DEFECT PHOSPHORESCENCE OF PYRAZINE CRYSTAL

The phosphorescence spectrum of crystalline pyrazine is observed in the temperature range of 1.6-15°K. The analysis of the fine structure, dependence on sample preparation, effect of zone refining, decay characteristics, and other data lead to the definite conclusion that the observed phosphorescence is coming from a number of crystalline defects. This is in contrast to the interpretation by Moomaw and El-Sayed who stated that the observed fine structures are due to the coupling with the ground-state phonons. A model for defect phosphorescence is set up. The observed temperature dependence as well as the decay behaviors are satisfactorily interpreted in terms of this model. Finally, an attempt is made to distinguish two types of crystalline defects, the structural defects and impurity-induced resonance defects; the observations seem to be in favor of the latter.