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

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 gamma-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, V--O vibrations, with intensities sensitive to Bi-doping and absorbed dose. Investigating the optical features reveals that the films are semitransparent. 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 gamma-ray doses. The CIE colorimetry was used to evaluate the CIE LAB L*, a*, b*, 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 Bidoping and gamma-irradiation for optoelectronic devices, dosimetry, and smart windows.