Colored radiative coolers designed by spectral-conversion phosphor and light-extracting structures

Passive radiative cooling, a method for lowering the temperature of outdoor objects without the need for electrical power, has garnered interest for its potential in energy conservation. However, the high reflectivity of the radiative cooler in solar spectra typically results in a white or silver color, posing limitations for aesthetic and practical applications. Here we provide the method for calculating the minimum thermal load across the CIE 1931 xy chromaticity diagram. In addition, we introduce a spectral-conversion microphotonic thin film as the colored radiative cooler based on photoluminescence (PL) phosphor. By using the microstructure array, 89% of the light trapped by total internal reflection (TIR) can be extracted from the film, which lowers the amount of heat produced. It proves the potential of the colored radiative cooler based on PL phosphor and light-extraction microstructures.