Hydrothermal synthesis and crystal structure of new red phosphors, KNaMF7:Mn4+ (M: Nb, Ta)

Publication date: Available online 30 March 2019Source: Materials Research BulletinAuthor(s): N. Kumada, S. Yanagida, T. Takei, B. HongAbstractSingle crystals of new alkali niobium and tantalum fluorides, KNaMF7 (M: Nb, Ta), were prepared by hydrothermal reactions using a perovskite-type oxides, KMO3 as one of the starting compounds. Their crystal structures were determined from single crystal X-ray diffraction data. These fluorides crystallized in the orthorhombic space group P212121 (#19) with a = 5.509(2), b = 9.100(4), and c = 11.234(5) Å for KNaNbF7 and a = 5.517(2), b = 9.093(3), and c = 11.273(4) Å for KNaTaF7. The crystal structures contained isolated MF7 polyhedra showing a monocapped trigonal prism geometry and the M5+ sites could be replaced partially by Mn4+ ions during the hydrothermal reaction. These Mn4+ ion-doped fluorides exhibited photoluminescence properties similar to those of red phosphors. The local environment of Mn4+ ions in these fluorides was confirmed by the X-ray absorption fine structure (XAFS) analysis.Graphical abstract
Source: Materials Research Bulletin - Category: Materials Science Source Type: research