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There is a demand for long afterglow composites due to their potential applications in nighttime signal boards, sensors, and biomedical areas. In this study, Polypropylene (PP)/strontium aluminate-based composites [SrAl₂O₄:Eu²⁺/Dy³⁺ (SAO₁) and Sr₄Al₁₄O₂₅: Eu⁺², Dy⁺³ (SAO₂)] with maleic anhydride grafted PP compatibilizer (PRIEX) were prepared, and their auto-glowing properties were examined. After UV excitation at 320 nm, the PP/5PRIEX/SAO₁ composites showed green emission at 520 nm, and blue emission was observed for PP/5PRIEX/SAO₂ around 495 nm. The intensity of phosphorescence emission and phosphorescence decay was found to be proportional to the filler content (SAO₁ and SAO₂). The FTIR analysis excluded the copolymerization reaction between the SAO₁ and SAO₂ fillers and the PP matrix during the high-temperature melt mixing process. The SAO₁ and SAO₂ fillers decreased the overall crystallinity of the composites without affecting the T_m and T_c (melting and crystallization temperature) values. The thermal stability of the composites was slightly improved with the SAO₁ and SAO₂ fillers, as seen from the TGA curve. Due to the plasticizing effect of the compatibilizer and the agglomeration of the SAO₁ and SAO₂ fillers, the tensile modulus, tensile strength, and storage modulus of the composites was found to be decreased with an increase in the SAO₁ and SAO₂ content. The decreasing effect was more pronounced, especially with the bulk-sized SAO₂ filler.