Structural and optical investigation of nanocrystalline lithium lanthanum praseodymium tetraphosphate powders

Lithium lanthanum praseodymium tetraphosphates nanopowders, LiLa1 xPrx(PO3)4, where x ¼ 0.01e1, were prepared by wet-chemistry synthesis route. The structure and morphology of phosphates were analyzed by collecting X-ray diffraction patterns, Raman and FT-IR spectra. The obtained materials were composed of submicron crystals in the elongated forms and plates. The monoclinic structure of the crystals with the space group C2/c was assigned for all investigated compositions. The decrease of unit cell parameters with the increase of praseodymium concentration, due to the lower ionic radius of the Pr3+ as compared to the La3+ cations, was evidenced. Spectroscopic properties of the LiLa1xPrx(PO3)4 powders were analyzed in details on the basics of the absorption, excitation, and emission spectra with luminescence lifetimes easurements. The intraconfigurational 4f2 transitions were observed under blue (l ¼ 440 nm) and UV (l ¼ 212 nm) excitation. The luminescence characteristic of the samples was dependent on the concentration of the Pr3þ ions in the host material. Significant concentration quenching in the whole range of investigated samples was observed leading to barely seen emission of the LiPr(PO3)4 crystals.