Site dependent thermoluminescence of long persistent phosphorescence of BaAl₂O₄:Ce³⁺

A very long persistent phosphor BaAl₂O₄:Ce³⁺ was prepared and studied. The Ce³⁺ 5d-4f emissions from two Ba²⁺ sites in the BaAl₂O₄ were observed at 450 and 402 nm. The lowest 4f-5d excitation peaks were recorded at 357 and 335 nm, respectively. The persistence times of the long afterglow emissions from Ce³⁺ at the two sites were found to be longer than 10 h. Site-selective thermoluminescence spectra of the sample were measured. Two sets of thermoluminescence peaks were detected at -43, -26 and 27 °C, and -53, -36 and 30 °C (heating rate 13.3 °C/min) corresponding to the two sites at 450 nm (site-1) and 402 nm (site-2), respectively. Dy³⁺, Ce³⁺ co-doped samples were also prepared, which introduce new defect-related traps at 18, 50, and 82 °C (heating rate 10 °C/min). These defect-related traps due to Dy³⁺ co-doping also contribute to the Ce³⁺ afterglow at the two sites.