Flexible and multifunctional composite films based on rare earth phosphors as broadband thermal emitters for high-performance passive radiative cooling

Passive daytime radiative cooling (PDRC) has been widely used in environmental protection, energy conservation and cooling. However, most PDRC designs primarily focused on improving the daytime cooling effect while ignoring the problem of nighttime overcooling. Here, we designed a flexible and multifunctional composite film doped with rare earth phosphors, which has high solar reflectivity and high infrared emissivity. During the daytime, it realizes subambient cooling of approximate to 11 degrees C at an average solar radiation density of 827.74 W m-2. Remarkably, it addresses the problem of nighttime overcooling by maintaining a minimal temperature difference of only 0.5-1.5 degrees C. Moreover, the rare earth phosphors doped in our design not only effectively compete with titanium dioxide nanoparticles for ultraviolet absorption during the day, but also exhibit significant luminescence at night, providing a useful color reminder effect. These findings highlight the exceptional properties of the radiative cooler and promote its applications in a variety of fields. Flexible composite films based on rare earth phosphors can be used as broadband thermal emitters for passive radiative cooling and energy conservation.