Trapping of Holes and Excitons in Scintillators: CsI and LaX3 (X = Cl, Br)

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 V-K center and STE in CsI is a distortion of two iodine atoms from the lattice to form an interstitial bound I-2(-) 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 X-2(-). The calculated luminescence energy for the STE in LaCl3 and LaBr3 is 4.1 and 3.7 eV, respectively.