Simultaneous enhancement of photoluminescence and afterglow luminescence through Bi3+ co-doping in the Sr3Al2O5Cl2:Eu2+ phosphor

Abstract

In this work, the Sr₃Al₂O₅Cl₂:Eu²⁺ and Sr₃Al₂O₅Cl₂:Eu²⁺,Bi³⁺ phosphors are synthesized by high temperature solid state reactions. Various characterization techniques, such as X-ray diffraction (XRD), Rietveld refinement, photoluminescence (PL) spectroscopy, afterglow spectroscopy, decay curves and thermoluminescence (TL) spectroscopy, are used to examine the phase purity and PL properties of all samples. The XRD results show that all samples belong to the targeted orthorhombic Sr₃Al₂O₅Cl₂ phase with the space group of P2₁2₁2₁. Upon excitation with UV light, Eu²⁺-related reddish photoemission and afterglow luminescence are observed in the Sr₃Al₂O₅Cl₂:Eu²⁺ samples. More remarkably, we find that co-doping with Bi³⁺ ions can enhance the Eu²⁺-related photoemission and afterglow intensity as well the afterglow duration. For the optimal Sr₃Al₂O₅Cl₂:Eu²⁺,Bi³⁺ sample, the afterglow luminescence can continue for nearly 550 min in the dark, which is almost 3-fold the duration of the afterglow luminescence of the optimal Sr₃Al₂O₅Cl₂:Eu²⁺ sample. The TL spectra reveal that co-doping with Bi³⁺ ions can enhance the defect population that corresponds to trap depths at 63 °C, 75 °C and 150 °C, of which the former two trap depths may help to improve the Eu²⁺-related luminescence in addition to the afterglow property. Due to an increase in the trap concentration, there is an increase in the re-trapping possibility for the released carriers. This work not only achieves enhanced afterglow luminescence of the Sr₃Al₂O₅Cl₂:Eu²⁺ phosphor by co-doping with the non-rare earth (RE) Bi³⁺ ions, but also provides new insights into the design of RE and non-RE related enhanced afterglow photonic materials for the future.