Emission dynamics from doped crystals of (${\mathrm{CH}}_3$${)}_4$${\mathrm{NMnCl}}_3$ (TMMC): Exciton trapping in a one-dimensional lattice

The emission decay curves from (${\mathrm{CH}}_3$ ${)}_4$ ${\mathrm{NMnCl}}_3$ [tetramethylammonium manganese chloride (TMMC)] crystals doped with small amounts of ${\mathrm{Cu}}^{2+}$ deviate dramatically from simple exponential form. Consistent with the linear chain structure of TMMC, the curves are adequately described by decay expressions derived for exciton trapping in one-dimensional systems. Analysis of the data indicates that exciton migration in TMMC is nearly one-dimensional with an intrachain hopping frequency at room temperature of ${10}^{11}$ to ${10}^{12}$ ${\sec }^{\mathrm{-}1}$ and an interchain hopping frequency of only ${10}^2$ to ${10}^4$ ${\sec }^{\mathrm{-}1}$. The presence of small concentrations of ${\mathrm{Cd}}^{2+}$, a scattering impurity, greatly reduces the rate of exciton trapping. The temperature dependence of the decay curves suggests an energy barrier of 800 to 1000 ${\mathrm{cm}}^{\mathrm{-}1}$ for migration along the chains in TMMC.