Preparation And Photoluminescence Properties Of Multi-color Long Lasting Phosphorescence Materials Activated By Eu²⁺

Long-lasting phosphorescence (LLP) materials have attracted considerable attention for various displays and signing applications as friendly environmental and energy economized materials. As the awareness of environmental protection and energy saving is increased, LLP material will have wider prospect of market. So the exploration of multiple color-emitting is promising and thus has attracted intensive research interests. Nowadays, a great amount of novel LLP materials based on different hosts have been reported in the literature. Only green LLP materials SrAl2O4:Eu2+, Dy3+ is commercially applied. Long wavelength emitting (>600 nm) materials with phosphorescence is in great scarcity. Therefore, there is a strong desire for the development of phosphors with long wavelength emissions in recent years. In addition, the phosphorescence mechanism in Eu2+containing phosphors has been the subject of many investigations. Up to now, countless reports have been published on the phosphorescence mechanisms of Eu2+-containing phosphors, but only a few mechanisms have outlived advances in experimental and theoretical methods. In this paper, a series of Eu2+ phosphors were synthesized by solid-state reaction and their luminescence properties were systematically investigated. In addition, the luminescence properties of M2TiA2O8:Pr3+(M=Sr, Ba, A=Si,Ge) were also studied with the aim of exploration of red LLP materials.In this paper, firstly, we try to improve the LLP properties of blue-luminescence Sr2MgSi2O7:Eu2+, Dy3+ by the addition of Ce3+. The triply doped phosphor Sr2MgSi2O7:Eu2+, Dy3+, Ce3+ exhibited higher brightness and longer lasting time than that of Sr2MgSi2O7:Eu2+, Dy3+, which could to ascribed to more traps formed by the incorporation of Ce3+. In addition, Eu2+, Dy3+ co-doped Sr2MgSi2O7 phosphors with deficient, stoichiometric or excess amounts of silicon are prepared by solid state reaction. We found that the addition of excess SiO2 into Sr2MgSi2O7:Eu2+, Dy3+ improves its photoluminescence and afterglow properties whereas SiO2 deficiencies quench its photoluminescence and afterglow. The underlying reason of photoluminescence and afterglow enhancement is discussed.In order to develop novel LLP materials, Eu activated CaMgSiO4, BaMgSiO4, Sr3Al2O5Cl2:Eu2+, R3+(R=Dy, Nd, Tm) and Pr3+ doped M2TiA2O8 (M=Sr, Ba, A=Si,Ge) were prepared and their luminescence properties were studied. The results indicate that:BaMgSiO4:Eu2+ and Sr3Al2O5Cl2:Eu2+,R3+(R= Dy, Nd, Tm) exhibited green and orange-yellow LLP; the other phosphors show no afterglow. It is worthwhile to mention that the emission of Eu2+ in CaMgSiO4 is badly quenched. In the paper, the location of the energy level of Eu2+ and the Fermi level in CaMgSiO4 was estimated to evaluate its luminescence behaviors.An important work of this paper is that ionization of Eu2+ to Eu3+ upon UV irradiation is observed in BaMgSiO4:Eu2+, but there is no indication that the photogenerated Eu3+ can change back to its divalent state at room temperature. In addition, the phosphor shows photochromism upon UV irradiation. No such photoionization and photochromism behavior is observed for the air-sintered BaMgSiO4:Eu phosphor. A possible Eu2+ photoionization mechanism is constructed on the basis of these experimental observations. The phosphorescence behaviors of Eu-doped BaMgSiO4 phosphors are discussed on the basis of the photoionization mechanism.