Synthesis and luminescence properties of Eu3+-doped ZnO nanocrystals by a hydrothermal process

Trivalent europium ions doped zinc oxide (ZnO:Eu3+) nanocrystals were prepared by a hydrothermal process. The obtained samples were characterized using X-ray diffraction (XRD) and photoluminescence (PL) spectra. The XRD patterns indicate that Eu3+ ions are successfully doped into the crystal lattice of ZnO matrix. The ZnO:Eu3+ nanocrystals exhibit a sharp red luminescence emission, which is from the intra-4f transitions of Eu3+ ions. The 5D0–7F2 emission comes from an allowed electric-dipole transition and its intensity is the strongest. This implies that Eu3+ ions are mainly in a large transition probability in the crystal field with inversion antisymmetry. The PL peaks of Eu3+ ions can be observed even under the nonresonant excitation of 325 nm. It is explained by an energy transfer mechanism in which the energy is transferred from the defect state of ZnO matrix to Eu3+ ions in ZnO:Eu3+ nanocrystals.