Tuning the structural and optical features of V2O5 nanostructured films by Bi-doping and γ-irradiation for smart window applications

Abstract

Doping and radiation exposure are two of the most preferred stratagems for enhancing the efficiency of V₂O₅ for optoelectronic and smart window applications. This work studies the effect of Bi-doping and γ-ray irradiation on the structural and optical properties and color change of V₂O₅ films developed by casting/spin coating processes. Firstly, pure and Bi-doped V₂O₅ nano-sized powders with batonnets-like morphology (packs of nano-rods having diameters in the range of 7.28–16.28 nm and 9.32–95.49 nm) were prepared by a facile chemical route. The films were prepared by casting/spin-coating a suspension solution of the powder on glass substrates. X-ray diffraction (XRD) results indicate the formation of a layered V₂O₅ of orthorhombic structure, highly oriented in the (001) direction, with a crystallite size in the range of 35.8–51.3 nm, depending on the irradiation dose. The Fourier transform-infrared spectroscopy (ATR/FTIR) exhibited the presence of V–O–V, VO vibrations, with intensities sensitive to Bi-doping and absorbed dose. Investigating the optical features reveals that the films are semi-transparent. The pure V₂O₅ and Bi-doped V₂O₅ films have optical direct (indirect) band gaps in the ranges of 2.6–3.0 eV (1.3–1.6 eV) and 2.3–2.9 eV (1.1–1.5 eV), respectively. The optical parameters (k-index and the refractive index) can be tuned by Bi-doping and γ-ray doses. The CIE colorimetry was used to evaluate the CIE LAB $L^{\ast }$, $a^{\ast }$, $b^{\ast }$, and the total color change ($\Delta E$) values. The results indicated that b∗ and L∗ can be used individually as a dosimetry index at doses ≤30 kGy. The results illustrate the feasible controlling of V₂O₅ films by Bi-doping and γ-irradiation for optoelectronic devices, dosimetry, and smart windows.