Structure and optical properties of Cd-substituted ZnO (Zn_1−xCd_xO) nanostructures synthesized by the high-pressure solution route

Abstract

We report the synthesis of Cd-substituted ZnO nanostructures (Zn_1−xCd_xO with x up to ≈0.09) by the high-pressure solution growth method. The synthesized nanostructures comprise nanocrystals that are both particles (∼10-15 nm) and rods which grow along the [002] direction as established by transmission electron microscope (TEM) and X-ray diffraction (XRD) analysis. Rietveld analysis of the XRD data shows a monotonic increase of the unit cell volume with the increase of Cd concentration. The optical absorption, as well as the photoluminescence (PL), shows a red shift on Cd substitution. The line width of the PL spectrum is related to the strain inhomogeneity and it peaks in the region where the CdO phase separates from the Zn_1−xCd_xO nanostructures. The time-resolved photoemission showed a long-lived (∼10 ns) component. We propose that the PL behaviour of the Zn_1−xCd_xO is dominated by strain in the sample with the red shift of the PL linked to the expansion of the unit cell volume on Cd substitution.