Clusters containing nine lanthanide and six sodium ions are crystallized with the help of a tridentate ligand bearing a phosphonic acid group; the structure of the Eu-III compound reveals a host-guest assembly Eu subset of Na6Eu8L16 with a substantial quantum yield (32%). A similar Eu-III-Yb-III structure displays dual luminescence in the visible (Eu-III) and NIR (Yb-III) ranges.