Preparation And Luminescent Properties Of Na₃Y?VO₄?₂?Ca₃TaAl₃Si₂O₁₄ Red Phosphor

As the fourth generation of green lighting source,white LED has many advantages,such as small volume,low energy consumption,long cycle life,fast response and so on.At present,the most mature way to obtain white light is to adopt the fluorescence conversion,including two kinds of programs as blue light excitation and near ultraviolet excitation.Among them,the traditional blue LEDs use blue light to excite the yellow phosphor(YAG:Ce³⁺)coated on the chip for achieving white light.But the lack of red components in the spectrum,results in white light with low color rendering index?CRI?.Near-ultraviolet excitation white LEDs is to use the near-ultraviolet light issued by LED chip to inspire RGB three-color phosphor for color combination to acquire white light.The white light achieved by this way has a wide spectral range,which is closer to the natural white light with excellent color rendering index.However,the current lack of efficient red phosphor restricts the development of white LED.Therefore,it is of great significance to develop a new type of highly efficient red phosphor material which can effectively absorb light in the near ultraviolet region.In this work,Na₃Y?VO₄?₂:Eu³⁺and Ca₃TaAl₃Si₂O_{14:Sm³⁺red phosphors were synthesized and characterized by XRD,scanning electron microscopy,photoluminescence and fluorescence lifetime.The main results are as follows:1}Na₃Y?VO₄?₂:Eu³⁺phosphors were synthesized by high temperature solid state method for the first time.The results of X-ray diffraction show that all samples with differet doping concentration have the same slightly distorted version of the glaserite lattices structure as pure Na₃Y?VO₄?₂ matrix,and there is no second phase.The result of elemental detection?EDS?also documents the actual composition of the sample.Scanning electron microscopy?SEM?results show that the sample consists of irregular particles with size about5 ?m.The phosphor can be effectively excited by 395 nm near ultraviolet light and 466 nm blue light,and the strongest excitation peak is located at 395 nm,which is well matched with the wavelength issued by near ultraviolet LED chip.At the excitation of 395 nm,emission spectrum of the sample is dominated by the forced dipole transition of⁵D₀?⁷F₂.Eu³⁺substitutes Y³⁺ to occupy the asymmetric lattice,and then bright red light is emitted.Theemission intensity is 20.6 times of the commercial Y₂O₃:Eu³⁺,and the CIE chromaticity coordinates is?0.643,0.345?,which is close to the international standard red?0.67,0.33?.Moreover,its color purity is 89% higher than that of Y₂O₃:Eu³⁺.When the doping concentration of Eu³⁺ is up to 50 mol%,the intensity of luminescence reaches the maximal value,and phenomenon of concentration quenching occurs when doping concentration beyond 50 mol%.The reason leading to concentration quenching is the dipole-dipole interaction.The emission spectrum of Na₃Y?VO₄?₂:Eu³⁺ phosphors at the different temperature shows that emission intensity of Na₃Y?VO₄?₂:Eu³⁺ phosphors at 200? remains74% of which at room temperature,and the activation energy of temperature quenching is0.336 e V,higher than 0.24 e V of Y₂O₃:Eu³⁺ phosphor.The reason for temperature quench is that when the temperature rises,the heat activated ⁵D₀ state electrons return to the ground state through the energy levels crossover point of the ⁵D₀ and 7Fj states,resulting the emission intensity of Eu³⁺ reducing.2)The Ca₃TaAl₃Si₂O₁₄:Sm³⁺ phosphor was synthesized by high temperature solid phase method.The crystal structure of Ca₃TaAl₃Si₂O₁₄ is lattice of langasite type and the Sm3+ ions is doped into Ca₃TaAl₃Si₂O₁₄ without changing the crystal structure of the matrix.The best excitation peak of Ca₃TaAl₃Si₂O₁₄:Sm³⁺ is 401 nm(⁶H_5/2?⁴F_7/2),which matches the Ga N-LED chip?350-410 nm?.At the excitation of 401 nm near ultraviolet light,the strongest emission peak at 598 nm(⁴G_5/2?⁶H^7/2)belongs to the permissible magnetic dipole transition?MD?,which indicates that Sm³⁺ ions replace Ca³⁺ ions and mainly occupy the symmetric lattice position in Ca₃TaAl₃Si₂O₁₄.The color coordinates of optimized phosphor is?0.5058,0.4037?,located in red and orange light area.