Visible light photochromism of polyoxometalates-based composite film with deposition of ZnFe2O4 nanoparticles

Abstract By introducing ZnFe 2 O 4 nanoparticles as light sensitizer into the silica sol–gel matrix, a novel phosphomolybdic acid (PMoA)-based composite film with high visible light photochromism was successfully prepared. The resulted thin film was denoted as PMoA/SiO 2 /ZnFe 2 O 4 . The microstructure, visible-light photochromic behaviors and mechanism were fully investigated. Characterizations revealed that the Keggin geometry of PMoA particles and structure of tetrahedral zinc ions were well retained in the film. With visible light irradiation, the colorless transparent PMoA/SiO 2 /ZnFe 2 O 4 composite film turned to blue and exhibited high photochromic responsiveness as well as reversible photochromism. According to the XPS analysis, the appearance of Mo 5+ species indicated the photo-reduction reaction occurred between PMoA naoparticles and ZnFe 2 O 4 sensitizers suggesting the photo-generated electron transfer mechanism during the photochromic process.