We propose an innovative covert tagging system based on five specific and unique rare earth crystalline compositions capable of converting wavelengths of light up or down the electromagnetic spectrum. By incorporating precise ratios of rare earth ions in unique host lattices and synthesizing them under exact conditions we can achieve excellent control and tunability of their optical properties through highly complex energy transfer mechanisms. The optical emissions of the upconverting rare earth crystals can be tuned for various parameters such as lifetime, emission spectra, and relative ratio between a phosphor with multiple emission peaks spectra. Additionally, a handheld detection platform will be developed that will be capable of identifying all of the unique optical signatures within a single composition and also differentiate from other compositions. The detection platform will provide a cost-effective and secure platform for identification of the various covert markers.