PNNL

Abstract

We present computational results for trapping of polarons and excitons in undoped CsI, LaCl$_{3}$ and LaBr$_{3}$, 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 LaCl$_{3}$ and LaBr$_{3}$, 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 LaCl$_{3}$ and LaBr$_{3}$ is 4.1 and 3.7 eV, respectively.