Correlation between size-induced lattice variations and yellow emission shift in ZnO nanostructures

Theoretical studies available in the literature for investigating the quantum size effects in band-gap and luminescence properties have excluded lattice variations that may occur in the nanoscale regime. This work addresses the lattice dimensions of highly crystalline ZnO nanorods as a function of diameter. The corresponding quantum size effects in band modifications were explored using the intrinsic yellow emission as the probe. It was found that with increasing nanorod diameter, the lattice volume decreased linearly, while the peak maximum of the yellow luminescence shifted towards lower energies. This redshift is found to be smaller than that calculated from band-gap theories. These findings have been interpreted in terms of the probable increase in height of the top of valence band induced by the lattice contraction associated with the increase in nanorod diameter.