To our best knowledge, only two transition types of electronic excited
states—ligand-to-ligand change-transfer (LLCT) and
ligand-to-metal change-transfer (LMCT)—have been
found in the Zn(ii)/Cd(ii) coordination complexes.[1–20,27]
However, it is hard to propose a correct mechanistic conclusion for their luminescence based only on emission spectra. Thus, several supporting experiments may be very helpful in verifying the photoluminescence mechanisms.