Delayed luminescence of organic mixed crystal. Delayed excimer fluorescence of pyrene in p‐terphenyl

Phosphorescence, fluorescence, delayed fluorescence, excimer fluorescence, and delayed excimer fluorescence of pyrene are studied in the host p‐terphenyl system. The delayed fluorescence and delayed excimer fluorescence are biexcitonic and exhibit a similar dependency of the emission intensity on temperature; they both originate in identical kinetic events. The excitation spectra for all the emissions are presented. The trapping of the host triplet excitons occurs more efficiently at monomer pyrene sites than at nascent excimeric pyrene sites. The conclusion is that the delayed excimer and delayed fluorescence are produced by the homofusion of defect triplets and the heterofusion of defect and guest triplets. The defect level situated below the host exciton band controls the thermal excitation processes and the luminescence characteristics by the thermal event \documentclass{article}\pagestyle{empty}\begin{document}$ T_{{\rm 1D}} \to T_{1{\rm D}}^* \to T_{1{\rm H}} |_{\to T_{{\rm 1G}}}^{\to T_{{\rm 1D}}}. $\end{document} .