A METHOD OF DOCUMENTATION PROTECTION AND IDENTIFICATION

摘要

This invention provides novel means protecting against forgery of important documents and labeled products. A new method is proposed for the protection and identification of documents and other objects based on the formation of at least one protection area on object's surface by applying a label of a luminescent material changing its luminescence color at varying observation conditions. Novelty of the proposal resides in using a luminescent material with a luminescence polarization degree variable, on excitation by linearly polarized light, over the range from 0.5 - 0.25 to 0.2 - (-0.33) when a short-to-long wavelength spectrum edge change is made so that a difference in luminescence colors can be provided on observation in mutually perpendicular components of polarized light. A material of the protective area is manufactured transparent, at any rate partially, and is containing unoriented luminescence centers of at least two different types, characterized by the distinct luminescence spectra and differing values of a luminescence polarization degree when excited by linearly polarized light. The luminescence centers may be represented by complex organic molecule or rare-earth ions or else particles of luminescent pigments. As an alternative, for luminescence centers one can use complex organic molecules of two types: being excited by linearly polarized light the first-type molecules emit polarized luminescence with a polarization degree ranging from 0.5 to 0.25, whereas for the second type molecules excited at the same conditions a polarization degree is ranging from 0.2 to -0.33. And for lower polarization degree of luminescence one can use the molecules whose structure has a symmetry axis higher than triad. For the second-type molecules a low luminescence polarization degree is provided either by the nonradiative energy transfer from molecules of the first type or through reabsorption of luminescence emitted by the first-type molecules. A negative luminescence polarization degree for the molecules of the second type is provided by molecular excitation to the second and subsequent bands of electron transitions, with the dipole moment direction of an electron transition making an angle of about 90to that of the electron transition to the first electron band. The proposed method offers high protection combined with a simplicity of realization.