Study On Rare-earths Doped Yellow Light-emitting Silicate Luminescent Phosphors

The unique electron shell structure of rare-earth elements result in the incomparable optical properties than those generally elements. At the age of energy exhausting, as the new energy conservation and environmental protection material, rare-earth doped luminescent materials are widely applied in lighting, display, architecture and handicraft etc. After a hundred years'development, people have been developed many kinds of rare-earth doped luminescent materials. And rare-earth doped blue and green light-emitting materials already have mature production process, and have been widely used. However, the research on red and yellow light-emitting phosphors is still in a relatively worse position. Not only the species are few, but also the performance of red and yellow materials is inferior to blue and green materials. Especially, preparing yellow light-emitting materials with excellent properties is a big problem in the field of rare-earth luminescent materials research. The silicate luminescent materials with high stability, good water resistance, and low lost, are regarded as the important phosphor matrix. So it makes sense to research the luminescent properties of rare-earth ions in silicate matrix. Especially it is meaningful searching for yellow, red light-emitting materials in silicates.In this paper, we prepared and investigated the rare-earth ions doped silicate yellow light-emitting materials. Firstly, we synthesized a series of rare-earth ions doped Sr₃SiO₅ yellow fluorescent materials with a high-temperature solid-state reaction. In the case of Li₂CO₃ doped as flux, the Eu²⁺ concentration dependent intensity was investigated. And the most suitable concentration of Eu²⁺ is obtained. It is observed that the Sr₃SiO₅: Eu²⁺ has excellent luminescence intensity and color rendering, which is a potential yellow fluorescent material. In addition, we synthesized the Sr₃SiO₅ yellow light-emitting fluorescent material with Ce³⁺ doped and Eu²⁺, Ce³⁺ co-doped in the condition of Li₂CO₃ doped. And the energy transfer is discussed between Eu²⁺ and Ce³⁺.In order to achieve effective afterglow luminescence in Sr₃SiO₅ matrix, yellow light-emitting long afterglow phosphors Sr₃SiO₅:Eu²⁺, Dy³⁺ doped with different kinds of fluoride are prepared by high-temperature solid-state reaction, whose main emission peak located at 575nm. The results show that the doped fluorides obviously improved both the luminescence and afterglow properties of Sr₃SiO₅: Eu²⁺, Dy³⁺. Among all the fluorides, the alkaline-earth metal fluorides are most suitable. And the afterglow duration of Sr₃SiO₅:Eu²⁺, Dy³⁺, 0.05 BaF₂ reaches 12 hours, which is one of the longest yellow long afterglow material ever reported. The investigation shows that the introduction of alkaline-earth metal fluorides can make the trap density at different depths of the materials tunable, making the improvement of afterglow properties possible.Finally, the Eu²⁺ or Dy³⁺ doped and Eu²⁺, Dy³⁺ co-doped yellow light-emitting phosphors Ca₂ZnSi₂O₇ were synthesized by high-temperature solid-state reaction. The spectroscopy characters of Ca₂ZnSi₂O₇ phosphors with different doped situation under different excitation are discussed. A white light is found in phosphor Ca₂ZnSi₂O₇: Dy³⁺ under 365nm ultra-violet (UV) excitation, which is compound by a 484nm blue light emission and 575nm yellow light emission of Dy³⁺. The results show that in the situation of Eu²⁺, Dy³⁺ co-doping, the sample emits yellow fluorescence under 365nm UV excitation. Removing of the light source, the sample shows the yellow-green afterglow lasting two hours. In addition, the afterglow mechanism of the phosphor was investigated.