Synthesis, crystal structure, electronic structure, and intensive zero-phonon-line emission of Mn4+ in K5Nb3OF18 lattice

Abstract

Manganese ions-activated fluorides and oxyfluorides have found applications in solid state lighting and display, but the coordination environments of Mn4+ activator and their effects on the photoluminescence (PL) properties in some host lattices have remained unclear. In this study, microcrystal powders of oxyfluoride K5Nb3OF18 with and without Mn4+-doped were synthesized by using a coprecipitation method. The morphology, crystal structure, electronic structure of K5Nb3OF18 and the coordination environments and PL properties of Mn4+ activator in K5Nb3OF18:Mn4+ were investigated. It is revealed that K5Nb3OF18 crystallizes in the tetragonal structure with the space group I4cm. There are two crystallographic sites for Nb5+ ions in the lattice, both of which have C4v symmetry. Mn4+ ions-activated K5Nb3OF18 shows characteristic emission due to the transition from 2E to 4A2, while with intensive zero-phonon-line (ZPL). Structure analysis indicates that the local environments of Nb5+ ions in K5Nb3OF18 are more contracted and distorted than those in Rb5Nb3OF18. These features along with the non-centrosymmetric nature of the Nb5+ sites are considered to response for the intensive ZPL emission.