Preparation And Properties Of Sr₂SiO₄:Eu²⁺ Phosphor For White Light-emitting Diodes

As solid-state semiconductor illumination, white light-emitting diodes（LEDs） are considered to be the fourth generation green lighting source.device because of their high efficiency, energy-saving and environment-friendly. As an important component of white LEDs, the performance of phosphor has great influence on luminescent efficiency, color-rendering index and other optical properties of white LEDs. Among many host materials for phosphors, silicates have been attracted much attention because of their simple structure, abundant raw materials, stable physical and chemical properties. In this study, Sr₂SiO₄:Eu²⁺ phosphors were prepared by a conventional solid state reaction, the structure and luminescence properties of Sr₂SiO₄:Eu²⁺ phosphor were investigated by X-ray diffraction and fluorescence spectrophotometer, the effect of synthesis temperature, carbon powder addition and Eu²⁺ concentration on the structure and luminescent properties of Sr₂SiO₄:Eu²⁺ phosphor were disccussed, and some partial substitution were happened in Sr₂SiO₄:Eu²⁺ structure with other ions for improving the luminescent intensity, the corresponding results show as follows:1. Sr^2-xSiO4:x Eu²⁺ phosphors were prepared via high solid state reaction, the optimum synthesis temperature is 1450℃, and the optimum carbon powder addition is n（C）/n（Sr）=1.2. The excitation and emission spectrum are located at the range of 200⁵00 nm and 420⁶80 nm, which are originate from 4f→5d and 4f65d1→4f7 transition of Eu²⁺, respectively. The luminescent intensity firstly increased and then decreased with Eu²⁺ concentration increased, and the best luminescent intensity of Sr^2-xSiO4:xEu²⁺ phosphors can be obtained at x=0.02.2. The structure transform between α phase and β phase with substitution of Ca²⁺ and Zn²⁺ in Sr sites. The luminescent intensity of samples firstly increased and then decreased with Ca²⁺/Zn²⁺ concentration increased, the best luminescent intensity of（Sr1-xMx）2SiO4:Eu²⁺ phosphors can be obtained at x=0.03 and x=0.04, and the emission intensity of（Sr0.97Ca0.03）2SiO4:Eu²⁺ and（Sr0.96Zn0.04）2SiO4:Eu²⁺ phosphors are improved with 67% and 260% range compared with Sr₂SiO₄:Eu²⁺ phosphor, respectively. The substitution of Ca²⁺ and Zn²⁺ can prolong the lifetime of Sr₂SiO₄:Eu²⁺ phosphor.3. After Si4+ substituted with Al³⁺, the percentage of β-Sr₂SiO₄ phase is increased, and the major structure of sample is α-Sr₂SiO₄ phase after P⁵⁺ substitute Si4+. The luminescent intensity of samples firstly increased and then decreased with Al³⁺/P⁵⁺ concentration increased, the maximum luminescent intensity of Sr2Si1-xAlxO4:Eu²⁺ and Sr2Si1-xPxO4:Eu²⁺phosphors can be obtained at x=0.08 and x=0.06, respectively. The luminescent intensity of Sr2Si0.92Al0.08O4:Eu²⁺ and Sr2Si0.94P0.06O4:Eu²⁺ phosphors are 1.55-fold and 1.38-fold higher than that of Sr₂SiO₄:Eu²⁺ phosphor, respectively. And the substitution of Al³⁺ and P⁵⁺ also can prolong the lifetime of Sr₂SiO₄:Eu²⁺ phosphor.4. With N^3- substituting O^2-, the structure of sample gradually transform to β-Sr₂SiO₄ phase. The luminescent intensity of Sr₂SiO₄-xN2x/3:Eu²⁺ phosphors increased with N^3- concentration increased, and the maximum luminescent intensity of Sr₂SiO₄-xN2x/3:Eu²⁺ phosphors can be obtained at x=0.5. The luminescent intensity of Sr2SiO3.5N1/3:Eu²⁺ is 2.16-fold higher than that of Sr₂SiO₄:Eu²⁺ phosphor.