The branching of triplet luminescent state and Frenkel defect pair in NaBr and KBr: an MD study

摘要

Recent molecular dynamics study of exciton relaxation shows that starting from a free Frenkel-type exciton in an undistorted lattice, the maximum relaxation is reached at 10 K within about 0.5 and 2 ps in NaBr and KBr, respectively. The question we try to address in this paper is how the branching between the characteristic triplet self-trapped exciton (STE) and the stable Frenkel pair takes place dynamically. In NaBr no F center was formed at 10 K, but the off-center triplet STE was obtained. At 100 K on the other hand the triplet STE disappeared and F center resulted instead. This corresponds to the quenching of pi band emission. In KBr both well-separated Frenkel defect pair and the triplet STE (pi band emitting) were obtained at 10 K. When temperature was raised above 30 K, the pi band was quenched. Instead an F center-like relaxation product was obtained. These results are discussed and compared with experimental data. (C) 2004 Elsevier Ltd. All rights reserved.