Methods for optically encoding an object with upconverting materials and compositions used therein

A method of uniquely identifying an object, wherein the method comprises the steps of:

• combining the object with at least a first lanthanide material, the first lanthanide material comprising a single host lattice, a single absorber, a first emitter, and a second emitter, wherein the first emitter emits at a different wavelength than the second emitter;
• irradiating the first lanthanide material with absorbable electromagnetic radiation, thereby inducing emission from the first and second emitters;
• measuring, emanating from the object, a first emission intensity of emission from the first emitter and a second emission intensity of emission from the second emitter;
• calculating a ratio of the first emission intensity to the second emission intensity;
• and
• uniquely identifying the object from the calculated ratio, wherein said first lanthanide material is in the form of a solid solution wherein the first and second emitters are randomly and isomorphously incorporated into the host lattice of the solid solution;
• wherein the ratio defines one of a number of resolvable ratios, and wherein the number of resolvable ratios correspond to a number of optical codes, the number of optical codes being determined by C=RM−, where C is the number of optical codes, R is the number of the resolvable ratios and M is the number of the emitters in the lanthanide material.