The Research Of Red Phosphors Used For White LED

The synthesis and characterization of phosphors used for white LED were paid more attention with the extension of application and the development of preparation technology in white LED. Especially, the properties of phosphor excited by blue or UV light affect directly the color rendering of white LED. Because of limitation of red phosphors applied nowadays, it's necessary to find a new type of red phosphors for white LED.A series of stable red phosphor R_2-xEu_x(MoO₄)₃(R=La, Y, Gd) and AR_1-xEu_x(MoO₄)₂ (A=Li, Na, K, Ag; R=La, Y, Gd) based on molybdates was prepared by sol-gel process. The factors that affect their luminescent properties, such as concentration of Eu³⁺ and the reaction temperatures were studied. Then we prepared some samples by solid-state process which were compared with the samples prepared by sol-gel process. And we found that the latter had some advantages.The phosphors Y_2-xEu_x(MoO₄)₃, Gd_2-xEu_x(MoO₄)₃ and KEu(MoO₄)₂ had phase change as the reaction temperature increasing, and their luminescent properties have also been influenced. It can be seen that the phosphor LiEu(MoO₄)₂ shows the most wonderful luminescent properties by compared with others. The excitation spectra of LiEu(MoO₄)₂ include a broad range from 250nm to 500nm, which have three excitation peaks at 296nm, 395nm and 465nm; the emission spectra are composed of many sharp lines ranged from 350⁷50nm, and the peaks at 616nm was the strongest lines which are corresponded to transition of ⁵D₀â†'⁷F₁.The excitation spectra show effective absorption wave lengths at ultraviolet (UV) (395nm) and blue (465nm) corresponding to the f-f transition of Eu³⁺ which are matched well with the wave-lengths of commercial GaN based LED, thus, the phosphor may be a better candidate for red component for white LED.The luminescent properties of LiGd_1-xEu_x(MoO₄)₂ were very close to that of LiEu(MoO₄)₂. So we could use Gd³⁺ to decrease the cost.