The following manganese‐activated fluorides were found to exhibit efficient cathodo‐luminescence : , , , , , , , , , and the solid solutions formed between and . With and , was found to be only a diluent; with , however, three compounds,, , and , were discovered, the first having a peak emission at 5380 Å and the latter two at 5250 Å. Emission of Mg and Zn compounds containing K or Na was almost identical with that of the original and . Although :Mn has an efficient green and :Mn a weak green emission, their K‐perovskites show strong yellow‐orange emission. From the above results, a hypothesis is advanced relating a coordination number of six for the divalent cation in fluorides to orange emission, and a coordination number of eight to green emission.