Defect Phosphorescence of Pyrazine Crystal. II. The Nature of the Defect

The phosphorescence of pyrazine crystal is due to the emissions from various crystalline defects. In this paper the nature of the crystalline defects which causes the emission and also quench the emission is investigated. Both the emissive defects and quenching defects are classified into impurity-induced resonance defects and structural defects. The concentration of the impurity-induced resonance defects may effectively be decreased by zone melting. The structural defects, on the other hand, are removed by annealing. The emissive impurity-induced resonance defects seem to be responsible for many sharp bands around the onset of the spectrum. The emissive structural defects are responsible for the broad bands often observed at somewhat longer wavelength region of the sharp bands. The analyses of the temperature dependence of the phosphorescence intensity yield the rate of triplet exciton migration to be larger than 5 × 1013 sec−1. Finally, suggestions are given as to in what ways one has to endevor to obtain crystals which exhibit genuine exciton phosphorescence.