Persistent luminescence from trivalent rare earth ions doped lithium strontium silicate under x-ray excitation

Long afterglow luminescence (LAL) phosphors hold potential for diverse applications. However, too many factors make it impossible to obtain a general afterglow mechanism, which hinders the exploration of the novel afterglow phosphors. Here, we take trivalent rare earth (RE³⁺) doped Li₂SrSiO₄ as an example for research, use X-rays as the excitation source to ensure host-band charging method regardless of the band gap and use RE³⁺ ions as the luminescent centers achieving the stability of emission wavelength in different hosts. The data results indicate that Ce, Pr, Tb, Dy, Sm, and Tm, which are easily variable in valence, exhibit afterglow emission, while Er, Nd, and Ho, which are not easily variable in valence, do not exhibit afterglow emission. A general afterglow mechanism based on the afterglow properties of Li₂SrSiO₄:RE³⁺ was proposed, in which the electrons and holes were generated under X-ray excitation formed excitons, subsequently bound by RE³⁺ where the ability of RE³⁺ ions to bind excitons is determined by their valence change trend.