Preparation And Luminescence Properties Of CaGd₂?WO₄?₄:RE?Eu,Sm? Phosphor Forwhite LED

At present,there are some disadvantages in commercial red phosphor for white LED,such as poor color purity,low luminous efficiency and poor thermal stability,which restrict the development of white LED.Therefore,it is urgent to develop suitable red phosphors with high efficiency,high color purity,chemical stability and high absorption in the near-UV/blue spectral region.In this paper,a novel scheelite structure CaGd₂?WO₄?₄:Eu³⁺red phosphor was investigated.Specific work carried out the following:Series of CaGd_2-x?WO₄?₄:xEu³⁺?0?x?1?novel red phosphors were successfully synthesized by the conventional solid-state method.The XRD results show that CaGd₂?WO₄?₄ phosphor has monoclinic scheelite structure with space group I2/b.The excitation and emission spectra present that CaGd₂?WO₄?₄:Eu³⁺phosphor can be effectively excited by near-UV?393nm?and blue light?464 nm?,and exhibits the strongest red emission peak located at 616 nm,which is ascribed to ⁵D₀?⁷F₂ transition of Eu³⁺ion.The optimal doping concentration of Eu³⁺is determined to be x=0.7.It can be confirmed that the dipole-dipole interaction type plays an important role in the energy transfer in CaGd₂?WO₄?₄:Eu³⁺phosphors through the concentration quenching curve.In addition,Judd-Ofelt theory was employed to evaluate various radiative parameters,such as the refractive index,the J-O parameters??_??and the branching ration???.Sm³⁺singly doped CaGd₂?WO₄?₄ and Sm³⁺,Eu³⁺co-doped CaGd₂?WO₄?₄ phosphors have been successfully synthesized by solid state method.The crystal structure,luminescent properties and energy transfer mechanism between Sm³⁺ions and Eu³⁺ions have been investigated.The results show that CaGd₂?WO₄?₄:ySm³⁺and CaGd_1.3-y?WO₄?₄:0.7Eu³⁺,ySm³⁺phosphors are single-phase scheelite crystal structure.CaGd₂?WO₄?₄:ySm³⁺phosphor can be effectively excited by near-UV?405nm?,and exhibits the strongest red emission peak located at 600 nm,which is ascribed to ⁴G_5/2?⁶H_7/2 transition of Sm³⁺ion.The optimal doping concentration of Sm³⁺is determined to be x=0.03.Sm³⁺as sensitizer can absorb energy effectively and transfer to the activator Eu³⁺ion,which lead to the enhancement of the luminous intensity of CaGd_1.3-y?WO₄?₄:0.7Eu³⁺,ySm³⁺phosphors.A series of red emitting phosphors MGd_1.3?WO₄?₄:0.7Eu³⁺?M=Ca/Ba,Ca/Sr?have been prepared by the conventional solid state method.The XRD showed that the structure of the SrGd₂?WO₄?₄ phosphor was a single phase,and the BaGd₂?WO₄?₄ phosphors was composed of BaWO₄ phase and Gd₂?WO₄?₃ phase.CaGd₂?WO₄?₄?SrGd₂?WO₄?₄ and BaGd₂?WO₄?₄ can be effectively excited by near-UV,and exhibits the strongest red emission peak located at 616 nm.In SrGd₂?WO₄?₄:Eu³⁺?BaGd₂?WO₄?₄:Eu³⁺and CaGd₂?WO₄?₄:Eu³⁺phosphors,the optimal doping concentration of Eu³⁺are determined to be x=0.8?x=0.7?x=0.7,respectively.In addition,the influence of M lattice modification on the optical properties of phosphors was investigated.The results show that M lattice substitution doping can effectively improve the luminescent intensity of Ca_1-xBa_xGd_1.3?WO₄?₄:0.7Eu³⁺and Ca_1-xSr_xGd_1.3?WO₄?₄:0.7Eu³⁺phosphors by changing the lattice environment around the Eu³⁺ion.