Hydrothermal synthesis and studies on photochromic properties of Al doped WO3 powder

•All of the WO3 powder were synthesized by a facile hydrothermal deposition process.•Al ions as the dopant were successfully incorporated into the crystal lattice of WO3.•The Al doping made the powder had an outstanding photochromic properties.•The mechanism for the improved photochromic performances of the powder was proposed.

A series of pure and aluminum (Al) doped WO3 powders were synthesized at low temperature. The as synthesized materials have been characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet–visible (UV–VIS) spectroscopy and color difference meter, respectively. A relation was found between the color difference and the UV–VIS photochromic activity. Moreover, the optical band gap of the as-prepared powder narrowed due to the appearance of impurity levels as the Al3+ ions migrated into the WO3 crystal lattice. Some rod-like particles have been found to decrease with the increase of Al concentration. An optimum Al concentration was found to be 0.25% to present the best UV-light induced photochromic activity. The mechanism of photochromic process of the Al-doped WO3 powders has been discussed in detail based on the characterization results.

Graphical abstractPure and aluminum (Al) doped WO3 were synthesized via a facile hydrothermal process. The XPS peaks indicated that the powders contained W, Al, O, means the Al ions as the dopant were successfully incorporated into the crystal lattice of WO3 even though it had a great different valence state with W6+. Compared with pure WO3, the binding energies of W4f of Al-doped WO3 was much lower, suggesting the presence of W5+ species, which induced a transition band to decrease the band gap of WO3. Urchin-like morphology WO3 had a special microstructure and large specific surface area of the powder. The result that Al-doped WO3 exhibited superior photochromic performance might own to the narrower band gap of WO3 and urchin-like morphology.Figure optionsDownload full-size imageDownload as PowerPoint slide