e demonstrate the conceptual advantage of using metal-organic frameworks (MOFs) for the creation of a polymetallic material that contains several different near-IR-emitting lanthanide cations and operates as a barcode material with unique luminescence properties. By choosing the ratio of lanthanide salts used during the synthesis, we can control the ratio of lanthanide cations present in the resulting material. We have demonstrated that the emission intensity of each of the different lanthanide cations is proportional to its amount in the MOF crystal, resulting in unique spectroscopic barcodes that depend on the lanthanide cation ratios and compositions.