Long lasting blue phosphorescence and photostimulated luminescence in 12CaȮ7Al₂O₃:Eu thin films grown by pulsed laser deposition

Long lasting blue emitting Eu-doped 12CaȮ7Al₂O₃ thin films have been prepared on quartz substrates by pulsed laser deposition combined with post-annealing. The 12CaȮ7Al₂O₃ phase is formed after annealing the films above 900 °C in vacuum ambient. Upon 323 nm excitation, the thin films exhibit a blue long lasting emission peaked at 444 nm, assigned to the 5d-4f transitions of Eu²⁺. The films annealed at 950 °C have stronger luminescence and longer lasting time than that annealed at 900 °C. The phosphorescence intensity of vacuum annealed film is better than that annealed in H₂/N₂ atmosphere, which might be due to the increase of shallow trap numbers during the vacuum annealing process. Thermoluminescence curves demonstrate that vacuum and H ₂/N₂ atmosphere annealing could introduce a large number of both shallow and deep traps into 12CaȮ7Al₂O₃:Eu thin films. After UV irradiation, excellent photostimulated luminescence can be observed under 980 nm excitation. Our results suggest that 12CaȮ7Al ₂O₃:Eu phosphor may serve as a promising blue luminescent materials used in fabrication of optical storage and illumination in dark environments.