Fig. 2. Exciton spectrum and two-color excitation of excitons in [Ni(chxn)₂Br]Br₂.

a The spectrum of imaginary part of the dielectric constant, ${\epsilon }_2$, along the 1D Ni-Br chains, in which the energies of odd-parity and even-parity excitons ($\hslash {\omega }_1=1.27\mathrm{eV}$ and $\hslash {\omega }_2=1.28\mathrm{eV}$) are indicated. b Schematic diagram of the two-color excitation of the odd-parity exciton $\mid {\phi }_{\mathrm{o}}⟩$ with the frequency of $2\omega$ and the even-parity exciton $\mid {\phi }_{\mathrm{e}}⟩$ with the frequency of $\omega$. $\mid {\phi }_{\mathrm{g}}⟩$ represents the ground state. $⟨{\phi }_{\mathrm{g}}\mid x\mid {\phi }_{\mathrm{o}}⟩$ ($⟨{\phi }_{\mathrm{o}}\mid x\mid {\phi }_{\mathrm{e}}⟩$) are the transition dipole moments between $\mid {\phi }_{\mathrm{g}}⟩$ and $\mid {\phi }_{\mathrm{o}}⟩$ ($\mid {\phi }_{\mathrm{o}}⟩$ and $\mid {\phi }_{\mathrm{e}}⟩$).