we have demonstrated considerable band narrowing into the visible region in our electrospun ternary ZnO-Zn 2 SnO 4 nanofibres. We also showed that band narrowing is highly dependent on the amount of Sn in the synthesized composite which could be attributed to the creation of localized states in the ZnO band and the attendant structural changes. However, beyond 15%wt doping there were observed changes in the trend of the bandgap reduction, crystallite sizes, and width of the localized states in the ternary ZnO-Zn 2 SnO 4 band. The details of experimental procedures and discussion of results have been included in this paper.

Optical Properties of Electrospun Nanofiber Mats

“…As shown in Figure 2, the band gap can be calculated from plotting (αhν) 2/n versus the energy of the absorbed light, here for direct transition semiconductors, and the band gaps are directly found by extrapolating the linear parts of the spectra towards the x-axis [55]. In the case of indirect band gaps, the y-axis is (αhν) 1/2 instead of (αhν) 2 in the case of direct band gaps [56,57]. The graphs often show a doubled minimum or similar unexpected features if the wrong y-axis is chosen, while it is also possible to use both plots for immiscible blends with direct and indirect band gaps [56,57].…”

“…linear parts of the spectra towards the x-axis [55]. In the case of indirect band gaps, the y-axis is (𝛼ℎ𝜈) / instead of (𝛼ℎ𝜈) in the case of direct band gaps [56,57]. The graphs often show a doubled minimum or similar unexpected features if the wrong y-axis is chosen, while it is also possible to use both plots for immiscible blends with direct and indirect band gaps [56,57].…”

“…In the case of indirect band gaps, the y-axis is (𝛼ℎ𝜈) / instead of (𝛼ℎ𝜈) in the case of direct band gaps [56,57]. The graphs often show a doubled minimum or similar unexpected features if the wrong y-axis is chosen, while it is also possible to use both plots for immiscible blends with direct and indirect band gaps [56,57]. Using this technique, Matysiak et al characterized the different blends of poly(acrylonitrile) (PAN) with the conductive polymers polypyrrole (PPy), polythiophene (PT), and polyaniline (PAni) and found a reduction in the band gap of pure PAN (4.08 eV) to minimum 3.77 eV for composite nanofibers containing 3% PAni [58].…”

Systematic exploration of electrospun polyvinylidene fluoride (PVDF)/multi-walled carbon nanotubes’ (MWCNTs) composite nanofibres for humidity sensing application

“…The diameters of the electrospun fibres range from micrometre to nanometre. Different process parameters influence the electrospun fibres' diameters, such as polymer solution concentration, magnitude of the applied voltage, gap distance between the collector and the tip of the needle and polymer flow rate, which affects the fibres' deposition time [9][10][11][12]. An electrically charged jet of the polymer solution is ejected and it discharges towards the oppositely charged electrode.…”