First-principles Study On Strontium Aluminate Long Afterglow Luminescent Materials

In recent years, strontium aluminate long afterglow luminescent materials have been widely used in various fields, despite a lot of the experimental study of SrAl₂O₄ the electronic structure and luminescence characteristics, but there are still differences in terms of reaction conditions and light emission mechanism. The research on agents and auxiliary activator is not under way deeply, to limit the practical application of strontium aluminate long afterglow luminescent material. This paper researches the synthesis conditions, electronic structure and luminescence of SrAl₂O₄ by high temperature solid-phase method and the first-principles method.This paper dealed the reaction temperature, reaction time and the ratio of the doping Dy₂O₃, Eu₂O₃ and luminescent properties of the product, which raw materials of SrCO₃, Al₂O₃, Eu₂O₃ and Dy₂O₃ was fully reacted by the high temperature solid phase method in a vacuum sintering furnace. The results showed that: the best synthetic condition of SrAl₂O₄:Eu²+,Dy³+ is reaction temperature 1500℃ and reaction time 3h; when Eu₂O₃ doping amount is 2wt%, SrAl₂O₄:Eu²+ luminous intensity is the largest, afterglow performance is best; when Eu₂O₃ doping amount of 2wt%, Dy₂O₃ doping quantity is 4wt%, SrAl₂O₄:Eu²+,Dy³+ the luminous intensity is the largest, afterglow performance is best.The SrAl₂O₄, SrAl₂O₄:Eu²+, SrAl₂O₄:Eu²+,Dy³+ electronic structure and the role of Eu and Dy in SrAl₂O₄ crystals investigated by first principles method respectively. The results show that SrAl₂O₄ crystal cell volume decreases after the Eu’s doping. The cohesive strength between O and Al is greater than the binding force between O and Sr. Eu doping makes covalent enhancement between the Sr and O, Al and O. SrAl₂O₄ is indirect semiconductor, valence band is mainly contribution by the O 2p orbit, conduction band is mainly contribution by the Sr 4d orbit. After blending Eu, Fermi level up, in the forbidden band Eu 4f orbit, appeared in the conduction band Eu 5d orbit, under the condition of illumination, Eu 4f orbit of electron in the band gaps are 5d to the conduction band of the Eu’s orbit, after the light, the electron jump from the excited state back to the ground state, in the form of light energy out, issued a yellow green with 519 nm. Eu and Dy doping, in Eu 4f orbit and Eu 5d orbit neighborhood there is Dy 4f orbit and Dy 5d orbit, when the light irradiate, the electron transition hole to be captured in Dy trap energy level, when the light stop, Dy trap energy level capture hole slow release, and in combination with the electronic which transition back to the ground state, release energy in the form of light. So the SrAl₂O₄:Eu²+,Dy³+ has a good long afterglow luminescence performance.