Photochromism and Size Effect of WO₃ and WO₃−TiO₂ Aqueous Sol

Abstract

The chromism of tungsten oxides has been investigated for a long time because of its academic and application importance. In this article the photochromism and its dynamics for a WO 3 aqueous sol and WO 3 −TiO 2 mixed sols are studied in detail. The chromic performance of the WO 3 aqueous sol is improved significantly by adding TiO 2 aqueous sol, and shows a clear size effect. The intrinsic absorption peak at around 777 nm from W 5+ in WO 3 nanocluster, which generally appears at around 1000 nm in a WO 3 film, shifts with cluster size because of the quantum confinement effect of delocalized carriers in WO 3 nanoclusters. Besides the 777 nm band from W 5+ in WO 3, a new extrinsic 640 nm band, due to the transient formation of WOCl x species in a WO 3 sol in the presence of Cl - and TiO 2 nanoclusters, appears after adding TiO 2 sol. These results are helpful to the understanding of the chromism of tungsten oxides.