Enhancing solar reflectance and infrared emissivity of rare earth Sm³⁺-doped perovskite ceramics for energy-saving applications

As climate change accelerates and the urban heat island effect intensifies, developing materials that simultaneously exhibit high solar reflectance and strong infrared emissivity is increasingly critical for thermal management, yet achieving this dual functionality remains challenging. Here, we report rare-earth Sm³⁺-doped yttrium molybdate ceramics (Y_2-xSm_xMoO₆, x = 0, 0.1, 0.2, and 0.3) prepared by the solid-state reaction to achieve synergistic optical enhancement through multi-structural engineering. The resulting ceramics crystallize in a monoclinic structure (space group C2/c), where Sm⁺³ induces lattice stabilization of grain boundaries and suppresses abnormal growth, transforming heterogeneous agglomerates (>50 μm) into uniform polyhedral grains (0-10 μm) with a narrow pore size distribution centered at 0.5-1.5 μm and increased porosity (50.55%). XPS confirms that Sm³⁺ substitution generates oxygen vacancies and moderate lattice distortion, thereby activating broadband phonon modes and enhancing emissivity. All ceramic samples exhibit bright white coloration (CIE: 0.31, 0.33; L* = 93.22) and wide band gaps (3.17-3.22 eV), calculated using Density Functional Theory (DFT), resulting in negligible near-infrared (NIR) absorption. The optimized SYM4 achieves superior NIR reflectance of 95.60% and a high infrared emissivity of 0.90, attributed to the synergy of electronic transparency, Mie scattering from a redefined microstructure, and vacancy-induced phonon emission. The accelerated weathering tests reveal excellent environmental durability, with only a minor NIR reflectance loss of 0.7% after 72 h of exposure, while the chemical resistance test confirms stability in acidic/alkaline environments with NIR reflectance loss of 1.09%. Outdoor testing of SYM4 coatings demonstrates sub-ambient cooling of 6.96 °C, corresponding to a net cooling power of 58.02 W/m² under real-world conditions. These findings indicate that the Sm⁺³-doped ceramics are suitable for sustainable cooling applications.