氧化物膜包覆碱土硫化物荧光粉的研究

Improving the Stability of Alkaline Earth Sulfide Based Phosphors by Oxide Coating

采用湿法在碱土硫化物为基质的红色长余辉发光材料Ca0 .8Sr0 .2 S∶Eu2 + ,Tm3 + 表面包覆一层惰性的氧化物膜 ,使其与外界的环境相隔离 ,从而提高其化学稳定性。用XRD、SEM及能谱表征了氧化物惰性膜的存在 ,讨论了核 壳结构间的键合作用 ;

Alkaline earth sulfides (AES) are excellent and versatile phosphor hosts, hold promise use for many fields. However, these phosphors are easy to hydrolysis in humidity air, and they are easy to dissociate and degrade under high-energy charge, which limit their applications. All of these problems can be solved by using appropriate protective coatings on the surface of phosphor to prevent from the reacting with the atmosphere around the phosphors. Chemical vapor deposition (CVD) method was used extensively, but this CVD process requires elaborate instrumentation, the cost is expensive. A simply wet method was firstly used to coat the unstable AES based phosphor in this paper. The phosphor was added into precursors solution of oxides (usually their soluble salts solution), and then their hydroxides were precipitated on the surface of phosphors through changing the value of pH. The coated phosphors were separated from the liquor resulting and dried at sufficiently high temperature (300～500 ℃) for a sufficient time (1～2 h) to remove water. During this process, part hydrolysis of the surface plays an important role, which make the oxide coating particles adhered better on the phosphor surface. A layer of oxide coating (such as Al_2O_3, SiO_2, MgO, ZnO)was covered on the surface of alkaline earth sulfides based phosphor Ca_(0.8)Sr_(0.2)S∶Eu^(2+), Tm^(3+) in aqueous medium. XRD, SEM and EDS were used to characterize the coating and the ideal model of coated phosphor and bonding between oxide coating particles and the surface of phosphor were discussed. The stability and optical properties of coated or uncoated phosphor were measured at room temperature. The results indicate that a layer of much smaller oxide coating particles indeed covered on the surface of phosphor, and the stability of coated phosphor has been enhanced to great extent; but oxide coating has no remarkable effects on their emission spectra except a little decrease of their PL intensities within the permitted range. Encapsulated with a layer of oxide coating is a good method to enhance the stability of alkaline earth sulfide based phosphor, and our method is simply and easy to carry out.