Phonon-assisted stimulated emission in Mn-doped ZnO nanowires

Well- crystallized Mn- doped ZnO nanowires were synthesized by a high-temperature chemical reduction method. The microscopic and macroscopic photoluminescence ( PL) spectra of these Mn- doped ZnO nanowires were studied. Both the free- exciton emission band and the second- order longitude optical ( 2LO) phonon- assisted emission band were observed in the microscopic PL spectra. Furthermore, from the power dependent macroscopic PL spectra, the stimulated emission was observed around the 2LO phonon- assisted emission band with an increase in pump fluence, which relates to the strong exciton phonon couplings along the c- axis in these Mn- doped ZnO nanowires. The nonresonant micro- Raman scattering spectrum demonstrates the strong 2LO phonon mode, which is enhanced by Mn doping. Resonant micro- Raman scattering shows multi- LO modes, due to the strong exciton - phonon coupling via a deformation potential induced by the Mn ions in these Mn- doped ZnO nanowires. Moreover, the low- temperature UV PL band is discussed to demonstrate the activity of phonons in the Mn- doped ZnO nanowires.