Security markings, material provided with security marks, and apparatus to detect the security mark

Security fibers and textiles threads, comprising at least one marking product, the marking product comprising rare-earth chelates or substrates including rare-earth chelates, the rare-earth ion present in the chelates arising from at least two different rare-earths, an energy transfer taking place between the two rare-earths causing a change in fluoroscence wavelength of the chelates when exposed to ultraviolet radiation as a function of the temperature of the chelate so made and/or of the substrate including the chelate,

• the marking product being introduced into the fibers or threads by a dyeing procedure, the fibrous threads being colorless in solar or artificial light, changing their fluorescence wavelengths as a function of temperature when under UV radiation.