Selective Emitter Based on MgF₂ Photonic Structure for Subambient Radiative Cooling

Passive radiative cooling offers a promising solution to achieve refrigeration and global carbon neutrality without energy consumption. To achieve deep radiative cooling, minimization of solar absorption and maximization of infrared radiation is the sole way. Herein, photonic radiative coolers based on a fluoride-metal multilayer stack structure are developed for subambient radiative cooling. The selective MgF₂ emitter exhibits ideal spectral properties, with reflectance up to 97.2% and atmospheric window emissivity of 0.80. Field tests illustrate that the MgF₂ emitter has excellent all-day subambient radiative cooling performance. It shows more than 19 °C all-day subambient cooling ability regardless of the season, demonstrating its superior cooling performance. Furthermore, the real-world application test shows that the cube MgF₂ cooler has a maximum cooling effect of 14 °C under sunlight and an average cooling effect of 2 °C during the night. The prototype cooler provides an innovative strategy for achieving deep radiative cooling and broad energy-saving applications.