Crystal Structure, Characterization, and Luminescence Properties of Mn4+‐Doped K3Nb2O4F5

In this paper, we present the high‐pressure/high‐temperature synthesis and characterization of the potassium fluoridooxidoniobate K3Nb2O4F5. Single‐crystal analysis revealed that the phase crystallizes in the trigonal space group R3‾ ${R\bar{3}}$ m (hR18) with a=5.799(2), c=21.371(4) Å, V=622.4(4) Å3 and Z=3 at T=299 K exhibiting a structure type closely related to that of Ba2RbFe2F9. The assignment of the anion positions to oxygen and fluorine is based on crystallographic data and BLBS/CHARDI calculations. Further characterization via EDX spectroscopy was carried out, corroborating the ratio of K to Nb. Doping of the title compound with Mn4+ was achieved in a secondary step using a ball‐mill, resulting in a red phosphor material, which was additionally analyzed by luminescence spectroscopy. The emission maximum is located at λmax=630 nm. This paper reports on the synthesis of the oxyfluoride compound K3Nb2O4F5 under high‐pressure/high‐temperature conditions. When Mn4+ is introduced into the crystal lattice, the compound exhibits red luminescence upon excitation with blue light.