Trapping of Holes and Excitons in Scintillators: CsI and ${\rm LaX}_{3}$ ( ${\rm X}={\rm Cl}$

We present computational results for trapping of polarons and excitons in undoped CsI, LaCl₃ and LaBr₃ , using plane-wave-pseudopotential density functional theory with Hartree-Fock exact exchange. The optimized VK center and STE in CsI is a distortion of two iodine atoms from the lattice to form an interstitial bound I₂^- molecule, consistent with previous theoretical and experimental results. In both LaCl₃ and LaBr₃, the relaxed STE configuration involves only one displaced halide ion, and does not form an X₂^-. The calculated luminescence energy for the STE in LaCl₃ and LaBr₃ is 4.1 and 3.7 eV, respectively.