Effect of Multiple Dopants on the Quantum Efficiency of LiF Thermoluminescent Dosimeters (TLD) and BaFX (X = Br,Cl,I) Storage Phosphors

摘要

The radiant quantum efficiency (RQE) of x-ray phosphors is defined as the ratio of the emitted luminescent power and the power absorbed by the material. For a given x-ray imaging technique, a high RQE phosphor means a lower x-ray exposure to patients and a better image quality. To improve RQE, phosphors such as LiF and BaFX:Eu (X = Br, Cl, I) host lattices, which are commonly used in medical dosimetry and imaging system, are always doped with Cu, Ti, or Tb. Experimental observations showed that these dopants can increase phosphor RQE significantly. In this study, we theoretically investigated the effect of additional dopants on the RQE of LiF:Mg and BaFX:Eu host lattices using Density Functional Theory (DFT) in the Local Density Approximation (LDA). Self-consistent charge density calculations were performed. The energy loss function L(w) was obtained and used to calculate the RQE for different phosphors. The results showed that additional dopants produced changes in the optical properties of the phosphors, particularly the energy loss function L(w). Doping with more substitutional impurities increased the RQE of all host lattices except the BaFI lattice where the RQE decreased.