Low-temperature transport of magnetic excitons in the quasi-one-dimensional antiferromagnet CsMnCl3

The emission decay kinetics and relative quantum yields of exciton luminescence of ${\mathrm{Cu}}^{2+}$-doped (3%) quasi-one-dimensional antiferromagnetic crystals ${\mathrm{CsMnCl}}_{3}$\ensuremath{\cdot}${2\mathrm{H}}_{2}$O have been studied in the temperature range from 4.2 to 77 K. The experimental emission decay curves have been approximated by the calculated curves obtained using computer simulation of incoherent excitons motion. The model assumes a slow interchain hopping process and a rapid intrachain migration of excitons. Exciton hopping (W) and trapping (U) rates at 4.2--77 K have been defined. A decrease of both U and W rates has been observed with a temperature lowering. The proposed model of exciton migration and trapping considered excitation passing potential barriers between ${\mathrm{Mn}}^{2+}$-${\mathrm{Mn}}^{2+}$ and ${\mathrm{Mn}}^{2+}$-${\mathrm{Cu}}^{2+}$ ions. To describe the deviation of U(T) and W(T) dependences from the Arrhenius law we suppose that excitons pass barriers by both hopping over it and tunneling. The energies and shapes of the barriers have been estimated. The tunneling processes were taken into account while determining the barriers energy. The role of both the exciton-phonon interaction in ${\mathrm{CsMnCl}}_{3}$\ensuremath{\cdot}${2\mathrm{H}}_{2}$O and the spin forbiddeness of the low-temperature (T\ensuremath{\le}30 K) exciton migration along a chain due to the antiferromagnetic spin ordering has been discussed. \textcopyright{} 1996 The American Physical Society.