Kinetic study on photochromism of WO3 aqueous sol and its enhancement accompanying spectral changes by the addition of TiO2 aqueous sol

Photochromism of a WO3 aqueous sol has been investigated in a nitrogen atmosphere under controlled temperature. Effects of ageing of the WO3 sols, concentrations of WO3 sols or Cl− ion and temperature on the coloring rate were examined. The coloring rate was the first-order with respect of the WO3 concentration. The coloring process was accelerated by an addition of TiO2 aqueous sols. Spectral changes were measured using the mixing sol with various molar ratios (γ) of WO3 and TiO2. The absorption spectra changed from those having the single peak at 775 nm to those with two peaks at 640 and 980 nm. Such spectral transformation was ascribed to the structural change of the WO3 nanoclusters, depending on the γ value and the concentration of Cl− ion.