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

• The BTO@TPU films were synthesized via electrospinning route. • The films are stretchable, flexible, waterproof and transparent. • The films can be used in the field of dynamic and multimodal anti-counterfeiting. [Display omitted] 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 Bi 2 Ti 4 O 11 :xYb3+, 0.02Er3+ (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) excitation. 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. [ABSTRACT FROM AUTHOR]