Magnetically responsive photonic watermarks on banknotes

A high performance photonic anti-counterfeiting watermark that can be incorporated into banknotes has been developed by combining a novel invisible photonic printing with a flexible, translucent and ultra-thin magnetic-responsive photonic display film. The photonic anti-counterfeiting watermark has latent colourful patterns that are lithographically printable and magnetically responsive, and can be easily perceived by the naked eye under magnetic fields. In addition, the distinct differences of the spectral characteristics between the invisible-form and the visible-form of the patterns can be accurately detected by using a special optical instrument, which makes the photonic anti-counterfeiting watermark provide double security information to identify the authenticity of banknotes. Moreover, the strategy allows accurate control of the optical diffraction colour and the structural design of the latent patterns. The fabrication process does not damage the banknotes and allows fast, convenient and scalable production at low-costs. The present work demonstrates that the fabrication of high performance photonic-crystal-based anti-counterfeiting devices on banknotes is possible.