Structure twinning and photoluminescence properties of sodium dysprosium phosphate Na3Dy(PO4)2

Abstract

Rare-earth phosphate with the general formula Na3Ln(PO4)2 (Ln = lanthanoids) have been known as good luminescent materials for a long time, but their crystal structures have not been recognized completely. In this work, compound Na3Dy(PO4)2 was prepared using molten salt (flux) method and was structurally determined on X-ray single-crystal diffraction for the first time. Interestingly, its structure solution was complicated by non-merohedral twinning, whose twin law can be characterized by a 180° rotation about the (1 0 0) direction of reciprocal lattice. Furthermore, the excitation and emission spectra, decay time and CIE chromaticity index of Na3Dy(PO4)2 were studied. Under near-UV light excitation (350 nm), the powdered Na3Dy(PO4)2 sintered at 1000 °C shows the strongest emission at around 484 and 574 nm, which originates from the 4F9/2→6H15/2 and 4F9/2→6H13/2 transformations of Dy3+ ion, respectively. The decay curve at 350 nm was measured and the decay curve can be well fitted by bi-exponential function, which can be explained by two crystallographic sites of Dy atom in the structure.