Secured documents identified with anti-stokes fluorescent compositions

Abstract

The present invention provides a secured document including a composition capable of anti-Stokes fluorescence containing an ion capable of absorption of electromagnetic radiation, an ion capable of emitting electromagnetic radiation, and a matrix composition comprising gadolinium, yttrium, lanthanum, and thulium, wherein the wavelength of the absorbed electromagnetic radiation is shorter than the wavelength of the emitted of the absorbed electromagnetic radiation, and wherein the concentrations of the absorbing and emitting ions are adjusted to achieve concentration quenching of anti-Stokes luminescence.

Dependencies are inferred from the claim text.