Abstract: The precursor was ultrasonically pretreated by the layer-by-layer (LbL) assembly method, and a new type of visible light photochromic inorganic organic multilayer film composed of phosphotungstic acid (PWA) and polyvinylpyrrolidone (PVP) was synthesized. Under visible light irradiation, the colorless film turned blue with a reversible photochromic effect. The bleaching process occurred when the film was in contact with oxygen in the dark or heated in the air. In the X-ray photoelectron spectroscopy (XPS), the W⁶⁺ in the W of the ultrasound-assisted LbL film was further reduced to W⁵⁺, indicating that a photoreduction reaction occurred between the PWA particles and the PVP matrix. Ultrasound assisted dispersion of PWA particles could enhance two photochromic properties, reduce the size of PWA to the size of quantum dots (10 nm to 3.4 nm), induce conversion effects and dielectric confinement effects. Within the same irradiation time, the intensity of the absorption peak increased (0.23 to 0.45), the excitation energy decreased (2.51 eV→2.23 eV), which expanded the range of absorption wavelength and absorption intensity of characteristic peak, and a higher coloring speed was obtained.

Key words: nanocomposite, layered, ultrasonic, polyvinylpyrrolidone, phosphotungstic acid, visible light photochromism