| Research Abstract |
The electroluminescent characteristics of ac-driven thin-film electroluminescent devices were studied. These devices were proposed and developed by the head investigatior, and differed from usual devices in the structure of the active layer, i.e., the additional intermediate layer ("gate layer") was buried in ZnS active layers. Thus, the strucure of devices is a glass substrate: electrode <I> ( <SnO_x> )-insulator <I> ( <Y_2> <O_3> )-active layer <I> (impurity doped ZnS)-gate layer-active layer <II> (impurity doped ZnS)-insulatalor <II> ( <Y_2> <O_3> )-electrode <II> (Al).
The results of the investigation are as follows.
(1). The emission color of the device was able to be continuously varied between the emission color of the active layer <I> and that of <II> by the driving voltage and frequency, only when the gate layer thickness was in the optimum range which was dependent on its material.
(2). The optimum range of a gate layer thickness was 10 - 60 <Ang> in the case of a metal gate, and 500 -1000 <Ang> of an insulator gate. In the case of a semiconductor gate it was wide considerably, for example, it was 200 - 3000 <Ang> when a gate layer material was <WO_3> . Further, it was not dependent on the thickness of each active layer or a kind of impurity doped in the active layer.
(3). The tendencies of the dependency of emisson color on the driving conditions were different according to gate materials. These were approximately grouped into two classes, and were contrary with each other.
(4). The changeablity of the emisson color was maintained at low temperature (approx. -100゜C). The electroluminescent spectrum of an active layer, however, was changed at low temperatuere depending on a kind of an impurity. This phenomenon had nothing to do with the existence of a gate layer.
(5). It was considered that the changeablity of the emission color of these devices was due to the accumulation and the emission of electrons at the gate layer.
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