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

ABSTRACT 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.