Efficient charge transfer over Cu-doped hexagonal WO3 nanocomposites for rapid photochromic response

Efficient charge transfer plays a key factor in the applicable photochromism of WO3 based materials, but how to regulate the transfer of photogenerated charge still is a challenge. This work investigated the photogenerated charge transfer of hydrothermally prepared Cu-doped hexagonal WO3 with a rapid photochromic response. The results showed that Cu-doped WO3 exhibited a light response below 5 s and a saturated coloring of 25 s under UV irradiation. The color difference of Cu-doped WO3 in the initial and equilibrium stages of coloring was 1.92- and 1.33-times to pure WO3, respectively. Further characterization found that doping Cu ions into WO3·0.33H2O induced the loss of structural water in the interlayer region to form WO3, whose relatively narrower pathway for excitons transportation led to the photogenerated electrons could not be smoothly embedded into the crystal. Cu species consequently acted as the photogenerated electron acceptor. More importantly, the Cu-O-W linkages formed between Cu, O, and W species endowed the efficient charge transfer from WO3 to Cu, which led to the prioritized photoreduction of Cu than W species to achieve color switching for photoinduced turning gray instead of blue. The obtained nanocomposites offered an alternative option for the application of WO3 based materials in UV sensors, information security, smart windows, etc.