Decay and buildup characteristics of delayed luminescence in a ’’real’’ organic mixed crystal: Naphthalene host–chrysene guest system

The decay and the buildup characteristics of delayed emissions in a naphthalene host–chrysene guest ’’real’’ four component mixed crystal consisting of the host, a physical defect, the guest, and a chemical impurity have been studied. Heterofusion of the defect–guest and the defect–impurity triplet excitions have been found to be responsible, respectively, for the guest and the impurity delayed fluorescence. The decay and the buildup kinetics observed are generally of second order though in the long time region first order kinetics predominates. Both first and second order kinetic analyses have been made. From various Arrhenius plots it has been estabilished that the thermal excitation energy is the T1H–T1D energy gap, suggesting T1D→T1D*→T1H→T1G (or T1(imp)) as the thermally activated process in the guest or the impurity delayed fluoresence generation. Some kinetic parameters have been evaluated and the values obtained suggest that at short times about 80% of the guest or impurity triplets undergo heterofusion and this reduces to about 10% in the long time region.