Colored radiative cooling coatings using phosphor dyes

Daytime radiative cooling materials, which can cool objects even under direct solar irradiance with zero electricity consumption, have attracted great interest in green buildings and temperature reduction of outdoor utility boxes and consumer products. However, the absence of esthetic versatilities of radiative cooling materials due to the white or silvery reflectance of these surfaces has limited their widespread applications. In this work, we demonstrated colored radiative cooling materials with highly selective dyes that have narrowband absorption over visible wavelengths. To achive this, the characteristics of highly selective dyes have an impurity band (for the narrowband visible absorption) in a large bandgap (to avoid large solar absorption). A collection of phosphors Y3Al5O12:Ce, Y3(Al,Ga)5O12:Ce, SrSiO4:Eu, and CaAlSiN3:Eu as yellow, yellow-green, green, and red pigments are employed to dye a bilayer radiative cooling coating, respectively. Yellow, yellow-green, green, and red colored radiative cooling coatings, have been demonstrated with a solar reflectance ≥0.90 and an LWIR emissivity ≥0.9, with sub-ambient temperature reductions of 2.5 °C, 2.7 °C, 2.2 °C, and 0.6 °C, respectively, under a peak solar intensity of 1000 W/m2, average humidity of 29.6%, and an average wind speed of about 1 m/s. This work demonstrates that the colored radiative cooling coatings can display esthetics and efficient cooling performance in a manner of feasibility, cost-effectiveness, and scalability.