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

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 (D-5(4) -> F-7(j) for Tb3+ and D-5(0) -> F-7(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.