Passive radiative cooling allows surfaces to cool without the need for external energy input, and typically involves materials designed to reflect sunlight while efficiently radiating heat. However, these materials often also absorb some sunlight, reducing their cooling efficiency. Approaches to address this issue include incorporating inorganic scattering or fluorescent particles, which can enhance efficiency but suffer from stability and compatibility issues, and designing ordered porous structures, which, despite their potential, are challenging to scale up. Now, writing in Science, Hai-Bo Zhao and colleagues introduce an intrinsically photoluminescent material with more than 100% light reflectance in visible regions that can be scaled up in an environmentally friendly manner and is reparable, recyclable and biodegradable.

Owing to its layered structure, the aerogel reflects a substantial portion of visible and near-infrared light, which makes up most of the solar energy. Importantly, the aerogel also absorbs ultraviolet light and then re-emits this energy as visible and near-infrared light through photoluminescence. Consequently, the aerogel can manage and reflect a larger portion of the Sun's energy, thereby improving its cooling performance. This dual action — high reflectance of visible and near-infrared light combined with the conversion of ultraviolet light to visible and near-infrared light — is key for the performance of the material.