<p>Security documents for high-speed verification contain up-conversion elements in the form of small inorganic particles, applied near the surface of the document, which allow high-speed verification by near infrared (NIR) light stimulation and detection of the emission bands in the visible and NIR wavelength range. An Independent claim is also included for security documents for high-speed verification, which contain an up-conversion phosphor comprising a thulium-activated and ytterbium-codoped gadolinium oxysulfide of the composition:</p>
