Four-Dimensional Incommensurate Modulation and Luminescent Properties of Host Material Na3La(PO4)2

A series of orthophosphates Na3Ln­(PO4)2 (Ln = lanthanoids) have for a long time been known as good luminescent materials, yet their crystal structures have not been studied in full detail. In this work, compound Na3La­(PO4)2 was prepared using molten salt (flux) method and for the first time was structurally determined on X-ray single-crystal diffraction data. Interestingly, it crystallizes in the four-dimensional incommensurately modulated structure with orthorhombic superspace group Pca21(0β0)­000 and modulation wave vector q = 0.387b*. Furthermore, to evaluate the potentiality of Na3La­(PO4)2 to be used as a luminescent host material, 5 mol % Eu3+, Tb3+, and Dy3+ doped phosphors were prepared, respectively. The excitation spectra, emission spectra, decay time, quantum efficiency, and the color purity of prepared phosphors, Na3La0.95Eu0.05(PO4)2, Na3La0.95Tb0.05(PO4)2, and Na3La0.95Dy0.05(PO4)2, were studied.