Preparation Of Rare Earth Ions Doped12CaO·7Al₂O₃Electron Trapping Materials And Their Optical Storage Properties

Electron trapping materials have wide application prospects in many fields, such asinfrared detection, infrared upconvertion imaging, optical storage, detectionmeasurement, optical computing, optical information processing and X ray storageimaging, etc.In this dissertation, rare earth ions doped12CaO·7Al₂O₃（C12A7） electron trappingmaterials, like C12A7:Eu²⁺,C12A7:Eu²⁺,Dy³⁺and C12A7:Eu²⁺, Nd³⁺were prepared bychemical coprecipitation method.X ray diffraction （XRD）, excitation and emissionspectra, afterglow decaying measurent,optical stimulated luminescence （PSL） andthermoluminescence （TL） techniques were used to characterize their microstructuresand optical properties. The optical storage mechanisms of these electron trappingmaterials were discussed and the X-ray storage characteristics of C12A7:Eu²⁺,Dy³⁺were studied. The clear X-ray storage graph was obtained.The experimental results showed that C12A7:Eu²⁺,Dy³⁺exhibited similar two broadexcitation peaks, respectively, located at254and325nm and the same wide emissionpeak at444nm, which is attributed to Eu²⁺emission between4f65d1to4f7. After325nm UV irradiation, when stimulated with980or808nm infrared light, the long lastingafterglow with blue emission was obtained.By using TL, we can observe the shallow（0.81eV） and deep traps （0.95eV） in C12A7:Eu²⁺,Dy³⁺.Comparing the excitation spectrum of C12A7:Eu²⁺with that of C12A7:Eu²⁺,Nd³⁺,two intense peaks of C12A7:Eu²⁺, respectively, at260and315nm can be observed, butthere is only one strong peak located at315nm and a weaker peak at260nm inC12A7:Eu²⁺,Nd³⁺can be seen. The above results indicated that the Nd³⁺dopping mighthave caused the change in the crystal field and the symmetry of Eu²⁺in C12A7. Afterultraviolet radiation, a blue luminescence phenomenon of long afterglow can be seen inthe dark environment. The afterglow decay curve was composed of a fast-and a slowprocess and the afterglow decay time was longer than that of C12A7:Eu²⁺,Dy³⁺. Theactivation energy of deep traps in C12A7:Eu²⁺,Nd³⁺was ascertained to be0.74eV byTL curve.By using PL, PSL and TL, the trap characteristics and optical storage mechanismof rare earth ions doped C12A7electron trapping materials trap were studied. Especially,X-ray storage characteristics of C12A7:Eu²⁺,Dy³⁺samples was discussed in details. When we burnt them at1380℃for10hours, their optical properties exhibited obviouschanges and excellent X-ray storage imaging was achieved.Their excitation spectrashowed s broadband excitation peaks in the range from250to470nm, located at349,362,385nm etc. For the emission spectra of the air treated samples, the emission peakswere detected at480and572nm, respectively, belonged to the transitions of⁴F_9/2â†'⁶H_15/2and⁴F_9/2â†'⁶H_13/2of Dy³⁺under UV excitation. No energy transfer fromEu²⁺to Dy³⁺was observed.These results indicated that the heat-treatment in air havecaused the transformation of doped Dy³⁺in C12A7from the traps into activatin centers.The afterglow of the air treated samples became short suggesting that the amount ofdeep traps decreased. After irradiated by UV, these samples exhibited strongphoto-stimulable luminescence when stimulated with980or808nm infrared light. Wehave obtained the clearer X-ray storage images of the air treated sample than that of thereduced sample. We also tried to find new ways to reduce the X-ray irradiation dose andto improve the X-ray imaging space resolution.Our research showed that C12A7material is a kind of ideal matrix materials dopedwith rare earth ions, which has a wide application prospect in the field of emergencylighting, optical information storage and X-ray storage image etc.