Abstract
We investigated H2O molecule adsorption that had an effect on the luminescence properties of the CsI(Na) crystal using experiments and first-principle calculations. We measured the emission spectra of the CsI(Na) crystal at different exposure times under gamma ray excitation. The experimental results showed that the energy resolution of the CsI(Na) crystal was worse when the crystal surface adsorbed more H2O molecules, and the crystal surface deliquescence decreased the luminescence efficiency of the CsI(Na) crystal. We studied the band structure, density of states, and optical properties changes caused by H2O molecule adsorption on the CsI(Na) (010) surface. The generalized gradient approximation (GGA) was used to describe the exchange and correlation potential between the electrons. Our calculation results showed that the band gap width of the CsI(Na) (010) surface decreased after adsorbing H2O molecules, while three new peaks appeared in the valence band, and the absorption coefficient decreased from 90,000 cm−1 to 65,000 cm−1, and the reflection coefficient decreased from 0.195 to 0.105. Further, the absorption coefficient was reduced by at least 25% because of H2O molecule adsorption, which led to the luminescence degradation of the CsI(Na) crystal.
Highlights
Cesium iodide doped with sodium (CsI(Na)) crystal has been used as a charged particle detection material since the late 1960s [1]
In order to explain how adsorbing H2 O molecules on the CsI(Na) (010) surface can affect the luminescence performance of the CsI(Na) crystal and discuss which factors induce crystal property changes resulting in the luminescence reduction, we measured the gamma ray spectra of the CsI(Na) crystal under different exposure conditions to investigate the luminescence efficiency changes after the adsorption of H2 O molecules on the CsI(Na)
(010) surface and optimized the structure of the CsI(Na) (010) surface to study the band structure, density of states, and optical properties using a first-principle calculation method based on density functional theory (DFT)
Summary
Cesium iodide doped with sodium (CsI(Na)) crystal has been used as a charged particle detection material since the late 1960s [1]. CsI(Na) crystal; the electronic structure, electronic density of states, and optical properties of the CsI and CsI:Ag have been studied using a first-principle calculation based on density functional theory (DFT) [8] All these facts result in the surface structure changes of the CsI(Na) crystals and the degradation of the CsI(Na) surface scintillation after the CsI(Na) crystal surface absorbs. We measure the pulse height spectra of the CsI(Na) crystal with different air exposure times and different air humidity environments under γ ray excitation and investigate the effect of the CsI(Na) crystal surface absorbing H2 O molecules on the scintillation degradation. We use Cambridge sequential total energy package (CASTEP) software to calculate band gap, density of states, and optical properties with the aim of determining the key factors leading to CsI(Na) crystal surface scintillation degradation after the absorption of H2 O molecules
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