The invention provides a lighting unit comprising a light source, configured to generate light source light and a luminescent material, configured to convert at least part of the light source light into luminescent material light, wherein the light source comprises a light emitting diode (LED) and wherein the luminescent material comprises a phosphor comprising M2AX6 doped with tetravalent manganese, wherein M comprises monovalent cations, at least comprising potassium and rubidium, wherein A comprises a tetravalent cation, at least comprising silicon, wherein X comprises a monovalent anion, at least comprising fluorine, and wherein M2AX6 has the hexagonal phase.