Reaction of a P/N/S hybrid ligand dpppyatc (N,N‐bis((diphenylphosphaneyl)methyl)‐N‐(pyridin‐2‐yl)‐amino‐thiocarbamide) with Au(tht)Cl (tht = tetrahydrothiophene) and [Cu(MeCN)4]BF4 afforded cluster complex [Au2Cu(dpppyatc)2](BF4)2Cl (1). Upon excitation at 480 nm, 1 emitted orange phosphorescence at 646 nm, which was red‐shifted to ~698 nm selectively in the presence of ammonia or amine vapor. This chromic photoluminescent response toward ammonia was sensitive and reversible. Complex1 could detect ammonia in aqueous solution down to concentrations of 2 ppm (w/w).