Origin of the red luminescence in Sr₃Al₂O₆:Eu phosphor ——From the synergetic effects of Eu²⁺ and Eu³⁺

陈雷¹，张昭¹，田云飞¹，费米¹，何良锐¹，张平娟²，张文华³

1. School of Materials Science and Engineering, Hefei University of Technology2. School of Electrical and Electronic Engineering, University of Science and Technology of Anhui3. National Synchrotron Radiation Laboratory, University of Science and Technology of China

摘 要：In order to uncover the real origin of red luminescence from Sr₃Al₂O₆:Eu and the physical mechanisms that were involved in the dynamical process of luminescence, variant amount of Eu and Dy activated Sr₃Al₂O₆ phosphors were synthesized with the solid-state reaction and the combustion-assisted solid-state reaction, respectively, using the fine graphite powder or the mixed H_<sup>2+N₂gases as a reducing agent. The phase was examined with XRD analysis and the photoluminescence properties were characterized by a fluorescence spectrometer. Although the phosphors possessed the same Sr₃Al₂O₆ phase, different emission colors（red or green） were obtained, relying on synthesis conditions. The simultaneous existence of Eu²⁺ and Eu³⁺ was not only observed in the emission and excitation spectra, but also identified with the near edge X-ray absorption fine structure spectroscopy（NEXAFS）.The mixed valence（higher than +2 and less than +3） of Eu may be related with the six different sites of Sr, whose effective valence ranged from +1.5058 to +2.2698, in the crystal lattice of Sr₃Al₂O₆ that could accommodate Eu. Moreover, the reduction of Eu³⁺ to forming Eu²⁺ depended on the amount of Eu³⁺ or Dy³⁺ doped, due to the different energy barrier in each site of Sr that Eu had to overcome. The residual Eu³⁺, similar to the doped Dy³⁺, played an important role in supplying the hole for Eu²⁺ to form a bound trap(Eu²⁺)* after excitation. During electron returning to the 4f⁷ ground state of Eu²⁺, the red luminescence was radiated. Therefore, the synergetic effects of Eu²⁺ and Eu³⁺(Dy³⁺) produce red luminescence.

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