Luminescence Spectra and Lattice Dynamics of NaNO₂ in the Ferroelectric Phase

Frenkel excitons in : excitation energy transfer and exciton coherence

“…More quantitative information about the vibron band was obtained by calculating the dispersion relation of the vibrational modes [77]. Lattice dynamics studies of NaNO 2 have been performed previously [31,[78][79][80].…”

“…Unfortunately none of the previous publications calculated the density of states of the vibrons to allow to calculate lineshapes for optical transitions. Janssen et al [77] modified the assumed charge distribution in such a way as to reproduce the experimentally observed LO-TO splittings of the vibron modes and took the atomic polarizabilities into account by means of the shell model as suggested by Castellucci and Schettino. For the calculations the experimental polarizabilities obtained from measurements of the refractive index were used [81].…”

“…Because the exciton state is composed of 1 B 1 molecular excited states which have a nodal plane perpendicular to the a axis, it was assumed that the exciton state at k = 0 is highest in energy. Calculating the density of states for the ν 2 vibron and the exciton band finally yielded the lineshape for the transition between these two bandstructures, which is compared in figure 6 with the experimental lineshape [77,82]. The displayed experimental spectrum corresponds to a crystal temperature of 15 K because it is known that below this temperature the excitons are not distributed uniformly over the Brillouin zone [70] (see the next section).…”