Preparation, characterization, and optical spectroscopic studies of nanocrystalline tungsten oxide WO3

Photochromic studies on tungsten oxide (WO3) with single and mixed phases are performed in the mid-infrared frequency range 400–4000 cm−1. Different crystalline phases of WO3 are synthesized by hydrothermal technique using two different procedures. Monoclinic and hexagonal (m-h-WO3) mixed phases and hexagonal single phase are produced. The optical properties of these two phases have been compared with the nanostructured WO3 thin films synthesized by pulsed laser deposition technique. The crystalline nature and crystallite size of the samples are obtained by X-ray diffraction. The High Resolution Transmission Electron Microscope HRTEM is used to demonstrate the sizes, morphologies and electron diffraction of the two powders micro-structures. Spectroscopic studies on the nano-crystalline m-h-WO3, and h-WO3 are executed in the infrared, visible and ultraviolet frequency range. The FTIR reflection of colorless samples before and after exposure to UV light irradiation at different times are recorded. Drude-Lorentz (DL) model have been used for fitting the reflection spectra of the samples under investigations. Quantitative information about the different stretching vibrational bands are obtained from the fitting curve and its component. Using DL model, the optical conductivity have been estimated from the optical parameters obtained from the data extracted from the differential complex IR analysis in the frequency range of 400–4000 cm−1. The results illustrate that the optical conductivity of samples are significantly changed due to their exposure to UV light at different times.