Extrinsic self-trapping of excitons in TlBr(I)

摘要

Luminescence spectra have been measured in TlBr doped with I- ions under pulsed-light excitation. Two broad emission bands were observed at 2.2 and 2.45 eV. The emission band at 2.2 eV decayed non-exponentially with a t(-1) dependence at long delay, and was attributed to radiative annihilation of a self-trapped exciton at the nearest neighbor of an I- ion. The exciton was formed by the tunneling recombination of a hole trapped at the nearest neighbor of an I- ion and an electron trapped at a distant lattice position. The emission band at 2.45 eV, which decayed with two time constants of 0.5 mu s and less than 20 ns, was attributed to annihilation of another type of a self-trapped exciton in Br-rich region of the crystal. These emission bands are discussed with a theory on extrinsic self-trapping in a mixed crystal, and ascribed to the two types of extrinsic self-trapping of the excitons. (c) 2004 Elsevier B.V. All rights reserved.