Core–shell ZnCo-PBA@WO2.72 heterojunctions with enhanced photo-responsive color switching ability for highly efficient rewritable media and information encryption

Abstract

Heterojunction engineering is an acceptable strategy in promoting the separation efficiency of electron/hole pairs in the photochromic process. Here, a series of novel solid-state photochromic ZnCo-PBA@WO2.72 heterojunctions have been designed and prepared in the current study. The cubic ZnCo-PBA were selected as templates to directly grow WO2.72 amorphous layer using phosphotungstic acid (PW12) as precursors with the assistance of polyvinyl pyrrolidone (PVP). The as-obtained ZnCo-PBA@WO2.72 heterojunctions have a core–shell structure and the appropriate band energy promote the UV-generated electrons transport from ZnCo-PBA to WO2.72. Consequently, the ZnCo-PBA@WO2.72 heterojunctions exhibit excellent photochromic performance, converting from white to light-grey in 10 s and finally turning into dark-grey in 60 s under UV lamp stimulation. Meanwhile, the WO2.72 outer layer was more easily in contact with oxygen in air and thus speeds up the oxidation process of W5+ to W6+, allowing the colored ZnCo-PBA@WO2.72 heterojunctions to return to their original colorless condition within 15 min. The solid-state photochromic ZnCo-PBA@WO2.72 heterojunctions was then used as repeatable information storage media, data encryption and decryption based on coloration-decoloration behaviors. This study presents a meaningful way to integrate WO2.72 with MOFs to expand the range of photochromic materials and further to broaden theirs application in optical devices.