New Synthesis Technology And Luminescence Properties Of Strontium Aluminate System Long Afterglow Phosphors With Flower-like Morphology

Research on the strontium aluminate phosphors doped with Eu²⁺ is made to develop new high-efficient, long-persistent and red phosphors without radioactive substance.In this paper, new flower-like Sr₃Al₂O₆: Eu²⁺, Dy³⁺ red phosphor powders were prepared by a sol-gel method in the reducing atmosphere. The synthesis, particle morphology, spectrum properties, luminescence mechanism and afterglow characteristics of Sr₃Al₂O₆: Eu²⁺, Dy³⁺ phosphors were detailed investigated. And the effects of preparation conditions, the concentration of rare earth ions and additive ions on the microstructure and luminescent properties of phosphors were systematically discussed. It is discovered that optimal temperature and time of calcining are 1200oC and 2h, respectively. The flower-like Sr₃Al₂O₆: Eu²⁺ phosphor powders exhibited a red abroad emission band with emission peak at 612nm under the excitation of 472nm and afterglow lased for more than 25min. It is discovered that the emission intensity of phosphors increased firstly then decreased with the concentration of Eu²⁺ ions and reaches its highest intensity at 8mol%. Based on the research on the thermoluminescence spectra and fluorescent decay, Dy³⁺ plays an important role in the system resulted in different decay time. With the concentration of Dy³⁺ increasing, the depth of trapping energy levels in the phosphor increases, but the emission intensity decreases. The optimal concentration of Dy³⁺ is 15mol%. The optimal content of S2- is 0.4mol and afterglow lased for 45min.Red Sr₃Al₂O₆: Eu²⁺, Dy³⁺ and green SrAl2O4: Eu²⁺, Dy³⁺ phosphor powders were firstly prepared by gel-microwave heating method in the reducing atmosphere. The effects of microwave power and heating time on the microstructure, particle morphology and luminescent properties of phosphors were discussed. It is discovered that optimal microwave power is 680W and heating times are 20min and 15min, respectively.The coordinate environment and site distribution of Sr²⁺ ions in the strontium aluminate phosphors activated by Eu²⁺ were investigated. It is determined that Eu²⁺ replaces for Sr²⁺ and the emitting fluorescence color is determined by the 4f65d1→4f7 transfer of Eu²⁺. A new method is firstly brought out for determining the influence of crystal field on 5d level of Eu²⁺. According to this method, the splitting of 5d of Eu²⁺ in Sr₃Al₂O₆: Eu²⁺ and SrAl2O4:Eu²⁺ are determined as 91nm and 56nm respectively. New morphology Sr₃Al₂O₆: Eu²⁺ phosphor powders were synthesized. The self-assembled formation mechanism is discussed. It is proved that flower-like Sr₃Al₂O₆ are assembled by nanowhiskers and nanorod. And the effects of new microstructure and morphology on luminescent properties of phosphors were investigated. Uniformity dispersive flower-like Sr₃Al₂O₆:Eu²⁺ phosphor powders showed the strongest luminescent intensity, and longest afterglow time.