Synthesis, Microstructural And Optical Properties Of Eu²⁺, Dy³⁺ Doped 12CaO·7Al₂O₃ Powders

A new blue phosphor 12CaO·7Al₂O₃:Eu²⁺,Dy³⁺(C12A7:Eu²⁺,Dy³⁺) was prepared by chemical precipitation method followed by annealing inorganic precursors. The X-ray diffraction (XRD), excitation spectra, emission spectra, the decay curves of the afterglow emission,thermoluminescence (TL) curves and photostimulated luminescence (PSL) were conducted to characterize the microstructure of C12A7: Eu²⁺,Dy³⁺ powders and study their optical properties.The results of XRD indicated that the cage structural polycrystalline C12A7 powders of single cubic phase were obtained. It demonstrated that Eu²⁺,Dy³⁺ had been incorporated into C12A7 lattice site. C12A7:Eu²⁺,Dy³⁺ shows a broad blue emission peaking at 444 nm when activated by UV irradiation . The excitation spectra shows two broad band from 200 to 400 nm with their peaks at about 254 and 325 nm. The emission spectra also has a broadband character which is atribute to the typical 4f⁶5d¹-4f⁷ transition of Eu²⁺, and the emission pesk is at about 444 nm. The phosphor can also exhibit a strong blue afterglow emission after UV irradiation. The decay curve of phosphorescence consists of a very fast and a slow component implying the existence of many shallow and deep traps. The results of TL indicated that traps levels(E) of C12A7:Eu²⁺,Dy³⁺ are about 0.48 ev and 0.87 ev. Kinetic order is 2. After C12A7:Eu²⁺,Dy³⁺ powder is irradiated by UV light, strong blue PSL is observed under infrared excitation at 980 nm. An very interesting phenomenon is that the PSL dose not cease immediately , but last several seconds after the termination of the infrared stimulation. The PSL is studied under 980 nm excitation . The slow rising and falling edge is atrributed to the result of electron(hole) retrapping by shallow traps .The PSL still exists 20 hours after UV irradiation. The information stored in C12A7:Eu , Dy can be stored for more than 20 hours .Our results suggested that C12A7 was an appropriate candidate for Eu²⁺ and Dy³⁺ co-doping. Simultaneously, C12A7:Eu²⁺,Dy³⁺ would be applied for emergency illumination in dark environment and optical storage .