Preparation And Luminescent Properties Of Strontium Aluminate With Different Crystal Phases

As a new kind of environmental protection and energy conservation material, aluminates long persistent phosphors has already been applied in many fields, and is leading to enormous economic benefit. In addition, it has potential application prospect in many areas. This kind of material has excellent luminescent properties, but also has their unresolved shortcomings mainly behaving as few emission colours, and limited work has been done on studying the mechanism of long persistence. As a result, their application area and further development have been limited. So further study on this material is of great importance in both theoretical and application fields.The luminescence of Eu²⁺ ions is caused by the transition between the ⁸S_2/7(4f⁷) ground state and excited 4f⁶5d configuration. And the 5d electrons are split easily by crystal field, so the luminescence of Eu²⁺ ions depends strongly on the crystal field. In this paper, strontium aluminate host materials with different phase structures and Sr_xCa_1-xAl₂O₄ host structures were synthesized through combustion method. The luminescent properties of Eu²⁺ ions in different host structures have been studied. The role of Sr/Ca(Al) ratio in adjusting the emission colours and decay times of phosphor samples has been investigated. And the mechanism of long persistence also has been discussed, according to the result of thomerluminescence spectra.Rare-Earth doped strontium aluminate phosphors were synthesized through combustion method at 600℃. With the increasing Al content, the host phase structure changed from SrAl₂O₄ to the Al-riched SrAl₁₂O₁₉ phase. The Sr₄Al₁₄O₂₅ was formed as a second phase. The luminescence of Eu²⁺ ions in the host lattice of SrAl₂O₄ and SrAl₁₂O₁₉ is different. The emission peaks lied around 519nm and 512nm,respectively, the peak shifted to the short wavelength. The decay speed of the afterglow for SrAl₂O₄ was faster than SrAl₁₂O₁₉.It revealed that there were electron-traps with different depth in the two samples, which was consistent with the study of thomerluminescence spectra.Long persistent phosphors Sr_xCa_1-xAl₂O₄:Eu²⁺,Dy³⁺(x=0,0.2, 0.4,0.6, 0.8,1.0) were prepared through solution-combustion method at 600℃.The phase structure of phosphors were characterized by X-ray diffraction. The major phase was monochlinic CaAl₂O₄ when x<0.8, and monoclinic SrAl₂O₄ phase was formed as minor phase. For x≥0. 8,the major phase was SrAl₂O₄ The diffraction peaks shift to lower angle with the increase in Sr content. A possible reason for this may be the expansion of CaAl₂O₄ crystal lattice, which is ascribe to the substitution of Sr²⁺ ions for Ca²⁺ ions sites in CaAl₂O₄ structure. The excitation and emission spectra of samples have been measured, the decay curves have also been studied extensively. The results revealed that both the emission colors and the decay times can be adjusted by the value of x (Sr/Ca ratio).