Optical size effects in ultrathin ZnO nanowires

Abstract

Single crystal ZnO wurtzite nanowires grown along the c-axis with diameters down to 4 nm were synthesized by a catalytic vapor transport technique. Photoluminescence spectra of these wires indicate a blue shift of the free exciton by 19 meV due to confinement. This result was obtained by analyzing the line shape of the blue-shifted LO phonon replica of the free exciton. In addition, a surface-related excitonic luminescence feature centered at 3.366 eV was observed with a strongly elevated thermal activation energy.