Rare Earth downconverting compositions for optical encoding objects and related methods and apparatuses. The rare earth (RE) downconverting phosphor compositions are capable of generating a unique optical spectrum or unique optical signature from which an optical code or barcode can be derived. In one exemplary embodiment, the RE downconverting phosphor composition may contain two or more lanthanide materials each having a host and at least one downconverting emitter. Each lanthanide material emits a detectable electromagnetic radiation emission peak at an intensity, which is proportional to the amount of emitter present, upon excitation with an absorbable electromagnetic radiation, the emitted radiation comprising a lower energy, i.e., a longer wavelength than the absorbable radiation. One or more ratios of the intensities of the emitted detectable electromagnetic radiation may be used to uniquely identify the composition. In another exemplary embodiment, the RE downconverting phosphor composition may contain a lanthanide material having a host and at least two emitters. The lanthanide material emits at least two different detectable electromagnetic radiation emission peaks each at intensity upon excitation with an absorbable electromagnetic radiation, the emitted radiation comprising a lower energy, i.e., a longer wavelength than the absorbable radiation.