A reversible photochromic switch based on self-assembly of layered double hydroxide and decatungstate

This paper reports the fabrication of photochromic anions/layered double hydroxide (LDH) films by alternate assembly of polyvinyl alcohol modified tungstate (PVA-W10O32) and CoAl-LDH nanosheets on quartz substrates using the layer-by-layer (LBL) deposition technique, and demonstrates their application as an optical switch through alternate irradiating using UV and visible light. UV-vis absorption spectroscopy indicates a stepwise and regular growth of the (PVA-W10O32/LDH)n film upon increasing deposition cycles. X-ray diffraction and scanning electron microscopy (SEM) demonstrate that the films possess a periodical layered structure perpendicular to the substrates with a thickness of ∼2.53 nm per bilayer. Furthermore, the optical switch with film thickness of 65 nm (25 bilayers) exhibits a reversible photochromic property, rapid response for UV and visible light (5 min), high storage stability (∼97.5% of its initial absorbance remained after one month) as well as mechanical stability. In addition, the study on mechanism of color change cycle of the optical switch shows that the reversible change of valence state for W element confirmed by XPS and ESR. Therefore, this work provides new opportunities for fabrication and application of photochromic anions/LDH films which can be used as optical devices and sensors.