Applied Surface Science 257 (2011) 8127–8133 Contents lists available at ScienceDirect Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc Structural transition and blue emission in textured and highly transparent spray deposited Li doped WO 3 thin films M. Kovendhan a,∗ , D. Paul Joseph b , E. Senthil Kumar c , A. Sendilkumar d , P. Manimuthu e , S. Sambasivam f , C. Venkateswaran e,∗ , R. Mohan a a Department of Physics, Presidency College, Chennai 600 005, India b Centre for Condensed Matter Sciences, National Taiwan University, Taipei 10617, Taiwan c Department of Physics, Indian Institute of Technology Madras, Chennai 600 035, India d School of Physics, University of Hyderabad, Hyderabad, 500 046, India e Materials Science Centre, Department of Nuclear Physics, University of Madras, Guindy Campus, Chennai 600 025, India f Department of Physics, Pukyong National University, Busan 608 737, South Korea article info Article history: Received 6 October 2010 Received in revised form 25 April 2011 Accepted 25 April 2011 Available online 1 May 2011 Keywords: Spray pyrolysis Tungsten oxide Lithium Textured growth Optical transparency Photoluminescence abstract The effect of Li (0–5 wt%) doping on the properties of WO 3 thin films deposited using an automated homemade spray pyrolysis unit is studied. Change in structural and optical properties is observed on doping with Li. The XRD patterns shows that undoped WO 3 film has an orthorhombic phase while the Li (1–5 wt%) doped WO 3 films have tetragonal phase. The SEM and AFM images confirm relatively smooth surface of Li doped WO 3 films compared to undoped WO 3 film. Transmission spectra reveal that the transparency of the Li-doped films is much greater than that of undoped film. From the transmission data, the direct, indirect bandgap and phonon energies were calculated. Room temperature photoluminescence spectra showed pronounced blue emission on doping with Li. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Optically transparent tungsten trioxide (WO 3 ) films find many applications in emerging technologies such as, display devices, eye wears, variable thermal emittance surfaces in temperature control windows (in temperature stabilization of space vehicles), non- emissive large area colour information displays, smart windows, and anti-dazzling mirrors [1–4]. Sodium doped WO 3 also showed superconducting transition around 90 K [5]. Wide band gap oxide semiconductor materials such as ZnO are of much applicability in the blue and ultra violet optical devices such as light emitting diodes and laser diodes [6,7]. Among the various transition metal oxides, n type WO 3 having wide band gap [8] is found to be stable enough towards UV and visible region also. WO 3 is also an excellent candidate for electrochromic devices, due to its ability to change its optical properties under application of an external potential [1]. The properties of these films strongly depend on the prepara- tive conditions. A variety of techniques including rf-sputtering [9], ∗ Corresponding authors. Tel.: +91 9884105157, fax: +91 44 28510732. E-mail addresses: mkovendhan@gmail.com (M. Kovendhan), cvunom@hotmail.com (C. Venkateswaran). thermal evaporation [10,11], sol–gel [12], dip-coating [13], spray pyrolysis [14–17], and electron beam evaporation [18] had been adapted to deposit WO 3 thin films. Among these techniques spray pyrolysis is a cost effective and large area coating method to prepare good quality thin films, under optimized conditions. Arakaki et al., [16] deposited WO 3 films using tungstenic acid in liquid ammo- nium. Bathe and patil [15] prepared by dissolving WO 3 powder in NH 3 and distilled water and then heated to 90 ◦ C. Polycrystalline WO 3 films under various preparative conditions were obtained by Regragui et al., [17]. The progress that has occurred during the recent years on this material due to its application, served as a motivation for this research. In this paper, we report the effect of Li dop- ing (0–5 wt%) in WO 3 thin films prepared from WCl 6 precursor solution at 400 ◦ C by spray pyrolysis by analyzing the struc- tural, morphological, optical and luminescence properties. Li doping was found to induce structural transition in WO 3 film from orthorhombic to tetragonal structure. We have calculated both the direct, indirect bandgap and phonon energies for the deposited films. We also observed pronounced blue photolumi- nescence emission at room temperature effected by Li doping for the WO 3 films since it has been reported difficult to observe [19,20]. 0169-4332/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2011.04.122