Photostimulated Luminescence And Optical Storage Mechanism Of Eu²⁺, Mn²⁺ Doped 12CaO·7Al₂O₃ Powders

The erasable optical storage phosphor 12CaO·7Al₂O₃: xEu²⁺, yMn²⁺ (x=0, 0.001; y=0, 0.01) were prepared by chemical precipitation method. The X-ray diffraction (XRD), SEM were conducted to characterize the microstructure of the powders; Excitation and emission spectrum, the decay curves of the afterglow, photostimulated luminescence (PSL) and thermoluminescence (TL) curves were analyzed to study their optical properties.The results of XRD indicated that the cage structural polycrystalline C12A7 powders of single phase were obtained. The Eu²⁺ and Mn²⁺ ions had been incorporated into C12A7 lattice site. SEM showed that C12A7: Eu²⁺ and C12A7: Eu²⁺, Mn²⁺ powders with the grain size of 500-600 nm were synthesized.For C12A7: Eu²⁺, Mn²⁺, a broad blue emission band centered at 444 nm corresponding to 4f⁶5d¹- 4f⁷ (⁸S_2/7) transition of Eu²⁺ was observed with the excitation band peaking at 330 nm. It can be fitted into two Gaussian components with wavelengths peaking at 441 nm and 468 nm, respectively which can be attributed to two different Eu²⁺ ions sites. And a weak yellow-green band at 568 nm originates from ⁴T₂ (G)-⁶A₁(S) transition of Mn²⁺ .The energy transfer (ET) from Eu²⁺ to Mn²⁺ never been observed in C12A7 hosts.The long lasting blue phosphorescence and photostimulated luminescence (PSL) after ultraviolet irradiation at room temperature in C12A7: Eu²⁺ and C12A7: Eu²⁺, Mn²⁺ powders were observed. The PSL spectra have the same shape as that of PL which indicates that the emission in both cases come from an identical origin. The codopant Mn²⁺ enhances the intensity of the persistent phosphorescence and PSL due to the existence of more shallow and deep electron traps in C12A7: Eu²⁺, Mn²⁺.To understand the trap properties and detailed mechanism of PSL, we studied the TL curves. The greatly enhanced intensity of the TL peak at low-temperature TL bands and its TL peak occurs at a very high temperature around 440 K in the C12A7: Eu²⁺, Mn²⁺ comparing to C12A7: Eu²⁺. The trap depth to be 0.64 eV for C12A7: Eu²⁺ and 0.64 eV, 0.86 eV for C12A7: Eu²⁺, Mn²⁺ are given.Therefore, rare earth ion activated C12A7 phosphor is promising candidate as erasable optical storage due to its unique crystal nanocage structure.