Effect of doping on the electronic structures and optical properties of Cesium Iodide.

摘要

Cesium Iodide (CsI) is an important phosphor in medical imaging. It converts x-rays into visible light. The effects of dopants on the electronic band structure and optical properties were studied theoretically using density functional theory with a local density approximation. The studies were done using Dmol 3 and visualized with Material Studio. The effect of Thallium (Tl) doping on the surfaces was simulated by introducing Thallium as a substitutional impurity. The effect of the dopant on the surfaces was investigated by calculating the plasma frequency edge and radiant quantum efficiencies (RQE) from the analysis of the band structure. The results for the plasma frequency edge are in agreement with the known experimental data on the transmission and reflectivity of thin CsI films as well as bulk CsI crystals. The radiant quantum efficiencies and relative light output increase for increasing doping concentrations and then level off probably due to saturation.;The effect of oxygen poisoning was simulated by substituting oxygen as an impurity on the CsI 110 surface. Water adsorption was simulated by docking a water molecule onto the CsI 110 surface. There was no significant change in the radiant quantum efficiency for different doping concentrations of oxygen on the surface. The effect of water adsorption on the surface, likewise, showed no effect on the radiant QE.;The effect of Europium (Eu) co-dopant was simulated by co-doping CsI:Tl with Europium as a substitutional impurity. The reduction in the afterglow of CsI:Tl,Eu is explained by the reduction in the contribution of Tl 0, and Tl2+ centers. The red-shift of luminescence is explained by the dominance of the Eu2+ ion that has a transition state emitting in the yellow part of the spectrum compared with the Tl transition that emits in the green range. Furthermore, the narrowing of the band gap with increasing Eu doping concentration contributes to reducing the emission from Tl. There were no significant changes in the effective electron masses for different Europium (Eu) doping concentrations. The plasma frequencies edges confirm that CsI has a wide optical window as expected.