Preparation And Properties Of Rare Earth Doped SrAl₂O₄Long-lasting Phosphors

SrAl2O4:Eu2+, Dy3+phosphor is a new type of long-lasting phosphorescent material, which is discovered in the nineties of the last century. Compared with traditional phosphors, this phosphor shows better performance, such as higher brightness, longer persistent phosphorescence, greater chemical stability, no radiation, pollution and radiation, which makes this kind of phoshphor widly used in the field of printing industry, plastic industry, paint and industry, glassenamel industrie and textile industry, et al. However, it is needed to improve the luminescent properties and manufacture process of the phosphorescent material in order to meet the higher requirements. Furthermore, although there are variety of luminescent mechanism models, no one can be is convinced by everyone. So, it is very necessary to make further research about Eu2+and Dy3+co-doped strontium aluminates (SrAl2O4:Eu2+, Dy3+).The SrAl2O4:Eu2+, Dy3+phosphor were prepared by two methods in this paper. One is solid state reactions. Carbon powder is used as reducing agent in this method, which replaced the wasteful and insecure mixed reducing gases in the traditional process.The other method is electron beam reduction method, which is propsed by our research group. This is a new phosphor preparation method with the advantage of fast, energy-saving and environmental protection. After preparing, the crystal structure, fluorescence spectrum, persistence characteristic, morphology characteristic and composition of SrAl2O4:Eu2+, Dy3+phosphor was analyzed using X-ray diffractometer (XRD), photoluminescent spectrometer (PL), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) to find out the influence of reducing agent content, holding time, electron beam irradiation time, doped content of europium and boric acid on the luminescent properties of the phosphor.This paper is mainly composed by the following six parts:Chapter1:This chapter firstly introduced the luminescence materials, the research history and development situation of the long-lasting phosphorescent material, then, introduced the application, preparation methods and the glow mechanism of long-lasting phosphorescent materials. The topic selection and research content of this paper was also given in this chapter.Chapter2:Mainly introduced the design and research method of this work, and then breafly introduced the instruments used in the preparation and testing of the experiment.Chapter3:The SrAl2O4:Eu2+, Dy3+phosphor was prepared using high temperature solid phase method with carbon powder acted as reduction gas. The luminous property, and the influence of carbon content and the temperature holding time on the performance of the material were also studied. The carbon powder was excessive in the experiment. The results indicate that, carbon powder content had great effects on the spectral intensity and phosphorescent properties of aluminum acid strontium phosphor. When prepared using7.359g raw materials, which was weighed based on the molecular formula of the product, the optimal content of carbon power was8g. In addition, the influence of temperature holding time on the material performance showed that,3h was needed under the high temperature of1350℃to synthetize pure SrAl2O4phase, otherwise, there will be some Sr3Al2O6impurity phases. The optimal holding time of this preparation method was5h, and the crystallite size was about100μm for the SrAl2O4:Eu2+, Dy3+phosphor prepared by carbon reduction method.Chapter4:In this chapter, the electron beam reducing method was used to prepare the SrAl2O4:Eu2+, Dy3+phosphor, the influence factors were also studied. In the electron beam reducing method, electron beam have dual function of heating and reduction. Firstly, the surface material warm up quickly when bombarded by the electron beam, some oxygen will be escape from the aluminum acid strontium in the vacuum with high temperature, which makes the Eu3+ions reduct into Eu2+ions. Then, after the bombardment of the electron beam, some electrons enter into the inside of the material. As the whole material warming up, the Eu3+ions reduct into Eu2+ions, the reduction reaction e-+Eu3+â†'Eu2+happening. This is a high efficient reduction method. Form the experiment, it was found that, rare earth elements, boric acid doping and electron beam bombarding almost not changed the crystal structure of the material and the4f65dâ†'4f7transition environment of the luminescence center Eu2+. The emission wavelength of SrAl2O4:Eu2+, Dy3+phosphor exhibited red shift with the increase of europium doped content, and there existed a quenching concentration. The particle size and crystallization degree of the aluminum acid strontium phosphor became bigger as the content of boric acid increased. The particle and crystallite size of SrAl2O4phosphor also could be effctively changed by electron beam irradiation time. The results showed that, the best irradiation time was15min, the best amount of Eu doping was2mol%, the best content of H3BO3addition was10mol%, and the crystallite size was about200μm for SrAl2O4:Eu2+, Dy3+phosphor prepared by electron beam reducing method.Chapter5:In this chapter, the influence of SrAl2O4:Eu2+, Dy3+phosphor preparation conditions on the material properties was discussed and summerized. Then, an improved luminescent mechanisms model of SrAl2O4:Eu2+, Dy3+phosphor is launched based on the analysis of our experimental results and the materials of other research.Chapter6:This chapter is a brief summary of the whole work.