Flexible and Rewritable Non‐Volatile Photomemory Based on Inorganic Lanthanide‐Doped Photochromic Thin Films

Abstract Emerging wearable electronics are spurring unprecedented enthusiasm in the pursuit of next‐generation memory realizable on flexible substrates. Photochromic materials enable reversible manipulation and possess erasable/rewritable capability, which ensure them to be adequate candidates as optical memories. Nevertheless, it has been challenging to develop a flexible optical memory with organic photochromic elements that simultaneously meets the stringent thermo‐ and photostable requirements. Inorganic lanthanide Er³⁺‐doped bismuth layer‐structure ferroelectric Na_0.5Bi_2.5Nb₂O₉ (NBN:Er) exhibits superior photochromic performance. The coupling between lanthanide upconversion emission and photochromic effect enables rewritable and nondestructive readout characteristics. Low‐dimensional complex oxide materials have superior mechanical properties and can be subject to large strain by integration with flexible substrates. Recent advances in synthesizing high‐quality inorganic oxide films on flexible substrates provide new opportunities to build flexible optical memories with dramatically higher performance. Herein, NBN:Er thin films have been integrated with flexible polyimide substrates. These hybrid heterostructures demonstrate comprehensive robust characteristics that sustain well during the 10⁵ bending cycles, and maintain stability over many write–read–erase cycles. This work addresses the main problems hampering the promising applications of inorganic photochromic materials and paves the way for developing more flexible and compact optical memories.