| ZnO has an efficient green emission band at 520nm. It is an attractive phosphor for low voltage emissive displays. In order to develop narrow band phosphors for color displays, rare earth doped ZnO has been intensively studied. Unfortunately, no positive results have been obtained up to now, because of the weak energy transfer from ZnO to the rare earth.; In this project, a further investigation on how the synthesis conditions affect the optical properties of ZnO was conducted. Also, new doping species were used in an attempt to improve the energy transfer from the host to the rare earth, Eu3+ ions. It was found that the optical quality of the ZnO samples was very sensitive to the synthesis conditions (sintering temperature and atmosphere) and was not easy to control. With reducing atmospheres and higher sintering temperatures, the concentration of oxygen vacancies was found to increase. Doping with sulfur and carbon did not increase the concentration of oxygen vacancies very much. Instead, they entered into the ZnO lattice, produced shallow lattice defects and the band edge absorption became stronger or extended to the longer wavelength. In the samples doped with Eu2O 3 or EUCl3, no obvious energy transfer from the host to the Eu3+ was observed. The results obtained helped to clarify some misled conclusions published in literature. On the other hand, in the samples doped with EuF3, quite strong energy transfer from the host to the Eu3+ was observed. It is believed that the anion F − formed interstitial defects, which served as donors. Photo excitation energy from the host can be efficiently transferred to Eu 3+ indirectly through the F− donors. Strong chemical bonds between F and Eu may be the important factor to ensure strong energy coupling. |
