Vacuum-Sealed Thermal Treatment Regulates Trap States and Red Persistent Luminescence in CaTiO3: Pr3+,Al3+ Phosphors

Red persistent phosphors remain less mature than green and blue-green systems because their afterglow is often weak and decays rapidly. Here, CaTiO3:0.3%Pr3+,0.3%Al3+ phosphors were prepared by a high-temperature solid-state route under either air or vacuum-sealed quartz-tube (QT) conditions. The effects of processing atmosphere and sintering temperature on phase structure, microstructure, steady-state photoluminescence, afterglow, thermoluminescence, and excited-state decay were examined. X-ray diffraction and Raman spectra show that all samples retain the orthorhombic CaTiO3 perovskite phase, with no detectable secondary phase. SEM observations show particle coarsening at higher QT temperatures, while EDS mapping indicates a homogeneous distribution of Ca, Ti, O, Pr, and Al within the examined region. The QT-treated samples exhibit stronger Pr3+ red emission near 612 nm and markedly improved afterglow compared with the air-treated sample. The QT-1300 sample shows the best afterglow among the present samples, with a reported 3.6-fold higher intensity at 1200 s than Air-1200{\deg}C. Thermoluminescence results indicate that QT treatment increases the population of thermally active traps and enhances the deeper trap component. These results suggest that a low-oxygen sealed environment regulates defect-related traps, most likely involving oxygen-vacancy-associated centers, and improves carrier storage and release through the Pr3+ and Ti4+ intervalence charge-transfer pathway. This work provides a practical processing strategy for improving CaTiO3-based red persistent phosphors and offers insight into trap-state regulation under low-oxygen thermal treatment.