Photoswitchable WO_3−<i>x</i> QD/Cu NC composite films for efficient UV detection and dual-mode anticounterfeiting

Photoswitchable fluorescent materials (PFMs) have attracted considerable attention owing to their intrinsic advantages of non-contact operation, cleanliness, and non-invasiveness. Conventional PFMs always require complicated preparation processes with poor fluorescence switching properties, which are affected by the Föster resonance energy transfer (FRET) or photoinduced electron transfer (PET) mechanism. Herein, WO_3-<i>x</i> QD/Cu NC composite films were prepared on different substrates <i>via</i> a solution casting method and display outstanding fluorescence switching properties owing to the super photochromic performance of WO_3-<i>x</i> QDs and aggregation-induced fluorescence of Cu NCs. The composite film exhibits reversible on/off switchable fluorescence under UV light irradiation and heat treatment based on the inner filter effect (IFE) mechanism. The composite film shows dynamic variations in dual-mode signals, and the applications of UV sensing and anti-counterfeiting are analyzed. Sensitive dual-mode detection is achieved in UV sensing, particularly for UVB. The composite film exhibits a dual-modal imaging capability with good reproducibility and high resolution for security information encryption and anti-counterfeiting. This work provides a novel strategy for fabricating advanced PFMs for multiple optical applications.