Broadband directional thermal radiator with flexible intensity–directivity tunability in the whole visible spectrum

Controlling spectral and directional distributions of thermal radiation plays an important role in designing functional structures for thermal management. As a wideband phenomenon, thermal radiation is supposed to be manipulated within broad wave ranges for the case of practical thermal applications. However, currently, it is still challenging to constrain broadband radiation into wanted directions in a controllable manner. In this work, based on light-trapping effects mediated by periodic germanium strips on a silver substrate, we design a thermal radiator with broadband directional (BBD) emissivity in the whole visible spectrum. The radiator is free from intricate nanofabrication and can achieve low-dispersive directional emissivity within a continuous wave range of 0.4–0.8 μm. In addition, the proposed radiator exhibits flexible tunability on the BBD performance and emission intensity, making it an outstanding candidate for functional surfaces in thermal energy management.