Tungsten oxide (WO3) thin films were deposited on to unheated Corning glass and silicon substrates by RF magnetron sputtering of metallic tungsten target at various oxygen partial pressures in the range – ？Pa. The influence of oxygen partial pressure on the structure and surface morphology and the optical and photoluminescence properties of the films were investigated. X-ray diffraction studies revealed that the deposited films were amorphous in nature. Fourier transform infrared transmission spectra confirmed that the presence of stretching vibration of W-O-W and deformation of W-O bonds related to the WO3. The optical transmittance of the films at wavelengths >500？nm increased from 62% to 85% with the increase of oxygen partial pressure. The optical band gap of the films increased from 3.00 to 3.14 eV and the refractive index of the films decreased from 2.26 to 2.08 with the increase of oxygen partial pressure from to ？Pa, respectively. The photoluminescence studies indicated that the intense blue emission which was assigned to band-to-band transition was observed at oxygen partial pressure of ？Pa. 1. Introduction Transition metal oxide thin films have attractive technological importance for electrochromic devices. Among the transition metal oxides, tungsten oxide (WO3) is an n-type semiconductor, exhibits electrochromic properties in the visible and infrared regions, is relatively low cost, and has high color efficiency [1]. It possesses excellent coloration efficiency and electrochemical stability after insertion with protons or other small monovalent cations such as Li+ and Ni+ [2]. Hussain et al. [3] reported on pulsed laser deposited WO3 films, formed at substrate temperature 573？K, that the crystallinity of the triclinic WO3 decreased with the increase of oxygen partial pressure from 10 to 26？Pa, and at higher oxygen partial pressure of 40？Pa the films were almost in amorphous structure. Kaushal and Kaur [4] achieved nanocrystalline WO3 films by pulsed DC magnetron sputtering at substrate temperature of 873？K with the optical band gap of 3.39？eV and the crystallite size, and optical band gap of the films increased with the increase of oxygen partial pressure. Bittencourt et al. [5, 6] reported on the WO3 thin films formed by RF magnetron sputtering at different argon: oxygen ratios on the structural and composition of the films and achieved the stoichiometric films at 1？:？1 of argon and oxygen ratio. Subramanyam and Karuppasamy [7] formed the WO3 films at room temperature by pulsed DC magnetron sputtering in active arc suspension mode at
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