Knowledge Bank

This work is an extension of earlier work by Nieman and Robinson on three-component, isotopically mixed crystals of benzene at liquid-helium temperatures. A typical system for study is composed of $99.6$ host crystal containing $0.2$ (super-trap) and $0.2$ (trap) which act to trap the excitation. These two isotopic traps have excitation energies of 200 and $167cm-1$, respectively, below that of $C6D6$. The point of these experiments is to detect long-range trap-to-super-trap triplet excitation migration. The dependence of this transfer upon isotopic constitution, concentration, and temperature is being studied by measurements of phosphorescent lifetimes and trap-super-trap phosphorescent intensity ratios. This detailed study leads to a considerable extension of the present understanding of the mechanism of excitation transfer in these crystals and of the role of high-frequency lattice modes in such processes.