Luminescence Properties Of Rare Earths Doped Silicate Phosphors And Adjustment Of Long Afterglow

Long lasting phosphor (LLP) is a kind of energy-storing material, which can store the absorbed energy then slowly release the energy as visible light. In the recent years, long afterglow phosphors are drawing more and more attention because of a constantly growing market for their applications in traffic signs, emergency signage, watches and clocks display, textile printing and so on. For its excellent luminescence properties, aluminate LLP holds a leading post in actual applications. However, it has worse water resistance, easy deliquescence, of which the luminous efficiency can be weaken by hydration. Here a series of silicate long lasting phosphors of high stability and good water resistance are prepared, of which luminescence properties are studied. Blue, green afterglow properties can be adjusted by doping, which have wider application prospects.For the practical applications, firstly, we prepare long-lasting phosphor Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺,aB³⁺,bP⁵⁺ by solid state reaction. To enhance its afterglow intensity, we have researched the adjustment of afterglow property with P⁵⁺ doping in the samples. It is observed that with P⁵⁺ doping, the afterglow intensity of the samples increases while its persistent time decreases, indicating that the P⁵⁺ doping can adjust the depth of the trap level and thus change the releasing rate of the trapped electrons. The adjustability of the afterglow properties is very helpful for different practical applications of illumination and displays, especially for long-lasting phosphor of more than 12 hours but relatively weak luminance.Secondly, the samples of both CaAl2Si2O8:Eu²⁺ and CaAl2Si2O8:Eu²⁺,Mn²⁺ doped with rare earths (Tb, Sm, Ce, Dy, Nd) are prepared by solid state reaction. It is found that the samples have a good stability just as silicate but high afterglow strength approaching that of the aluminate LLP's. The results indicate that the afterglow time of CaAl2Si2O8:Eu²⁺ can be lasted by both Dy³⁺ and Nd³⁺ doping, and the effect of Nd³⁺ doping is better than the Dy³⁺ doping. The reason is that the trap level of Nd³⁺ doping is deeper than Dy³⁺ doping. In addition, the white color rendering for Ca_0.74Al₂Si₂O₈:0.01Eu²⁺,0.25Mn²⁺ have been optimized by adjusting the Ce³⁺, Tb³⁺ or Sm³⁺ co-doping, of which Sm³⁺ co-doping is best of all.In order to avoid the toxicity of Cd2+, thirdly, we prepared nontoxic, environmental protection and new green-emitting LLP materials M(Ca2+, Sr²⁺, Ba2+)O?2ZnO?2SiO₂:Mn,RE (Sm³⁺, La³⁺, Tb³⁺) by introducing of CaO, SrO, and BaO composition to replace the Cd2+ doping. In the case of M=Sr, the sample has a good afterglow property, and the best afterglow performance is obtained at 1mol% Mn²⁺ concentration. The results indicate that the afterglow property of sample is better than Zn₂SiO₄:Mn²⁺, obtained under the same prepare condition. This is because Sr²⁺ ions can partly replace Zn²⁺ site in Zn₂SiO₄, which deepen the trap energy level and prolong the afterglow decay time. Furthermore, the effects of co-doping ions (Sm³⁺, La³⁺, Tb³⁺) on afterglow property of sample have also been investigated. It is found that the afterglow can be improved only by Tb³⁺ co-doping. The investigation is helpful for finding sensitizing agent for LLP.