Switchable Narrowband Diffuse Thermal Emission With an In 3 SbTe 2 ‐Based Planar Structure

Tailoring of thermal radiation is critical for applications like daytime radiative cooling, thermophotovoltaic energy conversion, and gas sensing. Phase‐change materials (PCMs) offer an additional degree of freedom, enabling reconfigurable thermal emission by actively triggering phase transitions. In particular, In 3 SbTe 2 (IST) features a unique non‐volatile phase transition in the infrared between an amorphous dielectric state and a crystalline metallic state. Although efficient and easily manufacturable alternatives to conventional infrared light sources will be highly desirable, achieving narrowband and diffuse emission using a simple, lithography‐free structure incorporating PCMs for dynamic functionalities has remained elusive. Here, a planar reconfigurable narrowband thermal emitter using an IST layer on top of a Salisbury screen is demonstrated. The design achieves high emissivity around the ambient thermal wavelength in the amorphous phase and low emissivity in the crystalline phase, featuring angle‐ and polarization‐independent behavior. Multiple patterns are optically written into the IST layer, demonstrating centimeter‐scale programmability as well as a resolution of 20 µm. This work paves the way toward reconfigurable and easily manufacturable devices, showing potential for applications in labeling and anticounterfeiting.