The Long-afterglow Properties Of CaO:Eu And ZnGa₂O₄:Cr

The rare-earth doped red long afterglow phosphors have caused much attention in recent years. In this work, Eu-doped CaO and Cr-doped ZnGa2O4-material are synthesized by a co-precipitation with high temperature solid state method, the crystal structure and the long afterglow properties are studied, and the results are as follows:1) The red long-persistent phosphor CaO:Eu3+is prepared by co-precipitation method with further thermal decomposition. The X-ray diffraction analysis shows that the crystal structure of calcium carbonate transform into a single-phase structure and then generate single-phase calcium oxide structure with the increasing of sintering temperature. The excitation spectrum of CaO:Eu3+shows a broad band around255nm which is attributed to the charge transfer of Eu3+-O2-and a sharp peak at393nm. The emission spectrum of samples corresponds to Eu3+transition between5D0and/Fj (J=0,2,3,4) electron configurations. The red long afterglow is observed at room temperature. A trap level located at0.69eV was found by thermolumihnescence measurement, which come from the Eu3+replaces Ca2+into the lattice. The afterglow luminescence mechanism of sample was discussed according to quantum tunneling.2) The red long afterglow phosphor ZnGa2O4:Cr3+was prepared by the high-temperature solid state reaction at1350℃. The excitation peaks located at254nm and300nm are a charge transfer band (CTB) which corresponds to the electron transition between2p orbitals of oxygen and empty4s4p orbitals of Ga3+Meanwhile, the other two bands at about410and550nm are ascribed to4A2â†'4T1and4A2â†'4T2transitions of3d-3d configuration of Cr3+ions, respectively. The emission lines around690nm all originated from4A2â†'2E of Cr3+ions. The long-lasting phosphorescence (LLP) spectra indicated optimal long-lasting luminescence could obtain from ultraviolet (UV) light excitation. The thermoluminescence (TL) curve implied two different depth of trap was caused by the dopant ions. The liner characteristic of the certain range of the afterglow curve may ascribe to the quantum tunneling process. 3) The red long-lasting phosphor ZnGa2-xGexO4:Cr3+0.005(x=0.1,0.3,0.5) were synthesized by a high temperature solid state reaction. The structure, photoluminescence and afterglow properties were studied. The XRD phase analysis illustrated the structure of the host lattice does not change very much. However, the diffraction peaks of these XRD patterns shift to the higher angles with the increased Ge content. At higher concentration, with the increasing of Ge4+content, the emission peaks perform a different degree of attenuation, and only one obvious emission peak around697nm can be observed in the emission spectrum of ZnGa1.5Ge0.5O4:Cr3+0.005. Furthermore, the emission spectra under different excitation wavelength appear a great difference. The results indicate that the luminescent properties change significantly with the Ga/Ge ratio. The testing of afterglow performance showed that all the decay curves conform to the double exponential decay with different type of decay rate, and a certain trap level was found by the thermolumihnescence measurements.