Coating Modification Of Strontium Aluminate Phosphor

Aluminates luminescent material with high luminous efficiency, long afterglow time,excellent chemical stability and non-radioactive, is one of the most excellent long afterglowluminescent materials. However, its water resistance and oxidation resistance are poor. And, itcan not be used for the preparation of luminous glaze. In this study, SrAl₂O₄:Eu²⁺,Dy³⁺phosphor was modified by chemical method, and luminous glaze was prepared. XRD, SEM,EDS and fluorescence spectrum were used to analyze phase composition, microstructure,chemical composition, fluorescence intensity of the coated phosphor and the luminous glaze.Firstly, SrAl₂O₄:Eu²⁺,Dy³⁺phosphor was coated with amorphous SiO₂by sol-gel method.The influence of the ethanol amount, the solution pH, the coating amount and the aging timeon the coating properties was discussed. In order to obtain a dense coating layer, coatingconditions were selected as following: the molar ratio of tetraethoxysilane, ethanol and waterwas1:15:20, the solution pH value was2.00, and the coating amount was at least0.1, theaging time was at least4hours.Then, zircon powder was synthesized at low temperature by sol-gel method with Lithiumfluoride as mineralizer. As the amount of LiF increasing, the synthesis temperature of zirconpowder would reduce. When the molar ratio of the fluoride ions to the zirconium ions were0.6or higher, zircon phase appeared at650℃and became well crystallized at700℃. As thepH value of gelation rising, the ZrSiO₄became more difficult to synthesize. The synthesistemperature affected the shapes of zircon particles. As the calcining temperature rising, theparticle shapes were from rod–like or elongated to ellipsoidal.Thirdly, the phosphor with ZrSiO₄-coating was prepared through the sol-gel method.When the coating ratio was3.0, a dense ZrSiO₄coating layer formed after calcined at900℃for30min. As the calcination temperature and the holding time increasing, the synthetic ratioof ZrSiO₄increased. However, if the temperature is too high or the holding time is too long,ZrSiO₄particles would abnormally grow, leading to the breaking of the coating layer. Inaddition, the coating prepared by two-step method was not satisfactory owing to the lowsynthesis rate of ZrSiO₄and the bad oxidation resistance.Finally, luminous glaze was prepared using the phosphor coated with ZrSiO₄. As the content of phosphor increasing, the luminous performance of the glaze was better. However,the melting temperature increased and the glazed became rougher. The glaze becamesmoother and the fluorescence intensity of the luminous glaze increased, since sinteringtemperature increased. The glaze with40%content of phosphor was smooth and still had astrong fluorescence after calcined at1100℃.