Synthesis And Properties Of Phosphate Light-emitting Materials For WLED

Due to its low preparation temperature, high brightness, stable physical and chemical properties, well controlled paritcle size, the phosphate, a convential host of phosphor, has been recongniced as an improtant light-emitting material. In the parper, a red light emitted poosphors excited by blue chip; a yellow one and a blue one excited by ultraviolet chip were prepared. The results are as follows:A series of samples Ca4(PO4)2O:Eu2+were prepared by conventional solid-state reaction method. The results indicated that a broad excitation band ranged343-585nm appeard. Therefore, this phosphor can be applicatted in white LEDs excited by the blue chip and ultraviolet chip. And the emission spectrum had2peak peaked at638nm and658nm, the full-width half-maximum (FWHM) was178nm. The influence of raw material, grinding way, calcinations temperature, holding time, sintering atmosphere, the concentration of active ions, charge compensation agent and flux to luminescent properties were studied systematically. In addition, luminescent properties were studied by doping with other alkaline earth metal ions. The result indicated that a new substance was formed with Ba2+instead of Ca2+. And with the concentration of Ba2+increased, the emission spectrum blueshifted, a new peak of540nm appeared, the full-width half-maximum (FWHM) increased to240nm. The color coordination shift from (0.58,0.408) to (0.392,0.577), corresponding to hue converted from blue to yellow.A series of samples (Cai-xBax)3(PO4):Eu2+were prepared by conventional solid-state reaction method. The XRD patterns of the samples indicated that there was no obvious influence on the structure of the host with Eu2+doped, and all the samples were indexed as (Cai-xBax)3(PO4). With the increasing of Ba2+, the band gaps were estimated ranging from5.5to5.9eV, and the crystal field splitting between two lowest Eu2+5d levels was enhanced from6085to6808cm-1in (Cai-xBax)3(PO4). As a result, the emission peak of the (Ca1-xBax)3(PO4):Eu2+shifted from447to550nm, which means that the emission color altered from blue to yellow. The redshift of the emission band of (Ca1-xBax)3(PO4):Eu2+were explained by crystal field strength, covalence, Stokes shift.A blue-emitting phosphor, Eu2+-activated Mg3Ca3(PO4)4phosphor, was synthesized by conventional solid-state reaction. X-ray powder diffraction (XRD) analysis confirmed the formation of Mg3Ca3(PO4)4. Photo-luminescence (PL) results showed that Mg3Ca3(PO4)4:Eu2+could be efficiently excited by UV-visible light from250to430nm, which matched well with the emission wavelengths of near-UV and UV LED chips. The effects of the concentration of doped-Eu2+in Mg3Ca3(PO4)4:Eu2+on the PL were also investigated.