DISPERSIONS OF RARE EARTH OXIDE PARTICLES LUMINESCENT, VARNISHED INCLUDING/UNDERSTANDING THESE PART

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Dispersion comprises particles of at least one oxide of at least one luminescent rare earth, disaggregated and stabilized in a hydrophobic liquid medium to which at least one surfactant is added, where the surfactant is a non-ionic surfactant having HLB (hydrophilic-to-lipophilic balance) lower than 12. Independent claims are included for the following : (1) preparing the dispersion involving adding the particles of the oxide of the luminescent rare earth to the hydrophobic medium to form a dispersion A; adding the non-ionic surfactant to dispersion A; and subjecting dispersion A containing the non-ionic surfactant to at least one mechanical action; (2) varnish comprising the disaggregated and stabilized particles of the oxide of the luminescent rare earth, at least one hydrophobic organic solvent, and at least one polymer; (3) preparing the varnish involving mixing a solution of at least one polymer in at least one hydrophobic organic solvent with the dispersion of particles of the oxide of the luminescent rare earth; and subjecting the mixture to at least one mechanical action; (4) method for marking substrates involving coating, impregnation of these substrates with the varnish; and (5) identifying objects, articles involving markings, marks, particularly security markings are prepared, on objects, e.g. a marking for each object, using the varnish, the markings is invisible to the naked eye and visible only when illuminated by ultraviolet radiation; subjecting the objects to excitation by ultraviolet radiation; reading the markings by detecting the luminescence radiation emitted by these markings; and identifying the objects according to the reading.