Stretchable and flexible Bi2Ti4O11: Yb3+, Er3+ @TPU film stimulated by near infrared for dynamic and multimodal anti-counterfeiting

Developing novel and practical anti-counterfeiting materials has always been at the forefront of protecting information security. However, achieving the multimodal anti-counterfeiting remains a huge challenge. In this work, we synthesized a series of Bi2Ti4O11:xYb(3+), 0.02Er(3+) (x = 0.1, 0.2, 0.4) nanoparticles by a sol-gel method and realized the upconverting red, yellow and green luminescence under near infrared (NIR) ex-citation. To confirm the practicality of the materials, we designed the novel anti-counterfeiting flexible films based on thermoplastic polyurethane (TPU) via electrospinning route. The composite film (BTO@TPU) is transparent, elastic, stretchable, waterproof and environmentally friendly. In addition, no trace of light can be observed under daylight, indicating the films have excellent concealment. Nevertheless, any patterns you desired can be written by a 980 nm laser pointer and the patterns with red, yellow and green luminescence can be "read" by the streamer camera of smart phone. The proof-of-concept experiment provided the novel and flexible BTO@TPU films keen insights in the application of anti-counterfeiting. This work will supply an arena to boost the application of upconverting materials in the field of dynamic and multimodal anti-counterfeiting. (C) 2021 Elsevier B.V. All rights reserved.