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Mn-activated Zn 2 SiO 4 and Ce-activated Y 2 SiO 5 multilayer thin film electroluminescent ͑EL͒ devices were prepared by rf magnetron sputtering. The EL response of the devices under different voltages, frequencies, and pulse widths, as well as the transferred charge and decay characteristics were studied. The EL device using Zn 2 SiO 4 :Mn as the phosphor layer is shown to achieve a brightness of over 200 cd/m 2 at 400 Hz and a field of 3ϫ10 6 V/cm ͑twice the threshold field͒ and a maximum efficiency of 0.78 lm/W, with a decay time of 0.6 ms. The main characteristics of the oxide phosphors include ͑a͒ strong trailing edge excitation in nonsymmetrical EL devices, ͑b͒ a narrow transferred charge loop, and ͑c͒ a time response sensitive to device structures. Compared with the nonsymmetrical structure, the more symmetrical double-insulated structure is shown to increase the efficiency of the EL device by generating strong EL excitation from both positive and negative voltage pulses.

Positron lifetime spectroscopy and cathodoluminescence were employed to study luminescence centers in normalZnO . The samples were high‐purity polycrystalline ceramics sintered at temperatures ranging from 800 to 1400°C for 2 to 40 h. Scanning electron microscopy shows that as annealing temperatures and/or times increase, the average grain size increases and can reach 30 μm for samples sintered at 1200°C. At the same time, the positron bulk lifetime approaches theoretically estimated single‐crystal values, while the integrated luminescence intensity increases significantly. A further increase of the sintering temperature beyond 1200°C results in a decrease in the luminescence intensity, in good agreement with the only weak luminescence observed in single‐crystalline material. The positron lifetime spectra clearly show the existence of one dominant vacancy‐type defect, most likely a complex involving VnormalZn , or the divacancy, VnormalZnVO , independent of sample thermal history. The concentration of this center steadily decreases with increasing sintering temperature. It is concluded that the yellow luminescence centers are related to charged zinc vacancies trapped in the grain boundary regions. We propose that the observed broadness of the spectra likely originates from the modification of the electronic configuration of the luminescence centers due to their complex environment. A direct connection between the positron and the luminescence results could not be established; instead, they appear to reflect two relatively independent aspects of the samples. It could be shown, however, that positron annihilation measurements can be used effectively to monitor the evolution of the microstructure of the samples, in good agreement with scanning electron micrographs.

A criterion for high performance electroluminescent (EL) phosphor based on the crystal structure of the phosphor host has been developed. The performance of some best-performing EL oxide phosphors is correlated to the fundamental atomic arrangements of the phosphor host and to the microstructural characteristics of their thin films. It is shown that, contrary to popular beliefs, oxide phosphors with certain crystallographic features do have the capability of transporting significant current densities of hot electrons. Examples of newly developed high brightness and efficiency oxide EL phosphors are presented.

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