and fluoresce at wavelengths in the near infra red region of the spectrum u s pat nos 5 424 006 and 5 674 437 describe phosphorescent substances and methods of their manufacture useful in the security fibers of the invention fluorescent substances cease fluorescing virtually instantaneously in less than about a thousandth of a second upon cessation of excitation phosphorescent substances may continue luminous emissions for some tens or hundreds of minutes after cessation of excitation an example is the material sral 2 o 4 eu dy described in u s pat no 5 424 006 the rate of decay of luminescence is one of the verifiable features of the fibers of the invention the security fibers of the invention are formed into security threads by conventional fiber processes such as twisting cabling braiding texturizing and heat setting the same or different security fibers may be incorporated in a security thread the security article of the invention can be security threads or other items such as passports currency or other important documents the threads can be used to reproduce luminescent logos in fabrics or clothing or may include such a logo as a complex cross section a cabled security thread can be tailored to specific end uses through any combination of colors and cross sections by way of example a security thread could have a star cross section fig1 with a red luminescent response such a security thread could be targeted for the chinese passport since the national color of chinese flag is red and its flag has five stars for italy the security thread.