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Keywords:

  • Photoluminescence;
  • upconversion;
  • anti-Stokes shift;
  • lanthanide;
  • reabsorption
Thumbnail image of graphical abstract

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 (Icode). The second emission band (Iref), by contrast, serves as an internal reference to obtain ratiometric codes. Combining UCNPs with distinct emission bands expands the coding capacity exponentially.