Preparation And Luminescent Properties Of Bule Persistent Phosphor SrAl₄O₇: Eu²⁺, Dy³⁺

The long afterglow phosphor of rare-earth activated alkaline earth metal aluminate, a new kind of phosphor that was developed during the 1990s, has been widely used in the fields of emergency lighting, military work, esthetic design and etc. Since most of the industrial products at present are materials of Yellow-green color whose illumination is unitary, these materials can not meet current market demands any longer. Now the strontium aluminate phosphor which has a good blue long afterglow performance has become a hot topic to study. As a material of blue long afterglow phosphor, SrAl₄O₇:Eu²⁺ has received more and more attention because it has got those outstanding qualities that aluminate blue long afterglow phosphor does.In the following essay, I will focus on talking about the synthesis of blue long afterglow phosphors SrAl₄O₇:Eu²⁺,Dy³⁺,its luminescent Properties and issues of the persistence mechanism. Firstly, with SrCO3,Al(OH)3,Eu₂O₃,Dy₂O₃,H₃BO₃ as raw materials, materials of SrAl₄O₇:Eu²⁺,Dy³⁺ blue long afterglow phosphor should be prepared, adopting the solid-state reaction. Secondly, the characterization of the phosphors'crystal structure should be done with XRD, and the emission spectrum and afterglow characteristics of the phosphors should be tested by using the fluorospectrophotometer and the illuminometer. Thirdly, the effects of Al/Sr molar ratio, the sintering temperature, the heating rates, the concentration of doped Eu²⁺,Dy³⁺ and H₃BO₃ on the SrAl₄O₇:Eu²⁺,Dy³⁺ blue long afterglow phosphor should then be studied.The experimental results are as follows:The phase of the SrAl₄O₇:Eu²⁺,Dy³⁺ blue long afterglow phosphor has been greatly influenced by Al/Sr molar ratio, the sintering temperature and the heating rates. When Al/Sr molar ratio changes between 3.5 and 4.3, the phase of the sample material changes according to the sequence of Sr₄Al₁₄O₂₅→SrAl₄O₇→SrAl₁₂O₉19), and when Al/Sr molar ratio remains 3.9, the phosphor with the main phase of SrAl₄O₇ is synthesized. And as the sintering temperature rises from 1300℃to 1500℃, the phase of the material gradually changes from rich Sr phase to rich Al phase, and it becomes SrAl₄O₇ when the temperature reaches 1400℃. When the heating rates change from 2℃/min to 6℃/min, the phase of the sample changes according to the sequence of SrAl₁₂O₁₉→SrAl₄O₇→Sr₄Al₁₄O₂₅, and when heated at a rate of 4℃/min to 1400℃, the phosphor with the main phase of SrAl₄O₇ is produced.The alteration of the concentration of doped Eu²⁺ produces no effect on the phase of the SrAl₄O₇:Eu²⁺,Dy³⁺ blue long afterglow phosphor, but it does affects the initial brightness and the afterglow time of the sample and the effects increase first and then decrease, and when the concentration of doped Eu²⁺ is 3%, we get the highest initial brightness and the longest afterglow time. The alteration of the concentration of doped Dy³⁺ influences the initial brightness and the afterglow time of the sample in the same way as the concentration of fraction Eu²⁺, and when Sr of the concentration is 3%, we get the best luminescence properties of the sample.The concentration of doped H₃BO₃ has a great influence on the phase and the luminescent Properties of the SrAl₄O₇:Eu²⁺,Dy³⁺ blue long afterglow phosphor. As the experimental result indicates, The amount of B³⁺ is 5% of Al, it helps synthesize the SrAl₄O₇ phrase and improve the luminous intensity and extend the afterglow time.After experimenting and comparing, the best formula of preparing materials of the SrAl₄O₇:Eu²⁺,Dy³⁺ blue long afterglow phosphor using the solid-state reaction has been determined as Sr_0.94Al_3.9O₇:0.03Eu²⁺,0.03Dy³⁺ and H3BO as the flux the amount is 5% of Al;The following best process parameters: the sintering temperature is 1400℃, the heating rate is 4℃/min,. When the emission spectrum reaches 480 nm, the longest afterglow time is 586 min (≥1mcd/m2), and the initial brightness is 12230 mcd/m², the best luminescent properties of the sample can be obtained.Combining the effects of the band transmission model on the luminescence mechanism of the long afterglow phosphors with the Electron-hole theory, the essay will put forward a new electronic transmission model. This model reasonably explains the Long-lasting phenomenon which is produced by Eu²⁺ ,Dy³⁺ and B³⁺ co-doped its 4 f⁶5d1→4 f 7transition existing in different materials of strontium aluminate long afterglow phosphors.