Synthesis Of Rare Earth Doped Phosphotungstate Phosphors By High Temperature Solid State Method And Their Luminescence Properties

White LED has the advantages of high brightness,good color rendering,low color temperature,etc.It is the first choice for lighting.At present,the mature method of implementing the LEDs is to generate the white light by blue GaN chips to excite YAG yellow phosphor powder.However,these white LEDs have low color reproducibility for lack of red emission component,which limits their further development and applications for white LEDs.In this paper,phosphotungstate is used as phosphor matrix because of its stable chemical properties and high energy transfer efficiency.The activated ions in phosphotungstate system are surrounded by phosphate ions in the same plane and tungstate ions in the upper and lower layers.This weakens the interaction between the active ions and improves the quenching concentration.Meanwhile,Eu³⁺and Sm³⁺have a rich energy level structure.They have strong absorption in near ultraviolet region,which meets the requirement of white LED fabricated by ultraviolet chip excitation.Because Sm³⁺has a close energy level of ⁴G_5/2 to ⁵D₀of Eu³⁺,it is possible to transfer energy between them.The influence of Sm³⁺on the energy transfer process of Eu³⁺can be studied by using this characteristic.Therefore,a series of red and orange phosphors doped with K₂Gd?PO₄??WO₄?with Eu³⁺doping and Sm³⁺doping were prepared by high-temperature solid phase reaction method.Their luminescence properties and phase structure were also characterized.?1?K₂Gd_1-x?PO₄??WO₄?:xSm³⁺?x=0.01⁰.05?phosphors were prepared by high temperature solid-state method.It is found that the sample belongs to scheelite-like structure and possesses the orthorhombic system of Ibca?73?space group by studying its structure and luminescent properties.The luminescence intensity of phosphors increase with the increase of Sm³⁺doping concentration until a maximum reaches at x=0.02 and concentration quenching occurs afterwards.It is found that K₂Gd?PO₄??WO₄?phosphors have excellent color purity,the color coordinate points are located in the orange-red region.The influences of temperature on emission intensity,lifetime and color coordinates are studied,the results show that the phosphors have good thermal stability.?2?The phosphors K₂Gd_1-x?PO₄??WO₄?:xEu³⁺?x=0.05?0.1?0.2?0.3?0.4?0.5?were synthesized via high temperature solid-state reaction.The crystallographic structure and luminescent properties of the samples were studied.The results show that x=0.3 is the optimum doping concentration of Eu³⁺.Under394 nm excitation,the lattice position of Eu³⁺in K₂Gd_0.7?PO₄??WO₄?:0.3Eu³⁺phosphor is non-centrosymmetric,which leads to the dominant electric dipole transition?⁵D₀?⁷F₂?and shows a good red emission.In addition,the color coordinates of the samples all fall in the red region and close to the chroma edge.Meanwhile,the lifetime and emission intensity of the sample do not change significantly with the increase of temperature.?3?The K₂Gd_1-x-yEu_y?PO₄??WO₄?:xSm³⁺novel red-emitting phosphors were prepared by solid phase reaction at high temperature.Luminescence properties of Eu³⁺,Sm³⁺co-doped samples were studied at 394 and 404 nm excitation,respectively,it demonstrated that the excitation peaks of the composite phosphors increased and broadened obviously after the addition of Sm³⁺ions,which confirmed that the energy transfer process from Sm³⁺to Eu³⁺ions.Moreover,the emission intensity of the sample at 150 ^oC is 78%of the initial value.All the above results indicate that this kind of phosphors have a promising application prospect in white light emitting diode lighting.