ZnO:Eu thin-films: Sol–gel derivation and strong photoluminescence from 5D0 → 7F0 transition of Eu3+ ions

ZnO:Eu films on silicon wafers were prepared by a simple sol–gel route. It was found that in order to achieve pure ZnO crystal phase, the annealing temperature could not be higher than 850 °C. The pronounced peaks in the photoluminescence (PL) spectra of the ZnO:Eu films were originated from 5D0 → 7F0,1,2 transitions. It is somewhat unexpected that the PL emission from the 5D0 → 7F0 transition, which is principally believed to be forbidden, was remarkable. In order to explain this phenomenon, it is proposed that a majority of incorporated Eu3+ ions in the films occupy the interstitial sites of ZnO host.