Electronic structure and optical properties of CsI under high pressure: A first-principles study

Cesium iodide (CsI) is an important scintillation material and it is widely used in high-energy physics experiments, medical imaging, security inspection and other fields as a key irradiation sensor. The detection efficiency of CsI depends on its electronic structure and optical properties. High pressure and doping are the two most commonly used methods which can regulate and control the electronic structure and optical properties of an ionic crystal material. In this paper, we investigated the effects of high pressure on the electronic structure and optical properties of a CsI crystal through a first-principles calculation method based on density functional theory, and the exchange and correlation functions among electrons were described using the revised Perdew-Burke-Ernzerhof generalized gradient approximation. The band gap of a CsI single crystal decreases with an increase in pressure; every part of the valence band becomes wider and wider, the conduction band moves in the direction of decreasing energy; the atomic charge transfers from Cs atoms to I atoms in CsI when the external high pressure is less than 15 GPa, on the contrary, the atomic charge transfers from I atoms to Cs atoms in CsI when the high pressure is greater than 15 GPa; a redshift occurs in the optical properties of a CsI single crystal under high pressure. Our prediction in this paper might be useful for enhancing the detection efficiency of CsI scintillators.