Defects-mediated energy transfer in red-light-emitting Eu-doped ZnO nanowire arrays

We report on the photoluminescence in perfectly aligned Eu-doped ZnO nanowire arrays that are prepared on sapphire substrates using a vapor transport method with doped sol-gel precursor powder as the vapor source. Under the UV light excitation, Eu³⁺-related red emission is observed in the Eu-doped ZnO nanowire arrays. By carrying out systematic temperature-dependent and time-resolved photoluminescence experiments, we identify a defect-mediated energy transfer pathway from the ZnO host to the Eu³⁺ ions. The energy transfer time increases from ∼9 to ∼130 ps after the nanowires are annealed in oxygen ambient, which reduces the defect concentration. This study suggests that defect engineering in bottom-up synthesis is a viable approach to modulate the energy transfer process, which may help to enable the future applications of ZnO-based nanomaterials in optoelectronics and full color displays.