The luminescence emission spectra of commercial CaWO4 and BaSO4:Pb phosphors and screens have been measured for excitation with a known x-ray spectrum at 40 kVp. The emission efficiency and quantum yield have been determined. Changes have been observed in the ultraviolet reflection spectrum after the phosphors had received large x-ray exposures. The light emission of these phosphors, when exposed to x-ray excitation, has been studied as a function of irradiation time.
F. GRUM, L. F. COSTA, and J. L. DONOVAN, "Measured Light-Emission Efficiency and Quantum Yield for X-Ray Screens and Phosphors," J. Opt. Soc. Am. 59, 848-848 (1969)