PNNL

Abstract

We present ab initio calculations studying the formation, mobility, and stability of self trapped excitons (STE) and self trapped holes (STH) and electrons in NaI and NaI(Tl). While previously proposed models assumed a highly mobile STE and a slower STH, we find that both carriers in pure NaI have similar mobilities, with an activation energy of about 0.2 eV. We propose an alternate interpretation of experimental record including a new migration mechanism for the STE. In the Tl-doped material excitons preferentially trap at dopants, inducing off center distortions that have a structure unlike an STE providing a mechanism for light emission at multiple wavelengths. The calculated results are generally in excellent agreement with available data.