Investigation of Persistent Luminescence of Strontium Aluminate in Polymer Films for Passive Daytime Radiative Cooling Application

Persistent Luminescent (PersL) materials have found applications in several fields; their integration into passive daytime radiative cooling systems remains largely unexplored. In this work, SrAl 2 O 4 :Eu 2 + , Dy 3 + (SAO) is synthesized via a combustion method and co‐doped with La 3 + or Tb 3 + to tailor the afterglow properties. The resulting phosphors are embedded into different polymer matrices (epoxy resin, PMMA, PVA, PVP, and PDMS) to investigate the impact of the polymers on photoluminescence (PL) and evaluate the cooling performance of the PersL‐polymer composites. The composites exhibited an emission centred at 520 nm, high luminance values (up to 3300 cd m − 2 ), enhanced afterglow compared with bare powders, and high mid‐infrared emissivity (ε 8 – 14 µm = 0.84–0.89). The PL contribution is evaluated through the calculation of the re‐emitted energy, accounting for 4–6% of the absorbed solar energy. Outdoor measurements under solar irradiation demonstrate temperature reductions of up to 5°C. The results highlight the role of polymer selection in balancing persistent luminescence and thermal performance: PDMS and epoxy resin provided enhanced afterglow properties, and PVP exhibited relevant radiative cooling behaviour due to its solar reflectance. This study demonstrates the potential of SAO‐based composites as coatings combining persistent luminescence and passive radiative cooling for sustainable thermal management applications.