Study On The Luminescence Process Of Long Afterglow Materials Of Eupium And Dysprosium Co-doped Strontium Aluminate

Long afterglow materials usually refer to the materials that continue to glow after the removal of excitation light and mainly used in pigments,emergency lighting,medical imaging,military covert lighting and information storage,high-energy ray detection.Among them,Sr Al2O4:Eu2+,Dy3+ are the first commercially available green long afterglow materials.However,the specific mechanism of luminescence and the specific role of rare earth ions Eu2+ and Dy3+ in the process of luminescence have been debated.In this paper,samples of three systems of Sr Al2O4:Eu2+,Dy3+?Sr Al2O4:Eu2+ and Sr Al2O4:Dy3+ were prepared by high temperature solid-state reaction in reducing atmosphere.The samples were analyzed by XRD,thermoluminescence test,and fluorescence test in high and low temperatures,transient life test and morphology test.XRD show that the peak of Sr Al2O4 crystal phase can be slightly changed by rare earth ion doping.The fluorescence spectrum peak of Sr Al2O4:Eu2+,Dy3+ present the emission peak of Eu2+ at 514 nm.The characteristic spectrum of Dy3+ has not been observed.Low temperature fluorescence test show that Sr Al2O4:Eu2+,Dy3+ has a low temperature peak at 400 nm except the normal temperature of 514 nm.It indicate the Eu2+ instead the cells of Sr12+ and Sr22+.It is found that the afterglow time of the double doped sample is significantly higher than the single doped Eu2+.High and low temperature thermoluminescence test and data fitting is conducted for the pyrolysis light curves of Sr Al2O4:Eu2+,Sr Al2O4:Dy3+,Sr Al2O4:Eu2+,Dy3+ samples.It is found that the trap concentration and depth of the samples are different.Therefore,the Eu2+ as the luminescence center and Dy3+ only plays the role of energy transmission.The incorporation of Dy3+ makes the distribution of Sr Al2O4:Eu2+ trap more continuous and conducive to improving the occurrence of afterglow.In conclusion,this paper adopts the high temperature solid phase method of europium series of dysprosium doped strontium aluminate long afterglow material,and put forward that Dy3+ have played an important role in energy transfer and modulation trap in the process of luminescence through the analysis and calculation of the thermoluminescence tests.According to the calculation results,the specific luminescent process of the europium dysprosium doped strontium aluminate is inferred: electrons storing in the energy level of at room temperature occur in shallow traps of electron transition.Due to its close to the conduction band,it can be captured in conduction band directly and occurs 4f65d1-4f7(8S7/2)transition;Electrons located in the deep trap under are captured by shallow trap in turn under the auxiliary of Dy3+.This relaxation time in the process is very long,resulting in a long afterglow phenomenon.