| 摘要 |
Water-based invisible red fluorescent inks provide machine-readable, invers e- contrast invisible images and can be printed using conventional ink jet printers. The inks employ rare earth complexed ligand fluorophores having narrow excitatio n and emission spectra. In one embodiment the images are printed with an ink comprising water and a water-soluble organic fluorescent fluorophore, which when printe d and dried on paper is invisible to the eye and fluoresces in the green to infrar ed range, e.g., from about 550 to 1200 nm, when irradiated with short wave length UV radiation, e.g., from 230nm to 280nm. The highly specific excitation and emission rates, coupled with a high inverse contrast on papers of all colors, makes them particularly useful as ink jet inks for postal and other purposes.
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