Pure exciton- and magnon-assisted optical transitions in the one-dimensional antiferromagnet CsMnCl3· 2H2O (CMC)

We report the first observation of the pure electronic transitions in the ${}_{}{}^4{}_{}{}^{}T_1^{}{}_{}{}^{}$ state of ${\mathrm{Mn}}^{2+}$ ions in the one-dimensional antiferromagnet CsMn${\mathrm{Cl}}_3$ · 2${\mathrm{H}}_2$O (CMC) in the absorption, excitation, and fluorescence spectra. Selection rules are analyzed: the exciton transition is electric dipole allowed, the magnon sideband in emission is a single-ion process, and is both electric and magnetic dipole allowed; however, the magnon sideband in absorption is an ion-pair process and is a weakened-electric-dipole and magnetic-dipole transition. The density of magnon states and the line profile of the magnon sideband have been calculated. The results explain the peculiar line shapes of the observed sideband emission. An exponential decay of the exciton is observed with a lifetime of 0.57 ms.