Preparation And Study Of Long Afterglow Silicate-based Phosphors

In the recent years, rare earth luminescent materials attracted more interest due to their excellent properties such as stability, high–efficiency, high brightness, no radiation, excellent repeatability and environmental capability. In this study, long lasting phosphorescence silicates were synthesized by solid state reaction and sol-gel method, respectively. The structure and luminescent properties of the phosphors were discussed using activations modification and micro-analysis measure. Luminescent mechanism of the phosphor was simply discussed.A phosphor of Sr₂MgSi₂O₇: Eu²⁺, Dy³⁺ (blue-emitting) was synthesized successfully by solid state reaction and sol-gel method in a weak reducing atmosphere. The phosphor with the best luminescent properties was obtained by changing the contents and ratio of activations, contents of H3BO3. And the decay characteristics of afterglows of the phosphors were investigated. Microstructure and luminescent properties of the phosphors were observed. The results show that the phosphor via the solid state reaction has the phase of Sr₂MgSi₂O₇ mainly and some SiO₂ impurity; and it is formed by massive agglomerated particles; the main emission peak is at 469nm, its initial luminescent intensity reaches 1925mcd/m² and persistence time lasts above 220min. Pure phased Sr₂MgSi₂O₇ phosphor with special morphology structure can be obtained by sol-gel method. This"flower-like"structure is detected for the first time in Eu2+ and Dy3+ co-doped long lasting phosphorescence silicates. The phosphor via sol-gel method exhibited a better afterglow property than that of the phosphor obtained by the solid state reaction. Its main emission peak is at 465nm and initial luminescent intensity reaches 7230mcd/m², persistence time lasts above 690min.A phosphor of CdSiO₃:Sm³⁺ (orange-emitting) was synthesized by sol-gel method. The CdSiO₃:Sm³⁺ phosphor with the best luminescent properties was obtained under 1000°C by changing the contents of activations, water and H3BO3. Microstructure and luminescent properties of the phosphor were investigated. The results show that the pure phosphor which is formed by massive agglomerated particles is observed. The emission spectrum of the phosphor exhibits a broadband centered at 445nm and three narrowband centered at 562, 598 and 643nm, and it would emit orange visible light after excited by UV. Its initial luminescent intensity reaches 601mcd/m² and persistence time lasts above 200min.The luminescent mechanism: In Sr₂MgSi₂O₇: Eu²⁺, Dy³⁺ systems, the detailed mechanism can be explained by the hole-transfer mechanism, the nano-sized"flower-like"morphology can improve the luminescent properties. In CdSiO₃:Sm³⁺ systems, luminescence is produced by the defects that is created by the inequivalent substitution of Sm³⁺ to Cd²⁺.