van der Waals epitaxy for highly tunable all-inorganic transparent flexible ferroelectric luminescent films

Abstract

Ferroelectric luminescent materials with more unique requirements, such as high-speed, low-cost, and low-power, and being light-weight, all-inorganic, transparent, flexible and wearable, are of great demand for future smart device applications. Here, we report the direct fabrication of highly flexible and transparent Eu-doped 0.94Bi_0.5Na_0.5TiO₃–0.06BaTiO₃ epitaxial thin films on mica substrates via van der Waals epitaxy. The photoluminescence switching of the films exhibits no noticeable decay after being flexed in or out to 2 mm radius for 10⁴ cycles, revealing the robust functionality against mechanical bending. Furthermore, we demonstrate that the photoluminescence intensity can be greatly enhanced by the bending-induced mechanical strain either in the tensile or compressive state, with a striking giant gauge factor of 3580. This work illustrates the role of MICAtronics, i.e., van der Waals epitaxy on mica, in designing all-inorganic flexible ferroelectric luminescent thin films with highly controllable optical properties for application in tunable transparent wearable memory devices, sensors and displays.