Tunable reflective color filters based on asymmetric Fabry-Perot cavities employing ultrathin Ge 2 Sb 2 Te 5 as a broadband absorber.

We demonstrated a tunable structural color filter based on an asymmetric Fabry-Perot cavity employing germanium antimony tellurium alloy GeSbTe (GST) as a switchable ultrathin lossy layer. The color tunability and switch mechanism of our designed structure were investigated by both simulation and analytical approaches. Both numerical simulations and analytical results show that the tunable reflective colors can be generated through the reversible phase transition of GST from amorphous to crystalline. Additionally, the generated colors possess high brightness, high saturation, and a wide gamut. Our designed structure will inspire phase-transition-based systems' potential applications in colorimetric sensing, smart windows, full-color printing and displays, anti-counterfeiting, and data encryption.