Enhanced afterglow performance of CaAl_2O_4:Eu~(2+),Nd~(3+) phosphors by co-doping Gd~(3+)

In order to effectively improve the afterglow properties of CaAl₂O₄:Eu²⁺,Nd³⁺ phosphors, a series of Ca_0.982–xAl₂O₄:0.012Eu²⁺,0.006Nd³⁺,xGd³⁺ (x = 0,0.012,0.024,0.036,0.048,0.060 mol) phosphors were prepared by a high-temperature solid-phase approach. Crystalline composition and microstructure were characterized by XRD, TEM, HRTEM, and XPS, luminescence properties were systematically analyzed by fluorescence spectra, afterglow decay curves and TL glow curve. Results show that all of Ca_0.982–xAl₂O₄:0.012Eu²⁺,0.006Nd³⁺,xGd³⁺ phosphors belong to monoclinic CaAl₂O₄, without other cystalline phase. The blue emission at 442 nm is observed, which is assigned to the 4f⁶5d →4f⁷ transition of Eu²⁺ ions. Doping with appropriate amount of Gd³⁺ ions (x = 0.036mol) significantly improves the afterglow properties of phosphors, but the excessive doping of Gd³⁺ induces the fluorescent quenching. The doping of moderate Gd³⁺ changes the traps states, the trap depth varies from 0.598 to 0.644 eV and the trap concentration is also greatly improved, thus significantly improving afterglow performance.