A series of strongly luminescent 5d/4f heterometal-organic macrocycles formulated as Ln2(Pt-L)2 have been constructed from a preformed cis-blocked alkynylplatinum metalloligand (Pt-L) and lanthanide (Ln = LaIII, EuIII, LuIII) ions. Open metal sites on the lanthanide centres of the heterometal-organic macrocycles facilitate not only the post-assembly modification leading to great enhancement of the luminescence, but also the displacement sensing toward toxic thiophosphonates.