A device and a method are disclosed, for energetic calibration of a photon-counting X-ray radiation detector by way of X-ray fluorescence radiation. The device includes a plurality of specifically selected elements, of which each element, upon being irradiated with electrons or with high-energy radiation, emits photons of X-ray fluorescence radiation of at least one specific or characteristic energy. The photons of X-ray fluorescence radiation of the at least one specific or characteristic energy are then useable or are used for energetic calibration of the photon-counting X-ray radiation detector. A calibration apparatus and an X-ray apparatus are also disclosed, which include such a device.