Determination of the Efficiency of Triplet Energy Migration in Benzophenone Crystals

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Abstract
The total emission—phosphorescence plus fluorescence—spectra of benzophenone crystals containing small quantities of 1,2-benzanthracene (BA) are described. The electronic states of BA and benzophenone are such that the lowest triplet state but not the lowest singlet state of BA can be populated directly by energy transfer from the lowest triplet of benzophenone. The relative efficiencies of fluorescence and phosphorescence of the BA provide evidence that triplet exciton migration is occurring in the host lattice. The fact that the host-crystal phosphorescence yield is temperature-dependent provides another experimental probe into the energy transfer probabilities for this crystal. The combination of these two types of experiment gives some indication of the interaction energy between an excited molecule of benzophenone in the lattice and neighboring excited molecules.