Absorption line shapes and triplet exciton scattering times in organic crystals

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Abstract
The low temperature singlet‐triplet absorption line shapes of single crystals of naphthalene and 1,4‐dibromonaphthalene are used to investigate the dynamic properties of triplet excitons. The line shapes although asymmetric, can be related to the approximate lifetimes of the k ≈ 0 exciton states. The temperature dependence of the line half‐widths can be explained by acoustic phonon or lattice defect scattering at temperatures below 20°K. For 1,4‐dibromonaphthalene an optical phonon mode begins to contribute to the line broadening above 20°K. The experimental linewidths indicate that exciton transport passes from an incoherent to a coherent process as the temperature decreases from 30 to 4°K.