Free exciton emission and dephasing in individual ZnO nanowires

We report on systematic measurements of the dephasing of the free excitonic transition in individual ZnO nanowires with a diameter of about 70 nm. The temperature-dependent intensity of the free exciton (FX) emission is well reproduced by a thermally activated behavior having two constant activation energies of 5.98 and 30.63 meV. The FX linewidth broadening with temperature reveals the dephasing of FX scattered by acoustic phonons rather than longitudinal optical phonons. These findings indicate that the dephasing mechanism scattering from acoustic phonons in individual ZnO nanowires result from the compensation of acoustic phonons to the nonconservation of crystal momentum.