Absorption, Fluorescence and Phosphorescence Spectra of Hexachlorobenzene Single Crystals at 4.2°K

Abstract

Abstract The low lying singlet and triplet states of high purity single crystals of hexachlorobenzene are investigated. The fluorescence quantum yield is 10−2 The polarized fluorescence spectrum at 4.2°K is analyzed as pure exciton emission. There is no evidence for emission from trap levels. The electronic origin for the first singlet transition is at 32736 cm−1. The phosphorescence quantum yield is 10−2. The triplet exciton emission origin is at 25685 cm−1 which coincides with the direct triplet exciton absorption origin in contrast to other reports. The crystal phosphorescence is very sensitive to crystal temperature between 4.2 and 15°K. At 4.2°K the emission origins is 39 cm−1 below the triplet exciton band. Emission from the triplet exciton band is observed when the crystal temperature is above 4.2°K. The spectrum is interpreted in terms of a low lying trap level due presumably to impurity induced displacement of the triplet energy level of some hexachlorobenzene molecules and a deep lying trap (134...