Phonon Side Bands of UV Absorption in NaNO₂

Abstract

Phonon side bands of u v absorption in NaNO 2 have been studied by the measurement of high resolution spectrum with light polarized along each crystallographic axis at low temperatures. Strong peaks in the side bands are assigned to the phonon branches in the first Brillouin zone by taking account of the selection rules for the optical transitions in which an exciton and a phonon are created simultaneously. The integrated intensities of the E // b and E // c absorptions have been found to increase with temperature obeying the coth ( h ν/2 k T ) law with ν b ≃220 cm -1 and ν c ≃130 cm -1 respectively. The relation between the temperature dependence of the E // b and E // c absorptions and the profiles of their phonon side bands is discussed in terms of the averaged phonon frequency \barν.