Synthesis And Luminescence Of Sr₂ZnSi₂O₇-based Phosphors Co-doped With Different Ions

Recently, alkaline earth silicates coped with rare earth ions have attracted research interests in the field of photoluminescence due to their excellent properties such as high brightness, no radiation, high chemical and physical stability, relative easy preparation and low cost.Sol-gel process is an efficient technique for the preparation of the phosphors due to the good mixing of starting materials and relatively low reaction temperature resulting in more homogeneous product than those obtained by direct solid state reactions. The first section: Novel green-emitting long lasting afterglow Sr₂ZnSi₂O₇:Mn²⁺, R³⁺(R=Er³⁺, Gd³⁺) phosphors are prepared by the sol-gel method and their luminescent properties are systematically investigated in this paper. DSC-TG, XRD, TEM, photoluminescence long-lasting phosphorescence, and thermoluminescence spectra are used to characterize the synthesized phosphors. These phosphors are well-crystallized by calcinations at 800℃for 10h in a reductive atmosphere of active carbon. This temperature is much lower than that (1100℃) by solid state reaction. Emission and excitation spectra showed Mn²⁺ emission are dominant in these materials. In the emission spectra of phosphors there is a broad emission band centered at 523nm, which can be attributed to the spin forbidden transition of the d-orbital electron associated with the Mn²⁺ ions (4T1→6A1). The afterglow of Sr₂ZnSi₂O₇:Mn²⁺ phosphors decrease with the concentration of Mn²⁺. It reaches a maximum at concentration of 0.2mol﹪and then diminishes tardily with increasing content, indicating concentration quenching. Sr₂ZnSi₂O₇:Mn²⁺,R³⁺(R=Er,Gd) emit green light and show long-lasting phosphorescence after they are excited with 254nm ultraviolet light. The luminescent intensity can be greatly enhanced with incorporation of Er³⁺ or Gd³⁺. Sr₂ZnSi₂O₇: Mn²⁺, Er³⁺ phosphors have better long afterglow properties with high emission intensity and longer decay time than the phosphors of Sr₂ZnSi₂O₇: Mn²⁺ or Sr₂ZnSi₂O₇: Mn²⁺, Gd3 +, which can be ascribed to the different trap levels and trap concentrations formed in the hosts. The mechanism of the origin of the long-lasting phosphorescence is discussed using the thermoluminescence curves.The second section: Sr₂ZnSi₂O₇:Eu3+,Gd³⁺ phosphors by long wavelength UV excitation...