摘要:
Methods and apparatus for variable data printing for security purposes using ceramic sub-micron infrared-luminescent particles in inkjet ink. An example apparatus includes an inkjet printer containing marked ink, the marked ink containing particles consisting of rare earth doped ceramics, wherein the particles are less than one micron in size, the particles are suspended in the marked ink, and the particles have luminescent properties such that when the particles are illuminated by first electromagnetic radiation having a first wavelength, the particles emit infrared light having a peak wavelength at a second wavelength.