Advanced luminescent metamaterials with porous structures and rare earth phosphors for efficient passive daytime radiative cooling and energy saving

Passive daytime radiative cooling (PDRC) has emerged as a promising solution to address the escalating energy and environmental challenges, owing to its zero energy consumption and emission-free operation. However, many existing PDRC systems suffer from low efficiency or limited practical applicability. Here, we propose a photonic-engineered porous polymer film based on rare earth phosphors. The incorporation of rare earth phosphors not only enhances light scattering but also enables the conversion of absorbed light energy into photoluminescence within the visible, near-infrared, and mid-infrared spectral regions. Under the synergistic influence of photoluminescence and the porous structure, the film achieves an exceptional reflectance of 94.5 % and an emissivity of 95.6 %. Our experimental results demonstrate a substantial enhancement in the radiative cooling performance of the composite film. During outdoor testing under an average solar irradiance of 746 W m⁻², the fabricated photonic-engineered porous composite film achieved an effective temperature reduction of 10.5 °C. Owing to its outstanding cooling capability, the photonic-engineered porous polymer film holds great promise for applications in the context of energy saving.