Thermally and optically stimulated luminescence in long persistent orthorhombic strontium aluminates doped with Eu, Dy and Eu, Nd

The long persistent luminescence, thermoluminescence (TL) and IR stimulated luminescence properties of two orthorhombic strontium aluminates (Sr₄Al₁₄O₂₅) co-doped with Eu²⁺, Dy³⁺ and Eu²⁺, Nd³⁺ exposed to beta radiation is reported. The phosphors were synthesized by the combustion method followed by a post-annealing treatment under a reductive carbon atmosphere. Photoluminescence emission spectra of both phosphors are typical for emission of Eu²⁺ ions with 7-fold and 10-fold coordination in Sr₄Al₁₄0₂₅ and consist of the main band at 480 nm and a weak band between 390 and 440 nm. After exposure to beta radiation the Sr₄Al₁₄0₂₅:Eu²⁺,Dy³⁺ phosphor exhibits two strongly overlapped TL peaks at about 70 and 100 °C while the low temperature TL of the Sr₄Al₁₄0₂₅:Eu²⁺,Nd³⁺ phosphor consist of two well separated peaks with maxima at about 60 and 130 °C. Additionally, both phosphors exhibit a weak TL between 180 and 400 °C. The traps responsible for the low temperature TL peaks are the Dy³⁺ and Nd³⁺ centers situated in two different Sr sites with 7-fold and 10-fold coordination. The thermal emptying of the Dy and Nd filled traps creates ultra-long intense afterglow, which gradually decays with time and remains detectable after 220 h storage in dark. IR stimulation of beta irradiated phosphors creates intense IR stimulated luminescence, which is related to the release of electrons from the filled Dy and Nd traps.