Fluoride Phosphors with Mn4+ Ions: Relations between Structure and Emission Spectra

Abstract

The search for new phosphor materials that can be excited by blue LED and emit in the red spectral range is a very important for development of white LED with high color rendering index and suitable color correlated temperature for emission either of cold or warm white light. Fluoride materials like K2SiF6, Na2GeF6 etc are suitable candidates for this role. High degree of iconicity of chemical bonds in fluorides ensures a weak nephelauxetic effect and results in shifting of the Mn4+ emission to shorter wavelengths. In the present work we consider how the structure of the fluorides affects the manganese emission wavelengths. Such factors as geometry of the fluorine octahedra around the Mn4+ ions, chemical bond lengths, angles between the chemical bonds, mutual arrangements of the octahedra (either they are aligned or tilted with respect to each other), the nature of chemical bonds with the ions from the second coordination sphere, polarizability of the chemical bonds etc are all very important for the formation of spectroscopic properties of the Mn4+ ions. Thus, they all should by analyzed carefully before making a final conclusion about suitability of a particular fluoride phosphor for applications.