A novel BaLu 2 Al 2 Ga 2 SiO 12 :Ce 3+ persistent phosphor was designed and synthesized through hetero-valence substituting Ba 2+ -Si 4+ ion pair for Lu 3+ -Al 3+ one in the Lu 3 Al 3 Ga 2 O 12 . XRD and Rietveld refinement results confirm the garnet typed crystal structure. SEM information shows that the constituent elements are uniformly distributed on the irregular particles. Under 360 or 430 nm excitation, the samples exhibit broad emission bands peaking at 510 nm. The luminescence intensity reaches to the maximum at 6 mol% Ce 3+ doping content, and an internal quantum efficiency of 51.2% is achieved. The concentration quenching between Ce 3+ ions is mainly originated from exchange interaction. Moreover, the phosphors exhibit bright cyan afterglow for minutes after removing the blue-light excitation source. The persistent luminescence decay process is studied by thermoluminescence spectra. The persistent luminescence mechanism and optical information writing and reading process are also discussed to explore the application in optical information storage.
In this article, we synthesized a series of new warm-white emitting persistent luminescent phosphors by co-doping Zn2+ into Pr3+ activated BaLu2Al2Ga2SiO12, and systematically investigated the effect of Zn2+ co-doping on both their photoluminescence and persistent luminescence properties. Following the removal of UV excitation, the phosphor emits warm-white persistent luminescence consisting of greenish-blue and red emissions originating from 3P0 and 1D2 multiplet electron transitions at the 4f level of Pr3+. The luminescence properties of the Ba1−xZnxLu2Al2Ga2SiO12:Pr3+ phosphors can be modified by changing the content of Ba/Zn in the host, which affects the non-radiative energy flow between 5d1–3P0–1D2 levels and resultantly enhances the intensity of the 4f → 4f transition. Compared with the undoped sample, Zn2+ co-doping can significantly enhance the persistent luminescence intensity of the phosphors in the range of 400–800 nm and reduce the intensity in the UV region. Meanwhile, Zn2+ co-doping can also change the intensity ratio between the greenish-blue and red emissions, and the persistent luminescence color can be tuned from red to warm-white with the increase of Zn2+ concentration. Besides, the Zn2+ ions entering the crystal lattice also enhance the persistent luminescence performance by modifying the defect levels in the phosphor. For the optimized phosphor, bright warm-white persistent luminescence can be observed by the naked eye in the dark after the removal of the excitation source for 4 h. Based on the experimental results, a feasible mechanism was also proposed to reveal the persistent luminescence generation process for the BaLu2Al2Ga2SiO12:Pr3+,Zn2+ phosphor.
Phosphors emitting visible and near-infrared persistent luminescence have been extensively studied and commercialized owing to their wide applications in emergency lighting, information storage and in vivo bioimaging. However, ultraviolet (200–400 nm) persistent phosphors are rarely reported. Here, we developed a new Pr3+ activated BaLu2Al2Ga2SiO12 persistent luminescence phosphor, which could be effectively excited by a standard 254 nm mercury lamp and exhibits excellent ultraviolet (280–400 nm) persistent luminescence lasting for more than 3 h. This exciting result encouraged us to comprehensively investigate its structural information, photoluminescence and thermoluminescence properties to reveal a feasible persistent luminescence mechanism. The results show that Pr3+ ions act as both photoluminescence and persistent luminescence emitters, and the ultraviolet light emission originates from its parity allowed 4f15d1 → 4f2 inter-configurational transitions. The suitable energy location of the lowest energy 4f2 → 4f15d1 excitation transition and small Stokes shift of less than 3000 cm−1 (0.37 eV) related to the composition and crystal structure of the host lattice BaLu2Al2Ga2SiO12 ensure the occurrence of Pr3+ 4f15d1 → 4f2 transitions. Moreover, the suitable trapping levels related to Pr4+ in BaLu2Al2Ga2SiO12:Pr3+ were also investigated utilizing thermoluminescence spectra, which could be effectively filled by carriers under 254 nm light irradiation to achieve ultraviolet persistent luminescence. This study opens up new avenues for future research on ultraviolet persistent luminescence and brings new application prospects in the fields of photocatalysis and photodynamic therapy.
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