Efficient doping and energy transfer from ZnO to Eu ³⁺ ions in Eu ³⁺-doped ZnO nanocrystals

Successful doping of Eu ³⁺ ions into ZnO nanocrystals has been realized by using a low temperature wet chemical doping technique. The substitution of Eu ³⁺ for Zn ²⁺ is shown to be dominant in the Eu-doped ZnO nanocrystals by analyzing the X-ray diffraction patterns, transmission electron microscopy images, Raman and selectively excited photoluminescence spectra. Measurement of the luminescence from the samples shows that the excited ZnO transfers the excited energy efficiently to the doped Eu ³⁺ ions, giving rise to efficient emission at red spectral region. The red emission quantum yield is measured to be 31% at room temperature. The temperature dependence of photoluminescence and the photoluminescence excitation spectra have also been investigated, showing strong energy coupling between the ZnO host and Eu ³⁺ ions through free and bound excitons. The result indicates that Eu ³⁺ ion-doped ZnO nanocrystals are promising light-conversion materials and have potential application in highly distinguishable emissive flat panel display and LED backlights.