Tuning the Dual Emission of Photon-Upconverting Nanoparticles for Ratiometric Multiplexed Encoding

Ratiometric encoding with two types of photon-upconverting nanoparticles is demonstrated. Different concentrations of filter dyes on the nanoparticle's surface are used to tune selectively one of the dual emission bands (I-code). The second emission band (I-ref), by contrast, serves as an internal reference to obtain ratiometric codes. Combining UCNPs with distinct emission bands expands the coding capacity exponentially.