Point‐Excitation Wide‐Field Upconversion Imaging via a Holographic Polymer Waveguide

Organizing upconversion functionality into an integrated material system holds great promise for high-security encryption and data diversification. However, the practical application of facile upconversion imaging has long been hindered by its limited active area. Herein, we address this challenge by designing a holographic polymer waveguide composed of liquid crystals (LCs) and dithienylethene (DTE) as the high-refractive-index phase, with a polymer matrix embedded with upconversion nanoparticles serving as the low-refractive-index phase. This design enables the transformation of upconversion emission from a localized point to a macroscopic area, expanding the imaging region by up to 225 times. Mechanistic studies reveal that the synergy between LCs and DTE is crucial: the high-refractive-index LCs facilitate waveguiding, while DTE promotes the formation of well-defined holographic waveguide structures. Beyond this conceptual advance, the holographic polymer waveguide has successfully enabled triple-mode image encryption-integrating solidified holograms with rewritable upconversion and photochromic images-thereby opening new avenues for high-security anticounterfeiting technologies.