Optical charge transfer absorption in lithium-intercalated tungsten oxide thin films

Amorphous tungsten oxide exhibits electrochromism when intercalated with protons or lithium ions. Thin films of the material were prepared by dc magnetron sputtering and subsequently electrochemically intercalated with lithium. The optical absorption in the wavelength range 300 to 2500 nm was measured for a number of lithium concentrations. All the spectra can be fitted by a superposition of three Gaussian peaks, representing the three possible electronic transitions between W6+, W5+, and W4+ sites. The variation of the peak strength with lithium concentration is consistent with the predictions of a statistical theory. (c) 2006 American Institute of Physics.