Crystal growth, structural properties, and photophysical characterization of Ln4Na2K2M2O13 (M = Nb, Ta; Ln = Nd, Sm, Eu, Gd).

Single crystals of Ln(4)Na(2)K(2)M(2)O(13) (Ln = Nd, Sm, Eu, Gd; M = Nb, Ta) were grown out of a reactive high temperature hydroxide melt. The structures were determined by single crystal X-ray diffraction. Ln(4)Na(2)K(2)M(2)O(13) crystallizes in the monoclinic space group C2/c in which niobium and tantalum are located in a rare 5-coordinate, square pyramidal coordination environment. Optical band gaps were estimated from diffuse reflectance UV/vis spectra. The magnetic susceptibility data were measured, and the intense room temperature photoluminescence of the europium containing compounds was studied.