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Upconversion Phosphors

AAC has developed rare earth based security pigments. The pigments are so called upconversion phosphors. If illuminated with an IR laser of certain wavelength, two photons can be absorbed and re-emitted in one step, thus the re-emission happens at shorter wavelength. The IR laser is converted into visible light, with a characteristic “finger print”, depending on the composition and doping of the rare earth material. By variation of the doping, the finger print can be varied and customer-specific pigments can be synthesised. The pigments can be incorporated into offset printing inks or also into thermoplastic polymers. They are a unique and secure way, to invisibly mark products such as documents, stamps, etc.

Link to publication

The benefit of the pigments is the 3-stage verification:

  1. Visible inspection: Fluorescence is present yes or no
  2. Fluorescence colour match yes or no
  3. Spectroscopic test: fingerprint match yes or no

Step 1 and 2 can be carried out with a simple IR laser pointer. Step 3 verification needs a VIS spectrometer.