Optical and chemical properties of electrochromic oxide films for smart windows

The band structures of cubic WO 3 and LiWO 3 and the vibronic properties of W x O y clusters ( x=1–12, y=2–52) were calculated. The band gaps of WO 3 and LiWO 3 are indirect and the incorporation of lithium ions results in the widening of the band gaps. Vibronic studies on clusters revealed that certain molecules give optical transitions from oxygen orbitals to tungsten orbitals, similar to the results of band calculations. However, accumulation of (WO 6) 6− up to 12 octahedra does not yield optical transition from O to W; but between oxygen atoms at different positions. An attempt to make a link between molecular and bulk characteristics of WO 3 is made to interpret its optical and chemical properties.