We are investigating pixellated radiation sensors based on cadmium zinc telluride (CZT) for gamma cameras in pre-clinical and clinical imaging applications. Each pixel allows one to acquire an energy spectrum in the range from 20 keV to 360 keV. We observe an energy resolution of 5.5 keV FWHM (3.90%)at 140 keV which allows one to distinguish different isotopes by their nuclear adiation emission energy or resolve characteristic x-rays to identify materials and locate their positions in the field-of-view. In this work we study x-ray fluorescence (XRF) from three heavy solid metals. The use ofXRF has the potential to simplify hardware calibrations and improve the performance in nuclear radiation imaging. Depending on the chemical elements we observe XRF emission with intensity up to 10-% of the incident x-ray flux. The XRF can be used in several ways. Firstly, the energy from characteristic x-rays, e.g., 58.8 keV from tungsten, and a second energy, e.g., 140 keV from 99mTc, allow one to calibrate the energy scale for each pixel using only one acquisition. Secondly, a configuration of objects made of different materials allows one to measure the position of the object by discriminating on the x-ray fluorescence energy. Given a known configuration of objects one could calibrate (align) the pixel positions relative to the object. Thirdly, the energy of emission allows one to identify the chemical element. In this article we compute the relative number of XRF emission from heavy materials and show results with CZT-based pixel sensors.