Photochromic materials based on tungsten oxide

Tungsten oxide exhibits pronounced photochromism upon bandgap photoexcitation, which makes it attractive and promising for applications in many areas. Some advances have been achieved during the past decades. The research on nanocrystalline films and single crystals indicates the critical importance of defects in tungsten oxide to its photochromism. Based on energy-band engineering of semiconductors, enhancement of photochromism has been achieved, for instance, extension of the photoresponse from UV to visible light by cathodic polarization, improved change in absorption before and after coloration through modification by a noble metal or another metal-oxide semiconductor, and increased photochromic reversibility via hybridization with organic amines. Nanocrystalline oxide films exhibit controllable wettability, which is coherent in nature with photochromism.