Synthesis And Surface Modification Of Sr₃SiO₅:Eu²⁺

In recent years,white LED has attracted significant attention due to their higher efficiency,energy saving,longer life and no pollution.As a very promising silicate-based yellow phosphor,Sr3SiO5:Eu2+ not only possesses excellent chemical resistance and high thermal stability,but the synthesis temperature is lower at least about 100? compared with the aluminate-based phosphor.However,this material is sensitive to water,when exposed to atmosphere of aqueous,the luminescent properties will decrease rapidly,which restricted their application.Moreover,the poor dispersity of phosphor powders in organism system is bad for the package of LED.So,the surface modification is necessary to obtain the excellent performance of the phosphor.In this paper,the Sr3SiO5:Eu2+ phosphor was synthesized by high temperature solid-state reaction method under reductive atmosphere,the effect of sintering temperature,mass fraction of fluxing agent and Eu2+ doping concentration on crystal structure and photoluminescence properties of the phosphor were investigated.The effect of S doping on structure and properties of Sr3SiO5:Eu2+ were also studied.The results show that when the sintering temperature is 1400?,the mass fraction of fluxing agent is 3%and Eu2+ doping concentration is 3mol%,the sample is of high purity with no impurity phase exists.The structure of phosphor is not changed with the slightly addition of S,the emission intensity is higher than that of Sr3SiO5:Eu2+ with no S doped.Moreover,the addition of S leads to an slightly shift of its emission spectra towards the red region.The phosphor shows the maximum emission intensity when the doping concentration of S2-is 1wt%,and the emission intensity decreases with the doping concentration of S2-increasing.The sample of Sr3SiO5:Eu2+ exhibits a strong orange yellow emission centering at 579.5nm.The excitation spectra of the sample is a broad spectra ranging from 300-500nm with a high excitation intensity under blue band.The Sr3SiO5:Eu2+ phosphor was treated with silane coupling agent and surfactant.The effect of coating time,temperature and mass fraction of silane coupling agent on surface modification of phosphor were studied and the process condition was optimized.The sample was characterized by scanning electron microscopy(SEM),fluorescence spectrometer and Infrared spectrometer(IR).The water-resistance and dispersity of uncoated and coated phosphor were characterized by the experiment of water-resistance,agglomeration and settle ability.The results show that the phosphor shows the maximum emission intensity when the coating time is 3h,coating temperature is 80?,the mass fraction of silane coupling agent is 2%.Through the analysis of SEM and IR,a compact homogeneous film was coated on the surface of the phosphor.The excitation and emission spectrum are not influenced by the film,only the intensity slightly decreases.Moreover,both the water-resistance and dipersity of the phosphor were improved after modification.