Optical isotropy in structurally anisotropic halide scintillators: Ab initio study

The present study explores the structural, electronic, and optical properties of XSrI 3 (X=K, Rb, and Cs) compounds within the framework of density functional theory. The ground state properties are calculated using the pseudopotential method with the inclusion of van der Waals interactions, which we find inevitable in reproducing the experimental structural properties of the above mentioned compounds with layered crystal structure. The electronic and optical properties are calculated using the full-potential linearized augmented plane wave method and the band structures are plotted with various functionals and we find the newly developed Tran and Blaha modified Becke-Johnson potential to improve the band gap significantly. From the band structures of these compounds, it is clearly seen that I-p states dominate the valence band. The optical properties such as complex dielectric function, refractive index, absorption spectra, and electron energy loss spectra are calculated which clearly reveal the optically isotropic nature of these materials though being structurally anisotropic, which is the key requirement for ceramic scintillators. The present study suggests that among the three compounds studied, CsSrI 3 can act as a fast scintillating compound, which is well explained from the band structure calculation