Synthesis of rare-earth doped ZnO nanorods and their defect–dopant correlated enhanced visible-orange luminescence

Abstract

We report the synthesis of size controlled ZnO and rare-earth doped ZnO nanorods in the sub-10 nm diameter regime. The preferential anisotropic growth of the nanostructures along the polar c-axis leads to the formation of wurtzite phase ZnO nanorods. Photoluminescence measurements reveal enhancement of visible luminescence intensity with increasing RE³⁺ concentrations upon excitation of host ZnO into the band gap. The broad visible luminescence originates from multiple intrinsic or extrinsic defects. The luminescence from RE³⁺ is enabled by energy transfer from defect centers of the host nanocrystal lattice to dopant sites. Host–guest energy transfer facilitates efficient intra-4f orbital transitions (⁵D₄ → ⁷F_j for Tb³⁺ and ⁵D₀ → ⁷F_j for Eu³⁺) related characteristic green or red emission. Interestingly, different decay rates of host defects and RE³⁺ emission transition also allow temporal control to achieve either pure green or red color. This study suggests that manipulation of defects through bottom-up techniques is a viable method to modulate the energy transfer dynamics, which may help enable the future applications of ZnO-based phosphor materials in optoelectronic and multicolor emission displays.