Secondary Emission in NaNO₂ under Selective Excitation: Dispersion and Relaxation of ν₀₀ Exciton

Abstract

Spectral and transient behavior of secondary emission in NaNO₂ has been studied under the selective excitation with frequency ν_i in the region of the phonon sideband of the zero-phonon line at ν₀₀ in the absorption spectrum. The emission line becomes broader and stronger as ν_i shifts from ν₀₀ toward higher energy, and it splits into two or more-components when ν_i falls into valley regions of the phonon sideband. The maximum separation of the split components amounts to about 5 cm⁻¹. The decay time of the emission is almost constant and about 7 ns for the change in ν_i. These results suggest that ν₀₀ excitons are created in some limited regions of the exciton band in the Brillouin zone by the phonon-assisted optical transition, and that radiative annihilation of the exciton occurs before thermalization of the exciton is established.