Inserting Bi atoms on the [WO6] framework: Photochromic WO3/Bi2WO6 nanoparticles enable visual sunlight UV sensing

Abstract

Photochromic tungsten oxide (WO3) offers incredible prospects for protecting human health by visually sensing ultraviolet (UV) radiation exposure from sunlight. Heterojunction engineering can improve the charge carrier separation efficiency in the photochromic procedure to implement this possibility, but it suffers from the finiteness of crystal phase interfacial contact and/or the complexity of synthetic protocols. Here, the construction of an atomic-scale crystal/amorphous WO3/Bi2WO6 nanoparticle results from introducing Bi atoms on the [WO6] framework to form [Bi2O2] components for in-situs incorporating Bi2WO6 into the WO3 matrix. The absence of well-defined interfaces in WO3/Bi2WO6 type II heterostructures ensures an efficient photoexcited electrons transfer from Bi2WO6 to WO3; abundant WO6 units serve as the sites for rapid capture and consumption of photogenerated electrons to facilitate electron-hole separation. Complexing the efficient photochromic products with hydroxyethyl cellulose, the WO3/Bi2WO6-based photochromic films (PCFs) and a colorimetric card indicating different UV intensities are developed. The invisible UV rays are converted into visible color changes; thus, the UV radiation intensity can be estimated from the dark change in the colored PCFs. This work presents a way to elevate the carrier utilization efficiency in WO3 and delivers candidates for exploring efficient and cost-effective UV radiation sensors.