Quick single-step mechanosynthesis of ZnO nanorods and their optical characterization: milling time dependence

Abstract

We report on the growth of ZnO nanorods (NRs) by a quick single-step mechanochemical process and investigated the milling time dependence on the structural and optical properties of the ZnO NRs. Mechanochemical reactions are carried out in a planetary ball mill for the time durations ranging from 30 min to 5 h. XRD and TEM studies revealed wurtzite structure of the as-grown ZnO NRs with length of several hundreds of nanometers to few micrometers after 30 min of reaction. Average diameter of the as-grown ZnO NRs decreases from 40 to 15 nm with increasing reaction time. Micro-Raman spectra show redshift in the characteristic Raman modes, indicating presence of milling induced strain. As-grown NRs show blueshift in the excitonic absorption peak with increasing milling time due to decrease in size and induced strain. Room temperature photoluminescence (PL) spectra show strong band-edge related UV emission and other three major emission peaks, two in the UV-blue region and one at the visible region. Post-growth annealing of the as-grown ZnO NRs completely eliminates the defect related visible PL band. Low-temperature PL studies show an additional sharp peak related to donor-bound excitonic transition, revealing the n-type nature of the as-grown NRs.