It is proposed a method for determining the authenticity of value and / or security documents and a corresponding sensor, wherein at least one security element (13, 13 ', 13' ') which appear in or on the value and / or security document and / or applied is. In this case, the security element with radiation of a preset fixed excitation wavelength is excited. The security element then emits radiation, wherein the radiation emitted by a detection unit (17) and detected by an evaluation unit (18) is evaluated. The intensity profile of the emitted radiation is detected in a fixed predetermined wavelength range over a predetermined sample period, after the excitation and analyzed for authenticity detection.