Ln-containing　polyoxoniobates(PONbs)have　appealing　applications　in　luminescence,information　encryp-tion　and　magnetic　fields,but　the　synthesis　of　PONbs　containing　high-nuclearity　Ln-O　clusters　is　challeng-ing　due　to　the　easy　hydrolysis　of　Ln3+ions　in　alkaline　environments.In　this　paper,we　are　able　to　inte-grate　CO32-and　high-nuclearity　Ln-O　clusters　into　PONb　to　construct　an　inorganic　giant　Eu19-embedded　PONb　H49K16Na13(H2O)63[Eu21O2(OH)7(H2O)5(Nb7O22)10(Nb2O6)2(CO3)18]·91H2O(1),which　contains　the　highest　nuclearity　Eu-O　clusters　and　the　largest　number　of　Eu3+ions　among　PONbs.In　addition,the　film　that　was　prepared　by　mixing　1　with　gelatin　and　glycerol,exhibits　reversible　luminescence　switching　be-havior　under　acid/alkali　stimulation　and　has　been　used　to　create　a　fluorescence-encoded　information　ap-proach.This　work　paves　a　feasible　strategy　for　the　construction　of　high-nuclearity　Ln-O　cluster-containing　PONbs　and　the　expansion　of　the　application　of　Ln-containing　PONbs　in　information　encryption.