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Facile hydrothermal synthesis and upconversion luminescence of tetragonal Sr2LnF7:Yb3+/Er3+ (Ln = Y, Gd) nanocrystals


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Alkali-earth–rare-earth complex fluoride materials, Sr2LnF7:Yb3+/Er3+ (Ln = Y, Gd) have been prepared via a facile hydrothermal method by using a chelating agent. X-ray diffraction (XRD) and transmission electron microscopy (TEM) assays revealed that the as-synthesized Sr2LnF7 nanocrystals (NCs) are of tetragonal structure with pure phase. The upconversion (UC) emission spectra of both Sr2YF7:Yb3+/Er3+ and Sr2GdF7:Yb3+/Er3+ NCs mainly include two parts, the green emission peaks at 524 and 540 nm are assigned to the (2H11/2, 4S3/2)–4I15/2 transitions of the Er3+ ions, and the red emission peaks centered at 653 nm are attributed to the Er3+ 4F9/24I15/2 transition. The luminescence mechanism analysis indicates that the energy transfer from Yb3+ to Er3+ is ascribed to the two-photon process.