Structural and Functional Stability of Strontium Aluminate-Based Luminescent Composites After 15 Years of Natural...

SrAl₂O₄: Eu²⁺, Dy³⁺ polymeric composites are the reference photoluminescent materials in passive signaling due to their high emission intensity and long luminescent persistence. But their real long-term outdoor durability is still poorly understood. This study analyzes a strontium aluminate polymer composite exposed to real weathering for 15 years to evaluate its degradation threshold, exceeding the frameworks of accelerated tests. Using FTIR, Raman, FE-SEM, colorimetry and phosphorescence decay, the weathered material was compared with its reference material. Results show that the luminescent composite retains its structural properties, its optical functionality improving its mechanical properties (increasing the flexural strength between 23 and 64% and microhardness between 136 and 164%), while suffering only a small yellowing, suggesting a longer service life than expected. Finally, it was established that the loss in the optical performance is not due to irreversible degradation of the polymer or pigment but is caused by the accumulation of surface dust and the formation of an opaque outer layer. The application of mechanical surface polishing removes this polluting layer, restoring optical transmittance and effectively recovering almost the original luminosity of the photoluminescent system.