Luminescence efficiency of calcium tungstate (CaWO4) under X-ray radiation: Comparison with Gd2O2S:Tb

The aim of the present study was to investigate the absolute luminescence efficiency (AE) of a CaWO4 screen, under X-ray irradiation and to compare it with a custom made PMMA/Gd2O2S:Tb composite film screen. The emitted light was evaluated by performing measurements of the AE under X-ray exposure conditions, with tube voltages ranging from 50 to 125 kV. The spectral compatibility of the CaWO4 screen, with various existing optical detectors, was investigated after emission spectra measurements. AE was found maximum at 50 kVp (2.34 Efficiency Units-E.U) which was slightly lower than the corresponding “gold standard” Gd2O2S:Tb (2.67 E.U), at the same X-ray energy. The emission spectrum of CaWO4 is excellent matched with the spectral sensitivities of photocathodes and silicon photomultipliers often employed in radiation detectors, and with good matching with amorphous silicon photodiodes. Considering the adequate luminescence efficiency values and the spectral compatibility with various photodetectors, CaWO4 could be also considered for use in X-ray imaging devices such as charged-coupled devices (CCD) and complementary metal oxide semiconductors (CMOS).